Active MHD Instability Control and Confinement in the TPE-RX RFP

Experimental results using active methods in order to control the locked mode and to improve the confinement in the TPE-RX (R/a = 1.72/0.45) 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 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 low plasma current (200 kA) with high filling pressure for the first time. As one of the active operations for an improvement of the confinement, pulsed poloidal current drive (PPCD) has been conducted by the auxiliary and main reversal toroidal field system. The soft X-ray in the PPCD becomes an order of magnitude larger than that in the standard case. The electron temperature, density and ion temperature increase during the PPCD. These results show considerable improvement of energy confinement. Another operation is the high electron density discharge using the fast gas puffing. The highest values of poloidal beta and energy confinement time are estimated to be obtained at the highest electron density case.