The sheer size of the LHC is clear from this aerial picture in which the LHC's position is shown by a while circle. Geneva airport is in the foreground, with the Jura mountains behind. A line of white crosses marks the French-Swiss border.
The LHC is installed in a tunnel ranging from 50 to 150 metres underground. Particle detectors called Alice, Atlas, CMS and LHCb surround the points at which particles collide, measuring the emerging showers of particles. The tunnel crosses the French-Swiss border six times, with the particle beams making 66000 border crossings per second. What is CERN?
The European Organisation for Nuclear Research (French: Organisation Européenne pour la Recherche Nucléaire), known as CERN (see Naming), pronounced /ˈsɝːn/ (IPA: [sɛʀn] in French), is the world's largest particle physics laboratory, situated in the northwest suburbs of Geneva on the Franco-Swiss border. The organization has twenty European member state and is currently the workplace of approximately 2600 full-time employees, as well as some 7931 scientists and engineers (representing 500 universities and 80 nationalities).
CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research. Numerous experiments have been constructed at CERN by international collaborations to make use of them. The main site at Meyrin also has a large computer centre containing very powerful data processing facilities primarily for experimental data analysis, and because of the need to make them available to researchers elsewhere, has historically been (and continues to be) a major wide area networking hub.
As an international facility, the CERN sites are not officially under Swiss or French jurisdiction. Member states' contributions to CERN for the year 2008 totaled (approximately €664 million, US$ 1 billion).
History
The convention establishing CERN was signed on 29 September 1954 by twelve countries in Western Europe. The acronym CERN originally stood, in French, for Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research), which was a provisional council for setting up the laboratory, established by 11 European governments in 1952. The acronym was retained for the new laboratory after the provisional council was dissolved, even though the name changed to the current Organisation Européenne pour la Recherche Nucléaire (European Organisation for Nuclear Research) in 1954.
Soon after its establishment, the work at the laboratory went beyond the study of the atomic nucleus, into higher-energy physics, an activity which is mainly concerned with the study of interactions between particles. Therefore the laboratory operated by CERN is commonly referred to as the European laboratory for particle physics (Laboratoire européen pour la physique des particules) which better describes the current research being performed at CERN.
Three decades after it was conceived, the world's most powerful physics experiment has sent the first beam around its 27km-long tunnel.
Engineers cheered as the proton particles completed their first circuit of the underground ring which houses the Large Hadron Collider (LHC).
The £5bn machine on the Swiss-French border is designed to smash particles together with cataclysmic force.
Engineers cheered as the proton particles completed their first circuit of the underground ring which houses the Large Hadron Collider (LHC).
The £5bn machine on the Swiss-French border is designed to smash particles together with cataclysmic force.
This will re-create conditions in the Universe moments after the Big Bang.
But it has not been plain sailing; the project has been hit by cost overruns, equipment trouble and construction problems. The switch-on itself is two years late.
The collider is operated by the European Organization for Nuclear Research - better known by its French acronym Cern.
The vast circular tunnel - the "ring" - which runs under the French-Swiss border contains more than 1,000 cylindrical magnets arranged end-to-end.
The magnets are there to steer the beam - made up of particles called protons - around this 27km-long ring.
Eventually, two proton beams will be steered in opposite directions around the LHC at close to the speed of light, completing about 11,000 laps each second.
At allotted points around the tunnel, the beams will cross paths, smashing together near four massive "detectors" that monitor the collisions for interesting events.
Scientists are hoping that new sub-atomic particles will emerge, revealing fundamental insights into the nature of the cosmos.
But it has not been plain sailing; the project has been hit by cost overruns, equipment trouble and construction problems. The switch-on itself is two years late.
The collider is operated by the European Organization for Nuclear Research - better known by its French acronym Cern.
The vast circular tunnel - the "ring" - which runs under the French-Swiss border contains more than 1,000 cylindrical magnets arranged end-to-end.
The magnets are there to steer the beam - made up of particles called protons - around this 27km-long ring.
Eventually, two proton beams will be steered in opposite directions around the LHC at close to the speed of light, completing about 11,000 laps each second.
At allotted points around the tunnel, the beams will cross paths, smashing together near four massive "detectors" that monitor the collisions for interesting events.
Scientists are hoping that new sub-atomic particles will emerge, revealing fundamental insights into the nature of the cosmos.
Major Effort
"We will be able to see deeper into matter than ever before," said Dr Tara Shears, a particle physicist at the University of Liverpool. "We will be looking at what the Universe was made of billionths of a second after the Big Bang. That is amazing, that really is fantastic." The LHC should answer one very simple question: What is mass? "We know the answer will be found at the LHC," said Jim Virdee, a particle physicist at Imperial College London. The currently favored model involves a particle called the Higgs boson - dubbed the "God Particle". According to the theory, particles acquire their mass through interactions with an all-pervading field carried by the Higgs. The latest astronomical observations suggest ordinary matter - such as the galaxies, gas, stars and planets - makes up just 4% of the Universe. The rest is dark matter (23%) and dark energy (73%). Physicists think the LHC could provide clues about the nature of this mysterious "stuff". According to Professor Virdee : "Nature can surprise us... we have to be ready to detect anything it throws at us."
Full Beam Ahead
Engineers injected the first low-intensity proton beams into the LHC in August. But they did not go all the way around the ring. On Wednesday, they sent a proton beam around the full circumference of the LHC tunnel.
Technicians had to be on the lookout for potential problems: There are on the order of 2,000 magnetic circuits in the machine. This means there are 2,000 power supplies which generate the current which flows in the coils of the magnets.
If there was a fault with any of these, it would have stopped the beam. They were also wary of obstacles in the beam pipe which could prevent the protons from completing their first circuit.
If there was a fault with any of these, it would have stopped the beam. They were also wary of obstacles in the beam pipe which could prevent the protons from completing their first circuit.
While working on the LHC's predecessor, a machine called the Large-Electron Positron Collider, engineers found two beer bottles wedged into the beam pipe - a deliberate, one-off act of sabotage.
The culprits - who were drinking a particular brand which advertising once claimed would "refresh the parts other beers cannot reach" - were never found.
After the beam makes one turn, engineers are due to "close the orbit", allowing the beam to circulate continuously around the LHC.
Engineers will then try to "capture" it. The beam which circles the LHC is not continuous; it is composed of several packets - each about a metre long - containing billions of protons.
The protons would disperse if left to their own devices, so engineers use electrical forces to "grab" them, keeping the particles tightly huddled in packets.
Once the beam has been captured, the same system of electrical forces is used to give the particles an energetic kick, accelerating them to greater and greater speeds.
After Wednesday's test, engineers will need to get two beams running in opposite directions around the LHC. They can then carry out collisions by smashing them together.
The culprits - who were drinking a particular brand which advertising once claimed would "refresh the parts other beers cannot reach" - were never found.
After the beam makes one turn, engineers are due to "close the orbit", allowing the beam to circulate continuously around the LHC.
Engineers will then try to "capture" it. The beam which circles the LHC is not continuous; it is composed of several packets - each about a metre long - containing billions of protons.
The protons would disperse if left to their own devices, so engineers use electrical forces to "grab" them, keeping the particles tightly huddled in packets.
Once the beam has been captured, the same system of electrical forces is used to give the particles an energetic kick, accelerating them to greater and greater speeds.
After Wednesday's test, engineers will need to get two beams running in opposite directions around the LHC. They can then carry out collisions by smashing them together.
Long Haul
The idea of the Large Hadron Collider emerged in the early 1980s. The project was eventually approved in 1996 at a cost of SFr2.6bn. However, Cern underestimated equipment and engineering costs when it set out its original budget, plunging the lab into a cash crisis. Cern had to borrow hundreds of millions of euros in bank loans to get the LHC completed. The current price is nearly four times that originally envisaged.
During winter, the LHC will be shut down, allowing equipment to be fine-tuned for collisions at full energy.
During winter, the LHC will be shut down, allowing equipment to be fine-tuned for collisions at full energy.
Over 1000 two-in one dipole magnets like this one make up the technological heart of the LHC. Designed to steer proton beams travelling at close to the speed of light around the LHC, their powerful magnetic fields are generated by superconducting cables carrying over 11000 amperes of electric current. Superconductivity is the ability of some materials to lose electrical resistance at very low temperatures. The LHC is installed in an enormous fridge, keeping it at about -271 degrees, or just 1.9 degrees above absolute zero. 
The Alice experiment is optimized to study head-on collisions between the nuclei of lead atoms, which will produce thousands of particle tracks in the detector. Alice hopes to study matter as it would have been in the first fraction of a second after the Big Bang. 
During final assembly and testing, LHC magnets were transported using a specially-built robot known as the crab. 
The ends of the Atlas detector are capped off with a series of so-called big wheels. These have the job of measuring particles called muons, the only detectable particles that escape the detector. 
Scientists on the beam line. This picture, taken during installation of the Atlas detector in 2007, shows scientists in a cherry-picker at the level of the LHC beam. A vacuum pipe now crosses the place where they are standing. 
The CMS experiment's inner tracker is made up of some 15000 silicon strip modules covering over 200 square metres, making it the largest detector if its kind by far. Its job is to measure the tracks of particles emerging from collisions at the heart of the CMS detector. 
A computer simulation of tracks emerging from a proton collision in the CMS detector. In this collision, a Higgs particle has been produced, lived for a fleeting instant and decayed into four particles called muon. 
A computer simulation of tracks emerging from a proton collision in the Atlas detector. In this collision, a Higgs particle has been produced, lived for a fleeting instant and decayed into four particles called muons, which are represented by the four yellow tracks. 
Superconducting magnets are cooled down using liquid helium
