TRANSVERSE KELVIN-HELMHOLTZ INSTABILITY IN A ROTATING PLASMA

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."