Change of the magnetic field structure during relaxation in the high pinch parameter regime of the reversed field pinch REPUTE-1

Magnetic field measurements in a reversed field pinch plasma have been made with an insertable magnetic probe in REPUTE-1. The relaxation process of the magnetic field configuration in a high θ (θ is the pinch parameter) regime has been studied. The safety factor on axis, q0, decreases as θ increases, and there exists a lower limit to q0(~0.10). Close to this limit, q0 increases when the magnetic field configuration relaxes. These observations agree well with numerical results of non-linear resistive MHD theory.