Electromagnetic kinetic toroidal eigenmodes for general magnetohydrodynamic equilibria

Abstract

A comprehensive analysis of low-frequency, high-toroidal-mode-number linear eigenmodes for tokamaks is presented. The most significant new features of this stability study are that the calculation is interfaced with a general numerical magnetohydrodynamic equilibrium, and that it is fully electromagnetic. The ballooning formalism is employed and all important kinetic effects, including those of trapped particles, are retained. In particular, the familiar trapped-electron drift-wave frequency regime is considered and results are presented for three sequences of artificial equilibria; one of increasing β(≡plasma pressure/magnetic pressure) values; one of varying equilibrium shape, from inverse-D to circular to normal-D; and one of increasing vertical ellipticity. The analysis is then applied to a realistic (self-consistent) high-β equilibrium generated with data obtained from the ISX-B tokamak experiment. Here it is found that for the usual trapped-electron branch, kinetic microinstabilities appear to be present over a wide range of toroidal mode numbers.