April 16, 2004  


Let the Light Shine: SPEAR3 Up and Running

By Mason Inman

SPEAR3’s shutters are open and users are getting their first taste of work with the completely rebuilt synchrotron radiation facility. The SPEAR3 upgrade is not yet complete as the current level is at 100 mA rather than the final 500 mA target. Like any new machine, it will continue to improve as it is broken in, users are already seeing improvements over SPEAR2.

Herbert Axelrod (Photo by Amanda Prado)

The top off injection technique is one improvement, in which more electrons are periodically injected at-energy into the synchrotron to keep the current high and maintain an intense x-ray beam. With SPEAR2, keeping the current high involved emptying the ring of electrons, refilling it at a lower energy, then increasing the ring energy back to 3 GeV, which could cause long down times for users.

“It’s wonderful. We love SPEAR3,” said Deanne Rudd (Stanford). “The best part is the top off.”

Right now, the top off has to be done four times a day. As the synchrotron continues to run, however, the vacuum chamber that holds the electrons will become cleaner, making less top offs necessary and the beam more stable. “It’s getting to be stable,” said Ritimukta Sarangi (Stanford).

So far, SPEAR3 hasn’t changed the nature of Sarangi’s work on solutions of metal-containing proteins. She is already looking forward to this fall, when the electron beam is scheduled to be ramped up from 100 mA to 500 mA, which will allow Sarangi and fellow group members to collect data much more quickly.

For Frank Bridges (UC Santa Cruz), who uses EXAFS spectroscopy, the stability of the beam is crucial. “It looks good at this point,” Bridges said. “The beam is very stable and the first few data traces look great.”

Once Bridges starts taking data at the full beam current, the benefits of SPEAR3 should be immediate. He said the more intense x-ray beam will allow them to take high-quality data more quickly, partly because they can use smaller crystals in their experiments.

“The best crystals are often the smallest ones,” Bridges said. Larger crystals have more imperfections and irregularities, which make the data less clear.

Along with the upgrade of SPEAR3, several robots were installed on the beamlines to help users.

“The robot is fantastic,” said Herbert Axelrod (SG), about the machine that loads crystal samples into a cryogenic gas stream, produced by liquid nitrogen. Before, Axelrod had to load the samples manually, which was much slower and left him with chilly hands despite the use of gloves. “Believe me,” Axelrod said, “it’s pretty nice.”


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

Last update Monday April 19, 2004 by Emily Ball