Charged particle beam

A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same position, kinetic energy (resulting in the same velocity), and direction. The kinetic energies of the particles are much larger than the energies of particles at ambient temperature. The high energy and directionality of charged particle beams make them useful for applications (see Particle beam#Usage and Electron beam technology).

For practical purposes, a charged particle beam is characterized by

• the species of particle, e.g. electrons, alpha particles, or hydrogen ions
• the energy of the particles, often expressed in Electronvolt (typically: keV to GeV)
• the particle current, often expressed in amperes,
• the beam diameter, and
• the beam emittance, a measure of the degree to which the particle trajectories are non-laminar.

These parameters can be expressed in various ways. For example, the current and beam size can be combined into the current density, and the current and energy (or beam voltage V) can be combined into the perveance K = I V ^-3/2.

The charged particle beams that can be manipulated in particle accelerators can be subdivided into electron beams (sometimes called cathode rays), ion beams and proton beams.