# Plasma and Fusion Research

## Volume 3, 016 (2008)

# Regular Articles

- Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
- 1)
- National Institute for Fusion Science, Toki 509-5292, Japan

### Abstract

High-energy particles in a finite beta plasma of the Large Helical Device (LHD) are numerically traced in a real coordinate system. We investigate particle orbits by changing the beta value and/or the magnetic field strength. No significant difference is found in the particle orbit classifications between the vacuum magnetic field and the finite beta plasma cases. The deviation of a banana orbit from the flux surfaces strongly depends on the beta value, although the deviation of the orbit of a passing particle is independent of the beta value. In addition, the deviation of the orbit of the passing particle, rather than that of the banana-orbit particles, depends on the magnetic field strength. We also examine the effect of re-entering particles, which repeatedly pass in and out of the last closed flux surface, in the finite beta plasma of the LHD. It is found that the number of re-entering particles in the finite beta plasma is larger than that in the vacuum magnetic field. As a result, the role of reentering particles in the finite beta plasma of the LHD is more important than that in the vacuum magnetic field, and the effect of the charge-exchange reaction on particle confinement in the finite beta plasma is large.

### Keywords

finite beta, re-entering particle, LHD, particle orbit

### Full Text

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This paper may be cited as follows:

Ryousuke SEKI, Yutaka MATSUMOTO, Yasuhiro SUZUKI, Kiyomasa WATANABE and Masafumi ITAGAKI, Plasma Fusion Res. 3, 016 (2008).