Instability of the spatial electron current distribution in hot cathode ionization gauges as a source of sensitivity changes

Abstract

When ionization gauges are being used as secondary standards in the high and ultrahigh vacuum, a stable sensitivity is essential. Our hypothesis is that the sensitivity stability may be affected by the path length changes of the electrons within the gauge. We have measured possible spatial changes of the electron current distribution onto the anode by subdividing the anode into nine separate, isolated partial electrodes. We found that up to about 10% of all emitted electrons change their target electrode on the anode after regular operation with the gauge, e.g., degassing, both for gauges with ring cathodes as well as for those with hairpin cathodes. These spatial changes of electron trajectories can explain the observed instabilities of the ionization gauge sensitivity.