Particle beams circulate for around 10 hours in the Large Hadron Collider (LHC). During this time, the particles make four hundred million revolutions of the machine, travelling a distance equivalent to the diameter of the solar system. The beams must travel in a pipe which is emptied of air, to avoid collisions between the particles and air molecules (which are considerably bigger than protons). The beam pipes are pumped down to an air pressure similar to that on the surface of the moon. Much of the LHC runs at 1.9 degrees above absolute zero. When material is cooled, it contracts. The interconnections must absorb this contraction whilst maintaining electrical connectivity.

Particles are accelerated using radio-frequency cavities. These contain an electric field which oscillates at just the right frequency to give a kick to the charged particles passing through.

With its 27-kilometre circumference, the Large Electron-Positron (LEP) collider was the largest electron-positron accelerator ever built. The excavation of the LEP tunnel was Europe’s largest civil-engineering project prior to the Channel Tunnel. Three tunnel-boring machines started excavating the tunnel in February 1985 and the ring was completed three years later. In its first phase of operation, LEP consisted of 5176 magnets and 128 accelerating cavities. CERN’s accelerator complex provided the particles and four enormous detectors, ALEPH, DELPHI, L3 and OPAL, observed the collisions. LEP was commissioned in July 1989 and the first beam circulated in the collider on 14 July. The collider's initial energy was chosen to be around 91 GeV, so that Z bosons could be produced. The Z boson and its charged partner the W boson, both discovered at CERN in 1983, are responsible for the weak force, which drives the Sun, for example. Observing the creation and decay of the short-lived Z boson was a critical test of the Standard Model. In the seven years that LEP operated at around 100 GeV it produced around 17 million Z particles. In 1995 LEP was upgraded for a second operation phase, with as many as 288 superconducting accelerating cavities added to double the energy so that the collisions could produce pairs of W bosons. The collider's energy eventually topped 209 GeV in 2000. This object is one of the superconducting cavities from this epoch.

Short section of beampipe from the Large Electron Positron collider (LEP, for short). With its 27-kilometre circumference, LEP was the largest electron-positron accelerator ever built and ran from 1989 to 2000 at CERN. During 11 years of research, LEP's experiments provided a detailed study of the electroweak interaction. Measurements performed at LEP also proved that there are three – and only three – generations of particles of matter. LEP was closed down on 2 November 2000 to make way for the construction of the Large Hadron Collider in the same tunnel.

The pulse of a particle accelerator. 128 of these radio frequency cavities were positioned around CERN's 27-kilometre LEP ring to accelerate electrons and positrons. The acceleration was produced by microwave electric oscillations at 352 MHz. The electrons and positrons were grouped into bunches, like beads on a string, and the copper sphere at the top stored the microwave energy between the passage of individual bunches. This made for valuable energy savings as it reduced the heat generated in the cavity.

Connection between two superconducting magnets Cryostat - Keeping the magnets cold The Large Hadron Collider superconducting magnets are cooled by liquid helium to 1.9 degrees above absolute zero, or around 300 degrees below the ambient temperature in the tunnel. To keep them cold, each 30 000 kg magnet sits inside a cryostat that isolates it from the tunnel. Inside the cryostat, air is pumped out to reduce heat in-flow. Bellows - Allowing expansion and contraction When the magnets are cooled, they contract: normally 15 metres long, each magnet shrinks by 4.5 cm on its way down to 1.9 degrees above absolute zero. One side of each 30 000 kg magnet is held stationary, while the other is left free to move. Stainless steel bellows such as these absorb the contraction. Notice that every single join needs to allow for such movement, even the electrical connections. Helium Pipe - The cooling supply This pipe carries superfluid helium at 1.9 degrees above absolute zero, around 300 degrees below room temperature. As helium is cooled and put under pressure, it becomes a superfluid, with excellent thermal conductivity, ensuring the temperature is the same everywhere in the circuit. However this gives engineers an extra challenge as superfluids have unusual quantum properties. They can even creep upwards – if there are leaks in the circuit a superfluid will find them! The Large Hadron Collider is cooled by sector, of which there are eight in total. Cool down of one sector takes around 6 weeks. When the accelerator is brought back to room temperature for maintenance works, CERN recuperates the helium and stores it, so it can be reused. Niobium Titanium Cable - Bringing current to the magnets This cable carries the 13 000 amps to the Large Hadron Collider magnets. It is made from a Niobium-Titanium superconductor which is embedded in copper, to ensure an electrical connection is maintained even if the superconductor warms up and stops conducting. This happens at around 10 degrees above absolute zero. The LHC is cooled to 1.9 degrees above absolute zero, to keep the current perfectly stable. Look at the joins in the cable, called splices. They allow the wires to move over each other and retain an electrical connection, when the magnet contracts during cooling. Beam-Pipe Fingers - Keeping the electrical connection Fingers of copper slide over the beam-pipe in every connection between magnets in the Large Hadron Collider. These fingers retain an electrical contact whilst the magnets contract during cooling. The beam-pipe has double layers. The outer layer is slightly colder than the inner one so that any residual gas molecules, left behind in the tube after pumping, are drawn outwards through small holes so they cannot be disturbed by the passing proton beam. Diode - Removing the current There are many mechanisms in place to prevent friction between cable windings that might generate heat and stop the superconductor from conducting. In the eventuality the magnets do stop working, around 13 000 amps of current needs to be taken out of the system. This happens via diodes situated at the extremity of every magnet. The diode conducts a current pulse ramping in less than a second up to 13 000 amps and then slowly decaying down to zero. This process raises their temperature by several hundred degrees, so the diodes are cooled by the LHC Helium circuit.

Dipole Magnet - Guiding the protons around the ring This is a cut-through of the coil of a dipole magnet, that generates the magnetic field used to bend the paths of circulating protons. Looking closely, you can distinguish insulated cables made of individual wires. High and extremely stable magnetic fields are needed for guiding the proton beams, so a superconducting material called Niobium-Titanium was chosen for the wires. At very low temperatures, superconductors have no electrical resistance and therefore no power loss. They carry a very stable current of 13.000 amps, about 20.000 times that used to power this screen. In addition to dipole magnets, the Large Hadron Collider contains quadrupoles and other higher order magnets, used to prepare the proton beams for collision. Dipoles are two pole magnets used for bending the beams of protons around the ring. Quadrupoles have four magnetic poles and are used for focusing the beam, squeezing protons closer together to increase the chance of collision when the beams cross inside the experiments. In total, the LHC uses more than 50 different types of magnet to adjust the particle beams even more finely. The Beam-Pipe - Where the beams of protons circulate Proton beams can circulate for over 10 hours in the Large Hadron Collider. Over this time, protons make four hundred million revolutions of the 27 km machine, traveling a distance equivalent to the diameter of the solar system. They must travel in a pipe that is emptied of air, to avoid collisions with molecules of gas. The beam-pipes are therefore pumped down to an air pressure similar to that on the surface of the moon. There are two pipes, one for each direction of the circulating beams. The two beams only meet inside the four experiments where collisions take place. Liquid Helium - Bringing in the cooling fluid This pipe carries liquid helium through the Large Hadron Collider magnets to keep them at 1.9 degrees above absolute zero - about 300 degrees below room temperature. 800'000 litres of superfluid helium are used to cool down the 36'000 tonnes of equipment. This is the world's biggest cryogenic installation and its reliability and efficiency is essential for the magnets. The pipe connects to the main cryogenic line that you can see running along behind the blue magnets via "jumper connections" like the one to your right. Support Post - Insulating and extremely tough The magnet supports bridge a difference in temperature of nearly 300 degrees! Electrical connections, instrumentation and the posts on which the magnets stand are the only points where heat transfer can happen through conduction. They are all carefully designed to draw off heat progressively. The posts are made of 4 mm thick glass-fibre - epoxy composite material. Each post supports 10'000 kg of magnet and leaks just 0.1 W of heat. There are three per magnet. Magnet Collars - Preventing the wires from moving The LHC accelerates two proton beams moving in opposite directions, so it is really two accelerators in one. To keep the machine as compact and economical as possible, two magnets are built into a single housing that must withstand enormous electromagnetic forces. These forces tend to open-up the coils, and squeeze them. At full field, the force on one metre of coil is comparable to the weight of a jumbo jet. Great care must be taken to prevent movements as the field changes - any friction could create hot spots that would cause the wire to lost its superconducting stage. Magnet collars made from reinforced steel keep the coils firmly in place. Insulation - Preventing heat from leaking In The LHC, beam-tube and magnets are inside a vacuum tank to reduce to a minimum the heat flowing in through convection. To prevent heat inflow through radiation, they are surrounded by a super insulator - multi-layer, reflective, aluminized Mylar. Then to prevent heat flow via conduction, ingenious solutions had to be found for the electrical connections and the support posts. Iron Yoke - Shielding the magnetic field The LHC magnet cables are surrounded by a layered iron yoke that shields the powerful magnetic field - 100'000 times stronger than the Earth's - so that stray fields outside the magnet are negligible. This action also helps enhance the magnetic field within the beam-pipe, where it is needed for control of the proton beams. In addition, the layers of iron yoke, called laminations, play a role together with the magnet collars in keeping cables from moving when the magnet powers up. The technical challenge of manufacturing the laminations centred on ensuring both strength and magnetic homogeneity across a large-scale production. Over 6 million laminations are needed for the 1232 dipole magnets installed around the LHC's 27km ring.

The magnetic field must be extremely uniform. This means the current flowing in the coils has to be very precisely controlled. 50’000 tonnes of steel sheets are used to make the magnet yokes that keep the wiring firmly in place. The yokes constitute approximately 80% of the accelerator's weight and, placed side by side, stretch over 20 km.

If all molecules in this bottle could be used, this hydrogen bottle contains enough protons to feed the Large Hadron Collider for 200’000 years of continuous operation! But since there are losses inside the source, in and between the accelerators, such a bottle only lasted for 4 to 6 months of operations and needed then to be replaced.

The Hadron-Elektron-Ringanlage (HERA) collided protons with energies up to 920 GeV with electrons or positrons with energies up to 27.5 GeV. It operated from 1992 to 2007, probing the internal structure of the proton. Many of the features of the HERA superconducting magnets became standards for later projects. The HERA ring was installed in a 6.3 km tunnel at Deutsches Elektronen-Synchrotron (DESY) Laboratory, Hamburg (Germany).