Runaway breakdown is a theory of
lightning
Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...
initiation proposed by
Alex Gurevich in 1992.
Electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s in air have a
mean free path
In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a ...
of ~1 cm. Fast electrons which move at a large fraction of the
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...
have a mean free path up to 100 times longer. Given the longer free paths, an
electric field
An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...
can accelerate these electrons to energies far higher than those of initially static electrons. If they strike air molecules, more
relativistic electrons will be released, creating an avalanche multiplication of "runaway" electrons. This process, called the
relativistic runaway electron avalanche, has been hypothesized to lead to
electrical breakdown
In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material (a dielectric), subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All ...
in thunderstorms, but only when a source of high-energy electrons from a
cosmic ray
Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...
is present to start the "runaway" process.
The resulting conductive
plasma trail, many tens of meters long, is suggested to supply the "seed" which triggers a lightning flash.
See also
*
Spark gap
A spark gap consists of an arrangement of two Conductor (material), conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential differenc ...
*
Avalanche breakdown
*
Electron avalanche
An electron avalanche is a process in which a number of free electrons in a transmission medium are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them ( impact ioniz ...
References
External links
How cosmic rays trigger lightning strikesRunaway Breakdown and the Mysteries of Lightning - Physics Today May 2005
Also available on-line at: http://www.phy.olemiss.edu/~jgladden/phys510/spring06/Gurevich.pdf .
Nova Science Now segment on Lightning - Aired on PBS October 18, 2005
Lightning
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