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  • richardmitnick 2:17 pm on February 16, 2018 Permalink | Reply
    Tags: , Fusion technology, , , PRIMA   

    From MIT: “Integrated simulations answer 20-year-old question in fusion research” 

    MIT News

    MIT Widget

    MIT News

    February 16, 2018
    Leda Zimmerman

    To make fusion energy a reality, scientists must harness fusion plasma, a fiery gaseous maelstrom in which radioactive particles react to generate heat for electricity. But the turbulence of fusion plasma can confront researchers with unruly behaviors that confound attempts to make predictions and develop models. In experiments over the past two decades, an especially vexing problem has emerged: In response to deliberate cooling at its edges, fusion plasma inexplicably undergoes abrupt increases in central temperature.

    These counterintuitive temperature spikes, which fly against the physics of heat transport models, have not found an explanation — until now.

    A team led by Anne White, the Cecil and Ida Green Associate Professor in the Department of Nuclear Science and Engineering, and Pablo Rodriguez Fernandez, a graduate student in the department, has conducted studies that offer a new take on the complex physics of plasma heat transport and point toward more robust models of fusion plasma behavior. The results of their work appear this week in the journal Physical Review Letters. Rodriguez Fernandez is first author on the paper.

    In experiments using MIT’s Alcator C-Mod tokamak (a toroidal-shaped device that deploys a magnetic field to contain the star-furnace heat of plasma), the White team focused on the problem of turbulence and its impact on heating and cooling.

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

    In tokamaks, heat transport is typically dominated by turbulent movement of plasma, driven by gradients in plasma pressure.

    Hot and cold

    Scientists have a good grasp of turbulent transport of heat when the plasma is held at steady-state conditions. But when the plasma is intentionally perturbed, standard models of heat transport simply cannot capture plasma’s dynamic response.

    In one such case, the cold-pulse experiment, researchers perturb the plasma near its edge by injecting an impurity, which results in a rapid cooling of the edge.

    “Now, if I told you we cooled the edge of hot plasma, and I asked you what will happen at the center of the plasma, you would probably say that the center should cool down too,” says White. “But when scientists first did this experiment 20 years ago, they saw that edge cooling led to core heating in low-density plasmas, with the temperature in the core rising, and much faster than any standard transport model would predict.” Further mystifying researchers was the fact that at higher densities, the plasma core would cool down.

    Replicated many times, these cold-pulse experiments with their unlikely results defy what is called the standard local model for the turbulent transport of heat and particles in fusion devices. They also represent a major barrier to predictive modeling in high-performance fusion experiments such as ITER, the international nuclear fusion project, and MIT’s own proposed smaller-scale fusion reactor, ARC.

    MIT ARC Fusion Reactor

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

    To achieve a new perspective on heat transport during cold-pulse experiments, White’s team developed a unique twist.

    “We knew that the plasma rotation, that is, how fast the plasma was spinning in the toroidal direction, would change during these cold-pulse experiments, which complicates the analysis quite a bit,” White notes. This is because the coupling between momentum transport and heat transport in fusion plasmas is still not fully understood,” she explains. “We needed to unambiguously isolate one effect from the other.”

    As a first step, the team developed a new experiment that conclusively demonstrated how the cold-pulse phenomena associated with heat transport would occur irrespective of the plasma rotation state. With Rodriguez Fernandez as first author, White’s group reported this key result in the journal Nuclear Fusion in 2017.

    A new integrated simulation

    From there, a tour de force of modeling was needed to recreate the cold-pulse dynamics seen in the experiments. To tackle the problem, Rodriguez Fernandez built a new framework, called PRIMA, which allowed him to introduce cold-pulses in time-dependent simulations. Using special software that factored in the turbulence, radiation and heat transport physics inside a tokamak, PRIMA could model cold-pulse phenomena consistent with experimental measurements.

    “I spent a long time simulating the propagation of cold pulses by only using an increase in radiated power, which is the most intuitive effect of a cold-pulse injection,” Rodriguez Fernandez says.

    Because experimental data showed that the electron density increased with every cold pulse injection, Rodriguez Fernandez implemented an analogous effect in his simulations. He observed a very good match in amplitude and time-scales of the core temperature behavior. “That was an ‘aha!’ moment,” he recalls.

    Using PRIMA, Rodriguez Fernandez discovered that a competition between types of turbulent modes in the plasma could explain the cold-pulse experiments. These different modes, explains White, compete to become the dominant cause of the heat transport. “Whichever one wins will determine the temperature profile response, and determine whether the center heats up or cools down after the edge cooling,” she says.

    By determining the factors behind the center-heating phenomenon (the so-called nonlocal response) in cold-pulse experiments, White’s team has removed a central concern about limitations in the standard, predictive (local) model of plasma behavior. This means, says White, that “we are more confident that the local model can be used to predict plasma behavior in future high performance fusion plasma experiments — and eventually, in reactors.”

    “This work is of great significance for validating fundamental assumptions underpinning the standard model of core tokamak turbulence,” says Jonathan Citrin, Integrated Modelling and Transport Group leader at the Dutch Institute for Fundamental Energy Research (DIFFER), who was not involved in the research. “The work also validated the use of reduced models, which can be run without the need for supercomputers, allowing to predict plasma evolution over longer timescales compared to full-physics simulations,” says Citrin. “This was key to deciphering the challenging experimental observations discussed in the paper.”

    The work isn’t over for the team. As part of a separate collaboration between MIT and General Atomics, Plasma Science and Fusion Center scientists are installing a new laser ablation system to facilitate cold-pulse experiments at the DIII-D tokamak in San Diego, California, with first data expected soon. Rodriguez Fernandez has used the integrated simulation tool PRIMA to predict the cold-pulse behavior at DIII-D, and he will perform an experimental test of the predictions later this year to complete his PhD research.

    The research team included Brian Grierson and Xingqiu Yuan, research scientists at Princeton Plasma Physics Laboratory; Gary Staebler, research scientist at General Atomics; Martin Greenwald, Nathan Howard, Amanda Hubbard, Jerry Hughes, Jim Irby and John Rice, research scientists from the MIT Plasma Science and Fusion Center; and MIT grad students Norman Cao, Alex Creely, and Francesco Sciortino. The work was supported by the US DOE Fusion Energy Sciences.

    See the full article here .

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  • richardmitnick 8:33 am on February 12, 2018 Permalink | Reply
    Tags: , , Fusion technology, ,   

    From GeekWire: “TAE Technologies pushes plasma machine to a new high on the nuclear fusion frontier” 

    1

    GeekWire

    February 10, 2018
    Alan Boyle

    1
    TAE Technologies’ Norman plasma generator is pushing the envelope in fusion research. (TAE Technologies Photo)

    TAE Technologies, the California-based fusion company backed by Microsoft co-founder Paul Allen, said its latest and greatest plasma generator has exceeded the headline-grabbing performance of its previous machine.

    “This announcement is an important milestone on our quest to deliver world-changing, clean fusion energy to help combat climate change and improve the quality of life for people globally,” Michl Binderbauer, the company’s president and chief technology officer, said in a news release. “This achievement further validates the robustness of TAE’s underlying science and unique pathway.”

    The $100 million machine, which went into operation less than a year ago, has been christened “Norman” in honor of physicist Norman Rostoker, the late founder of TAE (formerly known as Tri Alpha Energy). It takes the place of TAE’s C-2U plasma generator, which maintained high-temperature plasma rings in confinement for a record-setting 5 milliseconds back in 2015. Over the course of more than 100,000 experiments, the maximum confinement time eventually went even longer, to 11.5 milliseconds.

    TAE said that the C-2U experiment checked off half of what’s called the “Hot Enough, Long Enough” requirement — that is, demonstrating that a high-temperature plasma could be held in confinement long enough to sustain a nuclear fusion reaction. Such a reaction could take advantage of the same process that powers the sun to produce abundant, relatively cheap, relatively clean energy.

    Just as the C-2U machine met the “Long Enough” standard, the Norman machine is making progress on the “Hot Enough” standard. After 4,000 experiments, TAE said the temperature of Norman’s plasma has reached a high of nearly 20 million degrees Celsius (35.5 million degrees Fahrenheit).

    That’s almost twice as hot as C-2U’s top temperature, and hotter than the temperature of the sun’s core (which is estimated at 15 million degrees C, 27 million degrees F).

    TAE attributed its rapid progress to its collaboration with Google on machine-learning simulations of plasma physics. The company is also taking advantage of a U.S. Department of Energy supercomputer program to boost its data-processing resources.

    There’s still has a long way to go. TAE’s research team is aiming for a hydrogen-boron fusion reaction, which is cleaner than the typical deuterium-tritium reaction but more difficult to achieve. That means the target plasma temperature will eventually have to reach on the order of 3 billion degrees C, which will require building a successor to Norman and conducting years of follow-on experiments.

    Despite the challenges ahead, TAE Technologies CEO Steven Specker said he was heartened by the latest achievement.

    “It is profound to see TAE’s scientific innovations bear out in Norman’s performance,” Specker said in the news release. “Our remarkable
    progress signals the reality of a future powered by fusion energy, and hydrogen-boron is as safe and clean a fuel source as you can find. It’s a win-win for us all.”

    TAE’s approach to fusion involves shooting “smoke rings” of high-energy plasma at each other within a magnetic confinement chamber, with neutral beams directed into the chamber to improve plasma stability. In a recent interview, TAE’s Binderbauer told GeekWire that the technologies under development could be used for applications other than power generation.

    “There’s a medical application that’s particularly interesting that we’ve started,” he said, “and we’ve enabled that because we’ve gotten these beams to reactor-level performance already.”

    TAE says it has attracted $500 million in investment for private-sector fusion research over the past 20 years. In addition to Allen’s Vulcan Capital, institutional investors include the Rockefeller family’s Venrock venture capital firm and Rusnano, a Russian investment firm.

    Other privately funded fusion ventures include Helion Energy in Redmond, Wash., which has won backing from tech billionaire Peter Thiel’s Mithril investment firm; and General Fusion, which is headquartered in Burnaby, B.C., and counts Amazon’s billionaire founder, Jeff Bezos, among its investors.

    Those all come in addition to research efforts backed by government and academic funding, such as the multinational $20 billion ITER experimental reactor under construction in France, and the $1.1 billion Wendelstein 7-X stellarator in Germany.

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

    KIT Wendelstein 7-X, built in Greifswald, Germany

    For what it’s worth, the Joint European Torus, or JET, has achieved plasma temperatures of around 100 million degrees C (180 million degrees F). And for just an instant at a time, Europe’s Large Hadron Collider can create quark-gluon plasma at temperatures in excess of 5 trillion degrees C (9 trillion degrees F).

    See the full article here .

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

    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.

    1
    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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    AIP serves a federation of physical science societies in a common mission to promote physics and allied fields.

     
  • 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, Fusion technology, , , , 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” 


    PPPL

    December 21, 2017
    Raphael Rosen

    1
    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 9:18 pm on December 15, 2017 Permalink | Reply
    Tags: Fusion technology, Laser-boron fusion now ‘leading contender’ for energy, UNSW-University of New South Wales   

    From UNSW: ” Laser-boron fusion now ‘leading contender’ for energy” 

    U NSW bloc

    University of New South Wales

    14 Dec 2017
    Wilson da Silva

    Media Contacts
    Prof Heinrich Hora
    UNSW Physics
    +61 2 9544 4332
    h.hora@unsw.edu.au

    Dr Warren McKenzie
    HB11 Energy
    +61 400 059 509
    warren.mckenzie@hb11.energy

    Wilson da Silva
    Faculty of Engineering
    +61 407 907 017
    w.dasilva@unsw.edu.au

    A laser-driven technique for creating fusion that dispenses with the need for radioactive fuel elements and leaves no toxic radioactive waste is now within reach, says a UNSW physicist.

    1
    Artist’s impression of the core of a laser-ignited hydrogen-boron fusion reactor.

    A laser-driven technique for creating fusion that dispenses with the need for radioactive fuel elements and leaves no toxic radioactive waste is now within reach, say researchers.

    Dramatic advances in powerful, high-intensity lasers are making it viable for scientists to pursue what was once thought impossible: creating fusion energy based on hydrogen-boron reactions. And an Australian physicist is in the lead, armed with a patented design and working with international collaborators on the remaining scientific challenges.

    In a paper in the scientific journal Laser and Particle Beams, lead author Heinrich Hora from UNSW Sydney and international colleagues argue that the path to hydrogen-boron fusion is now viable, and may be closer to realisation than other approaches, such as the deuterium-tritium fusion approach being pursued by US National Ignition Facility (NIF) and the International Thermonuclear Experimental Reactor under construction in France.


    LLNL/NIF


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

    3
    The central core of the large laser-based inertial confinement fusion research device of the National Ignition Facility in the USA.

    “I think this puts our approach ahead of all other fusion energy technologies,” said Hora, who predicted in the 1970s that fusing hydrogen and boron might be possible without the need for thermal equilibrium.

    Rather than heat fuel to the temperature of the Sun using massive, high-strength magnets to control superhot plasmas inside a doughnut-shaped toroidal chamber (as in NIF and ITER), hydrogen-boron fusion is achieved using two powerful lasers in rapid bursts, which apply precise non-linear forces to compress the nuclei together.

    Hydrogen-boron fusion produces no neutrons and, therefore, no radioactivity in its primary reaction. And unlike most other sources of power production – like coal, gas and nuclear, which rely on heating liquids like water to drive turbines – the energy generated by hydrogen-boron fusion converts directly into electricity.

    But the downside has always been that this needs much higher temperatures and densities – almost 3 billion degrees Celsius, or 200 times hotter than the core of the Sun.

    4
    Schematic of a hydrogen-boron fusion reactor.

    However, dramatic advances in laser technology are close to making the two-laser approach feasible, and a spate of recent experiments around the world indicate that an ‘avalanche’ fusion reaction could be triggered in the trillionth-of-a-second blast from a petawatt-scale laser pulse, whose fleeting bursts pack a quadrillion watts of power. If scientists could exploit this avalanche, Hora said, a breakthrough in proton-boron fusion was imminent.

    “It is a most exciting thing to see these reactions confirmed in recent experiments and simulations,” said Hora, an Emeritus Professor of Theoretical Physics at UNSW. “Not just because it proves some of my earlier theoretical work, but they have also measured the laser-initiated chain reaction to create one billion-fold higher energy output than predicted under thermal equilibrium conditions.”

    Together with 10 colleagues in six nations – including from Israel’s Soreq Nuclear Research Centre and the University of California, Berkeley – Hora describes a roadmap for the development of hydrogen-boron fusion based on his design, bringing together recent breakthroughs and detailing what further research is needed to make the reactor a reality.

    An Australian spin-off company, HB11 Energy, holds the patents for Hora’s process. “If the next few years of research don’t uncover any major engineering hurdles, we could have a prototype reactor within a decade,” said Warren McKenzie, managing director of HB11.

    “From an engineering perspective, our approach will be a much simpler project because the fuels and waste are safe, the reactor won’t need a heat exchanger and steam turbine generator, and the lasers we need can be bought off the shelf,” he added.

    Other researchers involved in the study were Shalom Eliezer of Israel’s Soreq Nuclear Research Centre; Jose M. Martinez-Val from Spain’s Polytechnique University in Madrid; Noaz Nissim from University of California, Berkeley; Jiaxiang Wang of East China Normal University; Paraskevas Lalousis of Greece’s Institute of Electronic Structure and Laser; and George Miley at the University of Illinois, Urbana.

    See the full article here .

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    Welcome to UNSW Australia (The University of New South Wales), one of Australia’s leading research and teaching universities. At UNSW, we take pride in the broad range and high quality of our teaching programs. Our teaching gains strength and currency from our research activities, strong industry links and our international nature; UNSW has a strong regional and global engagement.

    In developing new ideas and promoting lasting knowledge we are creating an academic environment where outstanding students and scholars from around the world can be inspired to excel in their programs of study and research. Partnerships with both local and global communities allow UNSW to share knowledge, debate and research outcomes. UNSW’s public events include concert performances, open days and public forums on issues such as the environment, healthcare and global politics. We encourage you to explore the UNSW website so you can find out more about what we do.

     
  • richardmitnick 7:55 am on November 28, 2017 Permalink | Reply
    Tags: , Fusion technology, , , Max-Planck-Princeton partnership in fusion research confirmed, Plasmas in astrophysics are being investigated at Max Planck Institute for Solar System Research in Göttingen and of Astrophysics in Garching and at the Faculty of Astrophysics of Princeton Universit,   

    From Max Planck Gesellschaft: “Max-Planck-Princeton partnership in fusion research confirmed” 

    Max Planck Gesellschaft

    November 28, 2017

    Isabella Milch
    Press Officer, Head of Public Relations and Press Department
    Max Planck Institute for Plasma Physics, Garching
    +49 89 3299-1288
    isabella.milch@ipp.mpg.de

    Investigation of plasmas in astrophysics and fusion research / funding for another two to five years.

    The scientific performance of Max-Planck-Princeton Center for Plasma Physics, established in 2012 by the Max Planck Society and Princeton University, USA, has been evaluated and awarded top grade. The Max Planck Society has now decided to continue its support for another two to maximum five years with 250,000 euros annually. The center’s objective is to link up the hitherto less coordinated research on fusion, laboratory and space plasmas and utilise synergies.

    1
    Turbulence in solar wind plasma. The simulation shows the magnetic field fluctuations due to turbulence. Their spatial and temporal structures can be compared with space probe measurements
    © MPI for Plasma Physics / Daniel Told

    The center’s partners in fusion research are Max Planck Institute for Plasma Physics (IPP) at Garching and Greifswald and Princeton Plasma Physics Laboratory (PPPL) in the USA. Plasmas in astrophysics are being investigated at Max Planck Institute for Solar System Research in Göttingen and of Astrophysics in Garching and at the Faculty of Astrophysics of Princeton University. Primarily through exchange of scientists, particularly junior scientists, computer codes have been jointly developed in the past five years and experimentation has been pursued on the devices MRX at Princeton, Vineta at Greifswald and ASDEX Upgrade at Garching. “For the evaluation the center presented a total of 150 publications, accounting for significant progress in central areas of plasma physics and astrophysics”, states Professor Per Helander, head of IPP’s Stellarator Theory division and, alongside Professor Amitava Bhattacharjee from PPPL, Deputy Director of Max-Planck-Princeton Center since 2017.

    For example, the old question in astrophysics why solar wind is much hotter than the sun’s surface can now be treated with a computer code developed to describe turbulence in fusion plasmas. This enabled plasma theoreticians from IPP along with US colleagues to investigate in detail the heating mechanism in solar wind plasma – with hitherto unattained accuracy – and compare their results with space probe measurements.

    Another puzzle whose solution has been approached at Max-Planck-Princeton Center: Why is it that in outer space and in the laboratory magnetic reconnection, i.e. rupture and relinking of magnetic field lines, is much faster than theory predicts? Whether solar corona or fusion plasma, the rearrangement of the field lines is always accompanied by fast conversion of magnetic energy to thermal and kinetic energy of plasma particles. Physicists from Max Planck Institute for Solar System Research and from the University of Princeton have described a fast mechanism that could describe the observations in the solar corona: formation of unstable plasmoids. Also the sawtooth instability in fusion plasmas, i.e. continual ejection of particles from the plasma core, derives from instantaneous reconnection of magnetic field lines. In the framework of the Max-Planck-Princeton cooperation IPP scientists have now come up with the first realistic simulation that can explain the superfast velocity.

    Last but not least, a new theory ansatz for calculating magnetic equilibria, first developed at Princeton, led to a very fast computer code. With the new algorithm, equilibrium calculations for the complex magnetic fields of future stellarator fusion devices no longer take months, but just a few minutes.

    “As hoped, the center has created new cooperations and built sturdy bridges, on the one hand between research on plasmas in fusion devices, in the laboratory and in outer space, and on the other hand between US and German plasma physicists”, as IPP’s Scientific Director Professor Sibylle Günter sums up the past five years of Max-Planck-Princeton Center. Along with Professor Stewart Prager of PPPL she is one of the two Co-directors of the center. The successful cooperation has meanwhile attracted further partners. In July 2017, a Memorandum of Understanding for admission of Japan’s National Institutes of Natural Sciences was signed: “We look forward to the next years of joint research”, states Sibylle Günter, “made possible by the present confirmation by the Max Planck Society”.

    Max Planck Princeton Research Center for Plasma Physics

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    Welcome to the Max-Planck-Princeton Center for Fusion and Astro Plasma Physics

    The center fosters collaboration between scientific institutes in both Germany and the USA. By leveraging the skills and expertise of scientists and engineers in both countries, and by promoting collaboration between astrophysicists and fusion scientists generally, the center hopes to accelerate discovery in fundamental areas of plasma physics.

    An equally important mission of the center is to support education and outreach to train the next generation of scientists. In the USA, this includes hosting training workshops for K-12 science teachers, and sponsoring summer research experiences for undergraduates.

    In Germany, the host institutions are the Max-Planck-Institut für Plasmaphysik (IPP), the Max-Planck-Institut for Solar System Research (MPS), and the Max Planck Institute for Astrophysics (MPA). In the USA, the host institutions are the Princeton Plasma Physics Laboratory (PPPL), and the Department of Astrophysical Sciences at Princeton University.

    To find out more about the Center, follow the links here.

    Funding for the Center is generously provided by the DoE Office of Science, the National Science Foundation, the Max-Planck Society, NASA’s Heliophysics Division, and Princeton University.

    See the full article here .

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    The Max Planck Society is Germany’s most successful research organization. Since its establishment in 1948, no fewer than 18 Nobel laureates have emerged from the ranks of its scientists, putting it on a par with the best and most prestigious research institutions worldwide. The more than 15,000 publications each year in internationally renowned scientific journals are proof of the outstanding research work conducted at Max Planck Institutes – and many of those articles are among the most-cited publications in the relevant field.

    What is the basis of this success? The scientific attractiveness of the Max Planck Society is based on its understanding of research: Max Planck Institutes are built up solely around the world’s leading researchers. They themselves define their research subjects and are given the best working conditions, as well as free reign in selecting their staff. This is the core of the Harnack principle, which dates back to Adolph von Harnack, the first president of the Kaiser Wilhelm Society, which was established in 1911. This principle has been successfully applied for nearly one hundred years. The Max Planck Society continues the tradition of its predecessor institution with this structural principle of the person-centered research organization.

    The currently 83 Max Planck Institutes and facilities conduct basic research in the service of the general public in the natural sciences, life sciences, social sciences, and the humanities. Max Planck Institutes focus on research fields that are particularly innovative, or that are especially demanding in terms of funding or time requirements. And their research spectrum is continually evolving: new institutes are established to find answers to seminal, forward-looking scientific questions, while others are closed when, for example, their research field has been widely established at universities. This continuous renewal preserves the scope the Max Planck Society needs to react quickly to pioneering scientific developments.

     
  • richardmitnick 6:02 pm on November 21, 2017 Permalink | Reply
    Tags: , , , , , Fusion technology, , , Plasma-facing material   

    From BNL: “Designing New Metal Alloys Using Engineered Nanostructures” 

    Brookhaven Lab

    Stony Brook University assistant professor Jason Trelewicz brings his research to design and stabilize nanostructures in metals to Brookhaven Lab’s Center for Functional Nanomaterials.

    1
    Materials scientist Jason Trelewicz in an electron microscopy laboratory at Brookhaven’s Center for Functional Nanomaterials, where he characterizes nanoscale structures in metals mixed with other elements.

    Materials science is a field that Jason Trelewicz has been interested in since he was a young child, when his father—an engineer—would bring him to work. In the materials lab at his father’s workplace, Trelewicz would use optical microscopes to zoom in on material surfaces, intrigued by all the distinct features he would see as light interacted with different samples.

    Now, Trelewicz—an assistant professor in the College of Engineering and Applied Sciences’ Department of Materials Science and Chemical Engineering with a joint appointment in the Institute for Advanced Computational Science at Stony Brook University and principal investigator of the Engineered Metallic Nanostructures Laboratory—takes advantage of the much higher magnifications of electron microscopes to see tiny nanostructures in fine detail and learn what happens when they are exposed to heat, radiation, and mechanical forces. In particular, Trelewicz is interested in nanostructured metal alloys (metals mixed with other elements) that incorporate nanometer-sized features into classical materials to enhance their performance. The information collected from electron microscopy studies helps him understand interactions between structural and chemical features at the nanoscale. This understanding can then be employed to tune the properties of materials for use in everything from aerospace and automotive components to consumer electronics and nuclear reactors.

    Since 2012, when he arrived at Stony Brook University, Trelewicz has been using the electron microscopes and the high-performance computing (HPC) cluster at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory—to perform his research.

    “At the time, I was looking for ways to apply my idea of stabilizing nanostructures in metals to an application-oriented problem,” said Trelewicz. “I’ve long been interested in nuclear energy technologies, initially reading about fusion in grade school. The idea of recreating the processes responsible for the energy we receive from the sun here on earth was captivating, and fueled my interest in nuclear energy throughout my entire academic career. Though we are still very far away from a fusion reactor that generates power, a large international team on a project under construction in France called ITER is working to demonstrate a prolonged fusion reaction at a large scale.”

    Plasma-facing materials for fusion reactors

    Nuclear fusion—the reaction in which atomic nuclei collide—could provide a nearly unlimited supply of safe, clean energy, like that naturally produced by the sun through fusing hydrogen nuclei into helium atoms. Harnessing this carbon-free energy in reactors requires generating and sustaining a plasma, an ionized gas, at the very high temperatures at which fusion occurs (about six times hotter than the sun’s core) while confining it using magnetic fields. Of the many challenges currently facing fusion reactor demonstrations, one of particular interest to Trelewicz is creating viable materials to build a reactor.

    2
    A model of the ITER tokamak, an experimental machine designed to harness the energy of fusion. A powerful magnetic field is used to confine the plasma, which is held in a doughnut-shaped vessel. Credit: ITER Organization.

    “The formidable materials challenges for fusion are where I saw an opportunity for my research—developing materials that can survive inside the fusion reactor, where the plasma will generate high heat fluxes, high thermal stresses, and high particle and neutron fluxes,” said Trelewicz. “The operational conditions in this environment are among the harshest in which one could expect a material to function.”

    A primary candidate for such “plasma-facing material” is tungsten, because of its high melting point—the highest one among metals in pure form—and low sputtering yield (number of atoms ejected by energetic ions from the plasma). However, tungsten’s stability against recrystallization, oxidation resistance, long-term radiation tolerance, and mechanical performance are problematic.

    Trelewicz thinks that designing tungsten alloys with precisely tailored nanostructures could be a way to overcome these problems. In August, he received a $750,000 five-year award from the DOE’s Early Career Research Program to develop stable nanocrystalline tungsten alloys that can withstand the demanding environment of a fusion reactor. His research is combining simulations that model atomic interactions and experiments involving real-time ion irradiation exposure and mechanical testing to understand the fundamental mechanisms responsible for the alloys’ thermal stability, radiation tolerance and mechanical performance. The insights from this research will inform the design of more resilient alloys for fusion applications.

    In addition to the computational resources they use at their home institution, Trelewicz and his lab group are using the HPC cluster at the CFN—and those at other DOE facilities, such as Titan at Oak Ridge Leadership Computing Facility (a DOE Office of Science User Facility at Oak Ridge National Laboratory)—to conduct large-scale atomistic simulations as part of the project.

    ORNL Cray Titan XK7 Supercomputer

    “The length scales of the structures we want to design into our materials are on the order of a few nanometers to 100 nanometers, and a single simulation can involve up to 10 million atoms,” said Trelewicz. “Using HPC clusters, we can build a system atom-by-atom, representative of the structure we would like to explore experimentally, and run simulations to study the response of that system under various external stimuli. For example, we can fire a high-energy atom into the system and watch what happens to the material and how it evolves, hundreds or thousands of times. Once damage has accumulated in the structure, we can simulate thermal and mechanical forces to understand how defect structure impacts other behavior.”

    These simulations inform the structures and chemistries of experimental alloys, which Trelewicz and his students fabricate at Stony Brook University through high-energy milling. To characterize the nanoscale structure and chemical distribution of the engineered alloys, they extensively use the microscopy facilities at the CFN—including scanning electron microscopes, transmission electron microscopes, and scanning transmission electron microscopes. Imaging is conducted at high resolution and often combined with heating within the microscope to examine in real time how the structures evolve with temperature. Experiments are also conducted at other DOE national labs, such as Sandia through collaboration with materials scientist Khalid Hattar of the Ion Beam Laboratory. Here, students in Trelewicz’s research group simultaneously irradiate the engineered alloys with an ion beam and image them with an electron microscope over the course of many days.

    3
    Trelewicz and his students irradiated a nanostructured tungsten-titanium alloy with high-energy gold ions to explore the radiation tolerance of this novel material.

    “Though this damage does not compare to what the material would experience in a reactor, it provides a starting point to evaluate whether or not the engineered material could indeed address some of the limitations of tungsten for fusion applications,” said Trelewicz.

    Electron microscopy at the CFN has played a key role in an exciting discovery that Trelewicz’s students recently made: an unexpected metastable-to-stable phase transition in thin films of nanostructured tungsten. This phase transition drives an abnormal “grain” growth process in which some crystalline nanostructure features grow very dramatically at the expense of others. When the students added chromium and titanium to tungsten, this metastable phase was completely eliminated, in turn enhancing the thermal stability of the material.

    “One of the great aspects of having both experimental and computational components to our research is that when we learn new things from our experiments, we can go back and tailor the simulations to more accurately reflect the actual materials,” said Trelewicz.

    Other projects in Trelewicz’s research group.

    The research with tungsten is only one of many projects ongoing in the Engineered Metallic Nanostructures Laboratory.

    “All of our projects fall under the umbrella of developing new metal alloys with enhanced and/or multifunctional properties,” said Trelewicz. “We are looking at different strategies to optimize material performance by collectively tailoring chemistry and microstructure in our materials. Much of the science lies in understanding the nanoscale mechanisms that govern the properties we measure at the macroscale.”

    4
    Jason Trelewicz (left) with Olivia Donaldson, who recently graduated with her PhD from Trelewicz’s group, and Jonathan Gentile, a current doctoral student, in front of the scanning electron microscope/focused-ion beam at Stony Brook University’s Advanced Energy Center. Credit: Stony Brook University.

    Through a National Science Foundation CAREER (Faculty Early Career Development Program) award, Trelewicz and his research group are exploring another class of high-strength alloys—amorphous metals, or “metallic glasses,” which are metals that have a disordered atomic structure akin to glass. Compared to everyday metals, metallic glasses are often inherently higher strength but usually very brittle, and it is difficult to make them in large parts such as bulk sheets. Trelewicz’s team is designing interfaces and engineering them into the metallic glasses—initially iron-based and later zirconium-based ones—to enhance the toughness of the materials, and exploring additive manufacturing processes to enable sheet-metal production. They will use the Nanofabrication Facility at the CFN to fabricate thin films of these interface-engineered metallic glasses for in situ analysis using electron microscopy techniques.

    In a similar project, they are seeking to understand how introducing a crystalline phase into a zirconium-based amorphous alloy to form a metallic glass matrix composite (composed of both amorphous and crystalline phases) augments the deformation process relative to that of regular metallic glasses. Metallic glasses usually fail catastrophically because strain becomes localized into shear bands. Introducing crystalline regions in the metallic glasses could inhibit the process by which strain localizes in the material. They have already demonstrated that the presence of the crystalline phase fundamentally alters the mechanism through which the shear bands form.

    Trelewicz and his group are also exploring the deformation behavior of metallic “nanolaminates” that consist of alternating crystalline and amorphous layers, and are trying to approach the theoretical limit of strength in lightweight aluminum alloys through synergistic chemical doping strategies (adding other elements to a material to change its properties).

    5
    Trelewicz and his students perform large-scale atomistic simulations to explore the segregation of solute species to grain boundaries (GBs)—interfaces between grains—in nanostructured alloys, as shown here for an aluminum-magnesium (Al-Mg) system, and its implications for the governing deformation mechanisms. They are using the insights gained through these simulations to design lightweight alloys with theoretical strengths.

    “We leverage resources of the CFN for every project ongoing in my research group,” said Trelewicz. “We extensively use the electron microscopy facilities to look at material micro- and nanostructure, very often at how interfaces are coupled with compositional inhomogeneities—information that helps us stabilize and design interfacial networks in nanostructured metal alloys. Computational modeling and simulation enabled by the HPC clusters at the CFN informs what we do in our experiments.”

    Beyond his work at CFN, Trelewicz collaborates with his departmental colleagues to characterize materials at the National Synchrotron Light Source II—another DOE Office of Science User Facility at Brookhaven.

    BNL NSLS-II


    BNL NSLS II

    “There are various ways to characterize structural and chemical inhomogeneities,” said Trelewicz. “We look at small amounts of material through the electron microscopes at CFN and on more of a bulk level at NSLS-II through techniques such as x-ray diffraction and the micro/nano probe. We combine this local and global information to thoroughly characterize a material and use this information to optimize its properties.”

    Future of next-generation materials

    When he is not doing research, Trelewicz is typically busy with student outreach. He connects with the technology departments at various schools, providing them with materials engineering design projects. The students not only participate in the engineering aspects of materials design but are also trained on how to use 3D printers and other tools that are critical in today’s society to manufacture products more cost effectively and with better performance.

    Going forward, Trelewicz would like to expand his collaborations at the CFN and help establish his research in metallic nanostructures as a core area supported by CFN and, ultimately, DOE, to achieve unprecedented properties in classical materials.

    “Being able to learn something new every day, using that knowledge to have an impact on society, and seeing my students fill gaps in our current understanding are what make my career as a professor so rewarding,” said Trelewicz. “With the resources of Stony Brook University, nearby CFN, and other DOE labs, I have an amazing platform to make contributions to the field of materials science and metallurgy.”

    Trelewicz holds a bachelor’s degree in engineering science from Stony Brook University and a doctorate in materials science and engineering with a concentration in technology innovation from MIT. Before returning to academia in 2012, Trelewicz spent four years in industry managing technology development and transition of harsh-environment sensors produced by additive manufacturing processes. He is the recipient of a 2017 Department of Energy Early Career Research Award, 2016 National Science Foundation CAREER award, and 2015 Young Leaders Professional Development Award from The Minerals, Metals & Materials Society (TMS), and is an active member of several professional organizations, including TMS, the Materials Research Society, and ASM International (the Materials Information Society).

    See the full article here .

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    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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  • richardmitnick 4:49 am on November 15, 2017 Permalink | Reply
    Tags: Fusion technology, ,   

    From Texas A&M: “Channeling helium: Researchers take next step toward fusion energy” 

    Texas A&M logo

    Texas A&M

    1
    (Plasma Science and Fusion Center) Science Alert

    November 10, 2017
    Lorian Hopcus
    lorian.hopcus@tamu.edu

    1

    Fusion is the process that powers the sun, harnessing it on Earth would provide unlimited clean energy. However, researchers say that constructing a fusion power plant has proven to be a daunting task, in no small part because there have been no materials that could survive the grueling conditions found in the core of a fusion reactor. Now, researchers at Texas A&M University have discovered a way to make materials that may be suitable for use in future fusion reactors.

    The sun makes energy by fusing hydrogen atoms, each with one proton, into helium atoms, which contain two protons. Helium is the byproduct of this reaction. Although it does not threaten the environment, it wreaks havoc upon the materials needed to make a fusion reactor.

    “Helium is an element that we don’t usually think of as being harmful,” said Dr. Michael Demkowicz, associate professor in the Department of Materials Science and Engineering. “It is not toxic and not a greenhouse gas, which is one reason why fusion power is so attractive.”

    However, if you force helium inside of a solid material, it bubbles out, much like carbon dioxide bubbles in carbonated water.

    “Literally, you get these helium bubbles inside of the metal that stay there forever because the metal is solid,” Demkowicz said. “As you accumulate more and more helium, the bubbles start to link up and destroy the entire material.”

    Working with a team of researchers at Los Alamos National Laboratory in New Mexico, Demkowicz investigated how helium behaves in nanocomposite solids, materials made of stacks of thick metal layers. Their findings, recently published in Science Advances, were a surprise. Rather than making bubbles, the helium in these materials formed long channels, resembling veins in living tissues.

    “We were blown away by what we saw,” Demkowicz said. “As you put more and more helium inside these nanocomposites, rather than destroying the material, the veins actually start to interconnect, resulting in kind of a vascular system.”

    This discovery paves the way to helium-resistant materials needed to make fusion energy a reality. Demkowicz and his collaborators believe that helium may move through the networks of veins that form in their nanocomposites, eventually exiting the material without causing any further damage.

    Demkowicz collaborated with Di Chen, Nan Li, Kevin Baldwin and Yongqiang Wang from Los Alamos National Laboratory, as well as former student Dina Yuryev from the Massachusetts Institute of Technology. The project was supported by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.

    “Applications to fusion reactors are just the tip of the iceberg,” Demkowicz said. “I think the bigger picture here is in vascularized solids, ones that are kind of like tissues with vascular networks. What else could be transported through such networks? Perhaps heat or electricity or even chemicals that could help the material self-heal.”

    See the full article here .

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    Located in College Station, Texas, about 90 miles northwest of Houston and within a two to three-hour drive from Austin and Dallas.
    Home to more than 50,000 students, ranking as the sixth-largest university in the country, with more than 370,000 former students worldwide.
    Holds membership in the prestigious Association of American Universities, one of only 62 institutions with this distinction.
    More than $820 million in research expenditures generated by faculty-researchers
    Has an endowment valued at more than $5 billion, which ranks fourth among U.S. public universities and 10th overall.

     
  • richardmitnick 7:42 am on October 17, 2017 Permalink | Reply
    Tags: , Fusion technology, , , , SSEN-steady-state electrical network   

    From PPPL: “PPPL completes shipment of electrical components to power site for ITER, the international fusion experiment” 


    PPPL

    October 16, 2017
    Jeanne Jackson DeVoe

    1
    Electrical components procured by PPPL. Pictured clockwise: switchgear, HV protection and control cubicles, resistors, and insulators. (Photo by Photo courtesy of © ITER Organization, http://www.iter.org/)

    The arrival of six truckloads of electrical supplies at a warehouse for the international ITER fusion experiment on Oct. 2 brings to a successful conclusion a massive project that will provide 120 megawatts of power – enough to light up a small city − to the 445-acre ITER site in France.

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

    The Princeton Plasma Physics Laboratory (PPPL), with assistance from the Department of Energy’s Princeton Site Office, headed the $34 million, five-year project on behalf of US ITER to provide three quarters of the components for the steady-state electrical network (SSEN), which provides electricity for the lights, pumps, computers, heating, ventilation and air conditioning to the huge fusion energy experiment. ITER connected the first transformer to France’s electrical grid in March. The European Union is providing the other 25 percent.

    The shipment was the 35th and final delivery of equipment from companies all over the world, including from the United States over the past three years.

    “I think it’s a great accomplishment to finish this,” said Hutch Neilson, head of ITER Fabrication. “The successful completion of the SSEN program is a very important accomplishment both for the US ITER project and for PPPL as a partner in the US ITER project.”

    The six trucks that arrived carried a total of 63 crates of uninterruptible power supply equipment weighing 107 metric tons. The trucks took a seven-hour, 452-mile journey from Gutor UPS and Power Conversion in Wettingen, Switzerland, northwest of Zurich, to an ITER storage facility in Port-Saint-Louis-Du-Rhône, France. The equipment will eventually be used to provide emergency power to critical ITER systems in the event of a power outage.

    “This represents the culmination of a very complex series of technical specifications and global purchases, and we are grateful to the entire PPPL team and their vendors for outstanding commitment and performance”, said Ned Sauthoff, director of the US ITER Project Office at Oak Ridge National Laboratory, where all U.S. contributions to ITER are managed for the U.S. Department of Energy’s Office of Science.

    A device known as a tokamak, ITER will be the largest and most powerful fusion machine in the world. Designed to produce 500 megawatts of fusion power for 50 megawatts of input power, it will be the first fusion device to create net energy – it will get more energy out than is put in. Fusion is the process by which stars like the sun create energy – the fusing of light elements

    A separate electrical system for the pulsed power electrical network (PPEN), procured by China, will power the ITER tokamak.

    The first SSEN delivery in 2014 was among the first plant components to be delivered to the ITER site. The SSEN project is now one of the first U.S. packages to be completed in its entirety, Neilson said. He noted that the final shipment arrived 10 days ahead of PPPL’s deadline.

    In addition to the electrical components, PPPL is also responsible for seven diagnostic instruments and for integrating the instruments inside ITER port plugs. While PPPL is continuing work on an antenna for one diagnostic, most of the diagnostic and port integration work has been put on hold amid uncertainty over U.S. funding for its contributions to ITER.

    The SSEN project was a complex enterprise. PPPL researched potential suppliers, solicited and accepted bids, and oversaw the production and testing of electrical components in 16 separate packages worth a total of about $30 million. The effort involved PPPL engineers, as well as procurement and quality assurance staff members who worked to make sure that the components met ITER specifications and would do exactly what they are supposed to do. “It’s really important that we deliver to ITER equipment that exactly meets the requirements they specify and that it be quality equipment that doesn’t give them trouble down the road,” Neilson said. “So every member of the team makes sure that gets done.”

    Many of the components were for the high-voltage switchyard. A massive transformer procured by PPPL was connected to the French electrical grid in March. PPPL procured and managed the purchase and transportation of the 87-ton transformer and three others, which were built in South Korea by Hyundai Heavy Industries, a branch of the company known for producing cars. =

    The SSEN components came from as close to home as Mount Pleasant, Pennsylvania, to as far away as Turkey, with other components coming from Mexico, Italy, Spain, France, Germany, South Korea and the Netherlands.

    John Dellas, the head of electrical systems and the team leader for the project, has been working on the ITER SSEN project for the entire five years of the program. He traveled to Schweinfurt, Germany, to oversee testing of the control and protection systems for the high-voltage switchyard.

    Dellas took over the project from Charles Neumeyer after Neumeyer became engineering director for the NSTX-U Recovery Project last year. Dellas said Neumeyer deserves most of the credit for the program. “Charlie took the team down to the 10-yard line and I put everything in the end zone,” Dellas said. “I was working with Charlie but Charlie was the quarterback.”

    Neumeyer worked on the project from 2006, when the project was in the planning stages, until 2016. He said he was happy to see the project completed. “It’s very gratifying to see roughly 10 years of work come to a satisfying conclusion under budget and on schedule,” he said.

    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 8:51 pm on October 13, 2017 Permalink | Reply
    Tags: 2-D structure of turbulence in tokamaks, , Fusion technology, ,   

    From PPPL: “PPPL takes detailed look at 2-D structure of turbulence in tokamaks” 


    PPPL

    October 13, 2017
    John Greenwald

    1
    Correlation analysis of three plasma discharges on NSTX for each of five different radial locations near the plasma edge. The red regions marked with a blue cross have high positive correlation around the origin point, while the blue regions marked with a yellow cross have high negative correlation. Images courtesy of Stewart Zweben.

    A key hurdle for fusion researchers is understanding turbulence, the ripples and eddies that can cause the superhot plasma that fuels fusion reactions to leak heat and particles and keep fusion from taking place. Comprehending and reducing turbulence will facilitate the development of fusion as a safe, clean and abundant source of energy for generating electricity from power plants around the world.

    At the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), scientists have assembled a large database of detailed measurements of the two dimensional (2-D) structure of edge plasma turbulence made visible by a diagnostic technique known as gas puff imaging. The two dimensions, measured inside a fusion device called a tokamak, represent the radial and vertical structure of the turbulence.

    Step toward fuller understanding

    “This study is an incremental step toward a fuller understanding of turbulence,” said physicist Stewart Zweben, lead author of the research published in the journal Physics of Plasmas. “It could help us understand how turbulence functions as the main cause of leakage of plasma confinement.”

    Fusion occurs naturally in space, merging the light elements in plasma to release the energy that powers the sun and stars. On Earth, researchers create fusion in facilities like tokamaks, which control the hot plasma with magnetic fields. But turbulence frequently causes heat to leak from its magnetic confinement.

    PPPL scientists have now delved beyond previously published characterizations of turbulence and analyzed the data to focus on the 2-D spatial correlations within the turbulence. This correlation provides clues to the origin of the turbulent behavior that causes heat and particle leakage, and will serve as an additional basis for testing computer simulations of turbulence against empirical evidence.

    Studying 20 discharges of plasma

    The paper studied 20 discharges of plasma chosen as a representative sample of those created in PPPL’s National Spherical Torus Experiment (NSTX) prior to its recent upgrade. In each of these discharges, a gas puff illuminated the turbulence near the edge of the plasma, where turbulence is of special interest. The puffs, a source of neutral atoms that glow in response to density changes within a well-defined region, allowed researchers to see fluctuations in the density of the turbulence. A fast camera recorded the resulting light at the rate of 400,000 frames per second over an image frame size of 64 pixels wide by 80 pixels high.

    Zweben and co-authors performed computational analysis of the data from the camera, determining the correlations between different regions of the frames as the turbulent eddies moved through them. “We’re observing the patterns of the spatial structure,” Zweben said. “You can compare it to the structure of clouds drifting by. Some large clouds can be massed together or there can be a break with just plain sky.”

    Detailed view of turbulence

    The correlations provide a detailed view of the nature of plasma turbulence. “Simple things about turbulence like its size and time scale have long been known,” said PPPL physicist Daren Stotler, a coauthor of the paper. “These simulations take a deep dive into another level to look at how turbulence in one part of the plasma varies with respect to turbulence in another part.”

    In the resulting graphics, a blue cross indicates the point of focus for a calculation; the red and yellow areas around the cross are regions in which the turbulence is evolving similarly to the turbulence at the focal point. Farther away, researchers found regions in which the turbulence is changing opposite to the changes at the focal point. These farther-away regions are shown as shades of blue in the graphics, with the yellow cross indicating the point with the most negative correlation.

    For example, if the red and yellow images were a region of high density turbulence, the blue images indicated low density. “The density increase must come from somewhere,” said Zweben. “Maybe from the blue regions.”

    Going forward, knowledge of these correlations could be used to predict the behavior of turbulence in magnetically confined plasma. Success of the effort could deepen understanding of a fundamental cause of the loss of heat from fusion reactions.

    Also contributing to this study were Filippo Scotti of the Lawrence Livermore National Laboratory and J. R. Myra of Lodestar Research Corporation. Support for this work comes from the DOE Office of Science.

    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.

     
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