On mechanisms of energy/angular distribution of charge-exchange neutrals on the first wall in EAST

The erosion of first wall material will reduce the lifetime of first wall components, and deteriorate the core plasma confinement. For tungsten (W) wall, the charge-exchange neutrals (CXN) induced erosion may be the main steady-state erosion mechanism [1]. The understanding of the CXN deposition is the key to evaluate the CXN-induced erosion while still very insufficient. The low-energy neutral particle analyzer (LENPA) in the EAST tokamak has observed that the energy spectrum of deposited CXN strongly depend on the discharge condition [2]. To understand the distribution of CXN on the first wall, simulations using SOLPS-ITER code have been conducted.

A new output option is developed to obtain the CXN energy spectrum at a specific angle. Simulations reproduce the plasma profiles measured in experiments and obtain the energy spectrum of CXN deposited on the first wall matching well with the LENPA diagnostic. The dependencies of the CXN energy spectrum on the heating power, plasma density, fueling, and recycling are consistent with EAST experiments. Mechanisms of CXN energy/angular distribution are elucidated based on the CXN source/loss analysis and are verified by EAST experiments. Simulations reveal the characteristics of CXN distribution along the first wall. These results are valuable for the evaluation of first wall erosion in future fusion reactors.

[1] P.C. Stangeby, Journal of Nuclear Materials, 415 (2011) S278-S283

[2] N.X. Liu, Nuclear Materials and Energy, 33 (2022) 101256