Compact wide-range cold-cathode gauges

Abstract

Cold-cathode ionization gauges offer many advantages for routine high-vacuum measurements. They are simple and robust. Thermal outgassing and electron-stimulated desorption, both significant problems in hot-cathode gauges, are negligible. There are no x-ray effects to cause errors at low pressures. For many applications it would be useful to reduce the physical size of cold-cathode gauges and especially to reduce the volume in which the associated stray magnetic field is significant. We describe experiments to explore the role of the operating voltage and magnetic field strengths on the performance of cold-cathode gauges. The results allowed the design and development of compact wide-range gauges having internal volumes as low as 5–15 cm3, while maintaining a high sensitivity of 10 A Torr−1 at 10−6 Torr. The magnets are little more than one third the volume used in most conventional designs. This, combined with the use of a double inverted magnetron layout, reduces the external magnetic fields by more than an order of magnitude. At 15 cm from the center of the compact gauge, the external field is comparable with the Earth’s magnetic field. For ultrahigh vacuum applications, an internal field emitter provides quick starting. If necessary, an Americium 241 source or a carbon film cold emitter can be used for essentially instant starting. Testing in nitrogen has covered pressures from the mid-10−11 Torr range to above 10−2 Torr.