Charged particle beam

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A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same velocity (speed and direction). The kinetic energies of the particles are typically measured in keV or MeV, much larger than the energies of particles at ambient temperature. The high energy and directionality of charged particle beams make them useful for applications.

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, typically expressed in kiloelectronvolts or megaelectronvolts,
the particle current, expressed in amperes,
the beam diameter, and
the 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 (technologically) most important types of charged particle beams are: