Predicting Accessibility to the High-β_p Regime in Negative Triangularity Plasmas

We study accessibility to the high β_p regimes using negative triangularity (NT) plasmas on DIII-D to address magnetic confinement fusion's major challenge: maximizing core fusion performance while keeping power exhaust below damage thresholds. High β_p scenarios maximize energy confinement using internal transport barriers (ITBs) reaching H_98,y2 ≃1.5 at Greenwald fraction exceeding unity, while NT configurations reduce power exhaust constraints while maintaining H-mode confinement. Combining high β_p with NT plasmas would enable simultaneous high fusion performance with benign, ELM-free edges. This computational study uses FUSE for rapid parameter exploration to find optimal discharge parameters for high β_p NT plasmas. A diverted NT DIII-D discharge serves as the base case with variations in Z_eff, auxiliary power, plasma current, line-averaged density, core rotation, and confining magnetic field. FUSE self-consistently calculates plasma profiles by iteratively solving turbulent transport (TGLF) and equilibrium (TEQUILA). The reduced model TGLF-NN, trained on DIII-D data, enables exploration of 500 configurations, computing cases in 1-2 minutes each for ~16 cpu-hours total, achievable in hours through parallel execution on laptop hardware. Preliminary results show access to β_p > 2.5 is restricted to I_p ≤ 0.9 MA and has no dependence on line-averaged density n_e. Future work will determine accessibility for future fusion reactor conditions.