Multi-fidelity main-chamber heat load calculations for the optimization of first-wall protection limiters in reactor-scale tokamaks

The first wall of a fusion pilot plant must be capable of handling significant heat and particle fluxes, but at the same time must be compatible with adequate tritium breeding to support the device’s fuel cycle. One concept for solving this looming issue is to separate the first wall into breeding surfaces (focused on neutron compatibility) and protection limiters (focused on heat flux handling). This leads to a multi-parameter optimization, balancing management of the plasma exhaust while maximizing the area available for breeding. Accurately determining the heat loads on the main-chamber surfaces is a key part of this optimization but is complicated by uncertainties in far-SOL plasma physics, and the fact that inserting protection limiters modifies the magnetic topology of the far-SOL, introducing new uncertainties about poloidal and toroidal power sharing. This work reports on efforts to calculate main-chamber steady-state heat loads using models at multiple levels of fidelity: (1) a simple analytic model based on exponential decay lengths; (2) a reduced model for time-averaged ELM transport mapped along field lines to plasma-facing components; and (3) a full 3D EMC3 fluid model with grid to the wall. Strengths and weaknesses of each approach are discussed. Progress towards a self-consistent engineering optimization of the first wall (via coupling to computational fluid dynamics and neutronics calculations) is presented.