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Contents

Linac 2 duoplasmatron source Linac 3 - the lead supply
Linac 2 - Protons Linac 3 - Ions

Organization

The CERN Hadron Linacs and their sources are mainly the responsibility of the AB-ABP-HSL section, which provides the ion sources, Linac supervision during operation, and shutdown co-ordination and support. The Linac subsystems are the responsibility of the relevant groups.

A bit of History

CERN's original proton linac accelerated its first beam in 1958 and was fully commissioned in 1959 when one turn of 50 MeV protons went round the PS. It was the only supplier of protons to the CERN accelerators until Linac 2 took over in 1978. Between that date and its final retirement in the summer of 1992 (after 33 years of service), it not only continued to supply protons for machine experiments, it was also used to accelerate alphas, deuterons, oxygen and sulphur ions. The latter two ions required a 33% increase in the design accelerating and focusing fields. Additionally it acted as a test bed for the first Radio Frequency Quadrupole experiments. It even suffered the indignity of being moved backwards 12 meters to facilitate the ion acceleration tests. Eventually it was provided with two injectors (protons from a duoplasmatron and via the RFQ for LEAR tests and light ions {Oxygen and sulphur} for SPS fixed target physics). In spite of this it continued its faithful service until retirement after 33 years of service.

The present 50 MeV Alvarez Proton Linac

  Current Machine Status

On September 6 1978, what was then called the New Linac (now called Linac-2) produced it first beam of 50 MeV Protons. By 3 October the intensity out of the linac had been pushed up to its design intensity and on 6 October was used in a study session to inject into the original 800 MeV PS Booster (PSB). Soon afterwards it was used for a short time as the operational injector, a role it was to take over from the start of operations in 1979. Now, 25 years later, the linac is still going strong with even higher intensities. A small celebration was held on 3 October 2003 with a number of the original commissioning team (mainly now retired) present. Photographs of the event, do you recognise anyone?

The present Alvarez Proton Linac, first run in 1978, provides pulsed (1 Hz) beams of up to 175 mA at 50 MeV, now at the PSB entrance, with pulse lengths varying between 20 and 150 us depending on the number of protons required by the eventual user. The ion source is a Duoplasmaton giving up to 300 mA of beam current. Originally the pre-injector was a 750 kV Cockcroft-Walton (Photograph) but this has now been replaced by a 4-vane RFQ with an injection energy of 92 kV and an output energy, naturally, of 750 keV. A three tank, post coupled stabilised, drift tube linac with quadrupole focusing in the drift tubes follows. An 80 meter beam transport, partially in common with the ion Linac, carries the linac beam to the 1.4 GeV PSB .

Beams from this linac are used (after additional acceleration) for nuclear physics at ISOLDE; the East Experimental Hall and the neutron Time of Flight faciliy; 450 GeV SPS fixed target physics; for antiproton production in the future Antiproton Decelerator (AD); and in the future for LHC. The annual operation time is about 6000 hours.

The original design for this linac was for a 150 mA beam out of the machine. When the requirements for LHC became evident, effort was expended to increase the output to 180 mA at the transfer point to the PS Booster. On 10 Novermber 1999 this figure was attained in a controlled manner. However, to reduce the strain on the RF systems, we only run at these very high intensities when requested. The history of the intensity from the linac over the years and the evolution of the intensity along the machine are illustrated.

In 2007, a replacement of this accelerator was approved. The new Linac 4 accelerator will provide a 160MeV H- ion beam, firstly as an injector to the PS Booster, and in the future possibly as the front end of a high energy and high duty cycle Super Conducting Proton Linac (SPL).

The 4.2 MeV/u Heavy Ion Linac

 Current Machine Status

This linac, commissioned in summer 1994, presently provides beams of  208Pb53+. A 14.5 GHz ECR ion source operating in the "afterglow" mode produces Pb 27+  ions at 2.5 keV/u. This beam is accelerated in an RFQ and a three tank  IH linac to 4.2 MeV/u where stripping in a 1 um carbon foil to a charge state distribution centered around Pb53+ takes place. 53+ ions are selected from this mixture in a magnetic filter  before being transported to the PS Booster and other circular machines. Linac3, the  more common name for this machine,  was built by a truly international collaboration involving France, Italy, Germany, Italy, Sweden, Switzerland, India, the Czech Republic and CERN.

Although intended for 170 GeV/u experimental physics in the SPS, the lead beam was regularly injected into LEAR/LEIR for cooling experiments using beams with charge states between 52+ and 55+. In 1995, the machine was scheduled for about 2500 hours of operation but was only used for test beams in 1996 due to the cancellation of the ion run. In 2003, beams of Indium 21+, stripped to In 37+ were accelerated for the SPS.


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C.E.Hill for the Linac machine supervisors.
Comments and Suggestions to Richard Scrivens 28/01/2008