At the 151st session of the CERN Council today, CERN Director General Rolf Heuer confirmed that the Large Hadron Collider (LHC) remains on schedule for a restart this autumn, albeit about 2-3 weeks later than originally foreseen. Following the incident of 19 September 2008 that brought the LHC to a standstill, a great deal of work has been done to understand the causes of the incident and ensure that a similar incident cannot happen again.
"Many new tests have been developed," said CERN's Director for accelerators, Steve Myers. "That's given us a wealth of information about the LHC splices, and confidence that we will be in good shape for running this year."
The root cause of the September incident was a faulty splice in the high-current superconducting cable between two magnets in LHC sector 3-4. New non-invasive techniques have been developed to investigate the splices, of which there are some 10 000 around the LHC ring, and determine whether they are safe for running or whether they need to be repaired. As part of this process, one more sector of the LHC, sector 4-5, is currently being warmed up. This will bring increased confidence that the splices are fully understood.
Sector 4-5 has been measured at a temperature of 80 K, indicating at least one suspect splice. By warming the sector, the results of this measurement can be checked at room temperature, thereby confirming the reliability of testing at 80 K. If the 80 K measurements are confirmed, any suspect splices in this sector will be repaired. More importantly, validation of the 80K measurements will allow the splice resistance in the last three sectors to be measured at this temperature, thereby avoiding the time needed for re-warming. The measurements in these sectors will provide the information needed to determine the start-up date and initial operating energy of the LHC in the range 4-5 TeV, since running at 4 TeV should be possible without further repairs, whereas 5 TeV could require extra work to be done.
A key part of the modifications being made to the LHC is the so-called quench protection system (QPS), which triggers evacuation of the stored magnetic energy quickly and safely should a part of the LHC's superconducting system warm up slightly and cease to be superconducting. Following the September incident, a new enhanced QPS system was designed and is presently under construction. The new system will be fully tested and operational in late summer 2009. This new system will protect the LHC from incidents similar to that of 19 September 2008.
Work on the new QPS is just one aspect of the work in the LHC tunnel being carried out by teams from CERN, supported by scientists from other particle physics laboratories around the world. New pressure relief valves are being installed, the ultra-high vacuum system is being improved, and the systems anchoring the LHC magnets to the floor are being strengthened. All of this contributes to preparing the machine for a long and safe operational lifetime.
"We've received an unprecedented level of support from physics labs and institutes around the world through the manpower they've provided to help us through the repairs and consolidation, as well as the invaluable advice we've received from the external committees that have studied the measures we're taking," said Professor Heuer. "It's a sign of the increasingly global nature of particle physics, and we're extremely grateful for the solidarity we're seeing."
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