Numerical Study on Ripple Loss of Neutral-Beam-Injected Fast Ions in EAST

摘要

A systematic comparative study on the behaviors and loss processes of energetic beam ions in the rippled toroidal field on Experimental Advanced Superconducting Tokamak (EAST) is carried out by numerical simulations. The predicted loss fractions of either co-injected or counter-injected neutral beam ions for typical EAST experiments are 9-16 %; while for low current experiments, the ripple loss domain is enlarged with the increase of the safety factor q, resulting in enhanced beam ions loss. In addition, Counter-injected ions give rise to more lost fractions in the relatively high-energy range, and fewer of them distribute into the core plasma region, which suggest that the co-injection scheme is somewhat preferable for plasma heating. Moreover, the total losses of energetic beam ions in both co-injection and counter-injection geometries are seen to be due entirely to the delayed losses owing to a synergistic effect of collisions and ripple. Finally, potential first wall damage appears to be avoidable for long pulse neutral beam injection scenarios.