TJ-II: Infuence of AEs on ExB transport: role of phase shift effects

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Experimental campaign

2021

Proposal title

TJ-II: Infuence of AEs on ExB transport: role of phase shift effects

Name and affiliation of proponent

David Zarzoso and Samuel Mazzi / Aix Marseille University

Alexander Melnikov and the HIBP Kurchatov team

Alexander Kozachez and the HIBP Kharkov team

Jacobo Varela / UC3M

Jerónimo García / CEA, IRFM

Filip Papausek, Ulises Losada, Boudewijn van Milligen, Alvaro Cappa, Macarena Liniers, Marian Ochando, Enrique Ascasibar, Carlos Hidalgo and the TJ-II Ciemat

Details of contact person at LNF

If applicable, enter contact person here or write N/A

Description of the activity

In recent JET discharges, the 3-ion heating scheme [1] [2] was used to produce a significant population of MeV ions leading to the excitation of intense TAE. Under these circumstances, a significant improvement of thermal transport was observed, likely due to the reduction of turbulent transport. Such discharges were modelled using the state-of-the-art gyro-kinetic code GENE [3] in its flux-tube approximation in order to shed light on the underlying mechanism for such improved confinement. It was observed that the presence of highly energetic ions and intense TAE activity was accompanied by a dramatic reduction of turbulent transport. Also, the generation of large amplitude zonal flows was observed, suggesting a mechanism where TAEs lead to an excitation of zonal flows and hence to a subsequent reduction of turbulence [4]. However, a concomitant effect might take place due to the modification of the phase shift between the density/temperature and electrostatic potential induced by the parallel dynamics of Alfvén eigenmodes. The modification of the phase shift during the suppression of turbulent transport is evidenced in the attached PowerPoint presentation.

The dual HIBP system [5] as well as edge Langmuir probes [6] have provided direct measurements of transport induced by AEs in the TJ-II stellarator . Previous experiments by HIBP have shown evidence of both inwards and outwards transport with a cross-phase between density and potential fluctuations that is nearly constant as density increases [7]. These measurements were performed with poloidal wave number resolution up to 3 cm-1. Recent Langmuir probe measurements with AEs localized in the edge region have shown evidence of AEs with an associated transport due to local density and potential fluctuations that is comparable to the one due to broadband turbulence [8]. These measurements were done with wave-number resolution up to 10 cm-1. The goal of this proposal is to further investigate the influence of AEs on ExB turbulent transport. With this purpose, the strategy of the proposed TJ-II experimental program would be:

1. Investigation of AEs localized in the edge & core region by means of edge probes and HIBP [reference shot 43706] and AEs identification.

2. Influence of plasma density and magnetic configuration on AEs and associated ExB turbulent transport and their role on the phase relation between density and potential fluctuations using edge probes and HIBP diagnostics.

3. Comparative studies between gyro-kinetic code simulations and TJ-II experimental results.

International or National funding project or entity

If applicable, enter funding here or write N/A

Description of required resources

Required resources:

• Number of days of operation: 3

• Essential diagnostic systems: Dual Langmuir probe system in TJ-II [February & May/June] and HIBP [May / June]

• Type of plasmas (heating configuration): ECRH & NBI

• Wall conditioning: Sufficient density control for good reproducibility in NBI plasmas.

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. Ongena, J. et al. Synergetic heating of D-NBI ions in the vicinity of the mode conversion layer in H-D plasmas in JET with the ITER like wall. In EPJ Web of Conferences, volume 157, page 02006. EDP Sciences, 2017.
  2. Kazakov, Y. O., et al. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, 13(10):973–978, 2017.
  3. Jenko, F. et al. Electron temperature gradient driven turbulence. Physics of Plasmas, 7(5):1904–1910, 2000.
  4. Mazzi, S. et al. Towards enhanced performance in fusion plasmas via turbulence suppression by MeV ions, submitted to Nature Physics.
  5. Melnikov, A.V. et al “Internal measurements of Alfvén eigenmodes with heavy ion beam probing in toroidal plasmas” 2010 Nucl. Fusion 50 084023
  6. Papausek, Filip et al., Master Thesis 2021
  7. Melnikov, A.V. et al “Internal measurements of Alfvén eigenmodes with heavy ion beam probing in toroidal plasmas” 2010 Nucl. Fusion 50 084023
  8. Papausek, Filip et al., Master Thesis 2021

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