Re: Toroid Design .

  Jim -

  This is the first time I have heard that the Van deGraaf motor slows down
because of the upper electrode voltage. I thought the transfer of charges
from the belt to the inside of the sphere was because the potential on the
inside of the sphere was less than on the belt.

  John Couture


At 08:24 PM 12/21/98 -0700, you wrote:
>Original Poster: Jim Lux <jimlux-at-jpl.nasa.gov> 
>Tesla List wrote:
>> Original Poster: bertpool-at-ticnet-dot-com
>> Date forwarded:         Sat, 19 Dec 1998 14:00:43 -0700
>> The inside of a spherical or toroidal discharge electrode has zero volts
>> charge inside.
>Whoops, charge isn't measured in volts. Charge is, of course, measured
>in Coulombs (or electrons, for small charges), not volts. However, it is
>true that there is no net charge inside a conducting object (it is all
>on the outer surface).  The voltage that an object is at (relative to
>something else, of course), has to do with the force (Electromotive
>Force = EMF (measured in volts) required to get an additional charge to
>the object. The higher the voltage, the harder you have to push that
>incremental charge. This is why a Van deGraaf motor slows down as the
>the upper electrode voltage increases: it has to work harder to
>transport the charge to the electrode.
>  It does not matter whether you fill the inside with balls of
>> aluminum foil or even with Greg Leyhs (see his web site for a good
>> example), they will have no charge on them.  The surrounding electrode
>> effectively shields them.  The Tesla coil does not see anything inside the
>> toroid.  The outside, however is a different matter.  Hemispheres on the
>> surface of a toroid just may increase the effective capacitance (Tesla
>> constructed his largest top this way).
>I think that Tesla was using small hemispheres as a construction aid,
>not because a bumpy surface has higher C. He commented in several places
>that you can construct something of large effective radius (for higher
>voltage before breakdown) by combining things of smaller radius close
>together. Electrostatic field calculations, although tedious for any
>practical system, will confirm this. Some more modern practical
>applications include the construction of huge toroids used for testing
>at the IREC HV research center in Canada, field control rings on EHV
>transmission line terminations, and, of course, Greg Leyh's top load
>made from tubing welded into a sphere.
>> Bert Pool
>Jim Lux                               Jet Propulsion Laboratory
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