A Virtual Simons Hour Talk: Energetic Particle Loss Mechanisms In Reactor-Scale Equilibria Close To Quasisymmetry

Given by: Elizabeth Paul
Affiliation: Princeton University

Note the time: 8:00am EDT / 12:00 UTC.
Zoom link will be sent via email.

ABSTRACT:

The transport of fusion-born alpha particles in 3D equilibria is largely determined by collisionless physics. Several transport mechanisms have been implicated in stellarator configurations, including stochastic diffusion due to transitions, ripple trapping, and superbanana orbits. Given the guiding center evolution in a set of six quasi-helical and quasi-axisymmetric equilibria, we perform a classification of trapping classes and transport mechanisms. In addition to superbanana and ripple transport, diffusive banana tip motion associated with the non-conservation of the parallel adiabatic invariant is substantial among prompt losses, especially in quasi-axisymmetric equilibria. On longer time scales, many lost trajectories undergo transitions between trapping classes, either with periodic or irregular behavior. We discuss possible optimization strategies for each of the relevant transport mechanisms and perform a comparison between classified guiding center losses and metrics for superbanana transport.