Experimental and computational studies of reversed-field pinch in Japan

Recent results of experimental and computational studies of reversed-field pinch (RFP) in Japan are described. The TPE-1R(M) experiment (stainless-steel liner; R/a=50/10cm; Isub(p)=70-130kA rising in 450μs) at the Electrotechnical Laboratory, Sakura, in which RFP configuration is set up by programming control of external coil currents (aided reversal), shows that, with careful wall conditioning of the liner, an improved confinement phase is obtained from just after setting up the RFP to the end of the plasma current pulse with a rapid termination (at 700-800μs from the start of pulse). Particularly in the current decay phase, the fluctuation level of the plasma current derivative is reduced remarkably, and this phase is similar in many aspects to the 'quiescent period' observed in ZETA and ETA-BETA II. The electron temperature estimated from the loop voltage rises to about 70-90eV before plasma current disruption. In STP-1 (quartz torus; R/a=12/4.2cm; Isub(p) approximately 60kA, rise in 5-6μs) at Nagoya University, the RFP configuration is set up by using a new (fast) mode. However, the plasma column collapses from an instability after a stable phase of about 13μs. 1-D ideal-MHD stability analysis is applied to explain the observed behaviour of the plasma. 2-D and 3-D codes have been developed at Nihon University to investigate the plasma properties of the TPE-1R experiment and the non-linear resistive kink modes in RFP configurations, respectively. Calculations are compared with experiment. (author)