Diamond light, brighter than the sun
February 7, 2012 By
The Diamond Light source building at dusk.
Credit: Diamond Light Source.
Itís the size of five football pitches and
generates light 10 billion times brighter than the sun. As the
Diamond Light Source celebrates its tenth anniversary this year,
Penny Bailey visits one of the UKís biggest scientific
investments to see how it works.
Imagine that the only thing limiting you is your
imagination - that the physical means of achieving what you see
in your mind's eye is right in front of you. That, according to
Professor Mark Hodson, is how it is for scientists at the
Diamond synchrotron in Oxfordshire. With its curving walls,
lined with walkways, pipes and colourful, clunky-looking
machines and gadgets, it's a sight that wouldn't seem out of
place in an early episode of 'Doctor Who'.
From a birds-eye view, Diamond looks like a
massive ring doughnut or a spaceship half a kilometre in
circumference (roughly the size of five football pitches). In
fact, itís a polygon of 24 straight sides, and its size and
shape are dictated by its purpose.
As the name suggests, Diamond is a source of
intensely bright light, which can be up to 10 billion times
brighter than the sun. And it's not just visible light - Diamond
is optimised to produce light with much shorter wavelengths in
the form of X-rays and also generates infrared and ultraviolet
light invisible to the naked human eye.
Researchers go to the synchrotron to use that
brilliantly intense light in much the same way as they use
visible light in a microscope or X-rays: to reveal things we
can't see. Microscopes work by passing visible (optical) light
through an object. The refracted light passes through two lenses
that focus it to create an image of the object's microscopic
structures, then magnify the image so we can see it. An X-ray
machine passes X-rays through an object and captures the image
created of its internal tissues on negative film. X-rays reveal
the internal composition (tissues) of large objects such as
people, and microscopes reveal the innards of tiny objects such
as cells that are only a few microns (0.001 mm) in size, too
small to be visible to the naked human eye.
The Diamond synchrotron is millions of times
bigger than an X-ray machine or a microscope, yet the light it
generates enables scientists to see the internal structures of
things that are infinitely smaller, such as atoms. Atoms are
measured in angstroms: one angstrom (1 Ň) is 0.1 of a nanometre
(nm), which in turn is one-billionth of a metre. To give you
some context, a human hair is 100 000 nm wide and an ant is
approximately 5 million nm long.
In trying to look inside an atom, scientists are
trying to visualize something that is only 0.1 billionth of a
metre big. To distinguish two objects (atoms) that are only 1 Ň
apart, researchers need to pass a much more intense light
through them. They need to use light with far shorter
wavelengths than the visible light used in microscopes - either
ultraviolet light or X-rays. It's the job of Diamond to produce
that light and send it to the 'cabins', the laboratories
surrounding the storage ring where the experiments are actually
How does Diamond create those intense, invisible
forms of light? Like CERN in Switzerland, Diamond is a particle
accelerator, and it uses very similar technology. Both, as the
term suggests, are designed to get particles zipping along at
great speed. CERN sends neutrons and protons smashing into each
other at speeds approaching the speed of light to understand
what particles - and the universe - are made of. Diamond, by
contrast, accelerates electrons. It also doesn't smash them into
each other, and scientists don't actually do any experiments
with the electrons themselves; instead, they use the high speed
of the electrons to create intense light to use in their
The way the electrons are produced in the first
place will be familiar to anyone who's ever owned a big,
old-fashioned TV. The cathode ray tube in the back of the TV
heats up an alloy, causing it to release electrons and fire them
at the TV screen, which fluoresces, producing images. Diamond
works on a similar principle, although on a much vaster scale.
The bridge over the storage ring of the facility.
Credit: Diamond Light Source.
Rather than a screen, the electrons generated by
heating an alloy in an electron gun are fired into a sequence of
three accelerators. The first is the 30-m long Linac, which
increases the speed of electrons from almost no miles per hour
to something approaching the speed of light. They then pass into
the booster, where they gain energy until they have enough to
produce light of the kind and quantity needed to illuminate the
atoms the scientists are looking at.
They then pass into the storage ring - the vast
560 m2 tube that gives Diamond its shape and size. It is here
that the electron bundles (beams), which travel around the ring
roughly half a million times every second, generate synchrotron
light and send it into the beamlines leading to the experimental
stations (laboratories) surrounding the storage ring.
Magnets at the point of entry to the beamlines
bend the speeding electrons around the corners of the polygonal
storage ring, which causes them to release energy in the form of
light (photons). This light spans the electromagnetic spectrum
from infrared to visible and ultraviolet light and X-rays.
Diamond is a 'third-generation' synchrotron,
which broadly means that it uses more sophisticated magnets to
create more intense light. At the beamline point of entry,
'insertion devices' cause the electron beam to wiggle backwards
and forwards between the opposite magnetic poles. This
'constructive interference' produces very bright, very intense
beams of X-rays - so intense that safety procedures are
stringent. People cannot enter the lead-lined hutches in which
the experiments take place when the machine is operating, so
experiments are controlled remotely from a separate control
The power of these X-rays can help reveal the
atomic structure of proteins and inorganic elements like metals.
Mirrors and crystals help focus the beams down to the wavelength
required for each station, which then passes into the
experimental hutch where it interacts with the substance the
scientists want to 'see', the interaction revealing what it is
made of at the atomic level.
Around 2000 research groups a year come to do
experiments at Diamond that they could not do anywhere else.
Research ranges from solving protein structures to designing
Scientists have used the synchrotron's light to
look at the nutritional quality of wheat, assess the success of
attempts to increase levels of zinc and iron in food, and work
out which form of phosphate is best at locking up metal
contaminants in soil. iPod and iPad users might be interested to
know that the technology on which they are based - giant magneto
resistance - wouldn't exist without synchrotrons. With new
beamlines coming online in the forthcoming third phase of
Diamond's development, new possibilities for research abound to
push the limits of scientists' imaginations.
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