Confinement in TPE-RX reversed field pinch

Characteristics of the confinement properties of a reversed field pinch (RFP), the TPE-RX (R/a=1.72/0.45 m, R and a are major and minor radii), are presented for the plasma current, Ip of 0.2-0.4 MA. TPE-RX has been operational since 1998, and Ip=0.5 MA and duration time of up to 0.1 s have been obtained separately. It is found that Ip/N (=12x10-14 Am, N is the line density) is higher than those of other RFPs and poloidal beta, βp, and energy confinement time, τE, are 5-10% and 0.5-1 ms, respectively, which are comparable with those of other RFPs of comparable sizes (RFX and MST). Pulsed poloidal current drive has recently been tested and the result has shown a twofold improvement of βp and τE. The improvement is discussed in terms of the dynamic trajectories in the F-Θ plane, where F and Θ are reversal and pinch parameters, respectively. The global confinement properties are compared between the locked and non-locked discharges, which yields a better understanding of the mode-locking phenomena in RFP plasmas. (author)