As of my last post on the LHC, following the quench incident on Sept. 19, little was known about the cause of the incident nor the extent of the damage. In fact, so much liquid helium was released into the tunnel in the affected sector of the machine that it was too cold for people to enter until last week. A colleague of mine quoted the team who entered the sector as saying that when they got to the magnets that were affected, “it wasn’t a pretty sight”.
CERN has released a report today giving an initial summary of what happened and the extent of the damage, and indeed it turns out to have been quite serious: 24 of the long dipole magnets and 5 of the quadrupole magnets (which focus the beam) suffered serious mechanical damage when the liquid helium enclosure between two of the magnets ruptured, allowing helium into the vacuum jacket surrounding the enclosure. This led to a chain of events which resulted in an extreme overpressure in the vacuum jacket on a long chain of magnets, seriously damaging them. The forces were great enough to physically tear the magnet stands out of where they were bolted to the concrete floor.
Normally CERN shuts down accelerator operations every winter due to the high cost of electricity in the winter (Europeans mainly use electricity for home heating) and this was foreseen for December. Repairs to the damaged sector will proceed in parallel with the previously scheduled work during the shutdown. But clearly any hope of high energy colliding beams in 2008 was lost following this incident, and it looks likely to be months before the machine will turn on again. At that point, there is still a many-week period of commissioning before the machine can collide protons at high energies, probably 10 TeV initially.
But now the tough questions: what was the ultimate cause of this incident, and what can and must be done to prevent a similar occurrence in the future? The report concludes optimistically that improved quench detection systems and increased pressure relief devices will ensure safe powering of the machine. I take that to mean that they will do a retrofit on the entire 27 km accelerator. I guess we’ll see how long it really takes. The Director General’s statement accompanying the report only says the machine could be restarted “in 2009″…