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jpsmith123

Wed Sept 08 2010, 05:17PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Quite a while ago...maybe two or three years or so...I happened to come across a paper whose subject was, I believe, a "Tesla coil" of some sort, the novel feature of which was a primary "coil" with the capacitor built-in.

I thought I had saved this paper somewhere, but apparently I didn't (either that or I did but I lost it in a subsequent hard drive crash or something).

I'd like to look at this paper again, if only I could find it.

Unfortunately, I don't remember if it was someone's thesis, or the research of a private company, or maybe something published by one of the National Labs, or it could even have been a patent or patent application.

I'm wondering, has anyone else seen any papers dealing with something like this?

Mads Barnkob

Wed Sept 08 2010, 06:23PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I remember it being mentioned here on the forum...

jpsmith123

Wed Sept 08 2010, 07:28PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Well then at least I'm not crazy (or maybe I am, but I'm apparently not hallucinating this particular time, at least).

Anyway, I'm interested in, for example, what kind of performance characteristics you'd have if the primary "winding" was comprised of, say, an aluminum foil sheet capacitor wrapped around a plastic cylinder, of course with a spark gap to "short out" the capacitor and complete the primary circuit. IOW, the stray inductance of the capacitor itself would be the primary inductance.

I wonder if you could get nice short, efficient, high power pulses that way?

Proud Mary

Thu Sept 09 2010, 12:06AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Do you mean the one where the primary is but a single turn of two layers separated by a dielectric to form C, while the spark gap is formed along the entire height of the single turn where the two ends come almost, but not quite, together?

If I remember it right, it was the view of the author that TCs would be forever stalled in the slow lane rise-wise, unless the primary impedance and time constant were brought way down.

I don't think the paper looked into the idea that this single turn capacitor-spark gap may itself have acted as a vector inversion generator, doubling and sharpening the primary pulse, but it seems to me it might.

jpsmith123

Thu Sept 09 2010, 05:33AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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The simplest configuration I can imagine would be just two foil sheets separated by a dielectric sheet (although you could add other layers for more capacitance).

IOW, imagine building a flat plate capacitor; now just roll it around a plastic cylinder. Of course it would be sized so that the tabs of the foil sheets (where you would make electrical contact with it on the sides) are slightly separated from each other along the circumference, and that's where your spark gap would go.

Maybe later I'll try and draw it using the 3D modeler of CST.

I'd like to do a time-domain EM simulation of an arrangement like that, to see how it would perform, but unfortunately, one desirable feature that CST doesn't have is the ability to directly simulate switched charged conductors. It may be possible to use the Eigenmode solver to estimate the resonant frequency, but I imagine that trying to mesh the geometry with a hexahedral mesh (the CST Eigenmode solver can't use a tetrahedral mesh) would be a nightmare.

Mads Barnkob

Thu Sept 09 2010, 07:00PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I was thinking about the one where the string of capacitors was a part of the primary coil, they were if I remember correct, placed along the primary with some even length of cable between them...

jpsmith123

Mon Sept 20 2010, 05:05PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

When I think about it some more, it seems the "primary" would be something akin to a quarter wave transmission line resonator, short-circuited at one end by the spark gap, and "open-circuted" at the other end.

At first I thought this arrangement would best be represented by a simple transmission line pulse generator...but in that case the load would generally be a well-defined "lumped element" located at the end of the line, whereas in this case the load would seem to be "distributed".

It's somewhat confusing to me.

In any case, it seems you could create something functionally similar (but maybe easier to contemplate/analyze) by taking a piece of say, RG8 coax cable (with the center conductor sticking out a little bit on one side), and bending it into a circle (i.e., wrap it around a cylindrical form) and attaching the center conductor to one spark gap electrode, while the shield (at the other end of the cable) would be attached to the other spark gap electrode.

In the case of the sheet electrodes on a cylindrical form, say a foot in diameter by a fool long, with 5 conducting sheets (creating two "transmission lines" or whatever in parallel), and charged to 50 kv, I could see some really short 20 to 30 J pulses.

With short pulses, I could see rather thin insulation between primary and secondary, leading to strong coupling, which suggests to me that you could string a bunch of these things together in series and easily get multi-megavolt outputs...

Oh well I better get back to finishing my humble little ferrite transformer before I get ahead of myself...

UbuntuNinja

Sat Sept 25 2010, 09:48PM

Registered Member #2677 Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64

Is it this? http://www.megavolts.nl/en/projecten/tesla-spoelen/136-ohmse-spoel-eindhoven-primary I remembered something like what you described that I had seen a while back and after searching briefly I found what I remember seeing.

Finn Hammer

Sat Sept 25 2010, 11:08PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

All,

I think you'all thinkin' bout Ken Herrick his coil from back in 2001 the Socal Teslathon.

"Herrick's Patented Solid-State Alternating-Current Thunder and Lightning Entertainment Machine"

Cheers,

Finn Hammer

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