Starts With A Bang!

The Silver Lining of the LHC Accident

Weren’t we all so excited about the LHC, which had completed successful tests and looked to be in tip-top shape? This giant ring accelerating protons in both clockwise and counterclockwise directions was going to collide them into one another with record-breaking energies (at least for Earth): 14 Tera-electron-Volts, or 7,000 times the energy that you get from a proton at rest.

All of this fancy equipment is underground in tunnels beneath the Franco-Swiss border. Including miles and miles of electromagnets, which you need in order to keep the beam moving in a circle. Think about it: protons are charged particles, and if you want to bend a charged particle, you use a magnet. As the protons go faster and faster, you need your magnet to be more and more powerful to keep it moving in a circle. So you use electromagnets. Want an even stronger magnetic field? Try cooling the electromagnets, and you can pump more current into them faster, creating a stronger field.

So that’s how they keep these super-fast particles moving in the circular underground ring. In order to make the fields as strong as they do, you need to cool these magnets a lot. Know how much a lot is? They cool it with liquid helium, which has a boiling point of only 4 Kelvin! You need to be very careful when you store liquid helium, obviously. Especially when you’ve got it running through hundreds upon hundreds of electromagnets underground. The liquid helium at the LHC is kept at 1.9 Kelvin, and is run through a series of tubes to cool the electromagnet that it surrounds:

These tubes are then welded together and enclosed within the underground tunnels:

The problem? There was a small fault that opened up in one of the cylinders. And what happens to liquid helium in a tube? Same as any liquid in a broken tube: it leaks.

About one ton of liquid helium leaked out, causing about 100 of the supercooled electromagnets to heat up and fail. How long until this is fixed? The best estimates say six to seven more months, which means April 2009 as an optimistic estimate. They won’t even be able to survey the damage for another three weeks; apparently when your entire tunnel is at 4 Kelvin, it takes awhile for it to heat up enough to allow humans inside.

So, this is a substantial setback for the LHC. But there is a benefit to physics in the US: it means that Fermilab, the current record holder in terms of high-energy experiments, gets an extra 6 months (at least) on top:

This also means that all the physicists working at Fermilab likely have another six months before their funding is pulled. I have a lot of friends from graduate school who are working there, and they’re certainly worried about what will happen to their careers once the LHC is fully operational. (And rightfully so!) The LHC looms large and ominously for Fermilab, kind of a metaphor for something I’ve seen before:

It’s possible that Fermilab will beat the LHC and discover the Higgs before the LHC is ready; this accident, although a huge setback for physics as a whole, buys Fermilab physicists more time in their endeavors to do so.

So what will their results be? Well, they just ruled out a Higgs mass of 170 GeV, and Higgs masses below 110 GeV has previously been ruled out. The most common prediction is for a Higgs mass of between 120 and 140 GeV, so hopefully we’ll hear some very interesting news soon!