Direct Observation of a Cross-Field Current-Carrying Plasma Rotating Around an Unstable Magnetized Plasma Column

TL;DR

This paper reports direct visualization of a rotating, cross-field current-carrying plasma around an unstable magnetized plasma column, linking low-frequency instability with anomalous radial plasma convection.

Contribution

It provides the first direct observation of a rotating plasma channel caused by a radial cross-field current, clarifying the nature of the instability.

Findings

Observation of a rotating plasma channel using ultra-fast imaging

Identification of the plasma rotation as a consequence of charge neutrality and electron expulsion

Reinterpretation of the instability as a rotating plasma rather than a diamagnetic drift wave

Abstract

The low-frequency instability of a magnetized plasma column and the anomalous radial plasma convection are shown to be linked with the existence of a radial cross-field current along a plasma channel rotating around the central magnetized plasma. The direct observation of the rotating plasma is obtained using an ultra-fast intensified camera. The ionizing electrons injected along the axis of the plasma column contribute to the accumulation of negative charges when the axial collector is at floating potential. The required neutrality leads to the continuous radial expulsion of energetic electrons and to the formation of a rotating plasma channel (m=1 unstable wave). This situation has previously been interpreted erroneously as a diamagnetic drift wave.