Simulations of NBI ion losses with 3D magnetic perturbations and charge exchange on EAST

Abstract Guiding-center orbit-following simulations of fast ion losses for two neutral beam injections (NBIs) with three-dimensional (3D) magnetic perturbations and charge exchange (CX) by the GYCAVA code are presented. Here, 3D magnetic perturbations include the ripple field and resonant magnetic perturbations (RMPs). Loss fractions, loss regions, heat loads and steady-state densities of beam ions have been investigated on the EAST tokamak. The steady-state density of co-current perpendicular NBI ions near the edge can be significantly reduced by CX and the ripple field. In the presence of the ripple field, CX enhances NBI ion losses without RMPs, while it can reduce the particle loss of NBI ions with RMPs. This behavior is attributed to the overlap of loss regions induced by 3D magnetic perturbations and CX and the re-ionization (RI) effect. Both CX and RMPs can significantly broaden loss regions on the high-field side (HFS) of NBI ions, leading to increased losses of passing ions born on the HFS. Hit points of lost neutrals are influenced by the direction of the toroidal magnetic field, which is related to the gyromotion of fast ions. CX can significantly mitigate the heat loads of NBI ions in the presence of 3D magnetic perturbations. The mitigation effect, caused by background neutrals, may help reduce fast-ion-induced hot spots near the mid-plane, which can adversely affect the plasma performance in a tokamak. The neutral density at the edge can be enhanced by external gas puffing in experiments. This work provides numerical support for mitigation of heat loads of fast ions near the mid-plane by using external gas puffing.