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  • richardmitnick 12:41 pm on December 13, 2018 Permalink | Reply
    Tags: , , , , SLAC National Accelerator Laboratory, Tangled magnetic fields power cosmic particle accelerators   

    From SLAC National Accelerator Lab: “Tangled magnetic fields power cosmic particle accelerators” 

    From SLAC National Accelerator Lab

    December 13, 2018
    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    Written by Manuel Gnida

    SLAC scientists find a new way to explain how a black hole’s plasma jets boost particles to the highest energies observed in the universe. The results could also prove useful for fusion and accelerator research on Earth.

    Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe. That’s the result of a new computational study by researchers from the Department of Energy’s SLAC National Accelerator Laboratory, which simulated particle emissions from distant active galaxies.

    1
    SLAC researchers have found a new mechanism that could explain how plasma jets emerging from the center of active galaxies, like the one shown in this illustration, accelerate particles to extreme energies. Computer simulations (circled area) showed that tangled magnetic field lines create strong electric fields in the direction of the jets, leading to dense electric currents of high-energy particles streaming away from the galaxy. (Greg Stewart/SLAC National Accelerator Laboratory)

    At the core of these active galaxies, supermassive black holes launch high-speed jets of plasma – a hot, ionized gas – that shoot millions of light years into space. This process may be the source of cosmic rays with energies tens of millions of times higher than the energy unleashed in the most powerful manmade particle accelerator.

    “The mechanism that creates these extreme particle energies isn’t known yet,” said SLAC staff scientist Frederico Fiúza, the principal investigator of a new study that will publish tomorrow in Physical Review Letters. “But based on our simulations, we’re able to propose a new mechanism that can potentially explain how these cosmic particle accelerators work.”

    The results could also have implications for plasma and nuclear fusion research and the development of novel high-energy particle accelerators.


    These movies show how distortions of the helical magnetic field of a cosmic jet (center) generate a strong electric field in the jet direction (left). The electric field boosts the energy of charged particles, effectively creating a dense electric current along the jet (right). (arXiv:1810.05154v1)

    Simulating cosmic jets

    Researchers have long been fascinated by the violent processes that boost the energy of cosmic particles. For example, they’ve gathered evidence that shock waves from powerful star explosions could bring particles up to speed and send them across the universe.

    Scientists have also suggested that the main driving force for cosmic plasma jets could be magnetic energy released when magnetic field lines in plasmas break and reconnect in a different way – a process known as “magnetic reconnection.”

    However, the new study suggests a different mechanism that’s tied to the disruption of the helical magnetic field generated by the supermassive black hole spinning at the center of active galaxies.

    “We knew that these fields can become unstable,” said lead author Paulo Alves, a research associate working with Fiúza. “But what exactly happens when the magnetic fields become distorted, and could this process explain how particles gain tremendous energy in these jets? That’s what we wanted to find out in our study.”

    However, the new study suggests a different mechanism that’s tied to the disruption of the helical magnetic field generated by the supermassive black hole spinning at the center of active galaxies.

    “We knew that these fields can become unstable,” said lead author Paulo Alves, a research associate working with Fiúza. “But what exactly happens when the magnetic fields become distorted, and could this process explain how particles gain tremendous energy in these jets? That’s what we wanted to find out in our study.”

    2
    Composite image of the active galaxy Centaurus A, showing lobes and jets extending millions of light years into space. (Optical: ESO/WFI; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; X-ray: NASA/CXC/CfA/R.Kraft et al.)

    To do so, the researchers simulated the motions of up to 550 billion particles – a miniature version of a cosmic jet – on the Mira supercomputer at the Argonne Leadership Computing Facility (ALCF) at DOE’s Argonne National Laboratory.

    MIRA IBM Blue Gene Q supercomputer at the Argonne Leadership Computing Facility

    Then, they scaled up their results to cosmic dimensions and compared them to astrophysical observations.

    From tangled field lines to high-energy particles

    The simulations showed that when the helical magnetic field is strongly distorted, the magnetic field lines become highly tangled and a large electric field is produced inside the jet. This arrangement of electric and magnetic fields can, indeed, efficiently accelerate electrons and protons to extreme energies. While high-energy electrons radiate their energy away in the form of X-rays and gamma rays, protons can escape the jet into space and reach the Earth’s atmosphere as cosmic radiation.

    “We see that a large portion of the magnetic energy released in the process goes into high-energy particles, and the acceleration mechanism can explain both the high-energy radiation coming from active galaxies and the highest cosmic-ray energies observed,” Alves said.

    Roger Blandford, an expert in black hole physics and former director of the SLAC/Stanford University Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), who was not involved in the study, said, “This careful analysis identifies many surprising details of what happens under conditions thought to be present in distant jets, and may help explain some remarkable astrophysical observations.”

    3
    In simulations of a miniature version of a cosmic jet, SLAC researchers have found that when the jet’s helical magnetic field (left) is strongly distorted, the magnetic field lines become highly tangled (middle), producing a large electric field (right) inside the jet that can efficiently accelerate electrons and protons to extreme energies. (arXiv:1810.05154v1)

    Next, the researchers want to connect their work even more firmly with actual observations, for example by studying what makes the radiation from cosmic jets vary rapidly over time. They also intend to do lab research to determine if the same mechanism proposed in this study could also cause disruptions and particle acceleration in fusion plasmas.

    This work was also co-authored by Jonathan Zrake, a former Kavli Fellow at KIPAC, who is now at Columbia University. The project was supported by the DOE Office of Science through its Early Career Research Program and an ALCC award for simulations on the Mira high-performance computer. ALCF is a DOE Office of Science user facility.

    See the full article here .


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  • richardmitnick 1:50 pm on November 7, 2018 Permalink | Reply
    Tags: , , , , , , , Researchers create most complete high-res atomic movie of photosynthesis to date, SLAC National Accelerator Laboratory, ,   

    From SLAC National Accelerator Lab: “Researchers create most complete high-res atomic movie of photosynthesis to date” 

    From SLAC National Accelerator Lab

    November 7, 2018

    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    In a major step forward, SLAC’s X-ray laser captures all four stable states of the process that produces the oxygen we breathe, as well as fleeting steps in between. The work opens doors to understanding the past and creating a greener future.

    1
    Using SLAC’s X-ray laser, researchers have captured the most complete high-res atomic movie to date of Photosystem II, a key protein complex in plants, algae and cyanobacteria responsible for splitting water and producing the oxygen we breathe. (Gregory Stewart, SLAC National Accelerator Laboratory)

    Despite its role in shaping life as we know it, many aspects of photosynthesis remain a mystery. An international collaboration between scientists at SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory and several other institutions is working to change that. The researchers used SLAC’s Linac Coherent Light Source (LCLS) X-ray laser to capture the most complete and highest-resolution picture to date of Photosystem II, a key protein complex in plants, algae and cyanobacteria responsible for splitting water and producing the oxygen we breathe. The results were published in Nature today.

    SLAC/LCLS

    Explosion of life

    When Earth formed about 4.5 billion years ago, the planet’s landscape was almost nothing like what it is today. Junko Yano, one of the authors of the study and a senior scientist at Berkeley Lab, describes it as “hellish.” Meteors sizzled through a carbon dioxide-rich atmosphere and volcanoes flooded the surface with magmatic seas.

    Over the next 2.5 billion years, water vapor accumulating in the air started to rain down and form oceans where the very first life appeared in the form of single-celled organisms. But it wasn’t until one of those specks of life mutated and developed the ability to harness light from the sun and turn it into energy, releasing oxygen molecules from water in the process, that Earth started to evolve into the planet it is today. This process, oxygenic photosynthesis, is considered one of nature’s crown jewels and has remained relatively unchanged in the more than 2 billion years since it emerged.

    “This one reaction made us as we are, as the world. Molecule by molecule, the planet was slowly enriched until, about 540 million years ago, it exploded with life,” said co-author Uwe Bergmann, a distinguished staff scientist at SLAC. “When it comes to questions about where we come from, this is one of the biggest.”

    A greener future

    Photosystem II is the workhorse responsible for using sunlight to break water down into its atomic components, unlocking hydrogen and oxygen. Until recently, it had only been possible to measure pieces of this process at extremely low temperatures. In a previous paper, the researchers used a new method to observe two steps of this water-splitting cycle [Nature]at the temperature at which it occurs in nature.

    Now the team has imaged all four intermediate states of the process at natural temperature and the finest level of detail yet. They also captured, for the first time, transitional moments between two of the states, giving them a sequence of six images of the process.

    The goal of the project, said co-author Jan Kern, a scientist at Berkeley Lab, is to piece together an atomic movie using many frames from the entire process, including the elusive transient state at the end that bonds oxygen atoms from two water molecules to produce oxygen molecules.

    “Studying this system gives us an opportunity to see how metals and proteins work together and how light controls such kinds of reactions,” said Vittal Yachandra, one of the authors of the study and a senior scientist at Berkeley Lab who has been working on Photosystem II for more than 35 years. “In addition to opening a window on the past, a better understanding of Photosystem II could unlock the door to a greener future, providing us with inspiration for artificial photosynthetic systems that produce clean and renewable energy from sunlight and water.”

    Sample assembly line

    For their experiments, the researchers grow what Kern described as a “thick green slush” of cyanobacteria — the very same ancient organisms that first developed the ability to photosynthesize — in a large vat that is constantly illuminated. They then harvest the cells for their samples.

    At LCLS, the samples are zapped with ultrafast pulses of X-rays [Science] to collect both X-ray crystallography and spectroscopy data to map how electrons flow in the oxygen-evolving complex of photosystem II. In crystallography, researchers use the way a crystal sample scatters X-rays to map its structure; in spectroscopy, they excite the atoms in a material to uncover information about its chemistry. This approach, combined with a new assembly-line sample transportation system [Nature Methods], allowed the researchers to narrow down the proposed mechanisms put forward by the research community over the years.

    Mapping the process

    Previously, the researchers were able to determine the room-temperature structure of two of the states at a resolution of 2.25 angstroms; one angstrom is about the diameter of a hydrogen atom. This allowed them to see the position of the heavy metal atoms, but left some questions about the exact positions of the lighter atoms, like oxygen. In this paper, they were able to improve the resolution even further, to 2 angstroms, which enabled them to start seeing the position of lighter atoms more clearly, as well as draw a more detailed map of the chemical structure of the metal catalytic center in the complex where water is split.

    This center, called the oxygen-evolving complex, is a cluster of four manganese atoms and one calcium atom bridged with oxygen atoms. It cycles through the four stable oxidation states, S0-S3, when exposed to sunlight. On a baseball field, S0 would be the start of the game when a player on home base is ready to go to bat. S1-S3 would be players on first, second, and third. Every time a batter connects with a ball, or the complex absorbs a photon of sunlight, the player on the field advances one base. When the fourth ball is hit, the player slides into home, scoring a run or, in the case of Photosystem II, releasing breathable oxygen.

    The researchers were able to snap action shots of how the structure of the complex transformed at every base, which would not have been possible without their technique. A second set of data allowed them to map the exact position of the system in each image, confirming that they had in fact imaged the states they were aiming for.

    1
    In photosystem II, the water-splitting center cycles through four stable states, S0-S3. On a baseball field, S0 would be the start of the game when a batter on home base is ready to hit. S1-S3 would be players waiting on first, second, and third. The center gets bumped up to the next state every time it absorbs a photon of sunlight, just like how a player on the field advances one base every time a batter connects with a ball. When the fourth ball is hit, the player slides into home, scoring a run or, in the case of Photosystem II, releasing the oxygen we breathe. (Gregory Stewart/SLAC National Accelerator Laboratory)

    Sliding into home

    But there are many other things going on throughout this process, as well as moments between states when the player is making a break for the next base, that are a bit harder to catch. One of the most significant aspects of this paper, Yano said, is that they were able to image two moments in between S2 and S3. In upcoming experiments, the researchers hope to use the same technique to image more of these in-between states, including the mad dash for home — the transient state, or S4, where two atoms of oxygen bond together — providing information about the chemistry of the reaction that is vital to mimicking this process in artificial systems.

    “The entire cycle takes nearly two milliseconds to complete,” Kern said. “Our dream is to capture 50-microsecond steps throughout the full cycle, each of them with the highest resolution possible, to create this atomic movie of the entire process.”

    Although they still have a way to go, the researchers said that these results provide a path forward, both in unveiling the mysteries of how photosynthesis works and in offering a blueprint for artificial sources of renewable energy.

    “It’s been a learning process,” said SLAC scientist and co-author Roberto Alonso-Mori. “Over the last seven years we’ve worked with our collaborators to reinvent key aspects of our techniques. We’ve been slowly chipping away at this question and these results are a big step forward.”

    In addition to SLAC and Berkeley Lab, the collaboration includes researchers from Umeå University, Uppsala University, Humboldt University of Berlin, the University of California, Berkeley, the University of California, San Francisco and the Diamond Light Source.

    Key components of this work were carried out at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), Berkeley Lab’s Advanced Light Source (ALS) and Argonne National Laboratory’s Advanced Photon Source (APS). LCLS, SSRL, APS, and ALS are DOE Office of Science user facilities. This work was supported by the DOE Office of Science and the National Institutes of Health, among other funding agencies.

    SLAC/SSRL

    LBNL/ALS

    ANL APS

    See the full article here .


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    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 11:39 am on November 7, 2018 Permalink | Reply
    Tags: Acoustic phonons, , , , Dancing atoms in perovskite materials provide insight into how solar cells work, , , SLAC National Accelerator Laboratory,   

    From SLAC National Accelerator Lab: “Dancing atoms in perovskite materials provide insight into how solar cells work” 

    From SLAC National Accelerator Lab

    November 6, 2018
    Ali Sundermier

    1
    When the researchers scattered neutrons off the perovskite material (red beam) they were able to measure the energy the neutrons lost or gained (white and blue lines). Using this information, they were able to see the structure and motion of the atoms and molecules within the material (arrangement of blue and purple spheres). (Greg Stewart/SLAC National Accelerator Laboratory)

    A new study is a step forward in understanding why perovskite materials work so well in energy devices and potentially leads the way toward a theorized “hot” technology that would significantly improve the efficiency of today’s solar cells.

    A closer look at materials that make up conventional solar cells reveals a nearly rigid arrangement of atoms with little movement. But in hybrid perovskites, a promising class of solar cell materials, the arrangements are more flexible and atoms dance wildly around, an effect that impacts the performance of the solar cells but has been difficult to measure.

    In a paper published in the PNAS, an international team of researchers led by the U.S. Department of Energy’s SLAC National Accelerator Laboratory has developed a new understanding of those wild dances and how they affect the functioning of perovskite materials. The results could explain why perovskite solar cells are so efficient and aid the quest to design hot-carrier solar cells, a theorized technology that would almost double the efficiency limits of conventional solar cells by converting more sunlight into usable electrical energy.

    Piece of the puzzle

    Perovskite solar cells, which can be produced at room temperature, offer a less expensive and potentially better performing alternative to conventional solar cell materials like silicon, which have to be manufactured at extremely high temperatures to eliminate defects. But a lack of understanding about what makes perovskite materials so efficient at converting sunlight into electricity has been a major hurdle to producing even higher efficiency perovskite solar cells.

    “It’s really only been over the last five or six years that people have developed this intense interest in solar perovskite materials,” says Mike Toney, a distinguished staff scientist at SLAC’s Stanford Synchrotron Radiation Light Source (SSRL) who led the study.

    SLAC/SSRL

    “As a consequence, a lot of the foundational knowledge about what makes the materials work is missing. In this research, we provided an important piece of this puzzle by showing what sets them apart from more conventional solar cell materials. This provides us with scientific underpinnings that will allow us to start engineering these materials in a rational way.”

    Keeping it hot

    When sunlight hits a solar cell, some of the energy can be used to kick electrons in the material up to higher energy states. These higher-energy electrons are funneled out of the material, producing electricity.

    But before this happens, a majority of the sun’s energy is lost to heat with some fraction also lost during the extraction of usable energy or due to inefficient light collection. In many conventional solar cells, such as those made with silicon, acoustic phonons – a sort of sound wave that propagates through material – are the primary way that this heat is carried through the material. The energy lost by the electron as heat limits the efficiency of the solar cell.

    In this study, theorists from the United Kingdom, led by Imperial College Professor Aron Walsh and electronic structure theorists Jonathan Skelton and Jarvist Frost, provided a theoretical framework for interpreting the experimental results. They predicted that acoustic phonons traveling through perovskites would have short lifetimes as a result of the flexible arrangements of dancing atoms and molecules in the material.

    Stanford chemists Hema Karunadasa and Ian Smith were able to grow the large, specialized single crystals that were essential for this work. With the help of Peter Gehring, a physicist at the NIST Center for Neutron Research, the team scattered neutrons off these perovskite single crystals in a way that allowed them to retrace the motion of the atoms and molecules within the material. This allowed them to precisely measure the lifetime of the acoustic phonons.

    The research team found that in perovskites, acoustic phonons are incredibly short-lived, surviving for only 10 to 20 trillionths of a second. Without these phonons trucking heat through the material, the electrons might stay hot and hold onto their energy as they’re pulled out of the material. Harnessing this effect could potentially lead to hot-carrier solar cells with efficiencies that are nearly twice as high as conventional solar cells.

    In addition, this phenomenon could explain how perovskite solar cells work so well despite the material being riddled with defects that would trap electrons and dampen performance in other materials.

    “Since phonons in perovskites don’t travel very far, they end up heating the area surrounding the electrons, which might provide the boost the electrons need to escape the traps and continue on their merry way,” Toney says.

    Transforming energy production

    To follow up on this study, researchers at the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory will investigate this phenomenon in more complicated perovskite materials that are shown to be more efficient in energy devices. They would like to figure out how changing the chemical make-up of the material affects acoustic phonon lifetimes.

    “We need to fundamentally transform our energy system as quickly as possible,” says Aryeh Gold-Parker, who co-led the study as a PhD student at Stanford University and SLAC. “As we move toward a low-carbon future, a very important piece is having cheap and efficient solar cells. The hope in perovskites is that they’ll lead to commercial solar panels that are more efficient and cheaper than the ones on the market today.”

    The research team also included scientists from NIST; the University of Bath and Kings College London, both in the UK; and Yonsei University in Korea.

    SSRL is a DOE Office of Science user facility. This work was supported by the DOE’s Office of Science and the Solar Energy Technologies Office; the Engineering and Physical Sciences Research Council; the Royal Society; and the Leverhulme Trust.

    See the full article here .


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    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 10:11 am on November 2, 2018 Permalink | Reply
    Tags: "In materials hit with light, , , individual atoms and vibrations take disorderly paths", , , SLAC National Accelerator Laboratory, ,   

    From SLAC Lab: “In materials hit with light, individual atoms and vibrations take disorderly paths” 


    From SLAC Lab

    November 1, 2018
    Glennda Chui

    1
    Two studies with a new X-ray laser technique reveal for the first time how individual atoms and vibrations respond when a material is hit with light. Their surprisingly unpredictable behavior has profound implications for designing and controlling materials. (Greg Stewart/SLAC National Accelerator Laboratory)

    Revealed for the first time by a new X-ray laser technique, their surprisingly unruly response has profound implications for designing and controlling materials.

    Hitting a material with laser light sends vibrations rippling through its latticework of atoms, and at the same time can nudge the lattice into a new configuration with potentially useful properties – turning an insulator into a metal, for instance.

    Until now, scientists assumed this all happened in a smooth, coordinated way. But two new studies show it doesn’t: When you look beyond the average response of atoms and vibrations to see what they do individually, the response, they found, is disorderly.

    Atoms don’t move smoothly into their new positions, like band members marching down a field; they stagger around like partiers leaving a bar at closing time.

    And laser-triggered vibrations don’t simply die out; they trigger smaller vibrations that trigger even smaller ones, spreading out their energy in the form of heat, like a river branching into a complex network of streams and rivulets.

    This unpredictable behavior at a tiny scale, measured for the first time with a new X-ray laser technique at the Department of Energy’s SLAC National Accelerator Laboratory, will have to be taken into account from now on when studying and designing new materials, the researchers said – especially quantum materials with potential applications in sensors, smart windows, energy storage and conversion and super-efficient electrical conductors.

    Two separate international teams, including researchers at SLAC and Stanford University who developed the technique, reported the results of their experiments Sept. 20 in Physical Review Letters and today in Science.

    “The disorder we found is very strong, which means we have to rethink how we study all of these materials that we thought were behaving in a uniform way,” said Simon Wall, an associate professor at the Institute of Photonic Sciences in Barcelona and one of three leaders of the study reported in Science. “If our ultimate goal is to control the behavior of these materials so we can switch them back and forth from one phase to another, it’s much harder to control the drunken choir than the marching band.”

    Lifting the haze

    The classic way to determine the atomic structure of a molecule, whether from a manmade material or a human cell, is to hit it with X-rays, which bounce off and scatter into a detector. This creates a pattern of bright dots, called Bragg peaks, that can be used to reconstruct how its atoms are arranged.

    SLAC’s Linac Coherent Light Source (LCLS), with its super-bright and ultrafast X-ray laser pulses, has allowed scientists to determine atomic structures in ever more detail.

    SLAC/LCLS

    They can even take rapid-fire snapshots of chemical bonds breaking, for instance, and string them together to make “molecular movies.”

    About a dozen years ago, David Reis, a professor at SLAC and Stanford and investigator at the Stanford Institute for Materials and Energy Sciences (SIMES), wondered if a faint haze between the bright spots in the detector – 10,000 times weaker than those bright spots, and considered just background noise – could also contain important information about rapid changes in materials induced by laser pulses.

    He and SIMES scientist Mariano Trigo went on to develop a technique called “ultrafast diffuse scattering” that extracts information from the haze to get a more complete picture of what’s going on and when.

    The two new studies represent the first time the technique has been used to observe details of how energy dissipates in materials and how light triggers a transition from one phase, or state, of a material to another, said Reis, who along with Trigo is a co-author of both papers. These responses are interesting both for understanding the basic physics of materials and for developing applications that use light to switch the properties of materials on and off or convert heat to electricity, for instance.

    “It’s sort of like astronomers studying the night sky,” said Olivier Delaire, an associate professor at Duke University who helped lead one of the studies. “Previous studies could only see the brightest stars visible to the naked eye. But with the ultrabright and ultrafast X-ray pulses, we were able to see the faint and diffuse signals of the Milky Way galaxy between them.”

    Tiny bells and piano strings

    In the study published in Physical Review Letters, Reis and Trigo led a team that investigated vibrations called phonons that rattle the atomic lattice and spread heat through a material.

    The researchers knew going in that phonons triggered by laser pulses decay, releasing their energy throughout the atomic lattice. But where does all that energy go? Theorists proposed that each phonon must trigger other, smaller phonons, which vibrate at higher frequencies and are harder to detect and measure, but these had never been seen in an experiment.

    To study this process at LCLS, the team hit a thin film of bismuth with a pulse of optical laser light to set off phonons, followed by an X-ray laser pulse about 50 quadrillionths of a second later to record how the phonons evolved. The experiments were led by graduate student Tom Henighan and postdoctoral researcher Samuel Teitelbaum of the Stanford PULSE Institute.

    For the first time, Trigo said, they were able to observe and measure how the initial phonons distributed their energy over a wider area by triggering smaller vibrations. Each of those small vibrations emanated from a distinct patch of atoms, and the size of the patch – whether it contained 7 atoms, or 9, or 20 – determined the frequency of the vibration. It was much like how ringing a big bell sets smaller bells tinkling nearby, or how plucking a piano string sets other strings humming.

    “This is something we’ve been waiting years to be able to do, so we were excited,” Reis said. “It’s a measurement of something absolutely fundamental to modern solid-state physics, for everything from how heat flows in materials to even, in principle, how light-induced superconductivity emerges, and it could not have been done without an X-ray free-electron laser like LCLS.”

    A disorderly march

    The paper in Science describes LCLS experiments with vanadium dioxide, a well-studied material that can flip from being an insulator to an electrical conductor in just 100 quadrillionths of a second.

    Researchers already knew how to trigger this switch with very short, ultrafast pulses of laser light. But until now they could only observe the average response of the atoms, which seemed to shuffle into their new positions in an orderly way, said Delaire, who led the study with Wall and Trigo.

    The new round of diffuse scattering experiments at LCLS showed otherwise. By hitting the vanadium dioxide with an optical laser of just the right energy, the researchers were able to trigger a substantial rearrangement of the vanadium atoms. They did this more than 100 times per second while recording the movements of individual atoms with the LCLS X-ray laser. They discovered that each atom followed an independent, seemingly random path to its new lattice position. Computer simulations by Duke graduate student Shan Yang backed up that conclusion.

    “Our findings suggest that disorder may play an important role in some materials,” the team wrote in the Science paper. While this may complicate efforts to control the way materials shift from one phase to another, they added, “it could ultimately provide a new perspective on how to control matter,” and even suggest a new way to induce superconductivity with light.

    In a commentary accompanying the report in Science, Andrea Cavalleri of Oxford University and the Max Planck Institute for the Structure and Dynamics of Matter said the results imply that molecular movies of atoms changing position over time don’t paint a complete picture of the microscopic physics involved.

    He added, “More generally, it is clear from this work that x-ray free electron lasers are opening up far more than what was envisaged when these machines were being planned, forcing us to reevaluate many old notions taken for granted up to now.”

    The study published in PRL also involved researchers from Imperial College London; Tyndall National Institute in Ireland; and the University of Michigan, Ann Arbor. Preliminary measurements were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL). Major funding came from the DOE Office of Science.

    SLAC/SSRL

    The study published in Science also involved researchers at the Japan Synchrotron Radiation Research Institute and the DOE’s Oak Ridge National Laboratory. Calculations were performed using resources of the DOE’s National Energy Research Scientific Computing Center (NERSC), and computer simulations used resources of the Oak Ridge Leadership Computing Facility. Major funding came from the European Research Council under the European Union’s Horizon 2020 research and innovation program and from the DOE Office of Science.

    LCLS, SSRL and NERSC are DOE Office of Science user facilities.

    See the full article here .

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

    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 10:37 am on November 1, 2018 Permalink | Reply
    Tags: , , , , SLAC National Accelerator Laboratory, ,   

    From SLAC National Accelerator Lab: “Scientists make first detailed measurements of key factors related to high-temperature superconductivity” 

    From SLAC National Accelerator Lab

    October 31, 2018
    Glennda Chui

    1
    A new study reveals how coordinated motions of copper (red) and oxygen (grey) atoms in a high-temperature superconductor boost the superconducting strength of pairs of electrons (white glow), allowing the material to conduct electricity without any loss at much higher temperatures. The discovery opens a new path to engineering higher-temperature superconductors. (Greg Stewart/SLAC National Accelerator Laboratory)

    2
    An illustration depicts the repulsive energy (yellow flashes) generated by electrons in one layer of a cuprate material repelling electrons in the next layer. Theorists think this energy could play a critical role in creating the superconducting state, leading electrons to form a distinctive form of “sound wave” that could boost superconducting temperatures. Scientists have now observed and measured those sound waves for the first time. (Greg Stewart/SLAC National Accelerator Laboratory)

    In superconducting materials, electrons pair up and condense into a quantum state that carries electrical current with no loss. This usually happens at very low temperatures. Scientists have mounted an all-out effort to develop new types of superconductors that work at close to room temperature, which would save huge amounts of energy and open a new route for designing quantum electronics. To get there, they need to figure out what triggers this high-temperature form of superconductivity and how to make it happen on demand.

    Now, in independent studies reported in Science and Nature, scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University report two important advances: They measured collective vibrations of electrons for the first time and showed how collective interactions of the electrons with other factors appear to boost superconductivity.

    Carried out with different copper-based materials and with different cutting-edge techniques, the experiments lay out new approaches for investigating how unconventional superconductors operate.

    “Basically, what we’re trying to do is understand what makes a good superconductor,” said co-author Thomas Devereaux, a professor at SLAC and Stanford and director of SIMES, the Stanford Institute for Materials and Energy Sciences, whose investigators led both studies.

    “What are the ingredients that could give rise to superconductivity at temperatures well above what they are today?” he said. “These and other recent studies indicate that the atomic lattice plays an important role, giving us hope that we are gaining ground in answering that question.”

    The high-temperature puzzle

    Conventional superconductors were discovered in 1911, and scientists know how they work: Free-floating electrons are attracted to a material’s lattice of atoms, which has a positive charge, in a way that lets them pair up and flow as electric current with 100 percent efficiency. Today, superconducting technology is used in MRI machines, maglev trains and particle accelerators.

    But these superconductors work only when chilled to temperatures as cold as outer space. So when scientists discovered in 1986 that a family of copper-based materials known as cuprates can superconduct at much higher, although still quite chilly, temperatures, they were elated.

    The operating temperature of cuprates has been inching up ever since – the current record is about 120 degrees Celsius below the freezing point of water – as scientists explore a number of factors that could either boost or interfere with their superconductivity. But there’s still no consensus about how the cuprates function.

    “The key question is how can we make all these electrons, which very much behave as individuals and do not want to cooperate with others, condense into a collective state where all the parties participate and give rise to this remarkable collective behavior?” said Zhi-Xun Shen, a SLAC/Stanford professor and SIMES investigator who participated in both studies.

    Behind-the-scenes boost

    One of the new studies, at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), took a systematic look at how “doping” – adding a chemical that changes the density of electrons in a material – affects the superconductivity and other properties of a cuprate called Bi2212.

    SLAC/SSRL


    SLAC/SSRL

    Collaborating researchers at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan prepared samples of the material with slightly different levels of doping. Then a team led by SIMES researcher Yu He and SSRL staff scientist Makoto Hashimoto examined the samples at SSRL with angle-resolved photoemission spectroscopy, or ARPES. It uses a powerful beam of X-ray light to kick individual electrons out of a sample material so their momentum and energy can be measured. This reveals what the electrons in the material are doing.

    In this case, as the level of doping increased, the maximum superconducting temperature of the material peaked and fell off again, He said.

    The team focused in on samples with particularly robust superconducting properties. They discovered that three interwoven effects – interactions of electrons with each other, with lattice vibrations and with superconductivity itself – reinforce each other in a positive feedback loop when conditions are right, boosting superconductivity and raising the superconducting temperature of the material.

    Small changes in doping produced big changes in superconductivity and in the electrons’ interaction with lattice vibrations, Devereaux said. The next step is to figure out why this particular level of doping is so important.

    “One popular theory has been that rather than the atomic lattice being the source of the electron pairing, as in conventional superconductors, the electrons in high-temperature superconductors form some kind of conspiracy by themselves. This is called electronic correlation,” Yu He said. “For instance, if you had a room full of electrons, they would spread out. But if some of them demand more individual space, others will have to squeeze closer to accommodate them.”

    In this study, He said, “What we find is that the lattice has a behind-the-scenes role after all, and we may have overlooked an important ingredient for high-temperature superconductivity for the past three decades,” a conclusion that ties into the results of earlier research by the SIMES group Science.

    Electron ‘Sound Waves’

    The other study, performed at the European Synchrotron Radiation Facility (ESRF) in France, used a technique called resonant inelastic X-ray scattering, or RIXS, to observe the collective behavior of electrons in layered cuprates known as LCCO and NCCO.


    ESRF. Grenoble, France

    RIXS excites electrons deep inside atoms with X-rays, and then measures the light they give off as they settle back down into their original spots.

    In the past, most studies have focused only on the behavior of electrons within a single layer of cuprate material, where electrons are known to be much more mobile than they are between layers, said SIMES staff scientist Wei-Sheng Lee. He led the study with Matthias Hepting, who is now at the Max Planck Institute for Solid State Research in Germany.

    But in this case, the team wanted to test an idea raised by theorists – that the energy generated by electrons in one layer repelling electrons in the next one plays a critical role in forming the superconducting state.

    When excited by light, this repulsion energy leads electrons to form a distinctive sound wave known as an acoustic plasmon, which theorists predict could account for as much as 20 percent of the increase in superconducting temperature seen in cuprates.

    With the latest in RIXS technology, the SIMES team was able to observe and measure those acoustic plasmons.

    “Here we see for the first time how acoustic plasmons propagate through the whole lattice,” Lee said. “While this doesn’t settle the question of where the energy needed to form the superconducting state comes from, it does tell us that the layered structure itself affects how the electrons behave in a very profound way.”

    This observation sets the stage for future studies that manipulate the sound waves with light, for instance, in a way that enhances superconductivity, Lee said. The results are also relevant for developing future plasmonic technology, he said, with a range of applications from sensors to photonic and electronic devices for communications.

    SSRL is a DOE Office of Science user facility, and SIMES is a joint institute of SLAC and Stanford.

    In addition to researchers from SLAC, Stanford and AIST, the study carried out at SSRL involved scientists from University of Tokyo; University of California, Berkeley; and Lorentz Institute for Theoretical Physics in the Netherlands.

    The study conducted at ESRF also involved researchers from SSRL; Polytechnic University of Milan in Italy; ESRF; Binghamton University in New York; and the University of Maryland.

    Both studies were funded by the DOE Office of Science.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 4:56 pm on August 23, 2018 Permalink | Reply
    Tags: , How SLAC’s ‘electronics artists’ enable cutting-edge science, , , SLAC National Accelerator Laboratory,   

    From SLAC National Accelerator Lab: “How SLAC’s ‘electronics artists’ enable cutting-edge science” 

    From SLAC National Accelerator Lab

    August 23, 2018
    Manuel Gnida

    A team of electrical designers develops specialized microchips for a broad range of scientific applications, including X-ray science and particle physics.

    When Angelo Dragone talks about designing microchips for cutting-edge scientific applications at the Department of Energy’s SLAC National Accelerator Laboratory, it becomes immediately clear that it’s at least as much of an art form as it is research and engineering. Similar to the way painters follow an inspiration, carefully choose colors and place brush stroke after brush stroke on canvas, he says, electrical designers use their creative minds to develop the layout of a chip, draw electrical components and connect them to build complex circuitry.

    2
    This illustration shows the layout of an application-specific integrated circuit, or ASIC, at an imaginary art exhibition. Members of the Integrated Circuits Department of SLAC’s Technology Innovation Directorate artfully design ASICs for a wide range of scientific experiments. (Greg Stewart/SLAC National Accelerator Laboratory)

    3
    A production wafer of ASICs for an ePix10k X-ray camera. ASICs are cut from the wafer and assembled on carrier boards. (Dawn Harmer/SLAC National Accelerator Laboratory)

    Dragone leads a team of 12 design engineers who develop application-specific integrated circuits, or ASICs, for X-ray science, particle physics and other research areas at SLAC. Their custom chips are tailored to extract meaningful features from signals collected in the lab’s experiments and turn them into digital signals that can be further analyzed.

    Like the CPU in your computer at home, ASICs process information and are extremely complex, with a 100 million transistors combined on a single chip, Dragone says. “However, while commercial integrated circuits are designed to be good at many things for broad use in all kinds of applications, ASICs are optimized to excel in a specific application.”

    For SLAC applications this means, for example, that they perform well under harsh conditions, such as extreme temperatures at the South Pole and in space, as well as high levels of radiation in particle physics experiments. In addition, ultra-low-noise ASICs are designed to process signals that are extremely faint.

    Pietro Caragiulo, a senior member of Dragone’s team, says, “Every chip we make is specific to the particular environment in which it’s used. That makes our jobs very challenging and exciting at the same time.”

    From fundamental physics to self-driving cars

    Most of the team’s ASICs are for SLAC’s core research areas in photon science and particle physics. First and foremost, ASICs are the heart of the ePix series of high-performance X-ray cameras that take snapshots of materials’ atomic fabric with the Linac Coherent Light Source (LCLS) X-ray laser.

    SLAC/LCLS

    “In a way, these ASICs play the same role in processing image information as the chip in your cell phone camera, but they operate under conditions that are way beyond the specifications of off-the-shelf technology,” Caragiulo says. They are, for instance, sensitive enough to detect single X-ray photons, which is crucial when analyzing very weak signals. They also have extremely high spatial resolution and are extremely fast, allowing researchers to make movies of atomic processes and study chemistry, biology and materials science like never before.

    The engineers are now working on a new camera version for the LCLS-II upgrade of the X-ray laser, which will boost the machine’s frame rate from 120 to a million images per second and will pave the way for unprecedented studies that aim to develop transformative technologies, such as next-generation electronics, drugs and energy solutions.

    SLAC/LCLS II projected view

    “X-ray cameras are the eyes of the machine, and all their functionality is implemented in ASICs,” Caragiulo says. “However, there is no camera in the world right now that is able to handle information at LCLS-II rates.”

    4
    Exposed head of an ePix10k camera with prototype ASIC/sensors chips for X-ray science at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. (Dawn Harmer/SLAC National Accelerator Laboratory)

    In addition to X-ray applications at LCLS and the lab’s Stanford Synchrotron Radiation Lightsource (SSRL), ASICs are key components of particle physics experiments, such as the next-generation neutrino experiments nEXO and DUNE. The team is working on chips that will handle the data readout.

    SLAC SSRL PEP collider map


    SLAC/SSRL

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


    SURF DUNE LBNF Caverns at Sanford Lab

    “The particular challenge here is that these experiments operate at very low temperatures,” says Bojan Markovic, another senior member of Dragone’s team. nEXO will run at minus 170 degrees Fahrenheit and DUNE at an even chillier minus 300 degrees, which is far below the temperature specifications of commercial chips.

    Other challenges in particle physics include exposure to high particle radiation, for instance in the ATLAS detector at the Large Hadron Collider (LHC) at CERN in Europe.

    CERN/ATLAS detector

    “In the case of ATLAS we also want ASICs that support a large number of pixels to obtain the highest possible spatial resolution, which is needed to determine where exactly a particle interaction occurred in the detector,” Markovic says.

    SLAC’s ASICs can also be found in space. The Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope – a sensitive “eye” for the most energetic light in the universe – has 16,000 chips in nine different designs on board where they have been performing flawlessly for the past 10 years.

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    “We’re also expanding into areas that are beyond the research SLAC has traditionally been doing,” says Dragone whose Integrated Circuits Department is part of the Advanced Instrumentation for Research Division within the Technology Innovation Directorate that uses the lab’s core capabilities to foster technological advances. The design engineers are working with young companies to test their chips in a wide range of applications, including 3D sensing, the detection of explosives and driverless cars.

    5
    Members of the Integrated Circuits Department. From left: Faisal Abu-Nimeh, Camillo Tamma, Bojan Markovic, Angelo Dragone, Aseem Gupta, Aldo Pena Perez, Hussein Ali and Pietro Caragiulo. Not in the photo: Dieter Freytag, Lorenzo Rota and Umanath Kamath. (Dawn Harmer/SLAC National Accelerator Laboratory)

    A creative process

    But how exactly does the team develop a highly complex microchip and create its particular properties?

    It all starts with a discussion in which scientists explain their needs for a particular experiment. “Our job as creative designers is to come up with novel architectures that provide the best solutions,” Dragone says.

    After the requirements have been defined, the designers break the task down into smaller blocks. In the typical experimental scenario, a sensor detects a signal (like a particle passing through the detector) from which the ASIC extracts certain features (like the deposited charge or the time of the event) and converts them into digital signals which are then acquired and transported by an electronics board into a computer for analysis. The extraction block in the middle differs most from project to project and requires frequent modifications.

    Once the team has an idea for how they want to do these modifications, they use dedicated computer systems to design the electronic circuits blocks, carefully choosing components to balance size, power, speed, noise, cost, lifetime and other specifications. Circuit by circuit, they draw the entire chip – an intricate three-dimensional layout of millions of electronic components and connections between them – and keep validating the design through simulations along the way.

    6
    Left: Three ASICs for an ePix10k X-ray camera mounted on a carrier board. One ASIC has a prototype sensor bonded on top for tests with X-rays. Right: Zooming into an ASIC reveals its intricate three-dimensional network of 100 million transistors and the connections between them. (Greg Stewart/SLAC National Accelerator Laboratory)

    “The way we lay everything out is key to giving an ASIC certain properties,” Markovic says. “For example, the mechanical or electrical shielding we put around the ASIC components prepares the chip for high radiation levels.”

    The layout is sent to a foundry that fabricates a small-scale prototype, which is then tested at SLAC. Depending on the outcome of the tests, the layout is either modified or used to produce the final ASIC. Last but not least, Dragone’s team works with other groups in SLAC’s Technology Innovation Directorate that mate the ASICs with sensors and electronics boards.

    “The time it takes from the initial discussion to having a functional chip varies with the complexity of the ASIC and depends on whether we’re modifying an existing design or building a completely new one,” Caragiulo says. “The entire process can take a couple of years, with three or four designers working on it.”

    For the next few years, the main driver of ASICs development at SLAC is LCLS-II, which demands X-ray cameras that can snap images at unprecedented rates. Neutrino experiments and particle physics applications at the LHC will remain another focus, in addition to a continuing effort to expand into new fields and to work with start-ups.

    The future for ASICs is bright, Dragone says. “We’re seeing a general trend to more and more complex experiments, and we need to put more and more complexity into our integrated circuits,” he says. “ASICs really make these experiments possible, and future generations of experiments will always need them.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 4:32 pm on July 31, 2018 Permalink | Reply
    Tags: Accelerator on a chip, , , , SLAC National Accelerator Laboratory   

    From SLAC via NPR: “Physicists Go Small: Let’s Put A Particle Accelerator On A Chip” 

    NPR

    From National Public Radio (NPR)


    SLAC Lab

    July 18, 2018
    Joe Palca

    1
    An early prototype of the silicon-chip-sized particle accelerator that physicists at Stanford are working on. Eventually, miniature accelerators might have a role in radiating tumors, the scientists say. SLAC National Accelerator Laboratory

    When people think of particle accelerators, they tend to think of giant structures: tunnels many miles long that electrons and protons race through at tremendous speeds, packing enormous energy.

    But scientists in California think small is beautiful. They want to build an accelerator on semiconductor chips. An accelerator built that way won’t achieve the energy of its much larger cousins, but it could accelerate material research and revolutionize medical therapy.

    First of all, what is an accelerator?

    “An accelerator is a way to add energy to particles,” says Robert Byer, a physicist at Stanford University. Once you have those energetic particles, you can do things with them, like irradiate tumors or generate X-rays that scientists use to investigate new materials. An accelerator built this way would bring an accelerator’s usefulness within the reach of more researchers.

    Byer has been trying to shrink the size of particle accelerators for more than 40 years. His idea is to use lasers to add energy to electrons as they zip through a tiny channel in a semiconductor chip. Byer says this is a miniaturized version of what goes on in larger accelerators, but there are big challenges to doing this on such a small scale.

    “We need to focus the electrons,” Byer says. “We need to bunch them so they surf the wavelength of light right at the crest, so they get the maximum acceleration.”

    Byer and his colleagues are working on those challenges in a laboratory in the basement of the Spilker Engineering and Applied Sciences building on the Stanford campus. Byer took me on a tour there.

    We put on glasses to protect our eyes from the powerful laser light used in the pint-sized accelerator.

    2
    Lasers are key to adding the energy needed to accelerate the particles, and powerful lasers require powerful stop signs. This emergency shut-off button can quickly cut the electricity to the Stanford lab’s lasers. Courtesy of Dylan Black.

    A big red emergency shut-off button attached to a shelf suggests this is not equipment to trifle with.

    Peter Hommelhoff of the Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany says one of the big challenges is to keep the electrons in the accelerator traveling where you want them to.

    “The acceleration channel is very narrow, so you have to generate a very, very narrow electron beam that you can send through the channel,” Hommelhoff says.

    “It’s a little like threading an invisible needle,” says Dylan Black, a Stanford graduate student in physics.

    Testing their accelerator requires lasers and lenses and pumps scattered around benches in the lab, it takes up a fair amount of space. But this is just a prototype.

    Black points to a bright circle of light on a monitor’s screen.

    “That there is a picture of what the electron beam would look like if you put your eye right in front of the beam,” Black says.

    “Which I would not recommend,” interjects Ken Leedle, a research engineer working on the accelerator-on-a-chip project.

    I asked R. Joel England, a physicist at the SLAC National Accelerator Laboratory who has been working on the accelerator-on-a-chip project, how long it will be before the prototype turns into a working instrument.

    “Depending on how much progress gets made, I would say five to 10 years,” England says. England is enthusiastic about the promise of these small-scale accelerators.

    “One of the applications could be to take one of the fairly bulky, 10,000-pound accelerator devices that’s used in hospitals for radiation therapy and make that into something that’s chip-sized,” he says.

    In addition to saving huge costs and space, it might eventually be possible to insert a chip-sized accelerator into a patient’s body, where it could directly irradiate a tumor.

    Even though it may take a decade or more, Robert Byer is convinced smaller accelerators will become a reality. His isn’t the only lab working on the idea. And besides, he points out, new technologies often start out bulky. Take the first laser to come on the scene.

    “Early on, lasers were big — and they were inefficient and they took all the power and water in your building to operate them,” Byer says. “They got more and more efficient because we converted to semiconductor lasers and solid state lasers — and all of a sudden, lasers then became everywhere.”

    Even new mobile phones have lasers in them, Byer says.

    The day of the accelerator on a chip, he believes, is coming.

    See the full article here .

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

    Please help promote STEM in your local schools.

    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.

     
  • richardmitnick 5:55 pm on June 6, 2018 Permalink | Reply
    Tags: , Energy-Energy Correlation, , , SLAC National Accelerator Laboratory, ,   

    From Symmetry: “We’re going to need a bigger blackboard” 

    Symmetry Mag
    From Symmetry

    06/06/18
    Farrin Abbott
    Manuel Gnida

    1
    Farrin Abbott, SLAC National Accelerator Laboratory

    Watch SLAC theorist Lance Dixon write out a new formula that will contribute to a better understanding of certain particle collisions.

    Physicists on experiments at the Large Hadron Collider study the results of high-energy particle collisions, often searching for surprises that their formulas don’t predict. Finding such a surprise could lead to the discovery of new particles, properties or forces.

    One of the formulas they use to predict the outcome of collisions is the EEC, which stands for Energy-Energy Correlation. The EEC measures how much energy in the form of particles goes into two detectors placed at a specific angle to one another.

    A group including theorist Lance Dixon of the US Department of Energy’s SLAC National Accelerator Laboratory and former postdoc Hua Xing Zhu recently figured out the formula for the biggest correction to EEC in decades.

    It’s a formula their paper calls “remarkably simple.” For the video below, Dixon offered to write it down.

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:47 am on March 4, 2018 Permalink | Reply
    Tags: , , , , , JLab - Jefferson Lab, , , , , SLAC National Accelerator Laboratory, The Heavy Photon Search   

    From Symmetry: “First results from search for a dark light” 2017 But Important 

    Symmetry Mag
    Symmetry

    05/26/17 [Missed this one on first publication.]
    By Manuel Gnida

    1
    Chris Smith, SLAC National Accelerator Laboratory

    The Heavy Photon Search at Jefferson Lab is looking for a hypothetical particle from a hidden “dark sector.”


    JLab campus

    In 2015, a group of researchers installed a particle detector just half of a millimeter away from an extremely powerful electron beam. The detector could either start them on a new search for a hidden world of particles and forces called the “dark sector”—or its sensitive parts could burn up in the beam.

    Earlier this month, scientists presented the results from that very first test run at the Heavy Photon Search collaboration meeting at the US Department of Energy’s Thomas Jefferson National Accelerator Facility. To the scientists’ delight, the experiment is working flawlessly.

    2

    Dark sector particles could be the long-sought components of dark matter, the mysterious form of matter thought to be five times more abundant in the universe than regular matter. To be specific, HPS is looking for a dark-sector version of the photon, the elementary “particle of light” that carries the fundamental electromagnetic force in the Standard Model of particle physics.

    Analogously, the dark photon would be the carrier of a force between dark-sector particles. But unlike the regular photon, the dark photon would have mass. That’s why it’s also called the heavy photon.

    To search for dark photons, the HPS experiment uses a very intense, nearly continuous beam of highly energetic electrons from Jefferson Lab’s CEBAF accelerator.

    4
    Jefferson Lab’s CEBAF accelerator schematic

    When slammed into a tungsten target, the electrons radiate energy that could potentially produce the mystery particles. Dark photons are believed to quickly decay into pairs of electrons and their antiparticles, positrons, which leave tracks in the HPS detector.

    “Dark photons would show up as an anomaly in our data—a very narrow bump on a smooth background from other processes that produce electron-positron pairs,” says Omar Moreno from SLAC National Accelerator Laboratory, who led the analysis of the first data and presented the results at the collaboration meeting.

    The challenge is that, due to the large beam energy, the decay products are compressed very narrowly in beam direction. To catch them, the detector must be very close to the electron beam. But not too close—the smallest beam movements could make the beam swerve into the detector. Even if the beam doesn’t directly hit the HPS apparatus, electrons interacting in the target can scatter into the detector and cause unwanted signals.

    The HPS team implemented a number of precautions to make sure their detector could handle the potentially destructive beam conditions. They installed and carefully aligned a system to intercept any large beam motions, made the detector’s support structure movable to bring the detector close to the beam and measure the exact beam position, and installed a feedback system that would shut the beam down if its motions were too large. They also placed their whole setup in vacuum because interactions of the beam with gas molecules would create too much background. Finally, they cooled the detector to negative 30 degrees Fahrenheit to reduce the effects of radiation damage. These measures allowed the team to operate their experiment so close to the beam.

    “That’s maybe as close as anyone has ever come to such a particle beam,” says John Jaros, head of the HPS group at SLAC, which built the innermost part of the HPS detector, the Silicon Vertex Tracker. “So, it was fairly exciting when we gradually decreased the distance between the detector and the beam for the first time and saw that everything worked as planned. A large part of that success lies with the beautiful beams Jefferson Lab provided.”

    SLAC’s Mathew Graham, who oversees the HPS analysis group, says, “In addition to figuring out if we can actually do the experiment, the first run also helped us understand the background signals in the experiment and develop the data analysis tools we need for our search for dark photons.”

    So far, the team has seen no signs of dark photons. But to be fair, the data they analyzed came from just 1.7 days of accumulated running time. HPS collects data in short spurts when the CLAS experiment, which studies protons and neutrons using the same beam line, is not in use.

    A second part of the analysis is still ongoing: The researchers are also closely inspecting the exact location, or vertex, from which an electron-positron pair emerges.

    “If a dark photon lives long enough, it might make it out of the tungsten target where it was produced and travel some distance through the detector before it decays into an electron-positron pair,” Moreno says. The detector was specifically designed to observe such a signal.

    Jefferson Lab has approved the HPS project for a total of 180 days of experimental time. Slowly but surely, HPS scientists are finding chances to use it.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:53 pm on June 26, 2017 Permalink | Reply
    Tags: , BNL "science raft", , SLAC National Accelerator Laboratory   

    From BNL: “Brookhaven Lab Reaches Major Milestone for Large Synoptic Survey Telescope Project” 

    Brookhaven Lab

    June 26, 2017
    Stephanie Kossman
    skossman@bnl.gov
    (631) 344-8671, or

    Peter Genzer,
    genzer@bnl.gov
    (631) 344-3174

    1
    Paul O’Connor (left) and Bill Wahl (right) pictured with components of the science raft.

    Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have completed the first “science raft” for the Large Synoptic Survey Telescope (LSST), a massive telescope designed to capture images of the universe like never before. The raft is part of the sensor array that will make up the crucial camera segment of the telescope, and its completion is the first major milestone for Brookhaven’s role in the project.

    The LSST project is a collaborative effort among more than 30 institutions from around the globe, funded primarily by DOE’s Office of Science and the National Science Foundation. SLAC National Accelerator Lab is leading the overall DOE effort, and Brookhaven is leading the conceptualization, design, construction, and qualification of the digital sensory array, the “digital film” for LSST’s camera.


    LSST Camera, built at SLAC



    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    Now under construction on a mountaintop in Chile, LSST will capture an image of the entire sky in the southern hemisphere every three nights, allowing researchers to create a time-lapse movie of the universe. Its camera will have an unparalleled field of view and, coupled with the light gathering power of the telescope, LSST will have a far greater capacity to survey the sky than has ever been previously available.

    The 3,200 megapixel sensor array being developed at Brookhaven is what will enable LSST to capture this extraordinary view when it begins operations in 2023.

    “It’s the heart of the camera,” said Bill Wahl, Science Raft Subsystem Manager of the LSST project at Brookhaven Lab. “What we’re doing here at Brookhaven represents years of great work by many talented scientists and engineers, which will lead to a collection of images that has never been seen before by anyone. It’s an exciting time for the project and especially for the Lab.”

    LSST’s scientists have designed a grid composed of more than 200 sensors, divided into 21 modules called science rafts. Each raft can function as a camera on its own but, when combined, they will stitch together a complete image of the visible sky. After years of design and construction, the first raft was qualified for use in the LSST camera in late May 2017. Brookhaven is now scheduled to construct approximately one raft per month.

    “Completion of the first raft is a big stepping stone,” said Paul O’Connor, Senior Scientist at Brookhaven Lab’s Instrumentation Division. Scientists at Brookhaven have successfully captured high-fidelity images using the newly completed raft, confirming the functionality of its design.

    Brookhaven began its LSST research and development program in 2003, with construction starting in 2014. In the time leading up to this milestone, an entire production facility, along with production and tracking software, needed to be created. During the past three years, Brookhaven and its vendors have been tackling the painstaking task of constructing these incredibly precise imaging arrays.

    The science raft “is an object that is tricky enough to build alone, but it also has to operate perfectly when in a vacuum and cooled to -100° Celsius,” O’Connor said. Cooling the rafts improves the camera’s sensitivity; however, it also causes parts to contract, making it increasingly complicated to design the rafts precisely.

    Ultimately, even with these challenges, the first raft was completed on time and the full digital sensor array is on track to be delivered to Chile by the end of 2019.

    Once operational in the Andes Mountains, LSST will serve nearly every subset of the astrophysics community. It is estimated that LSST will find tens of millions of asteroids in our solar system, in addition to offering new information about the creation of our galaxy.

    The main interest of the DOE in supporting the development of the LSST camera, however, is to investigate dark energy and dark matter – two anomalies that have baffled astrophysicists for decades.


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    “This is what a lot of people would say is the most pressing question of fundamental physics,” O’Connor said. “The nature of dark energy and dark matter don’t fit into the rest of physics.”

    Scientists intend to use LSST to infer the spatial distribution of dark matter by looking at the way its gravitational force bends light from luminous matter (matter in the universe that emits light).

    Images captured by LSST will also be made available to the public through a full-sky viewer similar to the Google Earth platform. This technology will give students and independent scientists the opportunity to investigate dark energy and dark matter, as well as for an average person to see and explore the stars.

    For more information on LSST, please visit https://www.lsst.org/

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    BNL Campus

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