Streamer formation on the scope...

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

Tonight I hooked up my fiber-optically coupled current probe to the top of
the OLTC and made some "small" streamer measurements.  Admittedly, I did
all this pretty fast and loose ;-))

http://hot-streamer-dot-com/temp/P9050002.jpg

At first I just turned it up till I got some nice corona (sorry about the
blurry hand held):

http://hot-streamer-dot-com/temp/P9050003.jpg

The yellow waveform is secondary base current from a Pearson CT and is very
accurate.  The blue is from the current monitor from a wire spike off the
toroid.  The bandwidth of the toroid probe is 40MHz but the level is
uncalibrated here.

http://hot-streamer-dot-com/temp/SFarc01.gif 

You can see the corona current shoots out as negative current spikes
(negative voltages streamer far more easily than positive).  Here we are a
little closer:

http://hot-streamer-dot-com/temp/SFarc02.gif

That picture makes it look like there are many spikes, but really there is
only one during each bang.  The scope is trying to play it's
"digital-phosphor" trick and smearing many bangs into one picture.  The
spikes spreads out with a lot of jitter in time.  When we get closer and
trigger on the spikes it is much more clear:

http://hot-streamer-dot-com/temp/SFarc03.gif

Only about 400nS wide (got them RFI filters ready :-)).  Here is another
picture I got that shows a lot of harmonic content.  The "digital-phosphor"
things is cool here!:

http://hot-streamer-dot-com/temp/SFarc04.gif

Note the small frequency at about t=25nS...  F = 40MHz.  I worry when I see
things like that at the bandwidth of the probes.  Is it real, or a higher
order spike just kicking the probe bandwidth...  They are "supposed" to
roll of well and all that, but many grains of salt there...  They must be
-3dB down too...

As I turn up the juice I start to see these super spikes:

http://hot-streamer-dot-com/temp/SFarc05.gif

This is about what the top looks like now (maybe a little higher for the
scope pic.  I took the pics after the fact):

http://hot-streamer-dot-com/temp/P9050004.jpg

I "think" we are seeing the individual corona spikes beginning to gathering
into a 'streamer' in these "super spikes".  Here is a nice one.

http://hot-streamer-dot-com/temp/SFarc06.gif

Here is another spread out:

http://hot-streamer-dot-com/temp/SFarc07.gif

The event is only 135nS wide but it is probably a baby streamer just
starting out.  Seems to have about a 120nS harmonic or 8.3MHz.  There is
another 50MHz ring in there too.  We are seeing some serious current in
these super spikes.

http://hot-streamer-dot-com/temp/SFarc08.gif

Looks like 19.2nS or 52.08MHz....

I look back to Greg's Electrum scope pics of streamers currents at like
1000X the power:

http://www.lod-dot-org/electrum/sphere05us.jpg

Seems that the streamer is feed by spikes there too.  This suggests that
streamer currents are many powerful spikes rather than a nice sine wave.
Or a combination since Greg's and my waveforms have a nice heavy sine
content along with these spikes too...

So a rough qualitative look at how streamers begin to form...  Messy isn't
it :-))))

Cheers,

	Terry