DANIEL CHEEK
CERN's Large Hadron Collider (LHC) is currently the largest particle accelerator in the world, designed to accelerate protons at very high speeds so that they collide and shatter into subatomic particles, allowing us to discover these. It is located on the Swiss-French border, and was commissioned in 2007, beginning operation in September 2008. The LHC's main achievement is the discovery of the subatomic particle the Higgs Boson: the particle responsible for giving matter mass. More widely, CERN provided the location at which the World Wide Web was created by Sir Tim Berners-Lee and the technology at CERN is currently being used to investigate new medicines.
How it works
Firstly, protons are sent through the PS (Proton Synchrotron), then the SPS (Super Proton Synchrotron) and finally into the main Large Hadron Collider. Effectively these are three loops that help accelerate the protons to high speeds before they are crashed together. This is currently how the collider operates, however when it was built in 1959, the PS was intended for accelerating particles such as alpha particles (Helium nuclei) and electrons. The SPS was built in 1981 to accelerate hadrons and bosons. In addition, in 1989, the Large Electron-Positron collider (LEP) was built to accelerate leptons. Engineers at the Rutherford Appleton Laboratory worked on the design and simulation of programmable devices used in the Delphi (DEtector with Lepton, Photon and Hadron Identification) data acquisition and trigger system on the LEP. This led to the discovery of the Z boson.
[Figure 1 - The layout of the various detectors and colliders in the CERN complex]
However, these accelerators do wear out over time. In 2008 the Large Hadron Collider was built in the shell of the old LEP. Using 1,232 magnets around a 27km loop to accelerate protons to speeds just 6.2 mph short of the speed of light, it causes them to collide with other protons and shatter into subatomic particles that we can analyse. To power these magnets a 250,000km long superconductive (no electrical resistance) cable is used. For proper operation the magnets need to be cooled to -271.3C or 1.85K, a temperature lower than that of space. To do this the magnets are cooled with liquid helium, the same stuff used to cool refrigerators. The LHC contains 4 million fridges worth of liquid hydrogen, or 150 fridges every metre!
The supercool magnets have 3 main roles in the collider: to accelerate protons, to keep protons from hitting the side of the tube, and finally to concentrate them into a small beam to increase the chance of collisions. This last step is immensely important as, even with this effect, the chance of a collision occurring is akin that of two needles hitting each other after being fired from 10km apart. To increase the chance of actually collecting some data to a reasonable level, 100 billion protons have to be fired at once. This in fact leads to some 600 million collisions! Unfortunately, only direct collisions give us the data we want, but with this many, detectors still pick up plenty of signatures left by the particles.
The Subatomic Particles
The current standard model of the atom can first be simply divided into electrons, neutrons and protons, with electrons orbiting a nucleus made from neutrons and protons. This is the GCSE atomic model. However it turns out that the above particles can be broken down further into quarks (making up neutrons and protons), and leptons (electrons are a type of lepton, along with many other particles). Together, these solid particles can all be summarised as fermions. However, it turns out that there are yet more particles still being discovered. The new field of particles that the LHC has helped us discover is the bosons, including the Higgs Boson, discovered in 2012. These bosons are force carriers of electromagnetic forces; the Higgs Boson is incredibly important as it is the source of all mass in atoms.
The Future
An important future area of research for the Hadron Collider is antimatter. These are the anti-particles of the subatomic particles we know and love. This means that they have the same mass and properties but a different charge. That is to say that anti-electrons are positively charged positrons and anti-protons are negatively charged antiprotons. We can visualise this in the same way that mirrors reflect light, e.g. if you wave your left hand your right hand waves back. The LHC can create these particles and also combine them with the "normal" versions. These collisions are important to research as when a particle collides with its anti particle, both are "annihilated" in a huge explosion, releasing a large amount of energy. This could make antimatter a source of potentially dangerous weapons. 1 kg of anti-hydrogen could produce a similar amount of energy to the Tsar Bomba explosion: the largest nuclear bomb ever detonated.
The Problem
It is believed by some scientists that a black hole or wormhole could be created by incredibly high energies of particle collision. A black hole could expand and suck in the earth entirely and a wormhole bends space and time so could in essence create an uncontrollable time machine. This means that in its endeavours to further scientific understanding, the LHC could in fact cause humankind's downfall. That said, current tests haven’t shown any evidence that either of these could occur.
In spite of potential fears, CERN is planning an even larger particle accelerator than the LHC: the Future Circular Collider (FCC), which is to be built over the next 50 years for a total cost of £20 billion. At 100km long it is hoped that this will allow us to discover the next generation of particles, and maybe even understand dark matter.
Conclusion
In total the Large Hadron Collider cost £5 billion to build and costs £1 billion per year to run. This is a huge sum of money that could obviously be put to good use elsewhere. However, the current system has got results: we now know more about the atom than ever before and in the process we have managed to make progress in medical treatments as well as in many other fields. Therefore it could be argued that this is worth the economic cost.
Acknowledgements
Daniel's mother was lucky enough to work at CERN in a placement year at the Rutherford Appleton Laboratory, during her Electronic Engineering degree. We thank her for the useful information she provided which went into this article.