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Re: Why does top capacitance work?



Bert Hickman wrote:

> Greg,
> 
> You certainly make some compelling points. I agree that the "root" of a
> streamer, once formed, will act as a weakenned area during subsequent
> bangs, since it's the area of highest current density and should have
> the greatest degree of thermal ionization. The advantage a large toroid
> may provide on higher-impedance coils may come from providing a low
> impedance energy reserve (i.e., a capacitor to ground) during the time
> that the streamer is re-propagating along the weakenned path blazed by
> its predescessor. Adding larger capacitance will provide a
> proportionately larger reserve of energy once the voltage rises to the
> point where reignition occurs. 

I suppose that could be true, but does the toroid really store a significant
amount of the secondary energy?  What do you suppose the time constants would
be for the toroid capacitance alone discharging into the streamer? 20pF x 400k?
A high speed current probe at the toroid may be the only way to find out.

> The fact that there seems to be little
> benefit on your large coil may be due to it's relatively low impedance -
> it doesnt need any help, and adding the toroid merely reduces peak
> voltage. Ultimately, it IS power which governs ultimate streamer length.
> 
> Certainly your last point is true, although Wysock and Cox's coils tend
> to have BIG tank caps, small primary inductance and small top
> dischargers -- Adding tank capacitance alone seems to be sufficient for
> BIG streamers on larger coils.
> 
> Looks like there are still lots of mysteries to be solved! BTW, what do
> you do for a living that lets you play with these nice toys?? :^)
> 
> -- Bert --

My HV equipment doesn't come from work, but rather from a variety of sources;
most notably SRL, and a large local scrapyard that is closed to the public but
allows SRL to sift through the lots as they come in.  Also, SRL occasionally
receives donated equipment from companies seeking a tax writeoff.  We got an
80kJ cap bank with charger that way, a few years ago.  A lot of horse-trading
goes on with local companies, as well.

-GL