Mitigation approaches for the unprecedented SPARC divertor fluxes*

This work investigates divertor flux mitigation for the SPARC using fueling and neon seeding scans in steady-state and time-dependent SOLPS-ITER simulations to map the operational phase space to explore controllable detached scenarios within tungsten divertor surface limits.

    The simulations focus on single-null H-mode high-power (P_SOL ~ 29 MW, B = 12 T), and low-power (P_SOL ~ 10 MW, B = 8 T) scenarios [1, 2], investigating a range of SOL heat flux width, , to address experimental scaling [3] and simulation predictions [4].  Unlike ITER [5], no clamping of the upstream density with fueling rate has been observed, but trends in upstream density, neon concentration, and radiated power are consistent. Without seeding, with P_SOL = 10 MW and the conservative  = 0.15 mm, detached conditions can be achieved at f_GW > 0.6. With seeding, peak heat fluxes can be reduced to ~15 MW/m² for the conservative  at f_GW = 0.3. At full power operation, the required upstream density is significantly higher to obtain a given divertor state.

    In the simulations, strong hysteresis is observed in the divertor operation space at low densities across range of power, λ_q, fueling locations, and divertor geometries. In this hysteresis regime, target T_e asymmetries and strong SOL currents affect global particle and heat flow, with one divertor significantly hotter than the other. At broader  levels, the hysteresis density window is reduced. This presents challenges for heat flux control and strike point sweeping mitigation techniques.