How was the LHC repaired?

A short-circuit caused by a tiny defect in a weld warmed up and vaporized liquefied helium that cooled down the accelerator. The metal envelope did not sustain this sudden extra pressure and about 50 magnets were damaged. The repair work lasted one year. 53 magnets were removed, repaired, tested and reinstalled. A program for reinforcing the ground fixing of the magnets has been launched. 900 new helium pressure relief valves have been installed. They allow the release of 10 times more volume of gas than the previous ones. A new system for the detection of the least electrical resistance on the cables linking the magnets has been installed. Now a resistance over 10-9 ohms is detected (the failed weld had an electrical resistance of 100*10-9 ohms). The inside of a 4-km long part of the envelope has been cleaned carefully. (A.C.)