ATLAS solenoid

ATLAS solenoid
Name	ATLAS solenoid
Country	Switzerland
Location	CERN
Institution	ATLAS
Type	Superconducting solenoid
Status	Operational
Commissioning	2008
Field strength	2 T

ATLAS solenoid The ATLAS solenoid is a large superconducting magnet installed at CERN as part of the ATLAS experiment at the Large Hadron Collider. It provides a central axial magnetic field used for charged-particle momentum measurement inside the ATLAS Inner Detector, enabling precision studies related to the Higgs boson, Top quark, and searches for Supersymmetry and Dark matter. The device was developed and assembled through collaborations among European laboratories and institutions including DESY, INFN, and CEA.

Overview

The solenoid surrounds the ATLAS Inner Detector and complements the ATLAS Toroid magnet system and Muon spectrometer to form a multi-component magnetic environment for track curvature measurements used in analyses of collisions produced by the LHC. Designed contemporaneously with the ATLAS detector subsystems during the LHC construction era, the magnet contributed to milestone physics results announced in 2012 during the CERN announcement of the discovery of a Higgs-like boson. Its role interfaces directly with reconstruction algorithms developed by the ATLAS software and computing teams and with alignment work coordinated with the ATLAS calibration group.

Design and specifications

The solenoid is a thin-wall, aluminum-stabilized, superconducting coil engineered to deliver an approximately 2 tesla axial field across the ATLAS tracking volume. The design specifications included tight constraints on material budget to minimize multiple scattering effects affecting the Silicon Pixel Detector, Transition Radiation Tracker, and SCT. Electrical and mechanical parameters were defined alongside safety standards from European Organization for Nuclear Research partners and industrial suppliers. The coil parameters were optimized using simulations from groups affiliated with Imperial College London, University of Oxford, and RWTH Aachen University.

Construction and materials

Manufacture combined precision winding, aluminum alloy support structures, and a stabilized copper/aluminum conductor with embedded Niobium–Titanium superconducting filaments supplied by industrial vendors and laboratory workshops. The vacuum vessel, cryostat shells, and support posts were fabricated to meet specifications from laboratories such as CEA Saclay and CERN Technical Centre. Assembly required clean-room procedures coordinated with ATLAS subsystem teams including those from University of Manchester, Ludwig Maximilian University of Munich, and University of Tokyo. Mechanical interfaces were tested against standards referenced by European Committee for Standardization and coordinated with logistics handled by Geneva port operations.

Cooling and cryogenics

Cryogenic systems employ liquid helium to maintain the coil at superconducting temperatures around 4.5 kelvin, using distribution lines and heat exchangers supplied and maintained in collaboration with cryogenics groups from CERN Cryogenics, DESY, and Fermilab. The refrigerator plant interfaces with the ATLAS detector control system and SCADA infrastructure and was commissioned with input from specialists at Brookhaven National Laboratory and Harvard University. Maintenance and cryogen replenishment reflected coordination between ATLAS operations and the Large Hadron Collider cryogenic network.

Magnetic field performance and testing

Magnetic mapping and performance tests were carried out before and after installation, using probe systems developed by teams at University of Birmingham, University of Geneva, and Max Planck Institute for Physics. The measured central field uniformity, integral field strength, and fringe-field behavior were validated against simulations from groups at CERN Theory Division and experimental campaigns coordinated with the ATLAS magnet group. These tests ensured compatibility with muon momentum measurements provided by the Muon Chambers and tracking reconstruction algorithms developed by the ATLAS collaboration analysis teams.

Integration with the ATLAS detector

Integration required precise alignment with the ATLAS Inner Detector supports, services routing through the ATLAS service caverns, and interfaces with the Calorimeter cryostats and the ATLAS Muon spectrometer toroids. Workstreams included cable routing, cryogenic plumbing, and safety systems coordinated with infrastructure teams from CERN Accelerator and Technology Sector and detector installation groups from partner institutions like SLAC and KEK. Integration also accounted for maintenance access, detector commissioning schedules, and interoperability with ATLAS trigger and data acquisition systems developed by multinational consortia.

Operational history and upgrades

Commissioned for first physics runs in 2008, the solenoid has operated through multiple LHC run periods including Run 1, Run 2, and subsequent runs with planned upgrades in concert with ATLAS Phase-1 and Phase-2 upgrade programs. Upgrade activities involved service modularization and refurbishment coordinated with the LHC Long Shutdown periods and with participation from institutes such as CERN, INFN, and KEK. Operational records and performance summaries were produced for review by ATLAS management and external oversight from bodies including the European Research Council and national funding agencies.

Safety and quench protection

Quench detection and protection systems were designed to handle sudden transitions from superconducting to resistive states, employing sensors, dump resistors, and fast discharge circuits specified in collaboration with specialists from CERN Safety Commission and laboratories including Brookhaven National Laboratory and CEA. Emergency procedures were integrated with ATLAS safety plans, the CERN Fire Brigade, and interlocks tied to the LHC beam permit system overseen by the CERN Accelerator Beam Operations group. Regular training and testing ensured readiness for quench scenarios and compliance with international safety standards.

Category:Particle detectors Category:CERN magnets Category:Superconducting magnets