Re: High speed Tesla spark photographs - StreakScope

["Tesla list" <tesla@xxxxxxxxxx>]

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