LS1 report: achieving the unachievable

The dismantling and extraction of a defective DFBA module from LHC Point 6, announced a few weeks ago, has been completed without a hitch. The DFBAs in the LHC are unique and irreplaceable components that must be handled with care.

Dismantling and extracting part of an electrical feed box (DFBA) had not been planned and could not have been foreseen. Nonetheless, that is what had to be done. When the LS1 teams discovered that the bellows of one of the DFBAs in Sector 5-6 were damaged – and completely inaccessible – they were not exactly overwhelmed with solutions. In fact, they had only one option: to dismantle them and take them up to the surface.

Step 1: measure the alignment of the module to be taken out in relation to the beam lines to ensure that when the DFBA is put back in, it is in the right position for the beam to pass through. For that, a precise survey was carried out by CERN’s surveyors. Next, the superconducting cables and cryogenic pipes were disconnected by a team of experts from the TE-MSC Group.

Finally, it was time for the dismantling. The module in question, which weighs almost two tonnes, is a particularly tricky part. "This part of the DFBA, known as a 'shuffling module', was not, in principle, designed to be removable from the rest of the electrical feed box," says Antonio Perin (TE-CRG), project leader for the consolidation of the DFBAs during LS1. "So the dismantling, coordinated by Didier Lombard (EN-MME), was a delicate job to say the least." So much so that the superconducting cables that pass through the module could not simply be cut, but rather had to be fully disconnected, two metres further along, by a team of experts from the TE-MSC Group. The cables therefore had to be extracted from the module before it could be moved.

"Given the complexity of the operation and the fact that it had never been done before, we enlisted the help of numerous highly qualified people from various CERN departments (EN, TE, BE), possessing expertise in various fields (such as transport)," says Said Aiteh (EN-MME), coordinator of LS1 welding work. "Together, this team ensured that the dismantling and extraction was a success." The module is now in Building 112, where the EN-MME team is repairing it. It is scheduled to be reinstalled in its original position in early 2014; an operation that promises to be equally delicate.

Three other defective DFBAs have been identified in the LHC, of which one has already been repaired in situ and a second one is due to be repaired in situ shortly. The third, however, poses more of a problem. In all likelihood, it too will have to be brought to the surface like the Point 6 DFBA. Watch this space.