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Re: [TCML] Tesla Coil Secondary - What's really going on in there

A Barton wrote:

I'm looking for some good information on how the secondary of a Tesla coil
really operates.  Some web pages mention that it operates like some 1/4
wavelength helical waveguide with a voltage maximum at the topload.  I
haven't come across any electromagnetic descriptions on how it does so.
Could anyone recommend any good literature?

A bunch of a analysis, simulation, and testing over the last 10 years or so has pretty much put the "1/4 wavelength" theory to bed as not representative of what's going on. It's basically lumped elements and Bert has linked to Paul Nicholson's tssp analysis.

However, the 1/4 wave thing lives on for several reasons: 1) people using and repeating old references; 2) it "seems" like a good explanation, particularly if you're coming from a RF transmission line background; and 3) for physical sizes of practical coils, the length of the wire in the secondary is often very close to a 1/4 wavelength of the resonant frequency.

#1 will eventually wither away (it took centuries for people to use elliptical orbits in celestial mechanics rather than circles with epicycles)
#2 will do likewise
#3 will live forever, because it's driven by coincidence and physics

It is true that a long coil (which tesla secondaries are) can be treated as a loaded transmission line. But the impedance of that line is not constant, nor is the propagation velocity along the line (L/unit length is pretty constant, but C/length is not), so the idea of a "1/4 wavelength" line is not a good model. It's more like looking at a lumped pulse forming line with lots of segments.
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