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SSRL Launches 2010 User Run

Jason Holt of Lawrence Livermore National Laboratory checks detector alignment at SSRL during the 2007 user run.

Users are back at the Stanford Synchrotron Radiation Lightsource today following the annual three-month shutdown period. During the break, many updates were made to the SPEAR3 storage ring and beamline equipment, allowing the SSRL team to increase the operating current above the former baseline of 100 milliamperes, with the aim to test operations at the top design current of 500 milliamps.

"The next run is all about increasing the current while maintaining beam stability and user data quality," said SSRL's Tom Rabedeau, who works in beamline development.

The increased current will make SSRL's X-ray beamlines even brighter, allowing researchers to put more photons on each sample in a given amount of time. Increasing the number of photons can provide clearer experimental results, because the increased signal can be more easily distinguished from background noise. The enhanced signal also reduces the length of time needed for data collection, allowing for more samples to be examined in a given period of time.

"SSRL was running at 100 milliamps most of last run," Rabedeau said. "200 milliamp operations commenced with a test during the final two weeks of the last run and will continue as the normal operating mode during the fall run."

Starting this fall, during "accelerator physics" shifts, when SSRL users are not collecting data, the beamlines will be tested at currents as high as 500 milliamps. During these times, SSRL staff will characterize beamline performance and run experiments with well-known results to better understand any changes that occur as the intensity is increased. At the same time, Radiation Protection staff will conduct careful radiological surveys of the beamline shielding to ensure safe operations at the elevated current.

However, an increased current can be tricky to maintain. When the machine operates at a higher intensity, the stored current decreases more quickly, which necessitates more frequent replenishment. At 100 milliamps, SSRL is refilled with electrons three times a day, but as the current is increased above 200 milliamps, the electron current will decay faster and the machine will require more frequent injections.

For the 2010 user run, SSRL will continue previous work using "top-off" mode—injecting electrons with the beamlines open—and slowly increase the injection frequency in an effort to maintain constant beam current.

"During accelerator physics shifts we will study the frequency at which we can inject [electrons] with minimal impact on user data collection," Rabedeau said. "In the end, our main goal is to increase the performance of the machine while at the same time preserving or improving the quality of user data."

—Lauren Knoche
SLAC Today, October 26, 2009