Here’s an announcement from the CERN DG Rolf Heuer sent out to CERN employees today:
The foreseen shutdown work on the LHC is proceeding well, including the powering tests with the new quench protection system. However, during the past week vacuum leaks have been found in two “cold” sectors of the LHC. The leaks were found in sectors 8-1 and 2-3 while they were being prepared for the electrical tests on the copper stabilizers at around 80 K. In both cases the leak is at one end of the sector, where the electrical feedbox, DFBA, joins Q7, the final magnet in the sector.
Unfortunately, the repair necessitates a partial warm-up of both sectors. This involves the end sub-sector being warmed to room temperature, while the adjacent sub-sector “floats” in temperature and the remainder of the sector is kept at 80 K. As the leak is from the helium circuit to the insulating vacuum, the repair work will have no impact on the vacuum in the beam pipe. However the intervention will have an impact on the schedule for the restart. It is now foreseen that the LHC will be closed up and ready for beam injection by mid-November.
This is an extra two week or so slip with respect to the latest draft schedule I’d seen. In addition, the question of how to deal with defective splices remains open. Efforts now are directed towards determining what the maximum safe energy is, assuming that the cold sectors are not warmed up, with the plan to have an answer to this question by the second week of August. Part of this effort involves study of possible changes in the parameters that determine how quenches are detected and dealt with, in order to optimize the maximum safe energy.
Update: The latest CERN Bulletin is out, with more about this.