A ceremony held at CERN with the laying of the first stone marked the beginning of the works for the High Luminosity LHC – HiLumi LHC or simply HL-LHC – the project to strengthen LHC (Large Hadron Collider), the largest particle accelerator in the world. By 2026, the performance of the LHC will be greatly enhanced allowing to increase the number of collisions in the large experiments to be able to investigate even further the limits of physics phenomena.
The LHC began its activity in 2010 but already in 2011 a group 29 institutes from 13 nations started developing the HiLumi LHC project to make it even more powerful. The CERN Council approved the project in June 2016 and at that point the first prototypes of the new hardware components needed to run the particle accelerator’s new version were built.
A part of the components currently used in the LHC activities and the various CERN experiments will be replaced with others such as magnets, collimators and radiofrequency cavities. Magnets based on a new superconductive technology will allow new steps forward and new applications that go well beyond the research activities in the field of physics. That’s because there are advances in particle accelerators that are also applied to fields such as medicine, such as equipment for proton therapy.
With the HiLumi LHC the peak brightness, which is the amount of events per second produced, should be increased by at least a factor of 5, while the integrated brightness, which is the total amount of data collected by the experiments, should be increased by a factor of 10. To obtain those results, the updates must cover the LHC’s 27-kilometer large ring but also the experiments. There are four collision points where there are the detectors for the largest experiments, namely ATLAS, CMS, ALICE and LHCb, and the smaller ones, namely Totem and LHCf.
The detectors are key elements of LHC’s activity because they measure the particles generated by the billion proton-proton collisions per second that this accelerator is capable of in its current version. In the HiLumi LHC there will be sixteen of what are called in jargon crab cavities, superconducting equipment that will maximize the overlap of proton packets at collision points. The name is due to the fact that they tilt proton packets so that they move sideways, like crabs.
Half of the crab cavities will be part of the American contribution to the HiLumi LHC project, since there’s also the collaboration of Fermilab on behalf of the US Department of Energy. The superconducting magnets will be the other great contribution. This is a truly international collaboration that has seen scientists, engineers and technicians from all over the world working for years on the development of the new project.
The first prototypes of crab cavities were tested on May 23, 2018 using a beam of the Super Proton Synchrotron (SPS), the second accelerator for size of CERN with its 7 kilometers of circumference. The test lasted more than 5 hours with the two crab cavities cooled to a temperature of 4.2 Kelvin using a single bunch containing between 20 and 80 billion protons accelerated to 26 GeV.
For these tests the crab cavities were powered at only 10% of their nominal voltage and the results were positive. In the coming months, they’ll be tested at 3.4 million volts to verify that they will work in the conditions in which they will be used when the HiLumi LHC is activated.
During the years of the LHC activity there were already long periods of scheduled interruption to allow maintenance of the very complex equipment that make up the large accelerator and the various detectors. In the coming years this will continue with the difference that the breaks will also allow the installation of the new components that will eventually lead to the upgrade to HiLumi LHC to reach a new frontier in physics.