Physics design of a Spherical Tokamak Advanced Reactor (STAR)

This presentation will describe physics design activities for a fully nuclear A=2, R=4-4.5m Spherical Tokamak Advanced Reactor (STAR) targeting 100-500MWe net electric power, tritium breeding ratio > 1 and including integrated vertical maintenance, power exhaust, and neutronics analysis. STAR operational scenarios have emphasized full non-inductive current drive with approximately 80% bootstrap current fraction with the remaining current drive provided by electron cyclotron current drive (ECCD) and/or negative neutral beam injection (NNBI) with injection energies of 0.7MeV or above. These scenarios have elevated safety factor profiles with minimum q > 2. The no-wall stability limit is set by the n = 1 pressure-driven kink mode at normalized beta-N ≤ 3.5-3.8 with a weak dependence on q provided q-min > 1. These scenarios support fusion powers of 0.5-1GW with a nominal operating point of 800MW. With wall stabilization (bwall/a = 0.5), beta-N ~ 5 is accessible with fusion power = 1.5-2GW. Additional analysis includes Toroidal Alfven Eigenmode (TAE) stability, gyrokinetic analysis of the H-mode pedestal and core, pedestal MHD stability trends as a function of core current profile and plasma shaping, and divertor power exhaust. Extensive analysis using SOLPS-ITER has been dedicated to a lithium-based capillary porous system with flow (CPSF) divertor plasma facing components to mitigate very high edge power and heat fluxes. These and other important results will be described.