Firing up the Large Hadron Collider

The LHC is back up and running after almost 2 years of maintenance. Why did it take so long to turn it back on?
08 June 2015

Interview with 

Mike Lamont, CERN’s Head of Operations


The world's biggest particle accelerator - the Large Hadron Collider (LHC) - has  The Large Hadron Collider/ATLAS at CERNbeen successfully restarted this week after a two year maintenance shut down. Now it's back to smashing together protons, the positive particles that sit at the centres of atoms, to help scientists glimpse what the Universe is made of. Graihagh Jackson went to CERN to meet the LHC's Head of Operations, Mike Lamont, to find out more about the next run of tests...

Mike - The LHC is 27 kilometres in circumference and it's divided into 8 sectors. The first stage is to actually cool the magnets down. So, unless the magnets in the LHC are superconducting, they're cooled to 1.9 Kelvin.

Graihagh - Pretty cold.

Mike - Chilly! This is colder than outer space. Once the whole sector is cold then we can start putting current into the magnets and making sure that the magnets behave properly.

Graihagh - And then what's involved after that?

Mike - Our main magnets are the dipoles. These are the big guys which are bending and focusing the beams. These all have to be tested. The whole process for the whole machine lasted about 6 months to check out all the magnetic circuits. So, this is a huge, hundreds of thousands of tests. So, once that's done over the full 27 kilometres then we're in a situation where we think we start taking beam.

Graihagh - When you say 'take beam', what do you mean?

Mike - The protons come in bunches. So, we group the protons together. A bunch is about 30 centimetres long and typically about a millimetre in transverse dimensions. So, you think about a long thin worm. We're going to put 100 billion protons into each bunch and then spread out a lot of bunches around most of the LHC's circumference and that's what we call the beam.

Graihagh - And you're accelerating these round and then I suppose, you choose exactly where they collide. How many protons are actually colliding every single rotation?

Mike - So, the total number of protons in the beam is astronomical. We're talking like 2 x 1014. The number of collisions we generate a second is in the order 600 million which is actually quite a small proportion of the total number of protons circulating.

Graihagh - It sounds like a pretty good number to me. How can you keep track of all of them?

Mike - We got some rather cute beam instrumentation which measure the number of protons we have in the beam and where they're all going. We have to be very, very careful about not losing these guys because they have very high energy and they can damage the magnet. So, we have to be very careful about beam wrangling if you like and keeping control of all these protons.

Graihagh - Tough job.

Mike - Somebody has got to do it.

Graihagh - So, now that we're ready to go, we're going to be seeing the first few experiments in the next coming days, what can we expect for scientists to be looking out for in the next run?

Mike - So, the key thing about this run, run 2, we're starting now is, we can now take the protons to a higher energy. So rather than 40, at the end run 2, we're not going to 6.5 TeV. TeV is what we call a terror electron volt. On a terrestrial scale, this is about the same as a house fly, flying at a couple of miles an hour.

Graihagh - A house flying!

Mike - A house fly.

Graihagh - Oh a house fly! I was trying to imagine.

Mike - We've got strange analogies, but not a flying house, a house fly.

Graihagh - So, a house fly flying at 2 miles an hour is the same as 1 TeV.

Mike - The exact numbers escaped me, but at that order. So, on a terrestrial scale, this is not a huge amount of energy but what we're doing is we're giving that energy to a minusculy tiny particle the proton or a particle physics scale is really is a lot of energy. This is opening up new territory for the physicists. One of the big hopes is for signs of something called 'supersymmetry' which will open up a completely new world of high energy physics if it's there. the interesting thing here is we're probing the way the universe is structured. If the universe has chosen not to use supersymmetry as a solution to its problems then it's not there. and that is a fact that we will have to face and you don't have to develop other theories to explain things like dark matter.


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