Unstable Precession under the Influence of Drag Forces

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Abstract
Coherent precession of plasma particles in ▿B is generally subjected to drag forces associated with viscous or resistive energy dissipation in background plasma. The dissipated energy can be supplied by continual displacement of the processing entity along — ▿B. Precession in mirror machines therefore tends to be unstable against drag, while the converse is true for minimum‐B geometries. A heuristic mechanical model is first described. The precession of the E‐layer is next shown to be drag‐unstable if one uses the ``super‐particle model,'' which does not allow for a finite spread in particle precession frequencies. Similar results are obtained for ordinary mirror‐machine plasmas in the two limits that are ordinarily considered stable by virtue of the high‐density and low‐density finite‐Larmor‐radius conditions.