February 21, 2003  


SPEAR3: Standing on the Shoulders of a Giant

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 SPEAR.

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 Director.

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: http://www-ssrl.slac.stanford.edu/spear3/SPEAR3_main_page.htm  


The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Friday February 21, 2003 by Kathy B