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>

Ken Herrick's comments interspersed:

On Thu, 29 Mar 2001 19:14:37 -0700 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
> 
> Hi,
> 
> It is interesting to note that with a solid state gap, one may have 
> say a
> low BPS rate (higher voltage) at the beginning of the streamer 
> formation
> and then have a higher BPS rate (higher current) once the streamer 
> is
> formed and growing.  You could really vary the gap timing, dwell, 
> BPS as
> you wanted with a little monitor to know what the coil is up to at 
> that
> instant of time.  It is all just a matter of hooking up digital ICs 
> (I
> suppose you could hook up a microprocessor too ;-)).  I guess you 
> can kind
> of tweak the BPS rate and such to give the streamer just what it 
> wants.

Hmmm...I don't know that my s.s. system quite works that way:  For each
burst of ac flux from the primary I get 1 spark.  When the repeating
bursts occur far enough apart, the repeating sparks more-or-less randomly
emit from various points arount the toroid.  But when those bursts are
very close together, as they are when I establish the interrupted-burst
mode I've described, then the repeating sparks seem all to go along the
same (already-hot) path, for the duration of that set of flux bursts.  As
I'd said, in that latter instance, some 400 us elapses between the
repeating burst events and I can hear a very pronounced "ringing" quality
in what still appears to be one spark but what must, as evidenced by that
sound, actually be repeating sparks all traveling along the same path.

So I'm persuaded that >every< burst of flux (by which I mean ac magnetic
field, from the primary, at the secondary's Fr) elicits 1 spark (& now
that I re-read that, I'm sure I'm stating the obvious!).  And, as I
commented on in another posting of today, that flux burst has to be BIG,
and not necessarily of long duration, in order to get LONG sparks.

KCH

> Perhaps with a little more monitoring you could measure the 
> streamer
> impedance and adjust the coil to feed it...  An odd thought...
> 
> I also note that solid state gaps will have a "softer" turn on which 
> will
> eliminate that large initial energy spike.  I wonder if that giant 
> VHF,
> UHF, GHz... noise burst makes a difference in getting the streamer 
> started?

...don't know what you refer to, here.

KCH

> 
> An interesting idea Jim had about flash tubes to fire a solid state 
> gap.
> My design is all complex digital but a flash tube may be a cheap and 
> easy
> way to go for a simpler form of solid state gap trigger.  Have to be 
> sure
> the tube does not eat too much energy.  Solid state gaps really are 
> a study
> in not loosing energy to anything but the streamer...
> 
> I wonder if Kennan's coil performance is hurt buy the MOSFET's VI 
> curves.
> Maybe IGBTs would not waist as much energy as heat since they tend 
> to have
> a much lower voltage drop at high currents?  I have not been 
> following
> Kennan's experiments as much as I should have been...
> 
> Cheers,
> 
>         Terry

Yes, I commented on the MOSFETs in another posting.  They do soak up
power but not so much, if my measurements are correct: some 120 W if I
recall my figure, while some 1500 VA is being drawn from the mains.

KCH
> 
> 
> 
> At 05:25 PM 3/29/2001 -0800, you wrote:
> >
> >----- Original Message -----
> >From: "Tesla list" <tesla-at-pupman-dot-com>
> >To: <tesla-at-pupman-dot-com>
>  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.
> >
> >> >
> >
> >
> 
> 
> 
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