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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.
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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.” |
