Production of short straight sections hits 100 units
The 100th short straight section for the Large Hadron Collider was assembled at CERN at the beginning of April. These units combine superconducting quadrupoles and other multipole corrector magnets, housed in their cryostats, which are used to guide, focus and fine-tune the beam in the LHC. Building 904, where the 474 short straight sections are being assembled, is often called "Lego Land" by the workers, with a touch of humor and pride because of the wide variety of these sets of magnets and cryostats .
Probably very few people are aware of the hard work going on in building 904 in Prévessin. A 2000 m2 hall, formerly a machining workshop, at the rear of the building has been refurbished and organised for the assembly of the 474 short straight sections (SSS) needed for the LHC. Since the site became operational in January 2004, the production rate has gradually ramped up and last week the 100th SSS was finished.
Although much shorter than the 15-m long dipole units, the SSS are much more complex as they consist of various combinations of dipole, sextupole, octupole, and tuning-quadrupole corrector magnets, coupled with variations in the cryogenic and vacuum layouts. In all, 55 types of SSS cryostat are required, depending on the various combinations of cold masses (87 varieties) and the specific cryogenic and electrical powering schemes required by the topology of the LHC.
Assembly of the SSS was initially foreseen to be carried out in European industry, but in December 2003, due to the insolvency of the contractor and to avoid schedule slippage in re-tendering, CERN decided to in-source the activity under the responsibility of the AT-CRI group. As Vittorio Parma, Project Engineer in charge, explains, this set a new challenge to perform work at CERN more typical of industry. The engineers of CERN's Cryostats & Interconnections (CRI) group had to establish a network of more than 10 major suppliers of cryostat components, keeping the original suppliers whenever possible. Meanwhile the infrastructure and specific assembly tooling had to be set up in the new assembly facility in building 904. With limited human resources, a CERN team specifically dedicated to engineering, quality assurance and production follow-up was created, and by amending an existing contract with the ICS consortium, the resources to execute the activity were made available, with the aim of working on a result-oriented basis. Two service contracts for leak-detection tests and weld inspections were also established with the firms AL43 and IS respectively. At present, some 40 people from the three contractors work in close collaboration: mechanical technicians, welders, crane operators, electricians, electro-mechanical technicians, vacuum technicians and weld inspectors.
The work consists of assembling within their cryostats the cold masses for the superconducting quadrupoles of the LHC arcs, which are produced by the German company Accel under a contract supervised by the Magnets & Superconductors group (AT-MAS), and the so-called "insertion region" qua-drupole cold mas- ses, which are made at CERN by the Magnets and Electrical Systems group (AT-MEL). Hundreds of components have to be put together, involving mechanical fitting, welding of more than 5 km of leak-tight and 20-bar pressure pipelines in stainless steel and aluminium that will operate at cryogenic temperatures, and routing and brazing of the superconducting cables of the magnets and of the instrumentation wires required to monitor the operation of the magnets. Some 2500 leak-detection tests, using helium mass spectrometry, are required to check the tightness of the cryogenic circuits. Extensive electrical control work, to check the integrity of the magnet instrumentation and electrical circuits throughout the assembly of an SSS, must also be carried out. All the work is executed to a high standard, following detailed quality assurance procedures and with strict inspections.
The technology transfer from CERN to ICS is now coming to an end, and the hand-in-hand experience achieved during this first year of work is now showing its benefits: a stable production rate of some four SSS per week is now being achieved and augurs well for finishing the remaining SSS by the end of 2007. The challenge is yet to be won, but a solid basis has been set.
