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RE: Terry's New Plane Wave Antenna



Original poster: "Marco Denicolai" <marco.denicolai@xxxxxxxxxx>

Hi Paul,

> Some of the things I'm not clear about are
> a) What's the nature of the space charge, is it always one
> polarity or the other?

Positive discharges leave a POSITIVE space charge that makes more difficult
subsequent discharges.
For negative discharges I don't recall. I have at home one paper were it is
stated very clearly, I don't recall just now.

> b) After the bang, the grounded coil has no charge, therefore
> for overall charge conservation, there should be some opposite
> charge lying around somewhere. I mean, if the bang goes off inside
> a Faraday cage, and (say) there's a bunch of positive ions left
> hanging in the air, where has the negative charge gone?

Electrons move a lot faster than positive ions. During positive discharge
electron are attracted and "consumed" by the anode, leaving slow positive
ions in place in between anode and catode.

> c) How fast does this static charge distribution decay?

There are two factors (both have been measured, just haven't got the data
here with me). There is thermal dilatation of the gas (air) and also ion
repulsion. Together, we are talking about several tens of milliseconds
(20-40 ms) before the space charge effect gets sensibly reduced.

> d) Does it affect the next bang?  Does anything 'build up' over
> a series of bangs?

Oh yes, indeed. Affects even "within" the same bang. If the potential rises
too quickly, guess what, the streamer stops propagating! This happens
because the space charge prevents it. It's a complex story...

A steep perturbation (increase) of the applied voltage:
- during the first stages of the discharge as no effect
- in the middle of the discharge it chockes the leader
- near to the end of the discharge it starts the final jump (i.e. the
breakdown).

I'm still working on that discharge model, almost done with positive
discharges...:)

Best Regards