PHY3915 IFS Seminar with Ping-Yu Li

Self-consistent profile evolution is the ultimate benchmark for transport theory, determining whether local turbulent drives, neoclassical channels, and sources dynamically balance to reproduce experimental equilibria. In this seminar, we examine electron temperature gradient (ETG) turbulence and integrated pedestal profile modeling in the high-$\beta$ National Spherical Torus Experiment (NSTX). Using linear and nonlinear gyrokinetic simulations with GENE, we show that the conventional approximation of neglecting compressional magnetic fluctuations ($\delta B_\parallel = 0$) artificially suppresses mid-to-large-scale ETG modes ($k_y\rho_s < 50$); retaining the full electromagnetic response recovers the true physical instability drive and identifies ETG as a critical transport channel in the NSTX pedestal. To represent this transport in integrated profile modeling, we adopt a universal reduced heat flux model for ETG within the ASTRA transport solver. Coupled with neoclassical transport (NCLASS) and a quasilinear kinetic ballooning mode (KBM) limit, this model self-consistently reproduces experimental $T_e$ and $T_i$ pedestal profiles across both ELMy and ELM-free NSTX discharges.

To advance beyond standard mixing-length heuristics, we introduce an analytical gyrokinetic saturation theory grounded in nonlinear triplet interactions derived from an Eddy-Damped Quasi-Normal Markovian (EDQNM) closure. Benchmarked against local nonlinear GENE simulations across gradient scans, this framework provides a more realistic closure for direct profile prediction codes. Finally, we highlight ongoing work using GENE-X to simulate cross-separatrix turbulence in Alcator C-Mod I-mode, aimed at understanding edge-SOL boundary physics and providing self-consistent boundary conditions for whole-device integrated modeling.