Reversed-field-pinch research

Theoretical and experimental research in the reversed-field pinch (RFP) is reviewed. In this system, Bθ ~ B, q 10% has been observed. Following a historical review of pinch research, the basic theoretical properties of the RFP are established including the equilibrium, toroidal displacement, diffusion and confinement; studies of ideal and dissipative MHD stability theory are then described. Experimental and theoretical work on relaxation and self-reversal, the process whereby an RFP distribution can be set up spontaneously and subsequently sustained, is presented and discussed. There follows a general account of RFP experiments. These are divided into 'fast experiments', which utilize small-bore insulating tori in which the distribution is usually set up by fast programming on microsecond timescales, and 'slow experiments', carried out in large metal-walled tori in which the field configuration is set up slowly by self-reversal on millisecond timescales. A brief account of RFP reactor studies and of new and future experiments is then given, followed finally by a general discussion in which the main conclusions are presented.