By Tom Mead
Kirk French (ASD) and Eddie Guerra (ASD) stand in
front of magnets for SPEAR3. The magnets were made at the Institute
for High Energy Physics in Beijing, China.
(Photo by Diana Rogers)
It’s been a long time comin’. SPEAR2, named SPEAR when it
was built more than 30 years ago, will close down on March 31. But, it
won’t be a long time gone. In an enterprising example of close-order
scheduling, the upgrade to SPEAR3 will begin just two hours after the
event marking SPEAR2’s closing.
SPEAR2 is the venerable physics workhorse that enabled a
significant percentage of the spectacular science for which SSRL and SLAC
have become world-renowned. It is arguably one of the most productive
research facilities ever built.
The Stanford Positron Electron Asymmetric Ring (SPEAR)
first operated in 1972 for high energy physics (HEP) research. Of the many
high-energy experiments that were conducted, two have led to Nobel Prizes.
The first experiments with synchrotron radiation began at SPEAR in 1974.
As the HEP program evolved, so did synchrotron radiation science, and
through a gradual series of improvements during the late 1980s and early
1990s, SPEAR became a dedicated synchrotron light source for SSRL.
As a fully dedicated light source, improvements were made
to the operational modes to enhance its capabilities, particularly its
brightness—a measure of the laser-like concentration of the produced
radiation. The improved machine was called SPEAR2. In addition, new
sources of radiation pioneered at SSRL—wiggler and undulator insertion
devices—were installed to further increase SPEAR2’s brightness. The first
wiggler is now on display on the ring road near the Gate 17 access to
What is Synchrotron Radiation?
The visible and invisible forms of light produced by
electrons circulating in a storage ring at nearly the speed of light
are called synchrotron radiation. Synchrotron radiation, like
visible light, is electromagnetic waves. Part of the spectrum of
synchrotron radiation lies in the x-ray region, where the wave
oscillation rate is thousands of times faster than that of visible
light. The radiation is used to investigate various forms of matter
at the molecular and atomic scales.
While SPEAR2 could see quick and deep, SPEAR3, with 10-100
times higher photon brightness, will see even more quickly and deeply.
Herman Winick, Assistant Director of SSRL, explained that, "SPEAR3 can be
expected to extend SPEAR2’s remarkable legacy by enabling the 2,000 SSRL
users to investigate the atomic arrangements and electronic properties of
materials, including biological and semiconductor materials, at higher
spatial resolutions and at shorter time scales."
The main goals of the current upgrade are to significantly
increase photon brightness and provide more stable photon beams. These
goals will be reached by replacing the entire storage ring magnets, power
supplies, the 235 meter long vacuum system, 54 magnet support rafts, RF
system, cable plant and floor foundation.
The existing arrangement of 27 experimental stations with
wiggler, undulator and bend magnet source points will remain largely
unchanged, although new mirror systems and additional
liquid–nitrogen-cooled monochromators will be installed to handle the
higher power levels. The design of the new machine takes advantage of
technology developed for PEP-II, particularly the copper vacuum chamber
and the mode-damped RF cavities, according to Tom Elioff, SPEAR3 Project
In order to prepare for possible future applications, all
systems are designed for a maximum electron energy of 3.3 GeV. At its
planned operating level of 3.0 GeV, SPEAR3 will open new research horizons
in materials science, structural biology, materials and chemical research,
and environmental science, among others.
SPEAR3 is jointly and equally funded by
DOE Basic Energy
Sciences (BES) and National Institutes of Health (NIH). It will begin to
serve users in early 2004. Over the next 12 months its performance will be
increased as commissioning progresses. According to Keith Hodgson, SSRL
Director, "SPEAR3 will position SSRL to serve its growing synchrotron user
community well into the next decade at the same time that revolutionary
new opportunities are being opened up by LCLS. We are grateful to BES for
its ongoing operations support and investments in the future."
For more information, see: