Plasma-edge diagnostics based on Pd-MOS diodes

Pd metal-oxide-semiconductor (MOS) devices can be used to detect energetic hydrogen atoms. H isotopes implanted into a Pd-MOS diode quickly diffuse through the Pd layer and are accommodated at available Pd-SiO2 interface sites, causing an increase in the leakage current through the device. We find that a diode's response to energetic hydrogen is rapid, sensitive, dosimetric, and reproducible. Pd-MOS diodes can be regenerated when saturated with hydrogen by heating to 100-2000C for a few minutes. These properties make Pd-MOS diodes useful for plasma-edge diagnosis of hydrogen particle fluence when the energy distribution of the incident hydrogen is known. Pd-MOS diode sensors have been used in the laboratory and in the ZT-40M reversed-field pinch to measure energetic hydrogen fluxes. Their small size allows placement in locations inaccessible to conventional diagnostics and should provide a means for remote monitoring of hydrogen fluxes to plasma-facing surfaces. (orig.)