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Abstract. 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.
IAEA 2001
