CERN LINAC4

CERN LINAC4
Name	LINAC4
Location	Geneva
Operated	CERN
Type	particle accelerator
Beam	H− ions
Energy	160 MeV
Status	Operational

CERN LINAC4 is a linear accelerator at CERN located near Geneva, built to replace the previous LINAC2 as the injector for the Proton Synchrotron Booster and to increase the performance of the Large Hadron Collider. Designed and commissioned in the 2010s, it accelerates negative hydrogen ions (H−) to 160 MeV, enabling higher beam brightness and intensity for downstream machines such as the Proton Synchrotron and the Super Proton Synchrotron. The project involved collaborations among institutions including CERN, national laboratories, and university groups across Europe.

Introduction

LINAC4 was conceived as part of the long-term upgrade strategy for CERN’s accelerator complex, complementing projects like the Large Hadron Collider upgrades and upgrades to the Injector Complex. Its purpose was to replace LINAC2 to deliver higher energy H− beams into the Proton Synchrotron Booster, facilitating injection via charge-exchange into circular machines, reducing space-charge effects and improving SPS and LHC filling. The initiative aligned with CERN’s roadmap alongside programs such as the High Luminosity LHC and collaborations with agencies like the European Union and national funding bodies.

Design and Technical Characteristics

LINAC4’s design uses an H− source feeding a low-energy beam transport and a series of accelerating structures: a radiofrequency quadrupole (RFQ), a chopper line, a drift tube linac (DTL), a cell-coupled drift tube (CCDTL) and a side-coupled linac (SCL). The RFQ and DTL operate at frequencies linked to conventions used at facilities such as PSI and DESY, with RF power delivered by klystrons and solid-state amplifiers developed in collaboration with industrial partners and laboratories like STFC and CEA. Beam dynamics and emittance control benefitted from simulation codes and design tools shared with projects at Fermilab and KEK. The H− charge-exchange injection scheme employs stripping by thin foils and techniques compatible with systems in use at SNS and J-PARC. Components such as the ion source drew on designs proven at GSI and TRIUMF.

Construction and Commissioning

Construction took place on the CERN site, involving civil engineering adjacent to the SPS transfer lines and integration with the existing injector tunnels. Major hardware milestones included installation of the RFQ, magnets for the low-energy beam transport, vacuum systems, and beam instrumentation developed with partners including IN2P3 and university groups from Oxford and Helsinki. Commissioning phases followed staged beam tests similar to commissioning campaigns at DESY and SLAC, progressing from low-energy beam extraction to full-energy 160 MeV operation. The commissioning schedule coordinated with maintenance windows of downstream machines such as the Proton Synchrotron Booster and the SPS.

Operational History and Performance

Since first beam, LINAC4 has delivered H− beams for injection into the booster, contributing to increased intensity and brightness in the injector chain and enabling operational improvements for the LHC injectors. Performance metrics such as average current, pulse length, transmission efficiency, and normalized emittance were reported after commissioning and compared with expectations from design studies and with operational parameters at facilities like CERN SPS North Area, SNS, and LANSCE. Operational lessons informed tune-up procedures and maintenance regimes aligned with practices at INFN laboratories and other major accelerator facilities.

Role in the CERN Accelerator Complex

LINAC4 functions as the first stage of the modernised CERN injector chain, feeding the Proton Synchrotron Booster which in turn injects into the Proton Synchrotron and then the SPS before particles reach the Large Hadron Collider. Its upgrade of injector energy from 50 MeV to 160 MeV reduces space-charge limitations in the booster and enables higher-intensity beams for experiments at the North Area and for collider operation. LINAC4’s role interacts with programmes such as the Injector Upgrade and complements other CERN facilities including the Antiproton Decelerator and experimental areas like ISOLDE.

Upgrades and Future Developments

Future developments explore increasing average current, improving reliability, and integrating technologies from research at FRIB, ESS, and other accelerator projects. Potential upgrades include enhanced RF systems, improved ion sources, and advanced chopping and beam diagnostics drawing on R&D from laboratories like CERN partner institutes and consortia within the European Strategy for Particle Physics. LINAC4’s experience feeds into proposals for next-generation injectors, contributions to the High Luminosity LHC upgrade path, and cross-fertilisation with accelerator-driven projects in nuclear physics and spallation research.

Category:CERN accelerators Category:Particle accelerators Category:Linear particle accelerators Category:Particle physics facilities in Switzerland