LHC investigates short circuit solutions

The start of the second run of the Large Hadron Collider was delayed this week due to a short circuit in one of its sectors. The location of the ground fault was quickly determined. The cause now also seems clear: a piece of scrap metal is the culprit.

Cern reports this on its website on Friday. The 27-kilometer-long particle accelerator would be fully started up again this week to slowly work towards the first proton beams around the end of May. Unfortunately, a short circuit or grounding problem last Saturday delayed a full restart of the machine. The short circuit occurred in the wiring of one of the magnets that are supposed to direct the proton beams. Solving the problem is made more difficult because the magnets are cooled to below -270 degrees Celsius with liquid helium. It takes weeks to heat up and cool down the magnets.

No permanent damage was done to the circuits in the plagued sector. A small piece of metal is probably the culprit of the short circuit, whereby contact is made between the tube functioning as ground and one of the cables that lead to a diode box that is located under the magnet. X-ray images of the sector have been taken to determine what the problem is likely to be. It can be concluded from the images that there is some clutter in the tube, but the results are not yet convincing.

An example of a diode box

Now ways are being sought to get rid of the piece of metal. The first way the technicians look is to send a surge of current through the wiring to try to melt the piece of metal. The hope is that the metal will burn up and the problem will be solved in no time. Another option is to increase the pressure of the helium in that particular cryogenic sector and then quickly decrease the pressure, displacing the object. Unfortunately, it may be the case that the piece of metal is causing problems elsewhere.

The third method requires heating up part of the cryogenic sector and opening up the part where the piece is located. This whole procedure requires everything to be heated up and then cooled down again. That takes about six weeks.

The LHC was also delayed in 2008 due to a defect. Then the particle accelerator suffered serious damage, which meant that the start of the LHC had to be postponed for a year.