2002 Fiscal Year Final Research Report Summary
Study of interaction between energetic ions and MHD instabilities in a helical plasma
| Project/Area Number |
12480127
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear fusion studies
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| Research Institution | National Institute for Fusion Science |
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Principal Investigator |
TOI Kazuo Professor, Department Large Helical Device Project, National Institute for Fusion Science, 大型ヘリカル研究部, 教授 (20093057)
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| Co-Investigator(Kenkyū-buntansha) |
OHDACHI Satoshi Research associate, Department of Large Helical Device Project, NATIONAL Institute for Fusion Science, 大型ヘリカル研究部, 助手 (00270489)
OSAKABE Masaki Research associate, Department of Large Helical Device Project, NATIONAL Institute for Fusion Science, 大型ヘリカル研究部, 助手 (90280601)
ISOBE Mitsutaka Research associate, Department of Large Helical Device Project, NATIONAL Institute for Fusion Science, 大型ヘリカル研究部, 助手 (00300731)
NAKAJIMA Noriyoshi Associate professor, Department of Large Helical Device Project, NATIONAL Institute for Fusion Science, 大型ヘリカル研究部, 助教授 (30172315)
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| Project Period (FY) |
2000 – 2002
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| Keywords | energetic ions / Alfven eigenmodes / helical devices / energetic ion loss / shear Alfven soectrum / core-localized TAEs / helicity induced Alfven eigenmodes (HAEs) / Alfven eigenmode spectroscopy |
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| Research Abstract |
Characteristics of energetic ion driven MHD modes and their effects on energetic ion transport were studied in neutral-beam-injection (NBI) heated plasmas of the Large Helical Device(LHD). The following new and important results were obtained.
(1) Two types of toroidicity-induced Alfven eigenmodes (TAEs) were observed. One is a core-localized TAE(C-TAE) of which TAE gap location is near the plasma center with low magnetic shear. The other is a global TAE of which gap location is in the outer portion of the minor plasma radius. In a few shots, C-TAEs with even and odd parity were simultaneously excited.
(2) When the rotational transform at the plasma center exceeds a certain value, the relevant C-TAE has been converted to two global Alfven eigenmodes (GAEs) because the TAE gap is removed. This mode transition from C-TAE to GAE is also observed in a reversed shear configuration of the JT-60U tokamak.
(3) In high beta plasmas, high frequency Alfven eigenmodes of which frequency is by eight times higher than the TAE gap frequency were observed. Comparison of the modes with the calculated shear Alfven spectra suggests that the high frequency mode is a helicity-induced Alfven eigenmode (HAE).
(4) About 30-50 % of total energetic ions generated by NBI is transiently lost by bursting TAEs with rapid frequency chirping. The bursting TAEs often trigger the formation of internal transport barrier.
In the Compact Helical system (CHS) heliotron/torsatron, TAEs were excited by external magnetic perturbations generated by the inserted electrodes into a low density and low temperature plasma without energetic ions. This experiment was carried out as a basic study ofAlfven eigenmodes in a helical plasma.
This research project has demonstrated that the Alfven eigenmode spectroscopy using energetic ions and externally applied magnetic perturbations is very useful to study MHD properties of a helical plasma.
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