題   目：  Improved understanding of energetic ions impact on plasma confinement from theory and experiments

報告人： Jeronimo Garcia，教授，CEA, IRFM

時   間： 2023年07月12日（周三）  上午 10：00 

地   點： 聚變科學所二樓大會議室

摘   要：Self-plasma heating by the MeV fusion born alpha particles from Deuterium-Tritium (DT) reactions is one of the essential pillars of magnetically confined plasmas as the core of a fusion power generation power plant. However, energetic particles have some effects that are not optimum from the generation of energy point of view. For instance, they transfer their energy mostly to the electrons rather than to the ions or they can resonate with Alfvén waves producing turbulent transport that can degrade the fusion power output. At present, experimental validation of such studies has been elusive due to the inherent difficulties to produce highly energetic ions in present day tokamak plasmas, which mostly use deuterium plasmas.

In this seminar, there will be a review of recent theoretical and experimental progress that has allowed a significantly improved understanding of the impact of energetic ions on magnetically confined plasmas. Studies performed with Neutral Beam Injection (NBI) or Ion cyclotron Resonant Heating (ICRH) in several tokamak devices, such as JET, ASDEX-U and DIII-D, have shown that thermal turbulent radial heat transport can be reduced or even suppressed in the presence of energetic ions when electromagnetic fluctuations are not negligible. In particular at JET, in the presence of energetic ions in the range of alpha particles energies, strong electron heating is obtained and yet increasing ion temperatures are also obtained in dedicated electron heating power scans. This is in contrast with pure electron heating by electromagnetic waves with frequency in the range of the electron cyclotron gyromotion, such as the ones used in W7-X plasmas, in which the ion temperature remains clamped with increasing power.
Dedicated numerical studies point out that plasmas with energetic ions are a complex non-linear multiscale system in which the excitation of the Alfvén activity suppress smaller scale ion thermal transport and thus compensating any potential harm of the extra energetic ion transport generated by the Alfvén activity. Such results are obtained in different plasma mixtures, in particular in H-4He with a fraction of highly energetic 3He ions, and thus with a similar composition than solar corona plasmas in which such mixtures are dominant.  
Therefore, the presence of fusion born DT alpha particles can lead to beneficial and unforeseen effects in reactor relevant conditions.

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