Abstract
The Alfvén instability nonlinearly excited the energetic-particle-driven geodesic acoustic mode on the ASDEX-Upgrade tokamak, as demonstrated experimentally. The mechanism of the energetic-particle-driven geodesic acoustic mode excitation and the mode nonlinear evolution is not yet fully understood. In the present work, a first-principles simulation using the MEGA code investigated the mode properties in both the linear growth and nonlinear saturated phases. Here we show that the simulation successfully reproduced the excitation and coexistence of these two modes, and agreed with the experimental results well. Conclusive evidence showed that the resonance overlap is the excitation mechanism of the energetic-particle-driven geodesic acoustic mode. In the linear growth phase, energetic particles that satisfied different resonance conditions excited the Alfvén instability, which then caused energetic particle redistribution in phase space. These redistributed energetic particles caused resonance overlap, exciting the energetic-particle-driven geodesic acoustic mode in the nonlinear phase.
| Original language | English |
|---|---|
| Article number | 1130 |
| Journal | Scientific Reports |
| Volume | 15 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2025 |
Funding
Numerical computations were performed on the \u201CPlasma Simulator\u201D (NEC SX-Aurora TSUBASA) of National Institute for Fusion Science (NIFS) with the support and under the auspices of the NIFS Collaboration Research program (NIFS19KNXN397, NIFS20KNST156, NIFS21KNST196, and NIFS22KIST025), the JFRS-1 supercomputer system at Computational Simulation Centre of International Fusion Energy Research Centre (IFERC-CSC), and the Supercomputer Fugaku provided by the RIKEN Center for Computational Science (Project IDs: hp200127, hp210178, hp220165). This work was partially supported by MEXT as \u201CProgram for Promoting Researches on the Supercomputer Fugaku (Exploration of burning plasma confinement physics, JPMXP1020200103)\u201D, JSPS KAKENHI Grant Nos. JP18K13529, JP18H01202, JP21H04973, and \u201CPLADyS\u201D, JSPS Core-to-Core Program, A. Advanced Research Networks. Also, This work was partially supported by the NINS program of Promoting Research by Networking among Institutions (Grant Number 01422301) and by the International Research Exchange Support Program of the National Institutes of Natural Sciences. In addition, this work was partially carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200 - EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. The authors thank Prof. K. Nagasaki of Kyoto Univ., Dr. T. Hayward-Schneider of MPG-IPP, Mr. B. Rettino of MPG-IPP, Dr. F. Vannini of MPG-IPP, Dr. Z. Lu of MPG-IPP, Dr. X. Wang of MPG-IPP, Dr. G. Meng of MPG-IPP, Prof. S. Okamura of NIFS, Prof. M. Osakabe of NIFS, Prof. K. Ida of NIFS, Prof. K. Ichiguchi of NIFS for their sincere help and fruitful discussions.