Multipactor
From Wikipedia, the free encyclopedia
Multipactor is an effect that occurs when radio-frequency (RF) fields accelerate electrons in a vacuum (or near vacuum) and cause them to impact with a surface. The impact can, depending on its energy, release one or more electrons into the vacuum. These electrons can then be accelerated by the RF fields and impact with the same or another surface. Should the impact energies, number of electrons released and timing of the impacts be such that a sustained multiplication of the number of electrons occurs, the phenomenon can grow exponentially and may lead to operational problems of the RF system such as damage of RF components or loss/distortion of the RF signal.
The existence of multipactor is therefore dependent on the following three conditions being met:
The average number of electrons released is greater than one (this is dependent on the secondary electron yield of the surface) and the time taken by the electron to travel from the surface from which it was released to the surface it impacts with is an integer multiple of one half of the RF period and the average secondary electron yield is greater than one.
Multipactor was discovered in the 1920s by Philo T. Farnsworth, the inventor of electronic television, who attempted to take advantage of it as an amplifier. More commonly nowadays, it has become an obstacle to be avoided for normal operation of particle accelerators, vacuum electronics, radars, satellite communication devices, and so forth. A novel form of multipactor has been proposed (Kishek, 1998), and subsequently experimentally observed, in which charging of a dielectric surface considerably changes the dynamics of the multipactor discharge.
[edit] See also
[edit] References
More information on multipactor may be found in:
- J. Rodney M. Vaughan, Multipactor, IEEE Trans. Electron Devices, vol. 35, No 7, July 1988.
- Rami A. Kishek, Y.Y. Lau, L.K. Ang, A. Valfells, and R.M. Gilgenbach, Multipactor Discharge on Metals and Dielectrics: Historical Review and Recent Theories, Physics of Plasmas 5 (5), 2120 (1998).
