Author: Alistair M Arnold
Requested Type: Poster
Submitted: 2022-03-03 10:20:10
Co-authors: P.Aleynikov, B.N.Breizman
Max Planck Institute for Plasma Physics
Greifswald, Mecklenbur 17491
We present a model of the expansion of a pellet plasmoid along magnetic field lines which takes into account plasmoid heating by ambient electrons. The separation of scales between the electron bounce period, plasmoid electron self-collision time, and ambient electron collision time is the basis for the model. The model implies that the bounce period of a plasmoid electron is much shorter than the self-collision time. The bounce-averaged distribution of the plasmoid electrons is generally not Maxwellian in this limiting case. We find a closed-form expression for the electron distribution assuming that elastic scattering of the electrons is much faster than their energy equilibration. We perform numerical simulations of the plasmoid expansion with a view to understand the impact of the self-consistent electric potential well on the expansion rate and the energy balance between electrons and ions. The ambipolar electric field converts electron energy into ion flow energy. The presence of the electric potential well causes a drop in density and an increase in the typical kinetic energy of ambient electrons, resulting in suppression of the heating rate of plasmoid electrons. Due to the competing effects of electron heating and adiabatic cooling, even a modestly deep well relative to the ambient plasma temperature results in a drastically slower growth of the plasmoid electron temperature.