Quantitative modeling of neoclassical tearing mode driven fast ion transport in integrated TRANSP simulations

Abstract

The TRANSP-‘Kick’ energetic particle transport model has been extended to study neoclassical tearing mode (NTM) driven fast ion (FI) transport with zero free parameters. FI transport induced by the NTM is obtained by calculating perturbed FI orbits via the guiding center particle following code orbit in the magnetic field of an experimentally characterized island chain. Transport probabilities are then used in TRANSP’s Monte Carlo module NUBEAM to modify the FI distribution in every time step of the full TRANSP analysis. This procedure retains all TRANSP functionality and self-consistently predicts the NTM impact on beam torque, current drive and heating. Comparisons to DIII-D steady state, hybrid and ITER baseline plasmas are encouraging with the model quantitatively recovering the measured neutron rates. FI effects depend on the location and width of FI phase space resonances which are not accounted for by the former ad hoc beam diffusivity model of TRANSP. Resonance overlaps result in a transport threshold, for the cases investigated herein, at . When the FI transport is dominated by energy and momentum redistribution. In particular, m/n = 3/2 NTMs lead to hollow profile at q = m/n and broadened profile in the core. When FI losses increase, the neutral beam torque () and driven current () decrease across the entire plasma. The effects on NB profiles can strongly depend on the NTM frequency and mode numbers with the 3/2 (2/1) broadening (peaking) near the magnetic axis.