Multipaction

Multipaction is a process in which a charged particle inside a gap in a vacuum environment (or very low atmospheric pressure), oscillates due to the influence of an externally applied oscillating electric field of large strength, and every time it hits the gap walls it causes other charged particles to be released. The secondary charged particles that have been released then oscillate due to the externally applied electric field and release more charged particles upon impacting the gap wall. Eventually, enough charged particles participate in the process to create a spark, which is undesirable and usually causes damage.

Multipaction is usually seen only in vacuum environments because at atmospheric pressure, the charged particles are likely to collide with air particles, reducing the charged particle's velocity and energy. This reduces the likelhood that the charged particles will be able to cause release of secondary particles upon impact with the gap walls.

Because multipaction occurs in vacuum (or a low pressure environment), it may limit the power output of microwave frequency transmitters in spacecraft and high-altitude aircraft applications. Waveguide components in such applications are sometimes pressurized to overcome the limitation imposed by multipaction.

External links

* [http://www.ee.surrey.ac.uk/Personal/D.Jefferies/microwaves.html Microwave page] by Professor David Jefferies at the University of Surrey (see Multipaction section).
* [http://home.earthlink.net/~jimlux/hv/multipact.htm Multipaction page] on an Jim Lux's web site.
* [http://www.nasa.gov/offices/oce/llis/0770.html Explanation of Multipaction] on a NASA web site
* [http://www.astrolab.com/11.asp Explanation of Multipaction] on a commercial web site.