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

---------- Forwarded message ----------
Date: Thu, 18 Dec 1997 06:29:02 -0700
From: Scott Stephens <stephens-at-enteract-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: SPICE, Solid State Suk's, and Slugs

I'm posting my "solid state" thread articles I've been defering, as I've
finished some SPICE simulations, and read some past archived postings from
last year.

I came in to T-coiling thinking modern techniques would change the
status-quo. Thinking semiconductors could replace spark gap's, and ferrites
replace pole-pig's.

The big problem is an order-of-magnitude gap between the impulse power
ability of cheap transistors, and the Q of the 2ndary coil.

My goal is to build a solid state, effiecient TC that can put 25J, 1MV pulse
across a 50pf torroid-coil load.

My coil has a Q of 100-at-100KHz, and with a time constant of around 250uS,
their is no way, short of an array of 25 40A/400V pulsed FET's, or 5 IGBT's
(which will cost $100 EZ) I can deliver that much impulse power in that
short of time.

I would like to test some devices past the 40A level, but I'm too poor and
impatient for that kind of experimenting. I'm inclined to belive my SPICE
transient analysis (The AC/steady-state plots decieve!).

I've seen pulsed SCR data showing 100+ amp performance, but I'm don't think
their viable either.

The options I see are:

1) Building a switch-mode inverter to turn 120VAC to 20KV+, since the size
of the primary discharge capacitance decreases with the square of the
voltage, and it's dielectric thickness increases linearly with voltage, why
not use 100KV+ in spark gaps? This would make for a very compact and
effiecent supply, that could be shut down after the gap fires, for rapid

2) Use massive array's of semis. Too expensive. Too many tears over the high
body count.

3) This option I am pursuing now. Slug my secondary with ferrite. Bring its
resonance down to 25KHz. Increase it's time constant to 10milli-seconds. Now
I have time to put 50J of energy into it using semi's. My problem will be
dielectric heating and loss of all the poly I'll be using around the slugs.
Hopefully, the slugs I have (giant beads, 2"x2"dia with 3/4"hole) won't
saturate in a 5"dia coil, bring its inductance up from around 45mH to over
1H, and not have horrible core loss. My Q better be 750+. More simulations
to do.

I know, its not a Tesla Coil, its probably a Oudin coil. But it will make
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?

On the bright side, with such high L, a tiny little primary directly on the
core will result in a massive step-up / Z-match. No giant end-match
transformer. No flux-loss out the ends of the coil to eddy-heat terminaly
and supports. 

Comments anyone? Has anyone built a semi-coil that put out sparks over 1-1/2'?