H. Ueda

First Results and Future Research Plan of Divertor Simulation Experiments Using D-Module in the End-Cell of the GAMMA 10/PDX Tandem Mirror

In the new research plan of Plasma Research Center of the University of Tsukuba, a high heat-flux divertor simulator (E-Divertor) was proposed by using an end-mirror exit of a large tandem mirror GAMMA 10/PDX device. Experiments for characterization of end-loss plasma flux have been extensively performed at the end-mirror region of GAMMA 10/PDX and detailed behavior of end-loss particles has been investigated. In standard hot-ion mode plasmas (ne0 ~ 2×1018 m-3, Ti0 ~ 5 keV), the energy analysis of ion flux was performed by using end-loss ion energy analyzer (ELIEA). It was found that the high ion temperature (100 - 400 eV) is generated and has a liner relationship between diamagnetism in the central-cell. The ion temperature determined from the probe and calorimetric measurements gives a good agreement with the ELIEA measurement. Additional ICRF heating in the anchor-cell showed a significant increase of particle flux, which indicated an effectiveness of additional plasma heating in adjacent cells. Superimposing the ECH pulse of 380 kW, 5 ms induces a remarkable enhancement of heat flux and a peak value in the net heat-flux density more than 10 MW/m2 was attained during the ECH injection, which comes up to the heat-load level of the divertor plate of ITER. Recently a large-scale divertor simulation experimental module (D-module) was installed in the west end-cell and the first plasma irradiation experiments onto a new tungsten V-shaped target were successfully performed. A number of interesting results such as neutral compression, enhancement of recycling and impurity radiation during noble gas injection, have been observed.

Study on the Optimization of Fueling by Using the SMBI Method in GAMMA 10

We investigate the effect of nozzle on the particle transport in the SMBI experiments for optimization of fueling in the GAMMA 10 tandem mirror. The diffusion particle during SMBI was evaluated from the emission intensity captured by the fast camera. Compared with the results without nozzle, the particle diffusion was more convergent in the case using the straight nozzle. Simulation results by using Monte-Carlo simulation code (DEGAS) roughly reproduce the 2-D image captured by the fast camera.

Numerical Simulation Study for Background Plasma in the GAMMA 10 End-Mirror Cell

We have started a simulation study of background plasma in the GAMMA 10 west end-cell using a fluid-code in order to understand divertor simulation experiments. In this fluid-code, the configuration of magnetic field lines in the west end-cell of GAMMA 10 is adopted with a mesh structure and basic physical processes such as reflection coefficient and recombination are considered. An initial computation result reveals that in the case of the plasma density range: ne ~ 1019 m-3, ion and electron temperature could not be reduced significantly to the suitable temperature for achieving the detachment. The effect of heat transfer coefficient on the target plasma is also discussed.

Investigation of the Plasma Heating Effects on the End-Loss Ion Flux of the Tandem Mirror GAMMA 10

This paper reports the recent results of measurements on the effect of plasma heating on enhancement of the ion flux in GAMMA 10. Recently, by using its end-loss flux, a study of the divertor simulation experiment has been started in the tandem mirror GAMMA 10. From its large size and unique characteristics, we can expect that unique divertor simulation experiments, which could not be held in other simple, linear divertor simulation machines, can be performed in GAMMA 10. In the experiment, it was found that high ion temperature of the end-loss ion flux was already achieved. In addition, ion cyclotron range of frequency (ICRF) heating in the anchor region was found to be very effective to increase the end-loss ion flux, which supports the huge potential of GAMMA 10 for the divertor simulation experiment.

Initial Simulation Results of GAMMA 10 as NBI Driven Neutron Source

This paper describes the initial result of simulation study of neutron production by NBI heating in the GAMMA 10 tandem mirror by using a buildup numerical simulation code. In the GAMMA 10 central-cell, high energy ions have localized in the neutral beam injection port and the other bounce point due to the perpendicular injection. By considering this mechanism, the position of the test zone for neutron irradiation is assumed and the amount of the neutron flux is evaluated. The neutron flux is about 1.3 kW/m2, for high-density mode and about 1.2 kW/m2, for hot-ion mode.

Edge Turbulence/Fluctuation Observation at “High Density Mode” in GAMMA 10 by Fast Camera

Edge plasma behavior was observed by fast camera at high density central-cell plasma in GAMMA 10. The plasma performance was better when the plasma rotated clockwise to the magnetic field. Also, when the interaction with the central-cell limiter was observed, the plasma stored energy was deteriorated. These results were very similar that of high potential central-cell plasma experiment as previously reported. Several rotation mechanisms exist, and on the empirical basis it is suggested the interaction with the central-cell limiter is important.

Observation of Plasma Behavior During the ECRH Injection by Using a High-Speed Camera in GAMMA 10

A new high-speed camera (MEMRECAM GX-1, NAC Inc.) has been installed at the GAMMA 10 central-cell. This camera observes two directions through vertical and horizontal ports by using dual optical fiber bundles. This paper describes the results of 2-D image of visible emission observed from the central-cell plasma during Supersonic Molecular Beam injection (SMBI) in the C-ECRH experiments. Observational results showed that the instability of plasma light-emission on the central-limiter was suppressed during SMBI and the plasma sustainability increased along the SMBI plenum pressure. Relationship between plasma sustainability and power of C-ECRH and/or the quantity of SMBI is also investigated.