Last weekend was “Le CERN fête ses 60 ans avec ses voisins“, or public open day for CERN’s neighbours as part of the 60 years celebrations. If I’d known that I would definitely have been at CERN during the open day weekend, I would have volunteered to help, but instead I went along as a visitor myself. I have never been to visit the LHC tunnel before, so I was very excited yesterday when some friends said they were planning to go and that it was still possible to join a tour! It’s so rare to be able to visit the accelerator, because most of the time we are running and so it’s not open for tours – also, when the accelerator is on, it’s extremely radioactive!
Below are some of my photos from the trip underground and some extra explanations. Because my phone was already registered to connect to the CERN network, I had WiFi down there, so most of these were posted live.
The circumference of the LHC tunnel is 27 km, and there are only eight access points from the surface, so for the people working in the tunnel to get around easily there are bikes available.
For the LHC, there are two beams of protons; one goes clockwise and the other anticlockwise. These two beams need to be kept separate until we want to collide them inside one of the experiments around the ring.
We need strong magnets to bend the protons around the LHC, so they have to be cooled down to almost Absolute Zero (the coldest temperature there is at −273.15 degrees Celcius!).
The following is a sign to warn people working in the tunnel that there is gas being used or stored nearby. There are many people, however, who think that the person in the sign just looks a bit sad…
The tunnel that the LHC is based in was originally built for a previous CERN accelerator, called the Large Electron-Positron Collider (LEP), which ran until 2000. A positron is the antiparticle of the electron. Using electrons and positrons gives a much cleaner signal because they are not composite particles (they do not contain other particles inside them). But because they are very light, we cannot accelerate them up really high energies and so the new particles we are looking for aren’t created. This is why it was decided to build a new particle accelerator after LEP finished but with protons instead of electrons.
The following signs are left over from when LEP was in the tunnel and remind people which way round each beam went.
Earlier we saw the bicycles used to get around the tunnels, but sometimes you need to carry equipment with you too – so you use these vehicles!
I had a great time seeing the LHC and it was a rare treat to be able to go down and visit the accelerator! After the LHC tour, we decided we would check out how busy the open day was at CMS (another experimental detector on the LHC) – for this, see part two!
If you were at CERN for the open day last weekend, leave me a comment to let me know what you thought.
Clara Nellist 