What is CERN's Third Long shutdown and why is it happening?

CERN, which is the largest organisation for particle physics, is planning to close in July 2026, which will be it’s third long shutdown (LS3), to increase the Large Hadron Collider’s (LHC’s) luminosity.

World's largest superconducting magnet https://home.cern

What does this mean for the collider? Well, an increase of luminosity means a reduction of the size of the beam at the collision point within a detector, and luminosity is proportional to the number of collisions per unit time, meaning the detectors can observe more data to analyse rare processes. Since the phenomena scientists want to see has an extremely low probability of occurring, therefore the more data available to observe allows for more potential occurrences, so the scientists can have a better understanding of what is happening. The collider is planned to be closed for 4 years, only reopening in mid-2030, and during this time, many engineers and physicists will work together to ensure that the High Luminosity upgrade will be done correctly and effectively.

Work has already started on the collider, in April 2018 an 80 metre shaft was dug, as well as 300 metre service tunnels at the sites of ATLAS and CMS. Four connections have been made between the new and old infrastructure, as well as 5 surface buildings to house electrical, cryogenic, and cooling and ventilation systems for the new HL-LHC equipment. Equipment is currently being manufactured in Europe, Japan, the United States, China, and Canada. Each of the experiments will be getting upgraded to handle the increase of data by HL-LHC. When the collider undergoes it’s third long shutdown, most of the work will take place on the actual collider, given that it won’t be running for approximately 4 years.

The upgrade is set to cost approximately 1 billion Swiss Francs (1.2 billion USD) from 2015 to 2029 and will also receive contributions from global laboratories. CERN is supported by 20 countries; therefore this international collaboration will benefit everyone involved and the rest of the world. The HL-LHC will allow for more training for physicists, engineers and technicians. At the moment, there are more than 200 bachelor’s students, master’s students, doctoral students, postdoctoral researchers, and fellow researchers participating in the project. There will be many jobs provided by the upgrade, as there are major civil engineering projects happening, and teams of technicians and physicists will be working together to ensure the project is carried out successfully.

The HL-LHC aims to improve fundamental knowledge, which is the main mission of CERN. To develop the HL-LHC, CERN will push several commonly used technologies, such as superconductors, vacuum technologies, computing, electronics, and industrial processes. The greater knowledge of these technologies means that these innovations can be better integrated into our daily lives. For example, an increase of knowledge of superconducting applications in medical imaging means better cancer diagnosing, and treatment using particle beams (hadron therapy).