# Re: [TCML] RE: musing on lists ( Wireless Transmission Theory)

```William Beaty wrote:
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```On Sun, 10 Feb 2008, Scott Stephens wrote:
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```William Beaty wrote:
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```What if
I give the coil a 90deg kink, can I stop the waves and reflect them back?
```
```Sharp bends in wire affect the impedance, so yes the impedance
discontinuity will cause reflected power.
```
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What if it doesn't?
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Impedance is the combination of capacitive and inductive reactance. Capacitive reactance is a result of capacitance - the amount of charge displaced for a given voltage (Q=CV). Inductive reactance results from the amount of magnetic flux a given magneto-motive-force (measured in amp-turns-meters) creates. Bending a piece of wire into a loop or spiral concentrates flux, because there is more amps flowing around the same area, which displaces more flux.
```
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That's the principle behind the lovely flux-compression generator EMP bomb. Just like pulling the plates of a charged capacitor apart requires mechanical force which does work, resulting in an increased voltage. Yes, the capacitance decreases BUT since E=C x V^2, the energy increase is exponential where the capacitance decrease merely linear.
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When you dilate a copper pipe with a circulating current with explosives, again the inductance decreases linearly BUT since E= L x I^2 the current increases exponentially.
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And I've also read microwave designs should avoid acute transitions.
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```A sharp discontiuity would be << wavelength, so it
might be invisible to the travelling wave.
```
I usually don't think in terms of wavelength, but rather time-domain and what the impulse-response would be. Although, through the magic of a Fourier/inverse Fourier transform you can go back & forth. Some radar is pulse-echo, other kinds are FM chirps.
```  Or in other words, if a TC has a long narrow secondary,
```
Wouldn't you get crappy magnetic coupling from the primary to most of the coil?
```and we cut it in half to form an inverted "L"
shape, will the TC stop operating?  (Or perhaps only operate at 2x
frequency?)  I suspect that a chain of reasoning might not give the same
results as an actual experiment.
```
First why not use the usual equations to calculate the distributed inductance and capacitance, then use the free LTSpice to model the two legs as as transmission lines coupled with a transition impedance? I think that, using a model of the spark-excited primary LC tank, could give you a very accurate approximation and allow you to play with large variations much faster than you could build something. Although it wouldn't tell you that putting an acute kink will have a concentrated electric field, resulting in corona or breakout there.
```
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Anyways, just taking a SWAG I'd say the impedance transition would be really trivial in this application. In radar applications you want to know about really small impedance discontinuities, especially ones headed your way at high mach-numbers.
```(A kink in the "electricity hose.")  Or, can I connect three together to
form a "Y" junction and have the waves divide evenly?
```
```Google hybrid power combiners, transmission-line transformers, Wilkinson
power dividers/combiners.
```
```There is no shield conductor.  This is one wire.  It's like a G-line.  Of
course we could couple the signal back to coax cable, then use
conventional devices.  But if this is a waveguide for, say, 50KHz,
wouldn't it be interesting to try to develop some waveguide devices which
can connect directly to plastic tubes wrapped with wire?
```
That's a good point. But is it practical? Why don't they start using high-frequency AC in power transmission systems? They use 600 cycle in aircraft so the transformers are smaller. I can see them even boosting that to 6 KHz now that good ferrite is cheaper. But as the frequency goes up, the skin effect starts becoming significant, and the losses increase.
```And about that "Y" junction secondary: if the two branches are of slightly
unequal length, won't the TC generate a slow beat-note?  Perhaps the
corona discharges would squeal with audio difference frequency.
```
Yep. I think LTSpice has some demos you can watch the power slosh back & forth between the resonant sections. I like the mechanical depictions - http://www.walter-fendt.de/ph11e/cpendula.htm Somewhere I've seen one for multiple rather than two sections, but that applet at least depicts what goes on with the TC's primary & secondary.
```I can't help but suspect that if I knew how to make the right shape
waveguide, and stick it in my microwave, and ionize the plasma, I could
spew out hundreds of kilovolts if not megavolts of accelerated electrons.
```
```
A microwave *IS* a CW Tesla coil.  Well, it's a resonant RLC device being
driven by a sine wave.  And it's "secondary" is being driven at a high
overtone, with lots of nodes in a 3D array.  If we remove everything from
inside the oven (including the glass dish,) then e-fields approach
air-breakdown because of Resonant Rise.  Under these conditions a
sharpened rod of metal or carbon will give off a corona flame resembling a
blow-torch.  If a large plastic bag full of argon is placed in the oven, a
3D network of fine sparks results (and then the bag melts.)  Complete
description at http://amasci.com/weird/microwave/voltage2.html#storm
```
I think we've chatted about microwave plasma before. I've trapped the plasma in jars and melted the jars into white-hot goo, and posted the reference to an article about how to trigger it with a spark and keep it suspended in a glass chimney. But as the capacitive reactance becomes relatively low over a few megahertz, an awful lot of power is required to make high voltage.
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No, what I was getting at was making a traveling-wave electron accelerator. Take a fluorescent light's glass tube and put concentric rings of wire at certain intervals along its length. The microwaves excite these resonant rings, and electrons are accelerated.
```
ooh, lookie what I googled "traveling wave accelerator" :-D

Perhaps its time for some Radiation Therapy...

```
(pg15) Inject 50KV at the cathode, electrons are injected into a waveguide at .4C, electrons increase to near C in the first 30cm
```Magnetic field required :-(
```
(pg29) 10 MEV requires a 3 MW Magnetron. Sounds formidable, but I think that means pulsing the Maggie with 100KV for a millisecond, which sounds a bit brutal. Common oven maggies would probably arc over around unless pulsed for microseconds. You couldn't use massive magnets anyways, so you want to pulse the electromagnet around the waveguide too. And 100 amps sounds about right, but that pulse would need to be in milliseconds. You'd have to wrap some wire turns around the magnetron magnet too if the voltage is going to be bumped up because its tuning is fixed mechanically, and the voltage and magnetic field must match and change proportionately.
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Anyways, although it sound intriguing and plausible (since I'm so ignorant about accelerator design and physics) I suspect a dense plasma rather than a vacuum in the waveguide would dampen things down. Yet still, several kilowatts of power would be pushing a very thin, hot gas and its electrons apart, rather than back'n forth.
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