Effects of gas puff and pump on plasma detachment associated with molecular activated recombination in GAMMA 10/PDX

Abstract

Gas puff and pump experiments on the plasma applied in a divertor simulation were conducted in the GAMMA 10/PDX tandem mirror. Additional hydrogen gas was supplied to the plasma with and without a pump in the region of the divertor simulation. To decrease the electron temperature near the target plate, the gas is supplied at a higher plenum pressure with the use of a pump than without a pump. We observed differences in the characteristics of the plasma detachment caused by molecular activated recombination (MAR) between cases with and without a pump at the same electron temperature. Near the target plate, particle loss with the use of a pump is smaller than that without a pump. By contrast, the vibrational and rotational temperatures of hydrogen molecules in the two cases are almost identical. The density of hydrogen molecules with a pump is lower than that without a pump, indicating that the electron temperature can be decreased even with a lower hydrogen density when a pump is applied. These results suggest that one of reasons for the suppression of the MAR with the use of a pump is the low density of the hydrogen molecules. Keywords: Plasma detachment, Molecular activated recombination (MAR), Pumping, Hydrogen molecule