Development of compact charge-exchange detectors and initial testing on DIII-D

The erosion and non-local redeposition of first wall materials due to charge exchange sputtering is predicted to result in 10² - 10⁵ of kg/yr material migration in future tokamaks. To validate these predictions, benchmarking of the coupled edge plasma / neutral codes requires measurements of the energy and spatial distribution of charge exchange fluxes in existing experiments. We are working to develop rugged, compact solid-state detectors that detect atomic hydrogen by sensing the barrier height change of a metal-oxide-semiconductor (MOS) junction. Initial work to develop and calibrate the sensors, and evaluation of sensor response using the Divertor Material Evaluation System (DiMES) on DIII-D are described. Dosemetric measurements made during DIII-D operations have demonstrated sensitivity to the atomic hydrogen flux not only during plasma discharges, but also due to the hydrogen liberated during helium glow discharge conditioning used between shots. Changes in detector response of a few % of the saturation level of the sensors (nominally 2×10¹⁵ H /cm²) were observed for NBI discharges. Use of new materials to improve the fabrication of more rugged sensors is also presented.