Transverse Kelvin-Helmholtz Instability in a Rotating Plasma

Abstract

In thermally ionized alkali‐metal plasmas ($Q$ machines), two types of low‐frequency oscillations are found: the usual drift wave localized to the region of large‐density gradient, and a higher‐frequency wave localized to the region of the radial boundary. The latter “edge” oscillation is shown to be a Kelvin‐Helmholtz instability driven by the large shear in plasma rotational velocity at the boundary. An analytic solution of the finite‐Larmor‐radius dispersion equation for the unstable wave is found by making the simplifying assumption that the rotational velocity jumps discontinuously. The results agree reasonably well with experimental measurements.