A quasi-linear reduced turbulent transport model for STEP
A quasi-linear reduced transport model is developed from a database of high-β electromagnetic nonlinear gyrokinetic simulations performed with Spherical Tokamak for Energy Production (STEP) relevant parameters. This reduced transport model is based on a quasi-linear metric computed from linear gyrokinetic simulations and accounts for the effect of equilibrium flow shear using a novel approach. Quasi-linear fluxes are shown to agree quantitatively with predictions from nonlinear gyrokinetic simulations in a broad range of STEP relevant parameters. This reduced transport model is implemented in the T3D transport solver, which is used to perform the first flux-driven STEP simulations that account for the hybrid-KBM turbulent transport found to dominate in a wide region of STEP core. Nonlinear gyrokinetic simulations of the final converged steady state density and temperature STEP profiles predict turbulent fluxes that are compatible with the available STEP sources, showing that transport evolution based on this quasi-linear reduced model leads to realistic profiles.