Vinícius N. Duarte, Princeton Plasma Physics Laboratory, Princeton University

"First-principles formulation of resonance broadened quasilinear theory: applications to fast ion loss modeling in tokamaks and predictions for bar rotation in galaxy dynamics"

Abstract: A method has been recently developed to analytically formulate resonance broadened quasilinear transport theory from first principles, due to either Krook or Fokker-Planck collisions, for marginally unstable plasma systems where discrete resonance instabilities are excited without any mode overlap. It is found that collisional 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 and Krook collisions broaden the resonances in a symmetric fashion. Comparison with fully nonlinear simulations shows that the proposed quasilinear system, from which a resonance function (diffusion coefficient) emerges self-consistently, preserves the exact instability saturation amplitude and the corresponding particle redistribution of the more complex fully nonlinear kinetic theory. These findings have motivated the development of the numerical tool RBQ, that has been coupled to the tokamak whole-device code TRANSP, to quantify and propose solutions to mitigate energetic particle transport in fusion experiments. Its application to DIII-D experiments has shown encouraging agreement with measurements. Interestingly, the developed formulation, originally aimed at fusion plasmas, has recently been identified to be isomorphic to a longstanding problem in galactic dynamics - that of the resonant interaction between bars in the center of galaxies and stars and dark matter in the galactic halo. The application of the developed framework made it possible to predict the rate of slowdown of the pattern rotation of galactic spiral bars in the presence of realistic background diffusion.