Monday, July 27, 2009

Smashup at an Atom Smasher in Europe

Accidents at high-energy physics labs do not normally make the news. But when the lab is the European Union's crown jewel consortium CERN, and the accident puts their latest and greatest accelerator, the Large Hadron Collider, out of commission for up to a year, the incident is worthy of wider attention than it has gotten so far.

America used to dominate the field of experimental physics, as our first-out-of-the-gate development of nuclear weapons proved. But with the political collapse of the Superconducting Supercollider project, a Texas-based particle accelerator that was cancelled in 1993, the world leadership in high-energy experimental physics began to move to Europe, where last September the Large Hadron Collider was being put through its initial tests.

State-of-the-art particle accelerators are some of the most complex experimental systems ever built. The LHC resides in an underground tunnel 17 miles in circumference under the border between France and Switzerland. The basic idea is to shove atomic nuclei around a huge evacuated pipe with the aid of strong electromagnetic fields and the guidance of monstrous superconducting magnets that have to be submerged in tons of liquid helium. Such enterprises are of course very costly in comparison to more modest laboratory equipment, but a $5 billion expenditure these days when the U. S. Congress is cogitating about health-care programs costing 200 times that much doesn't seem like a lot of money. Nevertheless, you want to protect your investment even if it is only $5 billion, and that seems to be what got damaged the most in last fall's accident.

Superconducting magnets are used because once you get current running in them, no electrical power supply is needed for the magnet itself. To produce the tremendous magnetic fields needed with conventional magnets would require prohibitive amounts of power. But running a superconducting magnet is not a trivial task. The LHC's magnets have to be cooled down to about two degrees C above absolute zero, and only large amounts of liquid helium can do that. So CERN became the world's largest user of helium in its attempt to cool down all the magnets for their inaugural run of the LHC last September.

Nine days after the tests began, an electrical connection between two superconducting magnets apparently failed. In a normal magnet, this would not be that much of a big deal, since an open connection would just cause maybe a transient electrical discharge and then the whole thing would shut down. But with a superconducting magnet, a bad connection causes heat. Heat causes a superconductor to abandon its main desirable property, which is to be superconducting with no resistance. Once some resistance shows up, that generates more heat because the current cannot stop instantaneously in a large magnet. The heat boils off more helium, more of the magnet heats up and gets resistive, and you have a great big vicious circle called a "quench."

Being very large magnets, the LHC units quenched in a big way. The helium pressure was so high it blew all the way into the vacuum tunnel and spread insulation and trash everywhere. Since CERN policy is to clear the tunnel of personnel any time tests like this are going on, no one was injured. But successive press releases in the weeks and months after the accident cited longer and longer delays before the system could be up and running again. As of this writing (July 2009) repairs are still being made, and hopes now are that the LHC can go online again sometime this fall.

While the CERN managers are to be congratulated that this accident didn't hurt or kill anyone, having a multi-billion-dollar machine damage itself to the extent that it takes a year to fix is not exactly wise use of resources either. Any system as complex as the LHC will do unexpected things when first fired up, and CERN has decided to install fault detectors as part of the repair process that will give advance warning of a possible quench condition in the future. This is wise, prudent, and consistent with the highest engineering ethics principles. We just hope it will prevent such accidents in the future.

Which brings us to the larger question: what is all this billions of dollars of machinery and personnel good for? The holy grail of high-energy physics research right now is a thing called the Higgs boson, named after one of the six or seven theoretical physicists who thought of the concept in 1963 and 1964 (somebody had to be first, and it was Peter Higgs). According to the most widely accepted model of subatomic particles, called the Standard Model, the Higgs boson somehow gives mass to all elementary particles (such as electrons, I suppose) that have mass. No one knows how heavy this Higgs boson is, but guesses range from about the weight of a silver atom's nucleus on up. The problem with making really heavy particles like this in a particle accelerator like the LHC is, you need a lot of energy per particle. Current machines can get up to 120 billion electron-volts of energy (120 GeV) into a particle, and the LHC is supposed to reach values about ten times higher. When it finally works. So hopes are high that at long last the elusive Higgs boson will show its face, or tracks, or however they plan to catch one.

Fortunately, nobody has yet had to die for the chance to discover the Higgs boson. But a lot of people have put a lot of effort and money into looking for it, and now after the accident they're having to wait an extra year. Some may look at such work and criticize it on the basis that hey, people are starving in Rwanda and we're spending billions on chasing some pencil-pusher's pipe dream? But the fact that humankind can contemplate the universe and expend lots of energy searching for purely abstract products of the intellect such as the Higgs boson, is one of the things that distinguishes us from animals. I for one wish the CERN workers first safety, then success in their search. But being a Texan, I also wish we'd finished the Supercollider and made Higgs bosons first right here in Waxahachie.

Sources: Several news articles are available on the vicissitudes of the LHC accident. I used material from the U. S. LHC website, an article in Discover Magazine online at, and one at the Big Science News blog at For an instructive news video of what an unplanned superconducting-magnet quench looks like, see the YouTube version of a report on a hospital's MRI magnet that blew up at

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