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Where the LCLS Ends: The SXR Beamline

(Photo - the SXR team)
From left to right: Michael Holmes, Bill Schlotter, Plamen Velikov, Andrew Ringwall and Michael Rowen. (Photo by Brad Plummer.)

The Linac Coherent Light Source beam will pack a wallop, providing 10 trillion X-ray photons in a flash of about 100 femtoseconds. For comparison, it takes today's best storage-ring-based synchrotron radiation facilities a full second to provide that many photons. Beginning next spring, researchers will begin to conduct experiments with these powerful bursts of X-ray light using the Soft X-Ray instrument, located on the second LCLS beamline to begin operation.

"The SXR is very versatile—perhaps the most versatile of all the LCLS beamlines," said SXR Instrument Scientist Bill Schlotter. Schlotter just returned to SLAC after two years at FLASH, the free electron laser currently in operation at the German physics laboratory DESY.

Unlike the other five LCLS instruments, which have large dedicated end stations, the end of the SXR beamline will contain a valve and empty space. Users will bring their own instrumentation, rolling their experimental setups into the hutch and connecting them to the valve to access the LCLS' powerful X-rays.

"Some future users may already have end stations that they use at, say, DESY's FLASH," said SXR Beamline Engineer Michael Rowen. "They may bring instrumentation from these to the SXR beamline, or modify other instrumentation for use here."

Schlotter added: "The SXR is exciting because we can accommodate for a lot of different experiments."

Adding to the versatility of the SXR beamline is a monochromator system, which will allow users to precisely select the X-ray wavelength necessary for their experiments.

The end stations currently in the works for the beamline cover a large portion of the science researchers want to study with the SXR, Schlotter said. These studies will look at everything from gases to liquids to solids and delicate, nanofabricated samples with the beamline's "soft" X-rays—X-rays with relatively low energies and thus less penetrating power than their "hard" cousins. Using a wide range of techniques, researchers will study the ultrafast dynamics of chemical reactions, the nanoscale evolution of magnetic materials, and the mechanisms behind high temperature superconductivity—to name just a few.

Because the SXR experiments will be so diverse, Schlotter said, a big part of his job is to help build a very strong user community around the beamline. Fortunately, the basis of that community already exists. Unlike the LCLS's other five instruments, the SXR was funded both by the Department of Energy and by a consortium of institutions including the University of Hamburg through a grant from the German Ministry of Research and Education, the Center for Free Electron Laser Science, Stanford University and Lawrence Berkeley National Laboratory.

"The beamline wouldn't exist if not for this consortium and its collaboration with the Department of Energy and LCLS," Schlotter said.

Though the SXR instrument is being built by the consortium, it will be operated as a general user facility. All researchers, whether or not they are affiliated with a consortium member institution, are invited to submit proposals.

"The consortium members know that in the long term, we need more people in the field," Rowen said. "It drives more good science and future funding, and that's strong encouragement for bringing outside users in."

The first research proposals were submitted in May, and the final decisions are being made now about which groups will receive beamtime next spring.

"The first experiments will likely be performed by large groups," Schlotter said. "This will bring a collaborative atmosphere where people can teach and learn, creating a community to sustain the science. There are really endless opportunities for outstanding discovery with the SXR beamline."

This is the sixth and final story in a series exploring the scientific instruments of the LCLS. See also "The CXI Instrument," "The AMO Instrument," "The XPP Instrument," "The XCS Instrument" and "The MEC Instrument."

—Kelen Tuttle
SLAC Today, September 15, 2009