Scoping studies for a sustained high power density next-step tokamak facility

A sustained high power density (SHPD) facility may be an important bridge to a Compact Pilot Plant in the U.S. fusion energy development program. A SHPD facility would integrate: (1) sustainment -- for very long pulses from high to full non-inductive operation, (2) high power density -- high core and edge plasma pressure without transients, and (3) an exhaust solution compatible with sustainment and high pressure. Lower aspect ratio (A $=$ 1.8-2.5) tokamaks are considered potentially advantageous for SHPD by maximizing plasma performance per unit magnet cost. In this work, SHPD performance characteristics are studied as a function of device size, aspect ratio, and stability and confinement assumptions. Realistic shaping poloidal field coils based on free-boundary equilibrium calculations and superconducting magnet/conductor layout and stress analysis are also investigated. The impacts of incorporating liquid metal divertor and first-wall components are also considered. Physics and engineering design progress for a lower-A tokamak SHPD facility are described.