The role of the resistive wall mode in limiting tokamak plasma performance is well chronicled and is a central topic of the Feedback Stabilization Initiative (FSI). It is believed that stabilization of this mode, which is a converted branch of the ideal MHD external kink mode, may lead to the design of devices capable of accessing higher performance advanced operating regimes. We have developed a formulation of the resistive wall mode using the elementary physical concepts of self and mutual inductance. This results in a set of coupled lumped-parameter circuit equations with the variables being the perturbed plasma current, the helical component of induced current in the resistive shell, and (with feedback) the current in the active coil. These equations, which describe plasma perturbations of n ³ 1, have a one to one correspondence with plasma vertical positional (n = 0) control. Comparisons between the dispersion relations for the two cases show that the quantity that carries the strength of the instability for the resistive wall mode, equivalent to the negative decay index in vertical position control, is L_pl(1 - f) where L_pl is the helical inductance of the perturbed plasma current and (1 -f) is related to the helicity of the ideal MHD kink mode. This method has been successful in describing the resistive wall mode in general terms and has been used to successfully describe resistive wall mode feedback stabilization schemes analytically. We have started numerical simulation studies and are preparing a hardware simulator to evaluate some of the more promising proposed feedback schemes (e.g., Òsmart shellÓ, and Òfake rotating shellÓ). A hardware simulator provides a dedicated low cost, flexible, and high availability test-bed for comprehensive studies of electromagnetic issues of these feedback schemes prior to implementation on experimental devices whose the primary focus is fusion plasma physics not feedback studies. In this paper, we will describe the formulation in detail and show how the resulting circuit equations compare to analogous equations arrived at using traditional MHD analysis methods, particularly with the inclusion of feedback. We will also provide details of the resistive wall mode hardware simulator and report on our progress in both the numerical and hardware simulator model simulation studies.

*Work supported by U.S. DOE Contract No. DE-AC02-76-CHO3073.