Ideal MHD stability of pellet fuelled plasmas in JT-60

Stability against ideal infinite-n ballooning and low-n internal kink modes is analysed for pellet fuelled plasmas in JT-60, which have strongly peaked pressure profiles within the q = 1 resonance surface. The observed pressure gradient in pellet fuelled plasmas locally reaches the marginal value for the infinite-n ballooning mode limit just inside the q = 1 surface. After reaching the marginal value on the magnetic flux surface, the marginally stable region grows inside the q = 1 surface. However, the poloidal beta within the q = 1 surface, β p1 , does not reach the limit imposed by the ideal ballooning mode. The results of the analysis of the low-n kink mode using experimental observations show that the maximum β p1 attained is consistent with the beta limit imposed by the n = 1 internal kink mode.