Electrons on a straight path: A novel ionisation vacuum gauge suitable as reference standard

Karl Jousten,Matthias Bernien,Frédéric Boineau,Nenad Bundaleski,Claus Illgen,Berthold Jenninger,Gustav Jönsson,Janez Šetina,Orlando M.N.D Teodoro,Martin Vičar

doi:10.1016/j.vacuum.2021.110239

Abstract

The consortium of the European project 16NRM05 designed a novel ionisation vacuum gauge in which the electrons take a straight path from the emitting cathode through the ionisation space into a Faraday cup. Compared to existing ionisation vacuum gauges, this has the advantage that the electron path length is well defined. It is independent of the point and angle of emission and is not affected by space charge around the collector. In addition, the electrons do not hit the anode where they can be reflected, generate secondary electrons or cause desorption of neutrals or ions. This design was chosen in order to develop a more stable ionisation vacuum gauge suitable as reference standard in the range of 10−6 Pa to 10−2 Pa for calibration purposes of other vacuum gauges and quadrupole mass spectrometers. Prototype gauges were produced by two different manufacturers and showed predictable sensitivities with a very small spread (<1.5%), very good short-term repeatability (<0.05%) and reproducibility (<1%), even after changing the emission cathode and drop-down tests. These characteristics make the gauge also attractive for industrial applications, because a gauge exchange does not require calibration or re-adjustment of a process.

Highlights

The ionisation vacuum gauge [1] is the measuring instrument for high and ultrahigh vacuum
This should cover nitrogen gas, but all gas species relevant for applications in high and ultrahigh vacuum, i.e. relative gas sensitivity factors [1] should be known with small uncertainties
Some authors and manufacturers have significantly improved BA gauges [3], but not to the extent that this type of ionisation vacuum gauge meets the requirements for the applications mentioned above, in particular not for accuracy of relative gas sensitivity factors

Summary

Introduction

The ionisation vacuum gauge [1] is the measuring instrument for high and ultrahigh vacuum. While for many applications only a modest measurement accuracy is required, other applications like the measuring of pumping speeds of high vacuum pumps, calibrations and comparisons between national standards would greatly benefit from a good accuracy. This should cover nitrogen gas, but all gas species relevant for applications in high and ultrahigh vacuum, i.e. relative gas sensitivity factors [1] should be known with small uncertainties. Some authors and manufacturers have significantly improved BA gauges [3], but not to the extent that this type of ionisation vacuum gauge meets the requirements for the applications mentioned above, in particular not for accuracy of relative gas sensitivity factors. Since the latter depends on the type of gauge with a big spread between the individual gauges, the standard committee ISO TC 112 made a statement for the need of research on a stable and accurate ionisation vacuum gauge that can be standardised

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