Re: On sparks

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

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.
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?

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



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>
>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.
>
>> >
>
>