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Description
A SOLPS-DIVIMP-SDTRIM.SP integrative modeling framework has been established to simulate time-dependent material erosion, impurity transport, and boundary plasma transport for > 100s long-pulse discharges in EAST for the first time. The erosion and redeposition of plasma-facing materials (PFMs) during long-pulse discharges not only affect the boundary plasma conditions but also determine the lifetime of PFMs. The iterative simulation of plasma distribution and impurity migration with grids extended to the first wall are realized by sequential SOLPS and DIVIMP simulations. Then the material evolution is calculated by the SDTRIM.SP with the particle flux derived from SOLPS and DIVIMP. The simulation results reveal that there exist periodic formation and diminishment of tungsten-lithium (W-Li) multilayers at some locations near the strike point on the divertor. With an initial low-Z Li coating on the W amour due to wall conditioning, plasma impact effectively erodes the coating layer on the divertor surface, leaving a W-enriched top layer that protects the underlying low-Z Li from erosion and thus forms a multilayered structure. The multilayered structure is verified by dedicated post-mortem EDS analysis of the EAST divertor target [1]. As plasma impinges, the W enriched surface layer gradually diminishes, leading to a transition from the W-dominant surface material to underlying Li. The periodic formation and diminishment of the multilayered structure significantly influence local particle recycling processes through changing the reflection, reemission and deposition rates of D on PFMs [2]. Unlike the D reemission, which emits D at the thermal energy, the D reflection can lead to energetic D neutral emission with a much higher averaged energy even above 100 eV, which results in stronger neutral penetration. The dynamic evolution of the D recycling reshapes the boundary plasma distribution and can even affect the sustainment of divertor detachment in EAST long-pulse discharges. This phenomenon is evidenced by the corresponding variation of Da and Langmuir probe data.
Comparative studies of material evolution under Li and boron (B) coatings show that B coatings have over twice the lifetime of Li coatings under typical EAST high-recycling divertor conditions. Periodic W-B multilayer formation also occurs, but its impact on global particle recycling is less significant than that of Li coatings. Modeling advances in this work highlight the crucial role of wall material evolution in predicting dynamic boundary plasma behavior, especially during long-pulse discharges.
[1] G. Xu, et al. IAEA-FEC, 2025, Chengdu, China.
[2] Q. Long, et al. NME 41 (2024): 101840.