Those responsible for the LHC machine are having their yearly meeting this week in Chamonix to discuss the state of the project and plans for the future. Last week a subgroup met to discuss plans for beam commissioning to 3.5 TeV/beam, starting next month. The current schedule envisages beam commissioning to restart around February 19, and best estimate is that it will take about a month to establish safe, stable 3.5 TeV beams and begin extended runs for physics purposes. There’s a plan for a big media event when first collisions are achieved at 3.5 TeV/beam, something that may require discouraging experiments from announcing observation of high-energy collisions that happen before the planned moment (evidently this is what occurred last year, when Atlas saw 1.18 TeV/beam collisions before they were supposed to…).
This year’s schedule includes a possible one-month stop mid-year to increase the beam energy from 3.5 to 5 TeV, but based on the discussions at Chamonix, this looks very unlikely. The most serious problem with the LHC remains the bad splices which are known to exist in the machine, as well as sectors where definitive measurements of all the splices have not been possible (they would require warming up the sector, causing delays of months). The current knowledge of the splices leaves no room for error, even at 3.5 TeV, and going to 5 TeV would require warming up parts of the machine, something which cannot be done during a 1-month stop.
Discussions are beginning about how long a stop for repairs should be planned for after this year’s run ends in November. To be able to run at 5 TeV/beam will probably require keeping the machine off until May 2011 to fix splices. Going to the design energy of 7 TeV may require even more extensive work on the splices, work that could keep the machine off for all of 2011, with startup again in 2012. To get above 5 TeV, work also needs to be done on retraining the magnets through repeated quenches. Not much of this would be needed to get to 6.5 TeV/beam, but to go all the way to 7 TeV, problems that are still not understood with magnets from one manufacturer will have to be addressed.
Update: From the Chamonix summary talk, there are two main scenarios now being considered. In the first, the energy of the machine would stay at 3.5 TeV/beam this year and next, with .1-.5 fb-1 integrated luminosity in 2010, 1 fb-1 in 2011, then a year-long shutdown in 2012 to fix all splices before moving to 6.5-7 TeV/beam. In the second, splices would be fixed in stages, running for only 5 months in 2011, at 5 TeV/beam, 1 fb-1 integrated luminosity.
There will be a summary session at CERN next Friday.
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