Transport and Stability Analysis for STAR Tokamak Using TRANSP, GX, NIMROD, and ELITE Codes

We present integrated transport and stability modeling to assess operational regimes of the STAR spherical tokamak [1] using the TRANSP [2], GX [3], NIMROD [4], and ELITE [5] codes. TRANSP simulations incorporate first-principles turbulence using the T3D solver coupled with the nonlinear GPU-native GX gyrokinetic model. These simulations resolve ion- and electron-scale instabilities and reveal that anomalous transport in STAR is often dominated by electron heat flux driven by microtearing modes (MTMs), while ion heat transport remains largely neoclassical. Safety factor (q) profile scans show strong sensitivity of MTM stability to local magnetic shear and plasma beta, with electromagnetic effects playing a critical role. Reduced models such as MMM and TGLF, benchmarked against GX, are then used to explore broader transport parameter space efficiently. For pedestal stability, the NIMROD code assesses resistive MHD behavior and ELM onset, while ELITE is used to compute ideal peeling-ballooning stability boundaries across varying edge current and pressure gradient conditions. Together, this multi-code, multi-fidelity framework enables high-fidelity scenario development and operational space mapping for STAR, with the goal of optimizing performance while maintaining ELM-stable edge conditions.