Ion wind, ionic wind, coronal wind or electric wind describe the airflow induced by electrostatic forces linked to corona discharge arising at the tips of some sharp conductors (such as points or blades) subjected to high voltage relative to ground. Ion wind is an electrohydrodynamic phenomemon. Ion wind generators can also be considered electrohydrodynamic thrusters.
B. Wilson in 1750 demonstrated the recoil force associated to the same corona discharge and precursor to the ion thruster was the corona discharge pinwheel. The corona discharge from the freely rotating pinwheel arm with ends bent to sharp points gives the air a space charge which repels the point because the polarity is the same for the point and the air.
Francis Hauksbee, curator of instruments for the Royal Society of London, made the earliest report of electric wind in 1709. Myron Robinson completed an extensive bibliography and literature review during the 1950s resurgence of interest in the phenomena.
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 ionizes the air about the tip, and a small faint purple jet of plasma can be seen in the dark on the conductive tip. Ionization of the nearby air molecules result in generation of ionized 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. An opposite force acts on the tip that may recoil if not tight to ground.
A vaneless ion wind generator performs the inverse function, using ambient wind to move ions, which are collected yielding electrical energy.
- DIVISION OF ENGINEERING: ENGINEERING ASPECTS OF ELECTROGASDYNAMICS*- by MC Gourdine - 1968 - Transactions of the New York Academy of Sciences - Wiley Online Library
- Demo 41-06 Pinwheel - Video Encyclopedia of Physics Demonstrations
- Electrostatic pinwheel:Van de Graaff makes pinwheel spin - Lecture Demonstrations - UC Berkeley Physics
- Fun with Static Electricity, Elliott County 4H - Science Fun, Inc. - Alan Kuehner (ret.) Brookhaven National Laboratory
- Electostatic pinwheel - Indiana University Demo Reservation
- Electrostatic Pinwheel, European, later 19th century - The Bakken - A Library and Museum of Electricity in Life
- Robinson, M. (1962, May). History of the electric wind. American Journal of Physics, 30(5), 366-372.
- Robinson, M. (1960, June 8). Movement of Air in the Electric Wind of the Corona Discharge. (AD0262830)