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Re: Top Toroid

Hi Jim,
        Guess I'd better comment <some snip along the way>.....

> Subscriber: jim.fosse-at-bdt-dot-com Mon Jan 27 22:06:48 1997
> Date: Mon, 27 Jan 1997 06:30:27 GMT
> From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Top Toroid
> 
> 
> >Date: Sun, 26 Jan 1997 13:18:27 -0700
> >From: Jeff Detweiler <jd231825-at-engr.colostate.edu>
> >To: tesla-at-pupman-dot-com
> >Subject: Top Toroid
> >
> >Dear all,
> >
> >I am in the process of building my secondary coil, and I'm at the point
> >where I need to make a toroid for the top. Although I remember seeing
> >something about this on the list some time ago, would somebody please tell
> >me how I should determine the proper dimensions for my toroid, and would
> >the experienced coilers please share some of their clever ideas of how they
> >made their toroids?
> Jeff,
>     I'll not try to quantify the minor diameter of a toroid vs
> output voltage.
> 
> >As an aside, would somebody please remind me why a toroid is more ideal
> >than a sphere and such? (Was it that the self-capacitance is larger or is
> >there a better voltage gradient or something?)
> 
> Please visualize a 2' sphere sitting ontop of your coil. Now,
> visualize a 2' flat plate sitting ontop of your coil. Which has the
> larger shielding effect between your coil and the "rest-of-the-world"
> ?    The flat sheet, because it's in the same plane as the top turn of
> your coil ( and at the same voltage (potential)).
> 
> Next problem;)  Oops, that flat sheet has sharp edges! Can you say
> Corona? So let's shield that "sharp" edge. Round it. ... Soon you have
> transformed that flat sheet into the intermediary between a disc and a
> sphere.  The flat portion of the toroid provides the shielding (it's
> close) and the rounded edge provides the corona hold off.
> >
> >I understand that in general, the larger the toroid, the more energy is
> >needed to build up in the secondary before corona discharge happens. So am
> >I shooting for the largest possible toroid where I still get a discharge?
> >
> I'm going to skip the conservation of energy transforms tonight. Maybe
> Malcolm ( morning for him;) would like to take over;) He has a fine
> explanation.

     I think Richard Hull has already answered the question. In short, 
yes. 
     I think we are generally agreed that the output voltage is 
going to be a function of the energy that gets to the secondary at 
the end of the first primary ringdown, and the total secondary 
capacitance including top load. From first principles, this turns out
to be:  Vo = Vcap*SQRT(Cp/Cs).  As Bert Hickman has showed however,
this ideal will never be reached because of significant losses in the 
gap. I think in some instances, around 80% of the energy gets 
transferred. Papers by others use the formula: Vo = Vcap*SQRT(Ls/Lp).
This is true because Ls*Cs = Lp*Cp   (basic tuning requirement). 
Interestingly, the authors of some of those papers didn't mention gap 
losses but I think should have because they are time and current 
dependent and never zero. All were high powered machines and used
non-zero-loss switching devices.
      As always, I am happy to consider other views which exist out
there. I don't think anyone here has as yet accurately measured 
output voltages directly but I may be wrong about that. If anyone has,
I'd love to hear about it.

Malcolm