Simulation of charge-exchange induced NBI losses on EAST

Abstract

The neutral beam injection is widely adopted in tokamaks as a key heating tool, playing a crucial role in generating burning plasmas. However, the loss of beam ions can damage the first wall and reduce the heating efficiency, resulting in failure to maintain steady-state conditions. In this work, the effect of neutral particles in the edge on fast ions generated by NBI in the Experimental Advanced Superconducting Tokamak (EAST) device is studied using the particle tracer code (PTC). The poloidal distribution of neutral particles is calculated by edge plasma simulation code SOLPS-ITER. In this simulation, four beam lines in EAST are considered: co-current tangential (co-tang), co-current perpendicular (co-perp), counter-current tangential (ctr-tang) and counter-current perpendicular (ctr-perp). It is shown that, in the absence of neutral particles, the loss fraction of ctr-injection is considerably higher than that of the co-injection. When considering the neutral particles, it is found that the ctr-perp injection demonstrates a significant variation in particles loss fraction (ranging from 18.56% to 25.42%) compared to the other three injection configurations. In terms of the loss fraction induced by neutral particles, ctr-injection exceeds co-injection, and perpendicular configuration exceeds tangential configuration. Furthermore, the difference of charge exchange ratios of three different energy (full energy, half energy, one third energy) of the four injections can be attributed to variations in the poloidal trajectories associated with each of these injections. Moreover, approximately half of fast ions which undergo neutralization directly lose to the first wall while the rest re-enter the bulk plasma and re-ionize. Except for the ctr-tang injection, the reionization ions from the other three injections exhibit effective confinement.