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The energy distribution of charge-exchange neutral (CXN) measured on EAST is interpreted by SOLPS-ITER modeling with the wide grid version, and the CXN-induced all erosion near the inner midplane and baffles is found to be significant especially under the enhanced SOL transport regime. Simulations for ITER predict that plasma and CXN fluxes onto the first wall are very sensitive to the cross-field transport in the far-SOL [1,2], while the CXN transport has not been well investigated. Recently, self-consistent simulations for edge plasma and neutrals are conducted and compared with the measurements of CXN distribution by the low-energy neutral particle analyzer (LENPA) in EAST. The CXN energy spectrum obtained from the SOLPS-ITER simulations with realistic wall geometry matches well with LENPA measurements. A new EIRENE interpretive module has been developed to analyze the generation and transport mechanisms of CXNs with different energies.
The formation mechanism of the “turning point”, which is a typical characteristic of the CXN energy spectrum in H-mode plasmas that separates the low-energy part and the high-energy part with two slopes, is found to be caused by the steep Ti gradient in pedestal region. The modeling is verified by dedicated L-H transition experiments on EAST. Meanwhile, more than one half of CXNs generated in the plasma undergo collisional losses including charge exchange and ionization during their flight pathway to the first wall. The baffles experience a high integrated flux (Γ_{int}) but a low mean energy (Emean) of CXN, while the midplane region exhibits the opposite characteristics. The particle anomalous diffusion coefficient (D_{⊥}) is scanned in different locations in the SOL. Extending the grid to the full wall is found to significantly decrease the sensitivity of the solution with far-SOL D⊥ because of the less recycling sources from the wall surface. Whereas the CXN flux at the first wall increases with D_{⊥} mainly due to the enhanced recycling source at the baffles. The impact of CXN on material erosion is also analyzed for both boron and tungsten. The boron erosion mainly depends on the Γ_{int} and thereby peaks at the baffle regions near divertors. The tungsten erosion is sensitive to the incident particle energy so that it peaks near the inner midplane where the maximum Emean exists.
[1] J. Romazanov et al., Nuclear Materials and Energy, 26 (2021) 100904.
[2] N. Rivals et al., Nuclear Fusion, 65 (2025) 026038.