Re: Useless questions

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


> 
> Moving in a different direction then...
> 
> Can we shine a bright light across the topload to illuminate a
> screen?  Hot air channels caused by streamers might be visible
> as slightly darker lines on the screen, since light passing through
> a hot channel would be scattered by the altered refractive index.

I think that the shadowgraph approach is a good one... 

It's easy to come by a electronic strobe that has a 1 microsecond flash
duration (the GenRad Strobotac...), and which can be externally
synchronized (i.e. to the "bang").  A suitable digital camera which can
also be synchronized, etc. to capture the image (or, gods forbid, use a
film camera!)...

Schlieren approaches also come to mind, but I think the area you want to
look at is big enough that a Schlieren apparatus would be impractical.

You could set it up like:

Strobe/Tesla Coil/Translucent Screen/Camera

or 
Strobe/Tesla Coil/Field lens and stop/Camera


Shorter flashes than 1 microsecond are possible, but hard to do casually...
(transmission line pulse former, air/surface sparkgap).  A nitrogen laser
makes nice pulses that are a few nanoseconds long.

A Kerr cell can be used to make a very fast shutter (nanoseconds), but is a
project comparable to a TC in complexity (and, you have to fool with things
like nitrobenzene, which is a truly evil substance)
> 
> Then, if the screen was viewed by a TV camera, frames grabbed both
> during a bang, and between bangs, might give firm evidence that
> these hot channels persist between bangs, and might even show
> them being re-used at the next bang.
> 
> It might not be too easy to grab frames synchronously at two or more
> times the bps rate, but if frames were grabbed asynchronously, they
> could be sorted out if the primary gap was also visible in the
> image.  I recollect this kind of thing has been talked about before,
> but I don't know if it's been tried.



That said... I think that optical techniques are our best hope for spark
diagnostics.

Even a simple spinning mirror and camera might give useful information.  A
silvered prism is typical, spun with something like a diegrinder at
10-20,000 rpm. It would be like the Boys camera used for looking at
lightning. (Prisms have less air drag than a flat plate)


> --
> Paul Nicholson
> --