Resolving the ITEP Divertor Exhaust Physics GAP with DIII-D

Since dimensionless demonstrations of atomic physics-dominated regimes are not possible, DIII-D is proposing hardware upgrades to validate the underlying physics of models used to design and project exhaust solutions for a fusion pilot plant (FPP). To achieve this, DIII-D divertor plasmas must reach parameter regimes where the appropriate processes are significant in determining the boundary layer plasma conditions. With field, current, shape and power upgrades, the characteristic scale lengths of atomic physics processes of ionization, recombination, neutral interactions and radiation opacity are projected to be smaller than both the radial and poloidal lengths of the divertor. This will make possible the study of these processes in a regime similar to that for a FPP. Recent data has shown that increased radial transport can be driven at high power density, allowing for dissipative divertor operation at lower core electron and impurity density than predicted by empirical heat flux width scaling. Finally, DIII-D’s proposal for a modular divertor will provide a test of the minimum divertor leg length needed for maintaining a hot X-point and robust H-mode pedestal plasma. Working alongside other high-performance facilities, this will close a critical part of the ITEP gap for an FPP.