Evaluation and metrological performance of a novel ionisation vacuum gauge suitable as reference standard

Funding Information: This work has received funding from the EMPIR programme (projects 16NRM05 and 20SIP01) co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme and the Portuguese National Funding Agency for Science, Research and Technology in the framework of the project UIDB/FIS/ 00068/2020. Publisher Copyright: © 2023 The Author(s)Recently, a new type of ionization vacuum gauge was introduced, which was proposed as a reference and transfer standard in the range of 10-6 Pa to 10-2 Pa because of its excellent stability and linearity. In contrast to present models of ionisation vacuum gauges, all electrons have a well-defined path length through the ionisation space. This even allows one to predict the sensitivity for a gas species provided that the ionisation cross section of the gas molecules for electrons between 50 eV and 200 eV is known. Following the development of this gauge we investigated its metrological performance in terms of linearity, resolution, repeatability, reproducibility, transport and long-term stability, disturbances by magnetic fields, influence of the surrounding earth potential and so on. The gauge demonstrated excellent metrological properties and is indeed suitable as an accurate reference and transfer standard, but can also provide important economic benefits to manufacturers and users.publishersversionpublishe

Development of a design for an ionisation vacuum gauge suitable as a reference standard

UID/FIS/00068/2019The EURAMET EMPIR project “16NRM05 - Ion gauge” aims to develop an ionisation vacuum gauge suitable as a reference vacuum standard. In such a gauge the electron trajectories and their kinetic energy inside the ionisation volume should be well defined and stable. In the search for a suitable design, a series of simulations on different ionisation gauge concepts that have the potential to meet stringent stability requirements have been carried out. Different software packages were used for this purpose. This paper focuses on the design aspects and the performance of the different ionisation gauge concepts that have been investigated by simulation. Parameters such as ionisation gauge sensitivity, ion collection efficiency and electron transmission efficiency, have been determined as a function of emission current, pressure and electron source alignment.publishersversionpublishe

STUDY OF FEASIBILITY AND USEFULNESS OF MACHINE LEARNING METHODS TO HELP IDENTIFYING RESIDUAL GAS COMPOSITION

This report summarizes the outcome of the collaboration between CERN and Intelligent Data Analysis Laboratory (IDAL). In this feasibility study we investigated the potential usefulness of machine-learning applications to identify residual gas compositions. The report focus on the performance of the most promising machine-learning method that have been put in place during work package WP3 of the project

Comparison of ionization vacuum gauges close to their low pressure limit

Parts of CERN’s accelerator complex and experiments, especially in the antimatter field, require a vacuum in the  $10^{-12}$ mbar range or better. Thus gauges are needed to reliably measure XHV during experimental operation and in order to study the vacuum science needed for those experiments. We therefore built a setup to reach $1⋅10^{-13}$mbar  in order to simultaneously compare different hot cathode ionization gauges with the ability to measure high UHV and XHV close to their lower pressure limit: Barion extended, Extractor IE514, a modulated Bayard–Alpert gauge and two Improved Helmer gauges. All gauges but the Extractor behave similarly with respect to small pressure variations around the limit pressure, while the Extractor seems to overestimate high UHV hydrogen pressure. We show how gauge operation determines our ultimate achievable pressure due to outgassing, which was comparable for all gauges and in the order of $Q∼10^{-10}$mbar l s$^{-1}$. Further we show the disturbances caused in the static system due to gauge pumping (visible only as electronic pumping), and report some of the possible difficulties and origins of noise when measuring pressures in the XHV range, including the thermoelectric effect

Simulation and iterative deconvolution of residual gas spectra

Residual gas analysis may be time consuming if the identification of all gas species and their quantitative contribution to the mass spectrum is required. This is because the partial pressures of the residual gas cover several orders of magnitudes and fragmentation patterns are in general convoluted. Noise, offset, and the limited mass ranges of the analysers used in UHV applications further reduce the sensitivity of a spectrum. In this work, the authors propose a method to simulate residual gas spectra based on fragmentation patterns and partial pressures. With an iterative algorithm, residual gas spectra can be deconvoluted in logarithmic scale. The use of indicators simplifies the identification of residual gas compositions. The authors realised this algorithm in a prototype application. The performance of this tool is encouraging and opens the path for the development of an UHV specific web-based application

3D-simulation of ionisation gauges and comparison with measurements

3D-simulations using the Vector Fields OPERA 3D software have been carried out on the CERN-type modulated Bayard-Alpert gauge. The program allows to simulate the ion creation inside the gauge and takes into account space charge effects. Parameters such as sensitivity, ion and electron path lengths inside and outside the ionisation grid, location of ion creation, collection efficiency, and potential distribution were studied as a function of emission current. This investigation resulted in a deeper understanding about the behaviour of the gauge, in particular about the effect of space charge. The achieved results were compared with experimental measurements; the results are satisfactory and encourage further studies

Automatic mass spectra recognition for Ultra High Vacuum systems using multilabel classification

In Ultra High-Vacuum (UHV) systems it is common to find a mixture of many gases originating from surface outgassing, leaks and permeation that contaminate vacuum chambers and cause issues to reach ultimate pressures. The identification of these contaminants is, in general, done manually by trained technicians from the analysis of mass spectra. This task is time consuming and can lead to misinterpretation or partial understanding of issues. The challenge resides in the rapid identification of these contaminants by using some automatic gas identification technique. This paper explores the automatic and simultaneous identification of 80 molecules, including some of the most commonly present in this kind of environment by means of multilabel classification techniques. The best performance is drawn from a dependent binary relevance method trained by extreme gradient boosting. We obtain a Hamming loss of 0.0145 in the test set. The mean binary AUC for the test set was 0.986, and the minimum test AUC was higher than 0.89. A public interactive web app has been developed to allow vacuum users to test the model with their own data

Recovering about 5 km of LHC Beam Vacuum System after Sector 3-4 Incident

During the sec­tor 3-4 incident, the two apertures of the 3 km long cryogenic vacuum sectors of the CERN Large Hadron Collider (LHC) were brutally vented to helium. A systematic visual inspection of the beam pipe revealed the presence of soot, metallic debris and super insulation debris. After four month of cleaning, the beam vacuum system was recovered. This paper describes the tools and methodologies developed during this period, the achieved performances and discusses possible upgrade

The Upgrade of Control Hardware of the CERN NA62 Beam Vacuum

NA62 is the follow-up of the NA48 experiment, in the SPS North Area of CERN, and reuses a large fraction of its detectors and beam line equipment. Still, there are many new vacuum devices in the beam line (including pumps, valves & gauges), which required a thorough modification of the control system and a large number of new controllers, many of which were custom-made. The NA62 vacuum control system is based on the use of PLCs (Programmable Logic Controllers) and SCADA (Supervisory Control and Data Acquisition). The controllers and signal conditioning electronics are accessed from the PLC via a field bus (Profibus); optical fibre is used between surface racks and the underground gallery. The control hardware was completely commissioned during 2014. The nominal pressure levels were attained in all sectors of the experiment. The remote control of all devices and the interlocks were successfully tested. This paper summarizes the architecture of the vacuum control system of NA62, the types of instruments to control, the communication networks, the hardware alarms and the supervisory interface