Origin and transport role of rotating spokes in E x B discharges
In plain words
Hall thrusters, magnetrons and Penning discharges show bright regions called spokes that rotate around the device thousands of times per second. What drives them and how much electron leakage they cause is unknown.
Precise statement
Low-frequency (kHz) azimuthally rotating spokes appear in Hall thrusters, magnetrons and Penning discharges and can carry a large fraction of the cross-field current. Identify their driving instability (gradient-drift, ionization, or Simon-Hoh type) and quantify their share of cross-field transport versus operating parameters. An answer is a model predicting spoke mode number, rotation speed and transported current.
What would settle it
3D kinetic simulations and experiments agreeing on spoke mode number, speed and current fraction across devices.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
The first 3D kinetic simulation of a magnetron discharge (2026, arXiv:2608.27853) found an $m = 1$ spoke at $90\,\mathrm{kHz}$ counter-rotating with $m$ about 16 electron-drift filaments; validation against measurements is pending.
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