K. Ichimura

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.

Electron temperature and density distributions of detached plasma in divertor simulation experiments in GAMMA 10/PDX

Spatial characterization of plasma detachment attributed to molecular activated recombination (MAR) has been done by measuring distributions of electron temperature, electron density, space potential and floating potential of divertor simulation plasma in GAMMA 10/PDX tandem mirror with Langmuir probes. As the hydrogen pressure in the divertor simulation experimental module was increased by supplying additional hydrogen gas, the electron temperature near the target decreased from 30 eV to about 2 eV and the electron density first increased to an order of nearly 1017u2005m−3, and then decreased in contrast to the density measured at the upstream of the target which became saturated. The density decrement was higher near the corner of the V-shaped target although temperature distribution was almost flat near the target. In addition, space potential decreased, floating potential increased, and then the potential difference between those became small. The potential difference decreased to almost zero near the tar...

Ion sensitive probe measurement of divertor simulation plasma in GAMMA 10/PDX

An ion sensitive probe (ISP) has been installed in the divertor simulation module of the largest tandem mirror plasma device GAMMA 10/PDX in order to evaluate the property of the high temperature end loss plasmas. The ISP has the capability to evaluate ion temperature (Ti), electron temperature (Te), electron density and plasma space potential, simultaneously. We have tested the ISP measurement for several discharge and neutral gas pressure conditions. Tievaluated by using an ion collector of the ISP shows ∼6 eV which corresponds to the perpendicular component of Ti in principle. Te evaluated by the current-voltage characteristics of an electron guard electrode of the ISP shows ∼4 eV which is lower than Te obtained by Langmuir probes upstream and downstream of the ISP. These results indicate the existence of anisotropic ion and electron temperatures in the D-module.

Study of Plasma Behavior during ECRH Injection in the GAMMA 10 SMBI Experiments

Establishment of fueling system is one of the critical issues for the future fusion reactors. Fueling experiment supersonic molecular beam injection (SMBI) have been carried out in the central-cell of GAMMA 10. In GAMMA 10, electron cyclotron resonance heating (ECRH) is used at plug/barrier-cells for the formation of the axial confining potential. Recently, ECRH was applied during SMBI to plug the loss particles and increased the plasma density in the central-cell compared to without ECRH. This result suggests that the particles are confined during SMBI due to the injection of ECRH at plug/barrier-cells in GAMMA 10.

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.

Spatial distribution measurement of molecular activated recombination using hydrogen Balmer line intensities of divertor simulation plasma in GAMMA 10/PDX

In GAMMA 10/PDX, spatial distribution of the occurrence of molecular activated recombination (MAR) has been studied by measuring two dimensional distributions of Hα and Hβ line intensities of the divertor simulation plasma. The V-shaped target in the D-module which is installed in the west end region was exposed to the end loss plasma, and additional hydrogen gas was injected in the D-module. The electron temperature near the corner of the V-shaped target decreased to ∼2 eV with increase in the neutral gas pressure in the D-module and the density roll over was observed, indicating the plasma was detached. The two dimensional distributions of the intensity ratio of Hα and Hβ line intensities indicates that MAR was enhanced with increase in the neutral gas pressure and the region of the MAR occurrence spread and moved to the upstream side.In GAMMA 10/PDX, spatial distribution of the occurrence of molecular activated recombination (MAR) has been studied by measuring two dimensional distributions of Hα and Hβ line intensities of the divertor simulation plasma. The V-shaped target in the D-module which is installed in the west end region was exposed to the end loss plasma, and additional hydrogen gas was injected in the D-module. The electron temperature near the corner of the V-shaped target decreased to ∼2 eV with increase in the neutral gas pressure in the D-module and the density roll over was observed, indicating the plasma was detached. The two dimensional distributions of the intensity ratio of Hα and Hβ line intensities indicates that MAR was enhanced with increase in the neutral gas pressure and the region of the MAR occurrence spread and moved to the upstream side.