NONLINEAR PLASMA EVOLUTION AND SUSTAINMENT IN THE REVERSED FIELD PINCH

In this paper numerical results of three-dimensional (3-D) resistive magnetohydrodynamic (MHD) plasma simulations are presented. A system of coupled nonlinear differential equations is evolved in time over a significant fraction of the macroscopic resistive diffusion time scale. The dynamical evolution resembles the main features of the famous Lorenz system. In fact, sensitivity of MHD equations on initial distribution of spectral energy and stochastic oscillations in phase space have been found. At least two dynamic attractors of the motion have been identified. Moreover, in analogy with Lorenz's system, the stochastic motion can be damped by an enhanced dissipation and the fixed point can be recovered. In this paper more specific topics are also considered, which are relevant to the reversed field pinch (RFP), such as the role of different modes in the "dynamo" mechanism for plasma sustainment and the associated transport due to stochastic diffusion.