Re: Van de Graaff /Pelletron (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 18 Jan 2004 14:18:13 -0500
From: Charles Brush <cfbrush@xxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaff /Pelletron (fwd)

>---------- Forwarded message ----------
>Date: Fri, 16 Jan 2004 08:23:40 -0800
>From: Ed Phillips <evp@xxxxxxxxxxx>
>To: High Voltage list <hvlist@xxxxxxxxxx>
>Subject: Re: Van de Graaff /Pelletron (fwd)
>
>I guess all of those who've looked at those pictures again have come up
>with our own way of making a "belt".  In thinking about that I came up
>with a fundamental question which might inhibit further efforts.  If the
>individual pellets are conducting, which seems necessary, don't their
>edges form a chain of little spark gaps and isn't the maximum output
>voltage for a given length limited by breakdown between the pellets?  If
>so, it would seem that to get interesting voltages the machine would
>have to be run in an insulating gas under pressure.
>
>	Comments?
>
>Ed


Ed,

Makes sense, but the links in the chain must also form a series of
equipotentials dividing the voltage gradient from top to base by the
number of links.  Some of these machines appear to be using hundreds
of links, which would be necessary for multi megavolt differentials.
Here is a very interesting page with a bunch more info on the use of
large equipotential rings along the length of these machines to even
out the electrostatic field.  At the bottom Antonio Carlos M.
deQueiroz is quoted as stating that a pelletron does require a longer
chain than a a standard Van de Graaff to avoid belt sparking:

http://members.aol.com/lyonelb/vdg2.html

I think there are open air pelletrons.  As long as your belt is long enough...

Lastly according to the page above, a "string of beads" approach was
in fact one of the steps that led to the modern pelletron.   Whoever
proposed that idea on this list was on the mark!


Zap!

Charles Brush