Streamer discharge

A streamer discharge, also known as filamentary discharge, is a type of transient electrical discharge. Streamer discharges can form when an insulating medium (for example air) is exposed to a large potential difference. When the electric field created by the applied voltage is sufficiently large, accelerated electrons strike air molecules with enough energy to knock other electrons off them, ionizing them, and the freed electrons go on to strike more molecules in a chain reaction. These electron avalanches (Townsend discharges) create ionized, electrically conductive regions in the air near the electrode creating the electric field. The space charge created by the electron avalanches gives rise to an additional electric field. This field can enhance the growth of new avalanches in a particular direction. Then the ionized region grows quickly in that direction, forming a finger-like discharge called a streamer.

Streamers are transient (exist only for a short time) and filamentary, which makes them different from corona discharges. They are used in applications such as ozone production, air purification or plasma medicine. Streamers pave the way for arcs and lightning leaders, in which the ionized paths created by streamers are heated by large currents. Streamers can also be observed as sprites in the upper atmosphere. Due to the low pressure, sprites are much larger than streamers at ground pressure, see the similarity laws below.

The theory of streamer discharges was preceded by John Sealy Townsend's discharge theory from around 1900. However, it became clear that this theory was sometimes inconsistent with observations. This was especially true for discharges that were longer or at higher pressure. In 1939, Loeb and Raether independently described a new type of discharge, based on their experimental observations. Shortly thereafter, in 1940, Meek presented the theory of spark discharge, which quantitatively explained the formation of a self-propagating streamer. This new theory of streamer discharges successfully explained the experimental observations.

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