In an age of blogs there are seemingly no secrets, so by the time Lyn Evans gave his talk on the status of LHC commissioning on 13 September, everyone seemed to know about plug-in modules, beam position monitors and transmitters embedded in ping-pong balls. All the on-line speculation made for interesting reading, and is a clear sign of the growing interest there is in CERN as we approach LHC start-up. We are now entering the final phase of commissioning, and things are going well given the unprecedented complexity of the task in hand.
Following the cool-down, powering and warm-up of Sector 7-8 earlier this year, we have learned a great deal about what it means to commission the LHC. There have inevitably been hitches, including the plug-in modules, or PIMs. When the LHC is cooled down, each sector shrinks by about 10 metres in length, and this has to be absorbed by bellows between components and a system of sliding copper fingers (PIM) that ensure electrical connectivity around the ring. When warming up Sector 7-8, a small number of fingers buckled as the machine expanded and are being repaired. The problem is understood, and concerns only a small percentage of the PIMs. To identify precisely where the problem occurs, an ingenious system involving blowing an object like a ping-pong ball with a 40 MHz transmitter (the frequency of the beam bunches seen by the position monitors) along the beam pipe has been devised.
Lessons learned from Sector 7-8 are being put into practice in other sectors. A second sector has been rapidly cooled to 80 degrees above absolute zero, a third is undergoing pressure tests, and testing of the remaining five sectors will now start at the rate of one every two weeks. In the sectors currently under test, vacuum leaks have been isolated and are also being repaired.
Meanwhile, the repair of the LHC’s inner triplet magnets is complete. A team from CERN, Fermilab, KEK and the Lawrence Berkeley National Laboratory has successfully completed the repairs. So far, three of the eight triplets have been installed and successfully pressure-tested in the tunnel. The remaining triplets are in the process of installation and pressure testing.
All of this is business as usual when bringing a new particle accelerator on-line. There are inevitably hurdles to be overcome, but so far there have been no show stoppers. We can all look forward to the LHC producing its first physics in 2008.