# Re: SPICE, Solid State Suk's, and Slugs (fwd)

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From: 	Alan Sharp[SMTP:100624.504-at-compuserve-dot-com]
Sent: 	Friday, December 26, 1997 8:03 AM
To: 	INTERNET:tesla-at-pupman-dot-com
Subject: 	Re: SPICE, Solid State Suk's, and Slugs (fwd)

Message text written by INTERNET:tesla-at-pupman-dot-com
>>The bottom feeding magnifier arrangement means the energy can be
>>put in over say 10mS.

>Realy? wouldn't your Q (assuming Fr=100KHz, and the 63% time constant =
>Tc= [2Q/(2 PI Fr)] or (2 R/L); so your coil, which IIRC, uses .4mm
>non-litz wire, would need to have a Q of > (10mS 2 PI 100KHz)/2 or 3000!

>After approximately the first time constant period, 63% if the applied
>energy has gone to heating the coil's copper loss and capacitance loss. So
>if I fig'r right, You need to put 2x the desired output energy within 1
time
>constant to see your target power available. Is my math wrong?

Dah - your maths right - I was thinking about the time taken for the
discharge
to build up.

Here's the rub you build your superconductor coil - immerse it in liquid
helium.
Q of 10 zillion plus and then corona starts to be generated and the
impedence
goes up and the Q's only slighty better than if you had used aluminium
wire,
mylar coated and wound on a soggy cardboard former

>>I found a big improvement on increasing the inductance of my coil. But
this
>>means that coils have to be physicaly bigger or have more turns of
>>thinner wire - more resistance.

>Exactly, It the Q, the L/R ratio, which is the limiting factor in
>integrating the slow and constant (or even impulsed) power from semi's

You get maximum inductance for a given wire length when the hieght is
0.9 * radius - Bylund gives the proof on page 51 of his book.
Short fat coils definately work best for bottom feeding until we get to
the point where the discharge can strike the bottom.

Big toriods help but the spark may need help to break out.

>No doubt. But at low frequency (HF and lower) dielectrics like
poly-ethylene
>have very high Q's, I consider the reciprocal of the loss tangent Q, then
>poly has a Q of around 10,000. Beats the hell out of copper! Oils loss
>tangent reciprocal, IIRC, is only around 1000. But that's enough if you
>count on loss. And it lends itself to convection cooling, forced air &
>heatsinks. Is my thinking flawed? I know, plastic can't stand the thermal
>abuse copper will. I can see corona-blackened poly running out of my
plastic
>fusor after 30 seconds. But this is where thermal, and E-field simulations
>come in. I found some neet FEA (finite element analysis) freeware for such
>simulation available in the form of "Q-field".

>>It maybe that a modest bit of slugging at the
>>bottom of the core could be helpful.

If you don't try to keep the Mu0 (permiability) gradient of the core even,
hot zones may develop wich could lead to arcing between the sections of the
coil. If 90% of your L is at the bottom, 90% of the voltage drops there
too.

>>4'+ sparks, and quite a show. Its low frequency skin depth will probably
>>blow the surface layers clean off anything it zaps.
>>Has anyone made a study of exploding fruit/veggies?
>
>Or exploding fingers - even 6 feet away from my 500W coil - I can get
>sparks jumping from my fingers to the metal.

>I would prefer a safer high-frequency coil. But it occured to me, which I
>posted on the other tesla list, that a coil could be operated in higher
than
>the Fr, 1/4 wave mode. My former mentioned gradient breakdown accounted
for,
>a 10uS pulse (100KHz) might be propagated and integrated over the
Q-limited
>time constant of a 25KHz resonant coil. With the right chirp/impulse
signal,
>dispertion from the ferrite could even be compensated for.

I think I saw a post which gave 70KHz as the minimum frequency for safety
- I think Mark Barton's (3 foot sheet of flame) coil worked at this
frequency.

My scheme for maximum solid state spark would be two coils, 2 foot diameter
2 foot high - wound for 70KHz - (if I could afford the weight of copper)

>I've just gotten my feet wet with PS-Spice, and I'll need Aplac, or NEC or
>some decent code to do the type of non-linear transmission line simulation
>to evaluate the efficacy of such a design. And in the end, I'll just have
to
>deal with the junk I've torn out of TV's and found at the Hamfest.
>So maybe I'll just try it and see how hard it bites :)

It always come down to this - how are you going to model the corona?

>I thought of a couple of designs (well, I remember my college prof's
lecture
>on TC's) of designs that increase the inductance by using ferrite 'flux
>concentrators' (realy, just flux plugs) at the coils ends, and
multi-segment
>coils shaped in 'D''s and 'V's geometry to increase inductance, K-coupling
>and HV isolation.

Someone here must have experimented with ferrite and coils. I may try it
myself.

>I can imagine some truly evil contrivances, with incredible Q's, that
would
>be created from ferrites and piezo-ceramics. Mu and E values in the
1000's,
>the size of baseballs, that could store > 10's of KW's. These are
>acoustic-vibration devices, and have more in common with fly-wheels than
TC's.
>But if/when I get around to seriously evaluating them, acousticy, I'll
>probably find thermal or material stress factors will limit their
potential.

These are probably off topic here - but if you ever flesh these ideas out
send
me a copy. Could be a little noisy though!

>Just like these semi's. I looked at power dissipation, and frequency
>responce, and AC-steady state analysis, and got excited. But when I
>considered the systems from a transient analysis or time-domain, things
>don't look so good!

Thats life - the spark gap reigns a little longer.

Hope you all had a good christmas

Alan Sharp

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Rev Alan Sharp BSc BD
doing high voltage services at
St Ninian's Church of Scotland, Corby, England

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