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LNF:Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL): Difference between revisions

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== LNF - Nationally funded project ==
== LNF - Nationally funded project ==


'''Title''': '''Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL)e'''
'''Title''': '''Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL)'''


'''Reference''': PID2020-116599RB-I00
'''Reference''': PID2020-116599RB-I00
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1. The first aim is to investigate aspects of plasma fuelling that are still not fully understood and the effects of fuel pellets on plasma magnetic activity, plasma turbulence and plasma performance. For this, the medium-sized heliac TJ-II will be used. It is equipped with a cryogenic pellet injector (PI) for producing solid hydrogen pellets that can be injected at high velocity into the plasma. It is intended to investigate pellet fuelling as a means to enhance plasma confinement (higher stored energy, longer particle confinement) and to identify and explore new pellet phenomena. While TJ-II is equipped with a large number of modern diagnostics, it is proposed to develop a new system to measure pellet cloud density and temperature to extend knowledge of pellet physics.
1. The first aim is to investigate aspects of plasma fuelling that are still not fully understood and the effects of fuel pellets on plasma magnetic activity, plasma turbulence and plasma performance. For this, the medium-sized heliac TJ-II will be used. It is equipped with a cryogenic pellet injector (PI) for producing solid hydrogen pellets that can be injected at high velocity into the plasma. It is intended to investigate pellet fuelling as a means to enhance plasma confinement (higher stored energy, longer particle confinement) and to identify and explore new pellet phenomena. While TJ-II is equipped with a large number of modern diagnostics, it is proposed to develop a new system to measure pellet cloud density and temperature to extend knowledge of pellet physics.


2. The second aim is to continue to support impurity transport and accumulation studies in TJ-II and W7-X. Under the umbrella of a trilateral collaboration (2020-2029) with the National Institute for Fusion Science (Japan) and IPP-Max-Planck (Greifswald, Germany), Tracer-Encapsulated Solid Pellet (TESPEL) injections systems hare now operated on both TJ-II and W7-X. TESPELs are polystyrene spheres (diameter <1 mm) loaded with impurity tracers (atomic elements other than fuel). This allows delivering a precise quantify of tracer to a preselected location in the plasma core, after which its transport and confinement can be studied. An important aspect of the collaboration has been the establishment of a laboratory to fabricate TESPELs at Ciemat for both devices (project FIS2017- 89326-R). Key parts of this current project are to continue TESPEL fabrication for TJ-II and W7-X at this laboratory, thereby allowing Ciemat to maintain this fruitful collaboration, and to upgrade a vacuum ultraviolet spectrometer on TJ-II to provide important spectral line data for impurity identification in W7-X.
2. The second aim is to continue to support impurity transport and accumulation studies in TJ-II and W7-X. Under the umbrella of a trilateral collaboration (2020-2029) with the National Institute for Fusion Science (Japan) and IPP-Max-Planck (Greifswald, Germany), Tracer-Encapsulated Solid Pellet (TESPEL) injections systems are now operated on both TJ-II and W7-X. TESPELs are polystyrene spheres (diameter <1 mm) loaded with impurity tracers (atomic elements other than fuel). This allows delivering a precise quantify of tracer to a preselected location in the plasma core, after which its transport and confinement can be studied. An important aspect of the collaboration has been the establishment of a laboratory to fabricate TESPELs at Ciemat for both devices (project FIS2017- 89326-R). Key parts of this current project are to continue TESPEL fabrication for TJ-II and W7-X at this laboratory, thereby allowing Ciemat to maintain this fruitful collaboration, and to upgrade a vacuum ultraviolet spectrometer on TJ-II to provide important spectral line data for impurity identification in W7-X.


The PI and TESPEL systems on TJ-II share a common injection guide lines. This unique set-up allows direct comparative studies of ablation, deposition and plasma response to be made thereby facilitating the understanding of common physics. Given that fuelling and impurity control are critical issues for stellarator steady-state operation, the project will allow us to continue to contribute to, and participate in, research programmes on W7-X, the stellarator of reference. Finally, team members have significant experience in the formation of young researchers at Master and PhD levels and in disseminating research to second level students and to the general public. A PhD student will undertake research in these areas during the project.
The PI and TESPEL systems on TJ-II share a common injection guide lines. This unique set-up allows direct comparative studies of ablation, deposition and plasma response to be made thereby facilitating the understanding of common physics. Given that fuelling and impurity control are critical issues for stellarator steady-state operation, the project will allow us to continue to contribute to, and participate in, research programmes on W7-X, the stellarator of reference. Finally, team members have significant experience in the formation of young researchers at Master and PhD levels and in disseminating research to second level students and to the general public. A PhD student will undertake research in these areas during the project.
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[5] The effect of pellet injection on turbulent transport in TJ-II, L. García, I. García-Cortés, B. A. Carreras, K. J. McCarthy, B. van Milligen and TJ-II team, Phys. Plasmas 30 (2023) 092303. https://doi.org/10.1063/5.0163832
[5] The effect of pellet injection on turbulent transport in TJ-II, L. García, I. García-Cortés, B. A. Carreras, K. J. McCarthy, B. van Milligen and TJ-II team, Phys. Plasmas 30 (2023) 092303. https://doi.org/10.1063/5.0163832


[6] Impact of the rotational transform on enhanced confinement in the TJ-II stellarator. Part 1: experimental results, B. Ph. van Milligen, I. García-Cortés, K. J. McCarthy, T. Estrada, A. Cappa, P. Pons-Villalonga, B. A. Carreras, L. García, O. S. Kozachok, O. O. Chmyga, J. L. de Pablos, J. M. Barcala, A Molinero, D. Tafalla, I. Pastor, A. de la Peña, F. Lapayese, (...) and the TJ-II Team, in preparation for Nucl. Fusion.
[6] The rotational transform and enhanced confinement in the TJ-II stellarator, B. Ph. van Milligen, I. García-Cortés, K. J. McCarthy, B. A. Carreras, L. García, A. Cappa, P. Pons-Villalonga, T. Estrada, D. Medina-Roque, J. Hernández-Sánchez, R. garcía, O. S. Kozachok, O. O. Chmyga, J. L. de Pablos, J. M. Barcala, A. Molinero, I. Pastor, D. Tafalla, A. de la Peña, F. Lapayese and the TJ-II Team, J. Plasma Physics 91 (2025) E98. https://doi.org/10.1017/S0022377825100433.


[7] Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas, C. Hidalgo, ..., I. García-Cortés, ..., J. Hernández-Sánchez, ..., B. López-Miranda, ..., K. J. McCarthy, ..., P. Méndez, ..., N. Panadero, ..., N. Tamura, ..., et al., Nucl. Fusion 62 (2022) 042025, https://doi.org/10.1088/1741-4326/ac2ca1  
[7] Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas, C. Hidalgo, ..., I. García-Cortés, ..., J. Hernández-Sánchez, ..., B. López-Miranda, ..., K. J. McCarthy, ..., P. Méndez, ..., N. Panadero, ..., N. Tamura, ..., et al., Nucl. Fusion 62 (2022) 042025, https://doi.org/10.1088/1741-4326/ac2ca1  
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[10] Commissioning of the Tracer-Encapsulated Solid Pellet (TESPEL) Injection system for Wendelstein 7-X and first results, R. Bussiahn, N. Tamura, K. J. McCarthy, B. Buttenschön, C. Brandt, A. Dinklage, A. Langenberg and the W7-X team, Plasma Phys. Control. Fusion, 66 (2024) 115020. https://doi.org/10.1088/1741-4326/ac2cf5.
[10] Commissioning of the Tracer-Encapsulated Solid Pellet (TESPEL) Injection system for Wendelstein 7-X and first results, R. Bussiahn, N. Tamura, K. J. McCarthy, B. Buttenschön, C. Brandt, A. Dinklage, A. Langenberg and the W7-X team, Plasma Phys. Control. Fusion, 66 (2024) 115020. https://doi.org/10.1088/1741-4326/ac2cf5.


[11] Additional ECRH mitigates thermal quenches induced by tungsten TESPEL injection in LHD , H. Bouvain, A. Dinklage, N. Tamura, H. Igami, H. Kasahara, K. J. McCarthy, D. Medina Roque, I. García-Cortés and the LHD Experiment Group, sent to Nuclear Fusion for publication, NF-106861.  
[11] Additional ECRH mitigates thermal quenches induced by tungsten TESPEL injection in LHD, H. Bouvain, A. Dinklage, N. Tamura, H. Igami, H. Kasahara, K. J. McCarthy, D. Medina Roque, I. García-Cortés and the LHD Experiment Group, sent to Nuclear Fusion for publication, NF-106861.  


[12] Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X, T. S. Pedersen, ..., I. García-Cortés, K. J. McCarthy, …, N. Panadero Alvarez, ..., N. Tamura, ..., Nucl Fusion 62, 042022 (2022). DOI: 10.1088/1741-4326/ac2cf5.
[12] Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X, T. S. Pedersen, ..., I. García-Cortés, K. J. McCarthy, …, N. Panadero Alvarez, ..., N. Tamura, ..., Nucl Fusion 62, 042022 (2022). https://doi.org/10.1088/1741-4326/ac2cf5


[13] Overview of the first Wendelstein 7-X long pulse campaign with fully water-cooled plasma facing components, O. Grulke, …, R. Bussiahn, ..., I. García-Cortés, ..., K. J. McCarthy, ..., D. Medina Roque, …, N. Panadero Alvarez, ..., N. Tamura, et al., Nucl Fusion 62 (2024) 112002. https://doi.org/10.1088/1741-4326/ad2f4d.
[13] Overview of the first Wendelstein 7-X long pulse campaign with fully water-cooled plasma facing components, O. Grulke, …, R. Bussiahn, ..., I. García-Cortés, ..., K. J. McCarthy, ..., D. Medina Roque, …, N. Panadero Alvarez, ..., N. Tamura, et al., Nucl Fusion 62 (2024) 112002. https://doi.org/10.1088/1741-4326/ad2f4d.
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