Magnet damaged in LHC accelerator, probably out of operation for weeks

20 July 2023

The Large Hadron Collider at CERN in Geneva is likely to be out of operation for weeks after an electrical disturbance and emergency shutdown early Monday, July 17. In the process, one of the magnets was damaged.

Ripening on the damaged triplet magnet in the LHC accelerator at CERN.

Without proton beams, scientific experiments at CERN are at a standstill. Nikhef is closely involved in three of them: ATLAS, LHCb and ALICE. The interruption comes at an unfortunate time: LHC was on its way to record proton beam production in recent months.

The incident on July 17 triggered a split-second stop procedure in which the beams are neatly dumped. In the process, some magnets in the 27-kilometer-long accelerator ring lost their superconducting state. This is not unusual and usually not a major problem.

However, inside the magnet in question, a triplet focus magnet near the LHCb experiment, mechanical stresses during the stopping procedure caused a small helium leak to the insulating vacuum in the accelerator tube.

As a result, liquid helium entered the vacuum shell, which consequently became gaseous and took away the insulating vacuum. The outer wall of the magnet cooled to the point that frost froze on it. This is visible in photographs of the magnet.

In a brief announcement on the CERN Web site, the head of CERN’s accelerator section, Dutchman Rende Steerenberg, said Wednesday that the affected magnet needs to be repaired at room temperature. “The incident is likely to have great impact on the LHC work schedule, resumption of the beam is certainly going to take weeks,” Steerenberg said.

Update July 26: Meanwhile, CERN technicians have opened and inspected the damaged magnet. It is expected repairs will take several weeks. Whether the proton beams will return in full after that is still uncertain. Preparations may be made in the fall for beams of heavy ions, such as lead nuclei, for the ALICE experiment in particular.

Aug. 3 update: The damaged magnet has been repaired after heating up and is being cooled down again. “Beam restored in September,” CERN said.