Simulation of the mitigation of tungsten divertor target erosion by real-time lithium powder injection on EAST

Real-time lithium (Li) powder injection, a key wall conditioning method on EAST (Experimental Advanced Superconducting Tokamak), can mitigate tungsten (W) erosion and impurity generation through multiple mechanisms, including changes in the surface composition of plasma-facing materials. Investigating the evolution of divertor target surface composition during Li powder injection is crucial for understanding its impact on W impurity control, which is important for future fusion devices. This work developed the impurity migration and wall composition dynamics code based on the WallDYN physical model and coupled it with other codes to simulate the evolution of impurity migration and surface composition during particle irradiation. The background plasma is provided by SOLPS-ITER, the redistribution matrix is calculated by the kinetic impurity transport code IMPEDGE, and the sputtering and reflection databases are taken from SDTrimSP. The evolutions of Li and W compositions of the divertor target, and the eroded W impurity during real time Li power injection on EAST, are studied. The simulation results are benchmarked with EAST experimental data, showing qualitative agreement. It is found that carbon (C) plays a dominant role in W target erosion. Li injection reduces the W surface concentration and the C redistribution flux, effectively mitigating C-induced W sputtering and significantly lowering the W erosion flux. The reduction in W erosion is positively correlated with the amount of injected Li. When the injected Li is sufficient, an increase in background C flux further reduces W erosion, which is mainly due to the variation of the surface composition.