The effects of non-uniform drive on plasma filaments

TL;DR

This study uses simulations to understand how non-uniform magnetic curvature drive influences plasma filament propagation in complex magnetic geometries like Wendelstein 7-X, revealing coherent and variable filament behaviors.

Contribution

It demonstrates how non-uniform magnetic curvature drive affects plasma filament propagation, incorporating realistic Wendelstein 7-X magnetic geometry in simulations.

Findings

Filaments propagate coherently with the average drive when the mean curvature drive is non-zero.

Non-uniform drive causes variable filament propagation, reduced at higher temperatures.

Simulations suggest slow radial filament propagation despite highly non-uniform drive profiles.

Abstract

Wendelstein 7-X core fueling is primarily achieved through pellet injection. The trajectory of plasmoids from an ablating pellet is an ongoing research question, which is complicated by the complex magnetic geometry of W7-X; curvature drive varies significantly toroidally, including a change in the drift drive direction. Here we use the Hermes model in BOUT++ to simulate cold plasma filaments in slab geometries where the magnetic drift drive is non-uniform along the field line. It is shown that if the field-line-averaged curvature drive is non-zero, a filament will propagate coherently in the direction of average drive. It is also shown that a non-uniform drive will provide a non- uniform propagation; an effect which is reduced at higher temperatures due to an increased sound speed along the field line. Finally, simulations with curvature similar to that found in Wendelstein 7-X are performed which indicate a slow radial propagation of plasma filaments despite a highly non-uniform drive profile.