BOUT++ simulation of edge plasma dynamics during during thermal quench*

Recently upgraded BOUT++ six-field drift-reduced Landau fluid turbulence model with flux-driven capability is applied to investigate plasma turbulence and transport dynamics at the tokamak edge region, as well as the divertor power loads during the thermal quench phase of a disruption. In this study excessive particle and power are applied at the pedestal region for a short period of time (about 10-20% of the stored thermal energy within 0.1-1ms) to mimic the intensive particle and energy outflow from the core during the onset of thermal quench. 50 times larger than normal maximum divertor heat load and 4 times wider width are observed, for both DIII-D and ITER-like H-mode plasmas. These dramatic divertor heat load and width are due to enhanced turbulence activity inside the separatrix. As the particle and energy influx from core steepen plasma profiles, not only the level of turbulence fluctuation increases, but also the dominant modes (ballooning-type) shift to lower k (hence larger eddies). Meanwhile, magnetic perturbation amplifies at least one order of magnitude, particularly at the pedestal top and in the SOL. As a result, turbulence becomes a much more efficient radial transport channel to rapidly deposit particle and energy outflow from core to the divertor plates.