M. Iwamoto

Recent results of divertor simulation experiments using D-Module in the GAMMA 10/PDX tandem mirror

Abstract This paper describes the recent results of divertor simulation research toward the realization of the detached plasma using the end-mirror of a large tandem mirror device. The additional ion cyclotron range of frequency heating in the anchor-cells for higher particle flux generation significantly increases the density, which attained the highest particle flux up to 1.76 × 1023 particles/·m2 at the end-mirror exit. Massive gas injection (H2 and noble gases) into the divertor simulation experimental module (D-module) was performed, and a remarkable reduction of the electron temperature on the target plate was successfully achieved associated with the strong reduction of particle and heat fluxes in D-module. Two-dimensional images of Hα emission in D-module observed with a high-speed camera showed strong emission in the upstream region and significant reduction near the target plate. These results clarified the effect of radiation cooling and formation of detached plasma due to gas injection. It is also found that Xe gas is much more effective in achieving detached plasma than Ar gas. Numerical simulation studies also have been performed toward the understanding of the cooling mechanism of divertor plasma. The above results will contribute to establishment of detached plasma control and clarification of the radiation cooling mechanism toward the development of future divertor systems.

Electron Temperature and Density Distributions in a Divertor Simulation Experimental Module with Gas Injection in GAMMA 10/PDX

Abstract In tandem mirror GAMMA 10/PDX, H2 gas has been injected to a divertor simulation experimental module (D-module) for radiation cooling and detachment study. Electron temperature (Te) and density (ne) distributions have been measured by Langmuir probes in the D-module. With increase of H2 gas amount, Te has decreased especially at the V-shaped target plate from 30-40 eV to 3-5 eV. Moreover, ne and ion saturation current Iis have increased at the inlet but decreased at the target and had a steeper distribution toward the corner. These results suggest detachment. The movement of the ionization front to the upstream side with increase of the gas is suggested from the change in the plasma parameters profiles along the magnetic field line.

Spectroscopic Measurements in the Experiments of Gas Injection to the Divertor Simulation Experimental Module of GAMMA 10/PDX

Abstract In this paper, detailed results on spectral measurement are reported and the argument on impurity transport is presented from the comparison of the spectral measurements in the end-cell and the plug/barrier-cell. Spectroscopic measurement in the plug/barrier-cell was carried out for the first time. Ionization behavior in the plug/barrier-cell showed a significant difference from that in the end-cell. Discussion of detached plasma generation from the change of the electron temperature, density and emission spectrum by the gas injection conditions is also presented. In the case that the plenum pressure of noble gas was increased, the radiation of hydrogen neutrals decreased by 20~90% and the ion saturation current decreased by 90~95%, which indicated that electron density is reduced by recombination. It is suggested that the effect of molecular activated recombination may have appeared.