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 [1] and potentially 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 A=2, R=4-4.5m Spherical Tokamak Advanced Reactor (STAR) [2] targeting 100-500MWe net electric power, tritium breeding ratio > 1 and including integrated vertical maintenance, power exhaust, and neutronics analysis. Initial STAR results that will be described include equilibrium and global stability analysis, Alfvenic instability and energetic particle confinement analysis, pedestal structure, and pedestal stability projections, non-inductive current-drive analysis for ramp-up and sustainment, core radiation estimates, and power exhaust projections (utilizing SOLPS-ITER) and mitigation approaches including lithium vapor box operation and SOL heat-flux broadening.

[1] J.E. Menard et al 2022 Nucl. Fusion 62 036026

[2] T.G. Brown and J.E. Menard 2023 Fus. Eng. Design 192 113583