LHC Delay

So, by now, I'm sure you've read about the LHC delay until April 2009 (if not, read the official press release, and then come back). Don't worry, we have plenty to work on until then! I was bummed at first, but I'm sure this will make first collisions even sweeter!

While they're trying to make the tunnel safe and warm up the magnet enough for the engineers to get in there and really assess the damage, I thought I would remind you all what we're dealing with:



These magnets are HUGE! And really complicated. And really cold (because they have to be superconducting...). I found a nice explanation:

To harness the powerful beams of protons and steer them around the ring, scientists have to create strong magnetic fields. This requires superconducting electromagnets, whose wire coils can carry large electric currents with virtually no resistance. For the wire to become superconducting, the magnets must be kept very cold—in this case at a temperature of -271 degrees Celsius, close to absolute zero.

And the meaningful part for me is that although other accelerators (like the Tevatron at Fermilab) have used superconducting magnets before, the LHC magnets are really pushing the current limits of technology. Plus, each magnet stores a lot of energy. What happened last Friday was a quench. That means that the magnet all of a sudden was no longer superconducting, so it released a lot of energy.

When a quench begins, the beams are shut down and power to the affected magnet is immediately cut. Then heaters fire up, quickly raising the temperature of the whole 14.3-meter-long, 35-ton magnet and dissipating the energy.

Usually, this procedure should mitigate the damage. But something went wrong this time (according to the press release, possibly a bad electrical connection), and caused a lot of cold Helium gas to fill the tunnel. No one was hurt, because no one is allowed in the tunnels when the machine is running (there are lots of strict safety procedures), but any sort of damage to the accelerator pieces in that sector needs to be fixed before we can start running again.

On a positive note, one journalist (Lewis Page, of the Register) jokes that the last time physicists at CERN had some downtime, Tim Berners-Lee invented the World Wide Web :)

A bientôt!