Not far from Lake Geneva, the European Laboratory for Particle Physics (CERN) operates the world's largest particle accelerator: The Large Hadron Collider (LHC). Researchers are using particle acceleration to investigate fundamental questions of physics and trying to determine the composition of dark matter, for example. They have already proven the existence of the Higgs boson, the "God particle", that gives all other elementary particles their mass.
Super-sized detectors
The LHC particle accelerator is a gigantic ring tunnel that is approximately 27 kilometers long and peppered with four measuring points, including two general-purpose detectors: ATLAS and CMS. The impressive cylinders, which weigh as much as the Eiffel Tower, rest inside huge caverns. For the researchers, this is a window to the secrets of the universe.
The ATLAS detector was developed to make new particle discoveries resulting from head-on collisions of protons. The research contributes to studies on extra dimensions, unification of forces, and dark matter.
The CMS detector was developed to study particles produced in proton-proton and heavy ion collisions. The researchers want to find answers to fundamental questions such as: "Why is the world the way it is?", "Why do some particles weigh more than others?" and "What makes up the dark matter in the universe?"
To explore the hidden secrets, the ATLAS and CMS use precision measurements to record the path, momentum and energy of the released particles without errors. The detectors are covered with silicon sensor modules (over hundred square meters each) that record the particle collisions, which generate over a billion interactions per second.
Left image: The ATLAS and CMS detectors at the CERN laboratory in Switzerland use precision measurements to record the path, momentum and energy of released particles. The CMS detector studies particles produced in proton-proton and heavy ion collisions. Image credit: CERN
Right image: The ATLAS detector is used to make particle discoveries resulting from head-on collisions of protons. The research contributes to studies on extra dimensions, unification of forces, and dark matter. Image credit: CERN
Keeping it cool
To ensure that the measurements are precise and that the silicon sensors are not damaged by the high dose of radiation, temperatures as low as -55 °C are required. The electronics and sensors also generate a lot of heat that needs to be dissipated.
During a planned long shutdown in 2026 to 2029, the LHC accelerator and its experiments will undergo an important upgrade. One part is the complete replacement of the silicon tracking detectors.
“ATLAS and CMS will use a two-phase CO2 cooling system for all their silicon trackers and endcap calorimeter detectors. The system enables high heat transfer at a low viscosity and a temperature range that is well suited for operating the detector,” says Cooling Engineer and CMS Cooling Coordinator Jérôme Daguin from CERN.
The cooling system will be based on parallel modular units that circulate CO2 through special evaporators. Each cooling module will be equipped with a special diaphragm pump to circulate the liquid CO2.
To introduce the cooling medium precisely and safely, CERN is once again working with the pump experts from LEWA, a brand within the Atlas Copco Group. LEWA diaphragm metering pumps of various sizes will be used to precisely and constantly feed the liquid CO2 used into the cooling circuit.
Pushing boundaries
The diaphragm metering pumps were tested specifically for CERN’s requirements. Neither CERN nor LEWA wanted to leave anything to chance when it came to ensuring that transporting the sophisticated cooling medium from the service caverns to detectors without errors. Several prototypes were built for the adapted remote version, which functioned as test benches under real conditions. They were first tested with water, then cleaned with ethanol and then tested in continuous operation with CO2.
"It was important to implement a robust, durable solution. The list of requirements was quite ambitious and required some very special adjustments," explains Wieland Wolff, Area Sales Manager from LEWA.
For example, the existing seals of the basic version were first validated and then replaced by more suitable versions. To prevent the CO2 warning alarms from being triggered accidentally after installation on site, the hermetically tight units were also coated with the fluoropolymer PTFE at critical points. In addition, the drive unit and drive head were modified to provide appropriate measuring points for CERN’s instruments.
Furthermore, the forwarded temperature at the drive unit must not fall below -20 °C. To this end, the LEWA engineers added a reciprocating line in which the hydraulic oil can heat up, preventing the -55 °C CO2 from reaching the drive unit.
The LHC particle accelerator process relies on cool temperatures enabled by diaphragm metering pumps from LEWA, a brand within the Atlas Copco Group.
Mutual benefits
The extensive preparatory work has paid off and LEWA has now started delivering the first batch of a total of 18 ecoflow LDG pumps.
The pumps are installed away from the detectors in the service caverns, outside the radiation and magnetic field area found in the experimental caverns. This allows them to be controlled from the control room via electric stroke adjustment and a frequency inverter, eliminating the need for employees to be on site.
When the current shutdown is completed, the installed pumps will cool the electronics and the silicon sensors via a complex network of transfer lines, distribution collectors and small cooling pipes.
Further information can be found at: www.lewa.com and www.atlas.cern
