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A non-neutral plasma is a plasma for which the charge is sufficiently different from zero, so that the electric field created by the un-neutralized charge plays an important or even dominant role in the plasma dynamics. The simplest non-neutral plasmas are plasmas consisting of a single charge species. Examples of single species non-neutral plasmas that have been created in laboratory experiments are plasmas consisting entirely of electrons, pure ion plasmas, positron plasmas, and antiproton plasmas.

Non-neutral plasmas are used for research into basic plasma phenomena such as cross-magnetic field transport, nonlinear vortex interactions , and plasma waves and instabilities. They have also been used to create cold neutral antimatter, by carefully mixing and recombining cryogenic pure positron and pure antiproton plasmas. Cryogenic pure ion plasmas have been used in studies of quantum entanglement. More prosaically, pure electron plasmas are used to produce the microwaves in microwave ovens, via the magnetron instability.

Neutral plasmas in contact with a solid surface (that is, most laboratory plasmas) are typically non-neutral in their edge regions. Due to unequal loss rates to the surface for electrons and ions, an electric field (the "ambipolar field" ) builds up until the loss rates are the same, acting to hold back the more mobile species. The electrostatic potential (as measured in electron-volts) required to produce this electric field is typically on the order of the electron temperature.

Non-neutral plasmas for which all species have the same sign of charge have exceptional confinement properties compared to neutral plasmas. They can be confined in a thermal equilibrium state using only static electric and magnetic fields, in a Penning trap configuration (see Fig. 1). Confinement times of up to several hours have been achieved. Using the “rotating –wall” technique, the plasma confinement time can be increased arbitrarily.

Such non-neutral plasmas can also access novel states of matter. For instance, they can be cooled to cryogenic temperatures without recombination (since there is no oppositely-charged species with which to recombine). If the temperature is sufficiently low (typically on the order of 10 mK), the plasma can become a non-neutral liquid or a crystal. The body-centered-cubic structure of these plasma crystals has been observed by Bragg scattering in experiments on laser-cooled pure Beryllium plasmas.