Physics design of a Spherical Tokamak Advanced Reactor (STAR)*

Compact high-field superconducting tokamaks are being proposed in the U.S. as a means of potentially reducing the capital cost of a fusion pilot plant (FPP). Systems code analysis of steady-state tokamak FPPs with varied aspect ratio and fixed net electric power of 100 MWe (and other constraints) indicates that A ≈ 2 could significantly reduce the toroidal field and central solenoid coil volume and mass, which are major drivers for the fusion core cost. Further, if the favorable confinement regimes observed in NSTX, MAST, and other spherical tokamaks scale to larger reactors, the auxiliary power, neutron wall loading, and blanket replacement volume will also be reduced. 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 results that will be described include equilibrium and global stability analysis, H-mode power threshold and pedestal structure projections, non-inductive current-drive analysis, and power exhaust projections (utilizing SOLPS-ITER) and mitigation approaches including detachment and SOL heat-flux broadening. Special attention will be paid to projecting pedestal structure and pressure limits utilizing gyrokinetic stability analysis (CGYRO, GS2) combined with MHD stability calculations (BALOO, M3D-C1).