Speaker
Description
Managing power and particle exhaust is a central challenge for a compact, high-field fusion pilot plant, where power-plant-level exhaust in a limited divertor volume leads to severe thermal and particle loading to the material surfaces. Achieving stable, dissipative divertor operation under these conditions (while simultaneously ensuring effective helium removal) requires divertor geometries, magnetic configurations, and pumping arrangements capable of accessing and regulating high-density, strongly radiating regimes with sufficient helium exhaust capability. To rapidly explore this parameter space, the isolated-leg “Box” SOLPS-ITER framework (originally developed for MAST-U [1-3]) is extended to ARC-relevant operating conditions. The Box approach enables controlled comparisons across geometric configurations while maintaining fixed upstream boundary conditions determined from the ARC physics basis [4].
This work introduces several advances to the Box model framework. First, realistic baffle and vessel wall contours are incorporated, together with flexible specification of puffing and pumping locations, enabling targeted studies of neutral closure and divertor pumping efficiency. Second, an updated fixed-fraction radiative impurity model is implemented, and the framework is extended to include, for the first time, the full multi-charge-state impurity model. This higher-fidelity treatment is essential for accurately capturing helium behavior, as its long mean free path and distinct atomic characteristics make its exhaust highly sensitive to local flow stagnation, connection length, and divertor neutral pressure.
Using these expanded capabilities, systematic scans of flux expansion, baffle geometry, impurity concentration and species, and pump placement are performed at fixed upstream conditions with ARC-like parameters of 1e20 m-3 upstream density and 40 MW power to emulate a double-null outer divertor leg [4]. The influence of divertor closure, magnetic geometry, and pump placement on helium behavior is analyzed, and comparisons between the fixed-fraction and full multi-charge-state impurity formulations provide a framework for assessing how different modeling assumptions affect predicted detachment thresholds and radiation characteristics under ARC-class conditions within the context of the extended Lengyel model [5].
Together, these developments establish a workflow for rapid exploration of magnetic and geometric divertor concepts, and identify promising pathways for helium exhaust compatible with ARC’s liquid FLiBe immersion blanket environment.
Supported by Commonwealth Fusion Systems.
[1] Lipschultz, et al. Nuclear Fusion 2016, 56, 056007.
[2] Moulton, et al. Plasma Physics and Controlled Fusion 2017, 59, 065011.
[3] Cowley, et al. Nuclear Fusion 2022, 62, 086046.
[4] Body and Eich, et al. Submitted to Journal of Plasma Physics.
[5] Body, Nuclear Fusion 2025, 65 086002