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Kenichi Nagaoka,Akihiro Shimizu,Katsumi Ida,Katsunori Ikeda,Katsuyoshi Tsumori,Kazuo Toi,Keisuke Matsuoka,Kiyomasa Watanabe,Masaki Osakabe,Mikiro Yoshinuma,Mitsutaka Isobe,Osamu Kaneko,Shoichi Okamura 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
The characteristics of neutral beam driven current have been investigated in helical devices, which do not need ohmic current to produce a magnetic field configuration. The neutral beam current drive experiments have been performed in a wide range of Zb/Zeff in LHD and CHS. The Z dependence of neutral beam driven current in the region of Zb/Zeff < 1 obtained by neon discharges in LHD agrees with the Ohkawa model. On the other hand, the current driven by neon beam injection in CHS cannot be explained by the Ohkawa model.
Plasma-Confinement Physics Study in Compact Helical System
stoichi Okamura,A. Fujisawa,A. Shimizu,C. Takahashi,C. Suzuki,H. Iguchi,H. Nakano,H. Matsushita,K. Nagaoka,K. Matsuo,K. Ida,K. Toi,K. Nakamura,K. Matsuoka,M. Yoshinuma,M. Isobe,M. Takeuchi,R. Ikeda,S. 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
In a CHS experiment, various types of transport barrier have been studied. An internal transport barrier (ITB) for electrons in a stellarator was first found in CHS, and the ITB for improved ion confinement was also found. H-mode (edge transport barrier) study in CHS showed many common features in transition to tokamak experiments, although the magnetic surface quantities are very different. Discharges with a combination of ETB and ITB were also found. Two heavy ion beam diagnostics in CHS showed a new direct measurement of zonal flow structure in toroidal confinement. The relation between the fluctuation and the transport barrier was also studied.
Tanaka, K.,Nagaoka, K.,Murakami, S.,Takahashi, H.,Osakabe, M.,Yokoyama, M.,Seki, R.,Michael, C.A.,Yamaguchi, H.,Suzuki, C.,Shimizu, A.,Tokuzawa, T.,Yoshinuma, M.,Akiyama, T.,Ida, K.,Yamada, I.,Yasuhar IOP 2017 Nuclear fusion Vol.57 No.11
<P>Surveys of the ion and electron heat transports of neutral beam (NB) heating plasma were carried out by power balance analysis in He and H rich plasma at LHD. Collisionality was scanned by changing density and heating power. The characteristics of the transport vary depending on collisionality. In low collisionality, with low density and high heating power, an ion internal transport barrier (ITB) was formed. The ion heat conductivity (<I>χ</I> <SUB>i</SUB>) is lower than electron heat conductivity (<I>χ</I> <SUB>e</SUB>) in the core region at <I>ρ</I> < 0.7. On the other hand, in high collisionality, with high density and low heating power, <I>χ</I> <SUB>i</SUB> is higher than <I>χ</I> <SUB>e</SUB> across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at <I>ρ</I> = 0.7, and in normal confinement, fluctuation has a peak at <I>ρ</I> = 1.0. The two confinement modes change gradually depending on the collisionality. Scans of concentration ratio between He and H were also performed. The ion confinement improvements were investigated using gyro-Bohm normalization, taking account of the effective mass and charge. The concentration ratio affected the normalized <I>χ</I> <SUB>i</SUB> only in the edge region (<I>ρ</I> ~ 1.0). This indicates ion species effects vary depending on collisionality. Turbulence was modulated by the fast ion loss instability. The modulation of turbulence is higher in H rich than in He rich plasma.</P>