MHD equilibrium and stability of a stellarator plasma

A method is developed for studying MHD equilibrium and stability of plasmas confined in toroidal systems with a large constant magnetic field and a small field which varies rapidly in space. The method is used to obtain a system of magnetohydrodynamic equations averaged over the period of the rapidly varying field. In this form, the problem is greatly simplified, and the equations become similar to those used for axisymmetric tokamaks, for which methods have now been developed in some detail. – The problem of the limiting plasma pressure for equilibrium and stability in a stellarator is analysed, and it is shown that, within the framework of an ideal MHD model, β = 2P/B2 can be larger than 10% in systems with large shear and partial compensation of the magnetic fields produced by the diamagnetic currents. Also the question of toroidal drift compensation and, as a result, of the decrease in the neoclassical diffusion coefficient is discussed.