This award supports a series of six (6) workshops on the Cornell University Campus in June 2011. The workshops will explore the scientific potential of a continuous-duty, coherent (fully diffraction-limited), hard (l<1.5 Ã…) synchrotron x-ray source. A continuous-duty source (or CW source) is one that delivers x-rays in a continuous train of pulses at rates exceeding a million per second. CW hard x-ray sources will enable a variety of new coherent and nanobeam experiments that cannot be done otherwise. Such sources include ultimate storage rings, energy recovery LINACs (ERLs), and high-repetition-rate x-ray free-electron lasers (X-FELs). Fully coherent hard x-ray sources will enable revolutionary new techniques for examining non-crystalline and time evolving systems on atomic length scales and in femtoseconds time scale. Recently, a large effort has gone into developing techniques utilizing coherent x-ray beams produced by pulsed X-FELs (e.g., FLASH and LCLS). These are more suitable to single shot measurements. This workshop focuses on measurements which require more photons than are available in a single shot or which need to probe the same sample repetitively. The community is just beginning to explore which types of measurements and science are best performed on low-duty-cycle pulsed X-FELs and which are best performed on CW sources. The Workshop will engage the community in developing ideas for the science case of fully coherent CW hard x-ray sources. Talks and organizers summaries of the discussions will be made broadly available through the World Wide Web. Funds from the National Science foundation support participation of students, postdocs, and young scientists from a broad range of discipline, including members of underrepresented groups in science and engineering, and minority serving institutions. The workshop is jointly funded by programs and divisions from two NSF directorates, Biosciences, and the Mathematical and Physical Sciences Directorate (Chemistry, Division of Materials Research, Physics and the Office of Multidisciplinary Activities).
In June of 2011, Cornell University, SSRL, DESY, and KEK held a series of workshops on the Cornell University campus exploring the scientific potential of a continuous-duty, coherent (fully diffraction-limited), hard (λ ≤ 1.5 Å) synchrotron x-ray source. A continuous-duty source (also known as a continuous wave or "CW" source) is one that delivers x-rays in a continuous train of pulses at rates exceeding a million per second. CW sources will be especially advantageous in a variety of coherent and nanobeam experiments including: cases where the sample must be repetitively probed; cases where the samples are unique and the requisite scattering information cannot be obtained with a single pulse; and, cases such as spectroscopy where incident beam stability is paramount. Potential future sources meeting these constraints include ultimate storage rings, energy recovery LINACs (ERLs), and seeded high-repetition-rate, x-ray free-electron lasers (X-FELs). The modest coherent x-ray flux currently available at the partially-coherent 3rd generation synchrotron sources has enabled the development of exciting new experimental techniques such as X-ray Photon Correlation Spectroscopy (XPCS) and Phase Contrast Imaging. However, full utilization of these and other novel techniques awaits the deployment of more advanced hard x-ray sources with orders of magnitude more coherent flux. Fully coherent hard x-ray sources will enable revolutionary new techniques for examining non-crystalline and time-evolving systems on atomic length scales. Recently, a large effort has gone into developing techniques utilizing the coherent x-ray beams produced by pulsed X-FELs (e.g., FLASH and LCLS). Clearly, "single shot" measurements (those that can be performed using a single X-FEL pulse) can take full advantage of both the very high peak spectral brightness and the very short pulses of X-FELs. However, these same features also create significant experimental challenges due to sample heating. In contrast, CW sources offer the same high average brightness but deliver it in much smaller pulses much more frequently. The temperature rise is, therefore, tractable. Measurements which can be done in a single shot are best done at an X-FEL while measurements which require more photons than are available in a single shot or which need to probe the same sample at two or more times are better matched to a CW source. Never the less, a large number of measurements could be performed on either type of source. The community is just beginning to explore which types of measurements and science are best performed on low-duty-cycle pulsed X-FELs and which are best performed on CW sources. The six workshops covered (1) Diffraction-based imaging techniques, (2) Biomolecular structure from non-crystalline materials, (3) Ultra-fast science, (4) High-pressure science, (5) Materials research with nano-beams, and (6) X-ray Photon Correlation Spectroscopy (XPCS). In each workshop, invited speakers from around the world presented examples of novel experiments that require a CW, diffraction-limited source. During the workshop, each invited speaker provided a one-page description of the experiment and an illustrative graphic. After the workshops ended, the organizers selected the best ideas and created a presentation appropriate for scientific audiences, which has subsequently been presented by the organizers at a variety of international conferences. Reports on the workshops have also been published in Synchrotron Radiation News. This NSF award funded the participant support costs of twenty-one (21) graduate students and post-docs, enabling them to participate in the development of the science case for a large multi-user facility. The experiments identified by the workshops demonstrate the broad and deep scientific case for a CW coherent synchrotron x-ray source. The next step (currently in progress around the world) is to perform detailed simulations of the best of these ideas to test them quantitatively and to guide detailed x-ray beam-line designs. These designs are the first step toward developing detailed facility designs and cost estimates.
