| Topic: |
Science > Physics |
| User: |
"Greg" |
| Date: |
01 Sep 2005 04:07:35 AM |
| Object: |
Can an electron lens be negative? |
Hi,
if I have an electron lens that focusses an electron beam, and make the
current through the focus coil negative, do I get a negative lens like
a concave lens with respect to optical lenses?
And is the behaviour proportional to the current, like if I have a
"focal length" of 80mm with 1 Ampere throuvh the coil, will I get -80mm
when I reverse the current?
Is there any free literature on the internet that describes the BASICS
of electron lenses?
Greg
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| User: "Zigoteau" |
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| Title: Re: Can an electron lens be negative? |
01 Sep 2005 05:55:02 AM |
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Hi, Greg,
if I have an electron lens that focusses an electron beam, and make the
current through the focus coil negative, do I get a negative lens like
a concave lens with respect to optical lenses?
Not as I understand it. The most common configuration approximates to a
uniform magnetic field parallel to the optical axis, so that reversing
the field will change the sign only of the rotation of the image and
not of the lens power.
And is the behaviour proportional to the current, like if I have a
"focal length" of 80mm with 1 Ampere throuvh the coil, will I get -80mm
when I reverse the current?
No.
Is there any free literature on the internet that describes the BASICS
of electron lenses?
Did you Google first?
http://jan.ucc.nau.edu/~wittke/Microprobe/Column-Condenser.html
http://www.uam.es/otroscentros/cmam/cristalera/G.Grime_02.pdf
http://www.ensmp.fr/aflb/AFLB-295/aflb295m199.pdf
Cheers,
Zigoteau.
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| User: "Jan Panteltje" |
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| Title: Re: Can an electron lens be negative? |
01 Sep 2005 06:10:49 AM |
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On a sunny day (1 Sep 2005 02:07:35 -0700) it happened "Greg"
<gfoersler@gmx.de> wrote in
<1125565655.895418.224380@z14g2000cwz.googlegroups.com>:
Hi,
if I have an electron lens that focusses an electron beam, and make the
current through the focus coil negative, do I get a negative lens like
a concave lens with respect to optical lenses?
You have magnetic focus (as opposed to electrostatic focus).
Lenz law, reverse the wires and the world spins 180 degrees.
However:
And is the behaviour proportional to the current, like if I have a
"focal length" of 80mm with 1 Ampere throuvh the coil, will I get -80mm
when I reverse the current?
In case of a solenoid around the beam, the electrons will spiral in a spiral
with ever decreasing radius.
The focus point will not change, the magnetic effect is at right angle to
the beam!
Is there any free literature on the internet that describes the BASICS
of electron lenses?
Greg
Look up TV tube, type 'electron lens' in www.google.com
Prof TV.Tube
From the Panteltje lectures
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