Mode Structure of Disruption Precursors in TFTR Enhanced Reversed Shear Discharges
Authors: M. Okabayashi, E. Fredrickson, J. Manickam, G. Taylor, S. Batha, M. Bell, R. Budny, B. LeBlanc, F. Levinton, J. Jackson, K. McGuire, R. Nazikian, and M. Zarnstorff
The mode structure of the disruption precursors in the TFTR enhanced reversed shear parameters has been studied by using Te fluctuation profiles and q profiles obtained from Electron Cyclotron Emission (ECE) and Motional Stark Effect (MSE) measurements. The observed profiles of the radial displacement associated with the MHD modes were consistent with the displacement profiles expected from the ideal MHD external kink mode. The observed mode frequencies differ from the plasma toroidal rotation frequency measured with CVI charge-exchange recombination light. The independence of the mode frequency from the plasma rotation frequency supports the ideal MHD hypothesis. Possible causes of the frequency difference are discussed.