What Happened to the CERN Large Hadron Collider

Liquid Helium Leak & Warming Magnets Shut Down LHC until April 2009

Nov 24, 2008

Shortly after the CERN Large Hadron Collider accelerated its first protons, an accidental liquid He leak caused some magnets to warm up and necessitated repairs.

On September 10, 2008 CERN's Large Hadron Collider (LHC) accelerated its first protons amid considerable fanfare as well as unjustified trepidation. The goal was to finish the initial testing and to start doing physics by the end of October 2008. However as of this writing in November 2008, there has been little news coming from the LHC. What happened to the Large Hadron Collider?

Accident Damages Magnet

An accident occurred on September 19, 2008. It was not the type of accident that would put many lives in danger. Rather it was the type of accidental equipment mishap that damages equipment without endangering the public. The mishap caused some of the powerful magnets in the LHC to fail.

LHC Superconducting Magnets

Magnetic fields exert forces on moving protons, electrons, and other charged particles to alter their paths. The Large Hadron Collider therefore uses powerful superconducting magnets to steer the accelerated high energy protons. These magnets cost roughly one million dollars each.

The superconducting magnets are electromagnets in which a current passing through wire coils produces a magnetic field. However the wire coils are cooled to a temperature of 1.9 Kelvins (1.9 degrees above absolute zero) with liquid helium. At this low temperature the wires in the coils become superconductors. Superconductors have no electrical resistance. Hence as long as the coils stay cool, the electric current continues to flow and the coils remain magnetized.

Liquid Helium Leak

The September 19 accident was a leak in one of the liquid helium pipes used to keep the superconducting magnets cool. One to two tons of frigid liquid helium leaked out and evaporated. Of the LHC's 1232 bending magnets, 154 warmed up as a result of this leak. It will take some time for the necessary inspections and repairs.

The cause of the mishap must be isolated and fixed. Tentatively it seems to be an electrical fault. Then the magnets must be inspected for damage and any damage must be repaired. Finally the superconducting magnetic coils can be recooled.

The magnets, however, cannot be cooled quickly; they must be trained. The LHC magnets are so powerful that their magnetic field tugs on the coils enough to alter their shape. The training process involves slowly increasing the current in the magnets so that the coils can settle into their final position. Each time the magnets warm up they must be retrained and recooled.

When Will the LHC Be Working Again?

The repair process takes some time. In addition the LHC has a mandatory winter shutdown when energy costs are highest. Hence the LHC will be shut down at least until April 2009.

By then the repairs should be complete and the Large Hadron Collider should again be operational. If nothing else goes wrong, high energy particle physicists will be able to resume their search for the Higg's Boson and test the standard model of particle physics.