Birth of the synchrotron
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 could a cyclotron, the particle accelerator of the day. An accelerator
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. The General 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. Radiation by orbiting electrons in synchrotrons was predicted by, among others, John
Blewett, then a physicist for GE who went on to become one of Brookhaven's most influential accelerator physicists, working on
both the Cosmotron and the Alternating Gradient Synchrotron.
For high-energy physicists performing experiments at an electron accelerator, synchrotron radiation is a nuisance which causes
a loss of particle energy. But condensed-matter physicists realized 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.
The light spectrum
The part of the electromagnetic spectrum that the human eye can see is called visible light. In order of decreasing wavelength
and increasing frequency, it is known to school children as "ROY G. BIV," for red, orange, yellow, green, blue, indigo
and violet. 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
laboratory sources.
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Decision to build the NSLS
When the U.S. Department of Energy's Office of Basic Energy Sciences
recognized the need for "second generation" electron synchrotrons
dedicated to the production of light, it budgeted construction funding for
Brookhaven's National Synchrotron Light Source (NSLS), beginning in fiscal year
1978. Ground was broken for the NSLS on September 28, 1978, and the vacuum
ultraviolet (VUV) ring began operations in late 1982, while the x-ray ring
was commissioned in 1984.
The Chasman-Green lattice
Before the light at the NSLS was turned on, however, the two inspired
scientists responsible for the ingenious design of the two storage rings had
died. The late Renate Chasman and G. Kenneth Green had designed the
"double focusing achromat," or what is more commonly known as the
Chasman-Green lattice. The lattice is the periodic arrangement of magnets
that bend, focus and correct the electron beam, and their simple yet elegant
design included straight sections for the insertion of equipment.
When special magnets are inserted into two straight sections in the VUV
ring and five straight sections in the x-ray ring, the electron beam "wiggles"
and, therefore, emits even more intense synchrotron radiation. Chasman and Green's
inclusion of these devices in their design of the storage rings enables the
NSLS to deliver world-class beams of light today.
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