Linear and nonlinear properties of infernal modes

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Abstract
Infernal modes are pressure‐driven instabilities that can occur in low‐shear regions of tokamak plasmas for beta values well below the ballooning stability limit. They may be either resistive or ideal. In this paper, stability regions are determined in the plane of elongation versus triangularity to demonstrate the effects of shaping. Both ellipticity and triangularity are needed for stability. The effects of toroidicity, compressibility, and resistivity are also analyzed. A study of the nonlinear evolution of the mode with resistivity shows that complete flux rearrangement can occur suggesting a mechanism for observed internal disruptions.