Charged particle beam
A charged particle beam is a group of electrically charged particles that have approximately the same kinetic energy and move in approximately the same direction. Usually, the kinetic energies are much higher than the thermal energies of particles at ordinary temperatures.
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 energy of the particles, typically expressed in kiloelectronvolts or megaelectronvolts,
- the intensity of the particle current, expressed in amperes.
Both properties are often synthesized into the perveance 
.
Strictly speaking, a third parameter is required to characterize a charged particle beam, such as the emittance, which is a measure of the degree to which the particle trajectories are non-laminar.
The (technologically) most important types of charged particle beams are:
- electron beams, consisting of electrons.
- ion beams, consisting of ions.