Destabilization of diocotron modes inside structured anode cavities

Abstract

Previous stability analysis of low space charge ωe2/Ω2≪1, E×B drifting flows inside smooth anode cavities has shown that they are practically stable against slow wave ω/ck≪1 diocotron instabilities when the flow touches the cathode (cathode layer). It is shown here that the presence of periodically structured anode destabilizes cathode layer modes when their phase velocity matches that of an empty cavity eigenmode, as structured cavities support slow waves in vacuum. An analytic dispersion relation that self-consistently includes the structured anode effects is obtained in the guiding center approximation. The growth rate, related to the onset of magnetron oscillations, scales as γ/ω∼ωD/ω≃1/kd; it is independent of, and remains finite as, ωe2/Ω2→0. The most unstable frequency corresponds to a resonant layer below the flow surface (slightly below the Buneman–Hartree frequency) and the growth rate is found symmetric relative to the detuning from resonance.

Drift resonance in high density non-neutral plasmas

“…Riyopoulos has also used the GC approximation to study the initiation of the instability of a classical Brillouin sheath 7,24 which was then confirmed also in the cold-fluid approach. 14 He has also showed that in order to fit experimental data, it is necessary for the electron density at the diocotron resonance to be taken on the order of one-half of the maximum Brillouin value 8,25 with the density in the spokes being on the same order of magnitude.…”

Observation of the diocotron instability in a diode with split cathode

“…Sometimes this instability is undesirable, but sometimes it is useful. There is some evidence 14 that the diocotron instability can enhance formation of spokes in magnetrons.…”