Researchers are closing in on the potential of nuclear fusion, the process that powers the stars, as a clean and inexhaustible energy source.
At the heart of this effort is the tokamak reactor design, which uses magnetic fields to confine plasma and maintain the necessary conditions for fusion. A critical challenge has been managing the plasma edge instabilities, but recent breakthroughs in understanding how energetic particles interact with these instabilities suggest promising methods for improving reactor performance.
Sustainable Energy and Nuclear Fusion
Developing sustainable energy sources capable of meeting global energy demand is one of today’s most pressing scientific challenges. Among the potential solutions, nuclear fusion — the process that powers the stars — stands out as a clean, virtually limitless energy source.
The most promising approach to fusion energy is the tokamak reactor, which uses magnetic fields to confine plasma. High plasma confinement is critical for the success of nuclear fusion power plants and is the ultimate goal of ITER, the world’s largest tokamak, currently being constructed in Cadarache, France. A key factor in achieving this is maintaining plasma edge stability, which plays a vital role in effective confinement.
In current tokamaks, edge instabilities, known as Edge Localized Modes (ELMs), cause significant particle and energy losses, much like solar flares erupting at the Sun’s surface. These losses can lead to erosion and extreme heat fluxes on the reactor’s plasma-facing components—conditions that would be unsustainable for future fusion power plants.
Role of Energetic Particles in Fusion Reactors
Energetic (suprathermal) particles constitute an essential source of momentum and energy, especially in future burning plasmas. They must be well confined to guarantee a self-sustaining fusion reaction. An international collaboration has studied the impact of energetic ions on these ELMs. They have combined experiments, modeling, and simulations to understand the behavior of ELMs in the presence of energetic particles. The measurements were obtained by the team at the ASDEX Upgrade tokamak, a fusion device located at the Max Planck Institute for Plasma Physics (Garching, Germany). The simulations were done using a hybrid code named MEGA, which calculates the self-consistent interaction between the ELMs and energetic particles. Comparison of the modeling results to the experimental data provides a new physics understanding of ELMs in the presence of energetic particles. The results indicate that the spatio-temporal structure of ELMs is largely affected by the energetic particle population and indicate that the interaction mechanism between ELMs and energetic particles is a resonant energy exchange between them.
New Insights from Fusion Research
This interaction mechanism helps to qualitatively understand the striking similarities between the experimental signatures of ELMs visible in magnetic diagnostics and in fast-ion loss detectors. This experimental and computational work, which has been done within the framework of the European fusion consortium EUROfusion, has recently been published in Nature Physics.
“In our publication, we demonstrate that energetic ion kinetic effects can alter the spatio-temporal structure of the edge localized modes. The effect is analogous to a surfer riding the wave. The surfer leaves footprints on the wave when riding it. In a plasma, the energetic particle interacts with the MHD wave (the ELM) and can change its spatio-temporal pattern. Our results can have important implications for the optimization of ELM control techniques. For instance, we could use energetic particles as active actuator in the control of these MHD waves “, says main author Jesús José Domínguez-Palacios Durán.
This is a groundbreaking work, that provides, for the first time, a detailed understanding of the interaction between energetic ions and ELMs. The results indicate that, for ITER, a strong energy and momentum exchange between ELMs and energetic ions is expected.
Reference: “Effect of energetic ions on edge-localized modes in tokamak plasmas” by J. Dominguez-Palacios, S. Futatani, M. Garcia-Munoz, A. Jansen van Vuuren, E. Viezzer, J. Gonzalez-Martin, M. Toscano-Jimenez, P. Oyola, Y. Todo, Y. Suzuki, L. Sanchis, J. Rueda-Rueda, J. Galdon-Quiroga, J. Hidalgo-Salaverri, H. Chen, J. F. Rivero-Rodriguez, L. Velarde, the ASDEX Upgrade Team and the EuroFUSION MST1 Team, 6 January 2025, Nature Physics.
DOI: 10.1038/s41567-024-02715-6
This work has received funding from the European Research Council, EUROfusion Consortium, Spanish Ministry of Science, Innovation and Universities and Junta de Andalucía.
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