Re: Measuring Streamer characteristics

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Bob,

The actual streamer current is usually seen as a jagged edge on the current 
graphs.  This picture shows them well:

http://www.lod-dot-org/electrum/sphere10us.jpg

There is always an initial very short but very powerful "burst" when the 
spark gap first fires composed of MHz to GHz noise that swamps the 
equipment.  It often saturates the fiber optics creating longer apparent 
pulse widths.  also, when current is delivered, the top voltage may drop 
drastically very fast.

In ground strike pictures like this:

http://hot-streamer-dot-com/TeslaCoils/MyPapers/smallar/Image149.jpg

The powerful RF noise form the discharge simply wipes out the measurement 
equipment and any scale factors are lost.  Your just seeing radiated noise 
into the equipment and grounds.  One could conclude by the voltage and 
discharge time what the current "might" be.  But don't trust the scale of 
the graphs at those moments.

I hope that answers your question.  Plane wave antennas are far more 
capable in many instances:

http://hot-streamer-dot-com/TeslaCoils/MyPapers/planant/waveant3.html

Cheers,

         Terry







At 10:14 AM 10/1/2004, you wrote:
>Hi all,
>
>
> >Subject: Re: Measuring Streamer characteristics
> > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
> >
> > Hi Bob,
> >
> > Greg measured the streamer current for the Electrum directly from inside
> > the sphere (he was INSIDE it while it was running!) with a hand held
> > scope.  I have a top load sphere with fiber probes built into it.  This is
> > how we came up with the 220K +1pF per foot of capacitance model for a
> > streamer load.
> >
> > http://hot-streamer-dot-com/TeslaCoils/MyPapers/modact/modact.html
> >
> > http://hot-streamer-dot-com/TeslaCoils/MyPapers/smallar/smallar4.html
> >
> > http://www.lod-dot-org/electrum/electrumspecs.html
> >
> > http://www.lod-dot-org/electrum/electrumfull.jpg
> >
>
>Nice work Terry and Greg very interesting.
>
>I notice from both streamer current profiles there is an initial triangle
>pulse of current approximately at the peak positive top load voltage.
>The pulse has a duration of about 5us I assume this is the initial break
>out. Given the different sizes of the two system the pulses are very
>similar.
>
>In the case of  Electrum there are then three bursts of oscillation at
>alternate voltage minima of the top load while the current builds to an in
>phase value with the top load current.
>Which means its 90deg out of phase with the top load voltage.!!! I suspect
>the burst of oscillation is when the streamer connects to ground but then
>why the difference in top load current and streamer current.?????
>
>In the case of Terry's papers the second one seems to support the
>oscillation idea when the streamer connects to ground.
>
>Assuming the first paper is a streamer to air, in one cycle the streamer
>current develops in to an in phase (aprox) current with top load voltage.
>A visual estimate of the predominantly resistive impedance is 240kV/0.8A =
>300k . The streamers were believed to be between 12 and 24 inches long.
>Of cause  a better value could be obtained from processing the data points.
>
>Unfortunately we don't know if the streamer was growing during the
>successive current cycles. Its length may have formed in the first current
>pulse.
>
>Some cams have exposures times of a 1us and many have 10us.  Unfortunately
>most don't have a sync input.
>Even with minimum exposure times of 100us provided you could sync the start
>of the exposure to a particular peak of the output voltage and the was some
>repeatability form streamer to streamer it should be possible to determine
>of the there is significant streamer growth during repeated cycles.
>Assuming no sync is available perhaps a bar graph display could be
>synchronized to the coil and just take video at the shortest exposure with
>the bar in view with the streamer.  Occasionally the start of exposure could
>occur on a particular cycle of interest. Probably a very tedious experiment.
>Perhaps the coil could be synced to the cam. This could be very simple for
>those with the right kind of coil.
>
>Thinking about the above presumably the guys with variable burst width SSTCs
>can answer that if they have not done so already.
>
>
>Bob