Full Speed Ahead for LHC Magnet Tests

Installation work at SM18, the facility that is testing all the magnets before they are installed into the LHC, has been completed.

With its final test bench now entering service, the SM18 Test Facility is now complete, and working at full capacity as it evaluates all 1732 dipole and quadrupole superconducting magnets that will go in to the LHC. The last of the 12 benches has been fully commissioned following installation of the final two Cryogenic Feed Boxes built by contractor Air Liquide.
SM18 aims to test between 12-14 magnets per week: each takes about 5 to 7 days to evaluate. Each test is run at 1.9 K (-271ºC), with magnetic fields being pushed as high as 9 Tesla.
More than 200 dipole magnets have already been accepted for the LHC. After very few quenches* they surpassed the magnetic field of 8.3 Tesla needed to bend the beam of 7 TeV protons within the LHC. 'The tests done so far were essential to validate the design and construction of the LHC magnets', says Andrzej Siemko, coordinator of the Test Facility construction. 'Feedback to the manufacturers is an important part of our work'.
Due to the tight LHC schedule, the quality of the magnetic field will not be measured at 1.9 K on all magnets. However, this will not affect the commissioning of the accelerator since all magnets are measured warm and a solid correlation between warm and cold measurements now exists.
The tests have their origins in 1994 when the first LHC prototype magnets were developed. The sophisticated measurement techniques enable SM18's control room operation crew to quantify the characteristics of these state-of-the-art superconducting magnets, each of which is 15m long and weighs 35 tons.
Assembling SM18 has been a tremendous team effort, involving several groups of the AB, AT and TS departments working over more than 3 years. The facility includes more than 3000 data acquisition channels for magnet tests and cryogenic control, 64 high current circuits, and more than 120 water cooled cables, each 10 cm thick and carrying 5 kiloAmps.
The only part of SM18's infrastructure that will eventually work with the LHC is the new refrigerator in an adjacent building: it will supply one octant of the ring with liquid helium, but everything else is specific to the Test Facility.
More than 100 people are now working full time on the tests, including some 40 CERN staff, and others from the industrial contract consortiums (ALLS and ICS). Getting the job done is a 24-hour-a-day commitment, with several teams always on duty.
'No superconducting magnet can ever be a perfect magnet,' says Vinod Chohan, who is responsible for magnet tests in cryogenic conditions at SM18. 'But every one has to be tested to see how close it is to being acceptable and perfect.'
Running the tests are staff from the Operation group of the AB Dept, who have been joined by a number of collaborators from India who are working on 1-year secondment contracts. The Operation team has developed a strong ethos that ensures continuity of expertise by transferring knowledge to newcomers, essential to the success of the collaboration.
'We went from accelerator and S.C. magnet physicists to industrialists,' says Louis Walckiers, Group Leader For Magnet Tests & Measurement. 'Every day we have to take decisions on the spot, change priorities and adapt, the same as in any production industry. It's very interesting, cutting edge, and a very demanding technical challenge.'
















* A quench, or resistive transition, occurs when a magnet passes from the superconducting to the conducting state and the heat produced generates resistance. A quench in a magnet would disrupt the entire LHC operating chain. (back)