Development of rugged hydrogen sensors for measuring charge-exchange neutral flux at the wall and divertor*

Rugged Pd-MIS style hydrogen sensors have recently been demonstrated in the Divertor Materials Evaluation System (DiMES) at the DIII-D tokamak in upper and lower single null configurations. This pair of sensors utilized 7 nm thick gold overlayers to reduce sensitivity to low energy particles as well as thick palladium layers to protect against damage from high energy particles. Both sensors responded similarly to upper single null discharges until saturation occurred after approximately 3 shots. This is consistent with a thermal distribution of charge-exchange neutrals with a temperature ~1 keV and fluence ~ 10¹⁵ D/cm² per shot. Results are also presented from laboratory testing and calibration performed with mass-separated 340 eV and 1500 eV deuterium (D) ion beams with a total dose > 10¹⁶ D/cm² onto the sensors, which had a 1.7 mm diameter active area. Characterization of charge-exchange neutral flux in tokamaks is important to understanding wall erosion and redeposition in future devices.