The last quadripolar magnet was brought down into the tunnel of the world’s largest particle accelerator; the CERN’s1 LHC, or Large Hadron Collidor. This magnet is part of a series of 392 units which will ensure that the beams are kept on track all along their trajectory through the tunnel. Its installation marks the completion of a long and fruitful collaboration between the CERN, the CNRS/IN2P32 and the CEA/DSM3 in the field of superconductivity and advanced cryogenics. This collaboration has lasted over ten years and was part of the special contribution made by France, as the host country, to the construction of the LHC.

Built to answer the most fundamental questions in physics, the LHC accelerator is assembled at the CERN in a tunnel which has a circumference of 27 km and is buried 100 metres beneath the Franco-Swiss border. It is composed of 1700 large magnets of which 392 are quadripole magnets designed to guide and focus the beams. It also includes a significant quantity of corrective magnets. The final installation of the LHC will be completed in mid-2007, and start-up is planned for November 2007.

In order to meet the considerable technological challenges presented by the LHC, the CNRS, CEA and CERN collaborated closely in the construction of the accelerator. The protocol of collaboration amongst these three organizations was signed on February 14, 1996 in the presence of the Minister responsible for research.

The performance of the LHC’s beam-guiding magnets is ensured by their operating in a supra-conductive state which can only be reached if the system is maintained at very low temperatures. Therefore the LHC requires the largest cryogenic infrastructure ever created. Within this infrastructure the CNRS and the CEA, along with CERN teams, conceived and validated the cryogenics using superfluid helium at -271°C, a temperature lower than that of interstellar space. In addition, France played a principle role in the creation of the focusing units by conceiving the LHC’s principle quadripole superconductors and their cold mass assembly. The 392 quadripole magnets are now all in the tunnel and will ensure that the beams are kept on track. This means that they will control the beams’ millimetric dimension all the way along their trajectory. These magnets are inserted in enclosures of liquid helium along with corrector magnets as well as other components. This complex assembly is called cold mass. It is then itself surrounded by a cryostat and a server module. All of this forms what is known as a short-straight section.

The CEA-Dapnia created the prototypes and then participated in the technology transfer and monitoring of industrial production of the 392 quadripole cold masses in Germany. The Orsay Institute of Nuclear Physics (CNRS/IN2P3 – Paris University 11) participated in the design and creation of the short-straight section cryostats from prototype to industrialization. The institute’s contribution went as far as monitoring production and assembly of the series at the CERN. The first short-straight section, and thus the first quadripole magnet, was brought down into the LHC tunnel in April 2005.

The Orsay Institute of Nuclear Physics also developed and calibrated over 6000 thermometers which will measure and monitor all of the LHC supraconductor’s elements to the nearest tenth of a degree. The Low-Temperature division of the CEA participated in monitoring the production, delivery and installation of the -271°C refrigeration units, after having led the initial basic design work. This same division perfected the cryogenics for the experimental Tore Supra system in Cadarache, used for research on controlled fusion.

The installation of the last quadripole magnet marks the end of the collaboration related to France’s special contribution to the project. France’s commitments to the construction of the LHC have been honoured, and even significantly surpassed. French assistance to the LHC continues for putting the equipment into operation. Beyond the LHC, the technologies developed through this collaboration are transferable to several major pieces of equipment currently being studied, developed, or under construction.

Written from a news release by CNRS.