Last week was the annual Fermilab User’s Meeting, for all sorts of interesting talks see here. These included a talk by Sergio Bertolucci giving recent news about the LHC status. This week CERN is hosting a CERN-Fermilab Hadron Collider Physics summer school, talks here, including one from Jorg Wenninger about the LHC status.
The main concern now involves bad soldering of some of the 1700 or so bus-bar inter-connections between magnets. One of these seems to have been at the origin of the accident last September. For the sectors (four of them) that are warm, such bad joints can be identified relatively easily, by their higher-than-normal resistance, and repaired. Unfortunately, for the four sectors that are now cold, identifying such bad splices is much more difficult. Warming up these sectors and cooling them back down is a time-consuming process that could significantly push back the LHC schedule.
Late last week the decision was made to start warming up sector 45. Measurements at 80K had identified 3 cases of anomalously high resistance. The plan is to warm up the sector, take measurements which can be compared to the measurements made when the sector was cool, and fix splices as necessary. For this particular sector, things can be rearranged so that warming it up and cooling it back down will not seriously impact the schedule.
For the other three cold sectors though, the situation remains unclear. They’re gathering more data and analyzing it, trying to understand better what is going on, as well as analyzing the question of whether it’s possible to go ahead and find ways to run the machine safely, even given the possible existence of somewhat iffy interconnections.
The latest version of the schedule, from mid-last week, has powering tests ending in mid-October. So, as long as it does not turn out to be necessary to warm up more sectors, late October is the time-frame for trying again to circulate a beam and begin beam commissioning.
Update: There’s a video of Wenninger’s talk last week available here, where he gave some more details in the question session afterwards. Sector 45 will be warm and ready for measurements next Monday (June 22). If the results show good correlation with what was measured at 80K, at the end of the month the temperature of the three remaining sectors will be stabilized at 80K and measurements will be made on those.
About the current schedule for when to try and circulate a beam, he says “I know that officially it’s still September [last week] but I have problems to sell that…” with a better guess of sometime in October (assuming the three sectors at issue don’t need to be warmed up). He also remarks that it will be a while (2012?) if ever before the machine operates at 7 TeV. 5 TeV is the likely energy at the beginning, with a possibility of going up to 6 TeV.