Optimization of STEP poloidal field coils with superconducting coil constraints in STEP-Bluemira power plant design framework
The Spherical Tokamak for Energy Production (STEP) programme aims to deliver a UK prototype fusion energy plant, targeting 2040, and a path to commercial viability of fusion.
The conceptual design of such a prototype, meeting engineering and physics constraints, is complex due to the tight aspect ratio and limited space in compact spherical tokamaks. Overcoming this complexity involves considerations like re-mountable toroidal field coil joints for maintenance, which enables the strategic placement of poloidal field (PF) coils within the magnetic cage for the optimal layout and divertor shape. These coils, however, much not clash with other components.
Navigating these design intricacies, particularly in optimizing PF coils and addressing both the space and superconducting coil constraints, requires advanced design tools. The STEP-Bluemira power plant design framework provides a set of design optimization tools for the individual components and the whole-plant design. The workflow begins with the PROCESS systems code and JETTO fixed boundary equilibria, and then progresses to Bluemira, an integrated design tool that combines functionalities like 2D free boundary equilibrium solvers, magnetostatics solvers, and more.
This work reports recent progress in the STEP-Bluemira power plant design framework, focussing on newly added functionalities for nested optimization of PF coil positions and currents with superconducting coil constraints. A keep-in-zone module is introduced, defining regions for PF coils based on compatibility with the central solenoid, toroidal field coils and other components. Functionalities for superconducting coil constraints, such as the critical current density calculations for a given PF coil based on its superconducting properties and appropriate critical surface parameterizations, were introduced. This methodical approach enables the concurrent refinement of both PF coil positions and currents, contributing to achieving an optimal magnetic cage configuration.
We will present the results of coupled PF coils and equilibrium optimization including these design considerations for STEP, bringing us closer to realizing the potential of fusion energy.