How turbulence spreading improves power handling in quiescent high confinement fusion plasmas

Viable magnetic fusion devices necessitate combining good confinement with effective power flux handling. A major concern for ITER, and devices beyond, is the divertor heat load width, which sets peak boundary heat loads on the plasma-facing materials. Current estimates of the heat flux width are narrow for future reactors. Here, we demonstrate how pedestal turbulence can expand into, or entrain, the stable scrape-off-layer and so broaden the heat flux width beyond these neoclassical predictions. Employing combined theoretical, computational, and experimental approaches, we focus on quiescent high confinement discharges on the DIII-D tokamak, but the results are of broader significance. Our findings uncover common trends in the edge turbulence intensity flux, the pressure perturbation skewness, and the turbulence mixing length, which together determine the heat flux width. This research demonstrates the physics of scrape-off-layer broadening by turbulence and highlights the promise of a turbulent pedestal for successful core-edge integration in ITER and future fusion devices. Nuclear fusion is one of the avenues pursued to generate carbon-free energy for an increasingly demanding world, but technical instrumental concerns remain, which will impact the realisation and performance of future fusion power plants. The authors employ a combined experimental, computational and theoretical approach, to elucidate the mechanism by which turbulence spreading sets the divertor (a component that extracts heat and ash produced by the fusion reaction) heat load width in fusion tokamak, and demonstrate common trends in the upstream edge turbulence intensity flux, the pressure perturbation skewness, and the turbulence mixing length, which together determine the downstream heat load width.