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  • richardmitnick 1:45 pm on April 18, 2017 Permalink | Reply
    Tags: , , , Gabriella Carini, How do you catch femtosecond light?, , , , SLAC LCLS, ,   

    From SLAC: “How do you catch femtosecond light?” 


    SLAC Lab

    1
    Gabriella Carini
    Staff Scientist
    Joined SLAC: 2011
    Specialty: Developing detectors that capture light from X-ray sources
    Interviewed by: Amanda Solliday

    Gabriella Carini enjoys those little moments—after hours and hours of testing in clean rooms, labs and at X-ray beamlines—when she first sees an instrument work.

    She earned her PhD in electronic engineering at the University of Palermo in Italy and now heads the detectors department at the Linac Coherent Light Source (LCLS), the X-ray free-electron laser at SLAC.

    SLAC/LCLS

    Scientists from around the world use the laser to probe natural processes that occur in tiny slivers of time. To see on this timescale, they need a way to collect the light and convert it into data that can be examined and interpreted.

    It’s Carini’s job to make sure LCLS has the right detector equipment at hand to catch the “precious”, very intense laser pulses, which may last only a few femtoseconds.

    When the research heads in new directions, as it constantly does, this requires her to look for fresh technology and turn these ideas into reality.

    When did you begin working with detectors?

    I moved to the United States as a doctoral student. My professor at the time suggested I join a collaboration at Brookhaven National Laboratory, where I started developing gamma ray detectors to catch radioactive materials.

    Radioactive materials give off gamma rays as they decay, and gamma rays are the most energetic photons, or particles of light. The detectors I worked on were made from cadmium zinc telluride, which has very good stopping power for highly energetic photons. These detectors can identify radioactive isotopes for security—such as the movement of nuclear materials—and contamination control, but also gamma rays for medical and astrophysical observations.

    We had some medical projects going on at the time, too, with detectors that scan for radioactive tracers used to map tissues and organs with positron emission tomography.

    From gamma ray detectors, I then moved to X-rays, and I began working on the earliest detectors for LCLS.

    How do you explain your job to someone outside the X-ray science community?

    I say, “There are three ingredients for an experiment—the source, the sample and the detector.”

    You need a source of light that illuminates your sample, which is the problem you want to solve or investigate. To understand what is happening, you have to be able to see the signal produced by the light as it interacts with the sample. That’s where the detector comes in. For us, the detector is like the “eyes” of the experimental set-up.

    What do you like most about your work?

    2

    There’s always a way we can help researchers optimize their experiments, tweak some settings, do more analysis and correction.

    This is important because scientists are going to encounter a lot of different types of detectors if they work at various X-ray facilities.

    I like to have input from people who are running the experiments. Because I did experiments myself as a graduate student, I’m very sensitive to whether a system is user-friendly. If you don’t make something that researchers can take the best advantage of, then you didn’t do your job fully.

    And detectors are never perfect, no matter which one you buy or build.

    There are a lot of people who have to come together to make a detector system. It’s not one person’s work. It’s many, many people with lots of different expertise. You need to have lots of good interpersonal skills.

    What are some of the challenges of creating detectors for femtosecond science?

    In more traditional X-ray sources the photons arrive distributed over time, one after the other, but when you work with ultrafast laser pulses like the ones from LCLS, all your information about a sample arrives in a few femtoseconds. Your detector has to digest this entire signal at once, process the information and send it out before another pulse comes. This requires deep understanding of the detector physics and needs careful engineering. You need to optimize the whole signal chain from the sensor to the readout electronics to the data transmission.

    We also have mechanical challenges because we have to operate in very unusual conditions: intense optical lasers, injectors with gas and liquids, etc. In many cases we need to use special filters to protect the detectors from these sources of contamination.

    4
    And often, you work in vacuum. With “soft” or low-energy X-rays, they are absorbed very quickly in air. Your entire system has to be vacuum-compatible. With many of our substantial electronics, this requires some care.

    So there are lots of things to take into account. Those are just a few examples. It’s very complicated and can vary quite a bit from experiment to experiment.

    Is there a new project you are really excited about?

    All of LCLS-II—this fills my life! We’re coming up with new ideas and new technologies for SLAC’s next X-ray laser, which will have a higher firing rate—up to a million pulses per second. For me, this is a multidimensional puzzle. Every science case and every instrument has its own needs and we have to find a route through the many options and often-competing parameters to achieve our goals.

    X-ray free-electron lasers are a big driver for detector development. Ten years ago, no one would have talked about X-ray cameras delivering 10,000 pictures per second. The new X-ray lasers are really a game-changer in developing detectors for photon science, because they require detectors that are just not readily available.

    LCLS-II will be challenging, but it’s exciting. For me, it’s thinking about what we can do now for the very first day of operation. And while doing that, we need to keep pushing the limits of what we have to do next to take full advantage of our new machine.

    6

    SLAC LCLS-II

    See the full article here .

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  • richardmitnick 7:10 am on April 18, 2017 Permalink | Reply
    Tags: Agostino Marinelli, , , SLAC LCLS   

    From SLAC: “Seeing the World in Femtoseconds” 


    SLAC Lab

    Q&A series with SLAC scientists

    4.17.17
    Kathryn Jepsen

    1
    Agostino Marinelli
    Accelerator Physicist

    Joined SLAC: 2012

    Specialty: Improving the capabilities of the Linac Coherent Light Source

    SLAC/LCLS

    Agostino “Ago” Marinelli first met pioneering accelerator physicist Claudio Pellegrini as an undergraduate student at the University of Rome. It was 2007, a couple of years before the Linac Coherent Light Source (LCLS) came online at SLAC, and people were abuzz about free-electron laser physics.

    Caught up in the excitement, Marinelli pursued a PhD in accelerator physics at the University of California, Los Angeles under Jamie Rosenzweig’s mentorship. Today he is involved in research and development related to femtosecond science at LCLS.

    Marinelli focuses on research at the femtosecond timescale because, he says, “it’s the fastest we can reach now with X-rays, and as an accelerator physicist, I get excited about technical things like that.”

    Why did you get involved in X-ray science?

    2
    Claudio Pellegrini

    Part of it was Claudio—he’s a very charismatic character. He’s an inspiring character. The field was very interesting. I thought it was a good way to spend my PhD.
    LCLS was promising so much innovation: a laser 10 billion times brighter than we had then. That sounds like something that somebody who is 24 would love to get involved in. It just sounded like something that would change science in a positive way, and I wanted to be a part of it.

    What is a free-electron laser?
    Free-electron lasers were invented by John Madey at Stanford in 1971; later on in the ’90s Claudio Pellegrini and collaborators proposed to extend free-electron lasers to the X-ray regime. They were the next step after synchrotron light sources.

    Synchrotrons send electrons around in a circle. That gives you radiation you can use in experiments. The difference between a synchrotron and the free-electron laser is the same difference between this light [points to a ceiling light] and a laser. It’s the difference between a bunch of kids making noise and a choir.

    In a synchrotron, the electrons are all doing the same thing, going around in a circle, but they are unaware of each other. They are all emitting X-rays in a random way. What makes a free-electron laser a laser is that all the electrons are emitting radiation in a coherent way. They are all synchronized.

    Also, since in an FEL you are using very intense and short electron bunches, the X-ray pulses will also be very short, down to the femtosecond level.

    What do you do with the free-electron laser?

    We talk to the users—they’re researchers that have some science they want to study with the machine. Then we “shape” the X-rays—set up the machine in a way that’s ideal for that experiment. The LCLS accelerator is very flexible. You can do all sorts of tricks with it—like arbitrarily changing the pulse duration, varying the X-ray polarization or making multiple pulses of different colors.

    Speaking of which, in 2014 the European Physical Society awarded you the Frank Sacherer Prize for your work using “two-color” beams with LCLS. What is that about?

    Normally LCLS shoots 120 X-ray pulses a second. But you can also make it send two pulses of different energies, separated by a few to 100 femtoseconds. You excite your sample with the first one and probe it with the second. You have to observe it within femtoseconds after you excite it because reactions happen that fast.

    3
    Normally you would excite the sample with an external optical laser; that’s how pump-probe is done. But in molecular dynamics, if you can excite a molecule with X-rays instead of an optical laser, you can get atom specificity—you can target a specific atom in the molecule.

    Each atom has a core energy level. If you know that, you can shoot the X-ray and hit only the oxygen in a molecule; oxygen is the only thing that is going to react. With two pulses at separate energies, you can target different atoms in a molecule to see which one triggers a certain reaction.

    What kinds of things do you study on the femtosecond scale?

    A femtosecond is close to the fundamental scale of atomic and molecular physics—so, things like chemistry.

    A chemical reaction is essentially two molecules or atoms interacting in some way and sharing charge and giving away energy. Ultimately to understand that, you have to understand how charge and energy flow in a molecule. You have to understand the very fundamental motion of electrons and ions in the molecule. On the femtosecond scale, you can see the positions of the atoms rearranging as it happens.

    Chemical reactions are a dynamic process. They start with something. They end with something. We want to know what happens in between.

    Why?

    If you want the reaction to end with something else, if you want it to end with something slightly different, you want to understand how it happens so you can make changes on purpose.

    What are you most excited about now?

    I’m really excited about what I’m about to do, which is this sub-femtosecond project called XLEAP. We will shape the LCLS electron beam with a high-power infrared laser and use it to generate pulses that are shorter than a femtosecond! What we will be looking at is energy and electrons moving around a molecule, which happens even faster than the atoms rearranging.

    Right now we’re really blind to all of this. To me, the way I understand it is, going to that timescale, you’re peeking into the very fundamental, quantum nature of the electrons in the molecule.

    If you ask me, “What is the ultimate problem it will solve for us?”—the answer is: I don’t know. In general when you’re blind to some fundamental process in nature and suddenly you can see it, my guess is something good is going to come of it.

    See the full article here .

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  • richardmitnick 3:55 pm on April 17, 2017 Permalink | Reply
    Tags: , , , , , SLAC LCLS, , ,   

    From SLAC: “SLAC’s X-ray Laser Glimpses How Electrons Dance with Atomic Nuclei in Materials” 


    SLAC Lab

    September 22, 2016

    Studies Could Help Design and Control Materials with Intriguing Properties, Including Novel Electronics, Solar Cells and Superconductors.

    From hard to malleable, from transparent to opaque, from channeling electricity to blocking it: Materials come in all types. A number of their intriguing properties originate in the way a material’s electrons “dance” with its lattice of atomic nuclei, which is also in constant motion due to vibrations known as phonons.

    This coupling between electrons and phonons determines how efficiently solar cells convert sunlight into electricity. It also plays key roles in superconductors that transfer electricity without losses, topological insulators that conduct electricity only on their surfaces, materials that drastically change their electrical resistance when exposed to a magnetic field, and more.

    At the Department of Energy’s SLAC National Accelerator Laboratory, scientists can study these coupled motions in unprecedented detail with the world’s most powerful X-ray laser, the Linac Coherent Light Source (LCLS). LCLS is a DOE Office of Science User Facility.

    SLAC/LCLS

    1
    An illustration shows how laser light excites electrons (white spheres) in a solid material, creating vibrations in its lattice of atomic nuclei (black and blue spheres). SLAC’s LCLS X-ray laser reveals the ultrafast “dance” between electrons and vibrations that accounts for many important properties of materials. (SLAC National Accelerator Laboratory)

    “It has been a long-standing goal to understand, initiate and control these unusual behaviors,” says LCLS Director Mike Dunne. “With LCLS we are now able to see what happens in these materials and to model complex electron-phonon interactions. This ability is central to the lab’s mission of developing new materials for next-generation electronics and energy solutions.”

    LCLS works like an extraordinary strobe light: Its ultrabright X-rays take snapshots of materials with atomic resolution and capture motions as fast as a few femtoseconds, or millionths of a billionth of a second. For comparison, one femtosecond is to a second what seven minutes is to the age of the universe.

    Two recent studies made use of these capabilities to study electron-phonon interactions in lead telluride, a material that excels at converting heat into electricity, and chromium, which at low temperatures has peculiar properties similar to those of high-temperature superconductors.

    Turning Heat into Electricity and Vice Versa

    Lead telluride, a compound of the chemical elements lead and tellurium, is of interest because it is a good thermoelectric: It generates an electrical voltage when two opposite sides of the material have different temperatures.

    “This property is used to power NASA space missions like the Mars rover Curiosity and to convert waste heat into electricity in high-end cars,” says Mariano Trigo, a staff scientist at the Stanford PULSE Institute and the Stanford Institute for Materials and Energy Sciences (SIMES), both joint institutes of Stanford University and SLAC. “The effect also works in the opposite direction: An electrical voltage applied across the material creates a temperature difference, which can be exploited in thermoelectric cooling devices.”

    Mason Jiang, a recent graduate student at Stanford, PULSE and SIMES, says, “Lead telluride is exceptionally good at this. It has two important qualities: It’s a bad thermal conductor, so it keeps heat from flowing from one side to the other, and it’s also a good electrical conductor, so it can turn the temperature difference into an electric current. The coupling between lattice vibrations, caused by heat, and electron motions is therefore very important in this system. With our study at LCLS, we wanted to understand what’s naturally going on in this material.”

    In their experiment, the researchers excited electrons in a lead telluride sample with a brief pulse of infrared laser light, and then used LCLS’s X-rays to determine how this burst of energy stimulated lattice vibrations.

    2
    This illustration shows the arrangement of lead and tellurium atoms in lead telluride, an excellent thermoelectric that efficiently converts heat into electricity and vice versa. In its normal state (left), lead telluride’s structure is distorted and has a relatively large degree of lattice vibrations (blurring). When scientists hit the sample with a laser pulse, the structure became more ordered (right). The results elucidate how electrons couple with these distortions – an interaction that is crucial for lead telluride’s thermoelectric properties. (SLAC National Accelerator Laboratory)

    “Lead telluride sits at the precipice of a coupled electronic and structural transformation,” says principal investigator David Reis from PULSE, SIMES and Stanford. “It has a tendency to distort without fully transforming – an instability that is thought to play an important role in its thermoelectric behavior. With our method we can study the forces involved and literally watch them change in response to the infrared laser pulse.”

    The scientists found that the light pulse excites particular electronic states that are responsible for this instability through electron-phonon coupling. The excited electrons stabilize the material by weakening certain long-range forces that were previously associated with the material’s low thermal conductivity.

    “The light pulse actually walks the material back from the brink of instability, making it a worse thermoelectric,” Reis says. “This implies that the reverse is also true – that stronger long-range forces lead to better thermoelectric behavior.”

    The researchers hope their results, published July 22 in Nature Communications, will help them find other thermoelectric materials that are more abundant and less toxic than lead telluride.

    Controlling Materials by Stimulating Charged Waves

    The second study looked at charge density waves – alternating areas of high and low electron density across the nuclear lattice – that occur in materials that abruptly change their behavior at a certain threshold. This includes transitions from insulator to conductor, normal conductor to superconductor, and from one magnetic state to another.

    These waves don’t actually travel through the material; they are stationary, like icy waves near the shoreline of a frozen lake.

    “Charge density waves have been observed in a number of interesting materials, and establishing their connection to material properties is a very hot research topic,” says Andrej Singer, a postdoctoral fellow in Oleg Shpyrko’s lab at the University of California, San Diego. “We’ve now shown that there is a way to enhance charge density waves in crystals of chromium using laser light, and this method could potentially also be used to tweak the properties of other materials.”

    This could mean, for example, that scientists might be able to switch a material from a normal conductor to a superconductor with a single flash of light. Singer and his colleagues reported their results on July 25 in Physical Review Letters.

    The research team used the chemical element chromium as a simple model system to study charge density waves, which form when the crystal is cooled to about minus 280 degrees Fahrenheit. They stimulated the chilled crystal with pulses of optical laser light and then used LCLS X-ray pulses to observe how this stimulation changed the amplitude, or height, of the charge density waves.

    “We found that the amplitude increased by up to 30 percent immediately after the laser pulse,” Singer says. “The amplitude then oscillated, becoming smaller and larger over a period of 450 femtoseconds, and it kept going when we kept hitting the sample with laser pulses. LCLS provides unique opportunities to study such process because it allows us to take ultrafast movies of the related structural changes in the lattice.”

    Based on their results, the researchers suggested a mechanism for the amplitude enhancement: The light pulse interrupts the electron-phonon interactions in the material, causing the lattice to vibrate. Shortly after the pulse, these interactions form again, which boosts the amplitude of the vibrations, like a pendulum that swings farther out when it receives an extra push.

    A Bright Future for Studies of the Electron-Phonon Dance

    Studies like these have a high priority in solid-state physics and materials science because they could pave the way for new materials and provide new ways to control material properties.

    With its 120 ultrabright X-ray pulses per second, LCLS reveals the electron-phonon dance with unprecedented detail. More breakthroughs in the field are on the horizon with LCLS-II – a next-generation X-ray laser under construction at SLAC that will fire up to a million X-ray flashes per second and will be 10,000 times brighter than LCLS.

    “LCLS-II will drastically increase our chances of capturing these processes,” Dunne says. “Since it will also reveal subtle electron-phonon signals with much higher resolution, we’ll be able to study these interactions in much greater detail than we can now.”

    Other research institutions involved in the studies were University College Cork, Ireland; Imperial College London, UK; Duke University; Oak Ridge National Laboratory; RIKEN Spring-8 Center, Japan; University of Tokyo, Japan; University of Michigan; and University of Kiel, Germany. Funding sources included DOE Office of Science; Science Foundation Ireland; Volkswagen Foundation, Germany; and Federal Ministry of Education and Research, Germany. Preliminary X-ray studies on lead telluride were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility, and at the Spring-8 Angstrom Compact Free-electron Laser (SACLA), Japan.

    SLAC/SSRL

    SACLA Free-Electron Laser Riken Japan


    his movie introduces LCLS-II, a future light source at SLAC. It will generate over 8,000 times more light pulses per second than today’s most powerful X-ray laser, LCLS, and produce an almost continuous X-ray beam that on average will be 10,000 times brighter. (SLAC National Accelerator Laboratory)

    See the full article here .

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  • richardmitnick 7:48 am on November 4, 2016 Permalink | Reply
    Tags: , , , SLAC LCLS, ,   

    From SLAC: SLAC, Berkeley Lab Researchers Prepare for Scientific Computing on the Exascale” 


    SLAC Lab

    November 3, 2016

    1
    NERSC CRAY Cori supercomputer
    Development and testing of future exascale computing tools for X-ray laser data analysis and the simulation of plasma wakefield accelerators will be done on the Cori supercomputer at NERSC, the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory. (NERSC)

    Researchers at the Department of Energy’s SLAC National Accelerator Laboratory are playing key roles in two recently funded computing projects with the goal of developing cutting-edge scientific applications for future exascale supercomputers that can perform at least a billion billion computing operations per second – 50 to 100 times more than the most powerful supercomputers in the world today.

    The first project, led by SLAC, will develop computational tools to quickly sift through enormous piles of data produced by powerful X-ray lasers. The second project, led by DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), will reengineer simulation software for a potentially transformational new particle accelerator technology, called plasma wakefield acceleration.

    The projects, which will each receive $10 million over four years, are among 15 fully-funded application development proposals and seven proposals selected for seed funding by the DOE’s Exascale Computing Project (ECP). The ECP is part of President Obama’s National Strategic Computing Initiative and intends to maximize the benefits of high-performance computing for U.S. economic competiveness, national security and scientific discovery.

    “Many of our modern experiments generate enormous quantities of data,” says Alex Aiken, professor of computer science at Stanford University and director of the newly formed SLAC Computer Science division, who is involved in the X-ray laser project. “Exascale computing will create the capabilities to handle unprecedented data volumes and, at the same time, will allow us to solve new, more complex simulation problems.”

    Analyzing ‘Big Data’ from X-ray Lasers in Real Time

    X-ray lasers, such as SLAC’s Linac Coherent Light Source (LCLS) have been proven to be extremely powerful “microscopes” that are capable of glimpsing some of nature’s fastest and most fundamental processes on the atomic level.

    SLAC/LCLS
    SLAC/LCLS

    Researchers use LCLS, a DOE Office of Science User Facility, to create molecular movies, watch chemical bonds form and break, follow the path of electrons in materials and take 3-D snapshots of biological molecules that support the development of new drugs.

    At the same time X-ray lasers also generate giant amounts of data. A typical experiment at LCLS, which fires 120 flashes per second, fills up hundreds of thousands of gigabytes of disk space. Analyzing such a data volume in a short amount of time is already very challenging. And this situation is set to become dramatically harder: The next-generation LCLS-II X-ray laser will deliver 8,000 times more X-ray pulses per second, resulting in a similar increase in data volumes and data rates.

    SLAC/LCLS II schematic
    SLAC/LCLS II schematic

    Estimates are that the data flow will greatly exceed a trillion data ‘bits’ per second, and require hundreds of petabytes of online disk storage.

    As a result of the data flood even at today’s levels, researchers collecting data at X-ray lasers such as LCLS presently receive only very limited feedback regarding the quality of their data.

    “This is a real problem because you might only find out days or weeks after your experiment that you should have made certain changes,” says Berkeley Lab’s Peter Zwart, one of the collaborators on the exascale project, who will develop computer algorithms for X-ray imaging of single particles. “If we were able to look at our data on the fly, we could often do much better experiments.”

    Amedeo Perazzo, director of the LCLS Controls & Data Systems Division and principal investigator for this “ExaFEL” project, says, “We want to provide our users at LCLS, and in the future LCLS-II, with very fast feedback on their data so that can make important experimental decisions in almost real time. The idea is to send the data from LCLS via DOE’s broadband science network ESnet to NERSC, the National Energy Research Scientific Computing Center, where supercomputers will analyze the data and send the results back to us – all of that within just a few minutes.” NERSC and ESnet are DOE Office of Science User Facilities at Berkeley Lab.

    LBL NERSC Cray XC30 Edison supercomputer
    LBL NERSC Cray XC30 Edison supercomputer

    lcls-ii-image
    LCLS II

    X-ray data processing and analysis is quite an unusual task for supercomputers. “Traditionally these high-performance machines have mostly been used for complex simulations, such as climate modeling, rather than processing real-time data” Perazzo says. “So we’re breaking completely new ground with our project, and foresee a number of important future applications of the data processing techniques being developed.”

    This project is enabled by the investments underway at SLAC to prepare for LCLS-II, with the installation of new infrastructure capable of handling these enormous amounts of data.

    A number of partners will make additional crucial contributions.

    “At Berkeley Lab, we’ll be heavily involved in developing algorithms for specific use cases,” says James Sethian, a professor of mathematics at the University of California, Berkeley, and head of Berkeley Lab’s Mathematics Group and the Center for Advanced Mathematics for Energy Research Applications (CAMERA). “This includes work on two different sets of algorithms. The first set, developed by a team led by Nick Sauter, consists of well-established analysis programs that we’ll reconfigure for exascale computer architectures, whose larger computer power will allow us to do better, more complex physics. The other set is brand new software for emerging technologies such as single-particle imaging, which is being designed to allow scientists to study the atomic structure of single bacteria or viruses in their living state.”

    The “ExaFEL” project led by Perazzo will take advantage of Aiken’s newly formed Stanford/SLAC team, and will collaborate with researchers at Los Alamos National Laboratory to develop systems software that operates in a manner that optimizes its use of the architecture of the new exascale computers.

    “Supercomputers are very complicated, with millions of processors running in parallel,” Aiken says. “It’s a real computer science challenge to figure out how to use these new architectures most efficiently.”

    Finally, ESnet will provide the necessary networking capabilities to transfer data between the LCLS and supercomputing resources. Until exascale systems become available in the mid-2020s, the project will use NERSC’s Cori supercomputer for its developments and tests.

    esnet-map
    ESnet

    See the full article here .

    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.
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  • richardmitnick 7:40 am on October 12, 2016 Permalink | Reply
    Tags: , , , SLAC LCLS,   

    From SLAC: “X-rays Reveal New Path In Battle Against Mosquito-borne Illness” 


    SLAC Lab

    `
    The mosquito larvicide BinAB is composed of two proteins, BinA (yellow) and BinB (blue). Inside bacterial cells, BinAB naturally forms nanocrystals. Using these crystals and the intense X-ray pulses produced by SLAC’s Linac Coherent Light Source, scientists shed light on the three-dimensional structure of BinAB and its mode of action. (SLAC National Accelerator Laboratory)

    September 28, 2016

    SLAC’s X-ray Laser Provides Clues to Engineering a New Protein to Kill Mosquitos Carrying Dengue, Zika

    Structural biology research conducted at the U.S. Department of Energy’s SLAC National Accelerator Laboratory has uncovered how small insecticidal protein crystals that are naturally produced by bacteria might be tailored to combat dengue fever and the Zika virus.

    SLAC’s X-ray free-electron laser – the Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility – offered unprecedented views of the toxin BinAB, used as a larvicide in public health efforts against mosquito-borne diseases such as malaria, West Nile virus and viral encephalitis.

    SLAC/LCLS
    SLAC/LCLS

    The larvicide is currently ineffective against the Aedes mosquitos that transmit Zika and dengue fever, and therefore not used to combat these species of mosquitos at this time. The new information provides clues to how scientists could design a composite toxin that would work against a broader range of mosquito species, including Aedes.

    Today, Nature published the study.

    “A more detailed look at the proteins’ structure provides information fundamental to understanding how the crystals kill mosquito larvae,” said Jacques-Philippe Colletier, a scientist at the Institut de Biologie Structurale in Grenoble, France and lead author on the paper. “This is a prerequisite for modifying the toxin to adapt it to our needs.”

    Selective Mosquito Control, Courtesy of Bacteria

    The BinAB crystals are produced by Lysinibacillus sphaericus bacteria, which release the crystals along with spores at the end of their life cycle. Mosquito larvae eat the crystals along with the spores, and then die.

    BinAB is inactive in the crystalline state and does not work on contact. For the crystals to dissolve, they must be exposed to alkaline conditions, such as those in a mosquito larva’s gut. The binary protein is then activated, recognized by a specific receptor at the surface of cells and internalized.

    Because Aedes larvae can evade one of these steps of intoxication, they are resistant to BinAB. These larvae do not express the correct receptors at the surface of their intestinal cells. Many other insect species, small crustaceans and humans also lack these receptors, as well as alkaline digestive systems.

    “Part of the appeal is that the larvicide’s safe because it’s so specific, but that’s also part of its limitation,” said Michael Sawaya, a scientist at the University of California, Los Angeles-DOE Molecular Biology Institute and co-author on the paper.

    For public health officials who want to prevent mosquito-borne disease, BinAB could also offer an alternative for controlling certain species of mosquitos that have begun to show resistance to other forms of chemical control.

    Creating a Tailored Insecticide

    The research team already knew the larvicide is composed of a pair of proteins, BinA and BinB, that pair together in crystals and are later activated by larval digestive enzymes.

    In the LCLS experiments, they learned the molecular basis for how the two proteins paired with each other – each performing an important, unique function. Previous research had determined that BinA is the toxic part of the complex, while BinB is responsible for binding the toxin to the mosquito’s intestine. BinB ushers BinA into the cells; once inside, BinA kills the cell.

    The scientists also identified four “hot spots” on the proteins that are activated by the alkaline conditions in the larval gut. All together, they trigger a change from a nontoxic form of the protein to a version that is lethal to mosquito larvae.

    Using the information gathered during the crystallography study, the research team has already begun to engineer a form of the BinAB proteins that will work against more species of mosquitos. This is ongoing work at Institut de Biologie Structurale, UCLA, University of California, Riverside and SLAC.

    Solving the Structure

    Only coarse details were known about the unique three-dimensional structure and biological behavior of BinAB prior to the experiment at LCLS.

    “We chose to look at the BinAB larvicide because it is so widely used, yet the structural details were a mystery,” said Brian Federici, professor of entomology at UC Riverside.

    The small size of the crystals made them difficult to study at conventional X-ray sources. So the research team used genetic engineering techniques to increase the size of the crystals, and the bright, fast pulses of light at LCLS allowed the scientists to collect detailed structural data from the tiny crystals before X-rays damaged their samples.

    The researchers used a crystallography technique called de novo phasing. This involves tagging the crystals with heavy metal markers, collecting tens of thousands of X-ray diffraction patterns, and combining the information collected to obtain a three-dimensional map of the electron density of the protein.

    “This is the first time we’ve used de novo phasing on a crystal of great interest at an X-ray free-electron laser,” said Sebastien Boutet, SLAC scientist.

    The technique had so far only been used on test samples where the structure was already known, in order to prove that it would work.

    “The most immediate need is to now expand the spectrum of action of the BinAB toxin to counter the progression of Zika, in particular,” said Colletier. “BinAB is already effective against Culex [carrier of West Nile encephalitis] and Anopheles [carrier of malaria] mosquitos. With the results of the study, we now feel more confident that we can design the protein to target Aedes mosquitos.”

    Additional contributors to the research include scientists from the Howard Hughes Medical Institutes at UCLA, Lawrence Berkeley National Laboratory, and Stanford University. The Institut de Biologie Structurale is a research center for integrated structural biology funded by the Commissariat à l’Énergie Atomique, the Centre National de la Recherche Scientifique and the Université Grenoble Alpes. The Collaborative Innovation Award program of Howard Hughes Medical Institute (HCIA-HHMI), W.M Keck Foundation, National Institutes of Health, National Science Foundation, France Alzheimer Foundation, Agence Nationale de la Recherche, and DOE Office of Science supported the research.

    See the full article here .

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  • richardmitnick 11:13 am on September 22, 2016 Permalink | Reply
    Tags: , , SLAC LCLS,   

    From SLAC: “SLAC’s X-ray Laser Glimpses How Electrons Dance with Atomic Nuclei in Materials” 


    SLAC Lab

    September 22, 2016

    Studies Could Help Design and Control Materials with Intriguing Properties, Including Novel Electronics, Solar Cells and Superconductors

    1
    SLAC’s LCLS X-ray laser reveals the ultrafast “dance” between a material’s electrons and vibrations that accounts for many important properties of materials.
    An illustration shows how laser light excites electrons (white spheres) in a solid material, creating vibrations in its lattice of atomic nuclei (black and blue spheres). SLAC’s LCLS X-ray laser reveals the ultrafast “dance” between electrons and vibrations that accounts for many important properties of materials. (SLAC National Accelerator Laboratory)

    SLAC/LCLS
    SLAC/LCLS

    From hard to malleable, from transparent to opaque, from channeling electricity to blocking it: Materials come in all types. A number of their intriguing properties originate in the way a material’s electrons “dance” with its lattice of atomic nuclei, which is also in constant motion due to vibrations known as phonons.

    This coupling between electrons and phonons determines how efficiently solar cells convert sunlight into electricity. It also plays key roles in superconductors that transfer electricity without losses, topological insulators that conduct electricity only on their surfaces, materials that drastically change their electrical resistance when exposed to a magnetic field, and more.

    At the Department of Energy’s SLAC National Accelerator Laboratory, scientists can study these coupled motions in unprecedented detail with the world’s most powerful X-ray laser, the Linac Coherent Light Source (LCLS). LCLS is a DOE Office of Science User Facility.

    “It has been a long-standing goal to understand, initiate and control these unusual behaviors,” says LCLS Director Mike Dunne. “With LCLS we are now able to see what happens in these materials and to model complex electron-phonon interactions. This ability is central to the lab’s mission of developing new materials for next-generation electronics and energy solutions.”

    LCLS works like an extraordinary strobe light: Its ultrabright X-rays take snapshots of materials with atomic resolution and capture motions as fast as a few femtoseconds, or millionths of a billionth of a second. For comparison, one femtosecond is to a second what seven minutes is to the age of the universe.

    Two recent studies made use of these capabilities to study electron-phonon interactions in lead telluride, a material that excels at converting heat into electricity, and chromium, which at low temperatures has peculiar properties similar to those of high-temperature superconductors.

    Turning Heat into Electricity and Vice Versa

    Lead telluride, a compound of the chemical elements lead and tellurium, is of interest because it is a good thermoelectric: It generates an electrical voltage when two opposite sides of the material have different temperatures.

    “This property is used to power NASA space missions like the Mars rover Curiosity and to convert waste heat into electricity in high-end cars,” says Mariano Trigo, a staff scientist at the Stanford PULSE Institute and the Stanford Institute for Materials and Energy Sciences (SIMES), both joint institutes of Stanford University and SLAC. “The effect also works in the opposite direction: An electrical voltage applied across the material creates a temperature difference, which can be exploited in thermoelectric cooling devices.”

    Mason Jiang, a recent graduate student at Stanford, PULSE and SIMES, says, “Lead telluride is exceptionally good at this. It has two important qualities: It’s a bad thermal conductor, so it keeps heat from flowing from one side to the other, and it’s also a good electrical conductor, so it can turn the temperature difference into an electric current. The coupling between lattice vibrations, caused by heat, and electron motions is therefore very important in this system. With our study at LCLS, we wanted to understand what’s naturally going on in this material.”

    In their experiment, the researchers excited electrons in a lead telluride sample with a brief pulse of infrared laser light, and then used LCLS’s X-rays to determine how this burst of energy stimulated lattice vibrations.

    2
    This illustration shows the arrangement of lead and tellurium atoms in lead telluride, an excellent thermoelectric that efficiently converts heat into electricity and vice versa. In its normal state (left), lead telluride’s structure is distorted and has a relatively large degree of lattice vibrations (blurring). When scientists hit the sample with a laser pulse, the structure became more ordered (right). The results elucidate how electrons couple with these distortions – an interaction that is crucial for lead telluride’s thermoelectric properties. (SLAC National Accelerator Laboratory)

    “Lead telluride sits at the precipice of a coupled electronic and structural transformation,” says principal investigator David Reis from PULSE, SIMES and Stanford. “It has a tendency to distort without fully transforming – an instability that is thought to play an important role in its thermoelectric behavior. With our method we can study the forces involved and literally watch them change in response to the infrared laser pulse.”

    The scientists found that the light pulse excites particular electronic states that are responsible for this instability through electron-phonon coupling. The excited electrons stabilize the material by weakening certain long-range forces that were previously associated with the material’s low thermal conductivity.

    “The light pulse actually walks the material back from the brink of instability, making it a worse thermoelectric,” Reis says. “This implies that the reverse is also true – that stronger long-range forces lead to better thermoelectric behavior.”

    The researchers hope their results, published July 22 in Nature Communications, will help them find other thermoelectric materials that are more abundant and less toxic than lead telluride.

    Controlling Materials by Stimulating Charged Waves

    The second study looked at charge density waves – alternating areas of high and low electron density across the nuclear lattice – that occur in materials that abruptly change their behavior at a certain threshold. This includes transitions from insulator to conductor, normal conductor to superconductor, and from one magnetic state to another.

    These waves don’t actually travel through the material; they are stationary, like icy waves near the shoreline of a frozen lake.

    “Charge density waves have been observed in a number of interesting materials, and establishing their connection to material properties is a very hot research topic,” says Andrej Singer, a postdoctoral fellow in Oleg Shpyrko’s lab at the University of California, San Diego. “We’ve now shown that there is a way to enhance charge density waves in crystals of chromium using laser light, and this method could potentially also be used to tweak the properties of other materials.”

    This could mean, for example, that scientists might be able to switch a material from a normal conductor to a superconductor with a single flash of light. Singer and his colleagues reported their results on July 25 in Physical Review Letters.

    3
    This movie shows how a laser pulse hitting a chromium crystal causes charge density waves – alternating areas of high and low electron density within the crystal – to oscillate in height, or amplitude. The signal seen here is made by X-ray laser pulses scattering off the crystal. The timescale of the oscillations is shown in picoseconds, or trillionths of a second. (A. Singer/University of California, San Diego)

    The research team used the chemical element chromium as a simple model system to study charge density waves, which form when the crystal is cooled to about minus 280 degrees Fahrenheit. They stimulated the chilled crystal with pulses of optical laser light and then used LCLS X-ray pulses to observe how this stimulation changed the amplitude, or height, of the charge density waves.

    “We found that the amplitude increased by up to 30 percent immediately after the laser pulse,” Singer says. “The amplitude then oscillated, becoming smaller and larger over a period of 450 femtoseconds, and it kept going when we kept hitting the sample with laser pulses. LCLS provides unique opportunities to study such process because it allows us to take ultrafast movies of the related structural changes in the lattice.”

    Based on their results, the researchers suggested a mechanism for the amplitude enhancement: The light pulse interrupts the electron-phonon interactions in the material, causing the lattice to vibrate. Shortly after the pulse, these interactions form again, which boosts the amplitude of the vibrations, like a pendulum that swings farther out when it receives an extra push.

    A Bright Future for Studies of the Electron-Phonon Dance

    Studies like these have a high priority in solid-state physics and materials science because they could pave the way for new materials and provide new ways to control material properties.

    With its 120 ultrabright X-ray pulses per second, LCLS reveals the electron-phonon dance with unprecedented detail. More breakthroughs in the field are on the horizon with LCLS-II – a next-generation X-ray laser under construction at SLAC that will fire up to a million X-ray flashes per second and will be 10,000 times brighter than LCLS.

    “LCLS-II will drastically increase our chances of capturing these processes,” Dunne says. “Since it will also reveal subtle electron-phonon signals with much higher resolution, we’ll be able to study these interactions in much greater detail than we can now.”

    Other research institutions involved in the studies were University College Cork, Ireland; Imperial College London, UK; Duke University; Oak Ridge National Laboratory; RIKEN Spring-8 Center, Japan; University of Tokyo, Japan; University of Michigan; and University of Kiel, Germany. Funding sources included DOE Office of Science; Science Foundation Ireland; Volkswagen Foundation, Germany; and Federal Ministry of Education and Research, Germany. Preliminary X-ray studies on lead telluride were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility, and at the Spring-8 Angstrom Compact Free-electron Laser (SACLA), Japan.


    This movie introduces LCLS-II, a future light source at SLAC. It will generate over 8,000 times more light pulses per second than today’s most powerful X-ray laser, LCLS, and produce an almost continuous X-ray beam that on average will be 10,000 times brighter. (SLAC National Accelerator Laboratory)

    Citations: M.P. Jiang et al., Nature Communications, 22 July 2016 (10.1038/ncomms12291); A. Singer et al., Physical Review Letters, 25 July 2016 (10.1103/PhysRevLett.117.056401).

    See the full article here .

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  • richardmitnick 11:15 am on September 9, 2016 Permalink | Reply
    Tags: , SLAC LCLS, Snapshots of molecules,   

    From ANL: “Seeing energized light-active molecules proves quick work for Argonne scientists” 

    ANL Lab

    News from Argonne National Laboratory

    September 8, 2016
    Jared Sagoff

    For people who enjoy amusement parks, one of the most thrilling sensations comes at the top of a roller coaster, in the split second between the end of the climb and the rush of the descent. Trying to take a picture at exactly the moment that the roller coaster reaches its zenith can be difficult because the drop happens so suddenly.

    For chemists trying to take pictures of energized molecules, the dilemma is precisely the same, if not trickier. When certain molecules are excited – like a roller coaster poised at the very top of its run – they often stay in their new state for only an instant before “falling” into a lower energy state.

    1
    To understand how molecules undergo light-driven chemical transformations, scientists need to be able to follow the atoms and electrons within the energized molecule as it rides on the energy “roller coaster.”

    In a recent study, a team of researchers at the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory, Northwestern University, the University of Washington and the Technical University of Denmark used the ultrafast high-intensity pulsed X-rays produced by the Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility at SLAC National Accelerator Laboratory, to take molecular snapshots of these molecules.

    SLAC/LCLS
    SLAC/LCLS

    By using the LCLS, the researchers were able to capture atomic and electronic arrangements within the molecule that had lifetimes as short as 50 femtoseconds – which is about the amount of time it takes light to travel the width of a human hair.

    “We can see changes in these energized molecules which happen incredibly quickly,” said Lin Chen, an Argonne senior chemist and professor of chemistry at Northwestern University who led the research.

    Chen and her team looked the structure of a metalloporphyrin, a molecule similar to important building blocks for natural and artificial photosynthesis. Metalloporphyrins are of interest to scientists who seek to convert solar energy into fuel by splitting water to generate hydrogen or converting carbon dioxide into sugars or other types of fuels.

    Specifically, the research team examined how the metalloporphyrin changes after it is excited with a laser. They discovered an extremely short-lived “transient state” that lasted only a few hundred femtoseconds before the molecule relaxed into a lower energy state.

    “Although we had previously captured the molecular structure of a longer-lived state, the structure of this transient state eluded our detection because its lifetime was too short,” Chen said.

    When the laser pulse hits the molecule, an electron from the outer ring moves into the nickel metal center. This creates a charge imbalance, which in turn creates an instability within the whole molecule. In short order, another electron from the nickel migrates back to the outer ring, and the excited electron falls back into the lower open orbital to take its place.

    “This first state appears and disappears so quickly, but it’s imperative for the development of things like solar fuels,” Chen said. “Ideally, we want to find ways to make this state last longer to enable the subsequent chemical processes that may lead to catalysis, but just being able to see that it is there in the first place is important.”

    The challenge, Chen said, is to prolong the lifetime of the excited state through the design of the metalloporphyrin molecule. “From this study, we gained knowledge of which molecular structural element, such as bond length and planarity of the ring, can influence the excited state property,” Chen said. “With these results we might be able to design a system to allow us to harvest much of the energy in the excited state.”

    A paper based on the research, “Ultrafast excited state relaxation of a metalloporphyrin revealed by femtosecond X-ray absorption spectroscopy,” was published in the June 10 online edition of the Journal of the American Chemical Society.

    The research was funded by the DOE’s Office of Science and by the National Institute of Health.

    See the full article here .

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    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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  • richardmitnick 7:39 pm on August 29, 2016 Permalink | Reply
    Tags: , SLAC LCLS,   

    From SLAC: “Poof! The Weird Case of the X-ray that Came Out Blank” 


    SLAC Lab

    August 29, 2016

    A ‘Nonlinear’ Effect that Seemingly Turns Materials Transparent is Seen for the First Time in X-rays at SLAC’s LCLS

    1
    An illustration shows what happens in a typical experiment with SLAC’s LCLS X-ray laser, top, versus what happened in this study with an especially intense X-ray pulse. Normally the X-ray pulses — which are shown coming in from the right — scatter off electrons in a sample and produce a pattern in a detector. But when researchers cranked up the intensity of the X-ray pulses, the pulses seemed to go straight through the sample, as if it were not there, and the pattern in the detector vanished. Two recent papers describe and explain this surprising result, which is due to a ‘nonlinear’ effect where particles of X-ray light team up to cause unexpected things to happen. (SLAC National Accelerator Laboratory)

    Imagine getting a medical X-ray that comes out blank – as if your bones had vanished. That’s what happened when scientists cranked up the intensity of the world’s first X-ray laser, at the Department of Energy’s SLAC National Accelerator Laboratory, to get a better look at a sample they were studying: The X-rays seemed to go right through it as if it were not there.

    This result was so weird that the leader of the experiment, SLAC Professor Joachim Stöhr, devoted the next three years to developing a theory that explains why it happened. Now his team has published a paper in Physical Review Letters describing the 2012 experiment for the first time.

    What they saw was a so-called nonlinear effect where more than one photon, or particle of X-ray light, enters a sample at the same time, and they team up to cause unexpected things to happen.

    “In this case, the X-rays wiggled electrons in the sample and made them emit a new beam of X-rays that was identical to the one that went in,” said Stöhr, who is an investigator with the Stanford Institute for Materials and Energy Sciences at SLAC. “It continued along the same path and hit a detector. So from the outside, it looked like a single beam went straight through and the sample was completely transparent.”

    This effect, called “stimulated scattering,” had never been seen in X-rays before. In fact, it took an extremely intense beam from SLAC’s Linac Coherent Light Source (LCLS), which is a billion times brighter than any X-ray source before it, to make this happen.

    SLAC/LCLS
    SLAC/LCLS

    A Milestone in Understanding How Light Interacts with Matter

    The observation is a milestone in the quest to understand how light interacts with matter, Stöhr said.

    “What will we do with it? I think we’re just starting to learn. This is a new phenomenon and I don’t want to speculate,” he said. “But it opens the door to controlling the electrons that are closest to the core of atoms ­– boosting them into higher orbitals, and driving them back down in a very controlled manner, and doing this over and over again.”

    Nonlinear optical effects are nothing new. They were discovered in the1960s with the invention of the laser – the first source of light so bright that it could send more than one photon into a sample at a time, triggering responses that seemed all out of proportion to the amount of light energy going in. Scientists use these effects to shift laser light to much higher energies and focus optical microscopes on much smaller objects than anyone had thought possible.

    The 2009 opening of LCLS as a DOE Office of Science User Facility introduced another fundamentally new tool, the X-ray free-electron laser, and scientists have spent a lot of time since then figuring out exactly what it can do. For instance, a SLAC-led team recently published [Nature Physics] the first report of nonlinear effects produced by its brilliant pulses.

    “The X-ray laser is really a quantum leap, the equivalent of going from a light bulb to an optical laser,” Stöhr said. “So it’s not just that you have more X-rays. The interaction of the X-rays with the sample is very different, and there are effects you could never see at other types of X-ray light sources.”

    “The X-ray laser is really a quantum leap, the equivalent of going from a light bulb to an optical laser,” Stöhr said. “So it’s not just that you have more X-rays. The interaction of the X-rays with the sample is very different, and there are effects you could never see at other types of X-ray light sources.”

    A Most Puzzling Result

    Stöhr stumbled on this latest discovery by accident. Then director of LCLS, he was working with Andreas Scherz, a SLAC staff scientist, who is now with the soon-to-open European XFEL in Hamburg, Germany, and Stanford graduate student Benny Wu to look at the fine structure of a common magnetic material used in data storage.

    To enhance the contrast of their image, they tuned the LCLS beam to a wavelength that would resonate with cobalt atoms in the sample and amplify the signal in their detector. The initial results looked great. So they turned up the intensity of the laser beam in the hope of making the images even sharper.

    That’s when the speckled pattern they’d been seeing in their detector went blank, as if the sample had disappeared.

    “We thought maybe we had missed the sample, so we checked the alignment and tried again,” Stöhr said. “But it kept happening. We knew this was strange – that there was something here that needed to be understood.”

    Stöhr is an experimentalist, not a theorist, but he was determined to find answers. He and Scherz dove deeply into the scientific literature. Meanwhile Wu finished his PhD thesis, which described the experiment and its unexpected result, and went on to a job in industry. But the team held off on publishing their experimental results in a scientific journal until they could explain what happened.

    Stöhr and Scherz published their explanation last fall in Physical Review Letters.

    “We are developing a whole new field of nonlinear X-ray science, and our study is just one building block in this field,” Stöhr said. “We are basically opening Pandora’s box, learning about all the different nonlinear effects, and eventually some of those will turn out to be more important than others.”

    The study included other collaborators from SLAC and Stanford, and was funded by the DOE Office of Science.

    See the full article here .

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  • richardmitnick 10:18 am on August 18, 2016 Permalink | Reply
    Tags: , New X-Ray Matter Interaction Observed at Ultra-High Intensity, SLAC LCLS,   

    From SLAC via DOE: “New X-Ray Matter Interaction Observed at Ultra-High Intensity” 


    SLAC Lab

    1

    Basic Energy Sciences

    Previously unobserved scattering shows unexpected sensitivity to bound electrons, providing new insights into x-ray interactions with matter and opening the door to new probes of matter.

    08.05.16
    David A. Reis
    Stanford PULSE Institute
    dreis@stanford.edu

    1
    Artistic rendering of an intense x-ray beam interacting with metallic beryllium. In the central part of the image, two photons (white lines) interact simultaneously with a single electron of one of the beryllium atoms (sphere), emitting the electron (red streak) and a single higher energy photon (wavy blue line), while leaving the atom in an excited state (purple-blue color). Researchers found that the spectrum of the emitted high-energy photon disagreed with theoretical predictions. Image courtesy of Joel Brehm.

    The Science

    For the first time, researchers explored an extremely rare, but fundamental, process, in which two packets of light called photons scatter simultaneously from a single electron—in this case, from individual atoms in a beryllium metal target. Using the extremely high intensity x-ray laser at the Linac Coherent Light Source, they found that the details of this process deviated dramatically from expectations based on the usual assumption that the electrons behaved as quasi-free in the x-ray interaction.

    SLAC/LCLS
    SLAC/LCLS

    The researchers explain this anomaly in terms of a new x-ray matter interaction that they predict to have unprecedented specificity for light elements, like beryllium.

    The Impact

    In addition to providing new fundamental insights about x-ray interactions, this discovery has broad implications for understanding and controlling the fastest processes in chemical reactivity and energy conversion. The work may lead to powerful new probe techniques at x-ray free electron laser facilities to provide fundamental understanding of ultrafast chemical processes.

    Summary

    The basis for atomic‐scale structure determination involves the scattering of single x‐ray photons, one at a time, from the electrons that make up all materials. Spatial resolution is achieved through a combination of the short wavelength of x-rays and the concentration of the electron density around the individual atoms. For x-ray interactions, these atomic electrons generally behave almost as if they were free. In special cases involving heavy atoms, researchers can achieve simultaneously a level of chemical specificity and spatial resolution, but this is not the case for the lighter atoms that are ubiquitous in most biological and energy-relevant materials. Thus, new methods to achieve chemical specificity for light atoms in structure determination would be revolutionary. In the current work, the researchers used the unprecedented x-ray intensity produced by the Linac Coherent Light Source x-ray laser to observe the concerted nonlinear Compton scattering of two identical hard x-ray photons from the light element beryllium to produce a single higher-energy photon. Not only did the researchers make the first observation of this fundamental process, they also observed an anomalously large shift toward longer wavelengths for the scattered photon. The large wavelength shift is indicative of an interaction that shows properties of scattering from bound (non-free) electrons, which implies that this process could be used as a chemically specific probe. Furthermore, because the nonlinear interaction requires the x-rays to coincide at precisely the same location in time and space, the mechanism is also applicable to studying the fastest processes involving electron motion in chemical reactivity and energy conversion.

    Funding

    This work was supported primarily by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (BES) and the Volkswagen Foundation. Portions of this research were carried out at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. Preparatory measurements were carried out at the Stanford Synchrotron Radiation Light Source (SSRL). Both LCLS and SSRL are Office of Science user facilities operated for the U.S. Department of Energy’s Office of Science by Stanford University.
    Publications

    M. Fuchs, et al., Anomalous nonlinear x-ray Compton scattering. Nature Physics 11, 964 (2015). [DOI: 10.1038/nphys3452]

    See the full article here .

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  • richardmitnick 9:21 pm on August 9, 2016 Permalink | Reply
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    From SLAC: “Perfection in Sight: SLAC Receives New Mirrors for X-ray Laser” 


    SLAC Lab

    August 1, 2016

    The Mirrors Only Differ by One Atom in Flatness From End to End

    1
    SLAC engineer Corey Hardin inspects one of the newly-arrived mirrors in a clean room facility. (SLAC National Accelerator Laboratory)

    2
    May Ling Ng, SLAC engineer, makes adjustments to the mirror restraints during a test of the holding system’s effect on mirror shape. These measurements are needed to maintain the flatness of the mirror within one atom over the entire one-meter length. (SLAC National Accelerator Laboratory)

    Scientists are installing new mirrors to improve the quality of the X-ray laser beam at the Department of Energy’s SLAC National Accelerator Laboratory.

    The meter-long mirrors are the ultimate in flatness, smooth to within the height of one atom or one-fifth of a nanometer.

    If Earth had the same surface, the hills and valleys would only vary by the width of a pencil, says Daniele Cocco, engineering physicist and head of the optics group at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility.

    SLAC LCLS Inside
    SLAC/LCLS

    Right now, the mirrors are stored in a clean room to avoid dust and prevent damage. Cocco and other engineers only handle the mirrors while wearing gowns, hairnets, masks and gloves. They’re testing the mirrors to see how they will respond to heat and mechanical stress while the beam is running. Both cause tiny deformations on the surface, and even changes as small as half a nanometer can cause big problems.

    Five of these mirrors will be installed in LCLS by the beginning of next year and available for experiments in summer 2017. The new arrivals will join the 12 flat and curved mirrors that currently steer and focus light at LCLS, which is almost one mile long. Eventually, the upgraded mirror system will have a total of 28 mirrors.

    This is the first time the mirrors have been replaced at LCLS. The original mirrors were installed in 2009, when the free-electron laser came online.

    As the laser strikes the mirrors, some degradation of the reflective surface occurs over time. Since the originals were built, there have been improvements in how the mirrors are made, and engineers also better understand how the mirrors can be tailored to the LCLS beam.

    When light hits the reflective surfaces, the photons slant toward a specific point. The X-rays are shaped to the need of the experiment, from a focal spot less than a micron in diameter to as wide as a few millimeters. The beam quality also must be preserved in order to reveal the state of molecules and atoms during a range of processes that occur in biology, chemistry, materials science, and energy.

    “Time is lost when a beam isn’t perfectly uniform, and you’re not able to find the perfect spot on the sample,” Cocco says. “With mirrors this precise, it’s much easier.”

    A Japanese optics company, JTEC Corporation, fabricates the mirrors for synchrotrons and other X-ray laser research facilities such as Japan’s Spring-8 Angstrom Compact Free-Electron Laser (SACLA) and the European X-ray Free-Electron Laser (EXFEL), located in Hamburg, Germany and due to come online in 2017.

    Each mirror is made from an individual silicon crystal, artificially grown in a lab. After the mirror is polished with conventional techniques, the company uses a process called elastic emission machining, where a jet of ultra-pure water containing fine particles removes any remaining imperfections atom by atom.

    Blemishes in the mirror can create imperfections in the X-ray beam.

    “These latest mirrors preserve the beam quality within 97 percent, and the manufacturing technology is continuing to get better,” Cocco says.

    With a coherent laser beam, such as the one at LCLS, photons traveling at fixed wavelengths have a specific relationship to each other.

    “It’s not random. The light propagates as a perfect wave,” Cocco says. “Even minimal bumps alter the properties of the beam, irreversibly destroying the perfection of the wavefront.”

    The light beam also travels over a long distance, which means any disruption can amplify.

    Two of the mirrors will be installed adjacent to the front end of the undulator hall at LCLS. The other three will be located 200 meters further down the beam line, in the X-ray transport tunnel between the near and far halls.

    The mirrors will also be able to handle the higher energy range of LCLS-II, the next generation of SLAC’s X-ray laser.

    SLAC LSLS II new
    SLAC/LCLS-II work at LBL

    1
    SLAC/LCLS-II work at FNAL

    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.
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