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Damping Ring
The purpose of a damping ring is to
reduce the width of a beam of
electrons or positrons. Then they will
be extracted and speeded up to very
high energy by an accelerator.
At the heart
of the
Magnets are used to make the
electrons go round in a circle. These
are called bending magnets. When
the electrons feel the magnetic field,
they would experience a sideways
Each ring is made up of a hollow
Aluminium pipe that is about 6.7 km
long. There must be a very good
vacuum inside, or else the electron
beam would run into air molecules.
will be
two rings.
A clever arrangement of four magnets
provides a force that moves the
electrons towards the axis of the pipe.
This set of magnets is called a
Beam width
When the bending magnet pushes the
electron sideways, the electron emits
radiation. The radiation energy
comes from the kinetic energy of the
electrons. This reduces the
Why does the electron emit radiation?
Think of an electron at rest, and think
of the electric field lines coming out
from it. Imagine moving the electron
up and down.
Unfortunately, when electrons are
first injected into the pipe, they do not
fall exactly on the axis. So they
oscillate about the axis. This is
called betatron oscillation. The
amplitude is the beam width.
X rays
If you are very good and make sure
that the thousands of magnets are all
perfectly aligned, the oscillation will
drop to a few micrometers. This what
damping means. Then everyone will
be happy.
When you shake a string, you create a
wave. When you shake the electric
field, you create an electromagnetic
wave. This is the radiation given out.
It is called synchrotron radiation.
The Cockcroft Institute
An International Centre for Research in
Accelerator Science and Technology