Evolution of the SPARC divertor design: engineering and physics trade-offs

SPARC is a compact, high-field tokamak (B₀ = 12.2 T, R₀ = 1.85 m) with a close-fitting tungsten first wall. The resulting thermal and structural loads are challenging for the engineering design. Divertor targets will need to survive 10s pulses with unmitigated divertor parallel heat fluxes of ∽10 GW/m²; while disruptions can drive ∽2 kT/s changing magnetic fields, leading to large eddy current structural loads. Nonetheless, it is important that the divertor has sufficient diagnostic access and shaping to ensure that the SPARC divertor mission can be executed – exploration of highly dissipative, low erosion regimes, with neutral pumping for projections to next step devices. The present SPARC divertor is up-down symmetric, with both horizontal and vertical target plate configurations on the inner and outer divertors. In addition, the outer divertors feature highly baffled long legs (L_pol∽0.5 m, R_target/R_xpt∽1.2) and can form a X-point target divertor. The trade-offs between the engineering and physics requirements have driven the evolution of the divertor design from a beam-dump to the present SPARC divertor. These driving factors will be presented alongside the details of the SPARC divertor design.