Magnet production for the LHC is complete!
On 27 November, the LHC teams celebrated the end of production of the machine's main magnets. Some 1232 main dipole and 392 main quadrupole magnets have been manufactured in an unprecedented collaboration effort between CERN and European industry.
It was a moment they had been dreaming of for four years, when the electronic display panel above the entrance to the fourth floor of Building 30 clicked over to reveal a beautiful zero! This display panel, inaugurated at the end of 2002 (see Bulletin 44/2002), has been counting down the number of superconducting magnets remaining to be delivered to CERN. On Monday 27 November, Lucio Rossi and his MCS Group (Magnets, Cryostats and Superconductors) in AT Department finally saw the zero appear on the panel, marking the completion of production of the 1232 main dipole magnets. And what a splendid symbol it was, twenty years after the first design studies began, thirteen years after the first prototypes and six years after the start of series production. The event was celebrated the very same day at a ceremony in SMA18, the hall where the magnets are being assembled. The teams were not only celebrating the end of dipole production but also the completion of all the main superconducting magnets. Production of the 392 quadrupole magnets inserted into the short straight sections came to an end almost simultaneously. 'It's a great day for our team, the crowning moment of more than 10 years' intensive work and the end of the largest production run ever commissioned by a particle physics laboratory,' underlines Lucio Rossi. 'I would like to thank all the members of my team as well as our trusted partners from industry, who have been indispensable.'
The dipole magnets (15 metres long and weighing 35 tonnes) constitute the largest part of the LHC machine, accounting for some 20 of the ring's 27 kilometres. The purpose of these magnets, which are cooled to -271ºC, is to generate a magnetic field in excess of 8 tesla which bends the trajectory of the LHC protons. The difficulties encountered in industrialising these sophisticated components were legion. To overcome them it took the dogged perseverance of all members of the MCS Group, spurred on by a Group Leader with iron determination and boundless reserves of energy. 'We should also remember the work done by the other groups in AT and in other Departments, especially TS-MME and AB-ABP,' Rossi adds.
The most complex part of the magnet is the superconducting coil, consisting of a cable that carries 13000-amp electrical currents. Each cable is made up of some thirty strands containing 6000 to 9000 filaments ten times finer than a human hair, made of the superconducting alloy niobium-titanium. Production of the 250000 kilometres of strands for the 7000 kilometres of cable needed for the magnets, with consistent quality and rigorous checks, was a monumental challenge for industry and CERN. The coil is inserted into an austenitic steel collar structure. Twelve million of these were produced for the LHC dipoles! Last but not least, the assembly of these components and the dozens of others which make up the magnets required the three firms which shared this contract - Alstom-Jeumont (France), Ansaldo Superconduttori (Italy), Babcock Noell (Germany) - to embark upon a lengthy learning process. First they each had to manufacture a pre-series of 30 magnets before they were awarded contracts for the production of all the dipoles. CERN teams were involved throughout the entire project, from the definition of the industrial processes to the quality control. The Laboratory itself tested certain assembly processes on site before transferring them to the companies. One of the innovative techniques developed by CERN was the welding technique STT (Surface Tension Transfer), by which the cold mass enclosure can be welded at an otherwise impossible rate and quality level.
The quadrupole magnets, although three times less numerous and bulky, were no less complex to build. They were designed to focus the beams and are positioned in the short straight sections along with other corrector magnets. They were designed and produced in close collaboration with the CEA-Dapnia Institute in Saclay (France) as part of France's special contribution to the LHC. After the first design parameters were outlined in 1989, numerous prototypes and technical modifications were required before the specifications could be finalised and the manufacturing contract awarded to the German company ACCEL, in 2000. Production was made even more complex by the great variety of these magnets - there are no less than 32 different types of arc quadrupole. Here too, the manufacturing process called for strong collaboration between the company and the laboratories.
The production of the LHC superconducting magnets is a fine example of collaboration between research laboratories and industry,' Lucio Rossi concludes. 'We have learned a great deal from this cooperation process and our industrial partners are now reaping the benefits of these specially developed techniques.'
