M. Ohuchi

Measurement of neutral gas pressure in the D-module of GAMMA 10/PDX by using ASDEX type fast ionization gauge

In the divertor simulation experiments in the GAMMA 10/PDX tandem mirror, pressure of the neutral gas was investigated by using a fast ionization gauge. The gauge was absolutely calibrated for hydrogen gas by using a capacitance manometer. Change of the gauge sensitivity due to the magnetic field of GAMMA 10/PDX was also evaluated. The typical gas pressure measured in detached plasma experiments was 0.1-10 Pa. The degree of plasma detachment determined from the reduction of heat flux was enhanced as the gas pressure increases. Rapid increase of the gas pressure under the plasma flow was also observed.

Study of plasma behavior during impurity injection in the end-cell of GAMMA 10/PDX by fluid code

The effect of neutral Ar injection on the plasma parameters is investigated numerically by using a multi-fluid code in this research. Reduction of electron and ion temperature has been observed according to the increment in injected neutral Ar density. The heat flux on the target plate has been also reduced with the increasing of injected neutral Ar density. For Ar: 2.0 × 1018 m−3 injection, electron temperature on the target plate reduced to about 1.5 eV. Increase in electron and ion density has been observed at lower injected Ar density. However, at higher Ar injection, electron density and ion density goes to be saturated. These outcomes indicate that the plasma in the end region approaches towards the plasma detachment state.

Characteristics of SMBI fueling with laval nozzle in GAMMA 10 based on experimental and simulation results

Results of supersonic molecular bean injection (SMBI) with Laval nozzle has been carried out in the GAMMA 10 tandem mirror. The neutral transport during SMBI was investigated by the two-dimensional image of the light emission captured by the high-speed camera. We used the value of full width at half maximum (FWHM) of the distribution of emission intensity as an index of neutral transport. The FWHM value decreases with the increase of the plenum pressure which indicates that the particle diffusion was more convergent at high plenum pressure. Fully three-dimensional neutral transport simulation using a Monte-Carlo code DEGAS is applied to SMBI experiment and simulation results qualitatively explained the experimental results.

Study of the impurity transport by injecting the gas to D-module in GAMMA 10/PDX

In this study, spectroscopic measurement at the plug/barrier-cell, near the midplane in GAMMA 10/PDX was carried out for the first time. From the comparison of the spectroscopic data measured in the end-cell and plug/barrier-cell, transport of impurities injected to divertor simulation module in the end-cell is investigated. It was found that Ne hardly ionized at both observation points. On the other hand, N2 dissociated and ionized before reaches or at the plug/barrier-cell while emission spectrum derived from N2 was dominated at the end-cell. From the comparison of the emission spectrum at the end-cell and plug/barrier-cell, it suggests that Ne was more likely to transport toward upstream region through the plasma than N2. Time evolution of specific emission spectra, electron temperature and density suggests the reduction of the impurity transport during ECH pulse.

Study of beam-material interaction by using hydrogen ion beam

In this research, the effect of beam convergence with magnetic field of GAMMA 10/PDX has been investigated. The hydrogen ion beam is injected to the tungsten target under the various strength of magnetic field. The spatial distribution of emission light and rising temperature of the target are measured with a fast camera and a calorimeter, respectively. Effectiveness of beam convergence due to the magnetic field expansion is evaluated from the viewpoint of beam-material Interaction studies.

Evaluation of heat flux from the plasma flow by using calorimeter in the GAMMA 10/PDX end-cell

In this paper, detailed results of the heat flux measurements are presented and the improvement of heat flux evaluation method is also discussed. We measured the heat flux in the case that additional heating with electron cyclotron resonance heating (ECRH). The heat flux reaches about 17 MW/m2 in the case with ECRH power 380kW. It is found that solving one-dimensional inverse heat conduction problems provides a possibility of improving time response of the heat flux measurement under the condition of changing heat flux in 20Hz.