Fluctuation-driven mean flows and their effect on the dynamo mechanism in the reversed-field pinch

A computer simulation of a reversed-field pinch (RFP) has been used to model the phenomena of relaxation and sustained reversal. It is found that axisymmetric plasma flows are generated by the non-linear interaction of the dynamo modes and that these flows adjust the phases of the MHD resistive modes and act to increase the efficiency of the dynamo effect. However, these flows were not found to be essential to a functioning RFP. The quasi-linear description of the RFP is found to be inadequate and the dynamo modes were found to be highly correlated and possess a time-averaged component. The viscous damping of the dynamo modes is found to be related to the dynamo activity, consistent with this being the mechanism responsible for the observed anomalous ion heating. (Author)