Measurement of the Resistive-Wall-Mode Stability in a Rotating Plasma Using Active MHD Spectroscopy

H. Reimerdes, M. S. Chu, A. M. Garofalo, G. L. Jackson, R. J. La Haye, G. A. Navratil, M. Okabayashi, J. T. Scoville, and E. J. Strait

Phys. Rev. Lett. 93, 135002 – Published 20 September 2004

Abstract

The stability of the resistive-wall mode (RWM) in DIII-D plasmas above the conventional pressure limit, where toroidal plasma rotation in the order of a few percent of the Alfvén velocity is sufficient to stabilize the $n = 1$ RWM, has been probed using the technique of active MHD spectroscopy at frequencies of a few Hertz. The measured frequency spectrum of the plasma response to externally applied rotating resonant magnetic fields is well described by a single-mode approach and provides an absolute measurement of the damping rate and the natural mode rotation frequency of the stable RWM.