2014 Fiscal Year Research-status Report
Integrated multi-time-scale simulation of energetic ion dynamics in tokamak plasmas
| Project/Area Number |
25820443
|
|---|
| Research Institution | Japan Atomic Energy Agency |
|---|
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)
|
|---|
| Project Period (FY) |
2013-04-01 – 2016-03-31
|
| Keywords | Nuclear fusion / Tokamak / Energetic ions / Alfven waves / Wave-particle resonances / Multi-timescale dynamics / Nonlinear simulations |
|---|
| Outline of Annual Research Achievements |
The goal of this project is to clarify the mechanism that triggers abrupt large relaxation events observed in JT-60U tokamak. The following milestones of the research plan were achieved:
(1) The comprehensive multi-time-scale simulation code developed in FY 2013 was successfully validated. That is, we have reproduced many experimental observations made in JT-60 tokamak, both qualitatively and quantitatively: frequency-chirping in the 40-60 kHz range, bursts of instabilities with life times of a few milliseconds and intervals of 5-15 milliseconds. On the short time scale (10-100 ms), phase jumps were discovered in the simulations and subsequently confirmed by reexamining raw experimental data from JT-60.
(2) Wave-particle interactions in the JT-60 configuration studied were analyzed in detail and several observations were explained. This was made possible by our development of a new set of canonical coordinates and a new technique called "orbit-based resonance analysis".
(3) We discovered a new coupling mechanism between Alfven and sound waves in the frequency range of energetic particle modes. This implies that there is a noncollisional heating channel from energetic ions to thermal bulk ions. Consequently, the fusion performance of high-beta plasmas may be better than previously expected.
A major portion of the grant was used to present these results at IAEA Fusion Energy Conference. An invited talk was given at Plasma Conference in Niigata. Three papers were published in the peer-reviewed journals Physical Review Letters, Nuclear Fusion and Physics of Plasmas.
|
| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The successful implementation of a comprehensive model for self-consistent multi-time-scale simulations and its successful test runs accomplished in fiscal year (FY) 2013 have made the original plan for FY 2014 obsolete. Due to this unexpectedly good progress, we were able to already proceed to the next step, which was originally planned for FY 2015; namely, the validation of the multi-time-scale simulations against JT-60 tokamak experiments. The validation study was also successful and made us confident that our new code captures all the essential physics.
In addition, we completed another important task that was not part of the original plan but allows us to analyze the wave-particle interactions in unprecedented detail; namely, we developed a new technique that we call "orbit-based resonance analysis" (ORA) and applied it to explain observations that were made in previous simulations and experiments.
Furthermore, we have made an important discovery: we found a new coupling mechanism between Alfven waves and sound waves in the frequency band where energetic particle modes are located (> 20 kHz), including the abrupt large events (ALE) studied in this project. This discovery was made because we analyzed, for the first time, energetic particle modes in reactor-relevant regimes with high plasma beta. This discovery revives the research area of alpha particle energy channeling. Motivated by our discovery, we expect that this energy channeling may play a key role for the efficiency of the self-heating processes on which the idea of a burning plasma is based.
|
| 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 abrupt large relaxation events (ALE) as observed in JT-60 experiments.
Based on the good progress made in FY 2013 and 2014 - namely, (1) successful validation of a comprehensive multi-time-scale simulation code, (2) development of orbit-based resonance analysis (ORA) method, and (3) discovery of a new self-heating channel for burning plasmas - we intend to change the research plan for FY 2015 as follows.
(1) We continue the multi-time-scale simulations beyond 100 ms. The goal is to simulate ALEs directly. If this can be accomplished, the ALE trigger mechanisms can be studied by analyzing such an event directly. An explanation of ALEs based on such an analysis would be most convincing and make a strong impact.
(2) Our new ORA method was applied in FY 2014 for the analysis of energetic particle modes in the linear regime. In FY 2015, the method will be applied to clarify the physics of nonlinear dynamics seen in simulations and experiments, such as frequency chirping and mode amplification.
(3) Kinetic effects of thermal ions will be studied. These effects are not yet included in our code, but will be needed to make quantitative predictions for the efficiency of self-heating via the new noncollisional energy channel that we discovered. Moreover, kinetic thermal ion effects may play a role for the triggering of ALEs, since they provide a damping mechanism similar to the resistive dissipation that is already present in our simulations.
|
| Causes of Carryover |
Research progress has been more rapid than expected. Some parts of the plan were found to be unnecessary and were skipped, so that we already completed part of the work of FY 2015. Therefore, we are now able to investigate aspects that go beyond the original research plan; namely, kinetic thermal ion (KTI) effects.
KTI effects are important to elaborate on our new discovery (new self-heating channel) and possibly also for achieving the final goal of this project (to clarify trigger of abrupt large events). The inclusion of KTI effects requires us to gather additional know-how from leading experts in this challenging subject.
|
| Expenditure Plan for Carryover Budget |
The amount carried over from FY 2014 (about 500,000 Yen), with the addition of about 100,000 Yen from the FY 2015 budget, will allow me to pay for a three-week visit to Max Planck Institutes in Greifswald/Germany (1 week) and Garching/Germany (2 weeks). There I will meet with experts who have long-time experience in the study of kinetic thermal ion (KTI) effects on energetic-ion-driven Alfven waves. Through this collaboration, I expect to become able to continue to make extraordinarily rapid progress in this project as I have done until now, and maximize the probability of successfully explaining abrupt large events (ALE) in JT-60 plasmas.
|
Research Products
(12 results)
