https://phys.org/news/2018-05-world-crabbing-proton.html

In the LHC, the two counter-rotating beams are not a continuous stream of particles but are made up of "bunches" of protons a few centimetres long, each containing billions of protons. These bunches meet at a small angle at each collision point of the experiments. When installed at each side of the ATLAS and CMS experiments, the crab cavities will "tilt" bunches of protons in each beam to maximise their overlap at the collision point. Тhis way every proton in the bunch will be forced to pass through the whole length of the opposite bunch, increasing the probability of collisions and hence more luminosity. After being tilted, the motion of the proton bunches appears to be sideways – just like a crab. Crab cavities were already used in the KEKB collider in Japan for electrons and positrons, but never with protons, which are more massive and at significantly higher energies. "The crab cavities are expected to increase the overall luminosity by 15 to 20%," explains Rama Calaga, leader of the crab cavity project.

The two first crab cavity prototypes were manufactured at CERN in 2017 in collaboration with Lancaster University and the Science and Technology Facilities Council (STFC) in the United Kingdom, as well as the U.S. LHC Accelerator Research Program (USLARP). The cavities were assembled in a cryostat and tested at CERN. They are made of high-purity niobium superconducting material, operating at 2 kelvins (-271°C), in order to generate very high transverse voltage of 3-4 million volts. The cavities were installed in the SPS accelerator during the last winter technical stop to undergo validation tests with proton beams.