Re: High speed Tesla spark photographs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

The image will be smeared unless you are seeing something that just 
flashes on for less than say 10 us such as a spark or LED pulsing at 100kHz.
Anything like an incandescent globe will just be a continuous smear.
Hence anything that is hot or burning such as a dust mote (as I 
conjecture) will be a continuous line that persists for much longer 
than the range of the screen of perhaps 200us. A hot metal particle 
would also do this.
I could test this by throwing a handful of dust at the spark....
In terms of the thermal time constant of the plasma channel, 
experiment beats guessing again :)
Ionisation should go away rapidly but "hot" things will remain hot 
for a while. I'm not sure how well we can see hot air but I imagine 
(guessing again!) black body radiation of air is far dimmer than ionisation.

I'm working on a new add on that will give some nice info to 
complement this streak camera stuff but have tested it on ignition 
coil sparks only so far. Details when it gets "tidy".

Peter
http://tesladownunder.com

> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>
> I had the same question, but after studying one image on Peter's web
> page more carefully, I think I understand.  The photo that shows a
> burning dust mote:
> http://tesladownunder.com/HVRotMirrorTeslabigSpark1dustmote.jpg
> ...shows a single, more or less horizontal arc, with just one point
> within the arc smearing vertically.  Peter concludes this is a burning
> dust mote, and this demonstrates that the arc luminosity must be pulsing
> at 2xFres.  I found this to be very surprising, since I would have
> guessed that the thermal time constant of the plasma channel would be
> far longer than a fraction of the Fres period.
>
> Regards, Gary Lau
> MA, USA
>
> > Original poster: Russell L Thornton <Russell.L.Thornton@xxxxxxxx>
> >
> > I guess I am showing my ignorance or I missed a message somewhere,
> > but I am unclear as to why the image captured through a rotating
> > mirror will not be smeared.  Could someone please take a moment and
> > explain the process in a little more detail.  Off-line is OK if it
> > will be redundant to the list.
> > Thanks,
> > Russ