As part of the European IonGauge project, LNE took part in the development of a new ionization gauge prototype, enabling measurements of very low pressures with unrivalled accuracy. This work has been published in the leading journal Vacuum.
Ionization gauges are used to measure ultra-low pressures (ultra-high vacuum), particularly in fundamental physics research, metrology and the semiconductor industry. This ionization results from the collision of the electron beam emitted by the gauge's cathode, then accelerated, with the molecules of the gas being measured. The ion current collected is proportional to the gas's density, and hence its pressure.
However, control of the sensitivity of these instruments, essentially linked to the relationship between gas pressure and collected current, is currently unsatisfactory. Sensitivity depends on the geometry of the gauge used, the pressure to be measured and the gas under consideration, and also lacks stability over time.
To remedy this problem, the European project IonGauge1a partnership between LNE and several European metrology laboratories2 and industrial partners, was to develop a new, standardized ionization gauge model with improved metrological characteristics for use as a reliable reference standard.
An original design
Compared with existing ionization gauges, this new design has the advantage that the electron path length is well defined. In particular, electrons do not strike the anode, from which they can be reflected, generating secondary electrons or causing neutron or ion desorption. The design, validated by numerical simulations, has the advantage that the manufacture of the gauge by different manufacturers would result in specimens with not only predictable (and therefore reproducible) sensitivity for a large number of gases, but also good long-term stability. This type of gauge would then be particularly suitable as a reference standard in the 10 -6 Pa to 10 -2 Pa range for calibrating vacuum manometers or quadrupole mass spectrometers.
In particular, LNE took part in the characterization of several prototype ionization gauges built to these new specifications, as well as in a comparison between three national metrology laboratories. The result: a controlled sensitivity of 1 % for a given specimen, and reproducibility between specimens of the order of 2.5%, slightly exceeding expectations. In the long term, this should ensure unrivalled accuracy of pressure measurements in the range 10 -6 Pa to 10 -2 Pa.
This new ionization gauge can easily be reproduced by any experienced builder, and will offer greater measurement accuracy to demanding users in the ultra-low pressure range.
Reference :
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 Vacuum 189 (2021), 110239, https://doi.org/10.1016/j.vacuum.2021.110239
1 The 16NRM05 Ion Gauge project has received funding from the EMPIR program, co-funded by the Member States, and the European Union's Horizon 2020 research and innovation program.
2 CMI (Czech Republic), MIRS/IMT/LMT (Slovenia), PTB (Germany), RISE (Sweden)