Speaker
Description
The SPARC tokamak is projected to have high unmitigated heat fluxes to the divertor plasma-facing components, with q|| up to 10 GW/m2 in H-mode, due to its high magnetic field and current (8.7 MA, 12.2 T). Type-I ELMs will cause unacceptable energy fluence on the target for routine operation due to the high pedestal pressures in H-Mode conditions. The separatrix density is an important parameter for access to detachment and scenarios with reduced ELM activity such as the quasi-continuous exhaust regime. SPARC is predicted to be highly opaque to edge fueling [1].
At CFS, we are preparing a hierarchy of models to estimate the separatrix density as a function of engineering parameters, with the goal of predicting it as a function of injected neutral particle flux. The simplest is a 0D model which calculates the divertor neutral pressure from the injected neutral particle flux balanced with pumping throughput and calculates the separatrix density from a multi-machine attached H-mode scaling [2]. The separatrix density is predicted within 50% accuracy for the AUG database, and we additionally test the model on a database from Alcator C-Mod and extrapolate to SPARC. This model is used to find a lower limit for the separatrix density with no injected particle flux using the available pumping throughput and assumed background particle source. The model is extended to solve for divertor neutral pressure and separatrix density consistent with recycling fluxes. We compare the predictions of the 0D models to the Extended Lengyel model [3], SOLPS simulations, and SOLPS-NN predictions [4]. We use these tools to evaluate SPARC scenarios planned for the first campaign.
[1] S. Mordijck et al. 2024 Nucl. Fusion 64 126034
[2] D. Silvagni et al. IAEA FEC 2025
[3] T. Body et al. 2025 Nucl. Fusion 65 086002
[4] S. Dasbach et al. 2023 Nucl. Mater. Energy 34 101396