Numerical study of fast-ion loss in the Experimental Advanced Superconducting Tokamak

The plasma transport analysis code TRANSP and full-orbit following code LORBIT were used to study fast-ion loss in the Experimental Advanced Superconducting Tokamak (EAST) under varying discharge parameters and heating scenarios, considering the synergistic effect of neutral beam injection (NBI) and ion cyclotron range of frequency (ICRF). To more faithfully simulate fastion loss processes, the axisymmetric twodimensional poloidal contours of the EAST first wall and the antenna limiters were used as the loss boundary and then stretched toroidally to construct a threedimensional boundary structure. Results indicate that the fast ion loss diminishes as the plasma current (I_\rm P) and toroidal magnetic field (B_\rm t) increase. Furthermore, the impact of different magnetic configurations on the fast-ion loss was considered. Increasing the distance between the antenna and the separatrix (R_\rm gapout) can significantly reduce the fast-ion loss. When the toroidal magnetic field was reversed, i.e., B_\rm t>0, the lower single-null configuration was more effective in mitigating the fast-ion loss than double-null and upper single-null configurations. A significant reduction in the fraction of fast-ion loss was observed when an outer strike point was positioned on the vertical target plate. Finally, the effects of varying NBI energies, injection angles, and ICRF antenna phases were investigated. The results indicate that, within certain limits, fast-ion loss decreases as the NBI injection angle increases, whereas higher NBI injection energies lead to more fast ion escape. In contrast, variations in the ICRF antenna phase exert only a marginal effect on fast-ion loss.