How does an actual quadrupole work?

An actual quadrupole from the SPS machine

The image above shows a quadrupole that is ready to be installed in the SPS machine. You can see the shape of the poles, and the coil where the current flows, creating the magnetic field between the poles.
We said earlier that the nature of the magnetic field implied that if a quadrupole was horizontally focusing it would be vertically defocusing. Indeed, here is a simulation of a quadrupole which will vertically focus the positive particles entering the plane of the drawing.
Move the mouse pointer around between the poles and see how the direction and intensity of the magnetic field (green line) and of the magnetic force (yellow line) vary, depending on the position in the quadrupole.
You will see that
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Question: How would you make a quadrupole to horizontally focus the positive particles?
Answer: at the bottom of the page

Answer: If you rotate the quadrupole by ninety degrees along its axis, an N pole will replace an S pole and vice-versa. A horizontal offset will result in a restoring horizontal force. You can experiment by putting your computer monitor on its side :)

last update on Friday, December 19, 1997 - 2:25:58 PM