Re: DC secondary components

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



> The best you'll get is a small DC component to the base current
> resulting from asymmetrical conduction (partial rectification) within
> the topload discharge.
> 
> Can anyone remind me what polarity that will be?  I'd dearly like
> to know if/how this DC base current relates to streamer length,
> bang size, etc.  Does the current increase from bang to bang within
> a burst?
> 
> 
> There is no DC coupling between primary and secondary, so only the
> AC components can get through.  Any DC component present in the
> secondary must therefore be due to non-linearity of the secondary
> load, or of the ground return circuit.

I should think that a spark is a pretty nonlinear phenomenon... 
Measurement of average DC current might be very interesting, and a very big
measurement challenge in the presence of large AC currents and fields.  

Corona discharge isn't a particularly high current phenomenon ( a few mA),
and in the case of a TC, the duty cycle is very low (i.e. only when a
"bang" is in progress).  Most of the spark theory says that the charge for
a free air streamer moves back into the source as the spark collapses,
leaving essentially neutral (net) air behind (it might be ionized, but
there's an equal number of + and - ions).

Without giving it much thought, I would expect the DC average current to be
in the microamps, with the peak (during a bang) perhaps in the milliamp
range.  Measuring this in the presence of amps of RF would be a challenge
(you're not going to do it with your current probe and oscilloscope for
instance).  One approach might be to run the secondary current through an
electrolytic cell and measure the amount of metal added or removed (like
the old Edison Watthour meter).  You could get very long integration times
this way so the change would be noticeable.  Measuring part per million
values though (which is what you are doing) is never easy.

> 
> 
> What happens if you put a DC supply - several kV, in
> series with the base, to provide a genuine DC component to the
> topload charge, in the way that Robert describes - does that do
> anything to enhance the performance?

This is an intriguing idea.  Especially if you were to make the voltage a
significant fraction of the topload voltage during breakout, so that you
would effectively be favoring one polarity of leader.  I'll bet you would
notice a change in the nature of the streamers and sparks depending on the
polarity, since there is a well documented difference for corona discharge.

You'd want a good RF bypass cap across the power supply, or the series
impedance of the power supply would dominate. Most HV supplies use some
form of multiplier/filter arrangement, not known for great RF performance.
An RF choke would also be useful... 

Hmmmm... one of those HV brick supplies that put out several mA at 10-20 kV
from a copier..

You'd want a small TC (low voltage) for this so you could really make a
difference. A few kV out of 500 kV on a big coil might not make a
difference.  10-20 kV out of 75-100 kV though...


> 
> So many TC frontiers...so much real work to do.
> --
> Paul Nicholson
> --