Ion wind

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Ion wind, ionic wind, or coronal wind is a stream of ionized fluid generated by a strong electric field.

Electric charges on conductors reside entirely on their external surface (see Faraday cage), and tend to concentrate more around sharp points and edges than on flat surfaces. This means that the electric field generated by charges on a sharp conductive point is much stronger than the field generated by the same charge residing on a large smooth spherical conductive shell. When this electric field strength exceeds what is known as the corona discharge inception voltage (CIV) gradient, it ionises the air about the tip, and a small faint purple jet of plasma can be seen in the dark on the conductive tip. Ionisation of the nearby air molecules result in generation of ionised air molecules having the same polarity as that of the charged tip. Subsequently, the tip repels the like-charged ion cloud, and the ion cloud immediately expands due to the repulsion between the ions themselves. This repulsion of ions creates an electric "wind" that emanates from the tip, which is usually accompanied by a hissing noise due to the change in air pressure at the tip.

Unlike the functionality of the Electrohydrodynamic (EHD) thruster, the net force generated by an ion wind device does not rely on the momentum transfer between the charged and the neutral air molecules, but only on the impulse that the charged ions gain during their repulsion from the tip. It is analogous to recoil of a gun when it fires a bullet. Due to this property, ion impulse devices may find use in spacecraft propulsion, even though ion wind forces are much smaller than those of an EHD thruster operated in air.