Comparative study of neutral opaqueness and atomic density in single and double null configurations (MAST/MAST-U) using SOLPS-ITER

Neutral opaqueness and atomic neutral density are compared between single-null (SN) (from MAST) and connected double-null (CDN) (from MAST-U) magnetic configurations using SOLPS-ITER simulations. For fusion pilot plants operating at high density and temperature, effective plasma fueling is critical to maximizing fusion gain. Neutral opaqueness characterizes how the plasma limits neutral fueling and is defined as the ratio of the electron pedestal density width, Δn_e , to the neutral penetration length, λ_n0[2]. The double-null configuration is a promising option for mitigating divertor heat loads in future reactors [3]. The separation introduced between the high-field side and low-field side enables comparison between SN and CDN to study the differences in 2D neutral opaqueness and atomic density profile. Both cases are simulated using the same MAST vessel wall geometry and maintain identical core particle and heat fluxes per unit area. Additionally, both cases share the same transport coefficients to isolate the edge neutral fueling dynamics from the cross-field transport model assumptions. The comparison results help us understand how the magnetic configuration affects the edge neutral fueling.

[1] Bonnin, X., et al., Plasma and Fusion Research, 11, 1403102, 2016

[2] R. Reksoatmodjo, et al., Nuclear Materials and Energy, 27:100971, 2021

[3] Aho-Mantila, Leena, et al. Nuclear Materials and Energy 26 (2021): 100886.