electric strength for "x" cm of "y" material

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Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>

Hello, "bold electricians" :o)

i`m trying to find out if it`s possible to put my primary inside the
secondary, i.e. it would be inside _anyway_, and now i must know
what thickness of insulation should i use.
according to this i`ve remembered a recent post:

>  > The primary is inside the secondary, on a 3 inch diameter tube.
>  > Problem is, now the secondary is arcing. The secondary is
>  > ~700 turns of 22 awg wire on a 6 in diameter acrylic tube

>  > The arcing seems to happen at a consistent place. The arcing is
>  > clearly between the secondary's wire and the acrylic form

>  > It was arcing through the primary through 0.95 cm of acrylic

> 3J pulses in PP snubber caps.
> The topload is 25.75 pf (calculated)
> The winding is about 19 inches

by very _rough_ calculations the voltage at the secondary is
approximately 500kv, but the author didn`t told us about the height
of the primary. it is unlikely that the part of the primary that is
inside the secondary is lower than 10cm, then the voltage at the breakdown
point could be _rough_ equal to 100kv. electric strength of acrylic is
140kv/cm, but it`s not for the 1cm thickness material - very thinner,
so real electric strength of secondary coil form could be about those
100kv - everything is clear i guess.

a question to people who made magnifiers - what plastic did you use
for insulation between primary & secondary, what thickness and what
voltage was at the top of secondary?
i`m sure that at least Steve Ward had been working with it - any
advice, Steve?

p.s.
i`ve got LDPE pipes of different diameters and thickness - electric
strength is 370kv/cm, but what`s the real electric strength of 1cm of
LDPE? Fres is nearly 90 khz.