Hi Jeff,Gaps and bright regions within sparks seem to show up within relatively low energy HV systems - i.e., where terminal capacitances and follow-through currents are limited. They are easily observed within low energy electrostatic discharges, with lower power Tesla Coils, or within sparks from pulsed induction coils.
The root causes appear to due to fundamental differences between how sparks propagate across the gap from positive or negative electrodes and (in the case of Tesla coils or other repetitive discharges) as previous channels become reignited. These subtle effects tend not to be as readily observed within high energy sparks or arcs since the high. arc-like follow through currents brilliantly light the bridged gap. Best observations seem to require using a low energy/high impedance power source, low parasitic capacitance across the gap, and adjusting the gap so that the discharges can just barely bridge the distance.
In a positive discharge (where the discharge begins propagating from the more anode to the cathode), the leading edge of the propagating positive leader, and the leader channel that connects back to the anode, are bright and filamentary/spark-like. However, the streamer region ahead of the leader tip is diffuse, dimmer region that looks like a directed cone of corona pointing towards the cathode. If the HV source does not have sufficient energy to completely bridge the gap, or if the HV pulse is of very short duration, you get a miniature Tesla Coil-like air discharge: a bright length of spark that only goes part way across the gap, with a diffuse glow between the sharply defined leader tip and the cathode electrode.
A negative discharge ((where the discharge propagates from the more negative electrode to the anode) is much more complex. A bright, seemingly isolated, length of spark (called a space stem or space leader) appears in the space ahead of the main leader. Corona-streamers form on BOTH ends of this isolated space leader, and the space leader then grows backwards toward the main leader, eventually joining, and lengthening it. Negative leaders progress though a series of steps or jumps. This contrasts with positive leaders, where the propagation path tends to smoothly progress (assuming sufficient gap voltage). These negative propagation steps can be relatively small for low energy systems, or 100's of feet in the case of negative lightning (stepped leaders). If the growth process is terminated before the spark can fully bridge the gap, you'll see the bright filamentary main leader from the negative electrode, a diffuse corona filled gap, another isolated bright space leader segment, and then another diffuse corona region pointing towards the anode. Isolate bright regions within a spark may be space leader segments.
In systems where discharges simultaneously propagate from both electrodes, or where previous channels are being reignited, you may get a very complex interplay of both negative and positive discharges with various bright regions being illuminated.
You may also see another interesting effect where a leader has branched. These are points where the spark makes a very abrupt change in direction. These sudden changes cause the "tortuosity" of long air sparks. Only the "winning" (higher current) leader is usually observed. However, if you look closely at some spark photos, you can often see a short segment that went to the losing leader branch. The branch between the two leaders forms a small "V". The "branching angle" are similar for most discharges, and are centered at around 37 degrees for sparks at virtually all scales. This is seen for TC sparks, 2D and 3D Lichtenberg Figures, and lightning. The only exception that I'm aware of is the strange branching (sometimes almost 90 degrees!) seen within high power staccato VTTC discharges.
There's a virtual treasure trove of information lurking within your pictures, Jeff!
Bert -- *************************************************** We specialize in UNIQUE items! Coins shrunk by huge magnetic fields, Lichtenberg Figures (our "Captured Lightning") and out of print technical Books. Visit Stoneridge Engineering at http://www.teslamania.com *************************************************** Jeff Behary wrote:
Ed, You're right, I'm wondering on Antonio's input too. There are two things that interest me with this with the test of the previous posting...The first thing is that the output really can resemble an induction coil or static machine when things are set right... its close, but not quite exact yet. (I'm like an induction coil with inverse current, maybe!) [Those induction coil photos you sent are great!]In the past, I have been able to replicate the sound and appearance of the sparks from a TC like a Holtz machine or static machine, but the one thing that lacked was the color differences of white and violet in the same spark. In my previous tests, the sparks were thick and white, crackling, but still oscillatory. The electrostatic effects that accompanied the early tests were vivid, but again they weren't exactly like those from a static machine. The second thing that really interests me is the uniqueness of the sparks and effects when the whole concept is not rectifying properly. I'll call this "chaotic" for lack of better words :), but the sparks start off bright white (and thick) at the surface of the spheres, but quickly turn violet (and thin) and branch outward into thick rich purple effluves/brush. In the case a spark occurs, it isn't white on one side and violet on the other, but a "dashed line" of effects throughout. Its like seeing striations in a geissler tube, only in a spark! The next curious thing is to try the same effect with a different set of coils. The first set of coils I tried for those posts (when operating with normal dischargers to see the sparks) would make sparks of the type mentioned above - they were thick, loud, crackling, but still oscillatory Tesla Coil sparks. They were two Pancake Coils, 7" in diameter or so, around 350 turns each of 30 AWG, 2 1/2 turns heavy wire for the primary coils. Very briefly before this email, I tried a similar test with two Pancake Coils that produce the phantom streamers. These coils produce an abundance of thin sparks 1 - 6" long, depending on the setting of the gap. The phantom streamers can extend outward independently of the sparks 6" from each ball terminal when the spark gap is wide open. In the path of these Phantoms I placed the PVC pipe insulators with the two point-plane spheres. On one of the discharge balls of the coil I put a thin cotton covered wire, so that one discharger had a point and the other was simply a 1 1/4" ball that acted as a small plane. The latest test made some really interesting results so far. The static effects were felt greatly at both spheres this time, and when sparks a few inches long were being drawn from one terminal to a piece of metal in your hand, electrostatic effects could be seen and felt for over a foot away from the other terminal. I have some more Pancakes that produce large phantom streams. Tommorrow I will try similar tests wth those and see what happens... Jeff7. The sparks when things are erratic are really interesting in appearance. For me, this makes the test worth while. They are unlike any other I've seen from any machine. http://www.electrotherapymuseum.com/2008/PointPlaneCollectors1/StrangeSparks3.jpg This in person was really bizarre! Jeff" Surprised Antonio hasn't had something to say. If I understand the "bizarreness" you mention you are just seeing sparks for both polarities of the spheres - white and bright at one end and fuzzy and purple at the other. Very easy to say with an electrostatic generator and I'm pretty sure there are illustrative pictures on Antionio's pages. You can see the same effect with an induction coil producing a [relatively unipolar] output. I sent some pictures of same to Terry a while back in connections with a description of a little GMHEI coil driver I have here. Posted at: Pictures don't show as much contrast as I see with discharges between 2" spheres excited by my DIROD but effect is similar and similar to your pictures. Ed Of course maybe you're talking about some other feature of the sparks..................._________________________________________________________________ See how Windows Mobile brings your life together—at home, work, or on the go. http://clk.atdmt.com/MRT/go/msnnkwxp1020093182mrt/direct/01/_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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