An investigation into the instabilities of the hot cathode ionization gauge caused by operation in hydrogen

Abstract

This paper describes a series of measurements made over a long period of time of the sensitivity of Bayard Alpert ionization gauges for both hydrogen and deuterium. Short term variations in sensitivity from 5 to more than 10% were found in gauges with cathode operating temperatures of the order of 2000°K and above. Corresponding instabilities for gauges with cathode operating temperatures below 1400°K were less than 2%. The large instabilities were shown to be related closely to the production of atomic hydrogen, and the consequent accelerated rate of adsorption, in the gauge envelope. Evidence is presented which suggests that it is hydrogen contamination of the electron collecting grid which is the most important factor affecting the sensitivity. It is further postulated that the changes occur because of the strong dependence of the reflection coefficient of electrons at the grid on hydrogen adsorption.