FusionWiki - User contributions [en]

LNF:Organization

2023-03-17T08:03:11Z

Daniel.carralero: /* TJ-II Experimental Division */

== Laboratorio Nacional de Fusión ==

Asociación [[Euratom]]-[[CIEMAT]]: see [[Laboratorio Nacional de Fusión]].

Contact information is also available via the [http://www.ciemat.es/cargarFichaOrganizacion.do?idOrganizacion=F00 CIEMAT website]

The telephone numbers listed below are extensions; to call from outside the laboratory, dial: +34-91346xxxx, where xxxx is the extension. (When using 4-digit dialing from inside the laboratory: substitute any initial "0" by a "7".)

[https://www.gruptelecom.com/wp-content/uploads/2018/07/Manual_Unify_CP-200.pdf IP-phone manual]

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Hidalgo Vera, Carlos, Director || 6498 ||
|-
|}

=== TJ-II Experimental Division ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Alonso de Pablo, Arturo, Head Investigator || 6293 || 362401
|-
| Baciero Adrados, Alfonso || 6493 || 362601
|-
| Blanco Villareal, Emilio J. || 7904 ||
|-
| de la Cal Heusch, Eduardo || 6317 ||
|-
| de la Luna Gargantilla, Elena || 0849 || 362937
|-
| Carralero Ortiz, Daniel || 7852 || 363192
|-
| Castro Rojo, Rodrigo || 6419 ||
|-
| Fontdecaba Climent, Jose María || 6642 ||
|-
| García Cortés, Mª. Isabel || 6515 || 362625
|-
| Hernanz Hernanz, Francisco J. || 6641 ||
|-
| López Miranda, Belén || || 362093
|-
| McCarthy, Kieran Joseph || 0846 || 362934
|-
| Medina Yela, Francisco || 0847 || 362935
|-
| Ochando Garcia, Mª. Antonia || 6462 ||
|-
| de Pablos Hernández, Jose Luis || 6374 ||
|-
| Panadero Álvarez, Nerea || 6642 || 362781
|-
| Pastor Díaz, Ignacio || 6324 ||
|-
| Pastor Santos, Carmen || || 362564
|-
| Rattá Gutiérrez, Giuseppe A. || 7917 ||
|-
| Rodríguez Fernández, Mª. Carmen || 2611 ||
|-
| [[User:Admin|van Milligen, Boudewijn]] || 6379 || 362482
|-
| Vega Sánchez, Jesús Antonio || 6474 ||
|}

=== TJ-II Operation Division===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Estrada García, Teresa, Head Investigator || 6369 ||
|-
| Alegre Castro, Daniel || 0914 ||
|-
| Cappa Ascasíbar, Alvaro || 6646 Sala de Control ECRH 6828 || 362784
|-
| Cebrián Ruiz, Luis A. || 6338 ||
|-
| Chamorro Lastra, Manuel || 6641 ||
|-
| García Gomez, Raúl || 6641 ||
|-
| Guasp Pérez, Jose || 6510 ||
|-
| Guisse Arévalo, Víctor H. || 6285 ||
|-
| Liniers Vazquez, Macarena || 0844 Sala de Control NBI 6851 ||
|-
| Martín Diaz, Fernando || 0920 Sala de Control NBI 6851 || 363860
|-
| Martinez Fernandez, Jose || 6646 Sala de Control ECRH 6828 || 362785
|-
| Bueno Jañez, Luis Alberto || 6285 ||
|-
| Miguel Honrubia, Francisco J. || 6762 ||
|-
| Navarro Santana Miguel || 6824 ||
|-
| Pereira Gonzalez, Augusto || 0929 ||
|-
| Pons Villalonga, Pedro || 7926 || 363005
|-
| Portas Ferreiro, Ana Belén || 0929 ||
|-
| Ros Vivancos, Alfonso || 6642 Sala de Control ECRH 6828 Lab. μOndas 6808 || 362782
|-
| Sánchez Sarabia, Emilio || 6762 ||
|-
| Sebastián Alfaro, José Antonio || 6684 Sala de Control NBI 6851 || 362828
|-
| Tabarés Vazquez, Francisco Luis || 6458 ||
|-
| Tafalla García, David || 0843 ||
|-
| Tolkachev, Alexander || 6828 ||
|}

=== Fusion Theory Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Calvo Rubio, Iván, Head Investigator || 6739 || 362872
|-
| Escoto López, Francisco Javier || || 363002
|-
| García Regaña, José Manuel || 7850 || 362938
|-
| Godino Sedano, Guillermo Luis || 7920 || 362780
|-
| González Jerez, Antonio || 7916 || 363000
|-
| López Bruna, Daniel || 6638 ||
|-
| [[User:Esolano|Solano (Rodríguez-Solano Ribeiro), Emilia R.]]|| 6153 || 362254
|-
| Sánchez González, Edilberto || 6162 || 362264
|-
| Thienpondt, Hanne || 2538 || 362037
|-
| Velasco Garasa, José Luis || 6504 || 363504
|}

=== Engineering Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Medrano Casanova, Mercedes, Head Investigator || 6639 ||
|-
| Cabrera Pérez, Santiago || || 362994
|-
| Carrasco García, Ricardo || 7928 ||
|-
| Fernández Navarro, Alejandro || 6637 || 362771
|-
| Jimenez Denche, Andrés Enrique || 6584 ||
|-
| Kirpitchev, Igor || 6337 ||
|-
| Lapayese Puebla, Fernando || 0928 ||
|-
| Méndez Montero, Purificación || 6337 ||
|-
| de la Peña Gómez, Ángel || 6644 ||
|-
| Queral Mas, Vicente || 6419 || 362518
|-
| Ramos Rivero, Francisco || 6584 ||
|-
| Rincón Rincón, María Esther || 6637 ||
|-
| Soleto Palomo, M. Alfonso || 6636 ||
|-
| Weber Suárez, Moisés || 6636 ||
|}

=== Technology Division ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Rapisarda Socorro, David, Head Investigator || 0913/6335 (prov) || 362998
|-
| Brañas Lasala, Beatriz || 6289 ||
|-
| [[User:Elisabetta|Carella , Elisabetta]] || 6507 || 362253
|-
| D'Ovidio, Gianluca || 6419 || 362429
|-
| Fernández Berceruelo, Iván || 2579 ||
|-
| García Gonzalez, Juan Manuel || 7842 ||
|-
| Garcinuño Pindado, Belit || 6584 || 362717
|-
| Gonzalez Viada, María || 2582 || 362073
|-
| Gutierrez Pérez, Víctor || 6307 || 362413
|-
| Hernandez Diaz, Mª. Teresa || 2581 || 362071
|-
| Herranz Marco, Jesús Antonio || 0848 ||
|-
| Jimenez Baena, Francisco M. || 6204 ||
|-
| Jiménez Rey, David || 6640 ||
|-
| Malo Huerta, Marta || 6636 || 362769
|-
| Martín Laso, Montserrat || 6512 ||
|-
| Molla Lorente, Joaquín || 6397 || 362496
|-
| de la Morena Álvarez-Palencia, Cristina || 2600 ||
|-
| Moroño Guadalajara, Alejandro A. || 6372 ||
|-
| Mota García, Fernando || 6578 || 362708
|-
| Navas, Julia || || 362428
|-
| Ortíz, Christophe || 2582 || 362074
|-
| Ortiz Gandía, Maribel || 2582 || 362075
|-
| Palermo, Iole || 6784 ||
|-
| Patiño, Julian || || 362428
|-
| Regidor Serrano, David || 6584 ||
|-
| Roca Urgorri, Fernando || 6378 || 362480
|-
| Roldán Blanco, Marcelo || 2581 FIB-SEM 6790 || 362709
|-
| Román Chacón, Raquel || 6203 ||
|-
| Sánchez Sanz, Fernando José || 2581 FIB-SEM 6790 ||362702
|-
| Serrador Toledano, Laura || 2574 FIB-SEM 6790 ||
|-
| Valle Paisan, Francisco J. || 6204 ||
|-
| Vila Vazquez, Rafael Alberto || 6580 ||
|-
| Villamayor Callejo, Víctor || 6578 ||
|-
|}

=== Support Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Ríos Márquez, Luis || ||
|-
| Barrera Orte, Laura || || 362262
|-
| Fernandez-Mayoralas López, Lorena || 6663 ||
|-
| Moreno García, Sabina || 6159 ||
|-
| Sánchez Rubio, Cristina || 6738 ||
|-
| Guerard Ortego, Carlos Kjell || - ||
|-

|}

LNF:Organization

2023-03-10T10:20:15Z

Daniel.carralero:

== Laboratorio Nacional de Fusión ==

Asociación [[Euratom]]-[[CIEMAT]]: see [[Laboratorio Nacional de Fusión]].

Contact information is also available via the [http://www.ciemat.es/cargarFichaOrganizacion.do?idOrganizacion=F00 CIEMAT website]

The telephone numbers listed below are extensions; to call from outside the laboratory, dial: +34-91346xxxx, where xxxx is the extension. (When using 4-digit dialing from inside the laboratory: substitute any initial "0" by a "7".)

[https://www.gruptelecom.com/wp-content/uploads/2018/07/Manual_Unify_CP-200.pdf IP-phone manual]

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Hidalgo Vera, Carlos, Director || 6498 ||
|-
|}

=== TJ-II Experimental Division ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Alonso de Pablo, Arturo, Head Investigator || 6293 || 362401
|-
| Baciero Adrados, Alfonso || 6493 || 362601
|-
| Blanco Villareal, Emilio J. || 7904 ||
|-
| de la Cal Heusch, Eduardo || 6317 ||
|-
| de la Luna Gargantilla, Elena || 0849 || 362937
|-
| Carralero Ortiz, Daniel || 7852 || 362263
|-
| Castro Rojo, Rodrigo || 6419 ||
|-
| Fontdecaba Climent, Jose María || 6642 ||
|-
| García Cortés, Mª. Isabel || 6515 || 362625
|-
| Hernanz Hernanz, Francisco J. || 6641 ||
|-
| López Miranda, Belén || || 362093
|-
| McCarthy, Kieran Joseph || 0846 || 362934
|-
| Medina Yela, Francisco || 0847 || 362935
|-
| Ochando Garcia, Mª. Antonia || 6462 ||
|-
| de Pablos Hernández, Jose Luis || 6374 ||
|-
| Panadero Álvarez, Nerea || 6642 || 362781
|-
| Pastor Díaz, Ignacio || 6324 ||
|-
| Pastor Santos, Carmen || || 362564
|-
| Rattá Gutiérrez, Giuseppe A. || 7917 ||
|-
| Rodríguez Fernández, Mª. Carmen || 2611 ||
|-
| [[User:Admin|van Milligen, Boudewijn]] || 6379 || 362482
|-
| Vega Sánchez, Jesús Antonio || 6474 ||
|}

=== TJ-II Operation Division===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Estrada García, Teresa, Head Investigator || 6369 ||
|-
| Alegre Castro, Daniel || 0914 ||
|-
| Cappa Ascasíbar, Alvaro || 6646 Sala de Control ECRH 6828 || 362784
|-
| Cebrián Ruiz, Luis A. || 6338 ||
|-
| Chamorro Lastra, Manuel || 6641 ||
|-
| García Gomez, Raúl || 6641 ||
|-
| Guasp Pérez, Jose || 6510 ||
|-
| Guisse Arévalo, Víctor H. || 6285 ||
|-
| Liniers Vazquez, Macarena || 0844 Sala de Control NBI 6851 ||
|-
| Martín Diaz, Fernando || 0920 Sala de Control NBI 6851 ||
|-
| Martinez Fernandez, Jose || 6646 Sala de Control ECRH 6828 || 362785
|-
| Bueno Jañez, Luis Alberto || 6285 ||
|-
| Miguel Honrubia, Francisco J. || 6762 ||
|-
| Navarro Santana Miguel || 6824 ||
|-
| Pereira Gonzalez, Augusto || 0929 ||
|-
| Pons Villalonga, Pedro || 7926 || 363005
|-
| Portas Ferreiro, Ana Belén || 0929 ||
|-
| Ros Vivancos, Alfonso || 6642 Sala de Control ECRH 6828 Lab. μOndas 6808 || 362782
|-
| Sánchez Sarabia, Emilio || 6762 ||
|-
| Sebastián Alfaro, José Antonio || 6684 Sala de Control NBI 6851 || 362828
|-
| Tabarés Vazquez, Francisco Luis || 6458 ||
|-
| Tafalla García, David || 0843 ||
|-
| Tolkachev, Alexander || 6828 ||
|}

=== Fusion Theory Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Calvo Rubio, Iván, Head Investigator || 6739 || 362872
|-
| Escoto López, Francisco Javier || || 363002
|-
| García Regaña, José Manuel || 7850 || 362938
|-
| Godino Sedano, Guillermo Luis || 7920 || 362780
|-
| González Jerez, Antonio || 7916 || 363000
|-
| López Bruna, Daniel || 6638 ||
|-
| [[User:Esolano|Solano (Rodríguez-Solano Ribeiro), Emilia R.]]|| 6153 || 362254
|-
| Sánchez González, Edilberto || 6162 || 362264
|-
| Thienpondt, Hanne || 2538 || 362037
|-
| Velasco Garasa, José Luis || 6504 || 362610
|}

=== Engineering Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Medrano Casanova, Mercedes, Head Investigator || 6639 ||
|-
| Cabrera Pérez, Santiago || || 362994
|-
| Carrasco García, Ricardo || 7928 ||
|-
| Fernández Navarro, Alejandro || 6637 || 362771
|-
| Jimenez Denche, Andrés Enrique || 6584 ||
|-
| Kirpitchev, Igor || 6337 ||
|-
| Lapayese Puebla, Fernando || 0928 ||
|-
| Méndez Montero, Purificación || 6337 ||
|-
| de la Peña Gómez, Ángel || 6644 ||
|-
| Queral Mas, Vicente || 6419 || 362518
|-
| Ramos Rivero, Francisco || 6584 ||
|-
| Rincón Rincón, María Esther || 6637 ||
|-
| Soleto Palomo, M. Alfonso || 6636 ||
|-
| Weber Suárez, Moisés || 6636 ||
|}

=== Technology Division ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Rapisarda Socorro, David, Head Investigator || 0913/6335 (prov) || 362998
|-
| Brañas Lasala, Beatriz || 6289 ||
|-
| [[User:Elisabetta|Carella , Elisabetta]] || 6507 || 362253
|-
| D'Ovidio, Gianluca || 6419 || 362429
|-
| Fernández Berceruelo, Iván || 2579 ||
|-
| García Gonzalez, Juan Manuel || 7842 ||
|-
| Garcinuño Pindado, Belit || 6584 || 362717
|-
| Gonzalez Viada, María || 2582 || 362073
|-
| Gutierrez Pérez, Víctor || 6307 || 362413
|-
| Hernandez Diaz, Mª. Teresa || 2581 || 362071
|-
| Herranz Marco, Jesús Antonio || 0848 ||
|-
| Jimenez Baena, Francisco M. || 6204 ||
|-
| Jiménez Rey, David || 6640 ||
|-
| Malo Huerta, Marta || 6636 || 362769
|-
| Martín Laso, Montserrat || 6512 ||
|-
| Molla Lorente, Joaquín || 6397 || 362496
|-
| de la Morena Álvarez-Palencia, Cristina || 2600 ||
|-
| Moroño Guadalajara, Alejandro A. || 6372 ||
|-
| Mota García, Fernando || 6578 || 362708
|-
| Navas, Julia || || 362428
|-
| Ortíz, Christophe || 2582 || 362074
|-
| Ortiz Gandía, Maribel || 2582 || 362075
|-
| Palermo, Iole || 6784 ||
|-
| Patiño, Julian || || 362428
|-
| Regidor Serrano, David || 6584 ||
|-
| Roca Urgorri, Fernando || 6378 || 362480
|-
| Roldán Blanco, Marcelo || 2581 FIB-SEM 6790 || 362709
|-
| Román Chacón, Raquel || 6203 ||
|-
| Sánchez Sanz, Fernando José || 2581 FIB-SEM 6790 ||362702
|-
| Serrador Toledano, Laura || 2574 FIB-SEM 6790 ||
|-
| Valle Paisan, Francisco J. || 6204 ||
|-
| Vila Vazquez, Rafael Alberto || 6580 ||
|-
| Villamayor Callejo, Víctor || 6578 ||
|-
|}

=== Support Unit ===

{|class="wikitable" style="vertical-align:top;"||
|-
!Name!!Telephone (old)!!IP-phone
|-
| Ríos Márquez, Luis || ||
|-
| Barrera Orte, Laura || || 362262
|-
| Fernandez-Mayoralas López, Lorena || 6663 ||
|-
| Moreno García, Sabina || 6159 ||
|-
| Sánchez Rubio, Cristina || 6738 ||
|-
| Guerard Ortego, Carlos Kjell || - ||
|-

|}

TJ-II: Influence of magnetic configuration on filament dynamics

2021-12-21T15:49:27Z

Daniel.carralero:

== Experimental campaign ==
2022

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Igor Voldiner, Gustavo Grenfell, Boudewijn van Milligen, Marian Ochando et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>E. de la Cal and The TJ-II Team 2016 Nucl. Fusion 56 106031</ref><ref>B.Ph. van Milligen, J.H. Nicolau, B. Liu et al., Nucl. Fusion 58 026030 (2018)</ref><ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

From this, an overview of the experimental program would be:

a) In a first day of operation, ECRH and NBI plasmas in standard configuration would be probed replicating previous discharges by Kobayashi et al. In this ocasion, both probes would be used to characterize filaments across the SOL in their respective positions and to measure <math>n_e</math>, <math>\phi_f</math> and <math>T_e</math> profiles to the innermost posible position. Time permitting, polarization experiments could be attempted as well. Simultaneously, the GPI system would be used in a slow setting to provide a broad evaluation of <math>n_e</math> and <math>T_e</math> in the edge region.

b) On top of these main diagnostics, profile characterization will be carried out using TS, He beam, ECE, interferometry and profile reflectometry. DR will be used to provide measurements of <math>E_r</math> at the edge, thus complementing probe measurements from floating potential.

c) In a second day of operation, experiments would be repeated once again, using a magnetic configuration featuring enhanced connection length after the separatrix. One viable way to achieve this is to reduce the volume of the magnetically confined region, thus increasing the distance between the LCFS and the limiting elements of the vacuum vessel.

d) In a third day of operation, experiments carried out on the first day would be repeated using a magnetic configuration featuring a low rational in the vicinity of the LCFS, thus creating a set of islands in the edge. These measurements would as well be carried both with normal and reduced volume.

Required resources:
* Number of plasma discharges or days of operation: 3
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration): ECRH & NBI
* Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility in NBI plasmas.
* External users: need a local computer account for data access: yes
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals Spring 2022]]

TJ-II: Influence of magnetic configuration on filament dynamics

2021-12-21T15:45:52Z

Daniel.carralero:

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-11T10:07:07Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>E. de la Cal and The TJ-II Team 2016 Nucl. Fusion 56 106031</ref><ref>B.Ph. van Milligen, J.H. Nicolau, B. Liu et al., Nucl. Fusion 58 026030 (2018)</ref><ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

From this, an overview of the experimental program would be:

a) In a first day of operation, ECRH and NBI plasmas in standard configuration would be probed replicating previous discharges by Kobayashi et al. In this ocasion, both probes would be used to characterize filaments across the SOL in their respective positions and to measure <math>n_e</math>, <math>\phi_f</math> and <math>T_e</math> profiles to the innermost posible position. Time permitting, polarization experiments could be attempted as well. Simultaneously, the GPI system would be used in a slow setting to provide a broad evaluation of <math>n_e</math> and <math>T_e</math> in the edge region.

b) On top of these main diagnostics, profile characterization will be carried out using TS, He beam, ECE, interferometry and profile reflectometry. DR will be used to provide measurements of <math>E_r</math> at the edge, thus complementing probe measurements from floating potential.

c) In a second day of operation, experiments would be repeated once again, using a magnetic configuration featuring enhanced connection length after the separatrix. One viable way to achieve this is to reduce the volume of the magnetically confined region, thus increasing the distance between the LCFS and the limiting elements of the vacuum vessel.

d) In a third day of operation, experiments carried out on the first day would be repeated using a magnetic configuration featuring a low rational in the vicinity of the LCFS, thus creating a set of islands in the edge. These measurements would as well be carried both with normal and reduced volume.

Required resources:
* Number of plasma discharges or days of operation: 3
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration): ECRH & NBI
* Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility in NBI plasmas.
* External users: need a local computer account for data access: yes
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-11T10:06:00Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref><ref>B.Ph. van Milligen, J.H. Nicolau, B. Liu et al., Nucl. Fusion 58 026030 (2018)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

From this, an overview of the experimental program would be:

a) In a first day of operation, ECRH and NBI plasmas in standard configuration would be probed replicating previous discharges by Kobayashi et al. In this ocasion, both probes would be used to characterize filaments across the SOL in their respective positions and to measure <math>n_e</math>, <math>\phi_f</math> and <math>T_e</math> profiles to the innermost posible position. Time permitting, polarization experiments could be attempted as well. ''Simultaneously, the GPI system would be used in a slow setting to provide a broad evaluation of <math>n_e</math> and <math>T_e</math> in the edge region and in a fast setting to characterize filamentary structures in the SOL <ref>E. de la Cal and The TJ-II Team 2016 Nucl. Fusion 56 106031</ref>.''

b) On top of these main diagnostics, profile characterization will be carried out using TS, He beam, ECE, interferometry and profile reflectometry. DR will be used to provide measurements of <math>E_r</math> at the edge, thus complementing probe measurements from floating potential.

c) In a second day of operation, experiments would be repeated once again, using a magnetic configuration featuring enhanced connection length after the separatrix. One viable way to achieve this is to reduce the volume of the magnetically confined region, thus increasing the distance between the LCFS and the limiting elements of the vacuum vessel.

d) In a third day of operation, experiments carried out on the first day would be repeated using a magnetic configuration featuring a low rational in the vicinity of the LCFS, thus creating a set of islands in the edge. These measurements would as well be carried both with normal and reduced volume.

Required resources:
* Number of plasma discharges or days of operation: 3
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration): ECRH & NBI
* Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility in NBI plasmas.
* External users: need a local computer account for data access: yes
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T08:40:03Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

From this, an overview of the experimental program would be:

a) In a first day of operation, ECRH and NBI plasmas in standard configuration would be probed replicating previous discharges by Kobayashi et al. In this ocasion, both probes would be used to characterize filaments across the SOL in their respective positions and to measure <math>n_e</math>, <math>\phi_f</math> and <math>T_e</math> profiles to the innermost posible position. Time permitting, polarization experiments could be attempted as well. ''Simultaneously, the GPI system would be used in a slow setting to provide a broad evaluation of <math>n_e</math> and <math>T_e</math> in the edge region and in a fast setting to characterize filamentary structures in the SOL <ref>E. de la Cal and The TJ-II Team 2016 Nucl. Fusion 56 106031</ref>.''

b) On top of these main diagnostics, profile characterization will be carried out using TS, He beam, ECE, interferometry and profile reflectometry. DR will be used to provide measurements of <math>E_r</math> at the edge, thus complementing probe measurements from floating potential.

c) In a second day of operation, experiments would be repeated once again, using a magnetic configuration featuring enhanced connection length after the separatrix. One viable way to achieve this is to reduce the volume of the magnetically confined region, thus increasing the distance between the LCFS and the limiting elements of the vacuum vessel.

d) In a third day of operation, experiments carried out on the first day would be repeated using a magnetic configuration featuring a low rational in the vicinity of the LCFS, thus creating a set of islands in the edge. These measurements would as well be carried both with normal and reduced volume.

Required resources:
* Number of plasma discharges or days of operation: 3
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration): ECRH & NBI
* Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility in NBI plasmas.
* External users: need a local computer account for data access: yes
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T08:06:22Z

Daniel.carralero: /* Description of the activity */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

Required resources:
* Number of plasma discharges or days of operation:
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T08:05:29Z

Daniel.carralero: /* Description of the activity */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.

2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

Required resources:
* Number of plasma discharges or days of operation:
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T08:04:52Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.
2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.
b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.
c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.
d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.

b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.

c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.

d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

Required resources:
* Number of plasma discharges or days of operation:
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T08:04:31Z

Daniel.carralero: /* Description of the activity */

== Experimental campaign ==
2021

== Proposal title ==
'''TJ-II: Influence of magnetic configuration on filament dynamics'''

== Name and affiliation of proponent ==
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,

== Details of contact person at LNF ==
Daniel Carralero

== Description of the activity ==

SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.

In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.

In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.

Therefore, the goal of this research proposal is to :

1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.
2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.

In a previous characterization of the boundary of TJ-II <ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>, sufficient data for a preliminary evaluation of filaments was gathered <ref> G. Grenfell et al., to be submitted </ref>. Form this first analysis a number of additional requirements were established for a complete characterization of filaments, including:

a) Radially and poloidally separated <math>I_{sat}</math> measurements to carry out correlation-based analysis of filament shape and velocity.
b) Identical probeheads with similar layouts in both manipulators to provide equivalent filament measurements in regions with different curvatures.
c) The best possible characterization of <math>n_e</math> and <math>T_e</math> profiles at the edge and SOL regions.
d) Repeat experiments with a magnetic configuration featuring long connection lengths for several cm. after the LCFS.

== International or National funding project or entity ==
If applicable, enter funding here or write N/A

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:
* Essential diagnostic systems: Dual Langmuir probe system in TJ-II
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)


== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals 2021]]

TJ-II: Influence of magnetic configuration on filament dynamics

2020-12-10T07:51:00Z

Daniel.carralero: /* Description of the activity */

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-08T16:03:50Z

Daniel.carralero: /* Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages) */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.
Finally, one of the previous scans could be repeated in a high ripple configuration in order to check the impact on the measurements of the increased transport.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan). Ideally, both days would be separated in time in order to properly evaluate the results.

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration (100_44_64) with ECH heating. For the high ripple scan, additional shots would be carried out in ECH heated plasmas in 100_32_60 configuration.

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-08T16:02:44Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.
Finally, one of the previous scans could be repeated out in a high ripple configuration in order to check the impact on the measurements of the increased transport.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan). Ideally, both days would be separated in time in order to properly evaluate the results.

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration (100_44_64) with ECH heating. For the high ripple scan, additional shots would be carried out in ECH heated plasmas in 100_32_60 configuration.

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-08T16:01:55Z

Daniel.carralero: /* Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages) */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.
Finally, one of the previous scans could be repeated out in a high ripple configuration in order to check the impact on the measurements of the increased transport.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration (100_44_64) with ECH heating. Additional shots would be carried out in ECH heated plasmas in 100_32_60 configuration.

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-08T15:56:43Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration (100_44_64) with ECH heating. Additional shots would be carried out in ECH heated plasmas in 100_32_60 configuration.

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Experimental proposals

2018-03-08T15:48:36Z

Daniel.carralero: /* Experimental proposals, 2018 Spring */

[[File:TJII_model.jpg|400px|thumb|right|TJ-II Model]]

== Creation of a new proposal ==

# Log in to the FusionWiki. If you don't have an account, request one by clicking 'Create account' in the left-hand menu.
# ''Type the name of your proposal page in the field below''. The required format is: 'TJ-II:Title of my proposal' (without the apostrophes). Note the 'TJ-II:' at the beginning!
# Click 'Create new proposal'. Your proposal page will be created. Edit and save (please use 'Show preview' before saving the final version).

<inputbox>
type=create
default=TJ-II:Title of my proposal
buttonlabel=Create new proposal with this title
preload=TJ-II:Proposal_template
</inputbox>

The proposal page is created on the basis of this [[TJ-II:Proposal template|Proposal template]]. You do not need to view or modify it.

== Inclusion of your proposal in the proposal list ==

* Edit the table below and add your proposal (instructions in the table).
* The link to your proposal is as follows: <nowiki>[[TJ-II:Title of your proposal|]]</nowiki> (the final character before the closing brackets <nowiki>]]</nowiki> is a vertical slash).

== Experimental proposals, 2018 Spring==
Deadline: March 7, 2018

{| class="wikitable sortable" width="100%" border="1" cellpadding="5" cellspacing="0" style="text-align:left"
|- style="background:#FFDEAD;"
! width="10%"| '''Nr.'''
! width="60%"| '''Title'''
! width="30%"| '''Proponent(s)'''




|-
 | 1
 | [[TJ-II:Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator|Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator]]
 | [mailto:josepmaria.fontdecaba@ciemat.es J.M. Fontdecaba]



|-
 | 2
 | [[TJ-II:Poloidal 2D scans to investigate potential and density profiles in the TJ-II stellarator using dual Heavy ion beam probe diagnostic|Poloidal 2D scans to investigate potential and density profiles in the TJ-II stellarator using dual Heavy ion beam probe diagnostic]]
 | [mailto:ridhimas757@gmail.com R. Sharma]

|-
 | 3
 | [[TJ-II:Validation of bootstrap predictions|Validation of bootstrap predictions]]
 | [mailto:joseluis.velasco@ciemat.es J.L.Velasco]

|-
 | 4
 | [[TJ-II:Transport analysis by means of the Transfer Entropy|Transport analysis by means of the Transfer Entropy]]
 | [mailto:boudewijn.vanmilligen@ciemat.es B.Ph. van Milligen]

|-
 | 5
 | [[TJ-II:Understanding an often observed transient rise in core electron temperature during pellet injection into TJ-II plasmas|Understanding an often observed transient rise in core electron temperature during pellet injection into TJ-II plasmas]]
 | [mailto:kieran.mccarthy@ciemat.es K J McCarthy]

|-
 | 6
 | [[TJ-II:Improving fuelling efficiency in TJ-II ECRH plasmas|Improving fuelling efficiency in TJ-II ECRH plasmas]]
 | [mailto:kieran.mccarthy@ciemat.es M Calvo]

|-
 | 7
 | [[TJ-II:The influence of a core fast electron population on pellet fuelling efficiency in TJ-II|The influence of a core fast electron population on pellet fuelling efficiency in TJ-II]]
 | [mailto:nerea.panadero@externos.ciemat.es N Panadero]

|-
 | 8
 | [[TJ-II:Studies of LIquid Metal insertion in TJ-II|Studies of LIquid Metal insertion in TJ-II]]
 | [mailto:tabares@ciemat.es P.Tabares]

|-
 | 9
 | [[TJ-II:Fast Camera studies with triple bundle|Fast Camera studies with triple bundle]]
 | [mailto:e.delacal@ciemat.es E. de la Cal]

|-
 | 10
 | [[TJ-II:Validation of ECCD predictions in TJ-II ECRH plasmas|Validation of ECCD predictions in TJ-II ECRH plasmas]]
 | [mailto:jose.regana@ciemat.es J. M. García-Regaña]

|-
 | 11
 | [[TJ-II:Radiation asymmetries and potential variations|Radiation asymmetries and potential variations]]
 | [mailto:jose.regana@ciemat.es J. M. García-Regaña]

|-
 | 12
 | [[TJ-II:Turbulence and radial electric field asymmetries in high iota magnetic configuration measured by Doppler reflectometry|Turbulence and radial electric field asymmetries in high iota magnetic configuration measured by Doppler reflectometry]]
 | [mailto:teresa.estrada@ciemat.es Teresa Estrada]

|-
 | 13
 | [[TJ-II:Influence of electron / ion root and ion mass on the radial and frequency structure of zonal flows in TJ-II|Influence of electron / ion root and ion mass on the radial and frequency structure of zonal flows in TJ-II]]
 | [mailto:Bing.Liu@swjtu.edu.cn Bing Liu]

|-
 | 14
 | [[TJ-II:Blobs vs streamers|Blobs vs streamers]]
 | [mailto:Boudewijn.vanMilligen@ciemat.es B.Ph. van Milligen]

|-
 | 15
 | [[TJ-II:Investigation of the ECRH power level and deposition radius on impurity confinement after injection by laser blow-off in TJ-II|Investigation of the ECRH power level and deposition radius on impurity confinement after injection by laser blow-off in TJ-II]]
 | [mailto:belen.lopez@ciemat.es Belén López-Miranda]
|-
 | 16
 | [[TJ-II: Evaluation of Neoclassical transport correction terms in TJ-II|Evaluation of Neoclassical transport correction terms in TJ-II]]
 | [mailto:daniel.carralero@ciemat.es Daniel Carralero]

|-
|}

== Experimental proposals, 2017 Spring==
Deadline: January 26, 2017

{| class="wikitable sortable" width="100%" border="1" cellpadding="5" cellspacing="0" style="text-align:left"
|- style="background:#FFDEAD;"
! width="10%"| '''Nr.'''
! width="60%"| '''Title'''
! width="30%"| '''Proponent(s)'''




|-
 | 1
 | [[TJ-II:Search for physical mechanisms that lead to increase of turbulence following pellet injection|Search for physical mechanisms that lead to increase of turbulence following pellet injection]]
 | [mailto:kieran.mccarthy@ciemat.es Kieran McCarthy]


|-
 | 2
 | [[TJ-II:Effect of pellet injection on the radial electric field profile of stellarators|Effect of pellet injection on the radial electric field profile of stellarators]]
 | [mailto:silvagnidavide1@gmail.com,joseluis.velasco@ciemat.es Davide Silvagni, José L. Velasco]


|-
 | 3
 | [[TJ-II:Excitation of zonal flow oscillations by energetic particles|Excitation of zonal flow oscillations by energetic particles]]
 | [mailto:edi.sanchez@ciemat.es Edi Sánchez]


|-
 | 4
 | [[TJ-II:Radial electric field of low-magnetic-field low-collisionality NBI plasmas|Radial electric field of low-magnetic-field low-collisionality NBI plasmas]]
 | [mailto:joseluis.velasco@ciemat.es José L. Velasco]


|-
 | 5
 | [[TJ-II:Comparison of transport of on-axis and off-axis ECH-heated plasmas|Comparison of transport of on-axis and off-axis ECH-heated plasmas]]
 | [mailto:joseluis.velasco@ciemat.es,edi.sanchez@ciemat.es José L. Velasco, Edi Sánchez]
|-

 | 6
 | [[TJ-II:Impurity injection by laser blow-off: influence of main ions charge/mass on impurity confinement and transport|Impurity injection by laser blow-off: influence of main ions charge/mass on impurity confinement and transport]]
 | [mailto:belen.lopez@ciemat.es Belén López-Miranda]

|-

 | 7
 | [[TJ-II:PelletFuelling|PelletFuelling]]
 | [mailto:kieran.mccarthy@ciemat.es Kieran McCarthy]

|-

 | 8
 | [[TJ-II:Impurity density and potential asymmetries|Impurity density and potential asymmetries]]
 | [mailto:jose.regana@ciemat.es José M. García Regaña]

|-

 | 9
 | [[TJ-II:Investigation of turbulence spreading and information transfer in the TJ-II stellarator|Investigation of turbulence spreading and information transfer in the TJ-II stellarator]]
 | [mailto:boudewijn.vanmilligen@ciemat.es Boudewijn van Milligen]

|-

 | 10
 | [[TJ-II:Role of isotope effect on biasing induced transitions in the TJ-II stellarator|Role of isotope effect on biasing induced transitions in the TJ-II stellarator]]
 | [mailto:carlos.hidalgo@ciemat.es S. Ohshima]

|-

 | 11
 | [[TJ-II:Investigation of the mechanism of decoupling between energy and particle transport channels: Proposal for joint experiments in TJ-II and H-J|Investigation of the mechanism of decoupling between energy and particle transport channels: Proposal for joint experiments in TJ-II and H-J]]
 | [mailto:bing.liu@externos.ciemat.es,ulises.losada@ciemat.es Bing Liu, Ulises Losada]

|-

 | 12
 | [[TJ-II: Alfven Eigenmodes and biasing in TJ-II| Alfven Eigenmodes and biasing in TJ-II]]
 | [mailto:melnikov_07@yahoo.com A. Melnikov]

|-

 | 13
 | [[TJ-II: Potential asymmetries at low magnetic field | Potential asymmetries at low magnetic field ]]
 | [mailto:jose.regana@ciemat.es José M. García-Regaña]
|-

 | 14
 | [[TJ-II:NBI contribution to plasma fuelling|NBI contribution to plasma fuelling]]
 | [mailto:macarena.liniers@ciemat.es Macarena Liniers]

|-

 | 15
 | [[TJ-II: Investigation of plasma asymmetries in the TJ-II stellarator and comparison with Gyrokinetic simulations|Investigation of plasma asymmetries in the TJ-II stellarator and comparison with Gyrokinetic simulations]]
 | [mailto:Edi.sanchez@ciemat.es Edi Sanchez]

|-

 | 16
 | [[TJ-II:Effect of ECRH on the characteristics of Alfven Eigenmodes activity|Effect of ECRH on the characteristics of Alfven Eigenmodes activity]]
 | [mailto:alvaro.cappa@ciemat.es,enrique.ascasibar@ciemat.es,francisco.castejon@ciemat.es Álvaro Cappa, Enrique Ascasíbar, Paco Castejón]

|-

 | 17
 | [[TJ-II:Investigating the Alfvén Wave damping|Investigating the Alfvén Wave damping]]
 | [mailto:francisco.castejon@ciemat.es Paco Castejón, Álvaro Cappa, Enrique Ascasíbar]

|-

 | 18
 | [[TJ-II:L-H Transition and Isotope Effect in low magnetic ripple configurations|L-H Transition and Isotope Effect in low magnetic ripple configurations]]
 | [mailto:teresa.estrada@ciemat.es,Ulises.LosadaRodriguez@ciemat.es,Carlos.Hidalgo@ciemat.es Teresa Estrada,Ulises Losada,Carlos Hidalgo]

|-

 | 19
 | [[TJ-II:Measurements of radial correlation length and tilting of turbulent eddies by Radial Correlation Doppler Reflectometry|Measurements of radial correlation length and tilting of turbulent eddies by Radial Correlation Doppler Reflectometry]]
 | [mailto:teresa.estrada@ciemat.es,javier.pinzon@ipp.mpg.de,tim.happel@ipp.mpg.de Javier Pinzon, Tim Happel,Teresa Estrada]

|-

 | 20
 | [[TJ-II:Measurement of Te and ne of Blobs analyzing recycling helium emission in front of a poloidal limiter|Measurement of Te and ne of Blobs analyzing recycling helium emission in front of a poloidal limiter]]
 | [mailto:e.delacal@ciemat.es, Eduardo de la Cal]

|-
|}

== See also ==

* [[TJ-II:Experimental program]] (current)
* [http://intranet-fusion.ciemat.es/document-server/tj-ii-experimental-program/ Experimental programs for earlier years (2002-2016)] (Intranet, password required)

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:43:26Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration (100_44_64) with ECH heating

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:42:59Z

Daniel.carralero: /* Preferred dates and degree of flexibility */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration with ECH heating

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018

- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:42:48Z

Daniel.carralero: /* Preferred dates and degree of flexibility */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration with ECH heating

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates:

Any time from 01-05-2018 except:

- 22 to 24-05-2018
- 18 to 25-06-2018

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:39:21Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration with ECH heating

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:37:34Z

Daniel.carralero: /* Description of required resources */

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tuning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus all other diagnostics involved in the Bayesian profile determination, such as interferometer, ECE, Helium beam, etc).

Ti measurements from the NPA will be useful to estimate the ion temperature profiles used for NC simulations and e-i energy exchange estimations. Bolometry will be used to monitor radiation losses.

* Type of plasmas (heating configuration):

Standard configuration with ECH heating

* Specific requirements on wall conditioning if any:

Fresh lithiation is required in order to minimize the effect of impurities in the radiation profile.

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]

TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II

2018-03-07T16:33:51Z

Daniel.carralero: Created page with "== Experimental campaign == 2018 Spring == Proposal title == Evaluation of Neoclassical transport correction terms in TJ-II == Name and affiliation of proponent == D. Carral..."

== Experimental campaign ==
2018 Spring

== Proposal title ==
Evaluation of Neoclassical transport correction terms in TJ-II

== Name and affiliation of proponent ==
D. Carralero, J.L. Velasco, T. Estrada and the TJ-II team

== Details of contact person at LNF (if applicable) ==
email: daniel.carralero@ciemat.es

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

'''Background'''

Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Vanishing neoclassical viscosity and physics of the shear layer in stellarators'' Phys. Rev. Lett. 109 135003 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence.

Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>.

As for the Er dependence, it is worth noting that the contribution of the tangential magnetic drift (MTD) in the ion drift kinetic equation at low collisionalities has traditionally been considered negligible for high aspect ratio machines when the radial electric field is large. This assumption has recently been called into question for realistic values of Er, meaning that heat and particle fluxes calculated with NC transport coefficients derived without taking into account the MTD could be inaccurate. This would be specially the case when approaching the root transition, in which Er~0 and the role of MTD becomes particularly relevant. In this situation, conventional calculations predict a clear maximum on radial fluxes around Er=0, e.g. <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref>, while the peak in ion transport obtained with simulations carried out taking MTD into account <ref> S. Matsuoka et al., ''Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas'', Physics of Plasmas 22 (2015), 072511 </ref> <ref> B. Huang et al., ''Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas'', Physics of Plasmas 24 (2017), 022503 </ref> is reduced in amplitude and displaced towards Er < 0 (the peak in electron transport should appear then at Er>0). The difference between the two trends could be large enough to be clearly noticeable experimentally, thus representing a good method to evaluate the general validity of the NC transport predictions and the relevance of the MTD in a real-life plasma. It is important to notice that, while this effect should be noted within a wide range of collisionalities, this dependence on the Er does not appear at the plateau regime. Therefore, collisionality must be kept below the threshold for such regime.

With this purpose, we propose to characterize radial electron transport in ECH plasmas of the TJ-II stellarator by realizing density and power scans around the root transition. The objective of these scans would be to obtain a set of shots with comparable Te and ne gradients and different values of Er (comprising a wide range of 0 < Er and Er > 0 values) so that experimental qr,e (Er) can be determined and compared with the corresponding simulations with and without MTD.

'''Approach'''

In TJ-II, the radial electric field can be measured for a wide radial range by means of Doppler reflectometry (DR). Besides, although qr,e can’t be directly measured, in a stationary plasma, the divergence of qe is determined locally by source terms, which can be evaluated approximately based on data available in TJ-II: the most relevant source terms include radiation (which is considered to be small <ref name=Tallents />), ECH power deposition (which will be estimated at the beginning of the experimental day by means of fast modulation of one of the gyrotrons, and should also be small in the radial region probed by the DR) and energy transfer to the ion species, which can be calculated based on density and temperature profiles. In TJ-II, the root transition can be accessed either by a change in density or by a change in heating power. In particular, the Er measured by DR has been observed to change strongly with moderate increases of ne around a critical density determined by the injected heating power. These changes in the electric field seem to have a minor effect on ne and Te profiles, thus providing an scenario in which qr,e (Er) can be obtained experimentally for a range of roughly equivalent ne and Te gradients. This is important in order to allow for a meaningful comparison between measurements and theoretical predictions. Since the plateau regime is to be avoided, when selecting the combination of densities and heating powers for the experiments, collisionality must be minimized whenever possible (i.e., reducing density, or preferably, increasing Te). As well, freshly lithiated walls are required in order to minimize the role of radiation on the electron power balance.

'''Experiment description'''

First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values.
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range.

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation:

10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tuning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan).

* Essential diagnostic systems:

The essential diagnostics are those used to measure Er (Doppler reflectometer) and Te and ne profiles (Thomson scattering, plus

* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]