Looks like the LHC will miss its run this year.
Every once in a while, one of the 1232 superconducting dipole magnets that bend the beam can heat up to above the critical temperature, causing it go from being superconducting to normal conducting. This rise in temperature is usually caused by some small misalignment in the beam, causing a few stray particles to hit a magnet. Once this happens, the current passing through the magnet’s now significant resistance causes it to heat up like crazy – parts of the magnet can be heated up from -271 to 700 deg C in under a second! This is known as quenching, and it comes as no surprise to particle physicists, who have been dealing with it since superconducting magnets where first used in the Tevatron. They’ve come up with effective ways of dumping the heat and dealing with the problem – the LHC has failsafes built in to deal with quenches effectively, and they should normally be back online after a quench in a matter of hours.
However, in this case it seems that the quench was caused due to a faulty electrical connection between two magnets that likely melted at high current, resulting in mechanical failure and a leakage of liquid helium into the tunnel. The sector (number 23) of the ring will have to be warmed up for repairs, and the cooled down after. The process, which would take a few days to fix in a normally conducting machine, will delay the LHC by two months!
This news comes as a bit of a disappointment, as the experimentalists were hoping to use this years run with a lower energy beam to calibrate the detectors. It looks like they’ll now probably have to wait until the LHC runs at full energy in 2009. However, as long as next years run is not delayed, this should hopefully not be a setback to physics.
For more thorough coverage:
The US LHC Blog has very informative coverage
Last december’s issue of symmetry has an excellent fact-filled article on quenching
CERN has put up a press release
And you can see the incident and the progress of the warmup for yourself here