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  • richardmitnick 1:03 am on February 8, 2020 Permalink | Reply
    Tags: , , , “Introduction” to the Special Issue by Marcia Neugebauer, , , Dust-free zone, Link to Special ApJS Issue on Parker Solar Probe, , Plasma Physics, Plasma structures, Small energetic-particle events, ,   

    From AAS NOVA: “Early Results from Parker Solar Probe” 


    From AAS NOVA

    7 February 2020
    Susanna Kohler

    Artist’s illustration of the Parker Solar Probe. A special ApJS issue features around 50 articles detailing early results from this mission. [NASA/Johns Hopkins APL/Steve Gribben]

    What might we learn about the Sun if we could fly a spacecraft close enough to dip down and skim through its atmosphere? Thanks to the Parker Solar Probe, we don’t have to speculate!

    The Parker Solar Probe (PSP) is a telescope designed to orbit the Sun at least 24 times, dipping closer and closer to our star’s surface over its mission lifetime.

    NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker

    Its first few orbits have already been completed at a distance of about 35.7 solar radii from the Sun’s center. Just this past month, PSP used the gravitational pull of Venus to drop its orbit to 27.8 solar radii — and by 2024, after several such maneuvers, PSP will be flying just 8.86 solar radii (that’s less than 4 million miles) from the Sun’s surface, soaring through the Sun’s tenuous outer atmosphere.

    This innovative spacecraft will bring us our closest look yet at the magnetic structure and heating of this outer atmosphere — the Sun’s corona — and give us the chance to better explore the solar wind, the stream of energetic particles that flows off of the Sun and pervades our solar system.

    Though PSP’s orbit still has a lot further to drop, it’s already flying closer to the Sun than any other spacecraft ever has! This means we’ve already been able to do some remarkable science in the year and a half since its mission began. A new special issue of the Astrophysical Journal Supplement Series now presents roughly 50 studies detailing the findings from PSP’s first two orbits around the Sun.

    A few broad categories of topics explored among these articles are:

    Illustration of magnetic switchbacks in the solar wind, first discovered by Parker Solar Probe. Click to view an animation. [NASA’s Goddard Space Flight Center/Conceptual Image Lab/Adriana Manrique Gutierrez]


    On large scales, the solar wind looks like a smooth flow of particles streaming radially outward from the Sun. But on scales close to the Sun’s surface, this flow is much more complex. PSP has measured a phenomenon termed “switchbacks” — rapid reversals in the direction of the magnetic field that governs the solar wind flow. Several articles detail what PSP has revealed about this phenomenon.

    Plasma physics

    The high time and frequency resolutions of PSP’s instruments allow the probe to capture unprecedented observations of different plasma phenomena in the ionized gas close in around the Sun. PSP’s first two orbits have produced data on various wave modes, electron holes, magnetic reconnection, radio bursts, microinstabilities, plasma turbulence, and more. Several articles in this issue are devoted to analysis of these detections.

    Small energetic-particle events

    Some solar activity can rapidly accelerate particles to enormous speeds. Since such energetic-particle events can pose a serious hazard to spacecraft and astronauts, we want to better understand what triggers them and how the particles are accelerated. PSP detected a large number of small energetic-particle events associated with various phenomena — and several articles in this issue detail what we’ve learned from these observations.

    A huge variety of plasma structures — like this erupting filament — can be witnessed on the Sun. [NASA’s Goddard SFC]

    Plasma structures

    A huge variety of plasma structures — like this erupting filament — can be witnessed on the Sun. [NASA’s Goddard SFC]
    When plasma is ejected from the Sun, it erupts into space in a variety of structures. PSP carries a camera system that has imaged the complex features of smaller plasma structures; in this special issue, these observations are analyzed and even combined with data from other Sun-watching spacecraft to build three-dimensional views of the structures. From this, we can better understand how magnetic fields govern the geometry and motions of the ionized gas emitted from the Sun.

    Dust-free zone

    Though dust pervades our solar system, theory predicts that close to the Sun, the high temperatures should prevent dust from existing. Several articles describe PSP’s observations that suggest thinning dust levels; data from PSP’s future travels even closer to the Sun will hopefully confirm the presence of a dust-free zone and determine where, exactly, it lies.

    We’re likely at a solar minimum right now in between two activity cycles, as shown here in the predictions made from sunspot observations over the last several cycles. The Sun should become progressively more active over the course of PSP’s mission lifetime. [David Hathaway, NASA, Marshall Space Flight Center]

    These observations are just the start of what we can hope to learn from the Parker Solar Probe. We should expect to see many updates to our understanding of the corona and the solar wind as PSP explores regions closer to the Sun, as solar activity increases (we’re currently at a solar cycle minimum), and as in-flight calibrations of the PSP instruments continue. Stay tuned!


    Special ApJS Issue on Parker Solar Probe

    “Introduction,” Marcia Neugebauer 2020 ApJS 246 19.

    See the full article here .


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    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
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  • richardmitnick 2:01 pm on January 3, 2019 Permalink | Reply
    Tags: "Nuno Loureiro: Understanding turbulence in plasmas", , , Plasma Physics, ,   

    From MIT News: “Nuno Loureiro: Understanding turbulence in plasmas” 

    MIT News
    MIT Widget

    From MIT News

    January 3, 2019
    Peter Dunn

    “When we stimulate theoretically inclined minds by framing plasma physics and fusion challenges as beautiful theoretical physics problems, we bring into the game incredibly brilliant students,” says associate professor of nuclear science and engineering Nuno Loureiro. Photo: Gretchen Ertl

    Theoretical physicist’s focus on the complexity of plasma turbulence could pay dividends in fusion energy.

    Difficult problems with big payoffs are the life blood of MIT, so it’s appropriate that plasma turbulence has been an important focus for theoretical physicist Nuno Loureiro in his two years at the Institute, first as a assistant professor and now as an associate professor of nuclear science and engineering.

    New turbulence-related publications by Loureiro’s research group are contributing to the quest to develop nuclear fusion as a practical energy source, and to emerging astrophysical research that delves into the fundamental mechanisms of the universe.

    Turbulence is around us every day, when smoke rises through air, or milk is poured into coffee. While engineers can draw on substantial empirical knowledge of how it behaves, turbulence’s fundamental principles remain a mystery. Decades ago, Nobel laureate Richard Feynman ’39 referred to it as “the most important unsolved problem of classical physics” — and that still holds true today.

    But turbulence in air or coffee is a simple proposition compared to turbulence in plasma. Ordinary gases and liquids can be modeled as neutral fluids, but plasmas are electromagnetic media. Their turbulent behavior involves both the particles in the plasma (typically electrons and ions, but also electrons and positrons in so-called pair plasmas) and pervading electrical and magnetic fields. In addition, plasmas are often rarefied media where collisions are rare, creating an even more intricate dynamic.

    “There are several additional layers of complexity [in plasma turbulence] over neutral fluid turbulence,” Loureiro says.

    This lack of first-principles understanding is hindering the adaption of fusion for generating electricity. Tokamak-style fusion devices, like the Alcator C-Mod developed at MIT’s Plasma Science and Fusion Center (PSFC), where Loureiro’s research group is based, are a promising approach, and recent the spinout company Commonwealth Fusion Systems (CFS) is working to commercialize the concept. But fusion devices have yet to achieve net energy gain, in large part because of turbulence.

    Alcator C-Mod tokamak at MIT, no longer in operation

    Loureiro and his student Rogério Jorge, with co-author Professor Paolo Ricci from the École Polytechnique Fédérale de Lausanne, Switzerland, recently helped advance thinking in this area in a new paper, “Theory of the Drift-Wave Instability at Arbitrary Collisionality,” published in the journal Physical Review Letters.

    “This was amazing work by a fantastic student — a very complicated calculation that represents a qualitative advancement to the field,” Loureiro says.

    He explains that turbulence in tokamaks changes “flavor” depending on “where you are — at the periphery or near the core.”

    “Both are important, but periphery turbulence has important engineering implications because it determines how much heat reaches the plasma-facing components of the device,” Loureiro says. Preventing heat damage to materials, and maximizing operational life, are key priorities for tokamak developers.

    The paper offers a novel and more-robust description of turbulence in the tokamak periphery caused by low-frequency drift waves, which are a key source of that turbulence and regulators of plasma transport across magnetic fields. And because the computational framework is especially efficient, the approach can be easily extended to other applications. “I think it’s going to be an important piece of work for the fusion concepts that PSFC and CFS are trying to develop,” he says.

    A separate paper, “Turbulence in Magnetized Pair Plasmas,” which Loureiro co-authored with Professor Stanislav Boldyrev of the University of Wisconsin at Madison, puts forward the first theory of turbulence in pair plasmas. The work, published in The Astrophysical Journal Letters, was driven in part by last year’s unprecedented observations of a binary neutron star merger and other discoveries in astrophysics that suggest pair plasmas may be abundant in space — though none has been successfully created on Earth.

    “A variety of astrophysical environments are probably pair-plasma dominated, and turbulent,” notes Loureiro. “Pair plasmas are quite different from regular plasmas. In a normal electron-ion plasma, the ion is about 2,000 times heavier than the electron. But electrons and positrons have exactly the same mass, so there’s a whole range of behaviors that aren’t possible in a normal plasma and vice-versa.”

    Because computational calculations involving equal-weight particles are much more efficient, researchers often run pair-plasma numerical simulations and try to extrapolate findings to electron-ion plasmas.

    “But if you don’t understand how they’re the same or different from a theoretical point of view, it’s very hard to make that connection,” Loureiro points out. “By providing that theory we can help tell which characteristics are intrinsic to pair plasmas and which are shared. Looking at the building blocks may impact electron-ion plasma research too.”

    This theme of theoretical integration characterizes much of Loureiro’s work, and led to his being invited to present at a recent interdisciplinary event for plasma physicists and astrophysicists at New York City’s Flatiron Institute Center for Computational Astrophysics, an arm of a foundation created by billionaire James Simons ’58. It is also central to his role as a theorist within the MIT NSE ecosystem, especially on extremely complex challenges like fusion development.

    “There are people who are driven by technology and engineering, and others who are driven by fundamental mathematics and physics. We need both,” he explains. “When we stimulate theoretically inclined minds by framing plasma physics and fusion challenges as beautiful theoretical physics problems, we bring into the game incredibly brilliant students, people who we want to attract to fusion development but who wouldn’t have an engineer’s excitement about new advances in technology.

    “And they will stay on because they see not just the applicability of fusion but also the intellectual challenge,” he says. “That’s key.”

    See the full article here .

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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 2:33 pm on November 28, 2018 Permalink | Reply
    Tags: , , , , , , , , Plasma Physics   

    From physicsworld.com: “Cosmic expansion rate remains a mystery despite new measurement” 

    From physicsworld.com

    21 Nov 2018

    Galaxy far away: an image taken by the Dark Energy Camera. (Courtesy: Fermilab)

    Dark Energy Survey

    Dark Energy Camera [DECam], built at FNAL

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    A new value for the Hubble constant – the expansion rate of the universe — has been calculated by an international group of astrophysicists. The team used primordial distance scales to study more than 200 supernovae observed by telescopes in Chile and Australia. The new result agrees well with previous values of the constant obtained using a specific model of cosmic expansion, while disagreeing with more direct observations from the nearby universe – so exacerbating a long-running disagreement between cosmologists and astronomers.

    The Hubble constant is calculated by looking at distant celestial objects and determining how fast they are moving away from Earth. A plot of the speeds of the objects versus their distance from Earth falls on a straight line, the slope of which is the Hubble constant.

    Obtaining an object’s speed is straightforward and involves measuring the redshift of the light it emits, but quantifying its distance is much more complicated. Historically, this has been done using a “distance-ladder”, whereby progressively greater length scales are measured by using one type of “standard candle” to calibrate the output of another standard candle. The distance to stars known as Cepheid variables (one type of standard candle) is first established via parallax, and that information is used to calibrate the output of type Ia supernovae (another type of standard candle) located in galaxies containing Cepheids. The apparent brightness of other supernovae can then be used to work out distances to galaxies further away.

    Large discrepancy

    This approach has been refined over the years and has most recently yielded a Hubble constant of 73.5 ± 1.7 kilometres per second per magaparsec (one megaparsec being 3.25 million light-years). That number, however – obtained by starting close to Earth and moving outwards – is at odds with calculations of the Hubble constant that take the opposite approach — moving inwards from the dawn of time. The baseline in that latter case comes from length scales of temperature fluctuations in the radiation dating back to just after the Big Bang, known as the cosmic microwave background. The cosmic expansion rate at that time is extrapolated to the present day by assuming that the universe’s growth has accelerated under the influence of a particular kind of dark energy. Using the final results from the European Space Agency’s Planck satellite, a very different Hubble constant of 67.4 ± 0.5 is obtained.

    ESA/Planck 2009 to 2013

    To try to resolve the problem by using an alternative approach, scientists have in recent years created what is known as an “inverse distance ladder”. This also uses the cosmic microwave background as a starting point, but it calculates the expansion rate at a later time – about 10 billion years after the Big Bang – when the density fluctuations imprinted on the background radiation had grown to create clusters of galaxies distributed within “baryon acoustic oscillations”. The oscillations are used to calibrate the distance to supernovae – present in the galaxies – thanks to the fact that the oscillations lead to a characteristic separation between galaxies of 147 megaparsecs.

    In the latest work, the Dark Energy Survey collaboration draws on galaxy data from the Sloan Digital Sky Survey as well as 207 newly-studied supernovae captured by the Dark Energy Camera mounted on the 4-metre Víctor M Blanco telescope in Chile. Using spectra obtained mainly at the similarly-sized Anglo-Australian Telescope in New South Wales, the collaboration calculates a value for the Hubble constant of 67.8 ± 1.3 – so agreeing with the Planck value while completely at odds with the conventional distance ladder.

    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Siding Spring Mountain with Anglo-Australian Telescope dome visible near centre of image at an altitude of 1,165 m (3,822 ft)

    Fewer assumptions

    “The key thing with these results,“ says team member Ed Macaulay of the University of Portsmouth in the UK, “is that the only physics you need to assume is plasma physics in the early universe. You don’t need to assume anything about dark energy.”

    Adam Riess, an astrophysicist at the Space Telescope Science Institute in Baltimore, US who studies the distance-ladder, says that the new work “adds more weight” to the disparity in values of the Hubble constant obtained from the present and early universe.

    Cosmic Distance Ladder, skynetblogs

    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    (Indeed, the distance-ladder itself has gained independent support from expansion rates calculated using gravitational lensing.) He reckons that the similarity between the Planck and Dark Energy Survey results means that redshifts out to z=1 (going back about 8 billion years) are “probably not where the tension develops” and that the physics of the early universe might be responsible instead.

    Chuck Bennett of Johns Hopkins University, who led the team on Planck’s predecessor WMAP, agrees. He points to a new model put forward by his Johns Hopkins colleagues Marc Kamionkowski, Vivian Poulin and others that adds extra dark energy to the universe very early on (before rapidly decaying). This model, says Bennett, “proves that it is theoretically possible to find cosmological solutions to the Hubble constant tension”.

    Macaulay is more cautious. He acknowledges the difficulty of trying to find an error, reckoning that potential systematic effects in any of the measurements “are about ten times smaller” than the disparity. But he argues that more data are needed before any serious theoretical explanations can be put forward. To that end, he and his colleagues are attempting to analyse a further 2000 supernovae observed by the Dark Energy Camera, although they are doing so without the aid of (costly) spectroscopic analysis. Picking out the right kind of supernovae and then working out their redshift “will be very difficult,” he says, “and not something that has been done with this many supernovae before”.

    A preprint describing the research is available on arXiv.

    See the full article here .

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  • richardmitnick 4:13 pm on March 16, 2018 Permalink | Reply
    Tags: , FLARE- Facility for Laboratory Reconnection Experiment, , Plasma — the fourth state of matter, Plasma Physics,   

    From PPPL: “First plasma for new machine to study process that occurs throughout the universe” 


    March 16, 2018
    John Greenwald

    PPPL FLARE – Facility for Laboratory Reconnection Experiment

    The first plasma, a milestone event signaling the beginning of research capabilities, was captured on camera on Sunday, March 5, at 8:13 p.m. at Jadwin Hall at Princeton University, and marked completion of the four-year construction of the device, the Facility for Laboratory Reconnection Experiment (FLARE).
    Photo by Larry Bernard, Princeton Plasma Physics Laboratory

    A millisecond burst of light on a computer monitor signaled production of the first plasma in a powerful new device for advancing research into magnetic reconnection — a critical but little understood process that occurs throughout the universe.

    The first plasma, a milestone event signaling the beginning of research capabilities, was captured on camera on Sunday, March 5, at 8:13 p.m. at Jadwin Hall at Princeton University, and marked completion of the four-year construction of the device, the Facility for Laboratory Reconnection Experiment (FLARE).

    Magnetic reconnection, the breaking apart and explosive recombination of the magnetic field lines in hot plasma — the fourth state of matter composed of free electrons and atomic nuclei that makes up 99 percent of the visible universe — has impact throughout the cosmos. Reconnection gives rise to Northern Lights, solar eruptions and geomagnetic storms that can disrupt electrical networks and signal transmissions such as cellphone service. In laboratories where scientists are trying to create a “star on earth,” the process can degrade and even disrupt fusion experiments.

    Constructing FLARE, designed as a user facility for multiple institutions, was a team of physicists, engineers, designers, technicians and supporting staff for PPPL and Princeton, where the device was assembled. Support for construction of the project, whose future is being developed, came from the National Science Foundation with contributions from Princeton, the University of Maryland and the University of Wisconsin-Madison, with collaborators from Los Alamos National Laboratory, the University of California campuses at Berkeley and Los Angeles, and the Institute of Plasma Physics, Chinese Academy of Sciences.

    See the full article here .

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    PPPL campus

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

  • richardmitnick 1:30 pm on December 30, 2017 Permalink | Reply
    Tags: A.I.P., , , , Lifetime of primary runaway electrons estimated for high-plasma-current fusion devices, , Plasma Physics   

    From AIP: “Lifetime of primary runaway electrons estimated for high-plasma-current fusion devices” 

    AIP Publishing Bloc

    American Institute of Physics

    November 2017
    Meeri Kim

    Analysis of field and collision influence on runaway electrons produced during plasma disruptions provides insight into lifetime trends.

    No image caption or credit.

    For ITER and other high-plasma-current fusion devices, runaway electrons are a matter of concern.

    ITER Tokamak in Saint-Paul-lès-Durance, which is in southern France

    [ITER, way behind schedule and way over budget, is about as good as it gets in the search for Fusion Technology, which has been 30 years away for the last thirty years.]

    These highly accelerated electrons, produced in great numbers during plasma disruptions, can form a runaway beam that hits and damages the wall of the machine.

    A recent U.S. initiative called SCREAM (Simulation Center for Runaway Electron Avoidance and Mitigation) combines theoretical models with advanced simulation and analysis to address the runaway problem. As part of SCREAM, two physicists used kinetic analysis to predict the lifetime of primary runaway electrons, reporting the results in Physics of Plasmas.

    The authors wanted to understand the distribution of primary runaway electrons by taking into account the interplay of three factors: acceleration by electric field, collisions with plasma electrons and ions, and synchrotron losses. Their analysis dealt with the kinetic equation for relativistic electrons in a straight and homogeneous magnetic field, which they were able to simplify and rescale to highlight its similarity features.
    They found that the lifetime of seed runaways increases exponentially with the electric field, with the rate depending on a combination of parameters collectively called “alpha,” that includes the effects of ion charge and synchrotron time scale. For alpha much less than one, the lifetimes can be long when the electric field is only slightly about the renowned Connor-Hastie critical value, when the friction, or drag, on the relativistic electrons from ion collisions becomes energy independent and the electrons can be accelerated continuously. For alpha much larger than one, significantly stronger electric fields are necessary for runaway seed electron survival.

    Long-lived runaway electrons have greater opportunity to multiply via an avalanche effect. Knowing the parameter range that creates long lifetimes will inform ITER researchers about what regimes to avoid in planned experiments.

    See the full article here .

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  • richardmitnick 12:24 pm on December 24, 2017 Permalink | Reply
    Tags: As a result the fractal fibers can reduce secondary electron emission by up to 80 percent, , Charles Swanson and Igor Kaganovich, Feathers and whiskers help keep plasma superhot in fusion reactions, , , Plasma Physics, , This work builds on previous experiments showing that surfaces with fibered textures can reduce the amount of secondary electron emission   

    From PPPL: “Feathers and whiskers help keep plasma superhot in fusion reactions” 


    December 21, 2017
    Raphael Rosen

    Physicist Charles Swanson. (Photo by Elle Starkman/Office of Communications)

    Physicists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have found a way to prevent plasma — the hot, charged state of matter composed of free electrons and atomic nuclei — from causing short circuits in machines such as spacecraft thrusters, radar amplifiers, and particle accelerators. In findings published online in the Journal of Applied Physics, Charles Swanson and Igor Kaganovich report that applying microscopic structures that resemble feathers and whiskers to the surfaces inside these machines keeps them operating at peak performance.

    The physicists calculated that tiny fibers called “fractals,” because they look the same when viewed at different scales, can trap electrons dislodged from the interior surfaces by other electrons zooming in from the plasma. Researchers refer to the dislodged surface electrons as “secondary electron emissions” (SEE); trapping them prevents such particles from causing electric current that interferes with the functions of machines.

    Building on previous experiments

    This work builds on previous experiments showing that surfaces with fibered textures can reduce the amount of secondary electron emission. Past research has indicated that surfaces with plain fibers called “velvet” that lack feather-like branches can prevent about 50 percent of the secondary electrons from escaping into the plasma. The velvet only traps half of such electrons, since if the electrons from the plasma strike the fibers at a shallow angle the secondary electrons can bounce away without obstruction.

    “When we looked at velvet, we observed that it didn’t suppress SEE from shallowly incident electrons well,” Swanson said. “So we added another set of fibers to suppress the remaining secondary electrons and the fractal approach does appear to work nicely.”

    The new research shows that feathered fibers can capture secondary electrons produced by the electrons that approach from a shallow angle. As a result, the fractal fibers can reduce secondary electron emission by up to 80 percent.

    Swanson and Kaganovich verified the findings by performing computer calculations that compared velvet and fractal feathered textures. “We numerically simulated the emission of secondary electrons, initializing many particles and allowing them to follow ballistic, straight-line trajectories until they interacted with the surface,” Swanson said. “It was apparent that adding whiskers to the sides of the primary whiskers reduced the secondary electron yield dramatically.”

    Provisional patent

    The two scientists now have a provisional patent on the feathered-texture technique. This research was funded by the Air Force Office of Scientific Research, and follows similar experimental work done at PPPL by other physicists. Specifically, Yevgeny Raitses, working at PPPL; Marlene Patino, a graduate student at the University of California, Los Angeles; and Angela Capece, a professor at the College of New Jersey, have in the past year published experimental findings on how secondary electron emission is affected by different wall materials and structures, based on research they did at PPPL.

    See the full article here .

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    PPPL campus

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

  • richardmitnick 11:07 am on June 8, 2017 Permalink | Reply
    Tags: , Center for MicroNanotechnology (CMi) at EPFL, , EPFL’s Laboratory of Photonics and Quantum Measurements (LPQM), Institute of Microstructure Technology (IMT), KIT’s Institute of Photonics and Quantum Electronics (IPQ), LiGenTec SA, Optical frequency combs, , , Plasma Physics, Wavelength division multiplexing (WDM)   

    From EPFL: “Ultra-fast optical data transfer using solitons on a photonic chip” 

    EPFL bloc

    École Polytechnique Fédérale de Lausanne EPFL

    Nik Papageorgiou

    Optical micro resonators made from silicon nitride on a chip using for soliton based communications. © V. Brasch (LPQM, EPFL)
    Researchers from EPFL and Karlsruhe Institute of Technology use a soliton frequency combs from optical microresonators to transmit data at speeds of more than 50 terabits per second.

    Optical solitons are special wave packages that propagate without changing their shape. They are ubiquitous in nature, and occur in Plasma Physics, water waves to biological systems. While solitons also exist in optical fiber, discovered at Bell labs in the 1980’ies, there technological use so far has been limited. While researchers studied their use for optical communication, eventually the approach was abandoned. Now, a collaboration of a research group at KIT’s Institute of Photonics and Quantum Electronics (IPQ) and Institute of Microstructure Technology (IMT) with EPFL’s Laboratory of Photonics and Quantum Measurements (LPQM) have shown that solitons may experience a comeback: Instead of using a train of soliton pulses in an optical fiber, they generated continuously circulating optical solitons in compact silicon nitride optical microresonators. These continuously circulating solitons lead to broadband optical frequency combs. Two such superimposed frequency combs enabled massive parallel data transmission on 179 wavelength channels at a data rate of more than 50 terabits per second – a record for frequency combs. The work is published in Nature [link is below].

    Optical frequency combs, for which John Hall and Theodor W. Hänsch were awarded the Nobel Prize in Physics in 2005, consist of a multitude of neighboring spectral lines, which are aligned on a regular equidistant grid. Traditionally, frequency combs serve as high-precision optical references for measurement of frequencies. The invention of so-called Kerr frequency combs, which are characterized by large optical bandwidths and by line spacings that are optimal for communications, make frequency combs equally well suited for data transmission. Each individual spectral line can be used for transmitting a data signal.

    In their experiment, the researchers from KIT and EPFL used optical silicon nitride micro-resonators on a photonic chip that can easily be integrated into compact communication systems. For the communications demonstration, two interleaved frequency combs were used to transmit data on 179 individual optical carriers, which completely cover the optical telecommunication C and L bands and allow a transmission of data rate of 55 terabits per second over a distance of 75 kilometers. “This is equivalent to more than five billion phone calls or more than two million HD TV channels. It is the highest data rate ever reached using a frequency comb source in chip format,” explains Christian Koos, professor at KIT’s IPQ and IMT and recipient of a Starting Independent Researcher Grant of the European Research Council (ERC) for his research on optical frequency combs.

    The components have the potential to reduce the energy consumption of the light source in communication systems drastically. The basis of the researchers’ work are solitons generated in low-loss optical silicon nitride micro-resonators. In these, an optical soliton state was generated for the first time by Kippenberg’s lab at EPFL in 2014. ”The soliton forms through nonlinear processes occurring due to the high intensity of the light field in the micro-resonator” explains Kippenberg. The microresonator is only pumped through a continuous-wave laser from which, by means of the soliton, hundreds of new equidistant laser lines are generated. The silicon nitride integrated photonic chips are grown and fabricated in the Center for MicroNanotechnology (CMi) at EPFL. Meanwhile, a startup from LPQM, LiGenTec SA, is also offering access to these photonic integrated circuits to interested academic and industrial research laboratories.

    The work shows that microresonator soliton frequency comb sources can considerably increase the performance of wavelength division multiplexing (WDM) techniques in optical communications. WDM allows to transmit ultra-high data rates by using a multitude of independent data channels on a single optical waveguide. To this end, the information is encoded on laser light of different wavelengths. For coherent communications, microresonator soliton frequency comb sources can be used not only at the transmitter, but also at the receiver side of WDM systems. The comb sources dramatically increase scalability of the respective systems and enable highly parallel coherent data transmission with light. According to Christian Koos, this is an important step towards highly efficient chip-scale transceivers for future petabit networks.

    This work was supported by the European Research Council (Starting Grant ‘EnTeraPIC’), the European Union (project BigPipes), the Alfried Krupp von Bohlen und Halbach Foundation, the Karlsruhe School of Optics & Photonics (KSOP), and the Helmholtz International Research School for Teratronics (HIRST), the Erasmus Mundus Doctorate Program Europhotonics, the Deutsche Forschungsgemeinschaft (DFG), the European Space Agency, the US Air Force (Office of Scientific Research), the Swiss National Science Foundation (SNF), and the Defense Advanced Research Program Agency (DARPA) via the program Quantum Assisted Sensing and Readout(QuASAR).


    Pablo Marin-Palomo, Juned N. Kemal, Maxim Karpov, Arne Kordts, Joerg Pfeifle, Martin H. P. Pfeiffer, Philipp Trocha, Stefan Wolf, Victor Brasch, Miles H. Anderson, Ralf Rosenberger, Kovendhan Vijayan, Wolfgang Freude, Tobias J. Kippenberg, Christian Koos. Microresonator solitons for massively parallel coherent optical communications.Nature 08 June 2017.

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    EPFL is Europe’s most cosmopolitan technical university with students, professors and staff from over 120 nations. A dynamic environment, open to Switzerland and the world, EPFL is centered on its three missions: teaching, research and technology transfer. EPFL works together with an extensive network of partners including other universities and institutes of technology, developing and emerging countries, secondary schools and colleges, industry and economy, political circles and the general public, to bring about real impact for society.

  • richardmitnick 5:21 am on May 16, 2017 Permalink | Reply
    Tags: , , , , Particle acceleration, Plasma Physics, Rochester’s Laboratory for Laser Energetics,   

    From ALCF: “Fields and flows fire up cosmic accelerators” 

    Argonne Lab
    News from Argonne National Laboratory

    ANL Cray Aurora supercomputer
    Cray Aurora supercomputer at the Argonne Leadership Computing Facility

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


    May 15, 2017
    John Spizzirri

    A visualization from a 3D OSIRIS simulation of particle acceleration in laser-driven magnetic reconnection. The trajectories of the most energetic electrons (colored by energy) are shown as the two magnetized plasmas (grey isosurfaces) interact. Electrons are accelerated by the reconnection electric field at the interaction region and escape in a fan-like profile. Credit: Frederico Fiuza, SLAC National Accelerator Laboratory/OSIRIS

    Every day, with little notice, the Earth is bombarded by energetic particles that shower its inhabitants in an invisible dusting of radiation, observed only by the random detector, or astronomer, or physicist duly noting their passing. These particles constitute, perhaps, the galactic residue of some far distant supernova, or the tangible echo of a pulsar. These are cosmic rays.

    But how are these particles produced? And where do they find the energy to travel unchecked by immense distances and interstellar obstacles?

    These are the questions Frederico Fiuza has pursued over the last three years, through ongoing projects at the Argonne Leadership Computing Facility (ALCF), a U.S. Department of Energy (DOE) Office of Science User Facility.

    A physicist at the SLAC National Accelerator Laboratory in California, Fiuza and his team are conducting thorough investigations of plasma physics to discern the fundamental processes that accelerate particles.

    The answers could provide an understanding of how cosmic rays gain their energy and how similar acceleration mechanisms could be probed in the laboratory and used for practical applications.

    While the “how” of particle acceleration remains a mystery, the “where” is slightly better understood. “The radiation emitted by electrons tells us that these particles are accelerated by plasma processes associated with energetic astrophysical objects,” says Fiuza.

    The visible universe is filled with plasma, ionized matter formed when gas is super-heated, separating electrons from ions. More than 99 percent of the observable universe is made of plasmas, and the radiation emitted from them creates the beautiful, eerie colors that accentuate nebulae and other astronomical wonders.

    The motivation for these projects came from asking whether it was possible to reproduce similar plasma conditions in the laboratory and study how particles are accelerated.

    High-power lasers, such as those available at the University of Rochester’s Laboratory for Laser Energetics or at the National Ignition Facility in the Lawrence Livermore National Laboratory, can produce peak powers in excess of 1,000 trillion watts.

    Rochester’s Laboratory for Laser Energetics

    At these high-powers, lasers can instantly ionize matter and create energetic plasma flows for the desired studies of particle acceleration.

    Intimate Physics

    To determine what processes can be probed and how to conduct experiments efficiently, Fiuza’s team recreates the conditions of these laser-driven plasmas using large-scale simulations. Computationally, he says, it becomes very challenging to simultaneously solve for the large scale of the experiment and the very small-scale physics at the level of individual particles, where these flows produce fields that in turn accelerate particles.

    Because the range in scales is so dramatic, they turned to the petascale power of Mira, the ALCF’s Blue Gene/Q supercomputer, to run the first-ever 3D simulations of these laboratory scenarios. To drive the simulation, they used OSIRIS, a state-of-the-art, particle-in-cell code for modeling plasmas, developed by UCLA and the Instituto Superior Técnico, in Portugal, where Fiuza earned his PhD.

    Part of the complexity involved in modeling plasmas is derived from the intimate coupling between particles and electromagnetic radiation — particles emit radiation and the radiation affects the motion of the particles.

    In the first phase of this project, Fiuza’s team showed that a plasma instability, the Weibel instability, is able to convert a large fraction of the energy in plasma flows to magnetic fields. They have shown a strong agreement in a one-to-one comparison of the experimental data with the 3D simulation data, which was published in Nature Physics, in 2015. This helped them understand how the strong fields required for particle acceleration can be generated in astrophysical environments.

    Fiuza uses tennis as an analogy to explain the role these magnetic fields play in accelerating particles within shock waves. The net represents the shockwave and the racquets of the two players are akin to magnetic fields. If the players move towards the net as they bounce the ball between each other, the ball, or particles, rapidly accelerate.

    “The bottom line is, we now understand how magnetic fields are formed that are strong enough to bounce these particles back and forth to be energized. It’s a multi-step process: you need to start by generating strong fields — and we found an instability that can generate strong fields from nothing or from very small fluctuations — and then these fields need to efficiently scatter the particles,” says Fiuza.


    NASA Magnetic reconnection, Credit: M. Aschwanden et al. (LMSAL), TRACE, NASA

    But particles can be energized in another way if the system provides the strong magnetic fields from the start.

    “In some scenarios, like pulsars, you have extraordinary magnetic field amplitudes,” notes Fiuza. “There, you want to understand how the enormous amount of energy stored in these fields can be directly transferred to particles. In this case, we don’t tend to think of flows or shocks as the dominant process, but rather magnetic reconnection.”

    Magnetic reconnection, a fundamental process in astrophysical and fusion plasmas, is believed to be the cause of solar flares, coronal mass ejections, and other volatile cosmic events. When magnetic fields of opposite polarity are brought together, their topologies are changed. The magnetic field lines rearrange in such a way as to convert magnetic energy into heat and kinetic energy, causing an explosive reaction that drives the acceleration of particles. This was the focus of Fiuza’s most recent project at the ALCF.

    Again, Fiuza’s team modeled the possibility of studying this process in the laboratory with laser-driven plasmas. To conduct 3D, first-principles simulations (simulations derived from fundamental theoretical assumptions/predictions), Fiuza needed to model tens of billions of particles to represent the laser-driven magnetized plasma system. They modeled the motion of every particle and then selected the thousand most energetic ones. The motion of those particles was individually tracked to determine how they were accelerated by the magnetic reconnection process.

    “What is quite amazing about these cosmic accelerators is that a very, very small number of particles carry a large fraction of the energy in the system, let’s say 20 percent. So you have this enormous energy in this astrophysical system, and from some miraculous process, it all goes to a few lucky particles,” he says. “That means that the individual motion of particles and the trajectory of particles are very important.”

    The team’s results, which were published in Physical Review Letters, in 2016, show that laser-driven reconnection leads to strong particle acceleration. As two expanding plasma plumes interact with each other, they form a thin current sheet, or reconnection layer, which becomes unstable, breaking into smaller sheets. During this process, the magnetic field is annihilated and a strong electric field is excited in the reconnection region, efficiently accelerating electrons as they enter the region.

    Fiuza expects that, like his previous project, these simulation results can be confirmed experimentally and open a window into these mysterious cosmic accelerators.

    This research is supported by the DOE Office of Science. Computing time at the ALCF was allocated through the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program.

    See the full article here .

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

    About ALCF

    The Argonne Leadership Computing Facility’s (ALCF) mission is to accelerate major scientific discoveries and engineering breakthroughs for humanity by designing and providing world-leading computing facilities in partnership with the computational science community.

    We help researchers solve some of the world’s largest and most complex problems with our unique combination of supercomputing resources and expertise.

    ALCF projects cover many scientific disciplines, ranging from chemistry and biology to physics and materials science. Examples include modeling and simulation efforts to:

    Discover new materials for batteries
    Predict the impacts of global climate change
    Unravel the origins of the universe
    Develop renewable energy technologies

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  • richardmitnick 2:02 pm on January 1, 2015 Permalink | Reply
    Tags: , , Plasma Physics   

    From physicstoday: “Plasma wakefield acceleration shows promise” 

    physicstoday bloc


    January 2015
    Johanna L. Miller

    When electrons are precisely positioned in a region of high electric field, they can pick up a lot of energy in a small space.

    In their quest to test the standard model. and search for new physics beyond it, particle physicists have sought ever larger and more powerful facilities for accelerating and colliding charged particles.

    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Conventionally, accelerators rely on metal plates and resonators to generate electric fields and RF waves. The magnitude of those fields is limited to tens of megavolts per meter, so to accelerate particles to 125 GeV (the energy of the Higgs boson) or more requires a path of many kilometers. Protons and heavier particles can be accelerated in circles, but electrons and positrons must be accelerated in straight lines, lest they lose all their energy to synchrotron radiation. The 3-km linear accelerator at SLAC is currently the world’s longest; reaching the high energies relevant to particle physics with a conventional electron accelerator would require a much larger, costlier facility.

    Accelerators based on plasmas, which can sustain electric fields up to tens of gigavolts per meter, have the potential to be a smaller and cheaper alternative. An electron-density wave in a plasma, co-propagating with a charged-particle bunch, can keep the bunch in a high-field region over a path of a meter or more, thereby imparting a lot of energy to the particles in a compact space. But the precision engineering required to accelerate particles efficiently and uniformly has been a challenge.

    Now Chandrashekhar Joshi (at UCLA), Michael Litos, Mark Hogan (both at SLAC), and their colleagues have taken a leap forward. In their plasma wakefield accelerator, the plasma wave is created by a 20-GeV electron bunch from SLAC’s linac. A second bunch of equally energetic electrons follows close behind. With SLAC’s purpose-built Facility for Advanced Accelerator Experimental Tests, the researchers could place the trailing bunch at just the right spot in the plasma wave to increase the bunch energy by 1.6 GeV over just 30 cm of plasma.


    Energy boost

    Plasma acceleration schemes, first proposed by John Dawson in the 1970s, come in two basic types. (See the article by Joshi and Thomas Katsouleas, Physics Today, June 2003, page 47.) In laser wakefield acceleration, the plasma wave is created by the radiation pressure of an intense laser pulse. Because the wave can accelerate particles almost from rest, the scheme offers a way to create self-contained tabletop accelerators for moderate-energy applications, such as medicine and materials science. (See the article by Wim Leemans and Eric Esarey, Physics Today, March 2009, page 44.)

    In plasma wakefield acceleration, on the other hand, one bunch of fast-moving particles drives the plasma wave that accelerates another bunch. Both bunches must start out at ultrarelativistic energies, traveling so close to the speed of light that their separation doesn’t change even as the first bunch loses energy and the second gains energy. The scheme is therefore not suitable for free-standing accelerators; instead it is being developed as a way to boost the energy of large linacs. (For the same reason, it’s far better suited to accelerating electrons than protons, which would need 2000 times as much energy to reach the ultrarelativistic starting point.)

    Litos likens the plasma wakefield accelerator to an electrical transformer converting a large bunch of moderate-energy electrons into a smaller bunch at higher energy. That capability would be useful for particle-physics experiments, in which high collision energies are critical in the search for new physics. It also has the potential to reduce the size and cost of x-ray free-electron lasers. The Linac Coherent Light Source at SLAC, currently the only operating XFEL, uses electrons accelerated over 1 km of the linac. (See Physics Today, August 2009, page 21.) Plasma wakefield boosters on a smaller linac could, says Litos, “make XFELs more palatable to universities rather than just national labs.”

    SLAC LCLS Inside

    Riding the wave

    Figure 1 shows a simulation of the process under the conditions used in the new experiment. The drive bunch pushes away the plasma electrons, leaving a region of net positive charge in its wake. (The plasma ions, not shown in the figure, are heavy enough to be unaffected.) At the back of the wake, the longitudinal electric field E z is strongly negative, capable of accelerating electrons in the direction of travel.

    Figure 1. Simulations of a plasma wakefield interaction, with beam density shown in orange, plasma-electron density in blue, and the longitudinal electric field E z as an orange curve. (a) The drive bunch clears away the plasma electrons, leaving a region of strong but inhomogeneous electric field in its wake. (b) If the trailing bunch is large enough and positioned in the right spot, it can flatten the electric field so that the trailing bunch is uniformly accelerated.

    But the field in the wake of the drive bunch alone, shown in figure 1 a, is far from homogeneous. Electrons separated by just a few microns would gain energy at vastly different rates. That’s bad for collider experiments, which require particles as close to a single energy as possible.

    Fortunately, if the trailing bunch is large enough, its own effect on E z can be significant. As shown in figure 1 b, E z is reduced in magnitude, but also flattened, to a near constant −5 GV/m. Using a denser plasma would yield a stronger E z . But it would also reduce the size of the wake and make positioning the trailing bunch more difficult.

    Beam gymnastics

    Earlier proof-of-principle plasma wakefield experiments have used, instead of a pair of electron bunches, a single elongated bunch. The physics is the same—the electrons at the back of the bunch are accelerated by the wake produced by those at the front. But to achieve the desired small energy spreads, it’s necessary to use two discrete bunches separated by about 100 µm, or 300 fs. The only way to make such closely spaced bunches is by crafting them out of a single linac bunch.

    To accomplish that, the researchers first used magnets to elongate the bunch to about 2 mm, with the highest-energy electrons in the front. Then, as shown in figure 2 , they rotated the bunch and allowed it to collide with a thin tantalum bar. Electrons that struck the bar were scattered and removed from the beam, whereas those on either side kept going. Rotating the bunch again and compressing it down to submillimeter size gave the desired two-bunch structure.

    Figure 2. Two bunches from one. An electron bunch from the SLAC linear accelerator is dispersed according to its energy—here, the high-energy end of the bunch is shown in red and the low-energy end in blue. The bunch is then allowed to collide with a thin tantalum bar, which scatters the middle portion of the bunch out of the beam.

    The plasma was created from a chamber full of lithium vapor; 100 ps before the electrons’ arrival, the researchers shot a laser pulse through the vapor to ionize the Li atoms and create a 1-mm-wide tunnel of plasma, which remained ionized for several nanoseconds, plenty of time for the plasma wake to do its work.

    The researchers then measured the outgoing electrons to see what had happened. Figure 3 shows the energy spectrum of one of their trials compared with the outcome of the simulation from figure 1 b. In each case, both bunches started at 20.35 GeV; the drive bunch lost energy and broadened, whereas the trailing bunch gained energy and remained sharply peaked. The red dashed line shows a fit to the energetic core of the trailing bunch, with an energy spread of 2%.

    Figure 3. Energy profiles of the simulated and actual electron bunches after they interact with the plasma. In both cases, the drive bunch, which begins with an energy just above 20 GeV, loses energy and broadens. The trailing bunch gains energy and is dominated by the sharply peaked core.

    What lies ahead

    Clearly, much work remains to be done: An energy gain of less than 10% is hardly going to revolutionize high-energy physics. Furthermore, of the 800 pC that started out in the trailing bunch, only 74 pC remained in the accelerated core. Better preservation of the beam is a priority for the SLAC team’s future work.

    One way to reach higher energies is simply by making the plasma chamber longer. With the setup as it is, plasma wakefield acceleration can continue for several meters before the drive bunch runs out of energy. The researchers are working on ways to daisy-chain several plasma accelerators together to pass the same trailing bunch from one to the next but use a fresh drive bunch each time.

    A high-energy collider experiment would need not just accelerated electrons but also positrons of equal energy. Plasma wakefield acceleration of positrons is tricky because of their positive charge: They draw the plasma electrons toward them rather than clearing them away, and the resulting wake structure is much less conducive to accelerating a trailing bunch. “But we’ve been making progress,” says Litos, “and we hope to publish some results soon.”

    Some simulations of plasma wakefield acceleration have predicted a phenomenon called the hosing instability, in which the electric field perpendicular to the direction of travel causes the trailing bunch to wobble back and forth with increasing amplitude and eventually break apart. But not only did the researchers see no sign of the hosing instability in their experiments, they couldn’t produce it even when they tried. “That was an interesting surprise, and rather encouraging,” says Litos. “The hosing instability had been predicted to be a potential show stopper.”

    See the full article here.

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  • richardmitnick 5:32 pm on November 20, 2014 Permalink | Reply
    Tags: , , , Plasma Physics,   

    From NSF: “A deep dive into plasma” 

    National Science Foundation

    November 20, 2014
    No Writer Credit

    Renowned physicist uses NSF-supported supercomputer and visualization resources to gain insight into plasma dynamic

    Studying the intricacies and mysteries of the sun is physicist Wendell Horton’s life’s work. A widely known authority on plasma physics, his study of the high temperature gases on the sun, or plasma, consistently leads him around the world to work on a diverse range of projects that have great impact.

    Fusion energy is one such key scientific issue that Horton is investigating and one that has intrigued researchers for decades.

    “Fusion energy involves the same thermonuclear reactions that take place on the sun,” Horton said. “Fusing two isotopes of hydrogen to create helium releases a tremendous amount of energy–10 times greater than that of nuclear fission.”

    It’s no secret that the demand for energy around the world is outpacing the supply. Fusion energy has tremendous potential. However, harnessing the power of the sun for this burgeoning energy source requires extensive work.

    Through the Institute for Fusion Studies at The University of Texas at Austin, Horton collaborates with researchers at ITER, a fusion lab in France and the National Institute for Fusion Science in Japan to address these challenges. At ITER, Horton is working with researchers to build the world’s largest tokamak–the device that is leading the way to produce fusion energy in the laboratory.

    ITER Tokamak
    ITER tokamak

    “Inside the tokamak, we inject 10 to 100 megawatts of power to recreate the conditions of burning hydrogen as it occurs in the sun,” Horton said. “Our challenge is confining the plasma, since temperatures are up to 10 times hotter than the center of the sun inside the machine.”

    Perfecting the design of the tokamak is essential to producing fusion energy, and since it is not fully developed, Horton performs supercomputer simulations on the Stampede supercomputer at the Texas Advanced Computing Center (TACC) to model plasma flow and turbulence inside the device.

    “Simulations give us information about plasma in three dimensions and in time, so that we are able to see details beyond what we would get with analytic theory and probes and high-tech diagnostic measurements,” Horton said.

    The simulations also give researchers a more holistic picture of what is needed to improve the tokamak design. Comparing simulations with fusion experiments in nuclear labs around the world helps Horton and other researchers move even closer to this breakthrough energy source.

    Plasma in the ionosphere

    Because the mathematical theories used to understand fusion reactions have numerous applications, Horton is also investigating space plasma physics, which has important implications in GPS communications.

    GPS signaling, a complex form of communication, relies on signal transmission from satellites in space, through the ionosphere, to GPS devices located on Earth.

    “The ionosphere is a layer of the atmosphere that is subject to solar radiation,” Horton explained. “Due to the sun’s high-energy solar radiation plasma wind, nitrogen and oxygen atoms are ionized, or stripped of their electrons, creating plasma gas.”

    These plasma structures can scatter signals sent between global navigation satellites and ground-based receivers resulting in a “loss-of-lock” and large errors in the data used for navigational systems.

    Most people who use GPS navigation have experienced “loss-of-lock,” or instance of system inaccuracy. Although this usually results in a minor inconvenience for the casual GPS user, it can be devastating for emergency response teams in disaster situations or where issues of national security are concerned.

    To better understand how plasma in the ionosphere scatters signals and affects GPS communications, Horton is modeling plasma turbulence as it occurs in the ionosphere on Stampede. He is also sharing this knowledge with research institutions in the United States and abroad including the UT Space and Geophysics Laboratory.

    Seeing is believing

    Although Horton is a long-time TACC partner and Stampede user, he only recently began using TACC’s visualization resources to gain deeper insight into plasma dynamics.

    “After partnering with TACC for nearly 10 years, Horton inquired about creating visualizations of his research,” said Greg Foss, TACC Research Scientist Associate. “I teamed up with TACC research scientist, Anne Bowen, to develop visualizations from the myriad of data Horton accumulated on plasmas.”

    Since plasma behaves similarly inside of a fusion-generating tokamak and in the ionosphere, Foss and Bowen developed visualizations representing generalized plasma turbulence. The team used Maverick, TACC’s interactive visualization and data analysis system to create the visualizations, allowing Horton to see the full 3-D structure and dynamics of plasma for the first time in his 40-year career.

    This image visualizes the effect of gravity waves on an initially relatively stable rotating column of electron density, twisting into a turbulent vortex on the verge of complete chaotic collapse. These computer generated graphics are visualizations of data from a simulation of plasma turbulence in Earth’s ionosphere. The same physics are also applied to the research team’s investigations of turbulence in the tokamak, a device used in nuclear fusion experiments.Credit: Visualization: Greg Foss, TACC Visualization software support: Anne Bowen, Greg Abram, TACC Science: Wendell Horton, Lee Leonard, U. of Texas at Austin

    “It was very exciting and revealing to see how complex these plasma structures really are,” said Horton. “I also began to appreciate how the measurements we get from laboratory diagnostics are not adequate enough to give us an understanding of the full three-dimensional plasma structure.”

    Word of the plasma visualizations soon spread and Horton received requests from physics researchers in Brazil and researchers at AMU in France to share the visualizations and work to create more. The visualizations were also presented at the XSEDE’14 Visualization Showcase and will be featured at the upcoming SC’14 conference.

    Horton plans to continue working with Bowen and Foss to learn even more about these complex plasma structures, allowing him to further disseminate knowledge nationally and internationally, also proving that no matter your experience level, it’s never too late to learn something new.
    — Makeda Easter, Texas Advanced Computing Center (512) 471-8217 makeda@tacc.utexas.edu
    — Aaron Dubrow, NSF (703) 292-4489 adubrow@nsf.gov

    Wendell Horton
    Daniel Stanzione

    Related Institutions/Organizations
    Texas Advanced Computing Center
    University of Texas at Austin

    Austin , Texas

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