Linac 2

Linac 2. It was a linear particle accelerator and a critical proton source for the CERN accelerator complex for four decades. As the injector for the Proton Synchrotron, it formed the foundational first step for numerous landmark physics experiments. Its reliable operation was essential for the research programs at the Super Proton Synchrotron and, ultimately, the Large Hadron Collider.

History and development

The development of this accelerator was initiated in the early 1970s to replace the aging Linac 1, which had been in service since 1959. The project was driven by the need for higher intensity and more reliable proton beams to feed the expanding CERN research program. Construction was completed in 1978, and after extensive commissioning, it officially began its operational life, marking a significant upgrade in CERN's injector chain capabilities. Its design and construction involved numerous engineers and physicists from the CERN departments, leveraging experience gained from its predecessor and contemporary projects like the Super Proton Synchrotron.

Design and technical specifications

The machine was a room-temperature, or Drift tube linac, operating at a frequency of 202.56 Megahertz. It accelerated negative hydrogen ions, which were then stripped of their electrons to produce protons before injection into the downstream synchrotron. The accelerator structure was approximately 33 meters long and consisted of three distinct sections: a radio-frequency quadrupole, a Drift tube linac, and a side-coupled Drift tube linac. It boosted particles to an energy of 50 MeV, a substantial increase over the 50 keV provided by its pre-injector, the Duoplasmatron. Key components included copper-clad steel Drift tubes and powerful Klystron amplifiers to generate the required radio-frequency fields.

Role in the CERN accelerator complex

For forty years, this accelerator served as the indispensable proton source for the entire CERN fixed-target and collider physics program. It directly fed the Proton Synchrotron, which in turn supplied beams to the Super Proton Synchrotron and the Intersecting Storage Rings. This chain was the backbone for experiments like UA1 and UA2, which discovered the W and Z bosons. In the Large Hadron Collider era, it remained crucial, providing the initial proton beam that was accelerated and stored in the Low Energy Ion Ring before final injection into the Large Hadron Collider itself. Its stable beams were also used for the CERN Neutrinos to Gran Sasso project.

Operation and performance

The accelerator was renowned for its exceptional reliability and stability, often achieving an operational availability exceeding 98%. It typically operated with a pulse repetition rate of up to 2 Hertz, delivering beam intensities that met or exceeded its design specifications. Its consistent performance was vital for the long-term scheduling of experiments across the CERN complex, including those at the Antiproton Decelerator and the ISOLDE facility. Routine maintenance and upgrades were performed during the annual CERN shutdown periods to ensure its continued service.

Decommissioning and legacy

After four decades of service, the accelerator was permanently shut down in November 2018. Its role was assumed by the new, more powerful Linac 4, designed to provide higher brightness beams for the High Luminosity Large Hadron Collider project. The decommissioning process involved safely removing radioactive components and clearing the tunnel. Its legacy is profound, having provided the proton beams for Nobel Prize-winning discoveries, including those by Carlo Rubbia and Simon van der Meer. Key components, such as a tank module, were preserved for historical display at CERN, and its tunnel is being repurposed for parts of the Linac 4 beam transfer line.

Category:Particle accelerators Category:CERN