On Friday September, 2008 a large helium leak occured in the tunnel due to an incident which happended during commissioning (without beam) of the final LCH Sector (sector 34) at high current for operation at 5 Tev. However CERN ’s strict safety regulations ensured that there is no risk to people at any point of time.
The full reasons for the incident are being investigated. As for Preliminary investigations most likely cause of the problem was indicated at a faulty electrical connection between two magnets, which probably melted at high current leading to mechanical failure.
As per the report of CERN a full investigation is underway, but it is already clear that the sector will have to be warmed up for repairs to take place. Which implies a minimum of two months down time for LHC operation.
One may remember that on 10th September, 08 collider completed its successful startup, where it could make beams of protons circle in both clockwise and counterclockwise directions in the collider. However I just like to remind the readers that after a week after it first test it was closed because an incident.
The Collider was Shut because of a failure of a power transformer on one of the surface points of the LHC causing switch off the main compressors of the cryogenics for two sectors of the machine.
After this effort were immediately started to recover cryogenic conditions. Hence the transformer, weighing 30 tonnes and with a rating of 12 MVA, was replaced over the weekend thus the machine was lowered back to operating temperature to prepare for a resumption of operations.
However now it has been understood that the problem is even more severe, hence at least two months before it can start working.