Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P6: Condensed Matter Physics and Future Accelerator-based Light Sources |
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Sponsoring Units: FIAP DPB Chair: Alan Todd, Advanced Energy Systems Room: Colorado Convention Center 207 |
Wednesday, March 7, 2007 11:15AM - 11:51AM |
P6.00001: New x-ray sources illuminate hidden corners of space and time -- revolutionary solid-state science and how we'll get there through the Advanced Photon Source upgrade Invited Speaker: Third-generation x-ray storage ring sources have major impact in condensed-matter and materials physics. Many cutting-edge experiments, including nanoscale imaging and studies of fast dynamics, demand shorter and more spatially coherent x-ray pulses. Unfortunately, these parameters are intrinsically limited by the physics of storage rings. Many experiments at sources such as the Advanced Photon Source (APS) could benefit from revolutionary performance that is promised by fourth-generation capabilities. The key element which makes fourth-generation sources better in these respects is that the electron beam does not travel long enough (is not ``stored'') for the pulse to come to equilibrium. We are proposing to introduce such a beam into the APS storage ring through an Energy-Recovery LINAC concept, as part of a major upgrade. I will describe some of the research in condensed matter and materials physics which demand this upgrade, and outline the technical performance and our plans to realize the upgrade. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:27PM |
P6.00002: Energy Recovery LINAC: Experimental Challenges Invited Speaker: ERL projects are ongoing at JLab, Daresbury, KEK and Cornell. Here, we describe the experimental challenges of using high-coherence and ultra-fast pulses from the Cornell ERL and illustrate some potential opportunities. The Cornell ERL is designed to run in several different modes. In the hi-flux mode, the ERL runs at 5 GeV and 100 mA. Many experiments, such as inelastic x-ray scattering are photon-starved. In the high-coherence mode the ERL runs at 25 mA and the transverse emittances could be as low as 8 pm. The beam size will be at its smallest under this operating condition and an average spectral brightness as high as 10$^{23}$ (standard units) is predicted. We expect to produce a round (3 micron diameter) source for imaging and coherence experiments on individual biological cells. In the ultra-fast mode, the repetition rate is reduced from 1.3 GHz to 1 MHz, the bunch charge is increased to 1 nC per pulse, and the natural 2 ps bunch length is compressed to less than 100 femtoseconds. We will present opportunities for x-ray experiments on a single atom as well as the challenges in x ray optics, other experiments, and beam control issues when making a 1 nm focused x-ray beam size. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 1:03PM |
P6.00003: Seeded Free Electron Lasers: The Technical Challenges and the Scientific Impact Invited Speaker: The fields of laser and accelerator technology stand now at a point of remarkable opportunity---the creation of fully coherent and powerful pulses of x-ray radiation ranging in wavelength from 100 nm to 0.1 nm. Radiation in this essential wavelength range is unlikely to be produced with substantial power, particularly below wavelengths of 10nm, by table-top laser sources. Sources based solely on circular accelerators, such as synchrotrons and energy-recovery linacs, cannot achieve full coherence. Even the current generation of free-electron lasers (FELs) based on self-amplified spontaneous emission (SASE) expect to produce less than 1{\%} of the power in a single mode in their baseline designs. The key to achieving full transform-limited coherence is to imprint the electron bunch with a fully coherent seed pulse generated by either an external source or by clever manipulations of the FEL radiation itself. We will review the technological challenges presented by this approach in the context of efforts such as the Trieste FERMI project, and a major new soft x-ray/VUV FEL user facility being studied for the University of Wisconsin. Further, we will summarize the impact of such a source in various areas of science [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:39PM |
P6.00004: Studies of Dynamics Using Coherent X-rays Invited Speaker: X-ray photon correlation spectroscopy (XPCS) has emerged over the last decade as a new technique for studies of fluctuation dynamics at small length scales. Such dynamics is ubiquitous in countless processes in condensed matter systems, such as viscoelastic flow of glasses, polymer diffusion, phase transitions, or domain switching. Like the dynamic light scattering techniques originally developed using visible wavelengths, XPCS is based on scattering a coherent beam from structural fluctuations in a material to produce a speckle pattern. The speckle pattern reflects the exact arrangement of the disorder, and thus evolves in time in concert with fluctuations. The time correlations of the speckle intensity provide a direct measure of fluctuation dynamics at the length scale corresponding to the scattering wavenumber. The extension of this technique to x-ray wavelengths provides access to atomic-scale dynamics. In practice, however, XPCS studies using 3rd-generation synchrotrons have been limited by the available coherent flux. Experiments to date have been most successful using small-angle scattering to study dynamics of $\sim $100 nm structures, which have sufficiently high scattering efficiency and relatively long time constants (e.g. milliseconds). Future accelerator-based x-ray sources such as free-electron lasers and energy recovery linacs will provide significantly increased coherent x-ray flux, which will greatly expand the applicability of XPCS to shorter length scales, faster time scales, and more weakly scattering systems. In particular, the ultrashort pulse structure of the new x-ray sources will allow observation of dynamics into the femtosecond range. I will discuss potential experiments as examples of the anticipated capabilities. Work supported by the U.S. Dept. of Energy contract DE-AC02-06CH11357. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 2:15PM |
P6.00005: Research at DESY's VUV-FEL user facility FLASH Invited Speaker: FLASH is currently the only operating free electron laser providing lateral coherent radiation in the wavelength range from 13 to 48 nm in the fundamental in flashes of 10 femtoseconds duration. One obtains 10$^{12}$ photons per flash, i.e. as many as we get today from the best storage ring facilities per second. The maximum peak pulse energy for 13 nm is 120 $\mu $J, the peak power is larger than 4 GW, the average power goes up to 30 mW. The peak brilliance reaches 5x10E29. The intensity of the third harmonic at 4.6 nm (270 eV) is on the 0.5{\%} level of the fundamental. Since August 2005 FLASH operates as a user facility and experiments have been performed successfully on atoms, highly charged ions and clusters. First photoelectron spectra have been taken, materials damage problems have been studied and first pump and probe experiments with an additional optical laser beam have been performed successfully. With respect to single particle imaging it was demonstrated that a fully interpretable diffraction pattern can be obtained by one flash of 25 femtoseconds duration before the sample heats up to about 60 000 K and evaporates. The experiments show the importance of the combination of extremely high peak brilliance with very high average brilliance for future experiments at X-ray free electron lasers. [Preview Abstract] |
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