The Sciences

LHC 2009 Restart

Cosmic VarianceBy John ConwayFeb 9, 2009 9:39 PM


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After the devastating quench incident on September 19 of last year, resulting in the rupture of the cryogenic vessels within the LHC magnets , CERN has worked furiously to repair the damage, prevent any future similar failure, and get the LHC back to its commissioning program. Following a meeting of technical experts and the leadership in Chamonix, France last wee, the CERN Directorate has issued a press release with the new plan for LHC restart:

The CERN Management today confirmed the restart schedule for the Large Hadron Collider resulting from the recommendations from the Chamonix workshop. The new schedule foresees first beams in the LHC at the end of September this year, with collisions following in late October. A short technical stop has also been foreseen over the Christmas period. The LHC will then run through to autumn next year, ensuring that the experiments have adequate data to carry out their first new physics analyses and have results to announce in 2010. The new schedule also permits the possible collisions of lead ions in 2010. This new schedule represents a delay of 6 weeks with respect to the previous schedule which foresaw LHC "cold at the beginning of July". The cause of this delay is due to several factors such as implementation of a new enhanced protection system for the busbar and magnet splices, installation of new pressure relief valves to reduce the collateral damage in case of a repeat incident, application of more stringent safety constraints, and scheduling constraints associated with helium transfer and storage. In Chamonix there was consensus among all the technical specialists that the new schedule is tight but realistic. The enhanced protection system measures the electrical resistance in the cable joints (splices) and is much more sensitive than the system existing on 19 September. The new pressure relief system has been designed in two phases. The first phase involves installation of relief valves on existing vacuum ports in the whole ring. Calculations have shown that in an incident similar to that of 19 September, the collateral damage (to the interconnects and super-insulation) would be minor with this first phase. The second phase involves adding additional relief valves on all the dipole magnets and would guarantee minor collateral damage (to the interconnects and super-insulation) in all worst cases over the life of the LHC. One of the questions discussed in Chamonix was whether to warm up the whole LHC machine in 2009 so as to complete the installation of these new pressure relief valves or to perform these modifications on sectors that were warmed up for other reasons. The Management has decided for 2009 to install relief valves on the four sectors that were already foreseen to be warmed up. The dipoles in the remaining four sectors will be equipped in 2010.

That the delay would be a year, in total, was not unanticipated given the magnitude of the incident, and the good news here is that the root cause is now believed to be understood. The retrofit to the quench detection and pressure relief systems should prevent this from happening or causing such great damage in the future. Hopefully this was the worst of the birth pangs of the LHC! With such a complex and enormous machine, however, it would be overly optimistic to hope that it will be the last. The experiment I work on, CMS, is open now and in March we are going to remove the innermost detectors, the forward pixels, do minor repairs, and reinstall them by mid-April. We are taking advantage of the fact that so far, anyway, the detectors have not become radioactive from high intensity beam, after which any work on them will be far more difficult. And, we are preparing to do the physics once we do get data. The extra year, though painful, gave us extra time to refine our approaches, and physics will emerge faster as a result, I believe.

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