Re: On sparks

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

Original poster: "Kennan C Herrick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <kcha1-at-juno-dot-com>

>From KCH:  This just came in when I emailed my response to Bert Hickman's
posting...so I'll just stay in the responding mode, with comments
interspersed:


On Thu, 29 Mar 2001 11:32:49 -0700 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Jim Lux by way of Terry Fritz 
> <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>
> 
> >
> > There are some interesting energy insights here...
> > The E-field and base current measurements imply that it takes a
> > comparatively large amount of energy to initially form the leaders 
> versus
> > the amount required to maintain them (at least for near CW 
> operation).
> 
> This is pretty much to be expected... once the spark channel is 
> established,
> the resistance of the channel drops, so you don't need as much 
> voltage to
> keep the charge flowing fast enough to keep the leader head moving.  
> I
> suspect that the leader head only moves on one polarity of the RF, 
> and that,
> during the other half, the charge is flowing back down along the 
> spark
> channel (keeping it hot).  

Don't know that I can agree:  Is not the spark very like a mere hot
resistor?...in which the ac current from the coil/toroid flows back &
forth just as it does in those components?  A hot resistor with a pointy
end, of course, as you point out so pointedly below.

> However, there's no question that more 
> voltage,
> if not more energy, is going to be required to form the channel in 
> the first
> place.

The bigger the emitting radius, the larger the required voltage--but not
necessarily the larger the energy, just to start the spark.  Merely, the
larger energy to pump up the voltage to the required level in the first
place.  Not too well put, but more or less right?

> 
> The "optimum" long spark waveform might be a big spike at the 
> beginning (to
> cause breakdown), and then substantial low impedance current to flow 
> along
> the leader.  The end of the leader is pretty "pointy" so it probably 
> doesn't
> take much voltage to create a big enough field there to keep the 
> breakdown
> going, especially compared to the "top load" which has a big ROC, 
> and needs
> a fairly big voltage to even start to breakdown.
> 
> An interesting thought here.. If the topload breaks down too early, 
> not
> enough charge will be stored to support the leader growth, so you 
> kind of
> want a big smooth topload so that it can accumulate enough charge to 
> support
> a big long spark.  However, given that you can transfer charge into 
> the
> topload on every cycle of the RF, with the right circuit, a breakout 
> point
> (to force earlier breakdown), combined with the right tuned 
> circuits, might
> work even better.

It seems to me that that charge in a big top load doesn't do a whole lot,
if anything, in sustaining any given length of spark.  Once the spark
starts, that charge is history.  After that, it's what power the primary
can continue to pump in, via the inductance of the secondary partially
acting undesirably in series, perhaps, that's important.
> 
> The whole thing reminds me of a "peaking gap", as used in impulse 
> testing.
> 
> 
> 
> 
> 
> 
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