Prospects for Negative Triangularity Operation on NSTX-U

Negative triangularity (NT) plasmas have recently demonstrated desirable H-mode-like properties in L-mode-like conditions without ELMs [1], while also allowing the divertor heat fluxes to be spread over a wide surface area [2]. Given these promising results, there is a need for increased analysis of NT plasmas in low aspect ratio machines. This research identifies a wide range of NT equilibria that can be produced in the NSTX-U spherical tokamak given its coil configuration and geometry of conducting structures. To do so, a broad range of up-down symmetric NT plasma shapes are generated by scanning over triangularity, elongation, and squareness. TokaMaker [3], a new code from the Open FUSION Toolkit for solving the 2D Grad-Shafranov equilibrium equation, is used to produce plasma equilibria consistent with the target plasma shapes and machine configuration. The NT shapes are then assessed by calculating the growth rate of the n=0 instability that leads to vertical displacement events and the desirable NT configurations are identified.