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Dorfan Today: Why Love LUSI

The Linac Coherent Light Source (LCLS)'s unprecedented ability to produce high-intensity, laser-like x-ray beams will allow researchers to create images of atomic-size structures with new levels of resolution. Because of the short duration of the x-ray pulse, one will, in addition, be able to capture these atomic structures in motion, that is to capture a sequence of images that chronicles the structure's temporal behavior. With intelligently designed and built instrumentation, it will be possible to reconstruct images of three-dimensional atomic arrangements and track changes in the conformance of the structures.

Six such instruments are planned for the initial phase of the LCLS. The LCLS Ultrafast Science Instruments (LUSI) project will construct four of the instruments, each one optimized for a different aspect of the LCLS science agenda. Similar to how BaBar provides the tools to measure the results from PEP-II collisions, or how SPPS brought together a group of specialists to build a dedicated experiment to use the photon beam at the FFTB, the LUSI project will create and manage the construction of four instruments—each of which, as their respective names suggest, is designed to take advantage of a distinct experimental technique. Thus LUSI comprises: The Coherent X-ray Imaging Instrument, The X-ray Pump/Probe Instrument, The Soft X-ray Scattering Instrument and The X-ray Photon Correlation Spectroscopy Instrument.

With conventional x-ray sources, like our own SPEAR3, biological molecules must be crystallized if they are to be imaged in great detail. With the LCLS beam and the proposed design of The Coherent X-ray Imaging Instrument, there is no requirement for a "freezing" of the molecules, thus opening the way to the imaging of the many molecules that cannot be crystallized. The X-ray Pump/Probe instrument will capture images of molecules (the "probe" aspect) as they undergo changes in response to laser excitation (the "pump"). These changes will be captured at time intervals reaching below a picosecond (one trillionth (10-12) of a second). The Soft X-ray Scattering Instrument will use the longer wavelengths in the LCLS spectrum to study magnetic properties of iron, nickel, and cobalt that play a fundamental role in understanding the limits of magnetic data storage. And The X-ray Photon Correlation Spectroscopy Instrument will study the structure and motions of atoms and molecules in solids and liquids.

The instruments created by LUSI are part of the portfolio proposed by the scientific community and reviewed by the LCLS Science Advisory Committee. Two other scientific instruments, not included in LUSI, form a total of the six initial LCLS experimental stations. The LCLS project itself will create the Atomic, Molecular, and Optical Science Instrument to measure the interactions between the x-ray pulses and matter, beginning with atoms and extending to molecules and then clusters of 10's to 1000's of atoms. Researchers from Livermore National Laboratory will design the sixth experimental station, called High-Energy Density Science Instrument, to study matter under extreme conditions.

This summer, the LUSI project team will finish the concept design for the suite of instruments. The team of six will grow to some two dozen scientists, engineers, and designers. The four instruments will be completed between 2010 and 2012, and project managers hope to open the facility to outside users some one to two years thereafter. Innovation at SLAC has forged the way for photon science's fourth-generation instrument, the LCLS, and LUSI will lead the way towards accomplishing the ground-breaking science that the LCLS makes possible.

—Jonathan Dorfan, June 26, 2006