|Small Spot, Brighter Beam|
Do you notice the brighter beam? During the most recent shutdown, all of the corrector magnets were replaced with sextupoles, reducing the horizontal emittance and increasing beam brightness. “This is part of ongoing improvement to keep the ALS on the cutting edge,” says Alastair MacDowell, a beamline scientist on Beamline 12.2.2.
The brightness has increased by a factor of about three in the storage ring. Beamlines on superbend or center-bend magnets will see the most noticeable increase in brightness, but the horizontal beam size and divergence have been substantially reduced at all beamlines. “We are starting to approach the resolution of many beamlines. Therefore, not every beamline will be able to resolve the full improvement,” says Christoph Steier, project leader of the brightness upgrade. Though superbend and center-bend magnet source sizes are reduced by roughly a factor of three, “measured improvements so far range from a factor of 2-2.5,” Steier says. He and MacDowell agree that the beamline optics are likely the limiting factor in resolving the full improvement at the beamlines.
Martin Kunz and Nobumichi Tamura, staff scientists on microdiffraction Beamline 12.3.2, focus all the photons from the beam to a spot size of one micron. This upgrade increases the intensity of the spot by a factor of at least two, enabling data collection in less than half the time. Kunz's measurements (shown above) indicate a 2.9-times decrease in horizontal beam size and a slight increase in vertical beam size.