Mhd Instabilities In Heliotrons

Abstract

Abstract Stability studies with the MHD model have progressed significantly since the 1950s, when magnetic confinement research began. For tokamaks, it is considered that MHD stability theory was almost completed by the development of ballooning mode theory in the latter half of the 1970s. MHD studies for stellarators also began in the 1950s. However, progress was slow because it was not easy to obtain three-dimensional MHD equilibrium of finite-beta plasma. For toroidal stellarator MHD equilibrium, there are two problems as discussed in chapter 4: the existence of nested magnetic surfaces, and the viability of currentless equilibrium. Regarding the first point, the existence of general three-dimensional equilibrium has been disproved. However, since the existence of equilibrium in the straight stellarator configuration is guaranteed by the helical symmetry, we often study the equilibrium assuming that nested magnetic surfaces would exist if the toroidal effects were sufficiently small. In other words, it is accepted in practice that the magnetic surfaces exist when no magnetic islands or no stochastic magnetic field line regions appear in the calculation of the vacuum magnetic surfaces by line tracing.