Friday, September 25, 2009

Geek Side Trip: CERN

While over in Geneva for the Virus Bulletin 2009 conference I managed to make a side trip to see CERN. It turned out to be a great afternoon because the tour was guided by actual physicists and I took a school trip.

I am a little old for it, but when I organized my trip I was told that I would be added to a group from Steyning Grammar School. There I was with 23 final year A-level students on a whirlwind trip to Switzerland. They were extremely nice kids, and I could easily imagine that teaching such a group would be incredibly rewarding.

The visit started with a talk and a film. This told the story of CERN itself (it's almost 55 years old) and described the operation of the Large Hadron Collider.

Here's what part of the LHC looks like (this is a mock-up). The large blue thing is one of the super-conducting magnets. There are 1,232 of these in the 27km ring, each weighs about 27 tonnes.

After that we were bussed over to where the superconducting magnets used in the LHC are received and tested. This involves cooling them down to very close to 0 K (actually 1.7 K), turning on the pair of magnets and inserting a rotating rod inside the two tubes where the particle beam will pass.

Here's a view of a slice through one of the magnets. The two tubes in the middle are where the particle beams pass. The tubes contain a hard vacuum and are surrounded by super-conductors that form the magnet. The entire thing is bathed in liquid helium by a network of pipes.

The rotating rods inserted to test the magnets contain coils that have an electric current induced in them. Measuring the electric current it's possible to confirm that the magnetic field inside the tubes is perfect. The magnetic field is what bends the counter-rotating beams slightly so that they end up tracing out a circle.

This is a detail of one of the particle bean tubes with the valve used for maintaining the hard vacuum. I was surprised how small it was.

And here's a shot of a single dipole magnet ready to be attached to the test apparatus.

And if you are going to move one of those around you need a robot. This one floats around on an air cushion.

To join the magnets together in the circle you need a flexible coupling. The Bulgarian physicist who showed us this bit explained how the magnets were coupled and soldered together: 125,000 separate joints! This is where the LHC failure occurred.

As well as the magnets for bending the beam the beam has to be accelerated. That's achieved by one of these:

And to keep the beam focussed you need another sort of magnet (I don't have a picture of those, but there are 392 of them).

After all that we headed over to the AMS which is a satellite that will be attached to the International Space Station. The highlight of that part was that the designer of it (and friendly Italian man called Giovanni Ambrosi) was on hand to explain what he'd been up to for the last 15 years.

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If you enjoyed this blog post, you might enjoy my travel book for people interested in science and technology: The Geek Atlas. Signed copies of The Geek Atlas are available.

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