An Ionization Gauge Using a Channel Electron Multiplier for Pressures Below 10−12 Torr

Abstract

A new ionization gauge of an estimated low pressure limit below 10−15 Torr and of a sensitivity of 2×109 Torr−1 is presented. The ions, which are produced in an ionizer of conventional design, are extracted through a shield aperture and collected by the funnel-type cathode of a channel electron multiplier. Since the high gain of this multiplier allows the gauge to be operated with an emission current of only several nanoamperes, practically no heat is produced in the gauge. The gauge is mounted on a 412-in. flange and has approximately the size of a normal Bayard-Alpert gauge. A general expression for the low pressure limit of hot filament ionization gauges is given. The results as obtained from this expression for gauges of similar geometry are discussed together with the low pressure limit as found for the new gauge.