Linac2

Linac2
Name	Linac2
Country	Switzerland
City	Geneva
Institution	CERN
Type	Proton linear accelerator
Operational	1978–2013
Predecessor	PSB injector predecessors
Successor	Linac4

Linac2 was a proton linear accelerator operated by CERN from 1978 until 2013 that served as the primary high-current injector for a chain of machines including the Proton Synchrotron and the Super Proton Synchrotron. It provided long-pulse, high-intensity 50 MeV proton beams that enabled experiments at facilities such as the Intersecting Storage Rings-era programs, the Large Electron–Positron Collider, and early operations of the Large Hadron Collider. Linac2 played a pivotal role in sustaining beam intensities for colliders and fixed-target experiments, complementing developments at European Organization for Nuclear Research infrastructure projects and collaborations.

History

Linac2 originated from initiatives in the 1960s and 1970s to increase injector current for the Proton Synchrotron complex, succeeding earlier injector designs used for the PSB and operations tied to the Intersections of Proton Beams era. Construction and commissioning were coordinated by engineers and physicists at CERN with expertise drawn from collaborations including Fermilab-style injector developments and influence from work at the Brookhaven National Laboratory and DESY. The linac came online in 1978, replacing aging source and accelerating systems to meet the intensity demands of experiments such as those at the ISR and later to supply the LEP and LHC injector chain. Over decades Linac2 supported upgrades at the PSB, the PS, and the SPS while integrating improvements motivated by accelerator physics programs at institutions like Imperial College London and Oxford University.

Design and Technical Specifications

Linac2 was designed as a room-temperature, drift-tube linear accelerator delivering 50 MeV protons. The machine incorporated a high-current 90 kV duoplasmatron ion source feeding a low-energy beam transport (LEBT) line into a radio-frequency quadrupole (RFQ)-style bunching and drift-tube acceleration structure derived from research at CEA Saclay and technical developments from CERN laboratories. The accelerating sections used radio-frequency cavities operating at 202.56 MHz, inspired by designs at Los Alamos National Laboratory and adapted for the PSB injection energy. Key subsystems included a high-voltage platform, beam diagnostics developed in collaboration with INFN groups, vacuum and cooling systems influenced by practices at SLAC National Accelerator Laboratory, and control electronics integrated with CERN control frameworks. The ion source and pre-injector were capable of producing tens of milliamperes of H+ beam current with pulse lengths tailored to downstream accumulation in the PSB.

Operation and Performance

During routine operation Linac2 delivered stable 50 MeV proton pulses with currents up to several tens of milliamperes and repetition rates matched to the PSB injection cycle. Performance metrics emphasized beam current, emittance, transmission efficiency, and reliability for sustained operations feeding the PS and SPS. Operational teams at CERN implemented beam tuning, RF amplitude and phase control, and diagnostics employing devices developed in partnership with Paul Scherrer Institute and ETH Zurich specialists. Linac2 supported a variety of programs, from fixed-target experiments to collider commissioning campaigns for the LHC, demonstrating robustness in long-term availability and serviceability compared to contemporary injectors at facilities like KEK and TRIUMF.

Upgrades and Modifications

Throughout its life Linac2 underwent phased upgrades to enhance current, duty cycle, and beam quality. Modifications included improvements to the ion source inspired by research from Culham Centre for Fusion Energy and Swedish Royal Institute of Technology, replacement of aging RF amplifiers with solid-state and klystron-based systems, refurbishment of the drift-tube cavities, and installation of modern diagnostics and control systems using techniques pioneered at CERN accelerator schools and partner laboratories such as CEA and INFN. Specific campaigns addressed emittance reduction and beam halo control to optimize injection efficiency into the PSB, with contributions from academic collaborators at University of Manchester and Universität Hamburg.

Role in CERN Accelerator Complex

Linac2 was a cornerstone injector within the CERN accelerator complex, directly supplying proton beams to the Proton Synchrotron Booster. Its output determined achievable intensities in downstream machines including the Proton Synchrotron and the Super Proton Synchrotron and thereby influenced performance envelopes of the Large Hadron Collider and ancillary experiments. Operational coordination between Linac2 and machines such as the Antiproton Accumulator and the LEIR storage ring ensured timing, bunch structure, and longitudinal parameters compatible with accumulation and acceleration cycles. Linac2 also served as a testbed for injector technologies adopted in successors and contributed to training and knowledge transfer among accelerator physicists from institutions like CERN School of Accelerators affiliates and partner universities.

Decommissioning and Legacy

Decommissioning of Linac2 began as CERN prepared to commission Linac4 and modernize the injector chain. Decommissioning activities involved systematic dismantling, reclamation of reusable components, and documentation of technical lessons used to inform Linac4 designs and future injector programs at CERN. The legacy of Linac2 includes contributions to accelerator technology, operational expertise, and a generation of accelerator scientists and engineers who trained on the machine, many of whom continued work at institutions such as CERN, DESY, Fermilab, and national laboratories across Europe. Artifacts, technical reports, and institutional memory from Linac2 continue to influence injector design choices and collaborative projects across the international accelerator community.

Category:CERN accelerators