Crab cavities are a form of

electromagnetic cavity An electromagnetic cavity is a resonator, cavity that acts as a container for electromagnetic fields such as photons, in effect containing their wave function inside. The size of the cavity determines the maximum photon wavelength that can be trapp ...

used in

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...

s to provide a transverse deflection to particle bunches. They can be used to provide rotation to a

charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary particle, ...

bunch by applying a time varying

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. This rotation of the bunch can be used as a diagnostic tool to measure the length of a bunch (the longitudinal dimension is projected into the transverse plane, and imaged) or as a means of increasing the

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

at an

interaction point In particle physics, an interaction point (IP) is the place where particles collide in an accelerator experiment. The ''nominal'' interaction point is the design position, which may differ from the ''real'' or ''physics'' interaction point, where ...

of a

collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particle ...

if the colliding beams cross each other at an angle (then called ''crab crossing''). The KEKB accelerator introduced this technology in its last upgrade.

See also