A Physics-Based Reduced Model of the L-H Transition Incorporating Gyrokinetic Calculations and Self-consistent Mean-Field Evolutio

A comprehensive 1-D reduced model has been developed to investigate the complex feedback loops underlying L-H transition physics. It self-consistently evolves seven fields: turbulence intensity (I), ion and electron pressure (p_i, p_e), ion density (n_i), turbulence-driven zonal flow (v_ZF), and mean poloidal (v_θ) and toroidal (v_ϕ) flows. Turbulence intensity follows a predator-prey model, driven by linear ITG/TEM growth rates and saturated by nonlinear effects, E×B shear, and zonal flows, with coefficients calculated from gyrokinetic codes (e.g., TGLF, CGYRO). Density and pressure profiles evolve through transport equations using gyrokinetically computed turbulent fluxes and analytical neoclassical models interpolated across Banana-Plateau- Pfirsch-Schluter regimes. Mean flows are driven by turbulent Reynolds stress and damped by neoclassical friction and neoclassical toroidal viscosity. The model’s physics fidelity is further enhanced by pinch mechanisms (Ware, TEP, thermal), intrinsic effects like ion orbit loss and collisional energy exchange, and external sources including gas puffing, NBI, and ECH. The stiff, coupled system is solved using an adaptive RK45 integrator, efficiently capturing fast, multiscale transition. This enables extensive parameter scans to identify dominant L-H trigger mechanisms and develop high-fidelity, quantitative predictions for the L-H power threshold.



Work supported by US DOE under DE-FC02-04ER54698, DE-SC0020287 and DE-FG02-04ER54738.