LINAC4

LINAC4 is a high-energy linear accelerator built to inject negative hydrogen ions into the injector chain at CERN and replace an earlier injector to increase beam brightness for the Large Hadron Collider and other machines. The project involved collaborations between institutions such as DESY, RAL, CEA Saclay, and national laboratories across Europe. LINAC4 supports programmes including upgrades to the LHC injector chain and experiments at facilities like the Antiproton Decelerator indirectly via improved injector performance.

Overview

LINAC4 functions as a linac delivering 160 MeV H− beam pulses into the PS Booster to feed the Proton Synchrotron and eventually the Super Proton Synchrotron and Large Hadron Collider. The initiative was coordinated within the European Organization for Nuclear Research framework, tied to the LHC Injector Upgrade strategy and accelerator roadmaps developed by agencies such as CERN Council member states and partner laboratories including INFN, CIEMAT, and GSI Helmholtz Centre for Heavy Ion Research. The machine replaced the legacy proton injector, aligning with upgrade programmes like High Luminosity LHC and projects oriented by the European Strategy for Particle Physics.

Design and Technical Specifications

The design follows a sequence of ion source, radio-frequency quadrupole, drift tube linac, and cell-coupled-cavity accelerating structures. The front end begins with an H− ion source and a 45 keV low-energy beam transport developed in collaboration with groups from CEA, STFC, and PSI. Beam bunching is performed by a Radio-frequency quadrupole operating at 352 MHz, followed by a 3 MeV chopper line and a 50 MeV drift tube linac based on concepts tested at GSI and DESY. The high-energy section uses Pi-mode or cell-coupled structures to accelerate to 160 MeV compatible with injection into the PS Booster via charge-exchange foils; charge exchange was refined drawing on experience from TRIUMF and Los Alamos National Laboratory systems. Superconducting and normal-conducting radiofrequency technologies were evaluated with benchmarking against installations like the European XFEL and the Spallation Neutron Source.

Beam diagnostics include time-of-flight, beam current transformers, and transverse emittance measurements adapted from techniques at FNAL, KEK, and J-PARC. Vacuum, magnetics, and control systems were integrated using hardware and software practices drawn from ITER control frameworks and EPICS deployments common across laboratory infrastructures.

Construction and Commissioning

Construction phases spanned procurement, assembly, and subsystem testing across partner sites including CEA Saclay, RAL, and in-kind contributors from Poland, Switzerland, and Spain. Key milestones included RF power tests, low-energy beam commissioning in dedicated test stands influenced by methods from the CERN Proton Synchrotron upgrade and high-power conditioning tactics refined with input from IHEP and KEK. The tunnel installation was coordinated with civil works near the Proton Synchrotron complex and synchronized with injector shutdowns to minimize impact on experiments like ISOLDE and the n_TOF facility. Beam commissioning proceeded through energy staging — 3 MeV, 50 MeV, and full 160 MeV — with acceptance tests referencing criteria used at PSI and RAL accelerators.

Operation and Performance

Operational regimes include pulsed beam delivery with repetition rates and pulse lengths tuned to downstream machines such as the PS Booster and the Super Proton Synchrotron. Performance metrics emphasized transverse emittance preservation, transmission efficiency, and reliability to meet High Luminosity LHC demands. Early operational data showed improvements in injection brightness and reduced space-charge limitations compared with the previous injector, translating into higher intensity and lower losses in the PS Booster, influencing beam availability for experiments at CERN facilities including AD, ISOLDE, and the fixed-target programme. Routine maintenance and RF conditioning draw on practices from CERN operations teams and lessons from facilities like DESY and FNAL.

Upgrades and Future Developments

Future work contemplates higher duty cycles, improved source longevity, and upgraded RF and chopper systems to support evolving needs of the HL-LHC era and prospective projects such as a potential multi-MW proton driver or studies linked to neutrino facilities. Collaboration continues with institutions including INFN, GSI, CEA, and partner universities to evaluate superconducting linac modules, advanced diagnostics, and higher-repetition operation modes inspired by concepts from ESS, European XFEL, and the Spallation Neutron Source. Strategic planning aligns with directives from the European Strategy for Particle Physics and coordination through bodies such as the CERN Council and national funding agencies to ensure compatibility with future injector complex upgrades.

Category:Particle accelerators Category:CERN