Three-Dimensional Kinetic Simulations of Non-Equilibrium Partially Magnetized ExB Devices – Anomalous Transport & Coherent Structures

Non-equilibrium, partially magnetized low-temperature plasma devices with crossed ExB fields have proven useful in numerous applications. These include for spacecraft propulsion with Hall thrusters and material deposition using magnetrons. This configuration gives rise to a multiscale zoo of waves and instabilities as well as the emergence of large-scale structures such as rotating spokes, many of which have been studied in the somewhat simpler Penning discharge device. This complexity has precluded development of analytic models for these systems, necessitating kinetic numerical simulations, often via the particle-in-cell method.

Most such simulations have been conducted in two-dimensions, even though the third-dimension can play a critical role in the global behaviour of the plasma. Using the three-dimensional massively parallel GPU accelerated Low-Temperature Plasma Particle-in-Cell (LTP-PIC) code we explore three physical phenomena emerging in 3D simulations.

1. 1. The influence of radial wall boundary conditions on anomalous electron transport within a Hall thruster channel. It is observed that dielectric boundaries (as opposed to the assumed period boundaries in 2D) can significantly reduce the amplitude of ion-acoustic instabilities and corresponding anomalous cross-field electron transport.
   
   2. Similarly, we investigate the influence of axial boundary conditions on a Penning discharge, showing that conducting, as opposed to dielectric, boundaries can short-circuit the core plasma and reduce the amplitude of large-scale rotating structures.
   
   3. Finally, we explore rigid body rotation and precession of the plasma within a Penning discharge as a possible mechanism for spoke formation. A centroid theory that incorporates both electron and ion motion is proposed to predict the rotation frequency.