The road to HiLumi
As of mid-2026, the accelerator complex and experimental facilities at CERN are undergoing major maintenance and upgrade work. This phase, known as “Long Shutdown 3” or “LS3”, is expected to last up to four years and will involve thousands of experts across CERN’s sites and tunnels. The work will cover civil engineering, infrastructure consolidation, upgrades of facilities and the installation of cutting-edge technology.
The flagship project is the High-Luminosity Large Hadron Collider (HiLumi LHC), a major upgrade to dramatically improve the performance of the LHC, CERN’s largest accelerator. Over 1.2 kilometres of the LHC are being dismantled and replaced by new systems to increase the luminosity (the number of particle collisions).
The LHC experiments will be greatly improved with the installation of new subdetectors and revolutionary new systems, ready for the challenges and opportunities that the increased number of collisions will bring.
The entire accelerator complex will be shut down for maintenance, consolidation and upgrades. This work will ensure the high level of availability and reliability of particle beams that is required to meet the ambitious physics objectives of the next operating period. Several experiment facilities are being renovated, such as the North Area Hall, which houses many fixed-target experiments supplied by the SPS, CERN’s second largest accelerator. A significant improvement programme is also under way at ISOLDE, the nuclear physics facility. The accelerator complex and its experiment facilities will gradually resume operation from mid-2028 onwards.
The whole undertaking is a major logistical challenge, and CERN’s underground facilities will be with a hive of activity. Safety remains the top priority throughout this busy period.
Planned shutdowns like the LS3 are an integral part of the lifecycle of particle accelerators, especially those that operate at near absolute-zero temperatures. These periods group allow preventive and corrective maintenance, consolidation and upgrades to be carried out at the same time.
