What is Multi-Paction?

What is multi-pcation and when does it occur?

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- everything RF

May 7, 2017
RF Devices in Satellite communication systems, including filters and multiplexers are subject to high RF power levels. These high power levels can lead to a unique nonlinear breakdown voltage phenomenon in a vacuum or near-vacuum environment called Multipaction. This effect can render a device useless and, thus degrades the reliability of the satellite. All high power devices that are used in space have to be analyzed with regards to their breakdown behavior.

Multi-paction occurs in a vacuum when free electrons present in a satellite device are accelerated toward the walls of the device (usually a waveguide) with enough energy, that their impact against the wall could result in secondary electron emissions. As this process is repeated millions of times per second, the number of electrons multiplies rapidly, leading to a multi-paction discharge. This discharge is usually release a small amount of power, however causes increased outgassing in the component or system, which can lead to a gas discharge. A gas or corona discharge in a space system can release a large amount of power, thus causing component performance degradation or even system failure.

A Few Important Points about Multi-pation:

  • Multi-pation usually only occurs in a vacum or near-vacum environment because in air, the free electrons are more likely to collide with air particles, reducing their velocity as well as their potential to release secondary electrons.
  • The ambient pressure should be sufficiently low so that the electron mean free path is longer than the electron separation distance. This has usually the case at pressures less than 10-2 Torr.
  • Rounded metal surfaces and thin dielectric coatings within a component can lower the possibility of a multipaction discharge. This is because multi-paction effects are essentially arcing of electrons across a narrow gap. Sharp edges within an RF component can provide the geometry for bunching of free electrons in high concentrations, leading to a discharge event.

CST has an application note that talks about how to simulate Multi-paction within a component using their software. Click here to download the application note.

Although multi-paction effects are often difficult to predict and measure, properly equipped test systems with dedicated software can accurately identify microwave components that may multi-pact, effectively screening them to avoid damage in a deep-space application. There is a detailed article on NASA Tech Briefs about how to measure Multi-paction effects in system. Click here to read the article.