Active MHD instability control and confinement in the TPE-RX RFP

Experimental results obtained by using active methods to control the locked mode and to improve the confinement in the TPE-RX (R/a = 1.72/0.45) reversed field pinch (RFP), are presented. A phase- and wall locked mode (LM) was found in the case of high plasma current (> 300 kA) and/or high filling pressure. The rotation of the LM has been attempted by using an auxiliary rotating toroidal magnetic field. By applying the auxiliary field, the LM can be successfully delayed or even eliminated in the case of plasma current less than 250 kA. Double-pulse pulsed poloidal current drive (PPCD) has been conducted by using the auxiliary and main reversal toroidal field systems. The electron temperature, density and ion temperature increase during the PPCD. The result of the double-pulse PPCD is a fivefold increase in energy confinement time (τE) compared to that of the standard case. Moreover, the five-pulse PPCD result indicates the further improvement of poloidal beta (βP) and τE compared to the double-pulse PPCD. The high electron density discharges are obtained by using fast gas puffing. The higher values of βP and τE are realized in the highest electron density case. A neutral beam injection has been tested for another active control of the RFP plasma. (author)