The design and optimisation of tokamak poloidal field systems in the BLUEPRINT framework

As part of our aim to develop a reactor design framework, we present here our approach to the optimisation of plasma equilibria and tokamak poloidal field systems. A 2-D, free boundary, ideal magneto-hydrodynamic plasma equilibrium solver is described. We use it within the BLUEPRINT reactor design framework to design plasma equilibria and poloidal field coilsets for future fusion reactors in an integrated way. Plasma shape parameters (R-0, A, delta, kappa.) and integral parameters (I-p, beta(p), l(i)) are controlled for. Constrained optimisation procedures for the positions and currents of the poloidal field coils are presented; these account for current, field, force, and positional constraints on the coils. A pulse length constraint is incorporated in the optimisation procedure in the case of pulsed reactors. We demonstrate our approach on three different reactor concepts: single-null, double-null and negative triangularity tokamaks.