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Re: High speed Tesla spark photographs - StreakScope



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

I got the Streak Camera Oscilloscope all wired and put together and got the first pictures in:

http://drsstc.com/~streakcam/instruments/BarScope-04.JPG

http://drsstc.com/~streakcam/instruments/BarScope-02.JPG

Here it is on top of the toroid ready to go. It is set to measure the streamer current with a CT on the breakout point wire.:

http://drsstc.com/~streakcam/instruments/BarScope-05.JPG

Sorry, these are big like 1+Meg pictures but I did not want to loose detail.

First is the scope and all through the camera at 1/400s shutter speed. Each LED is 1/2 amp and time is from bottom to top. The calibration markers are 100kHz and positive is to the right: The four sided mirror is at ~10,000 RPM.

http://drsstc.com/~streakcam/instruments/Scope-000.JPG

This picture was at 1/40s shutter and the grid lines over lap badly. But the picture is cool in that you can see the ring up and sort of a current decay after the main strike. There is a leader above it that was caught too. If you look close you can easily see the 200kHz 2nd harmonic that Peter has reported and its leader just before the main strike.:

http://drsstc.com/~streakcam/instruments/Scope-001.JPG

Next I upped the shutter speed to 1/400 sec to get rid of the overlap. This picture had one overlap but it is pretty clear anyway. The streamer is negative and has a 2 Fo harmonic just before the strike and then there is a positive current after the main strike of 1 amp that lasts for about 7.5uS

http://drsstc.com/~streakcam/instruments/Scope-003.JPG

The last picture is just a leader with some odd details if you look close:

http://drsstc.com/~streakcam/instruments/Scope-004.JPG

I need to do that following:

1. Dim the grid LEDs so they are not so bright. They cause a little ambient light wash now.

2. Wire the grid and calibration LEDs to only turn on only while the current is > 0.5 amp (only during a current event). That will eliminate the overlap problem and allow a far higher chance of getting good shots with far slowwer shutter speeds (like 1/20s).

3. Make a little scaling control so that I can increase and decrease the sensitivity. The scope goes to +-5 amps now but it should probably be 2X to 4X that for leaders. Strikes are probably so powerful and fast I will never really catch them properly.

4. "Fiddle" with things to get the pictures a bit better.

Cheers,

   Terry