Application of a species-selective Penning gauge to the measurement of neon and hydrogen-isotope partial pressures in the plasma boundary

A species-selective Penning gauge, previously applied to He partial pressures, is now applied to the detection of small concentrations of Ne in a D₂ gas. This is important for the study of Ne in the boundary region of magnetic fusion devices, where this impurity is deliberately injected to enhance the radiated power in that region. The application of the technique to the detection of the partial pressure of a minority hydrogen isotope is also examined. In this latter application, the detection system and the data analysis are more complex, because of the proximity of the spectral lines of the isotopes. In both applications, it is found that use of a proper detection scheme permits reliable measurements of concentrations as low as 0.5% of the minority neutral species, without requiring changes to the standard commercial Penning gauge setup.