Some of the most amazing discoveries concerning the composition of the universe have come from particle detectors at CERN. What is the universe made of? That’s the primary question that scientists are trying to answer. CERN is a world-leading research facility that helps scientists with this search by probing the fundamental structure of particles that make up everything around us. 

Buried deep underground, partly in Switzerland, partly in France, various circular and linear particle accelerators are used for experiments that have already brought several groundbreaking achievements, such as the discovery of the Higgs boson and the isolation of antimatter in the form of antihydrogen.

Cancelling Out Environmental Impacts

To remove as many environmental impacts as possible, such as radiation, the largest particle accelerator at CERN (the Large Hadron Collider (LHC)) is located 100 meters (328 feet) underground. Its tunnel is 3.8 meters (12.5 feet) wide and nearly 27 kilometers (16.8 miles) long. In this space, particles are accelerated to just under the speed of light and collided with one another. A series of highly precise detectors record phenomena occurring during these collisions. 

When charged high-energy particles crash past noble-gas molecules, they leave a trail of ionization in their wake. These tiny signals can be amplified using electric fields and then measured electronically to reveal particle tracks with a high level of precision. From the results of these experiments, CERN scientists gain deeper insights into the structure of matter. The pumps that circulate specific gas mixtures through these particle detectors must be highly reliable and safeguard the gases from contamination. For this reason, CERN relies on KNF diaphragm pumps to meet these strict requirements.

CERN is fitted with close to 30 gas systems used to deliver just the right gas mixture to the corresponding detectors for the LHC experiments. The detector gas mixture is a sensitive medium. In it, a charge multiplication produces a signal that is then recorded and analyzed. This means that a correct and stable gas mixture composition is key to the reliable operation of each and every experiment. 

Gas mixtures for these particle detectors are composed of noble gases such as argon, xenon, helium, and other gases like tetrafluoromethane, tetrafluoroethane, sulfur hexafluoride, isobutane, and carbonic dioxide.

The four main particle detectors at CERN are known as A Large Ion Collider Experiment (ALICE), ATLAS, Compact Muon Solenoid (CMS), and Large Hadron Collider beauty (LHCb). The CMS detector, where KNF diaphragm pumps are used to purify and circulate the specific gas mixtures, is 21 meters (68.9 feet) long, 15 meters (49.2 feet) wide, 15 meters (49.2 feet) high, and weighs 14,000 metric tons. Constructed in 15 sections, it is located in a hall 100 meters (328 feet) underground near Cessy, France. The CMS experiments are primarily aimed at advancing research into the Higgs boson, which was detected at CERN in July 2012.

Gas Recirculation and Recuperation

Environmentally harmful chlorofluorocarbons, called freons, play an important role in detector gas mixtures. They help in achieving the detector performance required at the LHC experiments (high-rate capability, containment of charge multiplication, detector stability at long term, etc.). To deal with this issue, physicists at the LHC are conducting research into eco-gases for the next generation of detectors.

CERN’s EP-DT Gas Team is developing gas recuperation systems for the large experiment in addition to the already used gas recirculation systems. They are also developing a compact and flexible gas recirculation system for laboratory applications to eliminate any gaseous emissions from the detector activities. Recirculating and recuperating the gas mixtures also reduces CERN’s operating costs.

Custom Diaphragm Pumps

Two KNF pumps were chosen to purify and circulate the gas mixtures in the CMS particle detector. A third pump serves as a backup in case of failure during an experiment. Since detector gas mixtures must be free of contamination and have unimpaired circulation, KNF process pumps have proven to be the ideal solution due to their cleanliness, gas-tightness, and reliability.

The pumps in current use at CERN are the result of close collaboration and high level of customization. Based on a KNF N 0150, the pumps are equipped with the pump head geometry of a KNF N 1200. Further customization included combining a working diaphragm with an additional safety diaphragm_—which prevents gas from escaping in the unlikely event of a fracture. Despite the high level of customization, this process only took 18 months of development, including rigorous factory testing.

According to Roberto Guido, Project Leader, EP-DT Gas Team, “Particle detectors are extremely sensitive to the presence of impurities in concentrations even below the ppm level. KNF pumps were tested, and they ensure this requirement is met.”

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