[AMPS] breakdown in vacuum

[Steve Thompson]

In message <01BEA053.67272160.W4EF@pacbell.net>, Michael Tope
<W4EF@pacbell.net> writes
>
>Jon,
>
>I think the phenomenon you are discussing is know as "multipaction". I am
>not familiar with the details of the physics, but suffice it to say that your 
>friend
>is correct that ionization is more prevalent at low barometric pressures. I 
>have
>seen this demonstrated on a airborne HF antenna mast in an altitude chamber.
>
Somewhere I have a NASA study about multipaction in rf feeders - I'll
see if I can find it and look out the reference details if anyone is
interested.

Multipaction happens at very low pressure where an ion/electron landing
on a surface releases electrons or ions from the surface which then
provide more conduction - it's an avalanche type of effect. The
particles need collision free paths to build up enough speed to deliver
the energy to release more particles, so it only happens in very
rarefied atmospheres.

Steve


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