Experimental Study on Limit of the Safety Factor in JFT-2 Tokamak

Abstract

In medium q_a(q_a\simeq3) discharges, enhanced radiation loss power due to increased plasma-wall interaction plays an important role in the growth of low frequency oscillations. The m=2 tearing mode seems to be the most plausible cause of the disruption. The reduction of the impurity is essential in realizing the stable discharges of medium q_a. Attainable q_a is reduced with decreasing radiation loss power. In low q_a(q_a<2) discharges, no enhancement of the radiation loss power was observed until the disruption. The plasma disrupts at q_a\lesssim2. The m=2 kink mode is the probable cause of the disruption. Attainable q_a is reduced with decreasing the ratio of shell radius to plasma radius. The possibility of the shell stabilization against the m=2 kink mode is proposed,