WHAT IS THE LHC?
Where is it?
The LHC is being installed in a tunnel 27 km in circumference, buried 50-175 m below ground. Located between the Jura mountain range in France and Lake Geneva in Switzerland, the tunnel was built in the 1980s for the previous big accelerator, the Large Electron Positron collider (LEP). The tunnel slopes at a gradient of 1.4% towards Lake Geneva.
What will it do?
The LHC will produce head-on collisions between two beams of particles, either protons or lead ions. The beams will be created in CERN's existing chain of accelerators and then injected into the LHC. These beams will travel through a vacuum comparable to outer space. Superconducting magnets operating at extremely low temperatures will guide them around the ring. Each beam will consist of nearly 3000 bunches of particles and each bunch will contain as many as 100 billion particles. The particles are so tiny that the chance of any two colliding is very small. When the particle beams cross, there will be only about 20 collisions among 200 billion particles. However, the particle beams will cross about 40 million times per second, so the LHC will generate about 800 million collisions per second.
What is it for?
Due to switch on in 2007, the LHC will provide collisions at the highest energies ever observed in laboratory conditions and physicists are eager to see what they will reveal. Four huge detectors - ALICE, ATLAS, CMS and LHCb - will observe the collisions so that the physicists can explore new territory in matter, energy, space and time. A fifth experiment, TOTEM, installed with CMS, will study collisions where the protons experience only very small deflections.
The LHC is a machine for concentrating energy into a very small space. Particle energies in the LHC are measured in tera electronvolts (TeV). 1 TeV is roughly the energy of a flying mosquito, but a proton is about a trillion times smaller than a mosquito. Each proton flying round the LHC will have an energy of 7 TeV, so when two protons collide the collision energy will be 14 TeV. Lead ions have many protons, so they can be accelerated to even greater energy: the lead ion beams will have a collision energy of 1150 TeV. At full power, each beam will be about as energetic as a car travelling at 2100 kph. The energy stored in the magnetic fields will be even greater, equivalent to a car at 10 700 kph.
At near light-speed, a proton in a beam will make 11 245 turns per second. A beam might circulate for 10 hours, travelling more than 10 billion kilometres - far enough to get to the planet Neptune and back again.
How will it work?
To control beams at such high energies the LHC will use some 7000 superconducting magnets. These electromagnets are built from superconducting materials: at low temperatures they can conduct electricity without resistance, and so create much stronger magnetic fields than ordinary electromagnets. The LHC's niobium-titanium magnets will operate at a temperature of only 1.9 K (-271°C). The strength of a magnetic field is measured in units called tesla. The LHC will operate at about 8 tesla, whereas ordinary "warm" magnets can achieve a maximum field of about 2 tesla. If the LHC used ordinary "warm" magnets instead of superconductors, the ring would have to be at least 120 km in circumference to achieve the same collision energy.
LHC: the guide
A collection of facts and figures about the Large Hadron Collider (LHC) in the form of questions and answers.