2020 Fiscal Year Research-status Report
Simulation study of the energy channel and the particle radial transport due to the energetic particle driven geodesic acoustic mode
| Project/Area Number |
18K13529
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| Research Institution | National Institute for Fusion Science |
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Principal Investigator |
Wang Hao 核融合科学研究所, ヘリカル研究部, 助教 (30724760)
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| Project Period (FY) |
2018-04-01 – 2022-03-31
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| Keywords | energetic particles / energy channel / geodesic acoustic mode / Alfven eigenmode / stellarator / simulation / energy transfer / quasi-axisymmetric |
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| Outline of Annual Research Achievements |
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. Strong mode coupling is found, and this is consistent with the theoretical prediction.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
(1) The initially planned targets are achieved. The most important target is to clarify the mechanism of energy channeling of energetic particle driven geodesic acoustic mode (EGAM). In addition, the applicant planned to investigate more properties of EGAM channeling, like particle transport and isotope effects. Now, all of the above targets are achieved. For the mechanism of EGAM channeling, now it is clear that the sideband resonance is dominant for energy transfer. For particle transport, the moving of particles from the core region to the edge region is found in simulation. For isotope effects, the energy transfer efficiency in the deuterium plasma is lower than that in hydrogen plasma. Finally, the applicant concluded that the higher NBI power, the lower NBI velocity, the higher number of perpendicular injected particles, the higher bulk ion temperature, and the wider bulk ion temperature profile are probably applicable strategies for improving observation of EGAM channeling.
(2) An extension of the initially planned research has been started. The applicant has already carefully investigated EGAM properties, and naturally, next step, he is trying to study the mode coupling between EGAM and other energetic particle driven modes like Alfven eigenmode. Some preliminary results in a quasi-axisymmetric device named CFQS have already been obtained. Both global Alfven mode and toroidal Alfven eigenmode are found in simulation. It will be a good start point for future research of mode-mode coupling.
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| Strategy for Future Research Activity |
In the future, the applicant will continue the research in the quasi-axisymmetric device named CFQS. At present, both the global Alfven eigenmode and toroidal Alfven eigenmode are simulated using MEGA code, and the distribution of resonant particles in phase space is analyzed. However, the detailed particle trajectory is still not clear yet. The quasi-axisymmetric device is a kind of advanced stellarator, both the configuration and particle trajectory are very complicated. The applicant will analyze the resonant particle trajectory, and clarify the detailed resonant condition between energetic particles and the instabilities. Also, good visualization will be shown.
In addition, if possible, the applicant will visit Max Planck Institute for Plasma Physics (IPP) in Germany. In the past, the applicant planned to visit IPP to continue the international collaboration and discuss the details of energetic particle driven instabilities in ASDEX-Upgrade device. However, because of COVID-19, the trip became impossible. Now, since the vaccine is gradually distributed, collaboration in the present fiscal year becomes possible. Some details of mode-mode coupling will be discussed, and some related simulations will be implemented as a kick-off of a new collaboration.
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| Causes of Carryover |
The applicant planned to visit Germany to implement an international collaboration in fiscal year 2020. However, because of COVID-19, the trip was cancelled. That is the reason why the actual amount of expenditure in fiscal year 2020 was very small.
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Research Products
(6 results)
