What it’s Like to Take a Tour of the LHC at CERN

As a particle physicist student, I’m allowed certain privileges in the physics world. Most of these are dull. But in 2008, I was granted permission to visit CERN with my class for the day. We were to have a private tour of the experimental particle accelerator spread out over Switzerland and France.

The Large Hadron Collider by numbers.

I’ve always found the best way to try and explain the enormous magnitude of this machine is to look at the crazy numbers that describe how it works.

• The LHC is a particle accelerator built over the border of France and Switzerland.
• 10,000 physicists and engineers from 85 different countries are currently working on the LHC.
• It is built 200 metres underground.
• It has a circumference of 27 kilometers.
• It is used to accelerate beams of protons to speeds of 99.99% of the speed of light.
• Each beam consists of 3000 bunches of 100 billion particles each.
• In one second, each beam will make 11,245 laps of the accelerator.
• The beams are steered by a collection of 9600 magnets, which are cooled to a temperature of -456 fahrenheit.
• Over a space of a year the LHC will gather about 15 petabytes of data. A petabyte is a million gigabytes. That much data could fill 100,000 DVDs.

Just think about that… 3,000,000,000,000,000 particles making over 11,000 laps of a 27 kilometre ring… In ONE second! To this day, I still find these numbers staggering and impossible to even begin to get my head around.

After taking nine years to be built, the LHC finally went into operation in 2009. I had my tour in 2008 so was able to visit the accelerator itself, something which is no longer possible to do now that it is working.

What is the point of the LHC?

The LHC accelerates protons to extremely high energies and forces them to collide creating new particles which can then be studied. In doing so it is hoped that we will be able to recreate the conditions that were present at the Big Bang in order to answer some of the most fundamental questions of the universe – Why are we here? How was matter formed? Why do we have mass? What is dark matter? As well as trying to discover new physics, new particles and new theories that have previously been unheard of.

The Tour

The visit took place in the middle of December, and after having to wake up at 4 in the morning I was less than impressed at having to face the cold, snowy Swiss weather!

We were quickly ushered into the reception area and received a short briefing informing us on what our tour would include, followed by an informative talk describing the basics of the LHC and its individual detectors. What the poster shows is the main ring of the LHC as the biggest ring at the top, and all the other beam lines that are used to accelerate or store the beams of particles.

One of the things that I loved about CERN was the fact that the street names were named after famous physicists.

We made our way over to one of the six detectors – ATLAS, known as the general purpose detector. When the beams collide in the centre of the detector, may different particles will be produced with a large range of energies. What ATLAS does is measure the broadest possible range of the signals, rather than focusing on a specific region.

One of the fun parts of the building that holds the detector is the huge hole in the floor with a platform over the edge enabling visitors to peer 200 metres down to see the accelerator beamline below. I hate heights and so I was actually pretty terrified at this point and I have to confess I did not physicially look over the edge, I held my camera over, took a photo and squealed as I ran back to safety!

It was then time to view the components of the LHC itself. We started with the linear accelerator (LINAC) which is where it all begins. As is indicated by the name, the purpose of the LINAC is to accelerate the protons down a linear beamline. By the time the protons have reached the end of this accelerator they are already traveling at 1/3 the speed of light.

At these speeds, the proton beams are then passed through a series of booster rings to further increase their energy until it is high enough for them to enter the main LHC ring. Here they will keep circulating for hours continually colliding at the six different detectors.

We were given some time to walk around and take photos of random parts of the components.

I visited the Low Energy Ion Ring which can capture, cool and store matter and anti-matter in order to study them later. Unlike Angels and Demons this anti-matter cannot be sneaked out and stolen from CERN – It’s stored in an 80 metre ring!

I visited the brains of the operation – The ATLAS control room. Here the physicists test, calibrate, improve, fix, and tweak small parts of the ATLAS detector. It consists of 15 stations, each with 4 monitors, and 8 projection screens on the wall.

We learnt about how CERN used to store its data collected. I mentioned above that in a year of data taking the LHC could fill 100,000 DVDs, well in the 1960s THIS is what they used to store their data and it only held a few kilobytes of data!

And with that, my whirlwind tour of science’s most magnificent machine drew to a close, and there was only one thing left for me to do…

However as a final note… I thought I’d answer the question I am most asked by my non-physicist friends.

Is the LHC going to destroy the world and kill us all?

When the LHC went into operation there was a lot of craziness in the press about the possibility of it being able to generate black holes that would suck up the Earth and kill us all. There are hundreds of conspiracy theories out there, and a huge amount of websites dedicated to this. More recently I stumbled across a website that blamed the earthquake/tsunami in Japan on the LHC, saying the huge energies generated caused a shockwave through the Earth, thus creating the earthquake. I cannot put into words how angry that makes me and how completely ridiculous and uninformed these morons are!

Allow me to categorically state now that there is NO way that the LHC is going to kill us. What you have to realise is that the world, and indeed the universe, is constantly bombarded by high energy cosmic rays from extragalactic sources. Hold out your hand now, and these cosmic rays are passing through them every second. Some of these rays in the atmosphere induce particle collisions thousands of times more powerful than those that will ever be produced by the LHC. As this has been taking place for billions of years after the big bang, well, if these collisions could create black holes, lets just say it would have happened by now.

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