Re: Van de Graaff generator safety question (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 15 Jan 2004 23:29:34 -0500
From: Luc <ludev@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaff generator safety question (fwd)



High Voltage list wrote:
>
> Original poster: 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

Hi all,

May be I'm wrong but in my understanding the big charge carry by
pelletrons system is linked with the physical arrangement of the
chain AND the used of SF6 that limited the ionization and
permitted more density of charge to be carry.

Cheers,

Luc Benard