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Top-Off Upgrade Completed Successfully The largest upgrade of the Advanced Light Source since it was originally commissioned in 1993 culminated with the successful transition to top-off user operations on Wednesday, February 11. The top-off operational mode allows frequent injection of electron beam into the storage ring, resulting in a nearly constant current while keeping user-beam shutters open at all times. This mode presents several large advantages for users. Instead of having multiple injections of a large number of electrons in a short time period followed by uninterrupted beam decay over the course of eight hours, a small number of electrons is added to the storage ring at approximately every 30–60 seconds. The constant beam current enhances the flux and brightness of the radiation while simultaneously improving the thermal stability of the machine and its beamlines.
Screen shot of the storage ring status display on Friday, February 20. In the past, the graph of the electron beam current would have shown the familiar sawtooth pattern, spiking every eight hours as fresh electrons were injected into the ring. With top-off injection, the current appears steady at about 400 mA. The new average current level is about 450 mA, but plans are to ultimately increase that to 500 mA in the next few weeks. In terms of flux, this translates into a 50% increase now and 100% increase at full current. Also, the process of slowly decreasing the vertical emittance has begun. So far there has been about a 10–15% reduction of the vertical beamsize, with a resultant increase in brightness of twice that amount. The goal is to cut the beamsize by 50% over the next six months, increasing brightness by up to a factor of four. So, overall, the upgrade should increase the flux by a factor of two and the brightness by a factor of up to eight. The installation of newer insertion devices with smaller gaps will provide additional gains. In terms of stability, it’s estimated that by eliminating the current dependence of beam-position monitors and by reducing the thermal motion of magnets, girders, etc., the medium-term orbit drift has been reduced by a factor of two to three. On top of that, user beamlines might profit by the steady heat load no longer introducing thermal drifts in beamline components. Finally, it is of advantage to many users that they do not need to normalize their measurement data to their incoming photon flux anymore. This makes measurements easier and reduces noise and systematic errors. Responses from users, who have anxiously anticipated top-off operation for several years, have been uniformly positive. |
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Probing Core-Hole Localization in Molecular Nitrogen The behavior of the core hole created in molecular x-ray photoemission experiments has provided molecular scientists with a valuable window through which to probe the electronic structure and dynamics of molecules. But the answer to one fundamental quantum question—whether the core hole is localized or delocalized—has remained elusive for diatomic molecules in which both atoms are the same element. An international team of scientists from the University of Frankfurt in Germany, Berkeley Lab, Kansas State University, and Auburn University has now resolved the issue with an appropriate twist of quantum fuzziness. By means of coincident detection of the photoelectron ejected from molecular nitrogen and the Auger electron emitted femtoseconds later, the team found that how the measurements are done determines which description—localized or delocalized—is valid. Read more…
Publication about this research: M.S. Schöffler, J. Titze, N. Petridis, T. Jahnke, K. Cole, L. Ph.H. Schmidt, A. Czasch, D. Akoury, O. Jagutzki, J.B. Williams, N.A. Cherepkov, S.K. Semenov, C.W. McCurdy, T.N. Rescigno, C.L. Cocke, T. Osipov, S. Lee, M.H. Prior, A. Belkacem, A.L. Landers, H. Schmidt-Böcking, Th. Weber, and R. Dörner; “Ultrafast probing of core hole localization in N2,” Science 320, 920 (2008). |
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Enzyme Structure Provides Insights into Cancer and Aging XPD helicase is an enzyme that unwinds the DNA double helix; it is one component of an essential repair mechanism that maintains the integrity of DNA. XPD is unique, however, in that pinpoint mutations of this single protein are responsible for three different human diseases: in xeroderma pigmentosum (XP), extreme sensitivity to sunlight promotes cancer; Cockayne syndrome (CS) involves stunted growth and premature aging; trichothiodystrophy (TTD), characterized by brittle hair and scaly skin, is another form of greatly accelerated aging. At the ALS, researchers from Berkeley Lab and The Scripps Research Institute recently solved the structure of XPD. The structure gives novel insight into the processes of aging and cancer by revealing how discrete flaws—as seemingly insignificant as a change in either of two adjacent amino acid residues—can lead to diseases with completely different physical manifestations. Read more…
Publication about this research: L. Fan, J.O. Fuss, Q.J. Cheng, A.S. Arvai, M. Hammel, V.A. Roberts, P.K. Cooper, and J.A. Tainer, “XPD helicase structures and activities: Insights into the cancer and aging phenotypes from XPD mutations,” Cell 133, 789 (2008). |
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Guest House Survey: Room Layouts and Furnishings The Berkeley Lab Guest House is on schedule for a July completion and opening. The Guest House building is now watertight, and electrical installation has started. The Guest House will have 57 guest rooms with an additional lounge/kitchenette. It is expected that tentative bookings might be taken as early as April or May, to be confirmed in June. Sited near the ALS building, the Guest House is expected to be popular with ALS users. Room furniture will be ordered within the next few weeks and we would like your input to help us choose the appropriate room layouts and furnishings to meet your needs (see possible room layouts at the ALS Housing page). Your input is valuable and will be used to help the contractors make decisions. If you’re an ALS user who plans to utilize the Guest House, please complete the short survey at the link below so that we know what will work for you (the survey also includes a few short questions about light-source safety practices and the general-user proposal process). Take the ALS Guest House survey.
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Two Important Strategic Documents Now Available Online
Download “Science and Technology of Future Light Sources.”
Download “The Advanced Light Source Strategic Plan 2009–2016.” |
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Wanted: Energy-Related Highlights
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The beam reliability and completion numbers for the user runs from January 21 to February 15, 2009, were not available at the time of publication. Please check back here later this week, where the information will be postedk. Questions about beam reliability should be sent to David Richardson. Requests for special operations use of the “scrubbing” shift should be sent to Rick Bloemhard (ALS-CR@lbl.gov, x4738). Long-term and weekly operations schedules are available here. View the ring status in real time here.
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A white paper titled “Science and Technology of Future Light Sources,” a collaboration between scientists from Argonne National Laboratory, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and SLAC National Accelerator Laboratory, is now available in PDF format. This 87-page document envisions the scientific challenges that can be met by future x-ray sources and instrumentation and summarizes the research and development required to achieve that vision. Scientific challenges, or “drivers,” such as understanding and controlling dynamic phenomena, chemical reactivity, complex materials, novel materials design and behavior under extreme conditions, and life science and soft condensed matter are covered, with a discussion of “What Is Needed?” for each of these areas. Closing chapters discuss types of x-ray sources, their capabilities and trade-offs, and other considerations.
Working closely with our U.S. Department of Energy (DOE) sponsors, advisory committees, user community, and beamline scientists, the ALS has developed a new strategic plan titled “The Advanced Light Source Strategic Plan: 2009–2016.” Subtitled “Addressing the Scientific Grand Challenges and Our Energy Future,” the plan not only aims to keep the ALS at the forefront among its peers, but also responds to the challenge of establishing unique scientific programs capable of achieving the breakthroughs in fundamental research needed to put advanced energy technologies within reach. Four key focus areas provide the foundation for the new plan: New and upgraded beamlines, accelerator renewal, enabling technical capabilities, and user scientific support and future scientist pipeline. A chapter devoted to each focus area describes specific elements of the plan, including what funding will be needed, roughly in priority order.
The ALS is always on the lookout for science highlights to publish in ALSNews, post on our Web site, and send to our funding agency, DOE. In the past, our focus has been on research published in the so-called “high-profile” journals: Nature, Science, Physical Review Letters, and Cell (for structural biology). It has not escaped our attention, however, that many interesting and worthwhile experiments by ALS users get overlooked using this tight screen. Therefore, we would like to encourage users to submit their work for consideration as science highlights—particularly on energy-related topics—as long as it has been either published or accepted for publication in a peer-reviewed journal. “Energy-related” is of course a broad category, covering topics from catalysis and combustion to batteries and solar cells. If you would like to help “energize” our science highlights, please submit your research paper(s) to the