In 1945, the
synchrotron was proposed as the latest accelerator for high-energy
physics, designed to push particles, in this case electrons, to
higher energies than a cyclotron
was capable of, it was the particle accelerator of the day!
It is basically
lots of linacs in a circle with
a magnetic field to ensure the beam stays on track!
takes stationary charged particles, such as electrons, and drives
them to velocities near the speed of light. In being forced by
magnets to travel around a circular storage ring, charged particles
tangentially emit electromagnetic radiation and, consequently,
lose energy. This energy is emitted in the form of light and is
known as synchrotron radiation.
Electric (GE) Laboratory in Schenectady built the world's second
synchrotron, and it was with this machine in 1947 that synchrotron
radiation was first observed.
physicists performing experiments at an electron accelerator,
synchrotron radiation is a nuisance as it causes a loss of particle
energy. But condensed-matter physicists realised that this was
exactly what was needed to investigate electrons surrounding the
atomic nucleus and the position of atoms in molecules. So, in
the early days, the two branches of physics worked together in
so-called "parasitic" operation, where synchrotron light
illuminated the condensed-matter physicists' experiments while
particle physicists used the electron beam.
Many of the
synchrotron systems in commercial operation around the world were
no built to produce the high energy particles but to produce 'synchrotron
part of the electromagnetic spectrum that the human eye can see
is called visible light. In order of decreasing wavelength and
increasing frequency. The region with wavelengths shorter than
violet is the ultraviolet and, overlapping and going beyond it,
the X-ray region. Meanwhile, on the other side of red, with longer
wavelengths, is the infrared region. The shorter the wavelength,
the higher the frequency and the more "energetic" the
light. While it cannot be seen by the human eye, when used in
certain ways and viewed by appropriate detectors, this light can
reveal structures and features of individual atoms, molecules,
crystals, cells and more, especially when the wavelength and corresponding
energy of the light are matched to the size and energy of the
sample being viewed. Because synchrotron light is very intense
and well collimated, it is preferred to light produced by conventional
There is a
direct relationship between the speed of charged particles and
their radius of curvature of the path.
will then get an acceleration of the particles from an electric
field, according to:
magnetic force is equal to the centripetal force of the circular
movement (it is what makes it move in a circle!), so we get the
cyclotron equation from equating the two:
force = mv2/r
force = Bvq
mv2/r = Bvq
a ' v ' and rearranging we have
r = mv/qB
where r is
the radius of the particle orbit.
So for very
large velocities we would need a very large circular path.
would be impossible with a cyclotron.
is capable of producing such speeds because it is constructed
as a large circular tunnel. The acceleration in the ring is achieved
by small accelerating sections like in the LINAC but a magnetic
field is also present to produce the curved path.
are already travelling at very high speeds before they enter the
storage ring. This is a circular
(or near circular) structure in which either high energy electrons
and/or positrons, or protons and/or antiprotons can be circulated
many times and thus "stored" to produce synchrotron
light. They can then also be released and used to achieve high
energy collisions. Because of the very different masses of protons
and electrons a storage ring must be designed for one or the other
type and cannot work for both.
charged particle undergoes accelerated motion it radiates electromagnetic
energy. A common example is the emission of radio waves when electrons
move back and forth in a radio antenna. A charged particle traveling
in the arc of a circle is also undergoing acceleration, due to
its change in direction it cannot be travelling at constant velocity. The radiation emitted by such particles
is called synchrotron radiation and it is particularly intense
and very directional when electrons travelling at close to the
speed of light are bent in magnetic fields.
So when high
energy electrons are deflected by strong magnetic fields, they
emit electro-magnetic waves covering the whole spectral range
from microwaves to hard X-rays. The electromagnetic energy (or
synchrotron light) produced by the storage ring of a Synchrotron
comes in the form of a fine and very intense beam, similar to
that from a laser.
beams produced are about a trillion times brighter than
those of conventional X-ray sources used in laboratories and hospitals.
This makes the synchrotron
a powerful tool for scientists, helping to deepen our present
understanding of physics, materials and life sciences as well
as improving industrial processes.
(green), a 16 m long linear accelerator, brings electrons
to an energy of 200 MeV.
Synchrotron (red), 300 m in circumference, repeatedly
accelerates the electron bunches emitted from the Linac. Once
the electron beam reaches the operating energy of 6 GeV,
it is injected in the storage ring.
Storage Ring (magenta), 844 m in circumference, the electron
beam is maintained at the operating energy of 6 GeV. Here,
electrons travelling with nearly the speed of light emit synchrotron
In its normal mode of operation, the storage ring provides a
current of 200 mA for a lifetime of about 50 h. Energy
losses of the electron beam are compensated by 6 accelerating
cavities, operating at a frequency of 352 MHz.
In the storage
ring, the needle thin electron beam is travelling with nearly
the speed of light in ultra high vacuum.
When we look
inside the tunnel, we can see the functional elements of the synchrotron
X-ray source: bending magnets and insertion devices - furthermore,
focusing magnetscollimate the electron beam, while 'front-ends'
carry the X-ray beam to the experimental hall.
A level standard question
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