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56 පේළිය:
Although a plasma is loosely described as an electrically neutral medium of positive and negative particles, a definition can have three criteria:<ref>R. O. Dendy, Plasma Dynamics.</ref><ref>Hillary Walter, Michelle Cooper, Illustrated Dictionary of Physics</ref><ref>Daniel Hastings, Henry Garrett, Spacecraft-Environment Interactions</reF>
# '''The plasma approximation''': Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of charge carriers within the sphere of influence (called the ''Debye sphere'' whose radius is the [[Debye length|Debye screening length]]) of a particular particle
# '''Bulk interactions''': The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
#'''Plasma frequency''': The electron plasma frequency (measuring [[plasma oscillation]]s of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics.
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