SOLPS-ITER Simulations of SPARC Q>1 L-Mode Scenarios with Neon Impurity Seeding*

SPARC is a compact, high-field tokamak (R₀=1.85 m, B₀=12 T) under construction by Commonwealth Fusion Systems designed to achieve net fusion energy. A Q>1 L-mode scenario will be attempted in the first operation campaign [1]. In this work, the SOLPS-ITER code is used to investigate heat flux dissipation in candidate Q>1 L-mode scenarios in standard lower single-null divertor geometries, to identify operational regimes within the tungsten target material limits. Outboard midplane gas fueling and divertor pumping consistent with the SPARC hardware designs are utilized in the model. Divertor strike-point positions are varied between different target tile locations, to assess the impact of various divertor geometry choices on scrape-off layer conditions. Neon impurity models, in both fixed-fraction and multi-species forms, are employed to study power dissipation, and the impurity content is varied toward achieving full detachment of both targets. The impurity concentration required for ion flux rollover in the simulations is compared to that predicted by the Lengyel model, and scalings with collisionality parameters are also analyzed. Parameter scans of upstream density and scrape-off layer power are performed to explore the parameter space of the SPARC divertor scenarios.

[1] T. Body et al., APS-DPP 2023, NO05.00003