By Ron Cowen
The Large Hadron Collider, poised to become the world’s most powerful atom smasher, won’t reopen for business until the end of June at the very earliest, rather than in April as scientists had previously estimated. Actual collisions between protons might not occur until even later in the summer.
The accelerator was shut down in September after a faulty electrical connection between two magnets led to a leak of helium gas in a 3-kilometer section of the collider’s 27-km–long underground racetrack.
The electrical problem and leak affected magnets in the section and also scattered soot and chips of insulation material into the beam pipe, according to a report released December 5 by the European Organization for Nuclear Research, or CERN, which operates the collider and is based in Geneva.
The accelerator is designed to collide beams of protons together at unprecedented energies of 14 trillion electron volts as a way to search for exotic elementary particles, including the invisible dark matter believed to make up most of the mass of the universe. The circular, underground tunnel in which beams will collide straddles the border between France and Switzerland.
Engineers have already removed 28 magnets from the affected tunnel section and brought them above ground, where the devices will either be cleaned or repaired. Another 25 magnets will be hauled up by the end of December.
The electrical short contaminated beam pipes with soot. The pipes must now be replaced or cleaned. Inspectors have found chips of insulating material in the beam pipe at large distances from the leak, but these can be removed by simple vacuuming.
In a more time-consuming effort, engineers will also increase the number and size of pressure release valves throughout the underground accelerator, in order to minimize damage from any helium gas leaks that might occur in the future.
Given the time needed for final pressure tests and for cooling down to the operating temperature of 1.9º above absolute zero the repaired section won’t be ready to receive proton beams until late June. But the first collisions might not happen until some time later in the summer, says James Gillies, spokesman for the LHC at CERN. It’s possible, he adds, that CERN may be conservative and not collide proton beams at their maximum possible energy in 2009. Running the beams at lower energies presents less risk of triggering an electrical short, Gillies says.
