Boundary-induced effect on the spoke-like activity in ExB plasma

Abstract

The spoke instability in an $E\times B$ Penning discharge is shown to be strongly affected by the boundary that is perpendicular to $B$ field lines. The instability is the strongest when bounded by dielectric walls. With a conducting wall, biased to collect electron current from the plasma, the spoke becomes faster, less coherent and localised closer to the axis. The corresponding anomalous cross-field transport is assessed via simultaneous time-resolved measurements of plasma potential and density. This shows a dominant large-scale $E\times B$ anomalous character of the electron cross-field current for dielectric walls reaching $40-100$% of the discharge current, with an effective Hall parameter ${\beta }_{\mathrm{eff}}\sim 10$. The anomalous current is greatly reduced with the conducting boundary (characterised by ${\beta }_{\mathrm{eff}}\sim 10^2$). These experimental measurements are shown to be qualitatively consistent with the decrease of the $E$ field that triggers the collisionless Simon-Hoh instability.

References in corpus (3)

• Scaling of Spoke Rotation Frequency within a Penning Discharge
• Particle-in-cell simulations of anomalous transport in a Penning discharge
• Floating potential of emitting surfaces in plasmas with respect to the space potential

Cited by in corpus (5)

• Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies
• Azimuthal structures and turbulent transport in Penning discharge
• Mode transitions and spoke structures in ExB Penning discharge
• Three-dimensional Helical-rotating Plasma Structures in Beam-generated Partially Magnetized Plasmas
• The nonmodal kinetic theory for the electrostatic instabilities of a plasma with a sheared Hall current