Re: Re-entrant portion of the sphere (VDG) (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 13 Oct 2003 10:52:15 -0300
From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Re-entrant portion of the sphere (VDG) (fwd)

High Voltage list wrote:
>
> From: Lyonelb@xxxxxxx

>   A large diameter sphere with a small re-entrant radius is a must.The point
> of column entry is the electrically weakest region on the terminal. This can
> be offset to a considerable extent by arranging the electrode with a
> re-entrant portion into which the column fits. This results in a diminution of the
> field intensity at this point and thus in a shielding of this electrically weak
> region.
>   However  to make this re-entrant  portion is not easy.   Any idea ?

Probably just an adaptation of the method that you use to make the
sphere.
I have used metal spinning. The method would be similar to the one used
to make a half-toroid, using two forms, one for the inner curve, first,
and other for the outer curve.

Note that professional machines today always continue the terminal down
to ground using equipotential rings, biased through a string of
resistors
or corona points. The terminal can then be just a cylinder with one end
rounded, and there is no problem in using a sphere with a hole, or just
slits for the belt.

Antonio Carlos M. de Queiroz