Prediction of Alfvén eigenmode energetic particle transport in ITER scenarios with a critical gradient model

Abstract

A reduced 1D, local, critical-gradient model of energetic particle (EP) transport by Alfvén eigenmodes (AEs)—the TGLF-EP+Alpha model—is applied to a much-studied ITER base case and variations with lower plasma current and lower current penetration. The TGLF-EP+Alpha model is a highly reduced and computationally inexpensive model of EP transport. Such a reduced critical-gradient model, while inapplicable to transport driven by strongly nonlinear or non-local abrupt events, is a valuable tool for scoping studies needed in scenario optimization for ITER and beyond. It relies on the assumption of critical-gradient AE transport with the critical EP density gradient determined by linear AE stability calculations in the TGLF gyro-Landau fluid code automated with the parallel-processed TGLF-EP wrapper. EP transport is treated with simultaneous drive of AEs by fusion-born alpha particles and fast ions born from a MeV neutral beam injection heating. The effect of simultaneous drive creates about 50% increased particle transport in both EP channels. High magnetic safety factor and low shear are generally destabilizing to AEs, but low shear tends to be more important. A tailored q-profile, steady-state-relevant scenario can reduce AE-induced EP redistribution by more than 25% over the ITER base case despite having half the total current.