Learning Forum

[rtk]

In many satellite communication research papers I came across a phenomenon named as multipaction. What is this phenomenon and when does it occur? Thanks in advance!

[VivekKamble]

Multipaction is the phenomenon that can cause a breakdown, mainly avalanche breakdown, due to high electric fields in a vacuum or near-vacuum environments. It is an electron resonance effect that occurs when RF fields accelerate electrons in a vacuum and cause them to impact with a surface, which depending on its energy, release of one or more electrons into the vacuum.

[Charlotte Blair]

Hi -

Also those electrons can then impact the same surface or another surface as they will be further accelerated by the RF field. As the impact continues to energize, the release of the number of electrons increases which in turn increases the frequency of such impacts, resulting in a sustained multipacation. If this scenario got exponentially elevated it may lead to serious operational problems. In many RF space systems, such multipaction will increase the noise figure and/or bit-error-rate which causes RF signal distortions and can damage the system components or subsystems.

[rtk]

Thank you for the quick responses. So, are there any specific conditions at which the Multipaction will occur?

[VivekKamble]

Hello,

Mainly there can be four cases where multipaction can occur.

1. If free electrons are available to start the release of secondary electrons.

2. If the mean free path of the electrons is greater than the spacing between the surfaces opposite to each other (no obstruction should be present in the way).

3. If the average number of electrons released is greater than the electrons yielded secondarily on the surface. This is dependent on the RF field strength between the plates. 

4. If the time taken by the electron to travel from the surface on which it got created to the surface with which it will impacts, is an integer multiple of half the RF period.

Hope that addressed your query!