MHD stability in high β_t DIII-D divertor discharges

Stability against ideal low n kink and infinite n ballooning modes in high beta _T H-mode single null DIII-D divertor plasmas is examined. The equilibrium plasma pressure and current profiles are reconstructed self-consistently from experimentally measured magnetic data and kinetic profile data. The results show that the plasma is marginally stable to the ballooning mode near the central region and is stable to the ballooning mode over most of the plasma volume. Although the total volume averaged toroidal beta beta _T in these discharges has not reached the limit imposed by the ideal ballooning mode, the pressure gradient near the edge region approaches the ballooning limit locally, particularly just preceding the occurrence of a giant edge localized mode (ELM). The results also indicate that plasmas with high normalized toroidal beta beta _N>or=2.7-3.0 marginally stable to the ideal n=1 pressure driven kink mode without a conducting wall.