Interplay of pedestal structure, ELM dynamics, and divertor-plasma detachment

Pedestal and the SOL physics, along with divertor-plasma detachment, are significantly influenced by neutral and impurity sources and transport. To explore the interrelationship between the pedestal structure, ELM dynamics, and divertor-plasma detachment, the BOUT++ 6-field turbulence code incorporates the fluid neutral model and fixed-fraction model for impurity radiation. The simple neutral model solves a 3D diffusion equation based on neutral diffusion resulting from the strong charge-exchange collision rate. Ionization, recombination, and charge-exchange processes serve as sources and sinks in both the plasma and neutral models. Sheath boundary conditions and particle recycling are applied at the divertor plates. Additionally, gas puffing introduces an additional neutral source. Nonlinear simulations using BOUT++ and analyzing DIII-D discharges for both attached and detached plasmas reveal that large ELMs are triggered by the unstable peeling-ballooning mode at the peak gradient location for both cases. Gas puffing leads to an increase in the pedestal density, while the pedestal temperature decreases due to ionization effect. However, it is observed that the neutral and impurity radiation do not have a noticeable impact on the linear instability, despite a significant reduction in divertor plasma temperature due to strong impurity radiation. The results regarding the interplay between pedestal structure, ELM dynamics and divertor plasma detachment will be reported.