After a journey from Siberia of more than 13,000 km, a special delivery arrived at CERN on 14 September, bringing modules for Linac4, the new four-stage injector being built for the laboratory’s accelerator complex. A month earlier, the first major accelerating stage had made a shorter journey. Built entirely at CERN and designed in collaboration with CEA Saclay, the radio-frequency quadrupole (RFQ) was installed at the accelerator test stand in Building 152.
Linac4, which is the fourth hadron linac to be built at CERN, is set to replace Linac2 in 2017/2018 as the new first link in the acceleration chain for the LHC. Its four accelerating structures will increase the beam energy successively to 3 MeV, 50 MeV and 102 MeV before finally reaching 160 MeV. By accelerating hydrogen ions (H–) instead of protons, Linac4 will bring several advantages. The use of H– will enable injection into the PS Booster with essentially no losses and the increase in beam energy will allow a doubling of the maximum intensity from the Booster for the same emittance.
The 3-m-long RFQ will accelerate the beam from 45 keV to 3 MeV, directly from the source. The RF field not only accelerates the particles but also bunches them and provides longitudinal and transverse focusing, thereby defining the beam characteristics and the quality for the entire accelerator chain. The Linac4 team is currently performing the RF tuning of the RFQ cavity, while the ion source, which will provide protons for the tests, is being installed and connected. Once both of these steps have been completed, the team will begin testing the RFQ with beam.
The delivery from Siberia consisted of the first two of seven modules for a cell-coupled drift-tube linac (CCDTL). The first of its kind to be used in an accelerator, it will provide the energy increase from 50 MeV to 102 MeV. Weighing 2 tonnes each, the modules were disassembled into six components for transportation. Once at CERN, a visiting Russian team reassembled the modules before carrying out a series of tests. They repeated vacuum tests performed before the modules began their journey and made checks of radio-frequency properties and the alignment of the modules on their supports. Two further modules are due for delivery to CERN in December, while the final three will follow early next year.
The seven CCDTL modules took two and a half years to produce and were made entirely by a team outside CERN. The modules are the result of six years of close collaboration between two Russian research institutes: the All-Russian Institute of Technical Physics in Snezhinsk and the Budker Institute of Nuclear Physics in Novosibirsk, located in south-western and central Siberia. The collaboration was made possible by support from the International Science and Technology Centre, an intergovernmental organization set up in 1992 to help former weapons scientists redirect their skills towards peaceful activities.
• To keep up to date with news on the LHC, Linac4 and other developments, see The Bulletin, http://bulletin.cern.ch.