Evaluating Coil Sets for a High-Field Reactor at Negative Triangularity

This work investigates the feasibility of a reactor with a cross-sectional shape at negative triangularity (NegT) by evaluating coil set requirements of such a configuration in a high-field reactor. NegT plasmas are attractive for reactors since they have H-mode-grade normalized pressure and confinement levels despite their relaxed pressure profiles near the edge. As such, they are free of ELMs, have low impurity retention and a lower heat flux at the divertor plates.

To find requirements for a reactor coil set, a Python workflow was created that can generate equilibria and find coil stresses, currents and plasma shapes by running the FreeGS equilibrium solver. The workflow is applied to the ARC baseline design to evaluate 260,000 configurations of poloidal field coil locations and plasma shapes with both positive and negative triangularity. Configurations are assessed via cost analysis, penalizing those that can’t create desired shapes, require high coil currents or cause high coil forces. It was found that NegT cases are able to achieve costs comparable to and, on average, lower than positive triangularity cases in the costing workflow developed.