Re: Alternate toroid shapes

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

Oops.. hit the mousepad..
The hemisphere on hemitoroid was advocated by Craggs and Meek as well (and
probably Robert Van deGraaff as well), but probably not for any
electrostatic field reason, but because it was easy/feasible to make.  Some
of the designs in Craggs and Meek have a somewhat flattened top (rather than
a hemisphere), and you see, in the literature, references to "spherical
electrode with re-entrant curvature where the belts go through"

Some of the "big iron" vdg's (operating in pressure tanks) use a top
electrode that is basically cylindrical, with a hemispherical top and the
hemisphere with a hole with curved edges at the bottom, increasing the
electrode capacitance (and, making more room for "stuff" inside the
electrode, like ion guns, charging supplies, etc..
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, December 14, 2003 5:32 PM
Subject: Re: Alternate toroid shapes


 > Original poster: Dave Leddon <dave-at-leddon-dot-com>
 >
 > Back in the sixties I purchased a three foot diameter spun aluminum oblate
 > from F. B. Lee (anybody remember his contributions to the Amateur
 > Scientist) who claimed that this shape, which resembles a hemisphere on
top
 > of a toroid, was the best shape for a Van de Graff generator because it
 > would accumulate maximum charge while minimizing break down on the
 > supporting column.  I often wondered if this shape would represent any
sort
 > of improvement over the classical toroid.
 >
 > Dave
 >
 >
 > At 10:53 AM 12/14/03 -0700, you wrote:
 > >Original poster: Paul Nicholson <paul-at-abelian.demon.co.uk>
 > >John Richardson wrote:
 > >
 > > > Has anyone done any experimentation into toroid topload shapes
 > > > other than the typical round designs that all use?
 > >
 > >AFAIK little has been done.
 > >
 > >Toploads have two important parameters:
 > >
 > >a) the amount of charge they hold per unit volt, a.k.a the
 > >    capacitance.
 > >b) the voltage at which they begin to issue streamers.
 > >
 > >Toroids tend to have a larger capacitance for a given breakout
 > >voltage, compared with sphere terminals.  And they seem to be
 > >preferred for streamer formation, perhaps because of this.
 > >
 > >But who is to say there isn't a better shape?   It could be
 > >that the best streamer formation comes from toploads with modest
 > >breakout threshold plus large charge storage.
 > >
 > >You could approximate your proposed tear drop cross section with
 > >a sphere or toroid with a disc shaped skirt, so that from a
 > >distance it looks a bit like Saturn.   You would have to tell
 > >us whether it behaves any differently to a toroid plus breakout
 > >point.
 > >
 > >Plenty to do here for theorist and experimenter.  See recent posts
 > >by Antonio for the relevant modelling programs.
 > >--
 > >Paul Nicholson,
 > >Manchester, UK
 > >--
 >
 >
 >