Study on neutral particle behavior in non-axisymmetric minimum-B region of a tandem mirror

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The objective of this research is to measure he Hydrogen Balmer-alpha(Hα) line emission from the anchor cell and from the transition region in the anchor minimum-B region. We also performed a neutral transport simulation using a Monte-Carlo code "DEGAS". In this simulation, the density and temperature profiles of hydrogen atoms and molecules are predicted in non-axismmetric anchor mirror cell and hence a important knowledge with particle transport in such complicated configuration of this magnetic structure.In the last fiscal year, a newly designed two-dimensional Hα detector array was constructed. In order to measure the line emission from the narrow viewing area, the detector was required to obtain a high spatial resolution and its characteristics of the detector were investigated by using a standard lamp. A three-dimensional Monte-Carlo neutral particle simulation code "DEGAS ver.63" was applied to the GAMMA 10 anchor cell for the first time and a simulation study in this region was … More started. A preliminary mesh model was constructed and three-dimensional simulation was carried out. From this simulation, it was found that two particle sources (mirror throat gas puffer and a limiter at the outer transition region of the anchor cell) successfully explain the measured results of Hα line-emission in the anchor cell.In this fiscal year, the first measurement of detailed structure of the Hα line-emission in the anchor outer-transition region was successfully performed using the above detector array. It was found that the measured Hα line intensity has a strong peak along the miner axis of elliptically elongated plasma cross-section. On the contrary, in an axial direction along the magnetic field line, the spatial profile of the line intensity became flat. In order to explain the obtained results, a new mesh model covering from the anchor cell to the plug/barrier cell was constructed and detailed simulation based on the realistic structure of these cells was performed. The simulation results considering a particle source from the limiter at this region showed a good agreement with the measured profiles. A unified mesh mode covering from the central-cell to the anchor-cell was successfully built up, which enabled to precisely simulate the neutral transport in the connecting region between the two cells efficiently. From the above results, the three-dimensional structure of plasma and vacuum chamber wall plays an important roll in neutral transport in this region. Less