Particle accelerators were invented at the beginning of the 20th century. These super-microscopes enable to probe matter on a subatomic scale and have an effect on beams of charged particles (electrons, protons, ions) thanks to electromagnetic fields. Since then, other uses of these devices have appeared, especially in medicine or as a source of light.
The electric field that accelerates the particles is produced by radio-frequency (RF) resonant cavities, whereas the magnetic field that guides and focuses them is produced by electromagnets. Superconductivity gives access to stronger fields and reduces the energy loss in RF cavities and magnets: it enables to build more powerful and compact accelerators that are cheaper to use. Thus, the large hadron collider (LHC) of the CERN in Geneva uses several thousands superconducting magnets spread on the 27-km circumference, producing a magnetic field four times higher than classical electromagnets, with an electric intake ten times smaller (considering the power consumed by the cryogenic cooling device).
The European free-electron laser X-FEL in Hamburg and the spallation neutron source ESS in Lund, that are currently under construction, will soon use superconducting RF cavities to economically accelerate beams – respectively electrons and protons – that will produce intense X ray and neutron beams to study materials, living molecules and condensed matter.
In our everyday environment, compact superconducting accelerators – installed in hospitals – produce short-life radionuclides to make diagnoses and proton and ion beams to treat tumours by hadrontherapy. Superconductivity has hence become a key technology of particle accelerators, helping their progress and taking advantage of their development, from which it was able to spread to other applications such as magnetic resonance imaging.
