Tokamak MHD instabilities: small-scale ideal MHD modes

The history of small-scale ideal MHD modes are discussed. A general and preliminary analysis of the small-scale MHD perturbations of the high-beta /SUB j/ tokamak is presented. Such perturbations are described by a rather complicated small-oscillation equation. The author considers obtaining the Mercier criterion from the equation and discusses various forms of the description and the physical sense of this criterion. It is shown that for large beta /SUB j/ the Mercier stability condition is not reduced to the well known condition 'q2 is greater than 1', and that this condition is unsatisfied under certain conditions. The anit-Mercier perturbations are discussed, i.e., the ballooning modes at a smaller shear