Localized MHD Activity near Transport Barriers in JT-60U and TFTR
Authors: J. Manickam, T. Fujita, N. Gorelenkov, A. Isayama, Y. Kamada, M. Okabayashi, M. Bell, R. Bell, R. Budny, E. Fredrickson, S. Ishida, Y. Ishii, F. Levinton, T. Ozeki, H. Shirai, S. Takeji, and M. Zarnstorff
Localized MHD activity observed in JT-60U and TFTR near transport barriers with their associated large pressure gradients is investigated. Stability analysis of equilibria modeling the experiments supports an identification of this MHD as being due to an ideal MHD n = 1 instability. The appearance of the instability depends on the local pressure gradient, local shear in the q profile, and the proximity of rational surfaces where q ~ m/n and m and n are the poloidal and toroidal mode numbers, respectively. The mode width is shown to depend on the local value of q, and is larger when q is smaller. In addition, the role of the edge current density in coupling the internal mode to the plasma edge and of the energetic particles which can drive fishbone-like modes is investigated.