An improved ion gauge with gold coated electrodes for reliable operation in reactive gases and for use as reference standard

Abstract The ion gauge described here eliminates sources of error which cannot be removed with the grid-type ion gauge, for example, variation of the grid electron transparency, unstable mean ionization path length of the electrons, and losses of ions by exterior electrostatic fields and by ion pumping. In the pressure range from 10 − 7 to 10 − 1 Pa the response of the new ion gauge shows a high reliability. The gauge is operable in hydrogen without problems. The latter aspect is of interest for pressure measurement in equipment used for charged particle acceleration and storage, and for fusion experiments. The ionization gauge, in the form of a nearly closed system with pure gold layers on the electrodes, shows the following remarkable advantages with respect to grid-type gauges. (a) Shielded volume for effective ion formation, no influence of exterior electric fields. (b) Well defined and limited ionization path length for electrons. (c) Controlled heating of the gold plated electrode system during the operation at 250°C which diminishes disturbing effects by adsorbable gases and provides the same gauge coefficients in immersed or tubulated position—reduced variation of transpiration effects by changes of filament heating power. (d) A stable work function on the gold ion collector surface secures good long term stability of gauge coefficient. (e) V-shaped ion collector combines extension of linearity at high pressures by reducing space charges with a low X-ray limit. (f) Negligible ion pumping; undisturbed operation with hydrogen. Noteworthy and new, the grid is insulated from the anode cylinder. Thereby the interfering effects of the usual large variations in the grid electron transparency on the ionizing current may be eliminated. This results in high accuracy and stability of the gauge coefficient over nearly 5 pressure decades. The X-ray limit p x is approximately 2 × 10 − 7 Pa ( H 2 ). Construction and operation mode of the new screened ion gauge has been presented already in Gentsch and Messer, Proc 8th Int Vac Congr, Cannes 1980 , p. 203; the version described here was improved by the use of tungsten as supporting material instead of platinum-iridium alloy.