Effects of a hollow current profile on the ideal MHD stability of high betapplasmas in a tokamak

The effects of current profiles on the n = 1 internal kink mode, the infinite n ballooning mode and the infernal mode in a tokamak are analysed numerically. The stabilities of plasmas with a circular cross-section and a peaked pressure profile are investigated for three types of current profile, that is parabolic, flat and hollow with an inverted q profile. In a low beta state (βp < 0.5), the influence of the current profile on the n = 1 internal kink stability is small. However, the infernal mode appears in plasmas with a hollow current profile, although it is stable in plasmas with a parabolic profile. In a high beta state (βp > 0.5), the growth rate of the n = 1 internal kink mode for the plasma with the hollow current profile becomes larger, and the unstable region spreads to the region of higher qmin (qmin > 2). When the plasma has a more peaked pressure profile in the hollow part of the current profile, the unstable regions of the n = 1 internal kink mode and ballooning mode shrink, and the infernal mode disappears