Fast ion transport induced by Alfvénic resonance in perfectly omnigenous equilibria

Fast ion confinement is of great importance for all magnetic confinement nuclear fusion concepts. Recent progress in stellarator optimization has produced static magnetic configurations that are predicted to exhibit excellent fast ion confinement. However, Alfvénic perturbations will likely be ubiquitous in fusion reactors. Resonance between the motion of a fast ion and a shear Alfvén wave will lead to radial transport of the ion. Previous work* has shown that this effect can be significant even in perfectly quasi-symmetric magnetic configurations. In this work, we generalize the calculations to perfectly omnigenous magnetic configurations with an eye toward quasi-isodynamic stellarators. We evaluate the resonance condition in this more general setting, considering both passing and trapped particles. We apply the near-axis expansion to gain an intuitive understanding of how magnetic geometry influences resonance.

* E. J. Paul et al., JPP 89(5), 905890515 (2023).