The last magnet on the bench

A ceremony was held on Thursday, 1st March, to commemorate the end of the cryostat assembly and cryogenic testing on the LHC super-conducting magnets. The team, consisting of CERN staff, several industrial support teams and a hundred guest engineers from India, have tested 2000 magnets over the last four years.

Test benches (and a single magnet) at the cryogenic test plant at the beginning of 2004.

The sound of popping corks mingled with the hum of helium refrigerators in SM18 on 1st March as CERN celebrated the long-anticipated end of assembly and cryogenic testing for the LHC magnets. About 2000 magnets have passed through the test plant's 12 benches.

For the last three and a half years, the testing team has been working 24 hours a day for ten and a half months out of every year. 'It's really a big job just to test one magnet,' said Louis Walckiers, leader of the Magnet Tests and Measurement group. 'It takes 24 hours just to cool the magnet down to 1.9 K.' The process of checking the magnet for electrical and magnetic performance at the temperature of superfluid helium (1.9 Kelvin) could take anything between 15 hours and a week or more. Now, the 1,232 dipoles and 474 quadrupoles that have passed the test are in the final stages of installation in the LHC.

Before the cryogenic testing, the magnets had never been tested at the temperature of 1.9 K at which they will perform in the tunnel, since none of the production sites had the necessary facilities. 'This is the first and last functional test before the magnets are installed in the machine,' said Philippe Lebrun, head of the Accelerator Technology Department. Faulty magnets must be rejected or repaired before installation, since it is difficult to extricate them from the LHC once they have been integrated into the machine. A badly manufactured superconducting magnet can literally burn a hole in itself and have to be replaced entirely. 'If that happened here, the magnet would just be lost,' Walckiers said. 'If that happened in the machine, it would mean one to two months downtime just to change it. That would be a real nightmare.'

Once the magnets are all installed in the tunnel in April, there will be one final cooling and powering test in the tunnel itself. If a magnet has to be repaired, it will subsequently be retested. 'We should feel relieved but we still have a lot of similarly difficult activities to perform,' said Lebrun. 'So actually we don't have time to feel relieved.' Half of the benches in SM18 will still be active over the next couple of years as further measurements are made on the magnets to prepare for beam acceleration. For Vittorio Parma, leader of the Cryostats Section in the Magnets, Cryostats and Superconductors group, it feels as though he has finished a long race. 'I'm exhausted, but happy,' he says.

For more information, see Bulletin No. 47/2006.

Louis Walckiers, leader of the Magnet Tests and Measurement group, addresses the crowd.

Ceremony celebrating the end of cryostat assembly and cryogenic testing of the LHC super-conducting magnets on 1st March.