Long Shutdown 3

Long Shutdown 3
Name	Long Shutdown 3
Type	Accelerator maintenance period
Facility	Large Hadron Collider
Location	CERN, Geneva
Country	Switzerland
Period	2021–2027
Participants	European Organization for Nuclear Research; member states; international laboratories

Long Shutdown 3 Long Shutdown 3 was a multi-year maintenance and upgrade period at the Large Hadron Collider complex at CERN in Geneva, intended to prepare the collider and associated injectors for higher luminosity operations. The project involved collaborations among the European Organization for Nuclear Research, national laboratories such as Fermilab, DESY, and INFN, and industrial partners from Siemens, Thales Group, and General Electric, with oversight by agencies including the European Commission and funding from Euratom programs.

Background and Purpose

The shutdown followed earlier interventions after Run 2 (LHC) and the mixed outcomes of Run 1 (LHC), with strategic planning influenced by roadmaps from High Luminosity LHC (HL-LHC), the European Strategy for Particle Physics, and recommendations from advisory bodies such as the Particle Physics Project Prioritization Panel and the Physics Beyond Colliders study group. Objectives tied into results from experiments including ATLAS, CMS, LHCb, and ALICE, and responded to discoveries like the Higgs boson and precision measurements from the Standard Model. Stakeholders included funding agencies such as Science and Technology Facilities Council, National Science Foundation (United States), and ministries across France, Germany, Italy, and Switzerland.

Scope of Work and Upgrades

Major technical interventions encompassed upgrades to superconducting magnets inspired by developments at Brookhaven National Laboratory, cryogenics overhauls comparable to upgrades at SLAC National Accelerator Laboratory, and power converter replacements following designs tested at CEA Saclay and Max Planck Institute for Physics. The injector chain — involving the Proton Synchrotron, Super Proton Synchrotron, and Linac systems — received refurbishment informed by programs at TRIUMF and KEK. Detector-related work affected ATLAS inner detector refurbishments, CMS tracker replacement, LHCb upgrade I/O, and ALICE readout electronics, with component fabrication by firms like Nexans and Babcock International Group.

Schedule and Timeline

The timeline synchronized milestones from the HL-LHC project plan and milestones set by the International Committee for Future Accelerators, with critical path items coordinated against calendar slots used by experiments such as NA61/SHINE and COMPASS. Phases included an initial decommissioning window, magnet replacement campaigns, cryogenic commissioning, and progressive recommissioning aligned to beam tests used at CERN’s SPS and commissioning prototypes validated at Fermilab Test Beam Facility. Contingencies referenced historical delays captured during Long Shutdown 1 and Long Shutdown 2, and adjustments were negotiated with collaborating institutions including European Southern Observatory and national funding bodies.

Impact on Accelerator Operations

Operational impacts affected scheduled physics runs for ATLAS, CMS, ALICE, and LHCb, necessitating data-taking pauses and follow-up analysis work by collaborations such as the Worldwide LHC Computing Grid and computing centers like CERN IT and GridPP. The upgrades aimed to enable higher instantaneous luminosity similar to objectives in proposals advocated by the High Energy Physics Advisory Panel, and to support precision studies that complemented efforts at International Linear Collider concept studies and neutrino programs such as DUNE and T2K. Short-term impacts included workforce mobilization from institutes like University of Oxford, University of Cambridge, ETH Zurich, and Sapienza University of Rome.

Funding, Management, and Safety

Funding frameworks blended in-kind contributions from member states represented by entities such as CNRS, INFN, Max Planck Society, and national ministries, alongside cash commitments routed via instruments like the European Investment Bank and grants from the Horizon 2020 program. Management followed governance models used in multinational projects like ITER and James Webb Space Telescope, with safety protocols informed by standards from International Atomic Energy Agency and occupational guidelines from International Labour Organization. Regulatory interfaces included coordination with Swiss authorities in Canton of Geneva and French agencies near the Ain border.

Outcomes and Legacy

Post-shutdown operations were designed to transition the accelerator complex into the High Luminosity LHC era, enabling extended datasets for Higgs boson coupling studies, searches for supersymmetry, and rare processes complementary to experiments at KEK and SLAC. The program catalyzed technology transfer to industry partners like Thales Group and academic spin-offs from institutions such as CERN School of Computing, influenced future proposals like the Future Circular Collider, and informed workforce development across universities including Imperial College London and University of Tokyo. The legacy encompassed advances in superconducting magnet technology, cryogenics, detector instrumentation, and international collaboration frameworks modeled in subsequent large-scale physics endeavors.

Category:Particle physics Category:European Organization for Nuclear Research