Investigating the interactions of hydrogen and nitrogen with the tantalum cathode of a novel ionization vacuum gauge with a straight path of electrons

Abstract

The outgassing characteristics of a tantalum disk cathode mounted inside a novel ionization gauge were investigated in comparison to an yttrium-coated iridium-filament cathode mounted inside an extractor gauge. Both gauges were exposed to nitrogen or hydrogen at a pressure of 2.4 × 10−5 mbar, and the outgassing rates were measured periodically during subsequent pumping. For the novel ionization gauge, two contributions to the outgassing, i.e., the thermal outgassing from the cathode and the electron-stimulated desorption from the Faraday cup, were studied separately. The tantalum cathode showed rapid outgassing of nitrogen after exposure, while the outgassing after exposure to hydrogen was much lower. Hydrogen is mainly released from the Faraday cup when electrons collide with it. The extractor gauge showed a more-than-3-times higher outgassing rate after hydrogen exposure than after nitrogen exposure. The tantalum cathode and the Faraday cup in the novel ionization gauge showed absorption equilibrium after just 30 min.