Power and Temperature Asymmetries in the SPARC Divertor in SOLPS-ITER Simulations

SPARC is expected to have unmitigated parallel heat fluxes equal to or exceeding the highest values observed in existing devices. To support SPARC's breakeven and advanced-divertor missions, we perform scrape-off-layer (SOL) and divertor simulations using SOLPS-ITER. We observe strong divertor power and temperature asymmetries using SPARC geometries and parameters, with drifts not enabled. In a single-null (SN) horizontal-inner/vertical-outer divertor configuration, the inner target receives ∼60% of the power instead of the outer: an unexpected result compared to experiments. More dramatically, in an up-down-symmetric double-null (DN) configuration, several simulations converge to an up-down-asymmetric steady-state, with one target completely detached (∼5 eV) and the other completely attached (∼200 eV).

As these effects could impact SPARC operation, we are investigating whether their causes are physical or numerical. A dependence on input core power is found, indicating a power threshold necessary to trigger them. Initial conditions strongly affect steady-state currents and power-sharing in connected DN. We analyze parallel current as a potential driver, and we present a method to reach balanced steady-state solutions in DN, by initially disabling current terms in SOLPS-ITER.