A talk at CERN today by Jorg Wenninger gives an update on the problems at Sector 34 and more information about what the prospects are for restarting the machine next year.
The cause of the accident has been identified as excessive resistance in a busbar interconnection between two magnets. Looking at logged data from before the accident, evidence for this excessive resistance was seen. Checking all the other sectors, a hint of a similar problem was found in one other cell, and that dipole will be replaced.
50 magnets are in the process of being removed from Sector 34, all to be out by Christmas. To avoid future similar accidents, the quench protection system is being upgraded, and the commissioning procedures will include a systematic search for excessive resistance problems. These measures can be implemented before next summer. There is also a plan is to add pressure release valves on every dipole cryostat, but this is highly problematic since it will require warming up all the sectors and likely would not allow the LHC to run with beam during 2009. The summary for 2009 plans reads:
Restart in (late) summer of 2009 with beam. Beam intensity and energy limited to minimize any risk.
No beam before a complete ‘upgrade’ of the pressure relief system is implemented on all sectors. Excludes beam in 2009.
Final decision in February?
On a more cheerful note, tonight PBS will be broadcasting a documentary about the search for the Higgs at Fermilab called The Atom Smashers. It looks like this program should be about 10^(10^5) times better than a recent one featuring theorists. One of the filmmakers has a blog here. With the LHC out of commission for a while, the Higgs search at the Tevatron is where the action is, and the experimenters there may be the ones to find the Higgs or rule it out.
Update: Two more recent presentations with information (including pictures!) about the LHC accident, repairs and plans for the future are here and here. For now, the plan is for the machine to be cold again next July.