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Re: Streamer models used with Terry's new program



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Steve,

I got a book on plasma physics that I will see if I can find anything useful and maybe I should revist my old chemisty book too. Another approach might be a multidimensional table where entries might be excess charge, Ctop, ROC, etc all normalized to STP at sea level. This would be an empircally based table and maybe the entries could be normalized too and a freau like equation would result. I'll hit the books first.

The start point would be zero voltage on the topload and a bang is starting to ring up. One would integrate the RF current flowing into the topload and compute the accumulated charge and voltage on the topload using its capacitance (with no streamer loading present) and the time step used in the program. The voltage would increase (in a sinusoidal way) until the breakout voltage was reached. Any current flowing into the topload after breakout occurs would result in excess charge going into the streamer channel.

All sounds fine so far ;) Antonio's simulation code could easily do that.

If one could estimate the channel size needed to absorb the excess charge perhaps using ambient temp and pressure, one could estimate the added capacitance this presented to the topload.

Here's where it starts to get tricky. I thought of one possible simple way to do it. In chemistry handbooks you can find ionization energies for nitrogen and oxygen, ie so many kJ to ionise one mole of the stuff. Or maybe (since you're dealing in charge) you could use the Faraday constant, that says it takes 96500 (iirc) coulombs to singly ionise one mole of anything. Also you know one mole of any gas is about 22 litres at STP or whatever. So you could estimate what volume of gas gets ionized by a given amount of charge, and make some assumptions about how it's distributed (sphere, cone, fractal, whatever) to get a surface area and hence a capacitance.


Possible problems with the Faraday constant approach- It doesn't take impact ionisation into account (one loose electron- so one quantum of charge- can ionize several atoms) nor account for the fact that current might flow through previously ionized gas rather than creating fresh ions. I don't know enough about the physics of atmospheric pressure discharges to visualise how that would affect the result.

Maybe at first, one keeps things simple and see how accurate of a prediction it makes. I like the mole approach so may look into that first. The absolute accuracy may not be as important as getting a relative effect so long as it is reasonably useful for optimization. Then of course one could introduce a fudge factor
to improve the absolute accuracy like maybe a Reynolds number, but unfortunately that has already been taken. :o))



Dont know if this is a correct way of thinking of streamers (either partly or completely)

Neither do I :P I'm wondering if there is a way to digitize two waveforms from a coil (secondary base current and primary current?) and process them to graph streamer load impedance in real time as a bang progresses. I don't know if that is theoretically possible, maybe you need four waveforms since a dual resonant system has four state variables.


Steve Conner