Impact of electron density and temperature on neutral opaqueness using SOLPS simulation on MAST H-mode discharge*

Neutral opaqueness as a function of electron density and temperature is examined using SOLPS-ITER [1] simulation. Neutral opaqueness is defined as the ratio of electron density width, △n_e , to the neutral penetration length, λ_n0 [2]. It is approximated with n_e×a [3], where n_e is the average of electron density at the pedestal and the separatrix, and a is the minor radius of the tokamak. DIII-D database research comparing neutral opaqueness versus its approximation showed two slope branches caused by different ionization peak locations [4]. We increase the core density in a SOLPS-ITER simulation of MAST H-mode discharge. We will examine whether the ionization peak shifts from inside the separatrix to the Scrape-Off Layer (SOL) with increased core density. We will study neutral density and ionization change with respect to electron temperature. Results will be compared with the result from the 1-D kinetic neutral code, KN1D [5], for building a comprehensive edge fueling model.

[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] Mordijck, S., 2020. Nuclear Fusion 60, 082006.

[4] Julio Balbin-Arias, et al., TTF conference talk, 2024

[5] B. LaBombard, https://www-internal.psfc.mit.edu/~labombard/KN1D_Source_Info.html, 2001