New superconductor types and performance levels are being developed and have enabled consideration of higher-field, smaller-size devices. In this paper, sizing options for the next Fusion Energy System Study (FESS) design study are explored. The 2016/2017 baseline Fusion Nuclear Science Facility (FNSF) used a bucked and wedged solution with a large external case mainly to support out-of-plane loads and allow radial servicing. Use of a larger case to provide inner leg compression may be needed for the higher-field, smaller devices. These structural concepts have been employed in FIRE, IGNITOR, and C-Mod. Each of these concepts will be investigated as candidates for a next machine study. Recommendations will be made as to how these concepts can be incorporated into systems codes.

The iterative design of the poloidal field coil system and the iterative choice of scenario currents are needed to go along with toroidal field (TF) coil support concepts. Concepts that employ a bucked solution require assessment of cancellation of the central solenoid radially outward and the TF radially inward load, and thus affect the sizing of both. Ideally better but simple structural models of the poloidal coils can be built into the scenario development codes to address advanced TF support schemes. Simplified spreadsheet assessments of structural concepts are presented, and these are benchmarked against finite element analyses. Possible options for the FNSF and next machine studies are assessed in terms of achievable fields and space allocation.