A corona discharge occurs when fluid around a conductor becomes ionized due to a high electric field strength. The discharge requires a high potential electrode in an electrically neutral fluid. The curved electrode’s polarity determines the type of corona discharge. It has applications in removing electrical charges from aircraft and removing particulate matter from the air.
A corona discharge is an electric discharge that occurs when the fluid around a conductor becomes ionized. The electric field strength must be large enough to cause ionization but insufficient to cause a true arc. This process requires an electrode with a high electrical potential in an electrically neutral fluid, usually air. A fluid in this context includes gases and liquids.
Electric current creates charged particles known as ions from neutral molecules in the fluid if the potential gradient is large enough. This is more likely to occur when the conductor has a sharp point. When the air around the conductor begins to conduct electricity, it actually becomes part of the conductor. This makes the conductor less sharp and may prevent ionization from extending beyond a certain distance from the conductor.
The ions eventually travel beyond this conductive region and become neutral molecules again. Conditions around the electrode may also allow the ionization area to continue to grow and form a fully conductive path. This will result in a continuous arc, or sparks, rather than a corona discharge.
Ideal conditions for a corona discharge generally require a pair of electrodes. An electrode should be very curved and is typically a small wire. The other electrode should be flat, like a plate. This difference in curvature between the electrodes ensures a high potential around the curved electrode.
The polarity of the curved electrode determines the polarity of the corona discharge. This means that a positively charged curved electrode produces a positive corona and a negatively charged curved electrode produces a negative corona. These two types of crowns have very different behavior due to the difference in mass between positive ions and electrons. Positive ions do not collide as frequently as electrons. This means that only negative coronas produce the ozone, purple glow and hiss associated with coronas.
There are a variety of applications for a corona discharge. It can remove an electrical charge from the surface of a flying aircraft. This can prevent an electrical discharge from damaging the aircraft’s electronic systems.
A corona discharge can also remove particulate matter from the air. It ionizes the air, which charges the particulate matter. The air then passes over an oppositely charged comb. The comb attracts charged particles, thereby removing them from the air.
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