Capacitor design and Toroids

Hi All
I have started building a REAL coil. 8"dia 26" long secondary and would
like any feedback to keep the project on track.
Has any one used Kapton for the dielectric of a capacitor?
This stuff seems incredible with specs like..
dielectric strength of 7000V/mil
dielectric constant of 3.5
and dissipation factor of 0.003 at 1KHz?

Also I thought I would make a toroid ~ 4" x 12". My question is if
the center needs to be removed or can it be shaped like a
fat disk, (that is a 4" thick disk with rounded edges?)

I brought my secondary into work to measure it to see what numbers I get
to compare to the calculated values. I will disclose the results when available.

By the way I work at Fermilab which does high energy physics. I have worked
in the past as a technician in the RF section and worked on 200KW 30-50Mhz
systems. I had the opportunity to witness a 30MHz Tesla in action. This was a 
quarter-wave high power transmission line (about 8" outer conductor with 3" inner heavy
copper) with a 300Watt solid state amplifier driving the current end, about 2"
from the shorted end. When properly tuned the open end would have a very
nice plasma about an inch tall coming off the center conductor. If touched momentarilly
it would leave white ash as the skin surface was destroyed. It was quit an interesting sight. 
I also lite a 60W incandesent bulb off the end by holding the screw portion of the bulb
tightly with my hand an touching the center conductor to the bulb completing the circuit.
The only sensation was the heat from the filament.
Dave Huffman