Investigation of pedestal parameters and divertor heat fluxes in small ELM regimes on DIII-D*

A DIII-D database study investigated divertor heat flux and its dependencies on pedestal parameters across a range of small ELM regimes: high beta poloidal, type-II, and ELMs in negative triangularity H-modes. It demonstrated that type-II and high beta poloidal small ELM regimes have their parallel energy fluences fall below the Eich type-I scaling from [1]. The negative triangularity H-mode ELMs follow the Eich scaling for type-I ELMs. The parallel heat flux and total heat loads to the divertor were determined using high-time resolution infrared thermography, while pedestal parameters were obtained through self-consistent kinetic equilibrium reconstructions. Utilizing the fast thermography, the SOL power fall-off length for both inter-ELM and intra-ELM were calculated and compared to the Eich scaling with poloidal magnetic field in [2]. Projecting the parallel energy fluences for ITER’s 7.5 and 15 MA scenarios, the linear regression of the DIII-D type-II and high beta poloidal regimes’ heat fluxes fall below the ~3 MJ/m^2 leading edge melting limit, indicating these small ELM regimes would be tolerable when scaled up to ITER. These findings inform the feasibility of small ELM regimes in managing heat loads while offering a potential solution for core-edge integration.

[1] T. Eich et al. 2017 Nuclear Materials and Energy 12 84–90

[2] T. Eich et al 2013 Nucl. Fusion 53 093031