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High speed Tesla spark photos

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Terry Fritz

Sun Sept 24 2006, 03:12PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Peter Wrote:

Terry, try reducing your spark distance to 6 inches and I bet you will see the ring down.

Oh! OK!! I never understood that before. I see now.

I am working on a 20 segment LM3914 based LED array run from the current transformer. However I need to test the LM3914 first to see if it will work fast enough. I hope I can get one locally to test.

For focus, I have just been measuring the distance and setting the camera's manual focus to that distance. Seems to work fine. You could also set the camera up towards a picture on a wall or something at the same distance.

Cheers,

Terry

Tesladownunder

Sun Sept 24 2006, 03:33PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Hundreds of photos each a little different.

Back to the Australian standard of time going down and toroid on the left. Did the focus differently but I think the mirror is preventing better results. A bit like the Hubbles predicament after it got launched with a dodgy mirror.

Photo
1 Mirror stationary. LED monitors at both ends and read in the same direction. Cathode (negative) is closest to the spark at the toroid end
2 Streamer with ring up of a number of cycles but fades without a strike.
3 Streamer from toroid plus streamer from the ground (bypassed my LED's)
4 A horizontal spark with ring down, crosses a superimposed diagonal streamer with ring up. You don't get to see ring up and ring down on the same spark.

Check out the new current meter in the LEDs for spark monitoring thread. Should work well. Has 6 orders of magnitude coverage (theoretically).

Peter

1159112035 10 FT15766 Hvrotmirrordualmirrorstopped

1159112035 10 FT15766 Hvrotmirrordualledstreamerringup

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1159112035 10 FT15766 Hvrotmirrordualledstreamercrossespark

Tesladownunder

Sun Oct 01 2006, 05:17PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

I have been a bit busy with other pursuits such as picking up some big old
discarded physics equipment and attending the Tesla exhibition. A week
without new developments has been a long time in the high speed Tesla
photography field.
I was however able to obtain a new higher quality mirror of 10 x 15 cm which although rear silvered, does not show any distortion visibly when viewed
from a distance. It is well centered but moves a fearsome amount of air and
has some vibration at 3000 RPM (250 VAC) but 2000 RPM (85 VAC)seems
comfortable. It is a big mirror to spin fast but the aluminium supports seem
to hold it firmly without adding too much weight or obstructing the view.
The reduced revs should be countered by the much clearer and wider view.
Still needs to be tested in use though.

Now that my mirror is mounted it does have some distortion not present previously due to bending forces from the support. It remains to be seen how much this affects things.

I have also done some testing on a 7 stage LED meter to get the feel for how
it will work. Now have to make a reverse copy to indicate the opposite
polarity then run things with the new mirror.

Peter

1159723040 10 FT15766 Hvpolaritymotorlargemirror

1159723040 10 FT15766 Hvpolaritymotorlargemirrorside

Terry Fritz

Sun Oct 01 2006, 10:21PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi Peter,

Cool!! Looking forward to seeing this new system work!!!

I have not been able to get anything done lately

Busy this coming week too... But I'll try...

Since the mirror is always used at an angle and the small distortions don't really hurt this stuff much, I wonder if any cheap old rear silvered mirror would just just fine! Be very interesting to see what your quality mirror shows.

BTW - To followup on what Steve Conner mentioned about ground strikes, I found this blurb I wrote for ScanTesla's Streamer hit modeling:

Cheers,

Terry

Tesladownunder

Mon Oct 02 2006, 03:26PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Well, I've taken well over 500 photos today and have whittled them down to 100 for a closer look.

Photo 1 A little mirror aberration giving ghosting due to flex of the mirror in the support giving horizontal displacement. Seemed to get worse during the day so needs a new design with no stress and epoxied in place. Possibly a proper mirror.
Photo 2 A full 2 foot spark with a spark that is 3 pixels wide (1 pixel per microsecond in these shots). This was a daytime shot and in retrospect was probably sharper than the night shots as it was f18 and 1/10 sec. Night shots were f3.5 and longer duration.
Photo 3 I got quite interested since almost all of my photos showed the negative LED firing well, but I guess this was some asymmetry in the LED's as it seems to be just happening today. Makes you wonder though as I was using slow ASRG rates today.
Photo 4 I did try a current meter but I have had problems with it. Possibly overvolting the metal film 1.8 W resistors. Certainly looks like one resistor is open circuit here. They should fire at 0.01, 0.1, 1 and 10 amps respectively but the 1 amp LED is firing too readily. The 100A and above LED's never fired. (but did with a capacitor on a rectified ignition coil setup).
Photo 5 I was intrigued by this streamer shot showing a second and possibly third group of streamers following.
Photo 6 I added a spark arrestor and a disposable camera xenon flash in series with unprotected LED's and got this interesting but blurred streamer shot showing a remarkble 6 streamer groups that the camera and LED's weren't picking up. Seems like there is a another frequency superimposed of perhaps 8-10kHz. I presume that this is the difference between primary and secondary resonances (the "notch"). I am running it a bit out of tune still so that may account for that. It could actually explain a row of negative only ring down sparks as well.

Peter

1159802788 10 FT15766 Hvrotmirrorteslalargeaberration

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1159802788 10 FT15766 Hvrotmirrorteslalargecurrentspark2

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Terry Fritz

Sat Oct 07 2006, 06:43AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi Peter,

At 07:33 PM 10/5/2006, you wrote:
.......
Starting to work on my new "secret weapon" soon too.

))))

Terry has made up his own superfast rotating mirror unit (10,000 RPM) and is also getting great results. He is planning a voltmeter/current meter for his unit as below.
.............
Peter

It actually goes to near "50,000 RPM" with the 300A(!) stall current motor being run at "only" 2X voltage :o)) But I only take pictures at around 10,000 RPM. The motor is really scarry at 50,000 =:O I ran it up there once with the mirrors and all (NOT the camera!) and it was sort of like a jet engine!! But it held together fine!! I may have bent the motor shaft "just a little" pressing the mirror block on it at 4000 pounds and tapping with a hammer... Like the Egg of Columbus thing... It just "finds" its center highest "Q" of rotating mass...

I removed the safety Lexan shield now since it "got in the way". The camera lens is now very close to the spinning mirror:

(mirror "was" spinning there, but "cheap cam" is "fast" and froze the image)...

If it blows the old camera lens out, I could get one of these

)

I have not done much for a long time now..., but I did manage to order parts and started work on the streak camera "oscilloscope" today

)) Here is what I have so far:

The "Light Bar" has 24 high brightness LEDs. Three green ones define the top, middle, and bottom of the scale. 20 red LEDs fill in the bare graph scale on the +-5 volts at 0.5 volt increments. There is an extra green LED which will have the 100.0kHz calibration scale function. The holes were drilled in 0.75 inch angle aluminium to 0.192 inches and the LEDs are "pounded" in with a bit of 1/4 inch tubing "very tight". The LED spacing is 0.375 inch. The front was sprayed with matt black. The assembly is 9.75 inches long.

A proto board will hold the LM319s (all of them "cost less" than just "one" of the green LEDs!), the +-5V regulators, and the LMC555 circuit. I need to figure out how to do the voltage divider array and the LED drop resistors. That will be easily "creative"

)

I have two 9V batteries for +- 9V and 4 AA batteries to drive the LEDs. There is a block for the +-5V input and a power switch. I will sandwich it between copper FR4 board material cut to suit for HV/RF shielding. Running the circuit should not be any problem at all considering what I have done before

)

It should be able to sit on top of the toroid will a little aluminum foil field control stuff. Almost any CT can go into it. I have TI ICs which should go to 1MHz, and if they blow, they are $0.20 each... I will sprinkle in caps and 24V TVSs as needed... Should be cool!!!

Cheers,

Terry

Tesladownunder

Sat Oct 07 2006, 07:52AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Sorry my secret weapon is even more secret than that

But it will have other applications as well. It is really fairly easy in concept anyway but thats as far as I have got so far.

Some more pics:
Photo 1 shows a streamer branch with only alternate streamers progressing from left to right after the branch. This suggests some polarity effect at the time e.g. negative goes to the upright branch and positive continues on.
Photo 2 shows detail of a streamer that connects during the time when the harmonic is resulting in low voltages, hence the current is low and the spark is not strong. As the voltage picks up, there is enough energy for a second strike. The left LED's are not functioning properly but do indicate the first group of firings then a gap and then a second lot starting. I also have the spark arrestor running here which is the blue streak between the LED's and the spark.
Photo 3 A busy photo with lots of 3 foot sparks mainly to show one of the 1/8W LED shunt resistors burning up. Photos have better focus on these distant photos.
Photo 4 Another busy photo showing the ringdown better. I have spark arrestors on both ends and on the right antiparallel LED's shunted by antiparallel 3A schottkey's. The LED's still light but the layout is not ideal for nanosecond stuff (I can say that because I have no knowedge at all

).

Peter

1160207559 10 FT15766 Hvrotmirrorteslalargearrestorssparkstreamerbranch1

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1160207559 10 FT15766 Hvrotmirrorteslalargearrestorsmultisparkss

Terry Fritz

Sun Oct 08 2006, 04:04AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Cool pictures! I like #3

I got the streak camera oscilloscope mostly wired today:

It works perfectly and goes to 1MHz. I still have not gotten any of the calibration wired, but the bar graph functions work fine. It might need a little tweaking like the green grid LEDs might be too bright but that is easy to fix if needed.

Cheers,

Terry

UPDATE:

I got the scope all wired and put together and got the first pictures in:

Here it is on top of the toroid ready to go:

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.

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.:

Next I uped 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

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

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 Cal 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 (like 1/20s shutter speed).

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" witht things to get the pictures a bit better.

Cheers,

Terry

UPDATE:

All four items above have been fixed now

Should be good to go tomorrow morning!

Cheers,

Terry

Tesladownunder

Mon Oct 09 2006, 12:35AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Looking forward to your results.
Nothing really new here, just blowing LEDs. Added some information about partial failure in the LED's polarity thread.

I got better results using a groundplane around all the LEDs and resistors so there was little crosstalk/interference and the LED's were lighting nicely in proportion to the decades increments. So that is a start.

I guess dumbing down the spark current to a microsecond event rather than a multi nanosecond one would be kinder to the LED's so I might have to add an RLC filter. Just found some feedthrough caps that I got off eBay for goodness knows why a year or so ago so might be able to experiment with this. I hadn't actually blown my TVS and these might respond at that level or failing that a long string of Schottkeys.

I also think a Xenon flash tube should be the best indicator for very small currents but still be able to accept large ones. The output might be able to be tightened with a cylindrical lens.

Peter

Terry Fritz

Mon Oct 09 2006, 05:56PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi All,

My new streak camera scope is working pretty good now! So I picked a few real cool pictures to share.

This is the setup:

The LED bar graph goes from -2.5A to +2.5A in 0.25A increments. Center is ground and there is a 100kHz maker on the far right. It is directly measuring the current to the arc breakout rod. There are green LEDs at each end for a reference. Time is from the bottom toward the top.

Here is a typical steamer buildup and strike:

There is a 1/2 amp positive leader that goes about 1/4 the distance at 0.5A. On the next positive 1/2 cycle the negative leader goes 1/2 the distance at 0.75 amps. The next positive 1/2 cycle 1.75A leader just falls short of connecting (note the corona off the ground point). The next negative leader connects and discharges the system (a super fast thing the scope cannot report accurately).

Here are two superimposed images showing both positive (bottom) and negative (top) strikes.

I note that negative strikes seem to be brighter in general than positive ones.

Here is a set of three leaders just to the air that never connected:

They seem to be about 0.5A to 0.75A peak. The branching here seems like it draws more current than just a single leader.

Here is a negative leader (top) that connected but never "caught on fire" I guess.

The next positive leader (probably) quickly strikes hard.

Wild stuff!!!

FYI - The mirror speed was 10,000 RPM. At 15,000 RPM the vibration causes the lense to loose focus. I will try to add some hysteresis to the scope display next so it stays on instead of winks out at every zero current crossing. However, these were taken at 1/20s and almost 50% of the pictures are now "good ones"!! Overlaps and total misses are about even now. I still have some problems picking up shadows and glare at times. I think I'll tweak the current up to 0.1A/div too...

Cheers,

Terry

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