On the FLR stabilization of high poloidal mode number external kinks

High poloidal mode number ideal instabilities, localized near the edge of the plasma column and driven by the gradient of the plasma current, are thought to be a serious limitation to operation of long-pulse experiments, such as the Steady State Advanced Tokamak (SSAT/TPX). In particular, the kink (with toroidal mode number n = 1), which requires a close-fitting conductive wall for stability, will limit the maximum value of β for the experiment. Since wall stabilization is only effective for an L/R time, defined by the material properties of the conducting shell, this instability becomes of concern for the long-pulse experiments. It has been known for a long time that many classes of instabilities can have their linear growth rate reduced, and even eliminated, by the so-called finite Larmor radius (FLR) effect. Among them are interchange modes and pressure-driven m = 1 modes (here m is the poloidal mode number). This stabilization arises from the breaking of the single-fluid approximation of the plasma response to the perturbation. When the ion and electron responses are decoupled, diamagnetic effects (ω* = (kθc/enB)dp/dr) arise in the equation governing the linear stability and can bring about stabilization. This work is intended to be a preliminary investigation in the simple cylindrical geometry. Extension to a realistic toroidal configuration is planned