Behavior of neutral particles plays an important role in recycling phenomena on magnetically confined plasmas. In the GAMMA 10 tandem mirror, neutral hydrogen density in the central-cell has been estimated by measuring Hα line-emission together with neutral transport simulation. The DEGAS Monte-Carlo code [1] has been applied to investigate the neutral particle transport in the plasma [2,3].
In GAMMA 10, two minimum-B anchor cells are mounted for sustaining MHD stability. In the anchor-cell, there exist transition regions where the shape of the magnetic flux tube becomes flat and the cross section of plasma is elongated elliptically. In the transition region, the thickness of the plasma is the same order of the mean free path length of hydrogen molecules and is much shorter than those of Franck-Condon neutrals. Furthermore a narrow space between the plasma boundary and the vacuum vessel wall (a few cm) suspects strong wall-plasma interactions in this region. In order to evaluate the neutral density profile in non-axisymmetric region such as anchor-cell, a 3-dimensional neutral transport simulation by using the DEGAS ver.63 code has been utilized and the detailed behavior of neutrals in the anchor-cell was investigated. In the simulation, detailed mesh structure composing the inner-wall surface and non-axisymmetric plasma shape is designed. In this paper, we describe the results of neutral transport simulation and discuss the location and the intensity of particle source based on the temporal and spatial behavior of Hα line-emission in these regions.

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