Long Shutdown 2

Long Shutdown 2
Name	Long Shutdown 2
Facility	European Organization for Nuclear Research (CERN)
Location	Meyrin, Geneva, Switzerland
Period	2018–2021
Primary system	Large Hadron Collider
Goals	Upgrades to superconducting magnets, cryogenics, injectors, detectors

Long Shutdown 2 Long Shutdown 2 was a planned multi-year maintenance and upgrade period at the particle-physics complex near Geneva centered on the Large Hadron Collider and associated accelerator chain. It involved coordinated work across laboratories and collaborations such as CERN, ATLAS, CMS, LHCb, and ALICE to prepare for higher-energy and higher-luminosity operations. The program required interface with national laboratories and institutions including DESY, INFN, CEA Saclay, and STFC Rutherford Appleton Laboratory and affected experiments, computing centers, and industrial partners across Europe and beyond.

Background and Purpose

The shutdown was driven by performance goals set after the Higgs boson discovery by the ATLAS and CMS collaborations in 2012 and by long-term strategies from bodies such as the European Strategy for Particle Physics and the High-Luminosity LHC project. Objectives responded to findings from studies by the LHC Committee, engineering reviews involving CERN Council, and scientific roadmaps from agencies including the European Commission and national funding agencies like National Science Foundation and Deutsches Elektronen-Synchrotron. Motivations included increasing integrated luminosity for precision measurements of particles such as the top quark, probes of Beyond Standard Model scenarios pursued by collaborations like ATLAS, CMS, LHCb, and ALICE, and ensuring reliability of infrastructure inherited from earlier campaigns including Long Shutdown 1 and injector consolidation efforts coordinated with PS Booster and SPS teams.

Scope of Work and Upgrades

Major technical works targeted accelerator hardware, detectors, and infrastructure. Accelerator upgrades encompassed replacement and consolidation of superconducting busbars, work on cryogenics and magnet systems including spares for superconducting magnets, and consolidation of radiofrequency systems in the SPS and PS Booster. Injector chain refurbishments involved collaborations with CERN Proton Synchrotron teams and reconditioning of equipment used in fixed-target experiments like NA62 and COMPASS. Detector upgrades included pixel and tracker replacements in ATLAS and CMS, readout and trigger improvements in LHCb and ALICE, and calorimeter refurbishments referencing technologies used in experiments such as CMS HCAL and ATLAS Tile Calorimeter. Infrastructure and computing works interfaced with centers like CERN IT Department, WLCG partners including Fermilab, DESY, University of California, Berkeley, University of Oxford, and CNRS sites to expand data-handling and storage capacity. Safety and civil engineering projects aligned with standards from agencies such as European Commission nuclear safety frameworks and national regulators in France and Switzerland.

Timeline and Schedule

Planning drew on prior schedules from major projects like the High-Luminosity LHC upgrade path and operational cycles synchronized with experiments' run plans from ATLAS, CMS, LHCb, and ALICE. The multi-year window began after Run 2 and encompassed staged work packages, with critical-path items coordinated with suppliers such as Bruker-class vendors and cryogenic firms. Milestones included magnet interventions, injector upgrades, detector installation periods, and recommissioning phases tied to beam tests and system integration trials. Reviews and approvals passed through governance bodies including the CERN Council, program committees, and national funding authorities such as UK Research and Innovation and Agence Nationale de la Recherche.

Impact on Operations and Experiments

Operationally, the shutdown paused collisions and affected experiment schedules across collaborations like ATLAS, CMS, LHCb, ALICE, and non-LHC experiments hosted at CERN such as ISOLDE, n_TOF, and fixed-target programs. Detector teams used the interval for installation of new sensors and electronics, drawing on expertise from institutions including University of Manchester, University of Cambridge, Università di Bologna, Ludwig Maximilian University of Munich, and University of Tokyo. Computing and data challenges required coordination with grid sites including TRIUMF, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and GridPP partners. The hiatus also influenced international collaborations and schedules at associated laboratories like Fermilab, KEK, and DESY that depend on LHC timelines for complementary measurements.

Safety, Workforce, and Logistics

Safety management relied on protocols developed with national authorities in Switzerland and France, occupational standards from agencies such as International Labour Organization-related frameworks, and radiation protection guidelines consistent with international practice. Workforce planning involved thousands of engineers, technicians, and scientists from institutions including CERN, INFN, CNRS, University of Oxford, Imperial College London, Stanford University, and MIT; contractors from industrial partners across Germany, Italy, United Kingdom, and Spain supported civil and electrical works. Logistics encompassed supply-chain coordination with firms and workshops used by major projects like ITER and aerospace suppliers, customs arrangements at Geneva Airport, and on-site access controls integrated with CERN operations.

Outcomes and Legacy

The shutdown delivered upgraded hardware and systems that enabled subsequent runs with increased performance targets set by the High-Luminosity LHC roadmap and helped sustain precision programs including Higgs-property studies, flavor-physics measurements by LHCb, and heavy-ion physics by ALICE. Knowledge and technologies developed during the program influenced detector R&D communities at SLAC National Accelerator Laboratory, Brookhaven National Laboratory, TRIUMF, and university groups across Europe and Asia. Institutional lessons informed future large-scale projects and governance models referenced by initiatives such as the Future Circular Collider studies, the European Strategy for Particle Physics updates, and collaborative frameworks between CERN and partner laboratories.

Category:Particle physics