Experimental Observation of the Density Limit in Hot Ion Mode Plasmas of the GAMMA 10 Tandem Mirror

Abstract

We revealed experimental observation indicating density limit with gas-puff fueling in hot ion mode plasmas of the GAMMA 10 tandem mirror. The responses of the plasmas for the various gas fueling were studied. Despite the increase in the quantity of the particle source, the line average density was saturated with the degradation of the radial particle confinement at the periphery of the central plasma. It was clarified that the line density obtained with the pellet fueling is about 20–50% higher than that with gas-puffing in the same average ion temperature. The clear difference between the pellet fueling and the gas fueling was observed in the radial profile of particle deposition at the central midplane. From the consideration based on the experimental observation, a radial-loss mechanism of ions by charge exchange reaction was discussed as an explanation for the degradation of particle confinement at the plasma periphery.