| 研究実績の概要 |
Energetic-particle-driven geodesic acoustic mode (EGAM) in LHD plasmas are investigated using MEGA code. The energy transfer is analyzed and the bulk ion heating during the EGAM activity is observed. EGAM channeling is reproduced by simulation with realistic parameters for the first time. It is found that sideband resonance is dominant during the energy transfer from EGAM to the bulk ions, and the transit frequencies of resonant bulk ions are one-half of the EGAM frequency. Also, a systematic investigation of EGAM channeling is implemented for the first time. It is found that low-frequency EGAM makes the energy transfer efficiency higher, and this is confirmed by changing the energetic particle pressure, energetic particle beam velocity, and energetic particle pitch angle.
In addition, both global Alfven eigenmode and toroidal Alfven eigenmode in a quasi-axisymmetric device named CFQS are studied using MEGA code. The instability in 3-dimensional form is shown for the first time. Strong mode coupling is found, and this is consistent with the theoretical prediction. Also, the resonant condition caused by the absence of axial symmetry in CFQS was demonstrated for the first time. Finally, the nonlinear frequency chirpings of Alfven eigenmodes in CFQS were demonstrated for the first time.
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