  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.
