2013 Fiscal Year Research-status Report
Integrated multi-time-scale simulation of energetic ion dynamics in tokamak plasmas
| Project/Area Number |
25820443
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Research Institution | Japan Atomic Energy Agency |
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Principal Investigator |
BIERWAGE Andreas 独立行政法人日本原子力研究開発機構, 核融合研究開発部門 六ヶ所核融合研究所, 研究員 (10584691)
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| Project Period (FY) |
2013-04-01 – 2016-03-31
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| Keywords | Nuclear fusion / Tokamak / Energetic ions / Alfven waves / Wave-particle resonances / Multi-timescale dynamics / Nonlinear simulations |
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| Research Abstract |
The goal of this project is to clarify the mechanism that triggers the onset of abrupt large relaxation events observed in JT-60U tokamak. The following milestones of the research plan were achieved:
(1) The role of finite Larmor radius (FLR) and nonlinear mode coupling on energetic particle modes was examined. FLR is found to reduce the wave-particle coupling efficiency, so it reduces mode amplitudes. This means that a steeper energetic ion pressure gradient can be maintained. Instead of direct mode coupling, indirect coupling between modes via mutual scattering of respective resonant particles is found to play an important role. This increases the mode amplitude and the energetic ion transport.
(2) The effects of an anisotropic pitch angle distribution, a bump-on-tail distribution, and particles passing through vacuum were examined. Bump-on-tail structures are found to have no effect on the modes studied, confirming the dominance of spatial gradients. The inclusion of particles passing through vacuum allowed us to remove spurious gradients. This has a stabilizing effect in some cases, but for JT-60U the effect is found to be small. The anisotropy of the pitch angle distribution is found to be important in JT-60U: it facilitates strong instabilities since it happens to match the wave-particle resonance condition.
A major portion of the grant was used to present these results at international workshops and conferences, including one invited talk given at an IAEA Technical Meeting. One peer-reviewed journal paper was published and one was accepted for publication.
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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
All research goals set for fiscal year 2013 were achieved. The original plan was to use approximate analytical models of the energetic ion distribution function. However, we were already able to implement and use a new interface that connects the instability simulation code with a code that computes particle distribution functions based on realistic particle sources and a collision model. The simulation results that we published this year were obtained with this more realistic setup. Hence, we have already completed some of the tasks planned for fiscal year 2014; namely, the integrated modeling of multi-time-scale dynamics. In addition, we reevaluated the possibility of simulating all relevant processes in a single comprehensive simulation code, without using approximations based on time-scale separation. First test runs on the supercomputer Helios at IFERC CSC were successful and indicate that it is, after all, feasible to pursue this ambitious goal.
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| Strategy for Future Research Activity |
Motivated by the results obtained so far, we continue to work towards the goal of the project: to clarify the mechanism that triggers the onset of abrupt large relaxation events as observed in JT-60U experiments.
Based on the good progress made in fiscal year 2013 and due to the successful tests of a comprehensive simulation code, we intend to change the research plan for fiscal year 2014 as follows.
For the time being, we abandon the integrated modeling approach, which is based on time-scale separation and where two specialized codes would be run as a tandem. Instead, a single comprehensive code is used that solves all relevant processes simultaneously: wave-particle interactions (short time scale), particle injection and collisions (long time scale). Due to the absence of artificial interfaces, this method allows us to self-consistently study meso-scale phenomena that were observed in the experiments, such as intermittent bursts of plasma fluctuations and frequency chirping. We expect to be the first in the world to carry out such self-consistent long-time simulations for energetic ion physics in magnetically confined fusion plasmas. We also believe that the new approach will increase our chances to achieve the above goal of this research project. Using the most realistic model available will facilitate meaningful comparisons with experimental observations and maximize the credibility of the conclusions that will be drawn.
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| Expenditure Plans for the Next FY Research Funding |
It was planned to purchase a personal license for the PC software "Matlab Parallel Processing Toolbox" for about 150,000 Yen. However, it became possible to use an existing shared license to carry out the work, so buying the personal license is not crucial for the time being. On the other hand, we are facing a tight budget for covering travel expenses in fiscal year 2014, so it was decided that the remaining money would be better used for presenting our new research results at conferences and workshops.
The amount carried over from fiscal year 2013 (about 140,000 Yen) will allow us to cover most of our domestic business trips in fiscal year 2014. 60,000 Yen will be used to attend the Plasma Conference in Niigata in November 2014, where I will give an invited talk. The remaining 80,000 Yen will be used to cover the domestic travel expenses of trips going abroad. One of these will be to attend IAEA Fusion Energy Conference in St. Petersburg/Russia in October 2014. Presentations will be given at all conferences attended.
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Research Products
(6 results)
