Re: [TCML] Re: Position of baffle inside secondary

[Paul Nicholson <tcml88@xxxxxxxxxxx>]

> My guess is that voltage stresses are greatest the base
> as that is where racing arcs are, ...

The volts per turn are likely to max the highest near the base
and near the primary, for different reasons.  For normal TCs
these two places are the same of course.

Close coupling will increase the secondary voltage gradient
near the primary, and small topload will increase the volts
gradient near the base.

Actually, if coupling and loading are reasonable, the
difference is not much, if any.  Here's an animation of
the voltage gradient simulated for a coil, k=0.2

 http://abelian.org/tssp/pn040502/tfsm1-h1.grad.gif

It's highest near the base, but really not by much more
than the rest of the coil.

Same coil, topload and bang energy, but k=0.1,

 http://abelian.org/tssp/pn040502/tfsm1-h0.grad.gif

Reduced coupling has lowered the max vertical gradient
from about 8 to 7 kV/cm.  Peak topload achieved in both
cases of coupling is the same, but the lower k is slightly
kinder to the secondary. Hardly a big deal, though.

It is not high k exactly that causes the extra voltage
gradient, it's more a matter of how concentrated the
coupling is onto a portion of the secondary.  The conventional
flat spiral primary is better in this respect, compared to the
other extreme of a helical primary.

But even the helical is not very much worse for the voltage
gradient, k=0.27,

 http://abelian.org/tssp/pn040502/tfsm1-h6.grad.gif

(The radial voltage gradient is another matter). Note
a similar voltage gradient mirrored at the top end of
the coil.  They come from a HF transient that runs through
the secondary during the bang.  These 'overtone' components
become more pronounced the more concentrated the coupling.

As for where to put the baffle, I guess these comments suggest
it doesn't matter very much.   Wherever you put it, it will
just move the breakdown somewhere else, with Murphy's assistance.
--
Paul Nicholson
--


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