CERN has reported that an incident occurred at mid-day on 19th September during commissioning of the final LHC sector, resulting in a large helium leak into the tunnel.

During commissioning, without beam, of the final LHC sector (sector 34) at high current for operation at 5 TeV, the incident occurred.

Preliminary investigations indicate that the most likely cause of the problem was a faulty electrical connection between two magnets, which possibly melted at high current leading to mechanical failure. There was no risk to people, CERN notes.

A full investigation is underway, but it is already clear that the sector will have to be warmed up for repairs to take place. This implies a minimum of two months down time for LHC operation, perhaps inevitable for the sheer magnitude of the project – as the most powerful particle accelerator in the world and one of the most significant scientific projects in recent history.

For the same fault, not uncommon in a normally conducting machine, the repair time would be a matter of days.

CERN notes that further details will be made available as soon as they are known.