Mainz 2022 – scientific programme
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P: Fachverband Plasmaphysik
P 19: Poster II
P 19.30: Poster
Thursday, March 31, 2022, 16:00–17:30, P
Parallel expansion of a pellet plasmoid in a finite electric potential well — •Alistair Mark Arnold1, Pavel Aleynikov1, and Boris Breizman2 — 1Max-Planck-Institut für Plasmaphysik, Greifswald, Deutschland — 2Institute for Fusion Studies, University of Texas, Austin, USA
We consider the expansion parallel to magnetic field lines of the plasmoid produced by a fuel pellet. In particular, we take into account the finite height of the electric potential well confining the plasmoid electrons. If it is assumed that electron bounce motion occurs much more rapidly than collisions and trapped electron self-collisions occur much more rapidly than other kinds of collisions, a quasi-equilibrium state is reached with a non-Maxwellian electron distribution function. A closed-form expression for the distribution function is obtained for an arbitrary well under the assumption that pitch-angle scattering dominates. Corresponding analytical expressions are found for particle and energy exchange between the passing and trapped electrons. Agreement with literature on mirror machines and even classical thermodynamics is found in appropriate wells. The non-Maxwellian distribution function precludes rigorous modelling of the plasmoid expansion using the Braginskii equations. The trapped distribution function is, however, specified by only two time-dependent quantities -- a fluid closure of the system is possible despite the highly non-Maxwellian distribution. We seek to understand the influence of the above effects on the expansion rate and ultimate electron-ion energy balance during fuel pellet injection.