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  • richardmitnick 8:56 am on April 16, 2018 Permalink | Reply
    Tags: , Attosecond X-ray science, , , , SLAC LCLS, , 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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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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  • richardmitnick 3:52 pm on April 9, 2018 Permalink | Reply
    Tags: , , , SLAC LCLS, , Superconducting electron gun   

    From SLAC: “SLAC Produces First Electron Beam with Superconducting Electron Gun” 


    SLAC Lab

    1
    Image of the first electron beam (bright colors) produced with a superconducting electron gun at SLAC and analyzed with an energy spectrometer. The beam energy was more than a million electronvolts. (SLAC National Accelerator Laboratory)

    April 9, 2018
    Manuel Gnida

    Making a high-quality beam of high-energy electrons starts with an electron gun: It knocks electrons out of atoms with a laser beam so they can be accelerated to nearly the speed of light for experiments that explore nature’s fastest atomic processes.

    Now accelerator scientists at the Department of Energy’s SLAC National Accelerator Laboratory are testing a new type of electron gun for a future generation of instruments that take snapshots of the atomic world in never-before-seen quality and detail, with applications in chemistry, biology, energy and materials science.

    Unlike other electron sources at SLAC, the new one is superconducting: When chilled to extremely low temperatures, some of its key components conduct electricity with nearly 100 percent efficiency. This allows it to produce superior, almost continuous electron beams that will be needed for future high-energy X-ray lasers and ultrafast electron microscopes. The new superconducting electron gun recently produced its first beam of electrons at SLAC.

    “This is an important milestone,” says Xijie Wang, who leads the project. “The use of superconducting accelerator technology represents the beginning of a new era at the lab that will create unforeseen research opportunities, and will keep us at the forefront of science for decades to come.”

    2
    SLAC’s accelerator scientists are testing a superconducting electron gun (inside the large vessel at center), a new type of electron source that could be used in next-generation X-ray lasers and ultrafast electron microscopes. (Dawn Harmer/SLAC National Accelerator Laboratory)

    A Superior Electron Source

    At SLAC and other labs, beams of high-energy electrons are used as tools to precisely examine the atomic fabric of our world and to look at atomic-scale processes that occur within femtoseconds, or millionths of a billionth of a second. The beams are used directly, in instruments for ultrafast electron diffraction and microscopy (UED/UEM), or indirectly in X-ray lasers like SLAC’s Linac Coherent Light Source (LCLS), where the energy of the electron beam is converted into powerful X-ray light.

    SLAC LCLS

    In both approaches, the electrons are produced with an electron gun. It consists of a photocathode, where electrons are released when a metal is hit by a laser pulse; a hollow metal cavity, which accelerates the electrons with a radiofrequency field; and a magnetic lens that bundles the electrons into a tight beam.

    Conventional electron guns use cavities made of normal-conducting metals like copper. But the new device’s cavity is made of niobium, which becomes superconducting at temperatures close to absolute zero. Several groups around the world are actively pursuing the superconducting technology for next-generation particle accelerators and X-ray lasers.

    “Superconducting electron guns have the potential to outperform current guns,” says accelerator physicist Theodore Vecchione, coordinator of the SLAC project. “For instance, while the electron gun that’s being installed as part of the future LCLS-II will generate electron pulses at an extremely high repetition rate, the superconducting gun should be able to produce similar pulses at four times higher beam energy.

    SLAC/LCLS II projected view

    It should also be able to achieve twice the beam acceleration over a given distance, producing a tighter beam of electrons with extraordinary average brightness.”

    3
    SLAC schematic of superconducting electron gun

    LCLS-II will already use superconducting cryomodules to bring electrons up to speed, which will allow the X-ray laser to fire 8,000 times faster after the upgrade. A superconducting electron gun could be ready for a future high-energy upgrade that would further enhance its scientific potential.

    “In addition to advancing X-ray science, the superconducting technology could also turn into an electron source for the UED/UEM techniques we’re developing,” says SLAC accelerator physicist Renkai Li. “It would further improve the quality of atomic-level images and movies we’re able to capture now.”

    A Top R&D Priority

    The SLAC team is testing a superconducting gun that was originally built for a project at the University of Wisconsin, Madison. About two years ago, the DOE relocated the gun to SLAC, asking the lab to recommission it for R&D work in the field of future electron sources.

    “There is a lot of excitement at the lab and the DOE about the opportunity to develop the superconducting technology into something that will drive future applications that require powerful electron beams,” says Bruce Dunham, associate lab director for SLAC’s Accelerator Directorate. “It’s very exciting to see the new gun produce its first electron beam, as it represents the very first step toward that future.”

    Over the past few months, the team installed the gun at SLAC’s Next Linear Collider Test Accelerator (NLCTA) facility and built an experimental setup with diagnostics needed to analyze the generated electron beam. “This successful effort involved many different groups around the lab, including people working on lasers, metrology, vacuum and controls,” says Keith Jobe, the NLCTA facility manager. “We’re also grateful to Bob Legg and other members of the original Wisconsin team, who were very helpful in getting this effort underway here.”

    Now that the team has demonstrated the superconducting gun is working and capable of producing electron beams with energies above a million electronvolts, they are planning their next steps. They first want to make a number of upgrades to improve the gun’s performance, including an overhaul of its refrigeration system. Then, they will be ready to push the technology to higher beam energies that could pave the way for future applications.

    The project is funded by the DOE Office of Science. LCLS is a DOE Office of Science user facility.

    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 4:14 pm on April 4, 2018 Permalink | Reply
    Tags: , , SLAC LCLS, , Tick Tock on the ‘Attoclock:’ Tracking X-Ray Laser Pulses at Record Speeds,   

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


    SLAC Lab

    April 4, 2018
    Amanda Solliday
    Angela Anderson

    1
    In this illustration, ultrashort X-ray pulses (pink) at the Linac Coherent Light Source ionize neon gas at the center of a ring of detectors.

    SLAC/LCLS

    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. (Terry Anderson / SLAC National Accelerator Laboratory)

    When it comes to making molecular movies, producing the world’s fastest X-ray pulses is only half the battle. A new technique reveals details about the timing and energy of pulses that are less than a millionth of a billionth of a second long, which can be used to probe nature’s processes at this amazingly fast attosecond timescale.

    To catch chemistry in action, scientists at the Department of Energy’s SLAC National Accelerator Laboratory use the shortest possible flashes of X-ray light to create “molecular movies” that capture the motions of atoms in chemical reactions and reveal new details about the most fundamental processes in nature.

    Future experiments at the Linac Coherent Light Source (LCLS), SLAC’s X-ray free-electron laser, will use pulses that last just attoseconds (billionths of a billionth of a second). Such experiments will be even more powerful because they’ll be able to detect the motions of electrons within molecules during chemical reactions. However, to design such ultrafast experiments, researchers need meticulous measurements of the X-ray pulses so they can use that information to interpret the data they collect on the samples they study.

    Now an international team, including SLAC scientists, has created an X-ray “attoclock” that lets them analyze X-ray pulses on the attosecond timescale of electron motions.

    “Using this method, we can resolve details of the pulses in the attosecond domain for the first time,” says Ryan Coffee, a senior scientist at LCLS and the Stanford PULSE Institute and a principal investigator on the team. “This paves the way for X-ray free-electron laser science at a timescale that is key to understanding physical chemistry.”

    The team’s research was published in Nature Photonics on March 5.

    Timekeeping in Attoseconds

    2
    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. (Frank Scholz & Jens Buck / DESY)

    The term “attoclock” was coined by Swiss physicist Ursula Keller, who first demonstrated a technique to study attosecond processes with circularly polarized light 10 years ago. However, the LCLS version is the first one designed to measure individual X-ray pulses, one by one.

    It consists of a ring of detectors arranged like numbers on the face of a clock. When an X-ray pulse hits a target at the center of the clock, it knocks electrons out of the target’s atoms. Those electrons are hit by circularly polarized laser light that whirls the electrons around the ring before they land on one of the detectors. The position of that detector – the number on the clock face – tells scientists how much energy the X-ray pulse contained and when exactly it hit the target.

    “It’s like reading a watch,” Coffee says. “An electron may strike a detector positioned at one o’clock or three o’clock or anywhere around the clock face. We can tell from where it hits exactly when it was generated by the X-ray pulse.”

    In an experiment designed to test the technique, the researchers hit neon gas with an attosecond X-ray pulse and then read which of the 16 detectors arrayed around the attoclock the freed electrons hit.

    “In coming up with this technique, we combined ideas from different fields,” says principal investigator Wolfram Helml, then a Marie Curie research fellow at SLAC and the Technical University of Munich and now at the Ludwig-Maximilian University of Munich. “For our purposes, it just made sense to combine the circularly polarized light used in the original attoclock with a ring-shaped detector that has been used in other kinds of experiments.”

    Finding the True Colors

    The technique will be especially important for pump-probe experiments, in which a molecule is first excited with a “pump” pulse and then analyzed by a second “probe” pulse to see how it reacted.

    As short as they are, these pulses can contain many different colors or wavelengths. “The color can also vary widely from pulse to pulse, and our technique can sift through the pulses, finding those that are interesting for the experiment,” Coffee says, noting the importance that such sifting will have for the data deluge expected when an upgrade to the X-ray laser, LCLS-II, comes online a couple years from now.

    SLAC/LCLS II projected view

    With pulses that arrive up to a million times per second, LCLS-II will produce as much data in a few minutes as LCLS currently collects in a month.

    “For instance, only a certain color may excite a molecule when it is ‘pumped,’” Helml said. “With the attoclock we can see what part of the pulse is actually exciting the molecule because we know exactly when particular colors of light arrive. This lets us pinpoint more precisely when changes occur in the molecule as a result of the interaction with light.”

    What’s more, scientists can potentially excite individual elements in separate parts of the molecule at the same time using different colors of X-rays.

    “With this technique we could look within a single molecule at the interplay between atoms. For example, what’s going on with an oxygen atom and how might that affect the chemical environment surrounding a nearby nitrogen atom?” Helml says. “With that level of detail, we can discern completely new chemical behavior.”

    Progress in Motion

    The attoclock team is now working on a proposal to build more refined detectors.

    “With the next detector, we are aiming to precisely identify a broader spectrum of energies,” Coffee says. “This will be an important feature for our upgraded X-ray laser, LCLS-II, which will produce pulses with an even wider energy range and more multi-color flexibility than our current machine.”

    This is one of several ideas being tested at SLAC to give scientists detailed information about attosecond pulses. Two other teams are building similar systems with different types of detectors, including one at LCLS and PULSE that recently published a study in Optics Express.

    The international team on the Nature Photonics study also included scientists from Deutsches Elektronen-Synchrotron (DESY) and the European X-ray Free-electron Laser (Eu-XFEL), both in Germany, who also provided the unique ring-shaped detector; University of Kassel in Germany; University of Gothenburg in Sweden; University of Bern in Switzerland; University of Colorado at Boulder; University of the Basque Country in Spain; and Lomonosov Moscow State University in Russia.

    LCLS is a DOE Office of Science user facility.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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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 2:08 pm on February 1, 2018 Permalink | Reply
    Tags: , Magnetic Trick Triples the Power of SLAC’s X-Ray Laser, , SLAC LCLS,   

    From SLAC: “Magnetic Trick Triples the Power of SLAC’s X-Ray Laser” 


    SLAC Lab

    January 31, 2018
    Mark Shwartz

    The new technique will allow researchers to observe ultrafast chemical processes previously undetectable at the atomic scale.

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to triple the amount of power generated by the world’s most powerful X-ray laser. The new technique, developed at SLAC’s Linac Coherent Light Source (LCLS), will enable researchers to observe the atomic structure of molecules and ultrafast chemical processes that were previously undetectable at the atomic scale.

    SLAC/LCLS

    1
    From left, SLAC’s Yauntao Ding and Marc Guetg discuss their work at the lab’s Accelerator Control Room where beams that feed the X-ray laser are monitored.(Dawn Harmer/SLAC)

    The results, published in a Jan. 3 study in Physical Review Letters (PRL), will help address long-standing mysteries about photosynthesis and other fundamental chemical processes in biology, medicine and materials science, according to the researchers.

    “LCLS produces the world’s most powerful X-ray pulses, which scientists use to create movies of atoms and molecules in action,” said Marc Guetg, a research associate at SLAC and lead author of the PRL study. “Our new technique triples the power of these short pulses, enabling higher contrast.”

    2
    The research team, from left: back row, Yuantao Ding, Matt Gibbs, Nora Norvell, Alex Saad, Uwe Bergmann, Zhirong Huang; front row, Marc Guetg and Timothy Maxwell. (Dawn Harmer/SLAC)

    Magnetic Wiggles

    The X-ray pulses at LCLS are generated by feeding beams of high-energy electrons through a long array of magnets. The electrons, which travel near the speed of light, wiggle back and forth as they pass along the magnets. This wiggling motion causes the electrons to emit powerful X-ray pulses that can be used for nanoscale imaging.

    “When you image an atomic structure, you have a race going on,” said study co-author Uwe Bergmann, a distinguished staff scientist at SLAC. “You need an X-ray pulse strong enough to get a good image, but that pulse will destroy the very structure that you’re trying to measure. However, if the pulse is short enough, about 10 femtoseconds, you can outrun the damage. You can take the snapshot before the patient feels the pain.”

    One femtosecond is one millionth of a billionth of a second. Generating high-power X-ray pulses that last only 10 femtoseconds has been a major challenge.

    “The trick is to have the electrons packed together as tightly as possible when they start wiggling around,” Guetg explained. “It’s difficult to do, because electrons don’t like each other. They’re all negatively charged, so they repel one another. It’s a battle. We’re constantly trying to force them to together, and they’re constantly trying to move apart.”

    To win the battle, Guetg and his SLAC colleagues used a special combination of magnets designed to bring the electrons closer together before they start emitting X-rays.

    “One problem when you compress electrons is that they start kicking each other,” Guetg said. “As a result, the electron beam gets tilted, which impairs the light production and therefore the power of the X-ray pulses.”

    In previous studies, Guetg had theorized that correcting the tilt would compress the electrons and produce shorter, more powerful bursts of X-rays.

    “The electron beam is shaped like a banana,” said co-author Zhirong Huang, an associate professor at SLAC and at Stanford University. “We corrected the curvature of the banana to make it a straight, pencil-like beam.”

    Dramatic Results

    The results were dramatic. Straightening the beam increased the power of the X-ray pulses by 300 percent, and each pulse lasted only 10 femtoseconds.

    “In an ingenious way, Marc and his colleagues were able to compress these electrons like a pancake before they drifted apart,” Bergmann said. “That allowed them to create very short X-ray pulses that are about 1,000 times more powerful than if you focused all the sunlight that hits the Earth onto one square centimeter. It’s an incredible power.”

    Bergmann has already used the new technique to create nanoscale images of transition metals such as manganese, which is essential for splitting water to form oxygen molecules (O2) during photosynthesis.

    “By pushing the frontier of laser science we can now see more and hopefully learn more about chemical reactions and molecular processes,” he said.

    The SLAC team hopes to build on their results in future experiments.

    “We want to make the new technique operational and robust so that anyone can use it,” Huang said. “We also want to keep improving the power with this technique and others. I would not call this the final limit.”

    The study is co-authored by SLAC staff scientists Alberto Lutman, Yuantao Ding, Timothy Maxwell and Franz-Josef Decker. Financial support was provided by the Department of Energy’s Office of Science. LCLS is a DOE Office of Science user facility.

    See the full article here .

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    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 4:30 pm on December 19, 2017 Permalink | Reply
    Tags: , , CERN Large Hadron Collider, , , , , Large Electron-Positron Collider, , , , SLAC LCLS, ,   

    From Symmetry: “Machine evolution” 

    Symmetry Mag
    Symmetry

    12/19/17
    Amanda Solliday

    1
    Courtesy of SLAC

    Planning the next big science machine requires consideration of both the current landscape and the distant future.

    Around the world, there’s an ecosystem of large particle accelerators where physicists gather to study the most intricate details of matter.

    These accelerators are engineering marvels. From planning to construction to operation to retirement, their lifespans stretch across decades.

    But to get the most out of their investments of talent and funding, laboratories planning such huge projects have to think even longer-term: What could these projects become in their next lives?

    The following examples show how some of the world’s big physics machines have evolved to stay at the forefront of science and technology.

    Same tunnel, new collisions

    Before CERN research center in Geneva, Switzerland, had its Large Hadron Collider, it had the Large Electron-Positron Collider. LEP was the largest electron-positron collider ever built, occupying a nearly 17-mile circular tunnel dug beneath the border of Switzerland and France. The tunnel took three years to completely excavate and build.

    The first particle beam traveled around the LEP circular collider in 1989. Long before then, the international group of CERN physicists and engineers were already thinking about what CERN’s next machine could be.

    “People were saying, ‘Well, if we do build LEP, then we should make it compatible with the [then-proposed] Large Hadron Collider,’” says James Gillies, a senior communications advisor and member of the strategic planning and evaluation unit at CERN. “If you want to have a future facility, you often have to engage the people who just finished designing one machine to start thinking about the next one.”

    LEP’s designers chose an energy for the collider that would mass-produce Z bosons, fundamental particles discovered by earlier experiments at CERN. The LHC would be a step up from LEP, reaching higher energies that scientists hoped could produce the Higgs boson. In the 1960s, theorists proposed the Higgs as a way to explain the origin of the mass of elementary particles. And the new machine to look for it could be built in the same 17-mile tunnel excavated for LEP.

    Engineers began working on the LHC while LEP was still running. The new machine required enlargements to underground areas—it needed bigger detectors and new experimental halls.

    “That was challenging because these caverns are huge. As they were being excavated, the pressure on the LEP tunnel was reduced and the LEP beamline needed realignment,” Gillies says. “So you constantly had to realign the collider for experiments as you were digging.”

    After LEP reached its highest energy in 2000, it was switched off. The tunnel remained the same, says Gillies, but there were many other changes. Only one of the LEP detectors, DELPHI, remains underground at CERN as a visitors’ point.

    In 2012, LHC scientists announced the discovery of the long-sought Higgs boson. The LHC is planned to continue running until at least 2035, gradually increasing the intensity of its particle collisions. The research and development into the accelerator’s successor is already happening. The possibilities include a higher energy LHC, a compact linear collider or an even larger circular collider.

    2

    Large Electron-Positron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 1989
    Link to LEP Timeline: Timeline
    Courtesy of CERN

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Large Hadron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 2008
    Link to LHC Timeline: Timeline
    Courtesy of CERN

    High-powered science
    Decades before the LHC came into existence, a suburb of Chicago was home to the most powerful collider in the world: the Tevatron. A series of accelerators at Fermi National Accelerator Laboratory boosted protons and antiprotons to nearly the speed of light. In the final, 4-mile Tevatron ring, the particles reached record energy levels, and more than 1000 superconducting magnets steered them into collisions. Physicists used the Tevatron to make the first direct measurement of the tau neutrino and to discover the top quark, the last observed lepton and quark, respectively, in the Standard Model.

    The Tevatron shut down in 2011 after the LHC came up to speed, but the rest of Fermilab’s accelerator infrastructure was still hard at work powering research in particle physics—particularly on the abundant, mysterious and difficult-to-detect neutrino.

    Starting in 1999, a brand-new, 2-mile circular accelerator called the Main Injector was added to the Fermilab complex to increase the number of Tevatron particle collisions tenfold. It was joined in its tunnel by the Recycler, a permanent magnet ring that stored and cooled antiprotons.

    But before the Main Injector was even completed, scientists had identified a second purpose: producing powerful beams of neutrinos for experiments in Illinois and 500 miles away in Minnesota.

    FNAL/NOvA experiment map

    By 2005, the proton beam circulating in the Main Injector was doing double duty: sending ever-more-intense beams to the Tevatron collider and smashing into a target to produce neutrinos. Following the shutdown of the Tevatron, the Recycler itself was recycled to increase the proton beam power for neutrino research.

    “I’m still amazed at how we are able to use the Recycler. It can be difficult to transition if a machine wasn’t originally built for that purpose,” says Ioanis Kourbanis, the head of the Main Injector department at Fermilab.

    Fermilab’s high-energy neutrino beam is already the most intense in the world, but the laboratory plans to enhance it with future improvements to the Main Injector and the Recycler, and to build a brand-new neutrino beamline.

    Neutrinos almost never interact with matter, so they can pass straight through the Earth on their way to detectors onsite and others several hundred miles away. Scientists hope to learn more about neutrinos and their possible role in shaping our early universe.

    The new beamline will be part of the Long-Baseline Neutrino Facility, which will send neutrinos 800 miles underground to the massive, mile-deep detectors of the Deep Underground Neutrino Experiment.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    Scientists from around the world will use the DUNE data to answer questions about neutrinos, thanks to the repurposed pieces of the Fermilab accelerator complex.

    5

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Tevatron
    Location: Fermilab—Batavia, Illinois
    First beam: 1983
    Link to Tevatron Timeline: Timeline
    Courtesy of Fermilab

    6

    Neutrinos at the Main Injector (NuMI) beam
    Location: Fermilab—Batavia, Illinois
    First beam: 2004
    Link to Fermilab Timeline: Timeline
    Courtesy of Fermilab

    A monster accelerator

    When physicists first came up with the idea to build a two-mile linear accelerator at what is now called SLAC National Accelerator Laboratory, managed by Stanford University, they called it “Project M” for “Monster.” Engineers began building it from hand-drawn designs. Once completed, the machine was able to accelerate electrons to near the speed of light, producing its first particle beam in May 1966.

    SLAC Campus

    The accelerator’s scientific purpose has gone through several iterations of particle physics experiments over the decades, from fixed-target experiments to the Stanford Linear Collider (the only electron-positron linear collider ever built) to an injector for a circular collider, the Positron-Electron Project.

    These experiments led to the discovery that protons are made of quarks, the first evidence that the charm quark existed (through observations of the J/psi particle, co-discovered with researchers at MIT) and the discovery of the tau lepton.

    In 2009, the lab used the accelerator as the backbone for a different type of science machine—an X-ray free-electron laser, the Linac Coherent Light Source.

    “Looking around, SLAC was the only place in the world with a linear accelerator capable of driving a free-electron laser,” says Claudio Pellegrini, a distinguished professor emeritus of physics at the University of California, Los Angeles and a visiting scientist and consulting professor at SLAC. Pellegrini first proposed the idea to transform SLAC’s linear accelerator.

    The new machine, a DOE Office of Science user facility, would be the world’s first laser of its kind that could produce extremely bright hard X-rays, the high-energy X-rays that let scientists take snapshots of atoms and molecules.

    “Much of the physics and many of the tools learned and developed during the operation of the Stanford Linear Collider were directly applicable to the free electron laser,” says Lia Merminga, head of the accelerator directorate at SLAC. “This was a big factor in the LCLS being commissioned in record time. Without the Stanford Linear Collider experience, this significant body of work would have to be reinvented and reproduced almost from scratch.”

    Little about the accelerator itself needed to change. But to create a free-electron laser, scientists needed to design a new part: an electron gun, a device that generates electrons to be injected into the accelerator. A collaboration of several national labs and UCLA created a new type of electron gun for LCLS, while other national labs helped build undulators, a series of magnets that would wiggle the electrons to create X-rays.

    LCLS used only the last third of SLAC’s original linear accelerator. In part of the remaining section, scientists are developing plasma wakefield and other new particle acceleration techniques.

    For the X-ray laser’s next iteration, LCLS-II, scientists are aiming for an even brighter laser that will fire 1 million pulses per second, allowing them to observe rare and exceptionally transient events.

    SLAC/LCLS II

    To do this, they will need to replace the original copper structures with superconducting technology. The technology is derived from designs for a large International Linear Collider [ILC] proposed to be built in Japan.

    ILC schematic

    “I’m in awe of the foresight of the original builders of SLAC’s linear accelerator,” Merminga adds. “We’ve been able to do so much with this machine, and the end is not yet in sight.”

    7

    Fixed target and collider experiments

    Location: SLAC—Menlo Park, California
    First beam: 1966
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC

    8

    Linac Coherent Light Source
    Location: SLAC—Menlo Park, California
    First beam: 2009
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:40 pm on December 18, 2017 Permalink | Reply
    Tags: , , Major Technology Developments Boost LCLS X-Ray Laser’s Discovery Power, , SLAC LCLS,   

    From SLAC: “Major Technology Developments Boost LCLS X-Ray Laser’s Discovery Power” 


    SLAC Lab

    December 18, 2017
    Manuel Gnida

    1
    Smart computer programs improve the efficiency of X-ray laser operations and optimizations, allowing increased experimental time and potentially leading to new types of experiments. (Terry Anderson/SLAC National Accelerator Laboratory)

    Innovations at SLAC, including the world’s shortest X-ray flashes, ultra-high-speed pulse trains and smart computer controls, promise to take ultrafast X-ray science to a whole new level.

    Accelerator experts at the Department of Energy’s SLAC National Accelerator Laboratory are developing ways to make the most powerful X-ray laser better than ever. They have created the world’s shortest X-ray pulses for capturing the motions of electrons, as well as ultra-high-speed trains of X-ray pulses for “filming” atomic motion, and have developed “smart” computer programs that maximize precious experimental time.

    With its X-rays a billion times brighter than those available before, SLAC’s Linac Coherent Light Source (LCLS) has already revolutionized the field of ultrafast science and has opened new avenues for research in chemistry, biology and materials science. The new developments enhance the X-ray laser’s capabilities even further.

    SLAC/LCLS

    “Creating new capabilities for LCLS is a very important ongoing effort at SLAC,” said Axel Brachmann, head of the Linac and FEL Division of the lab’s Accelerator Directorate, at the 2017 SSRL/LCLS Users’ Meeting in September, where some of these developments were presented. “Our engineers and scientists are working hard to push the limits of what’s technologically possible and to make sure that SLAC stays a world leader in X-ray science.”

    Snapshots in Billionths of a Billionth of a Second

    3
    Two methods independently invented by scientists in SLAC’s Accelerator Directorate have produced the world’s first attosecond hard X-ray laser pulses at the lab’s LCLS facility. In one method, the shapes of electron bunches used to generate X-rays were manipulated with a radiofrequency field so that part of each bunch (dense area on the left) emits X-ray pulses with shorter-than-ever pulse lengths. (Yuantao Ding/SLAC National Accelerator Laboratory)

    LCLS’s discovery power is packed into extremely bright flashes of X-ray light, each lasting only a few femtoseconds – millionths of a billionth of a second. Like a strobe light that freezes motions too fast to see with the naked eye, these flashes capture images of atomic nuclei rapidly jiggling around in molecules and materials. But researchers would like to go further and film the even faster motions of an atom’s electrons.

    “These ultrafast motions are very fundamental because they set the stage for all the slower processes,” says staff scientist Yuantao Ding. “However, they occur in less than a femtosecond, and we need a faster ‘camera’ to capture them.”

    Two SLAC teams, led by Ding and fellow accelerator physicist Agostino Marinelli, have now made an important step in that direction. They demonstrated two independent methods for the generation of X-ray pulses of a few hundred attoseconds, or billionths of a billionth of a second, setting a record for X-ray lasers.

    Both groups manipulated the tightly packed bunches of electrons that fly through a special set of magnets, called an undulator, to generate LCLS X-ray pulses. They tweaked the bunches so only part of each bunch emitted X-ray laser light – resulting in a much shorter pulse length.

    “This is a major step forward, and actually uses relatively simple methods of generating attosecond pulses of X-rays with relatively high energy,” Marinelli says. “To take this even further, LCLS users want to use softer X-rays to allow them to study an atom’s outer electrons, which are the ones involved in chemical reactions. It turns out creating soft X-ray attosecond pulses is a much more complex process.”

    That’s why Marinelli and others are working on a third method, called X-ray Laser-Enhanced Attosecond Pulses (XLEAP). In this approach the electron bunches interact with an infrared laser inside the undulator and are chopped up into thin slices. Simulations suggest that this method, which is currently being tested at LCLS, can produce soft X-ray pulses that are only 500 attoseconds long.

    New Ways of Filming Atoms with Multiple X-ray Flashes

    4
    This illustration shows how three X-ray pulses with different energies, or colors, are generated with the fresh-slice technique from a single electron bunch traversing three separate sections of a special magnet, called an undulator. (Greg Stewart/SLAC National Accelerator Laboratory)

    To make movies of ultrafast processes at LCLS, researchers use the pump-probe technique, in which they hit a sample with a “pump” pulse from a conventional laser to trigger an atomic response and then examine the response with a “probe” pulse from the X-ray laser. By varying the amount of time between the two pulses, they can create a stop-action movie that shows how the sample’s atomic structure changes over time.

    This works well as long as the process, such as the breaking of a chemical bond in a molecule, can be initiated with a conventional laser emitting visible, infrared or ultraviolet light. However, some reactions can only be set off by the higher energies of X-ray light pulses.

    In principle, these experiments could be done at LCLS now, but the time between pulses would limit studies to processes slower than 8 milliseconds. Even with the future LCLS-II upgrade, which will “fire” up to a million pulses per second, this limit would still be a microsecond. Therefore, accelerator physicists are inventing methods that generate ultra-high-speed trains of X-ray flashes for the exploration of much faster processes.

    “SLAC is testing and implementing a number of multi-pulse techniques for X-ray pump-probe experiments with soft and hard X-rays, such as the split-undulator, twin-bunch, fresh-slice and two-bucket schemes,” says staff scientist Alberto Lutman. “Together they cover a broad range of very short pulse delays – from zero delay, meaning the pump and probe X-ray pulses hit the sample at the same time, to delays of just a few femtoseconds, and then all the way to more than 100 nanoseconds between pulses.”

    Lutman is spearheading the development of the fresh-slice technique, in which the head, tail and center of a single electron bunch can produce separate X-ray pulses in separate sections of the undulator. “This is an extremely flexible method,” he says. “It lets us finely vary the delay between the pulses, and it also allows us to tweak the color and polarization of each X-ray pulse individually.”

    Experiments with pulses of multiple colors, or X-ray energies, can, for example, enhance details in studies of the 3-D atomic structures and functions of molecules, such as medically important proteins. The fresh-slice method has also the potential to boost the power of extremely short X-ray pulses, and it has been used in seeding techniques that improve X-ray laser performance by making its light less noisy.

    Most of the multi-pulse methods have been demonstrated for rapid sequences of two or three X-ray flashes, but the use of even more pulses is on the horizon. A team led by accelerator physicist Franz-Josef Decker is currently working on a technique that uses multiple laser pulses for the generation of trains of up to eight X-ray pulses. This would allow researchers to follow the complex evolution of how a material responds to high-pressure shocks, for example in the study of meteorite collisions.

    ‘Smart’ Control of a Complex Discovery Machine

    Underpinning all of the above research is the need to find new ways of running LCLS in the most efficient way so more experiments can be accommodated. The facility is one of only five hard X-ray lasers operating in the world, and access to it is extremely competitive. One path to increasing the amount of experimental time is to minimize the time spent tuning the machine to meet the needs of specific experiments.

    “Each year we spend many hours optimizing the machine, which involves tedious adjustments of a large number of LCLS magnets,” says SLAC staff scientist Daniel Ratner. “We want to automate this procedure to free time for the activities that actually require human involvement.”

    Until about a year ago, he says, all fine-tuning was done manually. Now it’s done with the aid of computers, which has already cut the optimization time in half. But the lab’s accelerator experts want to take automation to the next level by using a type of artificial intelligence known as “machine learning” – an approach where “smart” computer programs learn from past X-ray laser optimizations instead of repeating the same routine every time.

    “This will lead to significant additional time savings,” says accelerator physicist Joseph Duris, who leads the machine learning initiative of SLAC’s Accelerator Directorate. “Smarter optimization algorithms will also help us explore completely new LCLS configurations to prepare for future experiments.”

    Last but not least, machine learning will help the lab efficiently operate two complex X-ray lasers side by side when the LCLS-II upgrade is complete.

    Financial support for this research was provided by the DOE Office of Science. Parts of these projects are supported by DOE’s Laboratory Directed Research and Development (LDRD) Program. To enhance LCLS performance and create new capabilities, SLAC’s Accelerator Directorate partners with X-ray instrument scientists of the LCLS Directorate and other groups across the lab, as well as with many members of the LCLS user community. LCLS is a DOE Office of Science user facility.

    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 4:54 pm on December 10, 2017 Permalink | Reply
    Tags: , , , , Bridgmanite, , Could super-Earths host geology similar to Earth’s?, Exogeology, Institute of Laser Engineering Osaka University, Laboratoire d' Optique Appliquee Palaiseau France, National Ignition Facility at Lawrence Liver­more National Laboratory in California, , Sandia Z machine, SLAC LCLS   

    From SA: “The Labs That Forge Distant Planets Here on Earth” 

    Scientific American

    Scientific American

    December 10, 2017
    Shannon Hall

    1
    Could super-Earths such as the one depicted here host geology similar to Earth’s? Credit: NASA Ames, JPL-Caltech, T. Pyle

    Yingwei Fei and his colleagues had spent a month carefully crafting the three slivers of dense silicate—shiny and round, each sample was less than a millimetre thick. But in early November, it was time to say goodbye. Fei carefully packed the samples, plus a few back-ups, in foam and shipped them from Washington DC to Albuquerque, New Mexico. There, the Z Pulsed Power Facility at Sandia National Laboratories will soon send 26 million amps surging towards the slivers, zapping them, one by one, into dust.

    Sandia Z machine

    The Z machine can replicate the extreme conditions inside detonating nuclear weapons. But Fei, a high-pressure experimental geologist at the Carnegie Institution for Science’s Geophysical Laboratory in Washington DC, has a more otherworldly goal in mind: he hopes to explore how bridgmanite, a mineral found deep beneath Earth’s surface, would behave at the higher temperatures and pressures found inside larger rocky planets beyond the Solar System.

    The experiment is one small contribution to exogeology: a research area that is bringing astronomers, planetary scientists and geologists together to explore what exoplanets might look like, geologically speaking. For many scientists, exogeology is a natural extension of the quest to identify worlds that could support life. Already, astronomers have discovered thousands of exoplanets and collected some of their vital statistics, including their masses and radii. Those that orbit in the habitable, or ‘Goldilocks’, zone—a region around the host star that is temperate enough for water to exist in liquid form—are thought to be particularly life-friendly.

    But Earth has a lot more going for it than its size, mass and favourable orbit, says Cayman Unterborn, an exogeologist at Arizona State University in Tempe. Its churning molten core, for example, creates and sustains a magnetic field that shields the planet’s fragile atmosphere from the solar wind. And the motion of tectonic plates helps regulate global temperatures, by cycling carbon dioxide between rocks and the atmosphere. Exoplanet discoveries keep pouring in. But astronomers are “just now realizing, ‘Well wait, we want to understand these systems a lot more than just stamp collecting’”, Unterborn says. “Bringing geology into the mix is a natural factor.”

    Researchers are using simulations and experiments, such as Fei’s at the Z machine, to learn what kinds of exoplanet might have Earth-like geology. The work could help researchers prioritize which exoplanets to study.

    But the field faces several challenges, not least that mystery still surrounds much of Earth’s geology—such as how and when tectonic activity first began. “It’s a fundamental discovery that changed geology,” says Richard Carlson, a geochemist at the Carnegie Institution. “But we still don’t know why it works the way it does.” What’s more, confirming that an exoplanet actually boasts Earth-like geology could be difficult; astronomers rarely observe these planets directly, and if they do, the planet might be the size of a single pixel in their image.

    Even indirect evidence—or the smallest suggestion—of geological activity could give researchers a more complete picture of these distant worlds, and which ones are the best candidates to search for indications of life. “It’s like if you came across a giant crime scene with very little evidence,” says Sara Seager, an astrophysicist at the Massachusetts Institute of Technology in Cambridge. “You work your hardest to take what little evidence there was and try to piece it together somehow.”

    Turning outwards

    One of the most exciting targets of exoplanetary science has been super-Earths. These rocky planets—with as many as ten times Earth’s mass—have no parallel in the Solar System. But they are now known to be quite common in the Galaxy and, because many are fairly big, they could make easier targets for detailed observation than Earth-sized planets.

    Early studies of super-Earth geology, published about ten years ago, examined what these planets would look like if they were simply scaled-up versions of Earth. But the scorching-hot planet 55 Cancri e, first spotted in 2004, underscored the idea that super-Earths could be quite different. Observations in 2011 revealed the planet to have roughly twice Earth’s radius and a little more than eight times its mass, yielding an average density only marginally higher than Earth’s—and that presented a conundrum.

    If 55 Cancri e had an iron core and silicate mantle, like Earth, it should be more massive given its size. An ocean wrapped around the whole planet would bring 55 Cancri e’s density down to Earth-like levels. But the planet is too hot for water to survive for long; it orbits so close to its host star that the day-side temperature is roughly 2,500 kelvin.

    A resolution came in 2012, when Nikku Madhusudhan, an astronomer then at Yale University in New Haven, Connecticut, and his colleagues decided to take a fresh approach. Previous research had suggested that the planet’s host star has a much higher ratio of carbon to oxygen than the Sun. Stars and their planets are built from the same swirling disk of dust and gas, so it seemed fair to assume that 55 Cancri e would also be carbon-rich. When Madhusudhan accounted for this carbon in his model of the planet’s interior, it produced a match with the mass and radius of the world. “That was a revelation,” says Madhusudhan, now at the University of Cambridge, UK. And such a world would be truly alien. Madhusudhan suspects that its crust could be dominated by graphite; inside the planet, the pressure would probably crush vast amounts of the element into diamond. “It would look pretty radical compared with what we see in the Solar System,” he says.

    A planet made of diamond would fire up the imagination, although 55 Cancri e’s host star might not actually contain as much carbon as thought. Even if it did, astronomers caution against assuming that a planet’s composition matches that of its host star. Seager notes that this idea wouldn’t account well for the variety of planets in the Solar System. “At this point, it’s a reasonable inference, but I think it’s important to realize that it’s not iron-clad,” says Gregory Laughlin, an astronomer at Yale.

    Exoplanet-building

    Exogeologists have embraced this uncertainty, and are trying their best to pin down how distant worlds form and evolve. To get from a list of starting elements to geology, scientists need to know what minerals form, when they melt and how their density changes with pressure and temperature. Those data can be used to simulate how a planet develops from an undifferentiated, molten ball into a layered structure, with minerals forming—and sinking or floating—as the planet cools. “We can build up a mineralogical, let’s say, onion-skin model of what the planet would look like initially,” says Wim van Westrenen, a geologist at the Free University of Amsterdam. Then, he says, researchers can use numerical models to predict how that planet will evolve and whether the migration of materials will be enough to drive plate tectonics.

    To gather information to feed these models, geologists are starting to subject synthetic rocks to high temperatures and pressures to replicate an exoplanet’s innards—as Fei and his colleagues are doing. Although the goal of these experiments is new, the approach is not. For decades, experimental petrologists have built instruments to simulate the conditions of Earth’s interior, anywhere from a few centimetres below the surface to Earth’s core. Many use a device called a diamond anvil cell. This apparatus squeezes materials by pushing the blunted tips of two gem-quality diamonds together. While a sample is under pressure, a laser can be used to heat it. At the same time, experimentalists can bombard the mat­erial with X-rays to investigate its crystalline structure and explore how the material changes as it is pushed to high temperatures and pressures.

    Groups including Sang-Heon Dan Shim, a mineral physicist at Arizona State University, and his colleagues have used this process to squeeze carbon-rich samples that might reflect the composition of 55 Cancri e. The work has revealed how planets dominated by carbon-containing compounds called carbides might transport heat, and how they might differ from planets that, like Earth, are dominated by silicates.

    Carbon is not the only element of interest. Unterborn points to magnesium, silicon and iron as “the big three” that will affect a planet’s bulk structure, influencing how heat flows in the mantle and the relative size of the planet’s core—and so the presence of plate tectonics and a global magnetic field, respectively. Ratios of these elements vary widely in stars. The Sun has one magnesium atom for every silicon atom; in other stars, that ratio ranges from 0.5 to 2. The difference might seem small, but if the same ratios are present in planets, they could drastically affect geology.

    Most textbooks argue that magnesium-rich rocks would be softer than those containing high concentrations of silicon—so much so that walking on a magnesium-rich world might feel like walking on mud. Shim’s diamond-anvil-cell work on rocks with various magnesium-to-silicon ratios suggests these worlds could also boast deeper reservoirs of magma than a silicon-rich planet and, as a result, more catastrophic volcanoes. But Shim notes that other parameters, such as the concentration of water in minerals, must also be taken into account.

    High pressure

    With two diamonds, Shim can apply no more than 400 gigapascals of pressure, a little higher than the pressure in Earth’s core. To probe the interiors of super-Earths, he has turned to the world’s brightest X-ray laser: the Linac Coherent Light Source at SLAC National Accelerator Laboratory in Menlo Park, California.

    SLAC/LCLS

    The instrument can generate shocks inside the sample, producing pressures as high as 600 giga­pascals—enough to simulate the cores of planets twice as massive as Earth.

    Geologists are also using other large facilities to probe potential exoplanet formulations. The Z machine can reach 1,000 gigapascals—the condition expected inside planets nearly three times Earth’s mass. Laser facilities in Palaiseau, France, and Osaka, Japan, can reach a similar range.

    3
    Laboratoire d’ Optique Appliquee, Palaiseau, France

    4
    Institute of Laser Engineering, Osaka University

    And some researchers have turned to the National Ignition Facility at Lawrence Liver­more National Laboratory in California, which is used to study nuclear fusion and can subject samples to as much as 5,000 giga­pascals, the pressure of Jupiter’s deep interior.


    LLNL/NIF

    These experiments are still in their preliminary stages, as researchers compete for time at these facilities and slowly accumulate data on a variety of basic compounds.

    At the end of the day, exogeologists hope to find the right combination of elements to build exoplanets with Earth-like geologies. “I would like to identify the compositional Goldilocks zone,” says Wendy Panero, a geologist at the Ohio State University in Columbus. “What is the not-too-soft, not-too-stiff habitable zone for rock composition?”

    The answer might not be clear-cut. Even perfect knowledge of composition might not tell exogeologists much about the state of a planet. Earth, for example, did not host plate tectonics in its early history, and it is not expected to do so forever. And its neighbour Venus shows how widely planetary evolution can diverge. The planet’s mass, radius, composition and distance from the Sun are similar to those of Earth. But Earth supports life, whereas Venus, swaddled in a haze of carbon dioxide, is quite dead. Stephen Mojzsis, a geologist at the University of Colorado Boulder, suspects that the loss of plate tectonics on Earth will eventually cause it to resemble its super-heated sibling. “It’s inevitable,” he says. “We’re just not sure when that will happen.” So, although most early exoplanet models are focusing on composition, exogeologists might ultimately have to include additional factors such as billions of years of planetary evolution.

    Some expect that this work will help astronomers determine which planets to target in the search for life. If scientists know the conditions needed to sustain a magnetic field for billions of years, or the proportions of elements required to drive convection in the mantle, they could advise their colleagues to scrutinize the worlds that meet those criteria. Then astronomers could turn powerful telescopes, such as NASA’s James Webb Space Telescope, slated to launch in 2019, towards those planets to search their atmospheres for potential signatures of alien life.

    It might also be possible to spot geological activity from a distance. A transient spike in atmospheric sulfur, for example, might be indirect evidence of the presence of an active volcano. Changes in reflectivity as a planet rotates might hint at the presence of continents and oceans, which could also suggest tectonic activity.

    Already, there has been talk of a possible detection of volcanic activity—on 55 Cancri e.

    4
    55 Cancri e

    In 2016, Brice-Olivier Demory, an astronomer at the University of Bern, and his colleagues published the first heat map of the planet, created using NASA’s infrared Spitzer Space Telescope.

    4
    http://actualinfo.website/2016/04/02/astronomers-have-compiled-the-first-heat-map-of-super-earths/

    NASA/Spitzer Infrared Telescope

    The planet is tidally locked to its star, so one hemisphere is eternally bathed in sunlight and the other is dark. The planet should be hottest closest to the star, but Demory and his colleagues discovered that the hottest point seems to be offset. They posited that flowing lava is carrying heat away (although more recent work has argued that winds might be responsible instead).

    It’s clear that 55 Cancri e is no place for life. But other worlds may be much more inviting. Earlier this year, Unterborn completed a study that looked at more than 1,000 Sun-like stars. Using their compositions, he determined that one-third of those stars could host planets whose crust was dense enough to sink into the mantle—a process that might let plate tectonics thrive for billions of years.

    Although researchers are just the beginning to explore the geology of exoplanets, Carlson notes that the study of these worlds has already yielded a number of surprises, not least evidence of planets that seem to have undergone dramatic migrations from their original orbits. This discovery caused astronomers to rethink the Solar System’s evolution, and theorize that similar movements could have helped carry materials, such as water ice, to Earth. “I don’t think humans are anywhere near as imaginative and creative as nature is,” Carlson says. “So, understanding the diversity of what’s out there will just open our eyes to other possibilities. And it’s those other possibilities that will help us understand our situation better.”

    See the full article here .

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    STEM Icon

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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 10:55 pm on November 27, 2017 Permalink | Reply
    Tags: , , SLAC LCLS, SLAC-led Study Shows Potential for Efficiently Controlling 2-D Materials With Light,   

    From SLAC: “SLAC-led Study Shows Potential for Efficiently Controlling 2-D Materials With Light” 


    SLAC Lab

    November 27, 2017
    Manuel Gnida

    In experiments with the lab’s ultrafast ‘electron camera,’ laser light hitting a material is almost completely converted into nuclear vibrations, which are key to switching a material’s properties on and off for future electronics and other applications.

    1
    Simulation of a laser pulse’s effect on two layers of molybdenum diselenide. (Hiroyuki Kumazoe/USC)

    Materials that are only a few atomic layers thick have generated a lot of excitement in recent years. These 2-D materials can have intriguing properties, such as extraordinary mechanical strength and superior electrical and heat conductivity, and could benefit a number of next-generation applications, including flexible electronics, data storage devices, solar cells, light-emitting diodes and chemical catalysts. Researchers also think they may be able to customize the properties of these materials by using light pulses to rapidly switch them from one state, or phase, to another, for example from an insulating to a conducting state.

    However, the ability to do this depends on how efficiently the light’s energy is transferred to the material’s atomic nuclei. Now, a team led by researchers from the Department of Energy’s SLAC National Accelerator Laboratory has demonstrated for the first time that the energy transfer is very fast and extremely efficient.

    “Our data show that essentially all of the light energy gets converted into vibrations of the material’s atomic nuclei within a trillionth of a second,” says SLAC’s Ming-Fu Lin, the lead author of a study published Nov. 23 in Nature Communications. “This efficient energy conversion is crucial, because those nuclear motions can initiate what we call a phase transition in the material – a change that alters its properties.”

    The researchers looked at a sample made of two layers of molybdenum diselenide – a model system for 2-D materials that can potentially be switched from a semiconducting state to a metal state and vice versa. They first hit the sample with a very brief laser pulse and then observed how its energy spread into the material over time with SLAC’s ultrafast “electron camera” – an apparatus for ultrafast electron diffraction (UED) that uses a highly energetic electron beam to probe a sample’s atomic structure and nuclear motions.

    “UED is a powerful tool for studies of these very thin 2-D materials,” says SLAC staff scientist Xiaozhe Shen, a co-author of the paper. “The technique yields relatively strong signals, high spatial resolution, and it nicely complements X-ray laser studies in making movies of a material’s atomic structure.”

    Although the researchers didn’t see a phase transition in molybdenum diselenide, their results help them better understand the energy transfer from the laser light to the material.

    “It’s an important first step toward designing 2-D materials that we can control with light,” Lin says. “The next steps will be to find out if we can see light-induced phase transitions in other materials and if we can make materials whose properties we can alter in a controlled way by steering phase transitions in particular directions.”

    The results are also used for the validation of novel software developed by the Materials Genome Innovation for Computational Software (MAGICS) center, led by the University of Southern California, Los Angeles. Another MAGICS partner involved in the study was Rice University, where the 2-D material was synthesized.

    “Similar to biological genome projects that want to find out everything about the genomes of organisms, our goal is to learn everything about materials and to develop computational tools that allow us to make accurate predictions of material properties,” says SLAC’s Uwe Bergmann, the center’s associate director for validation and the principal investigator of the study. “MAGICS brings together researchers who develop advanced computer code, who take on the challenging synthesis of 2-D materials, and who provide the experimental data needed for testing the computer models. At SLAC, we’re doing UED experiments and ultrafast X-ray studies, but without the center’s team effort, this work wouldn’t be possible.”

    Experiments for this study were carried out by researchers from SLAC’s Linac Coherent Light Source (LCLS),

    SLAC/LCLS

    a DOE Office of Science User Facility; the Stanford PULSE Institute, which is jointly operated by SLAC and Stanford University; and the lab’s Accelerator Directorate. Samples came from Rice University, and computer simulations were done at USC. Additional MAGICS partners not involved in this study are DOE’s Lawrence Berkeley National Laboratory, the University of Missouri and the California Institute of Technology. The study was funded by the DOE Office of Science and the National Science Foundation.

    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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  • richardmitnick 10:04 am on November 22, 2017 Permalink | Reply
    Tags: , , Scientists Make First Observations of How a Meteor-Like Shock Turns Silica Into Glass, SLAC LCLS   

    From SLAC: “Scientists Make First Observations of How a Meteor-Like Shock Turns Silica Into Glass” 


    SLAC Lab

    November 16, 2017
    Julia Goldstein

    Research with SLAC’s X-ray laser simulates what happens when a meteor hits Earth’s crust. The results suggest that scientists studying impact sites have been overestimating the sizes of the meteors that made them.

    1
    Meteor Crater in Arizona, formed by a meteor impact 50,000 years ago, contains bitsof a hard, compressed form of silica called stishovite. (Nikolas_jkd/iStock).

    Studies at the Department of Energy’s SLAC National Accelerator Laboratory have made the first real-time observations of how silica – an abundant material in the Earth’s crust – easily transforms into a dense glass when hit with a massive shock wave like one generated from a meteor impact.

    The results imply that meteors hitting Earth and other celestial objects are smaller than originally thought. This new information will be important for modeling planetary body formation and interpreting evidence of impacts on the ground.

    The experiments took place at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility whose ultrafast pulses can reveal processes taking place in millionths of a billionth of a second with atomic resolution.

    SLAC/LCLS

    “We were able for the first time to really visualize from start to finish what happens in a material that makes up a major portion of the Earth’s crust,” said Arianna Gleason of the DOE’s Los Alamos National Laboratory (LANL), the principal investigator for the study, which was published Nov. 14 in Nature Communications.

    How Does Shocked Glass Get That Way?

    Scientists have long known that impacts from meteors convert silicates into a dense, amorphous phase known as shocked glass. The question is how this shocked glass forms.

    In the past, scientists have tried to estimate the amount of pressure needed to cause this transformation by examining debris from meteor impacts and squeezing mineral samples in pressure cells in the lab, but they were unable to observe the process as it unfolded.

    At LCLS, researchers can use an intense laser beam to create a shock wave that compresses a silica sample, and then use the X-ray laser to examine its response on a timescale of nanoseconds, or billionths of a second.

    A previous SLAC study, published in 2015, demonstrated that silica forms stishovite, a crystalline phase, within 10 nanoseconds of being hit by the initial laser pulse. That research showed that the transformation occurred much more rapidly than was previously believed. But the existence of debris from meteor impacts that is composed entirely of shocked glass suggests that stishovite may be a short-lived phase that can convert permanently to shocked glass after impact.

    Overturning Assumptions

    In the latest study, the scientists took advantage of the Matter in Extreme Conditions instrument at LCLS to generate shock waves that induced various peak pressures in silica samples. After sending the laser pulse, “We just watch what the silica does naturally,” said Gleason, who is the LANL Fredrick Reines Postdoctoral Fellow.

    Analysis of X-ray diffraction data taken at various intervals after peak pressure was reached showed that when the pressure is high enough, stishovite forms, but it then reverts to shocked glass. The diffraction data from the LCLS samples matched data from impact debris collected in the field.

    3
    This drawing depicts the process that turns silica into shocked glass after it’s hit with a shock wave like one from a meteor impact. At right, compression has transformed the silica into stishovite crystals. On the left, the compression has been released and the stishovite crystals have transformed into shocked glass. The LCLS X-ray laser beam recorded this process, which happens within 30 nanoseconds. (A.E. Gleason et al., Nature Communications)

    Scientists have previously assumed that peak pressures of roughly 40 gigapascals – equivalent to 400,000 times the atmospheric pressure around us – are required to create shocked glass from silica. But the results from this study suggest that the threshold is about 25 percent lower than that, and that stishovite then reverts to the shocked glass state due to thermal instability rather than higher pressure.

    “An impact event has a short timeline,” said Gleason, “making LCLS an ideal instrument for understanding the fundamental thermodynamics of glasses formed by impacts.” Gleason envisions using the MEC at LCLS to investigate other Earth-abundant minerals, such as feldspar, and to better understand the “rule book” for transformation processes.

    Gleason’s research is more broadly applicable to debris from other planets, such as meteorites from Mars that also contain shocked glass. Martian meteorites often contain trapped volatile compounds, such as water vapor and methane. No one understands how these compounds become locked inside meteorites or why they don’t escape, but continued work at LCLS could provide answers.

    In addition to LANL and SLAC, researchers contributing to this study came from the Stanford Institute for Materials and Energy Sciences (SIMES), the DOE’s Lawrence Livermore National Laboratory, the Center for High Pressure Science and Technology Advanced Research in Shanghai, the Carnegie Institution of Washington’s High Pressure Synergetic Consortium, Friedrich Schiller University Jena in Germany and Stanford University. Major funding came from the DOE Office of Science and the National Science Foundation. Part of the work was carried out at the Advanced Light Source, a DOE Office of Science User Facility at DOE’s Lawrence Berkeley National Laboratory.

    See the full article here .

    Please help promote STEM in your local schools.

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    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 5:10 pm on November 13, 2017 Permalink | Reply
    Tags: Elusive Atomic Deformations, , , Matter in Extreme Condition (MEC) experimental station at SLAC’s LCLS, SLAC LCLS, SLAC X-ray Laser Reveals How Extreme Shocks Deform a Metal’s Atomic Structure, The Tremendous Shock of a Tiny Recoil, , , When hit by a powerful shock wave materials can change their shape – a property known as plasticity – yet keep their lattice-like atomic structure   

    From SLAC: “SLAC X-ray Laser Reveals How Extreme Shocks Deform a Metal’s Atomic Structure” 


    SLAC Lab

    November 13, 2017
    Glennda Chui

    1
    This image depicts an experimental setup at SLAC’s Linac Coherent Light Source, where a tantalum sample is shocked by a laser and probed by an X-ray beam. The resulting diffraction patterns, collected by an array of detectors, show the material undergoes a particular type of plastic deformation called twinning. The background illustration shows a lattice structure that has created twins. (Ryan Chen/LLNL)

    SLAC/LCLS

    When hit by a powerful shock wave, materials can change their shape – a property known as plasticity – yet keep their lattice-like atomic structure. Now scientists have used the X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to see, for the first time, how a material’s atomic structure deforms when shocked by pressures nearly as extreme as the ones at the center of the Earth.

    The researchers said this new way of watching plastic deformation as it happens can help study a wide range of phenomena, such as meteor impacts, the effects of bullets and other penetrating projectiles and high-performance ceramics used in armor, as well as how to protect spacecraft from high-speed dust impacts and even how dust clouds form between the stars.

    The experiments took place at the Matter in Extreme Condition (MEC) experimental station at SLAC’s Linac Coherent Light Source (LCLS). They were led by Chris Wehrenberg, a physicist at the DOE’s Lawrence Livermore National Laboratory, and described in a recent paper in Nature.

    “People have been creating these really high-pressure states for decades, but what they didn’t know until MEC came online is exactly how these high pressures change materials – what drives the change and how the material deforms,” said SLAC staff scientist Bob Nagler, a co-author of the report.

    “LCLS is so powerful, with so many X-rays in such a short time, that it can interrogate how the material is changing while it is changing. The material changes in just one-tenth of a billionth of a second, and LCLS can deliver enough X-rays to capture information about those changes in a much shorter time that that.”

    Elusive Atomic Deformations

    The material they studied here was a thin foil made of tantalum, a blue-gray metallic element whose atoms are arranged in cubes. The team used a polycrystalline form of tantalum that is naturally textured so the orientation of these cubes varies little from place to place, making it easier to see certain types of disruptions from the shock.

    When this type of crystalline material is squeezed by a powerful shock, it can deform in two distinct ways: twinning, where small regions develop lattice structures that are the mirror images of the ones in surrounding areas, and slip deformation, where a section of the lattice shifts and the displacement spreads, like a propagating crack.

    But while these two mechanisms are fundamentally important in plasticity, it’s hard to observe them as a shock is happening. Previous research had studied shocked materials after the fact, as the material recovered, which introduced complications and led to conflicting interpretations.

    The Tremendous Shock of a Tiny Recoil

    In this experiment, the scientists shocked a piece of tantalum foil with a pulse from an optical laser. This vaporizes a small piece of the foil into a hot plasma that flies away from the surface. The recoil from this tiny plume creates tremendous pressures in the remaining foil – up to 300 gigapascals, which is three million times the atmospheric pressure around us and comparable to the 350-gigapascal pressure at the center of the Earth, Nagler said.

    While this was happening, researchers probed the state of the metal with X-ray laser pulses. The pulses are extremely short – only 50 femtoseconds, or millionths of a billionth of a second, long – and like a camera with a very fast shutter speed they can record the metal’s response in great detail.

    The X-rays bounce off the metal’s atoms and into a detector, where they create a “diffraction pattern” – a series of bright, concentric rings – that scientists analyze to determine the atomic structure of the sample. X-ray diffraction has been used for decades to discover the structures of materials, biomolecules and other samples and to observe how those structures change, but it’s only recently been used to study plasticity in shock-compressed materials, Wehrenberg said.

    And this time the researchers took the technique one step further: They analyzed not just the diffraction patterns, but also how the scattering signals were distributed inside individual diffraction rings and how their distribution changed over time. This deeper level of analysis revealed changes in the tantalum’s lattice orientation, or texture, taking place in about one-tenth of a billionth of a second. It also showed whether the lattice was undergoing twinning or slip over a wide range of shock pressures – right up to the point where the metal melts. The team discovered that as the pressure increased, the dominant type of deformation changed from twinning to slip deformation.

    Wehrenberg said the results of this study are directly applicable to Lawrence Livermore’s efforts to model both plasticity and tantalum at the molecular level.

    These experiments, he said, “are providing data that the models can be directly compared to for benchmarking or validation. In the future, we plan to coordinate these experimental efforts with related experiments on LLNL’s National Ignition Facility that study plasticity at even higher pressures.”

    In addition to LLNL and SLAC, researchers from the University of Oxford, the DOE’s Los Alamos National Laboratory and the University of York contributed to this study. Funding for the work at SLAC came from the DOE Office of Science. LCLS is a DOE Office of Science User Facility.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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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