A gyrokinetic discovery of fast L-H bifurcation physics in a realistic, diverted, tokamak edge geometry S. Ku et al. TH/2-1 A fast edge turbulence bifurcation achieved in XGC1 when heat accumulation ~PL-H in the edge layer in an L-mode diverted C-Mod edge geometry with neutral particle recycling (R=0.99) Two mechanisms of the 𝑬×𝑩 flow shearing works together to yield turbulence suppression Turbulent Reynolds stress: conservative eddy tilting-stretching process (starting at t~0.175ms) Neoclassical X-loss physics  dissipative shearing (starting t~0.2ms). Finishes up the turbulence quenching process and keeps the turbulence suppressed in the absence of Reynolds stress Bifurcation when the combined 𝑬×𝑩 shearing rate from the Reynolds and neoclassical forces exceeds the turbulence source rate. Contour plot of the turbulent |δφ| in the frequency-time space observed from ψN=0.94.