Speaker: Dr. Vinícius Duarte, Princeton Plasma Physics Laboratory
Title: Quantification of resonant fast ion transport in tokamaks via a transparent reduced model
Abstract:
Wave resonances, while delicate fine structures in plasmas, can mediate massive transport of energetic particles in fusion devices. These losses can constitute an obstacle to achieving burning plasmas, in which most of the heating of the thermal species is expected to stem from the confined alpha particles. In this seminar, it will be shown that a relatively simple quasilinear plasma transport theory that incorporates Fokker-Planck dynamical friction (drag) and pitch angle scattering self-consistently emerges from first principles for an isolated, marginally unstable mode resonating with an energetic minority species. It is found that drag fundamentally changes the structure of the wave-particle resonance, breaking its symmetry and leading to the shifting and splitting of resonance lines. In contrast, scattering broadens the resonance in a symmetric fashion. Comparison with fully nonlinear simulations shows that the emergent quasilinear system preserves the exact instability saturation amplitude and the corresponding particle redistribution of the more comprehensive fully nonlinear theory. Even in situations in which drag leads to a relatively small resonance shift, it still underpins major changes in the redistribution of resonant particles. This novel influence of drag is equally important in plasmas and self-gravitating systems. In fusion plasmas, the effects are especially pronounced for fast-ion-driven instabilities in tokamaks with low aspect ratio or negative triangularity, as evidenced by past observations. Interestingly, the same theory directly maps to the resonant dynamics of the rotating galactic bar and massive bodies in its orbit, providing new techniques for analyzing galactic dynamics. Finally, the development of a new code that simulates the developed transport model in realistic tokamak scenarios is reported along with its application to DIII-D experiments and ITER projections. In particular, the code shows good agreement with the measured fast ion losses, even in the presence of multiple Alfvénic instabilities.
Ref.: VND et al, Phys. Rev. Lett. 130, 105101 (2023); https://doi.org/10.1103/PhysRevLett.130.105101
Bio: Vinícius Njaim Duarte's research is focused on the resonant interaction between energetic particles and Alfvénic waves in fusion devices via analytical and numerical modeling. His interests include collisional kinetic theory and fast ion transport in tokamaks with concomitant neutral beam and radiofrequency heating. He is a recipient of a 2023 DOE Early Career Award and the 2024 IUPAP Early Career Scientist Prize. He is a Member of the ITPA Energetic Particle Physics Topical Group and serves on the Editorial Board of Physics of Plasmas and on the Executive Committee of Transport Task Force (TTF). He obtained his PhD in Physics in 2017 from the University of São Paulo, for which he received the Brazilian Physical Society thesis prize. After a postdoc at the Princeton Plasma Physics Laboratory, he moved to the research staff in 2020.
Seminar Access: In-person seminars are only available to CU ID holders. At this time, Non-Columbia affiliates and the general public are only invited to participate remotely. Contact [email protected] if you would like the Zoom link for this seminar.