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  • richardmitnick 12:45 pm on August 3, 2018 Permalink | Reply
    Tags: , , , , , , Pratt & Whitney tests for jet engines, X-ray absorption spectroscopy, X-ray Technology   

    From Brookhaven National Lab: “High-Caliber Research Launches NSLS-II Beamline into Operations” 

    From Brookhaven National Lab

    August 2, 2018
    Stephanie Kossman
    skossman@bnl.gov

    Pratt & Whitney conduct the first experiments at a new National Synchrotron Light Source II beamline.

    1
    Bruce Ravel is the lead scientist at the Beamline for Materials Measurement (BMM), a new, state-of-the-art experimental station at NSLS-II. BMM was constructed and is operated by the National Institute of Standards and Technology (NIST).

    A new experimental station (beamline) has begun operations at the National Synchrotron Light Source II (NSLS-II)—a U.S. Department of Energy (DOE) Office of Science User Facility at DOE’s Brookhaven National Laboratory. Called the Beamline for Materials Measurement (BMM), it offers scientists state-of-the-art technology for using a classic synchrotron technique: x-ray absorption spectroscopy.

    “There are critical questions in all areas of science that can be solved using x-ray absorption spectroscopy, from energy sciences and catalysis to geochemistry and materials science,” said Bruce Ravel, a physicist at the National Institute of Standards and Technology (NIST), which constructed and operates BMM through a partnership with NSLS-II.

    X-ray absorption spectroscopy is a research technique that was developed in the 1980s and, since then, has been at the forefront of scientific discovery.

    “The reason we’ve used this technique for 40 years and the reason why NIST built the BMM beamline is because it adds a great value to the scientific community,” Ravel explained.

    The first group of researchers to conduct experiments at BMM came from jet engine manufacturer Pratt & Whitney. Senior Engineer Chris Pelliccione and colleagues used BMM to study the chemistry of jet engines.

    2
    Pratt & Whitney Senior Engineer Chris Pelliccione (left) with NIST’s Bruce Ravel (right) at BMM’s workstation.

    “We investigated the ceramic thermal barrier coatings used in jet engines,” Pelliccione said. “Due to the extreme temperature and pressure that these components operate in, the data from this investigation will help us design for durability. Our experiment at BMM was designed to understand some of the chemical interactions in more detail for today’s programs as well as tomorrow’s new breakthroughs.”

    Coupling BMM’s advanced design with NSLS-II’s ultra-bright x-ray light, the scientists at Pratt & Whitney were able to determine the spatial distribution of chemical interactions in the coating.

    3
    The Beamline for Materials Measurement (BMM) at the National Synchrotron Light Source II.

    “We needed a beamline with a small focused beam size and high flux to obtain the quality of data we were interested in,” Pelliccione said. “BMM offers both of these capabilities and our measurements were very successful. We were able to extract valuable information about the coatings that is not easily accessible through other research techniques.”

    Pratt & Whitney conducted its experiments at BMM during the final “commissioning” stage of the beamline, and the high-caliber research launched BMM into general operations.

    “We hope to take advantage of the fantastic beamlines that are already up and running at NSLS-II, as well as those that are coming online soon,” Pelliccione concluded.

    Ravel added, “It was incredibly gratifying to send Pratt & Whitney home with such valuable data. It is a very important part of NIST’s mission to work with companies and to promote U.S. innovation and industrial competitiveness.”

    More about NIST and NSLS-II

    NSLS-II is one of the world’s newest and most advanced synchrotron light sources. NSLS-II currently has 26 beamlines in operations and three in commissioning and construction phases. The facility has space for an additional 30 beamlines to be constructed. With the goal of “seeing” detailed views of chemical reactions, NSLS-II partnered with NIST to develop and operate three beamlines—SST-1, SST -2 and BMM—at NSLS-II.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 12:18 pm on August 3, 2018 Permalink | Reply
    Tags: , , Gears in a quantum clock, , , X-ray scattering, X-ray Technology   

    From Brookhaven Lab: “New Magnetic Materials Overcome Key Barrier to Spintronic Devices” 

    From Brookhaven National Lab

    August 1, 2018
    Justin Eure
    justin.eure@gmail.com

    Custom-engineered structure enables unprecedented control and efficiency in otherwise impervious antiferromagnetic materials.

    1
    Brookhaven scientists Derek Meyers (left) and Mark Dean (right) using their x-ray diffractometer to characterize the atomic structure of the samples for the experiment.

    Consider the classic, permanent magnet: it both clings to the refrigerator and drives data storage in most devices. But another kind of impervious magnetism hides deep within many materials—a phenomenon called antiferromagnetism (AFM)—and is nearly imperceptible beyond the atomic scale.

    Now, a team of scientists just developed an unprecedented material that cracks open this hermetic magnetism, confirming a decades-old theory and creating new engineering possibilities. The team, led by the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and the University of Tennessee, designed AFM materials with spin—the quantum mechanism behind all magnetism—that can be easily controlled with minimal energy.

    “Material synthesis finally caught up to theory, and we found a way around the most prohibitive quantum quirks of exploiting antiferromagnetism,” said Brookhaven Lab physicist and study corresponding author Mark Dean. “This work dives deeper into the underpinnings of magnetism and creates new possibilities for spin-based technologies.”

    The results, published this summer in Nature Physics, could dramatically enhance the emerging field of spintronics, where information is coded into the directional spin of electrons.

    “The real surprise was just how well this synthetic material functioned right out of the gate,” said coauthor and Brookhaven Lab scientist Derek Meyers. “Not only can we manipulate this remarkable spin, but we can do it with extreme efficiency.”

    Twisting electron spins

    The spin orientation of electrons within atoms and can be visualized as simple arrows pointing in well-defined directions.

    “In ferromagnets, these spins are all aligned,” said University of Tennessee professor and corresponding author Jian Liu. “They all point up or down, creating an external magnetic effect—like refrigerator magnets—that can be flipped when an external field is applied.”

    This flipping process powers the writing of digital information on most data storage devices, among other things.

    “Antiferromagnets are much stranger,” Meyers said. “Every arrow points in the opposite direction of its nearest neighbor, alternating up-down-up-down across the material. And it stays synchronized, such that one flip reverses all the others. That means, essentially, they all cancel each other out.”

    This perfect balance makes AFM spin notoriously impervious to manipulation, requiring too much energy to make the process useful. So the scientists introduced a little imperfection.

    “If we tilt, or cant, the spins, we create asymmetry and make the material more susceptible to influence,” Dean said. “External magnets can couple with the spin. But prior to this work, there was a built-in compromise to this approach.”

    While the canted spin can “feel” magnetic fields, the directional freedom is lost—the spins can no longer change direction.

    Gears in a quantum clock

    Imagine adjacent electrons as gears in a clock: the teeth all fit together to move in tandem and preserve precise relationships. Tilting the spin realigns those gears, almost as if they abruptly began to rotate in opposite directions and locked in place. How, then, to set those gears back in motion?

    “We followed a long-standing theory to create an unprecedented material that both cants the spin and keeps it free to rotate, which we would call preserving isotropy,” said first author Lin Hao of the University of Tennessee. “To do this, we designed a structure that cancels out those competing anisotropies, or directional asymmetries.”

    In a way, they built another gear into their antiferromagnetic clock. The extra gear slots in between the jammed electron spins, giving them a balance and space that would never naturally occur. The “gear” is actually a hidden symmetry called SU(2), a mathematical term describing the isotropic freedom.

    Layered crystalline lattice

    “The extreme sophistication of two-dimensional materials synthesis made this possible,” Liu said. “We grew a crystalline lattice with fully customized geometries to prevent the spins from locking—this is engineering with almost quantum precision.”

    The team used pulsed laser deposition to create a lattice composed of strontium, iridium, titanium, and oxygen. In this way, atomically thin layers could be stacked in different configurations to induce artificial and much desired properties.

    In this work, the team exploited special “gearing” properties of the iridium oxide layers in which the spins can be tilted, but remain free to respond to an applied magnetic field.

    The collaboration turned to the Advanced Photon Source (APS)—a DOE Office of Science User Facility at DOE’s Argonne National Laboratory—to confirm the crystal structure of the material. Using advanced resonant x-ray diffraction, the scientists revealed details of both the lattice and the electron configuration.


    ANL/APS

    “Because of the precision possible at the APS, we were able to see the fruits of the difficult synthesis process,” Meyers said. “We saw the precise layered structure we wanted, but the real test was in the magnetic function.”

    Again turning to APS, the team used x-ray scattering to measure the antiferromagnetic order, the alignment of the spins within the material.

    “We were pleased to see our canted spins retain the freedom of motion we expected,” Dean said. “It’s rare and thrilling to see things come together so seamlessly. And crucially, we proved that manipulating that AFM spin required very little energy—a must for spintronic applications.”

    Toward superior storage

    Traditional magnetic devices have an intrinsic limit: packed too closely together, ferromagnetic materials affect each other. This translates into a functional cap on data density beyond which the spins become corrupted. However, AFM materials—or discrete AFM crystals in this instance—exert no external influence.

    “We can, in theory, pack much more information into devices by manipulating antiferromagnetic spin,” Dean said. “That’s part of the promise of spintronics.”

    The combination of low energy input—think efficient writing of data—and density make the new material an ideal candidate for investment.

    “The obstacle right now has to do with scale,” Liu said. “This is a first-of-its-kind material, so no industrial-scale process exists. But this is how it starts, and the demand for this kind of functionality might rapidly move this innovation into applications.”

    Additional collaborating institutions include Charles University in Prague.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 11:23 am on August 2, 2018 Permalink | Reply
    Tags: , , , , X-ray Technology   

    From European XFEL: “Third light source generates first X-ray light” 

    XFEL bloc

    European XFEL

    From European XFEL

    1
    All three light sources, SASE 1,2 and 3, are now operational and have been successfully run in parallel for the first time. Copyright: DESY/European XFEL.

    European XFEL starts operation of its third light source, exactly a year after the first X-ray light was generated in the European XFEL tunnels.

    DESY European XFEL

    The third light source will provide light for the MID (Materials Imaging and Dynamics) and HED (High Energy Density Science) instruments scheduled to start user operation in 2019.

    The MID instrument at European XFEL, currently under construction

    All three light sources, successfully run in parallel for the first time on the anniversary of European XFEL’s first light, will eventually provide X-rays for at least six instruments. At any one time, three of these six instruments can simultaneously receive X-ray beam for experiments. “The operation of the third light source, and the generation of light from all sources in parallel, are important steps towards our goal of achieving user operation on all six instruments” said European XFEL Managing Director Robert Feidenhans’l. “I congratulate and thank all those involved in this significant accomplishment. It was a tremendous achievement to get all three light sources to generate light within the space of one year.”

    XFEL Undulator

    To generate flashes of X-ray light, electrons are first accelerated to near the speed of light before they are moved through long rows of magnets called undulators. The alternating magnetic fields of these magnets force the electrons on a slalom course, causing the electrons to emit light at each turn. Over the length of the undulator, the produced light interacts back on the electron bunch, thereby producing a particularly intense light. This light accumulates into intensive X-ray flashes. This process is known as ‘self-amplified spontaneous emission’, or SASE. European XFEL has three SASE light sources. The first one, SASE 1, taken into operation at the beginning of May 2017, provides intense X-ray light to the instruments SPB/SFX (Single Particles, Clusters and Biomolecules and Serial Femtosecond Crystallography) and FXE (Femtosecond X-ray Experiments), the first instruments available for experiments and operational since September 2017. The second light source, SASE 3, was successfully taken into operation in February 2018 and will provide light for the instruments SQS (Small Quantum Systems) and SCS (Spectroscopy and Coherent Scattering), scheduled to start user operation in November 2018. SASE 1 and SASE 3 can be run simultaneously – high speed electrons first generate X-ray light in SASE 1, before being used a second time to produce X-ray light of a longer wavelength in SASE 3. Now, exactly a year after the first laser light was generated in the European XFEL tunnels, the third light source, SASE 2, is operational. SASE 2 will generate X-ray light for the MID (Materials Imaging and Dynamics) and HED (High Energy Density Science) instruments scheduled to start user operation in 2019. The MID instrument will be used to, for example, understand how glass forms on an atomic level, and for the study of cells and viruses with a range of imaging techniques. The HED instrument will enable the investigation of matter under extreme conditions such as that inside exoplanets, and to investigate how solids react in high magnetic fields.

    DESY and European XFEL staff and scientists have worked hard over the last year to ensure the timely start of operation of all three light sources, and have also continually improved the parameters of the X-ray beam and instruments. Since the first users arrived in September 2017, the number of X-ray pulses available for experiments has been increased from 300 to 3000 per second for the next experiments, scheduled from August to October 2018. At full capacity, the European XFEL is expected to produce 27,000 pulses per second and DESY and European XFEL teams are working towards achieving this rate in test conditions during the next few months. In addition, the construction and commissioning of the remaining four instruments continues this year. Once MID and HED start operation in 2019, European XFEL will have a total of six experiment stations available for users, running from the three light sources.

    4
    Graphic showing the layout of the European XFEL tunnels, three SASE undulators and the instruments. Copyright: European XFEL

    Since the start of user operation in September 2017, European XFEL has hosted over 500 researchers in international and interdisciplinary teams for experiments on the first two instruments. SPB/SFX and FXE share the X-ray beam generated in SASE1, each using the beam for alternate 12 hours per day during an experiment. Each user group generally has five days of beamtime. For the next round of experiments due to start in August, 61 proposals were received from which twelve experiments, six per instrument (SPB/SFX and FXE), will be granted.

    A next call for user proposals for experiment time, now at all six instruments, will open shortly.

    See the full article here .

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    XFEL Campus

    XFEL Tunnel

    XFEL Gun

    The Hamburg area will soon boast a research facility of superlatives: The European XFEL will generate ultrashort X-ray flashes—27 000 times per second and with a brilliance that is a billion times higher than that of the best conventional X-ray radiation sources.

    The outstanding characteristics of the facility are unique worldwide. Started in 2017, it will open up completely new research opportunities for scientists and industrial users.

     
  • richardmitnick 11:35 am on July 3, 2018 Permalink | Reply
    Tags: , , , , X-ray Technology   

    From SLAC Lab: “X-Ray Experiment Confirms Theoretical Model for Making New Materials” 


    From SLAC Lab

    July 2, 2018
    Glennda Chui

    1
    In an experiment at SLAC, scientists loaded ingredients for making a material into a thin glass tube and used X-rays (top left) to observe the phases it went through as it was forming (shown in bubbles). The experiment verified theoretical predictions made by scientists at Berkeley Lab with the help of supercomputers (right). (Greg Stewart/SLAC National Accelerator Laboratory)

    By observing changes in materials as they’re being synthesized, scientists hope to learn how they form and come up with recipes for making the materials they need for next-gen energy technologies.

    Over the last decade, scientists have used supercomputers and advanced simulation software to predict hundreds of new materials with exciting properties for next-generation energy technologies.

    Now they need to figure out how to make them.

    To predict the best recipe for making a material, they first need a better understanding of how it forms, including all the intermediate phases it goes through along the way – some of which may be useful in their own right.

    Now experiments at the Department of Energy’s SLAC National Accelerator Laboratory have confirmed the predictive power of a new computational approach to materials synthesis. Researchers say that this approach, developed at the DOE’s Lawrence Berkeley National Laboratory, could streamline the creation of novel materials for solar cells, batteries and other sustainable technologies.

    “In the last 10 years, computational scientists have gotten really good at predicting the properties of new materials, but not so good at telling experimentalists like me how to make them,” said Michael Toney, a distinguished staff scientist at SLAC. “The theoretical framework developed at Berkeley Lab can help guide us in thinking about ways to synthesize and test these promising materials.”

    This team described their findings June 29 in Nature Communications.

    Metastable Materials

    “Most theoretical approaches are great for predicting the endpoints of a reaction – what chemicals you start with, and what material you get at the end,” said study co-author Laura Schelhas, an associate staff scientist with SLAC’s Applied Energy Program. “But other interesting materials that form along the reaction pathway are often overlooked.”

    These intermediate materials are said to exist in a state of metastability.

    “Materials always want to be in their lowest-energy phase or ground state,” Schelhas explained. “Materials in a metastable state are higher in energy and will eventually transition to the more stable ground state. A diamond, for example, is a metastable state of carbon that will revert to its ground state, graphite, over millions of years.”

    During synthesis, materials can crystallize into a series of metastable phases – some lasting only a few minutes, others persisting for hours. Some of these phases have properties that are potentially useful for technological applications. Others may block the formation of a material you want to make. Scientists want to isolate the useful phases and avoid creating the undesirable ones.

    Co-authors Wenhao Sun and Gerbrand Ceder at Berkeley Lab and Daniil Kitchaev of the Massachusetts Institute of Technology recently developed a theoretical model to predict which metastable phases a material will form during synthesis.

    “The key insight is to consider influences other than temperature and pressure that can affect a material’s formation,” Sun said. “For example, at a very small scale, surface energy is important, and impurities that materials take up from the surrounding environment can stabilize some types of crystalline structures. We developed a theory to quantify how these factors govern the formation of metastable phases, and then worked with SLAC to design an experiment to test it.”

    The experiment, conducted at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), focused on manganese oxide, a compound whose formation can involve a variety of metastable crystalline structures. Some of these metastable structures are useful for battery applications or catalysis.

    SLAC/SSRL

    2
    Schematic representation of remnant metastability in a crystallization pathway. a Free-energy of three phases (supersaturated solution (gray), M (green), S (blue)) as a function of the surface-area-to-volume ratio, 1/R (R is a particle radius). The gray line corresponds to the free-energy of a supersaturated solution, green is a metastable phase M that is size-stabilized by a low surface energy (given by the slope), and blue is the bulk equilibrium phase S, with high surface energy. b Phase diagram in the 1/R axis created from the projection of lowest free-energy phases. c A multistage crystallization pathway (red arrow in a ) proceeds downhill in energy, but phase transformations are limited by nucleation. Crystal growth of M prior to the induction of S means M can grow into a size-regime where phase M is metastable. S will then nucleate, and quickly grow by consuming M via dissolution-reprecipitation. The characteristic length scale of size-driven phase transitions lies in the 2 nm–50 nm range. Nature Communications

    “Although manganese oxide has been widely studied, we still don’t have a good understanding of how to make specific metastable phases of the material,” Toney said. “Figuring out why certain recipes favor certain metastable structures will help us predict recipes for synthesizing not just this material, but others as well.”

    Theory vs. Experiment

    Sun and Schelhas designed an experiment to carefully manipulate a single ingredient in a recipe for making manganese oxide and track its effect on the formation of metastable crystals.

    SLAC scientists led by postdoctoral researcher Bor-Rong Chen used powerful X-ray beams at SSRL to observe the chemical reaction as it happened.

    “It’s pretty simple,” Schelhas said. “We load up manganese salts and other reaction materials into a small glass capillary, seal it and heat it. Then we shoot X-rays through the capillary while the reaction is occurring and watch the signal that reflects off the crystals. That signal allows us to determine the atomic structure of each metastable phase as it forms.”

    At first, the metastable phases identified by X-ray diffraction didn’t seem to match the theoretical predictions, Chen said.

    “We worked with the theorists at Berkeley Lab to retool the model,” she said, “and arrived at some explanations for why certain metastable phases might be skipped in a reaction, or why they might persist longer than we anticipated.”

    To continue developing their understanding of synthesis, the researchers plan to conduct experiments on more complicated materials.

    “This work marks only the initial steps in a much longer journey towards a predictive theory of materials synthesis,” Sun said. “Our goal is to build a powerful toolkit to design recipes for making exactly the materials we want.”

    The team also found that they could stop the reaction at the point where a metastable material has formed, which will make it possible to test those materials for desirable properties in future studies, Schelhas said.

    “We’re starting to push science into a new space in terms of understanding how you go about synthesis,” she added. “Predictive models have the potential to profoundly alter the way that materials design is done. That could greatly speed up the adoption of more advanced materials in areas like photovoltaics, batteries, thermoelectrics and a whole host of other sustainable technologies.”

    Other co-authors of the study are from the Colorado School of Mines and the DOE’s National Renewable Energy Laboratory.

    SSRL is a DOE Office of Science user facility. Funding for this work came from the Center for Next Generation of Materials Design, an Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory and funded by the DOE Office of Science.

    See the full article here .


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    Please help promote STEM in your local schools.

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

     
  • richardmitnick 11:30 am on June 11, 2018 Permalink | Reply
    Tags: , , , , , X-ray Technology   

    From SLAC Lab: “Work Begins on New SLAC Facility for Revolutionary Accelerator Science” 


    From SLAC Lab

    June 11, 2018
    Manuel Gnida

    The goal: develop plasma technologies that could shrink future accelerators up to 1,000 times, potentially paving the way for next-generation particle colliders and powerful light sources.

    The Department of Energy’s SLAC National Accelerator Laboratory has started to assemble a new facility for revolutionary accelerator technologies that could make future accelerators 100 to 1,000 times smaller and boost their capabilities.

    The project is an upgrade to the Facility for Advanced Accelerator Experimental Tests (FACET), a DOE Office of Science user facility that operated from 2011 to 2016.


    SLAC FACET

    FACET-II will produce beams of highly energetic electrons like its predecessor, but with even better quality.

    These beams will primarily be used to develop plasma acceleration techniques, which could lead to next-generation particle colliders that enhance our understanding of nature’s fundamental particles and forces and novel X-ray lasers that provide us with unparalleled views of ultrafast processes in the atomic world around us.

    FACET-II will be a unique facility that will help keep the U.S. at the forefront of accelerator science, said SLAC’s Vitaly Yakimenko, project director. “Its high-quality beams will enable us to develop novel acceleration methods,” he said. “In particular, those studies will bring us close to turning plasma acceleration into actual scientific applications.”

    2
    SLAC is upgrading its Facility for Advanced Accelerator Experimental Tests (FACET) – a test bed for new technologies that could revolutionize the way we build particle accelerators. FACET-II will use the middle third of the lab’s 2-mile-long linear accelerator (SLAC ground plan at top). It will send a beam of electrons (bottom, blue line) from the electron source (bottom left) to the experimental area (bottom right), where it will arrive with an energy of 10 billion electronvolts. The design allows for adding the capability to produce and accelerate positrons (bottom, red line) later. (Greg Stewart/SLAC National Accelerator Laboratory)

    The DOE has now approved the $26 million project (Critical Decisions 2 and 3). The new facility, which is expected to be completed by the end of 2019, will also operate as an Office of Science user facility – a federally sponsored research facility for advanced accelerator research available on a competitive, peer-reviewed basis to scientists from around the world.

    “As a strategically important national user facility, FACET-II will allow us to explore the feasibility and applications of plasma-driven accelerator technology,” said James Siegrist, associate director of the High Energy Physics (HEP) program of DOE’s Office of Science, which stewards advanced accelerator R&D in the U.S. for the development of applications in science and society. “We’re looking forward to seeing the groundbreaking science in this area that FACET-II promises, with the potential for significant reduction of the size and cost of future accelerators, including free-electron lasers and medical accelerators.”

    Bruce Dunham, head of SLAC’s Accelerator Directorate, said, “Our lab was built on accelerator technology and continues to push innovations in the field. We’re excited to see FACET-II move forward.”

    Surfing the Plasma Wake

    The new facility will build on the successes of FACET, where scientists already demonstrated that the plasma technique can very efficiently boost the energy of electrons and their antimatter particles, positrons. In this method, researchers send a bunch of very energetic particles through a hot ionized gas, or plasma, creating a plasma wake for a trailing bunch to “surf” on and gain energy.

    3
    Researchers will use FACET-II to develop the plasma wakefield acceleration method, in which researchers send a bunch of very energetic particles through a hot ionized gas, or plasma, creating a plasma wake for a trailing bunch to “surf” on and gain energy. (Greg Stewart/SLAC National Accelerator Laboratory)

    In conventional accelerators, particles draw energy from a radiofrequency field inside metal structures. However, these structures can only support a limited energy gain per distance before breaking down. Therefore, accelerators that generate very high energies become very long, and very expensive. The plasma wakefield approach promises to break new ground. Future plasma accelerators could, for example, unfold the same acceleration power as SLAC’s historic 2-mile-long copper accelerator (linac) in just a few meters.

    3
    Aerial view of SLAC’s 2-mile-long linac. The longest linear accelerator ever built, it produced its first particle beams in 1966 and has been the lab’s backbone for accelerator-driven science ever since. (SLAC National Accelerator Laboratory)

    Researchers will use FACET-II for crucial developments before plasma accelerators can become a reality. “We need to show that we’re able to preserve the quality of the beam as it passes through plasma,” said SLAC’s Mark Hogan, FACET-II project scientist. “High-quality beams are an absolute requirement for future applications in particle and X-ray laser physics.”

    The FACET-II facility is currently funded to operate with electrons, but its design allows adding the capability to produce and accelerate positrons later – a step that would enable the development of plasma-based electron-positron particle colliders for particle physics experiments.

    4
    Future particle colliders will require highly efficient acceleration methods for both electrons and positrons. Plasma wakefield acceleration of both particle types, as shown in this simulation, could lead to smaller and more powerful colliders than today’s machines. (F. Tsung/W. An/UCLA; Greg Stewart/SLAC National Accelerator Laboratory)

    Another important objective is the development of novel electron sources that could lead to next-generation light sources, such as brighter-than-ever X-ray lasers. These powerful discovery machines provide scientists with unprecedented views of the ever-changing atomic world and open up new avenues for research in chemistry, biology and materials science.

    Other science goals for FACET-II include compact wakefield accelerators that use certain electrical insulators (dielectrics) instead of plasma, as well as diagnostics and computational tools that will accurately measure and simulate the physics of the new facility’s powerful electron beams. Science goals are being developed with regular input from the FACET user community.

    “The approval for FACET-II is an exciting milestone for the science community,” said Chandrashekhar Joshi, a researcher from the University of California, Los Angeles, and longtime collaborator of SLAC’s plasma acceleration team. “The facility will push the boundaries of accelerator science, discover new and unexpected physics and substantially contribute to the nation’s coordinated effort in advanced accelerator R&D.”

    Fast Track to First Experiments

    To complete the facility, crews will install an electron source and magnets to compress electron bunches, as well as new shielding, said SLAC’s Carsten Hast, FACET-II technical director. “We’ll also upgrade the facility’s control systems and install tools to analyze the beam properties.”

    FACET-II will use one kilometer (one-third) of the SLAC linac – sending electrons from the source at one end to the experimental area at the other end – to generate an electron beam with an energy of 10 billion electronvolts that will drive the facility’s versatile research program.

    FACET-II has issued its first call for proposals for experiments that will run when the facility goes online in 2020.

    “The project team has done an outstanding job in securing DOE approval for the facility,” said DOE’s Hannibal Joma, federal project director for FACET-II. “We’ll now deliver the project on time for the user program at SLAC.”

    SLAC’s Selina Green, project manager, said, “After two years of very hard work, it’s very exciting to see the project finally come together. Thanks to the DOE’s continued support we’ll soon be able to open FACET-II for groundbreaking new science.”

    5
    Members of SLAC’s FACET-II project team. From left: Nate Lipkowitz, Kevin Turner, Carsten Hast, Lorenza Ladao, Gary Bouchard, Vitaly Yakimenko, Martin Johansson, Selina Green, Glen White, Eric Bong, Jerry Yocky. Not pictured: Lauren Alsberg, Jeff Chan, Karl Flick, Mark Hogan, John Seabury. (Dawn Harmer/SLAC National Accelerator Laboratory)

    For more information, please visit the website:

    FACET-II Website

    Press Office Contact:
    Andy Freeberg
    afreeberg@slac.stanford.edu
    (650) 926-4359

    See the full article here .


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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

     
  • richardmitnick 10:57 am on May 23, 2018 Permalink | Reply
    Tags: Paving the way toward advanced computers lasers or optical devices, Quantum dots don’t always behave as expected, Quantum dots need to be close to perfect, Right now there are multiple sources of decoherence quantum dots, Strain game: Leveraging imperfections to create better-behaved quantum dots, , X-ray Technology   

    From University of Wisconsin Madison: “Strain game: Leveraging imperfections to create better-behaved quantum dots” 

    U Wisconsin

    From University of Wisconsin Madison

    May 17, 2018
    Sam Million-Weaver
    perspective@engr.wisc.edu

    1
    Postdoctoral scholar Anastasios Pateras adjust an X-Ray instrument used to detect previously unknown defects in quantum dots. Photo credit: Sam Million-Weaver.

    Potentially paving the way toward advanced computers, lasers or optical devices, University of Wisconsin-Madison researchers have revealed new effects in tiny electronic devices called quantum dots.

    In their work, published recently in the journal Nano Letters, the researchers developed and applied analysis methods that will help answer other challenging questions for developing electronic materials.

    “We can now look at a set of structures that people couldn’t look at before,” says Paul Evans, professor of materials science and engineering at UW-Madison. “In these structures, there are new sets of crucial materials problems that we previously weren’t able to think about solving.”

    The structures Evans and colleagues looked at are thousands of times narrower than single sheets of paper, and smaller than the dimensions of individual human cells. In those structures, quantum dots form inside very thin stacks of crystalline materials topped by an asymmetrical arrangement of flat, spindly, fingerlike metallic electrodes. Between the tips of those metallic fingers are small spaces that contain quantum dots.

    Creating such precise structures and peering inside those tiny spaces is technically challenging, however, and quantum dots don’t always behave as expected.

    Previous work by Evans’ collaborators at the Delft University of Technology in the Netherlands, who created and extensively studied the crystal stack structures, led to suspicions that the quantum dots were different in important ways from what had been designed.

    Until now, measuring those differences wasn’t possible.

    “Previous imaging approaches and the modeling weren’t allowing people to structurally characterize quantum dot devices at this tiny scale,” says Anastasios Pateras, a postdoctoral scholar in Evans’ group and the paper’s first author.

    Pateras and colleagues pioneered a strategy for using beams of very tightly focused X-rays to characterize the quantum dot devices—and that hinged on a new method for interpreting how the X-rays scattered. Using their approach, they observed shifts in the spacing and orientation of atomic layers within the quantum dots.

    “Quantum dots need to be close to perfect,” says Evans. “This small deviation from perfection is important.”

    The team’s discovery indicates that the process of creating the quantum dots—laying down metallic electrodes atop a lab-grown crystal—distorts the material underneath slightly. This puckering creates strain in the material, leading to small distortions in the quantum dots. Understanding and exploiting this effect could help researchers create better-behaved quantum dots.

    “Once you know these quantities, then you can design devices that take into account that structure,” says Evans.

    Designs with those small imperfections in mind will be especially important for future devices where many thousands of quantum dots must all work together.

    “This is going to be very relevant because, right now, there are multiple sources of decoherence quantum dots,” says Pateras.

    The researchers now are developing an algorithm to automatically visualize atomic positions in crystals from X-ray scattering patterns, given that performing the necessary calculations by hand would likely be too time-consuming. Additionally, they are exploring how the techniques could add insight to other hard-to study structures.

    The work was supported by the United States Department of Energy Basic Energy Sciences, Materials Sciences and Engineering (contract no. DE-FG02-04ER46147), the National Science Foundation Graduate Research Fellowship Program (grant no. DGE-1256259), and the Netherlands Organization of Scientific Research (NOW). Use of the Center for Nanoscale Materials and the Advanced Photon Source, both Office of Science user facilities, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (contract no. DE-AC02-06CH11357). Laboratory characterization at UW–Madison used instrumentation supported by the NSF through the UW–Madison Materials Research Science and Engineering Center (DMR-1121288 and DMR-1720415).

    See the full article here .


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    In achievement and prestige, the University of Wisconsin–Madison has long been recognized as one of America’s great universities. A public, land-grant institution, UW–Madison offers a complete spectrum of liberal arts studies, professional programs and student activities. Spanning 936 acres along the southern shore of Lake Mendota, the campus is located in the city of Madison.

     
  • richardmitnick 1:56 pm on May 16, 2018 Permalink | Reply
    Tags: , , , Water is more complicated than it seems, X-ray Laser Reveals Ultrafast Dance of Liquid Water, X-ray Technology   

    From SLAC Lab: “X-ray Laser Reveals Ultrafast Dance of Liquid Water” 


    From SLAC Lab

    May 16, 2018
    Water is more complicated than it seems. Now a study led by researchers at Stockholm University has probed the movements of its molecules on a timescale of millionths of a billionth of a second.

    1
    An illustration shows the “blurring” effect caused by water molecules moving during imaging with the X-ray laser. As the laser pulse gets longer, from left to right, the diffraction pattern produced by X-rays hitting the molecules changes (bottom row), reflecting the motion of the water molecules (top row). Experiments at SLAC’s LCLS X-ray laser were able to provide the timescale of the water dynamics by using pulses less than 100 millionths of a billionths of a second long. (Fivos Perakis/Stockholm University)

    Water’s lack of color, taste and smell make it seem simple – and on a molecular level, it is. However, when many water molecules come together they form a highly complex network of hydrogen bonds. This network is believed to be responsible for many of the peculiar properties of liquid water, but its behavior is not yet fully understood.

    Now researchers have probed the movements of molecules in liquid water that occur in less than 100 millionths of a billionth of a second, or femtoseconds. An international team led by researchers at Stockholm University carried out the experiments with the Linac Coherent Light Source (LCLS) X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory. They published their report this week in Nature Communications.

    SLAC/LCLS

    The study is the first to “photograph” water molecules on this timescale with a technique called ultrafast X-ray photon correlation spectroscopy, which bounces X-rays pulses off the molecules to produce a series of diffraction patterns. Varying the duration of the X-ray pulses essentially varies the exposure time, and any motion of the water molecules during an exposure will blur the resulting picture. By analyzing the blurring produced by different exposure times, the scientists were able to extract information about the molecular motion.

    On this timescale, it was assumed that water molecules move randomly due to heat, behaving more like a gas than a liquid. However, the experiments indicate that the network of hydrogen bonds plays a role even on this ultrafast timescale, coordinating the motions of water molecules in an intricate dance, which becomes even more pronounced when water is “supercooled” below its normal freezing point.

    “The key to understanding water on a molecular level is watching the changes of the hydrogen-bond network, which can play a major role in biological activity and life as we know it,” says Anders Nilsson, a professor at Stockholm University and former professor at SLAC.

    Adds Stockholm University researcher Fivos Perakis, “It is a brand-new capability to be able to use X-ray lasers to see the motion of molecules in real time. This can open up a whole new field of investigations on these timescales, combined with the unique structural sensitivity of X-rays.”

    The experimental results were reproduced by computer simulations, which indicate that the coordinated dance of water molecules is due to the formation of transient tetrahedral structures.

    “I have studied the dynamics of liquid and supercooled water for a long time using computer simulations, and it is very exciting to finally be able to directly compare with experiments,” says Gaia Camisasca, a postdoctoral researcher at Stockholm University who performed the computer simulations for this study. “I look forward to seeing the future results that can come out from this technique, which can help improve the current water computer models.”

    LCLS is a DOE Office of Science user facility. SLAC’s Thomas J. Lane, Sanghoon Song, Takahiro Sato, Marcin Sikorski, Andre Eilert, Trevor McQueen, Hirohito Ogasawara, Dennis Nordlund, Jake Koralek, Silke Nelson, Philip Hart, Roberto Alonso-Mori, Yiping Feng, Diling Zhu and Aymeric Robert contributed to this study, along with researchers from KTH Royal Institute of Technology in Stockholm and DESY in Hamburg.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

     
  • richardmitnick 12:42 am on May 13, 2018 Permalink | Reply
    Tags: , , , , X-ray Technology, X-rays from tabletop lasers allows scientists to peer through the ‘water window’   

    From Imperial College London: “X-rays from tabletop lasers allows scientists to peer through the ‘water window’” 

    Imperial College London
    From Imperial College London

    11 May 2018
    Hayley Dunning

    1

    Studying the fleeting actions of electrons in organic materials will now be much easier, thanks to a new method for generating fast X-rays.

    The technique means advanced measurements of fast reactions will now be possible in physics labs around the world, without having to wait to use expensive and scarce equipment. It could be used, for example, to study and improve light-harvesting technologies like solar panels and water splitters.

    When ‘soft’ X-rays, beyond the range of ultraviolet light, strike an object, they are strongly absorbed by some kinds of atoms and not others. In particular, water is transparent to these X-rays, but carbon absorbs them, making them useful for imaging organic and biological materials.

    However, a challenge has been to generate very fast soft X-rays. Creating pulses of X-rays that only last one thousandth of a millionth of a millionth of a second would allow researchers to image the extremely quick motions of electrons, crucial for determining how charge travels and reactions occur.

    Smallest and fastest reaction steps

    Fast soft X-rays have been created with large facilities, such as multi-billion dollar costing free-electron lasers, but now a research team from Imperial College London have generated fast and powerful fast soft X-ray pulses using standard laboratory lasers.

    The method, which can produce bright soft X-ray pulses that last hundreds of attoseconds (quintillionths of a second), is published today in Science Advances.

    With the new technique, researchers will be able to watch the movement of electrons on their natural timescale, giving them a dynamic picture of the smallest and fastest reaction steps.

    Senior author Professor Jon Marangos, from the Department of Physics at Imperial, said: “The strength of this technique is that it can be used by many physics labs around the world with lasers they already have installed.

    “This discovery will allow us to make measurements at extreme timescales for the first time. We are at the frontiers of what we can measure, seeing faster-than-ever processes important for science and technology.”

    Generating X-rays

    Generating X-rays in a lab requires exciting atoms until they release photons – particles of light. Normally, atoms in a long, dispersed cloud are excited in sequence so that they emit photons in ‘phase’, meaning they add up and create a stronger X-ray pulse. This is known as phase matching.

    But when trying to generate soft X-rays this way, effects in the cloud of atoms strongly defocus the laser, disrupting phase matching.

    Instead, the team discovered that they needed a thin, dense cloud of atoms and short laser pulses. With this setup, while the photons could not stay in phase over a long distance, they were still in phase over a shorter distance and for a short time. This led to unexpectedly efficient production of the short soft X-ray pulses.

    The team further measured and simulated the exact effects that cause high harmonic generation in this situation, and from this were able to predict the optimum laser conditions for creating a range of X-rays.

    Lead researcher Dr Allan Johnson, from the Department of Physics at Imperial, said: “We’ve managed to look inside what was before the relatively black-box of soft X-ray generation, and use that information to build an X-ray laser on a table that can compete with football-field spanning facilities. Knowledge is quite literally power in this game.”

    Improving solar technologies

    The team at Imperial plan to use the technique to study organic polymer materials, in particular those that harvest the Sun’s rays to produce energy or to split water. These materials are under intense study as they can provide cheaper renewable energy.

    However, many currently used materials are unstable or inefficient, due to the action of electrons that are excited by light. Closer study of the fast interactions of these electrons could provide valuable insights into methods for improving solar cells and catalysts.

    • ‘High-Flux Soft X-ray Harmonic Generation from Ionization-Shaped Few-Cycle Laser Pulses’ by Allan S. Johnson, Dane R. Austin, David A. Wood, Christian Brahms, Andrew Gregory, Konstantin B. Holzner, Sebastian Jarosch, Esben W. Larsen, Susan Parker, Christian S. Strüber, Peng Ye, John W. G. Tisch, and Jon P. Marangos is published in Science Advances.

    See the full article here .

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    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

     
  • richardmitnick 3:42 pm on May 5, 2018 Permalink | Reply
    Tags: , , , , , Freeze-framing nanosecond movements of nanoparticles, , , X-ray Technology   

    From DESY: “Freeze-framing nanosecond movements of nanoparticles” 

    DESY
    From DESY

    2018/05/03
    No writer credit

    New method allows to monitor fast movements at hard X-ray lasers.

    A team of scientists from DESY, the Advanced Photon Source APS and National Accelerator Laboratory SLAC, both in the USA, have developed and integrated a new method for monitoring ultrafast movements of nanoscopic systems.

    Argonne APS

    SLAC LCLS

    With the light of the X-ray laser LCLS at the research center SLAC in California, they took images of the movements of nanoparticles taking only the billionth of a second (0,000 000 001 s).

    SLAC LCLS

    In their experiments now published in the journal Nature Communications they overcame the slowness of present-day two-dimensional X-ray detectors by splitting individual laser flashes of LCLS, delaying one half of it by a nanosecond and recording a single picture of the nanoparticle with these pairs of X-ray pulses. The tunable light splitter for hard X-rays which the scientists developed for these experiments enables this new technique to monitor movements of nanometer size fluctuations down to femtoseconds and at atomic resolution. For comparison: modern synchrotron radiation light sources like PETRA III at DESY can typically measure movements on millisecond timescales.

    DESY Petra III interior

    1
    Scheme of the experiment: An autocorrelator developed at DESY splits the ultrashort X-ray laser pulses into two equal intensity pulses which arrive with a tunable delay at the sample. The speckle pattern of the sample is collected in a single exposure of the 2-D detector (picture: W. Roseker/DESY).

    he intense light flashes of X-ray lasers are coherent which means that the waves of the monochromatic laser light propagate in phase to each other. Diffracting coherent light by a sample usually results in a so-called speckle diffraction pattern showing apparently randomly ordered light spots. However, this speckle is also a map of the sample arrangement, and movements of the sample constituents result in a different speckle pattern.

    For their experiments the researchers developed a special optical setup – a so-called optical autocorrelator – capable of splitting 100 femtosecond long XFEL pulses into two sub-pulses, deviate them into separated detours and recombining their paths with a tunable time delay between zero and a few nanoseconds. These pairs of XFEL pulses hit the sample with the tuned delay, spotting the sample´s structure at the two exposure times. The sum of both speckle pictures was recorded by a two-dimensional photon detector within one exposure time. The trick: If the constituents of the sample move during the two illuminations, the speckle pattern changes, resulting in an integrated picture of less contrast at the detector. The contrast is a measure on how strong the photon intensity varies on the detector. However, the intensity and especially the intensity difference measured at the detector are very weak. In their experiments the researchers had to work with only some 1000 detected photons on the one-million-pixels size detector.

    “Such type of experiments has been done for much slower movements of nanoparticles at storage ring light sources,” explains first author Wojciech Roseker from DESY. “But now, the high coherence and intensity of the X-ray laser light at XFELs open up the opportunity to get pictures bright enough to provide reasonable information about quick movements in the nanosecond to femtosecond regime.”

    In their work the researchers around Roseker used a suspension of two nanometers size gold particles undergoing Brownian motion. The experiment was in perfect agreement with the theoretical predictions thus proving not only the performance of the autocorrelator setup but also the validity of the data analysis procedure, demonstrating the first successful experiment of this kind. One of the challenges in this experiment, carried out at the XCS experimental station at LCLS, was to autocorrelate thousands of extremely weak double shot 2D images which was achieved with the help of a newly developed maximum likelihood analysis technique.

    “This experiment paves the way to dynamics experiments of materials on atomic length and femtosecond-nanosecond timescales,” explains Gerhard Grübel, head of the DESY FS-CXS group. “Split-pulse X-ray Photon Correlation Spectroscopy (XPCS) can potentially track atomic scale fluctuations in liquid metals, multi-scale dynamics in water, heterogeneous dynamics about the glass transition, and atomic scale surface fluctuations.” Additionally, time-domain XPCS at FEL sources, especially at the European XFEL, is well suited for studying fluctuations in non-equilibrium processes that go beyond time-averaged structural descriptions.


    DESY European XFEL


    European XFEL

    This will allow the elucidation of dynamics of ultrafast magnetization processes and can address open questions concerning photo-induced phonon dynamics and phase transitions.

    See the full article here .

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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 8:56 am on April 16, 2018 Permalink | Reply
    Tags: , Attosecond X-ray science, , , , , X-ray Technology, XLEAP X-ray Laser-Enhanced Attosecond Pulse generation   

    From European XFEL: “Entering the realm of attosecond X-ray science” 

    XFEL bloc

    European XFEL

    European XFEL

    2018/04/13

    New methods for producing and characterizing attosecond X-ray pulses.

    1
    Ultrashort X-ray pulses (pink) at the Linac Coherent Light Source ionize neon gas at the center of a ring of detectors. An infrared laser (orange) sweeps the outgoing electrons (blue) across the detectors with circularly polarized light. Scientists read data from the detectors to learn about the time and energy structure of the pulses, information they will need for future experiments. Copyright: Terry Anderson / SLAC National Accelerator Laboratory.

    SLAC/LCLS

    European XFEL produces unfathomably fast X-ray pulses that are already being used by scientists to explore the unchartered territory of the atomic and molecular cosmos. Intense X-ray pulses lasting only a few femtoseconds – or a few millionths of a billionth of a second – are being used to reveal insights into the dynamics of chemical reactions and the atomic structures of biological molecules such as proteins and viruses. And while there is much more to discover in this femtosecond time range, scientists are already looking to take European XFEL to the next time dimension, exploring reactions and dynamics that occur on an even briefer time scale – the attosecond time regime.

    If you leave the shutter of your camera open for too long while photographing a race, the resulting pictures will only be a smear of colour. To capture clear and sharp images of the athletes’ movements you need to make sure the shutter is only open for the shortest time; in fact the best shutter speed to capture a clear snapshot of the runners’ legs frozen in action would be faster than the time the runner needed to move their legs. Good light conditions help too to make sure your photos are sharp and in focus. And so it is as scientists attempt to take snapshots of some of nature’s fastest processes such as the movements of electrons within atoms and molecules. To capture snapshots of these movements in action we need pulses of intense X-rays that reflect the timescale on which these reactions occur – and these reactions can occur even down to the attosecond timescale.

    XLEAP

    Attosecond X-ray science is expected to allow scientists to delve even deeper into ultrafast chemical and molecular processes and the tiniest details of our world than already possible. But how to produce X-ray flashes that are even shorter than the already ultrafast femtosecond flashes? One of the methods currently being explored by scientists is ‘X-ray Laser-Enhanced Attosecond Pulse generation’ (XLEAP). The method, being developed at the SLAC National Accelerator Laboratory in the USA, is expected to be possible with only moderate modifications to the layout of existing FEL facilities. If successful, the usually chaotic time and energy structure of XFEL (X-ray Free-Electron Laser) pulses, consisting of a sequence of many intensity spikes based on the so-called SASE (Self-Amplification by Spontaneous Emission) principle, can be reliably narrowed down to one single, coherent intensity spike of only few hundreds of attoseconds. In a recent review article in the Journal of Optics, European XFEL scientists propose how the XLEAP method might be implemented at the SASE 3 branch of the facility, eventually providing attosecond pulses for experiments.

    2
    European XFEL scientist Markus Ilchen working on the original angle resolving time-of-flight spectrometer at PETRA III, DESY. Copyright: European XFEL

    DESY Petra III


    DESY Petra III interior

    Angular Streaking diagnostics

    While the free-electron laser technology is almost ready to provide attosecond pulses, another hurdle is to actually prove and characterize their existence. Experiments to date at XFEL facilities have often relied on indirect measurements and simulations of X-ray pulses to calibrate results. However, only with detailed information from direct measurements of the exact time and energy structure of each X-ray pulse, can X-ray science enter a new era of time resolved and coherence dependent experiments.

    With this in mind, a novel experimental approach was conceived as part of an international collaboration including scientists from SLAC, Deutsches Elektronen-Synchrotron (DESY), European XFEL, the Technical University of Munich, University of Kassel, University of Gothenburg, University of Bern, University of Colorado, University of the Basque Country in Spain, and Lomonosov Moscow State University in Russia. In a study published in the journal Nature Photonics, the international groupdemonstrated the capability of a so-called ‘angular streaking’ method to characterize the time and energy structure of X-ray spikes. The scientists used the shortest pulses available at the Linac Coherent Light Source (LCLS) at SLAC in the USA for their experiment. Using the new angular streaking diagnostic method, millions of pulses, each of a few femtoseconds in length, were successfully captured and analyzed. “Being able to get the precise information about the energy spectrum, as well as the time and intensity structure of every single X-ray pulse is unprecedented” explains Markus Ilchen from the Small Quantum Systems group at European XFEL, one of the principal investigators of this work. “This is really one of the holy grails of FEL diagnostics” he adds enthusiastically.

    The new angular streaking technique works by using the rotating electrical field of intense circularly polarized optical laser pulses to extract the time and energy structure of the XFEL pulses. Interaction with the XFEL pulse causes atoms to eject electrons which are then strongly kicked around by the surrounding laser field. Information about the electron’s exact time of birth is not only imprinted in the energy of the electron but also in the ejecting angle. This all provides a ‘clock’ by which to sort the resulting experimental data. Pulses generated by the SASE process, as implemented at European XFEL and SLAC, are intrinsically variable and chaotic. Some of the recorded pulses during the experiment at SLAC were, therefore, already single spikes in the attosecond regime which then were fully characterized for their time-energy structure.

    Angle resolving time-of-flight spectrometer

    1
    An illustration of the ring-shaped array of 16 individual detectors arranged in a circle like numbers on the face of a clock. An X-ray laser pulse hits a target at the center and sets free electrons that are swept around the detectors. The location, where the electrons reach the “clock,” reveals details such as the variation of the X-ray energy and intensity as a function of time within the ultrashort pulse itself. Copyright: Frank Scholz & Jens Buck, DESY.

    he underlying spectroscopic method is based on an angle resolving time-of-flight spectrometer setup consisting of 16 individual spectrometers aligned in a plane perpendicular to the XFEL beam. These are used to characterize the X-ray beam by correlating the electrons’ energies and their angle dependent intensities. An adapted version of the spectrometer setup originally developed at the PETRA III storage ring at DESY, was built in the diagnostics group of European XFEL and provided for the beamtime at SLAC.

    At European XFEL the diagnostic goal is that scientists will eventually be able to use the method to extract all information online during their experiments and correlate and adjust their data analysis accordingly. Furthermore, although the method has so far only been designed and tested for soft X-rays, Ilchen and his colleagues are optimistic that it could also be used for experiments using hard X-rays. “By reducing the wavelength of the optical laser, we could even resolve the few hundreds of attosecond broad spikes of the hard X-ray pulses here at the SASE 1 branch of European XFEL” Ilchen says.

    Time-resolved experiments

    During the experiment at SLAC the scientists also showed that it was even possible to use the acquired data to select pulses with exactly two intensity spikes with a variable time delay between them. This demonstrates the capability of FELs to enable time-resolved X-ray measurements attosecond to few femtosecond delay. “By determining the time duration and distance of those two spikes, we can sort our data for matching pulse properties and use them to understand how certain reactions and processes have progressed on an attosecond timescale” explains Ilchen. “Since our method gives us precise information about the pulse structure, we will be able to reliably reconstruct what is happening in our samples by producing a sequence of snapshots, so that much like a series of photographs pasted together makes a moving film sequence, we can make ‘movies’ of the reactions” he adds.

    From principle to proof

    Due to the limited pulse repetition rate currently available at most XFELs, however, moving from a proof-of-principle experiment to actually using specifically structured pulses for so-called pump-probe experiments requires a large leap of the imagination. European XFEL, however, already provides more pulses per second than other similar facilities, and will eventually provide 27,000 pulses per second, making the dream of attosecond time-resolved experiment a real possibility. “Although, currently, no machine in the world can provide attosecond X-ray pulses with variable time delay below the femtosecond regime in a controlled fashion,” says Ilchen, “the technologies available at European XFEL in combination with our method, could enable us to produce so much data that we can pick the pulse structures of interest and sort the rest out while still getting enough statistics for new scientific perspectives.”

    Further reading:

    News from SLAC – “Tick, Tock on the ‘Attoclock’: Tracking X-Ray Laser Pulses at Record Speeds

    Overview of options for generating high-brightness attosecond x-ray pulses at free-electron lasers and applications at the European XFEL
    S. Serkez et al., Journal of Optics, 9 Jan 2018 doi:10.1088/2040-8986/aa9f4f

    See the full article here .

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    XFEL Campus

    XFEL Tunnel

    XFEL Gun

    The Hamburg area will soon boast a research facility of superlatives: The European XFEL will generate ultrashort X-ray flashes—27 000 times per second and with a brilliance that is a billion times higher than that of the best conventional X-ray radiation sources.

    The outstanding characteristics of the facility are unique worldwide. Started in 2017, it will open up completely new research opportunities for scientists and industrial users.

     
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