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P: Fachverband Plasmaphysik

P 10: Poster Session 2

P 10.16: Poster

Dienstag, 10. März 2020, 16:30–18:30, Empore Lichthof

Self-similar hydrodynamics and pellet injection — •Alistair Arnold, Per Helander, and Pavel Aleynikov — IPP Greifswald, Stellarator Theory Department

Pellet injection is a kind of refuelling used in stellarators and tokamaks (in particular the Wendelstein 7-X stellarator[1]), and is associated with a large and rapid net exchange of energy between electrons and ions[2]. From a hydrodynamic perspective, assuming that pellet ions remain at zero temperature, the result of the cold pellet electrons being heated by a background of hot electrons is ambipolar expansion of the entire cloud, with the electrons 'dragging along' the cold ions. The early phase of the expansion is self-similar in nature, due to the lack of inherent length scale associated with the hydrodynamic problem. Approximately half of the heating power provided to the cold electrons is transferred to the cold ions in the form of flow velocity kinetic energy, which is eventually converted to heat by collisions with the background. The limits of the validity of the hydrodynamic approach are investigated as well as the microscopic collisional picture of pellet injection, in particular the role of energy transfer between cold ions and electrons, and the conversion of the pellet ions' parallel energy to heat on a collisional timescale that is slow compared to the cloud expansion.

[1] R C Wolf et al. Major results from the first plasma campaign of the wendelstein 7-x stellarator. Nuclear Fusion, 57(10):102020, 2017.

[2] A Aleynikov et al. Plasma ion heating by cryogenic pellet injection. Journal of Plasma Physics, 85(905850105), 2019.