A multiple scale approach to plasma relaxation, stability and transport

In the suggested approach the three dominant timescales of ideal MHD, turbulent relaxation and resistive diffusion and, as length scales, the thickness of a resistive layer and the plasma radius are considered. The multiple scale ordering is applied to the transport equations of a single fluid plasma. The zero order quantities are determined by the assumption that the plasma relaxes on the first two timescales towards stationary (static) states of minimum energy with fluctuations around them, described by higher order quantities. The minimization of the total energy of the plasma is performed for the case of static equilibria. The resulting finite-β minimum energy equilibria are represented in a F-θ-β diagram. Two small windows of stable operation are found, the tokamak and RFP windows, where the predicted parameter ranges are well in agreement with the experimental ranges. (author). 5 refs, 2 figs