From: Jim Adney
Subject: Re: In Need of a 50-KV Electron-Gun
Date: Sat, 26 Oct 2002 22:10:42 -0600
Organization: University of Wisconsin, Madison
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NNTP-Posting-Date: Sun, 27 Oct 2002 03:09:51 +0000 (UTC)
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On 26 Oct 2002 11:31:39 -0700 email@example.com (N. Thornton) wrote:
>Jim Adney wrote in message news:...
>> On 24 Oct 2002 17:55:09 -0700 firstname.lastname@example.org (N. Thornton) wrote:
>> I'm afraid that this doesn't work, although intuitively I can see why
>> it might seem possible. In the end the only way this could work would
>> be to violate Conservation of Energy.
>Not sure I follow you on that. I am suggesting a very open weave gris,
>which doesnt have the same affect as a close mesh one.
It all comes down to what the total voltage difference is between the
starting and ending points for the electron. The change in voltage,
times the charge on the elctron, gives us the energy that the electron
has when it arrives at the target. This is also the energy that has to
be supplied to either the cathode or the target (whichever is not
grounded) to keep them at voltage, ie to replace the energy carried
away by the electron and dissipated in the target as heat, secondary
electrons, etc when it hits.
It really doesn't matter what kind of grids you put along the way, as
whatever acceleration is necessary will occur no matter if the
distance is small. Keep in mind that if you make the distances too
small the grid is likely to spark to your target.
As a bit of an analogy you can think about 2 battery terminals with
some voltage V between them and think about whether there is a way
that you can allow a current I to flow from one to the other without
dissipating an amount of power equal to I*V. No matter how you arrange
resistors, you won't be able to get away from P=I*V, and similarly, if
V = zero, you will have trouble getting I to be anything other than
If you could move an electron from one grounded place to another and
have it arrive with some kinetic energy, then you would end up with
more energy than you used to move the electron (which was none in this
case) and you would have created energy.
Now John Woodgate said, "An obvious reason to try it. (;-)" and I
appreciate the humor in that, but it ain't gonna happen. ;-)
I worked for many years for a company that makes particle
accelerators. This is one of the basic principles of particle
accelerators of all kinds, although the RF kind can play games with
the particles and add energy to an electron that is already in flight.
In that case the energy still comes from somewhere and the electron
still ends up with the energy due to its potential drop plus that
added in flight by RF means.
Jim Adney email@example.com
Madison, Wisconsin USA