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>

Comment from KCH at the end...

On Thu, 29 Mar 2001 18:49:01 -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>
> 
> 
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Thursday, March 29, 2001 3:55 PM
> Subject: Re: On sparks
> 
> 
> > 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.
> 
> but its a resistor that changes value dramatically in the early 
> stages of
> development.  High at first, low after it's gotten good and hot.
> 
> 
> > >
> > 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 source impedance of the secondary is really high in comparison 
> to how
> fast the spark channel develops.  I think that any growth in the 
> spark has
> to come from charge stored in the top load, where it has a low 
> inductance
> path to the channel.  With everything set up right, I can see the 
> spark
> growing, and charge flowing from the secondary L into the topload 
> and thence
> into the spark on sort of a continuous basis, but I'm not sure that 
> this
> would really work.  Sparks grow pretty fast, so you're talking 
> nanosecond
> time scales for the growth, and microsecond time scales for charge 
> to move
> from L into C.

No, I'm still skeptical of that charge in the top-load.  Upon overnight
reflection, I'm beginning to conclude (and this point has no doubt been
made by others, before) that the big difference between s.s. and
spark-gap systems--exhibited in the difference between the natures of the
sparks obtained--lies in the power-vs.-time relationship of the primary
excitation.

In my s.s. system, I establish a spark duration of 7 ms but I only
presently generate the primary's magnetic flux from about 36 A x 3 turns
= 108 ampere-turns.  That situation produces relatively short sparks
(although they're 3' or so: not too bad, I will say, from the 160 V power
source) but relatively fat, bushy and branched ones because there's time
for those qualities to develop.

In a spark-gap system on the other hand, I conjecture that the flux is a
whole lot higher--many more amperes, maybe orders of magnitude, through
more-or-less the same quantity of turns--and the duration of that flux,
per spark, is a whole lot less.  Thus, the spark "gets out there in a
hurry"; it's longer but it doesn't have time in which to develop as much
thickness or as many branches.  But the power taken from the mains is
much the same in the two cases; it's just that that power is applied to
the primary in shorter, more-intense bursts in the spark-gap system.

I think that the relatively small effect of the size of the top load is
clear from the fact that I can readily generate enough voltage to break
down the smooth 6" x 24" Landergren toroid but I still can push the spark
length only to 3' or so, even though I keep pushing for all of 7 ms.  It
has some effect, certainly since--all else remaining the same--I find
that my 7 ms sparks as emitted from the toroid are at least half-again as
long as those emitted from a surface having half the radius.  But the big
factor that gets the spark 'way out there is that initial ZOT!! of
primary flux.

I'm sure this subject needs more clarification & perhaps correction.

Ken Herrick
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