Re: Van de Graaff generator safety question (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 15 Jan 2004 09:55:19 -0800
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>, hvlist@xxxxxxxxxx
Subject: Re: Van de Graaff generator safety question (fwd)


You can run a chain much faster than a belt, for one thing, because the
mecahnical dynamics are better.  (Chains aren't as "stretchy")  ALso, if
you want to run parallel chains, it's much easier to do than using a big
wide belt.

There are some other schemes similar to pelletrons that appear in the
literature, such as a belt carrying metal plates.

In my recollection, Pelletrons charge by induction, as opposed to using
brushes or charge spray bars.  Perhaps this is a more "efficient" way of
getting charge on the belt, although, as Antonio points out, the
fundamental limit is the surface charge density on what ever is carrying
the charge.

Chains might also be more consistent, making field control as you move up
the column easier, so the field gradients are smaller.

At 09:58 AM 1/15/2004 -0700, High Voltage list wrote:
>Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Wed, 14 Jan 2004 14:57:06 -0200
>From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
>To: High Voltage list <hvlist@xxxxxxxxxx>
>Subject: Re: Van de Graaff generator safety question (fwd)
>
>High Voltage list wrote:
> >
> > From: Dr. Resonance <resonance@xxxxxxxxxx>
> >
> > Yes, we built one about 12 years ago.  Current increase, as compared to a
> > belt, is approx 1,200%.
>
>This doesn't seem possible. The belt in a regular VDG operates already
>close to the limit of charge density that would cause ionization of
>the air. The conductive sections of a pelletron chain would at most
>operate at this same density. The current is always directly
>proportional to the area per second of charge transport surface that
>reaches the terminal. For a given belt speed, it's very difficult to
>get something better than what a belt can give.
>
>Antonio Carlos M. de Queiroz