Pumping of argon, nitrogen and hydrogen in a Bayard-Alpert gauge

Abstract

The pumping of nitrogen and hydrogen in Bayard-Alpert gauges has been investigated as a function of the electrode potentials, the gauge temperature and the gas charge upon the walls. The results are compared with earlier values obtained in argon and in which the pumping mechanism is known. It is shown that ion pumping cannot account for the high pumping speed of nitrogen and it is concluded that mechanisms such as sputtering of the tungsten filament and the formation of tungsten nitride or the production of metastable nitrogen are unlikely to explain the observations. The pumping of hydrogen is confirmed to be due to dissociation of H2 at the cathode with subsequent physical adsorption of H atoms at the walls, and is found to be greatly in excess of any ion pumping which may occur. The presence of liquid nitrogen traps during experiments was found to exert a profound effect on the gauge pumping of nitrogen.