TSSP: List Archives

From: Paul
Date: Sun, 12 May 2002 20:50:49 +0100
Subject: Re: [TSSP] Topload breakout potentials

For Bart's coil,

Bang energy = 0.5 * 61nF * 15.3kV^2 = 7.1J

Cee = 47pF, so peak topvolts is at most

   sqrt( 2 * 7.1J/47pF) = 550 kV.

The model is only registering around 460 kV so I guess I haven't
quite got the primary in tune.  Are you able to measure the
secondary Fres with everything in-situ, with primary gap open?

Have I got the toroid size correct: 30" outer diameter and a 9"
diameter tube?

The surface gradient is 0.026 V/cm/V so could achieve 0.026 * 550 =
14.3 kV/cm. That seems to fall well short of the 26kV/cm we expect,
yet you're getting substantial breakout.  The only quantity used
from the tssp model is the Cee=47pF, which we know isn't going to be
very far out - a couple of percent at most.  You have a smooth
toroid so we can't blame surface rugosities.  Maybe I'm working out
the surface gradient incorrectly.  The method I'm using is based
very directly on the charge distribution computed for the toroid as
a step in the capacitance determination.  I tried another different
method too, which gave similar values.

>From your description, I'd say that the coil started out being 
well in tune at 13 turns, and by tuning low to turn 14 you got fewer
and longer streamers, which is similar to John's and Marc's coils.
So that bit makes sense.  You detuned the primary further by
raising the secondary Fres and this further concentrated the 
breakout into a single long streamer.  Again that makes sense.

Unless something odd is happening in Bart's charging circuit to
give a bang something approaching four times the 7.1J estimated, then
we may have to conclude that for some reason toploads are breaking
out at less than 14kV/cm rather than up around 26kV/cm.

I think we could really do with an example of a coil that is not
breaking out out at all, so that we can put a lower limit on the
surface gradient at which breakout starts.

I wonder if Marco is following this thread?  Thor has the advantage
that the firing voltage can be accurately set.  Does Thor break out
without a breakout point?

Meanwhile I'll go find a way to triple check those surface gradients.
--
Paul Nicholson,
--


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.