A synthetic diagnostic framework for measuring the detachment front in a close divertor slot on DIII-D

Synthetic diagnostics have been employed to optimize spectroscopic diagnostic positioning for a new dissipative-focused upper divertor planned for DIII-D. This deep-baffled divertor is designed to confine a long outer leg of at least 30 cm in poloidal length, with the pumping location upstream of the divertor target on the SOL side. This strategic placement of the pump duct is expected to increase the target plasma and neutral densities between the duct and the target, enhancing dissipation and reducing plasma temperature at the material surface. SOLPS-ITER simulations indicate that this divertor design can also robustly stabilize the detachment front without compromising plasma performance at the X-point and in the core. To validate this design during experimental operation, spectrometers and filterscopes will be used to measure the detachment front by measuring neutral and impurity emission lines along the divertor leg. To optimize the optical design, a synthetic diagnostic workflow has been developed integrating SOLP-ITER simulations in conjunction with Cherab/Raysect codes to calculate the plasma spectral radiance and perform raytracing of the optical lines of sight, thereby quantifying the expected experimental signal on the diagnostics. This workflow is used to determine optimal locations for the lines of sight to minimize the need for in-situ hardware and the transmission filters for the filterscope system to accurately measure the expected detachment front.