Fast-ion transport in quasisymmetric equilibria in the presence of a resonant Alfvénic perturbation
Abstract
Significant progress has been made in designing magnetic fields that provide excellent confinement of the guiding-centre trajectories of alpha particles using quasisymmetry (QS). Given the reduction in this transport channel, we assess the impact of resonant Alfvén eigenmodes (AEs) on the guiding-centre motion. The AE amplitudes are chosen to be consistent with experimental measurements and large-scale simulations. We evaluate the drift resonance condition, phase-space island width and island overlap criterion for quasisymmetric configurations. Kinetic Poincaré plots elucidate features of the transport, including stiff transport above a critical perturbation amplitude. Our analysis highlights key departures from the AE-driven transport in tokamaks, such as the avoidance of phase-space island overlap in quasihelical configurations and the enhanced transport due to wide phase-space islands in low magnetic shear configurations. In configurations that are closer to QS, with QS deviations $δ B/B_0 \lesssim 10^{-3}$, the transport is primarily driven by the AE, while configurations that are further from QS, $δ B/B_0 ∼ 10^{-2}$, experience significant transport due to the QS-breaking fields in addition to the AE.
- Publication:
-
Journal of Plasma Physics
- Pub Date:
- October 2023
- DOI:
- 10.1017/S0022377823001095
- arXiv:
- arXiv:2306.12531
- Bibcode:
- 2023JPlPh..89e9015P
- Keywords:
-
- fusion plasma;
- plasma confinement;
- plasma simulation;
- Physics - Plasma Physics