Optimizing Stability and Performance in DIII-D and Beyond Using Predictive, Integrated Modeling

Tokamak fusion reactors will require predictive, integrated models to optimize performance while maintaining robustness against disruptions. The STEP (Stability, Transport, Equilibrium, \& Pedestal) module, developed in OMFIT, predicts stable equilibria self-consistently with core-transport and pedestal calculations by coupling together the following codes: ONETWO, TGYRO, EFIT, CHEASE, EPED, DCON, GATO, and CHEF (a current-drive, heating, \& fueling module). Each code reads and writes data from a centralized IMAS data structure, allowing them to be run in arbitrary order and enabling open-loop, feedback, and optimization workflows. Core-pedestal calculations with STEP have been validated against DIII-D, and used to assess performance in ITER and the suppression of turbulence in DIII-D negative-triangularity plasmas. We use STEP to optimize heating and current drive to maximize plasma pressure while maintaining MHD stability. Stability maps are generated and validated against stability limits in DIII-D. Predictive optimization for potential DIII-D upgrades and other next-step devices are performed to assess their capability to explore sustained, high-power-density scenarios.