Particle-in-cell simulations of anomalous transport in a Penning discharge

TL;DR

This paper uses particle-in-cell simulations to study azimuthally asymmetric spoke-like structures in a Penning discharge, revealing their formation, rotation, and role in enhanced radial electron transport, consistent with experimental observations.

Contribution

It demonstrates the formation and dynamics of spoke-like structures in Penning discharges through simulations, highlighting ion inertia's role and the resulting anomalous transport.

Findings

Spoke-like structures form and rotate in simulations, matching experimental behavior.

Spokes increase radial electron transport beyond classical predictions.

Simulation results agree with experimental data on anomalous current levels.

Abstract

Electrostatic particle-in-cell simulations of a Penning discharge are performed in order to investigate azimuthally asymmetric, spoke-like structures previously observed in experiments. Two-dimensional simulations show that for Penning-discharge conditions, a persistent nonlinear spoke-like structure forms readily and rotates in the direction of ExB and electron diamagnetic drifts. The azimuthal velocity is within about a factor of two of the ion acoustic speed. The spoke frequency follows the experimentally observed scaling with ion mass, which indicates the importance of ion inertia in spoke formation. The spoke provides enhanced (anomalous) radial electron transport, and the effective cross-field conductivity is several times larger than the classical (collisional) value. The level of anomalous current obtained in the simulations is in good agreement with the experimental data. The rotating spoke channels most of the radial current, observable by an edge probe as short pulses.