SPARC power exhaust workflows using open source tools for plasma facing component design and operational scenario planning*

Coupling plasma power exhaust physics directly to 3D engineering models has become a crucial component of design and operations for high power fusion machines. This work provides a tutorial designed to guide the audience through a series of physics-to-engineering workflows that were used to finalize the SPARC tungsten Plasma Facing Component (PFC) design, which will be presented for the first time. These SPARC PFC power exhaust workflows leverage the HEAT software suite, which is a modular and open source tool used for heat load predictions on tokamaks across the globe. HEAT is capable of predicting time-varying 3D heat loads from inter-ELM sources, gyro-orbit sources, Edge Localized Modes (ELMs), disruptions, and photon radiation. HEAT provides a balance between physics fidelity and computational speed, which is mandatory to enable rapid scans through high dimensional design space to prune inadequate design candidates. While SPARC plans to achieve Q>1 in L-mode during the initial operational campaign, the PFCs are being designed to withstand a high power Q~11 H-mode scenario during later campaigns. These H-mode pulses are expected to operate with up to 140 MW of D-T fusion power and a maximum of ~25 MW of combined Ohmic and ICRF heating power. SPARC’s high field results in a narrow heat flux width that could potentially load the PFCs with ~300 MW/m² steady state surface heat fluxes, which must be managed via strike point sweeping and divertor impurity seeding.  Additionally, the SPARC PFCs must be capable of surviving a finite number of transient events such as disruptions and ELMs, which has led to the development of a HEAT filament tracer. Throughout the presentation examples will be provided that demonstrate how optimization of the 3D PFC geometry was achieved despite sometimes conflicting requirements from physics and engineering.  By coupling the physics directly to the engineering models, design closure is possible and operational scenarios can be defined.