End of the line to build a circle

The installation of the cryogenic distribution line in the LHC tunnel is finally finished! All the sectors have undergone pressure and helium leak tests at room temperature, and one complete sector was cold tested in cryogenic conditions.

Some of the QRL team in UJ22 of the LHC tunnel, where the last sector of the cryogenic distribution line was installed.

It must have been a joyous moment in UJ22 of the LHC tunnel (near Point 2, Saint Genis Pouilly) on 19 October. This was where the last external weld of the cryogenic distribution line, also known as QRL, was made, thus completing the full distribution ring. The QRL is a circle built in 8 sectors, each approximately 3 km in length. It will circulate helium in liquid and gas phases, at different temperatures and pressures, to provide the cryogenic conditions for the superconducting magnets in the LHC tunnel.

The last sector installed (sector 1-2) passed the pressure and helium leak tests at room temperature on 28 October. As part of the warm test, each sector was pressurised to 1.25 times its design pressure and maintained at this value for one hour to validate its mechanical design. During the pressurisation, the helium signal in the insulation vacuum was checked for internal leakage. All sectors successfully passed the pressure and helium leak test - an excellent result considering that each one is comprised of about 2100 internal welds.

Sector 8-1 and a portion of sector 7-8 were cooled down to between 20 to 4 K for cold testing. Measurements of heat leaking into the cold internal components from the exterior at room temperature showed that the specified values were achieved. The equipment needed to perform these tests were designed and made at CERN especially for the QRL. Data from all the instrumentation were continuously monitored and recorded by a dedicated data logging system.

The installation of the QRL originally commenced in August 2003. Series productions of its components were subcontracted to five European companies (Air Liquide, 2C, both in France; Simic in Italy; FCM in Spain; Tuboplan in Portugal), each dedicated to particular types of modules. The project was fraught with problems during different stages of realisation. In May 2004, the production process was interrupted following the installation of the first sector, as technical and quality issues emerged, such as faulty components and poor quality welding. The junction region of all the sectors had to be redesigned, with corresponding repairs made to the first sectors that were installed. Some internal sliding supports also required reinforcement to increase their resistance to impacts. As a result, the entire first sector installed (sector 7-8) had to be removed, repaired and reinstalled by CERN. Further delays were minimised thanks to the dedication of the teams who carried out the repairs, both outside and within the Cryogenics for Accelerators Group (AT/ACR). The sliding supports were mainly fixed by members of the ICS consortium, who even worked throughout the Christmas period in 2004 (Bulletin no. 03/2005). A number of magnet test personnel also provided a period of assistance. The service modules were repaired by a team of 14 people from the TS/MME group, who worked long hours for about a year to complete the job (Bulletin No. 28-29/2005).

New specifications for the sliding supports were drawn up in collaboration with the manufacturer Air Liquide. The external supports were also redesigned and reinforced following further calculations. To help meet the LHC's schedule, production capacity was scaled up to at least twice its original size. Air Liquide recommenced the installation of the remaining seven sectors at the end of 2004. After the original installation of the first sector, the quality assurance plan was largely improved, with detailed installation procedures drawn up. The installation activities were followed daily by Air Liquide supervisors and CERN inspectors.

The core QRL team of approximately 100 people (~30 from CERN and ~70 from Air Liquide) must be breathing a collective sigh of relief. 'In about 11 months the seven sectors installed by Air Liquide have been pressure and leak tested, and one of them has been fully tested in cryogenic conditions. It's very satisfying to have finished after all the problems we've experienced,' said QRL project leader Germana Riddone. 'The contractual part of the project will end in a few weeks time. With respect to the contractual schedule, the QRL completion was delayed by 10 months. The delay was minimised thanks to the hard work put in by all the groups inside and outside the AT department. All the eight sectors will be individually tested with the magnets, with the cool down of the last sector scheduled at the end of September 2007.'

Did you know?

Each sector of the QRL is composed of 238 straight pipe elements, 30 vacuum barrier and fixed point elements, 38 service modules (of 15 types), and 10 other components such as steps and elbows. The overall QRL installation process was carried out by six teams spread over two to three sectors. The installation of a sector involves about 325 elements with around 700 external supports, corresponding to approximately 2000 internal and 700 external welds.