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.

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.

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.

The Large Electron-Positron Collider (LEP) was the largest lepton collider ever built, and gave high precision measurements of the W and Z particles. LEP was commissioned in 1989 and shut down in 2000, to leave room for the LHC. In conjunction with an energy upgrade, new, superconducting, final- focus (low-$\beta$) quadrupole magnets were built. The new magnets resembled much those built for the ISR luminosity upgrade, i.e., the coils were wound with a single rectangular wire. They operated at 4.5 K in a cryostat especially developed to fit into the limited space available in the shield placed in front of the experiment.

The Tevatron was the first synchrotron built with superconducting magnets and paved the way for large scale applications of superconductivity. It was installed in the tunnel at Fermi National Accelerator Laboratory, Batavia, Illinois (USA). It operated reliably from 1983 to 2011, producing protons and anti-protons with energies up to 980 GeV. Besides the technology prowess, the Tevatron enabled the discovery of the top quark in 1995, the last fermion of the Standard Model to be observed.

Slice through an LHC superconducting quadrupole (focusing) magnet. The slice includes a cut through the magnet wiring (niobium titanium), the beampipe and the steel magnet yokes. Particle beams in the Large Hadron Collider (LHC) have the same energy as a high-speed train, squeezed ready for collision into a space narrower than a human hair. Huge forces are needed to control them. Dipole magnets (2 poles) are used to bend the paths of the protons around the 27 km ring. Quadrupole magnets (4 poles) focus the proton beams and squeeze them so that more particles collide when the beams’ paths cross. Bringing beams into collision requires a precision comparable to making two knitting needles collide, launched from either side of the Atlantic Ocean.

A short test version of coil of wire used for the LHC dipole magnets. The high magnetic fields needed for guiding particles around the Large Hadron Collider (LHC) ring are created by passing 12’500 amps of current through coils of superconducting wiring. At very low temperatures, superconductors have no electrical resistance and therefore no power loss. The LHC is the largest superconducting installation ever built. The magnetic field must also be extremely uniform. This means the current flowing in the coils has to be very precisely controlled. Indeed, nowhere before has such precision been achieved at such high currents. Magnet coils are made of copper-clad niobium–titanium cables — each wire in the cable consists of 9’000 niobium–titanium filaments ten times finer than a hair.

3 accelerating cavities.

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.