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Temperature, Density, Magnetic Field and Pitch Angle Dependence of Neutral Particle Spectrum in Large Helical Device
OZAKI Tetsuo, GONCHAROV Pavel, MURAKAMI Sadayoshi1), SANUKI Heiji, OKAMURA Shoichi , SUDO Shigeru, KUBO Shin, SHIMOZUMA Takashi, NOTAKE T. 2), OHKUBO K. , OKA Yoshihide, OSAKABE Masaki, TAKEIRI Yasuhiko, TSUMORI Katsuyoshi, IKEDA K. , KANEKO Osamu, KUMAZAWA, Ryuhei, MUTOH Takashi, SEKI Tetsuo, WATARI Tetsuo, SAITO Kenji, TORII Hiroki, NARIHARA Kazumichi, NAGAYAMA Yoshio, IDA Katsumi, OHDACHI Stoshi, MORITA Shigeru, GOTO Motoshi, SAKAKIBARA Satoru, SHOJI Mamoru, NAKANISHI Hideya, KOJIMA Mamoru, PETERSON Byron, KAWAHATA Kazuo, NAKAMURA Yukio, NODA Nobuaki, OHYABU Nobuyoshi, MOTOJIMA Osamu and LHD Experimental Group
National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
In helical device, the particle loss by the resonance between the gradient B drift and E x B drift is well known as the resonant loss. The behavior is observed as the dip in the charge exchange neutral particle spectrum. It is not easy directly nor experimentally to observe the loss cone itself, which is the characteristic effect in the helical device because it appears in the velocity space. However the experimental observation of resonant loss suggests the evidence of the loss cone. The depth of the dip is strongly depended on the electric field. It is hard to appear notably with the NBI plasma in LHD since NBI is tangentially injected in order to avoid pouring of the particle into a loss cone region. In the ECH plasma, which has the isotropic ion pitch angle distribution, it is observed clearly. In addition, since an electron is strongly heated in low ECH density, the positive electric field can be easily obtained. Therefore it is easy to observe change of a spectrum by the strength of ECH power. The neutral particle analyzer with the time-of-flight tube, which has an ability of particle mass separation can be used in LHD. Since an anti-coincidence technique is adopted in the time-of-flight tube, the strong electromagnetic wave noise during ECH can be removed. Two-dimensional scan of the neutral particle spectra is possible by moving the analyzer stage in order to clarify the pitch angle dependability of the neutral particle. Horizontal scan angle is from 40 to 100 degrees in pitch angle. In this paper, the density and the temperature, the magnetic field, the magnetic axis, and the pitch angle dependability of a resonance loss are clarified by classification of the spectrum for every condition. According to the present analysis, the dip in the spectrum becomes deeper by the outer shift of the magnetic axis. The tendency for change of dip depth in the spectrum against change of density or temperature, i.e., change of the electric field is common to be theoretically prediction. This means that the dip on the spectrum in ECH plasma has suggested the resonance loss.
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