Electron avalanche

An electron avalanche is a process in which a number of free electrons in a medium (usually a gas) are subjected to a strong electric field accelerate, ionizing the mediums' atoms by collision (creating positive ions), forming "new" electrons to undergo the same process in successive cycles. This ionization , and a free electron. Streamers in lightning discharges propagate by formation of electron avalanches. The streamers' high electric field strength moves ahead of the advancing tips. Avalanche processes are intensified in value or beauty and quality by formation of photoelectrons as a result of ultraviolet radiation emitted by the excited medium's atoms in the aft-tip region

Related Topics:
Free electron - Medium - Gas - Electric field - Ion - Lightning

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These high-energy electrons, accelerated by the field, (whichever their direction of travel) often collide with neutral atoms inelastically, potentially ionizing those atoms. In a chain-reaction - or 'electron avalanche' - those additional electrons are also separated from their positive ions by the strong potential gradient, causing a large cloud of electrons and positive ions to be momentarily generated by just a single initial event.

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Avalanche sustenance requires a reservoir of charge. A number of mechanisms can sustain this process, creating avalanche after avalanche, to create a constant corona current. A secondary source of plasma electrons is required as the electrons are always accelerated by the field in one direction, meaning that avalanches always proceed linearly toward or away from an electrode. The dominant mechanism for the creation of secondary electrons depends on the polarity of a plasma. In each case, the energy emitted as photons by the initial avalanche is used to ionise a molecule creating another accelerable electron. What differs is the source of this electron.

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A plasma begins with a rare natural 'background' ionization event of a neutral air molecule, perhaps as the result of photo-excitation or background radiation. If this event occurs in an area with a high potential gradient, the positive ion will be strongly attracted toward, or repelled away from, the curved electrode (depending on the polarity of the corona), whereas the electron will be attracted in the opposite direction. This will, occasionally, prevent the recombination of electron and positive ion.

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