Resonant transport of fusion alpha particles in quasisymmetric stellarators

Abstract In modern, highly optimized stellarator configurations where prompt fusion alpha particle losses from the plasma core are absent, particles can still be lost due to stochastic orbits which result in delayed losses. One mechanism leading changes trapping class during drift motion along contours of parallel adiabatic invariant J ∥ jumps when crossing boundaries. Another mechanism, is main interest here, resonance between and bounce (drift-orbit resonance). The first affects mainly trapped near trapped-passing boundary phase space quasi-symmetric quasi-isodynamic devices, minimized there by aligning local magnetic field maxima on a given flux surface. second may affect broader range domain remain closed. Drift-orbit resonances modify topology island-like structures Poincaré plots these islands overlap thus transport. this report, we study stochastization with help Hamiltonian drift-kinetic code NEO-RT as well orbit classification direct computation within symplectic following SIMPLE. width phase-space studied using perturbation theory. Based reactor assess if approach used fast metric for optimization.