A Study of Reversed Field Pinch Experiment in a Small Compact Torus STP-1

抄録

MHD instabilities which destroy a stable reversed field pinch (RFP) plasma are investigated in a small tight aspect ratio torus, STP-1. Special attention is paid on programing of setting up the RFP configuration. It starts with screw pinch and then external fields is reversed while the plasma current is kept increasing in order to maintain equilibrium relation with respect to minor radius of the plasma. Consequently plasma-wall interaction during RFP setting up phase is minimized and increased trapped toroidal flux by factor two is achieved compared with usual programing mode. In this way a stable RFP plasma is created with density of 3.5×10¹⁵/cm³, temperature of 20 eV and discharge current of 58 kA. After 13 μsec stable operation time, the plasma is rapidly deformed and moves from its equilibrium position by a violent MHD m=1 instability, of which structures are observed by B_r magnetic probes. A theoretical calculation of one dimensional stability analysis based on ideal MHD model is applied to our experimental results. It is found that the instability may be m=1 resistive tearing mode under the influence of viscosity.