Direct determination of midplane background neutral density profiles from neutral particle analyzers

Abstract Here we present a new method that allows the determination of background neutral density profiles based on measurements from particle analyzers (NPA). Bayesian optimization is used to obtain reliable 5-parameter representation inferred profiles. The has been benchmarked using forward modelling FIDASIM against measured data. systematic errors coming assumptions made in analysis were evaluated and they are lower than ≲5%. tested data ASDEX Upgrade tokamak. When reconstructed profiles, good agreement found between NPA fluxes neutralized fast ions with predictions TRANSP FIDASIM. Moreover, clear drop observed at plasma boundary after edge localized mode (ELM) activity. As suggested by KN1D simulations, this mainly due an increase scrape-off layer (SOL) ionization rate, resulting higher SOL densities temperatures ELM crash. calculating local source which will be important for future transport studies.