CERN releases preliminary failure analysis

By Phil Plait | October 19, 2008 10:15 pm

The mammoth Large Hadron Collider is offline after a pretty big malfunction during testing. CERN, the agency in charge of the LHC, has released its preliminary findings of what happened.

The current flow in the LHC depends critically on it being a superconductor. That means the electricity flows with almost no resistance (think of it like water flowing in a pipe that has no friction). For some reason — why it happened is still unknown — a small patch of resistance developed in the circuit. If left alone, something like this can cause massive damage; for example electricity flow can generate a vast amount of heat in such a patch. However, the LHC automatic safeguards kicked in, and appeared to work as designed.

However again, an electric arc was triggered, and we’re not talking about a little spark. It was big enough to punch a hole in the dewars containing the liquid helium needed to cool the magnets down to superconducting temperatures. The helium leaked out, and started to fill a region of the LHC which is supposed to be kept in vacuum. It also leaked out into the tunnel holding the LHC itself, causing some damage to the structure, including partially tearing the 1 ton magnets out of their brackets holding them down.

Yikes. So there is some mechanical damage, but it’s limited to where the problem occurred (other magnets appear to be fine). About 30 magnets were damaged, and they lost about six tons of helium, which needs to be replaced. The repair will take some time, as will figuring out exactly what happened, and, more importantly, why.

They’re being cautious about this, as you might expect:

Although the cause of the initial growth of connection resistance has not yet been established, and knowing that a similar event has not occurred in the test of all other sectors and of their thousands of connections, it has nonetheless been decided that additional measurements to generate early warnings and interlocks, improvements in pressure relief devices and in external anchoring of the quadrupole [magnet] cryostats with vacuum barrier will be implemented before any further powering of the LHC circuits at high current.

So they will proceed carefully, but I’m guessing they will have it up and running in a few months time, certainly sometime next year. This is a major setback for the program, of course, and will cost them time, money, and some PR, no doubt. But they will get it back up to speed, and soon they’ll be back in the business of science, poking and prodding the Universe on a quantum scale.


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