Initial Scoping of the SPARC Divertor

Although the divertor heat flux is expected to be intense in SPARC, initial scoping shows that it should be manageable with a combination of modest radiation fractions and strike point sweeping on an inertially-cooled target. The small size, and therefore short current relaxation time, of the SPARC core plasma allows the core to reach steady state in under 10 seconds. This has two important benefits for the divertor: (1) The divertor does not need to be actively cooled during the pulse, greatly reducing the demands on first-wall component engineering. (2) The total plasma fluence on the divertor is greatly reduced in comparison to ITER, easing erosion lifetime concerns. Using the empirical inverse poloidal magnetic field heat flux width scaling and various assumed radiation fractions, thermal simulations are performed of the divertor target with active strike point sweeping. Results indicate that only a modest radiation fraction (~50%) is needed to maintain the divertor surface temperature to acceptable levels.