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.

Additional resources

HiLumi LHC

Accelerator complex

Experiments

Snapshots of the ongoing upgrades

So long and thanks for all the collisions!

Date: 29 June 2026

On Saturday 27 June at 6 am, the LHC’s Page 1 — the accelerator’s dashboard — said “goodbye” to collisions. The LHC operators dumped the last beams before the accelerator’s metamorphosis. The LHC is now entering a major upgrade phase: four years during which the world’s most powerful collider will be transformed into an even better performing machine. The other CERN accelerators will continue running until the end of August before entering their third long shutdown.

ISOLDE beam dumps successfully dismantled

Date: 09 July 2026

ISOLDE has reached a major milestone in its ISOLDE Improvement Programme with the dismantling of its two beam dumps. Designed in the early 1990s, this equipment had seen the facility through more than three decades of operation. As the energy and intensity of the beam delivered by the Proton Synchrotron Booster gradually increased, the dumps were pushed to their thermal and mechanical limits, making their replacement essential. Installed downstream of the target stations, the dumps consisted of massive steel blocks shielded by concrete blocks and 10 metres of earth. Extracting them was no mean feat: not only were they highly radioactive, but they were also buried under 8000 m3 of earth. Over the course of three years of studies carried out in collaboration with several groups, the radiological characterisation of the soil was completed (HSE-RP) and excavation and dismantling protocols were drawn up (SCE-PPM and SY-STI, respectively). The most radioactive components were then successfully removed using heavy-duty handling equipment (EN-THE) and robotic systems (BE-CEM). Work will now focus on the construction of an underground technical building that will provide access to the new water-cooled beam dumps, which are currently in production.

Delivering power to the HiLumi magnets

Date: 07 July 2026

The HiLumi LHC’s new magnets will be powered by very high currents. These currents need to be transferred without losses between power converters operating at room temperature in underground galleries and superconducting magnets at extremely cold temperatures. This is achieved through an innovative system called the Cold Powering System which uses high-temperature and intermediate-temperature superconductors to transport the current over around 100 metres. Discover how it works.

Safety kicks off the LHC’s transformation

Date: 30 June 2026

On 29 June, the doors of the LHC opened for a major phase of work that will transform the collider into the HiLumi LHC, an even better performing machine. The initial interventions focus on securing the accelerator, particularly from an electrical standpoint. To minimise risk as much as possible, the electrical circuits are locked out that is, powered down and secured. A team intervened as early as this afternoon at Point 1 of the LHC to carry out this safety procedure. Similar interventions will take place across the entire LHC in the coming days, and then, in September, throughout the rest of the accelerator complex.

So long and thanks for all the collisions!

Date: 29 June 2026

ISOLDE beam dumps successfully dismantled

Date: 09 July 2026

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