Scaling of Spoke Rotation Frequency within a Penning Discharge*

A rotating plasma spoke is shown to develop in two-dimensional full-sized kinetic simulations of a Penning discharge cross-section. Electron cross-field transport within the discharge is highly anomalous and correlates strongly with the spoke phase. Similarity between collisional and collisionless simulations demonstrates that ionization is not necessary for spoke formation. Parameter scans with discharge current I_d applied magnetic field strength B and ion mass m_i show that spoke frequency scales with (eEr L_n/m_i)^1/2, where E_r is the radial electric field, L_n is the gradient length scale and e is the fundamental charge. This scaling suggests that the spoke may develop as a non-linear phase of the collisionless Simon-Hoh instability. Field geometry is modified in an attempt to influence spoke behaviour and these modifications are compared with experimental observations.

 

Powis, Andrew T., et al. "Scaling of Spoke Rotation Frequency within a Penning Discharge." arXiv preprint arXiv:1805.04438 (2018).