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Re: [TCML] Ultraviolet Observations?

Carl and all,

This sounds like the millions of brushy streamers that grow off the tips (and feed current into) brighter, higher-current leader discharges. Although often called corona, these filamentary streamers are significantly more complex. Much of their color comes from excited neutral and charged nitrogen molecules, with long wave (UVA) wavelengths of approx. 391.4, 380.5, 375.5, 356, 337, and 315.9 nm.

BTW, something I tried many years ago with my 10" diameter 3.5 kVA spark gap coil - it's probably in the archives somewhere. You may want to try something similar...

From memory:
1. Shield the spark gap(s) so that no gap light can escape.

2. Top the secondary with a toroid that has a relatively large minor diameter, and remove any breakout point(s).

3. Adjust voltage to the coil so that it is a bit _below_ the level where it begins breaking out into a leader discharge

4. Wait until dark. Turn off all room lights, and let your eyes become dark-adapted for at least 10-15 minutes.

5. Carefully fire up the coil and look closely at the region around the topload. If necessary, look away from the coil and view it instead with your more sensitive peripheral vision. Stay away from the coil for safety.

If the experiment works, you should see a faintly flickering glowing bluish-purple region that may appear a bit more whitish on voltage peaks. This region spreads away from the toroid, becoming fainter with increasing distance from the toroid. On closer inspection, the glowing region is actually made up of millions of tiny, barely-visible filamentary discharges that are best seen just outside of the center of field of view.

This region extended for several feet around the toroid, being brightest in the plane of the toroid (i.e., where the E-field was the greatest?). As long as the toroid is smooth enough, no leaders will form. However a veritable zoo of interesting luminous pre-breakdown phenomena, avalanches and microscopic streamers, pulsed corona, and perhaps other forms of cold plasma discharges can sometimes be seen.

With lower-power coils, longer and thicker (but still quite faint) discharges can sometimes be seen. Jeff Behary has researched these unique discharges and he has also had some success photographing them. To my knowledge, these particular discharges have not been described in the technical literature, nor do they correspond to currently-defined discharge types and structures.


Carl Noggle wrote:
We have noticed a purple glow around TC streamers which doesn't seem to
be there in film camera pix.  There's no obvious structure, but it's
always there if the background is black enough.  Are the lenses made of
different glass?  Fused quartz, maybe?  You can get black flock paper
from astronomy stores which is very black and would make a good
background.  It would be interesting to find out what is going on here.


On 5/17/2015 3:50 PM, David Thomson wrote:
Why would you want to be limited to ultraviolet? If you are aiming to
measure the output radiation at the breakout of a high voltage system,
which can produce x-rays if sufficiently powered and designed, then you
will still be missing the active frequency of the output. Of course,
if you
were interested in the secondary ionization of the surrounding
ultraviolet could be useful. To maximize the ionization, however, means
having top load capacity in excess of the potential so that no streamers
are produced. I suspect in the case of ionized atmosphere there would
be a
visual blob roughly equivalent to the shape of the E field.

Dave Thomson

On Sun, May 17, 2015 at 3:05 PM, illuminated <illumination00@xxxxxxxxx>

In a similar vein to my other message, but more specific, has anyone
used a UV filter to view / record high energy experiments?  (400 nm
to 250
nm to be specific)

I am working on putting together a full spectrum camera for such
observations and am curious as to whether others have taken this
before to see what additional non visible light spectrum observations
have been made.

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