How does a Synchrotron work?
A Synchrotron accelerates charged particles, such as electrons
into an orbit at almost the speed of light. When electrons are
deflected through magnetic fields they create extremely bright
light, million times brighter than sunlight.
A synchrotron uses powerful magnets and radio frequency
waves to accelerate charged particles. The powerful magnet and
radio frequency waves accelerate negatively charged electron
along a stainless steel tube, where they reach high speed.
As the magnets are turned on and off, electrons get pulled along
the ring of tubes. Since the fast-moving electrons emit a
continuous spectrum of light, with various wavelengths and
strength, scientists can pick whatever wavelength they need for
their experiments e.g. visible light, ultraviolet light or
X-rays (soft or hard x-rays).
Structural features of a Synchrotron
A Synchrotron consists of the electron gun, linear accelerator
(LINAC), booster ring, storage ring (or rings), bending magnets
(not shown in diagram), beam lines
and the end stations (see picture below). Click on the name of
each part of the Synchrotron to the left to the diagram to read descriptions.
goes on in each of the parts of a Synchrotron?
1. Electron Gun
In the Basement of the Synchrotron building a
transformer feeds approximately 220,000 volts DC (compare with a car's battery's 12 volts) of electricity through a cathode
causing electrons to boil off the surface. The cathode is a tungsten-oxide disk called a button
(tungsten is the same material as light bulb
filaments). As electricity flows through the disk, the disk
gets heated to about 1000oC the
temperature that electrons are released. A screen near the
button is given a short, strong positive charge
125 times per second, which pulls the negative charge
particles, the electrons, away from
the disk. This procedure is
similar to that found in a television picture tube (see
the picture of the Electron Gun below).
2. Linear Accelerator (LINAC)
The Electron gun feeds into the LINAC.
Microwave radio frequency fields provide energy to accelerate
the electrons to almost the speed of light. The speed of the
electrons is approximately 3x108
m/s. The electrons are pushed
by the microwaves much like the same way as a surfer is pushed
by water waves. The LINAC produces electron
pulses approximately up to 132 nano seconds (ns) in duration. The electrons
(and later photons) must travel in a vacuum to avoid being
slowed down by colliding with atoms and molecules. The
vacuum chamber pressure is lower than 10-11
torr (1.0 torr =133 pascels). This means that there are fewer molecules in
the vacuum chamber than in the space surrounding the
International Space Station. Below is a picture of the LINAC.
Back to the
parts of the Synchrotron
3. Booster Ring
As the electrons circulate in
the Booster ring, they receive a boost in energy from approximately 250 MeV
(Mega electron volt) to
approximately 2.9 to 6 GeV (Giga electron volts) —
power equivalent to about 2 billion flashlight
generated in a Radio Frequency Cavity. In particle physics, the
standard unit to measure energy is the electron volt (eV). One electron
is the amount of energy that an electron gains when it moves
through a potential difference of 1 volt
(in a vacuum).
A synchrotron generates energy in the realm of
2.9 to 6 GeV and higher!
charged particles in a nuclear explosion range from 0.3 to 3 MeV.
The Booster Ring increases the speed of the electrons close to
the speed of light
(approximately 99.9999985 percent of the
speed of light).
There are two types of electro magnets shown in
the picture below of the booster ring. The blue dipole magnets
weigh over 3000 kg. The Synchrotron uses the magnetic field
created by these magnets to direct the electrons around the
booster ring. The magnetic field of the green quadruple magnets
are used to force the bunches of electrons into a fine beam
within the vacuum chamber. Above is a picture of booster
ring, and it's magnets.
to the parts of the Synchrotron
Ring, Beam line, and End Station
When the electrons have enough energy to produce light, an
injection system transfers them from the booster ring to the
storage ring. The process of transferring electrons from booster
to storage ring occurs approximately once per second up to 600
cycles (about 10 minutes) as required to reach an average
circulating current of. Once in the storage ring, the electrons
will circulate for four to twelve hours producing photons every
time the 6800kg dipole magnets change the direction of the flow
of electrons. While the ring looks circular, it is really a
series of 12 straight sections. After each turn there is a
photon port to allow the light to travel down the beamlines to
the research stations. The magnets and steerage ring are shown
in the picture below.
Each beamline has an optics
cabin, the experimental cabin, and the control cabin. The optics
cabin has optical instruments used to "tailor" the type of
radiation to have the characteristics for the experiment. The
cabin contains the support mechanism, and the environment for
the sample study. Instruments called detectors record the
information produced from the sample. the control cabin allows
the researchers to control the experiments and collect the
The Synchrotron described above is a basic Synchrotron.
There are Synchrotrons that are even bigger, and
brighter. These Synchrotrons achieve this by using
multi-magnet insertion devices called undulators and
wigglers, and having more storage rings. While dipole
magnets change the direction of the electrons, thus
producing light, multi-magnet insertion devices called
undulators and wigglers move the electrons back and forth
creating a narrow beam of much more intense light. For
example, Spring_8 of Japan is the brightest synchrotron in
the world, and the biggest.
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