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End-on spark view - broken sparks

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LAN_403

teravolt

Mon Sept 04 2006, 03:54AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Indeed that is an efect that is real I have seen this with my own eyes. I you can see it with ignition coils, VGraph, any blue arch. Maby has it something with different charges meating or a step leader maeting the arch. I would like to know why do VTTC's have steight archs. N.B.

Tesladownunder

Mon Sept 04 2006, 12:49PM

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

To get a two axis view of a spark, I have set up a first surface mirror to give a 90 degree view. I have kept the aperture small to accomodate the different focal lengths.

Look at the 5 spark example with 3 discontinuities present in both images.

I don't believe that this is a camera effect or a lensing effect. The brightness of the spark to the right is visible to the eye and often seen for thin low power sparks but not higher power sparks. EVR's sparks are much brighter than mine most of the time I suspect.
The spark discontinuity is not usually visible to the eye though, due probably to the rapidity of the event to the eye.

I will try a different camera and a rear view to show reversal of sides to confirm that it is not a camera view issue.

Peter

1157374171 10 FT15549 Hvbrokensparksmirror5

Steve Maurer

Mon Sept 04 2006, 06:59PM

Registered Member #133 Joined: Fri Feb 10 2006, 10:27PM
Location: Pensacola, Florida
Posts: 47

Peter,

Thanks for sharing these interesting photographs. Maybe we can offer some additional insight if you would tell us what camera you are using for these pictures. Is it a film or digital camera? What are the camera settings (shutter speed, aperture (f-stop), film ISO rating, lens type and focal length, distance from the sparks to the camera)?

- Steve

Bjørn

Mon Sept 04 2006, 10:32PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The last picture contains this EXIF information:
Nikon D70s
70 mm
f/16
1s

The shutter moves from bottom to top or possibly from top to bottom in the frame.

Nik

Mon Sept 04 2006, 11:43PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I have seen this broken spark effect from my tesla coil when I just started. The gap did not quench properly and the tank circuit was fed with 2 doubled mots, this made the coil output more like an induction coil then a tesla. I could see the broken spark pretty often untill I switched to a 4 stack of mots for a power suply.

Tesladownunder

Tue Sept 05 2006, 01:15AM

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

Perhaps one in 3 or 4 sparks have a discontinuity in my setup.
Some more photos with different settings result in the spark being a bit overexposed but still show the same effect.

Also a reversed photo from the rear of the same setup to show it's not a camera side thing. Most of these were 1 second exposures. None showed any sign of camera interference. Some of the earlier ones were taken with my Sigma 180 lens from about 3 feet and some with the 18-70 lens from closer.

I guess I need to pull out my 300kV diode and check polarity stuff.

Peter

1157418919 10 FT15549 Hvbrokensparkssingle2

1157418919 10 FT15549 Hvbrokensparksreversedsingle

WaveRider

Tue Sept 05 2006, 08:21AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

You may be witnessing the "magnetic pinch" effect. See

and

Essentially, the current in the arc creates a magnetic field that encircles the discharge. However, this creates a force on the moving charges in the arc which tends to constrict the flow...hence the "pinch"

Some experimentalists have measured the discharge currents and observed current decreases suddenly after the initiation of the discharge as the pinch effect causes current to drop off. Then the current increases again as the pinch effect is reduced or the discharge finds another path...

Tesladownunder

Tue Sept 05 2006, 10:43AM

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

Here is a DC spark with left side negative. Hence this is a negative side effect.

1157453012 10 FT15549 Hvbrokensparksrightpos1

WaveRider

Tue Sept 05 2006, 12:21PM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

TDU, Looking closely at your last photo, you can just see channels of ionisation (leaders) widely avoiding the pinched off region (as a result of a concentrated magnetic field "ring" near the pinched off zone..). The current is becoming choked off at the center, so the potential drop in the gap becomes large, generating a corona "pre-discharge" which circles outside of the concentrated magnetic field region...

My 2 cent theory...

Lovely photos BTW!!

Tesladownunder

Tue Sept 05 2006, 03:04PM

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

My guess is that it isn't a magnetic pinch effect. The main reason is that the discontinuity occurs in only part of the spark near the negative electrode. Secondly Crooke's spaces vary greatly in site and number depending on pressure of the gas rather than current.

I have now taken pics in a high speed rotating mirror withe perhaps 10us resolution and am not seeing any other "structure" at that level.

Peter

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