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  • richardmitnick 2:08 pm on August 25, 2016 Permalink | Reply
    Tags: , Fusion technology, ,   

    From PPPL: “How to keep the superhot plasma inside tokamaks from chirping” 


    PPPL

    August 19, 2016
    Raphael Rosen

    1
    Graduate student Vinícius Duarte. (Photo by Elle Starkman)

    Chirp, chirp, chirp.” The familiar sound of birds is also what researchers call a wave in plasma that breaks from a single note into rapidly changing notes. This behavior can cause heat in the form of high energy particles — or fast ions — to leak from the core of plasma inside tokamaks — doughnut-shaped facilities that house fusion reactions.

    PPPL NSTXII
    NSTX tokamak at PPPL

    Physicists want to prevent these waves from chirping because they may cause too many fast ions to escape, cooling the plasma. As the plasma cools, the atomic nuclei in the tokamak are less likely to come together and release energy and the fusion reactions will sputter to a halt.

    “Chirping modes can be very harmful because they can steal energy from the fast ions in an extended region of the plasma,” said Vinícius Duarte, a graduate student from the University of São Paulo. Duarte is at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) conducting research for his dissertation. Support for this work comes from the DOE Office of Science.

    Chirping modes often have frequencies far above what the human ear can hear. The name — “chirping” — stems from the change in the waves’ frequency over time. Typically, the modes start with a high frequency and drop down in frequency very rapidly. The chirping of modes has been studied for decades as physicists seek to understand and eliminate them.

    In a recent theoretical study, Duarte discovered some conditions within plasma that can make the chirping of modes more likely. A paper he is preparing on this topic explains the phenomenon and may help to optimize the design of fusion energy plants in the future. Collaborating on the research were physicists at PPPL, General Atomics, the University of California-Irvine, and the University of Texas at Austin. Physicist Nikolai Gorelenkov, Duarte’s PPPL advisor, introduced him to the software code that enabled this work, Prof. Herbert Berk of the University of Texas co-advised on the project and researchers from the DIII-D National Fusion Facility that General Atomics operates for the DOE provided the data for comparison with the theory.

    The researchers began by noting that the chirping of modes seems to occur in some tokamaks more often than in others. They are rare in the DIII-D tokamak, for example, but were common in the National Spherical Torus Experiment (NSTX), PPPL’s former flagship fusion device, which has recently been upgraded.

    By running simulations on PPPL computers, Duarte and the team found that plasma turbulence — or random fluctuation — was a factor that helped explain the chirping of modes. Chirping can occur when there is a strong concentration of fast ions bunched together, while other particles are widely spaced.

    The surprise is that substantial turbulence can break up concentrations of fast ions, and therefore help to extinguish the chirping of modes.

    The simulations matched the data from experiments. In NSTX, the turbulence has little effect on fast ions and chirping modes are common, whereas DIII-D has relatively high interaction between turbulence and fast ions and chirping modes are rare. In DIII-D, chirping starts only when the interaction between the turbulence and fast-ions markedly decreases.

    These findings could lead to fusion facilities that leak less heat than current machines and could improve the efficiency of ITER, the international tokamak under construction in France to demonstrate the feasibility of fusion power.

    ITER Tokamak
    ITER Tokamak, France

    “In ITER, where fast ions from fusion reactions are expected to sustain a burning plasma, the good confinement of these particles is a crucial issue,” said Duarte.

    See the full article here .

    Please help promote STEM in your local schools.

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    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 1:49 pm on August 24, 2016 Permalink | Reply
    Tags: Fusion technology,   

    From PPPL: “Major next steps proposed for development of fusion energy based on the spherical tokamak design” 


    PPPL

    August 24, 2016
    John Greenwald

    Among the top puzzles in the development of fusion energy is the best shape for the magnetic facility — or “bottle” — that will provide the next steps in the development of fusion reactors. Leading candidates include spherical tokamaks, compact machines that are shaped like cored apples, compared with the doughnut-like shape of conventional tokamaks. The spherical design produces high-pressure plasmas — essential ingredients for fusion reactions — with relatively low and cost-effective magnetic fields.

    A possible next step is a device called a Fusion Nuclear Science Facility (FNSF) that could develop the materials and components for a fusion reactor. Such a device could precede a pilot plant that would demonstrate the ability to produce net energy.

    1
    PPPL/NSTX-U

    PPPL NSTXII
    PPPL/NSTX

    Spherical tokamaks as excellent models

    Spherical tokamaks could be excellent models for an FNSF, according to a paper published online in the journal Nuclear Fusion on August 16. The two most advanced spherical tokamaks in the world today are the recently completed National Spherical Torus Experiment-Upgrade (NSTX-U) at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), and the Mega Ampere Spherical Tokamak (MAST), which is being upgraded at the Culham Centre for Fusion Energy in the United Kingdom.

    2
    Mega Ampere Spherical Tokamak (MAST)

    “We are opening up new options for future plants,” said Jonathan Menard, program director for the NSTX-U and lead author of the paper, which discusses the fitness of both spherical tokamaks as possible models. Support for this work comes from the DOE Office of Science.

    The 43-page paper considers the spherical design for a combined next-step bottle: an FNSF that could become a pilot plant and serve as a forerunner for a commercial fusion reactor. Such a facility could provide a pathway leading from ITER, the international tokamak under construction in France to demonstrate the feasibility of fusion power, to a commercial fusion power plant.

    ITER Tokamak
    ITER Tokamak, France

    A key issue for this bottle is the size of the hole in the center of the tokamak that holds and shapes the plasma. In spherical tokamaks, this hole can be half the size of the hole in conventional tokamaks. These differences, reflected in the shape of the magnetic field that confines the superhot plasma, have a profound effect on how the plasma behaves.

    Designs for the Fusion Nuclear Science Facility

    First up for a next-step device would be the FNSF. It would test the materials that must face and withstand the neutron bombardment that fusion reactions produce, while also generating a sufficient amount of its own fusion fuel. According to the paper, recent studies have for the first time identified integrated designs that would be up to the task.

    These integrated capabilities include:

    • A blanket system able to breed tritium, a rare isotope — or form — of hydrogen that fuses with deuterium, another isotope of the atom, to generate the fusion reactions. The spherical design could breed approximately one isotope of tritium for each isotope consumed in the reaction, producing tritium self-sufficiency.

    • A lengthy configuration of the magnetic field that vents exhaust heat from the tokamak. This configuration, called a “divertor,” would reduce the amount of heat that strikes and could damage the interior wall of the tokamak.

    • A vertical maintenance scheme in which the central magnet and the blanket structures that breed tritium can be removed independently from the tokamak for installation, maintenance, and repair. Maintenance of these complex nuclear facilities represents a significant design challenge. Once a tokamak operates with fusion fuel, this maintenance must be done with remote-handling robots; the new paper describes how this can be accomplished.

    For pilot plant use, superconducting coils that operate at high temperature would replace the copper coils in the FNSF to reduce power loss. The plant would generate a small amount of net electricity in a facility that would be as compact as possible and could more easily scale to a commercial fusion power station.

    High-temperature superconductors

    High-temperature superconductors could have both positive and negative effects. While they would reduce power loss, they would require additional shielding to protect the magnets from heating and radiation damage. This would make the machine larger and less compact.

    Recent advances in high-temperature superconductors could help overcome this problem. The advances enable higher magnetic fields, using much thinner magnets than are presently achievable, leading to reduction in the refrigeration power needed to cool the magnets. Such superconducting magnets open the possibility that all FNSF and associated pilot plants based on the spherical tokamak design could help minimize the mass and cost of the main confinement magnets.

    For now, the increased power of the NSTX-U and the soon-to-be-completed MAST facility moves them closer to the capability of a commercial plant that will create safe, clean and virtually limitless energy. “NSTX-U and MAST-U will push the physics frontier, expand our knowledge of high temperature plasmas, and, if successful, lay the scientific foundation for fusion development paths based on more compact designs,” said PPPL Director Stewart Prager.

    Twice the power and five times the pulse length

    The NSTX-U has twice the power and five times the pulse length of its predecessor and will explore how plasma confinement and sustainment are influenced by higher plasma pressure in the spherical geometry. The MAST upgrade will have comparable prowess and will explore a new, state-of-the art method for exhausting plasmas that are hotter than the core of the sun without damaging the machine.

    “The main reason we research spherical tokamaks is to find a way to produce fusion at much less cost than conventional tokamaks require,” said Ian Chapman, the newly appointed chief executive of the United Kingdom Atomic Energy Authority and leader of the UK’s magnetic confinement fusion research programme at the Culham Science Centre.

    The ability of these machines to create high plasma performance within their compact geometries demonstrates their fitness as possible models for next-step fusion facilities. The wide range of considerations, calculations and figures detailed in this study strongly support the concept of a combined FNSF and pilot plant based on the spherical design. The NSTX-U and MAST-U devices must now successfully prototype the necessary high-performance scenarios.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    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 7:25 pm on August 15, 2016 Permalink | Reply
    Tags: Alfvén waves, , Fusion technology, ,   

    From PPPL: “Simulations by PPPL physicists suggest that external magnetic fields can calm plasma instabilities” 


    PPPL

    August 15, 2016
    Raphael Rosen

    1
    Magnetic Perturbations. (Photo by Gerrit Kramer.)

    Physicists led by Gerrit Kramer at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have conducted simulations that suggest that applying magnetic fields to fusion plasmas can control instabilities known as Alfvén waves that can reduce the efficiency of fusion reactions. Such instabilities can cause quickly moving charged particles called “fast ions” to escape from the core of the plasma, which is corralled within machines known as tokamaks.

    Controlling these instabilities leads to higher temperatures within tokamaks and thus more efficient fusion processes. The research was published in the August issue of Plasma Physics and Controlled Fusion and funded by the DOE Office of Science (Fusion Energy Sciences).

    “Controlling and suppressing the instabilities helps improve the fast-ion confinement and plasma performance,” said Kramer, a research physicist at the Laboratory. “You want to suppress the Alfvén waves as much as possible so the fast ions stay in the plasma and help heat it.”

    The team gathered data from experiments conducted on the National Spherical Torus Experiment (NSTX) at PPPL before the tokamak was recently upgraded.

    PPPL NSTXII
    NSTX

    Then they conducted plasma simulations on a PPPL computer cluster.

    The simulations showed that externally applied magnetic perturbations can block the growth of Alfvén waves. The perturbations reduce the gradient, or difference in velocity, of the ions as they zoom around the tokamak. This process calms disturbances within the plasma. “If you reduce the velocity gradient, you can prevent the waves from getting excited,” notes Kramer.

    The simulations also showed that magnetic perturbations can calm Alfvén waves that have already formed. The perturbations alter the frequency of the plasma vibration so that it matches the frequency of the wave. “The plasma absorbs all the energy of the wave, and the wave stops vibrating,” said Kramer.

    In addition, the simulations indicated that when applied to tokamaks with relatively weak magnetic fields, the external magnetic perturbations could dislodge fast ions from the plasma directly, causing the plasma to cool.

    Along with Kramer, the research team included scientists from General Atomics, Oak Ridge National Laboratory, the University of California, Los Angeles, and the University of California, Irvine.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 11:26 am on August 12, 2016 Permalink | Reply
    Tags: , Experimental Advanced Superconducting Tokamak (EAST), Fusion technology,   

    From PPPL: “PPPL wins contract for plasma-materials interaction studies on EAST tokamak” 


    PPPL

    August 11, 2016
    John Greenwald

    The U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) has been named principal investigator for a multi-institutional project to study plasma-materials interaction (PMI)on the Experimental Advanced Superconducting Tokamak (EAST) in China.

    4
    EAST

    The centerpiece of the PPPL role in this project is the optimization of lithium delivery systems. The tests will be designed to optimize the production of long-pulse plasmas that last from 30 seconds to more than one minute. This project is supported by Fusion Energy Sciences in the DOE Office of Science.

    The three-year, approximately $2.1 million contract — subject to annual budget availability — is synergistic with other PPPL collaborations funded by DOE to investigate long-duration plasma confinement. These collaborations involve EAST, the Korean Superconducting Advanced Research (KSTAR) tokamak, and the Wendelstein-7X (W-7X) stellarator in Germany.

    1
    The KSTAR (Korea Superconducting Tokamak Advanced Research), a magnetic fusion device.

    PPPL Wendelstein 7-X
    Wendelstein 7-X, built in Greifswald, Germany

    For the PMI project, PPPL will use devices called flowing liquid lithium limiters and granule injectors, as well as optimization of coating techniques, to protect the plasma-facing components inside the EAST facility. PPPL has applied lithium to its National Spherical Torus Experiment (NSTX), which has recently been upgraded, and will continue to use lithium.

    PPPL NSTXII
    PPPL NSTX

    Also housed at PPPL is the Lithium Tokamak Experiment (LTX), a small, short-pulse complementary experiment that explores the effect of a liquid-lithium boundary on the plasma.

    PPPL LTX Lithium Tokamak Experiment
    PPPL LTX Lithium Tokamak Experiment

    The new experiments will test the ability of lithium to protect the EAST walls and prevent impurities from bouncing back into the core of the plasma and halting fusion reactions. Success of such efforts could point to a method for optimizing long-running plasmas. “We’re trying to make a cohesive program so the things that we’ve learned in this country can be tried over there,” said physicist Rajesh Maingi, who will lead the PPPL effort. “Then we can bring back what we learn there to help us here.”

    Collaborating with PPPL on the PMI project are the Los Alamos and Oak Ridge national laboratories, together with Johns Hopkins University, the Massachusetts Institute of Technology, the University of Illinois and the University of Tennessee.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 9:19 am on July 29, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “PU Energy Scholars report focuses on fusion energy” 


    PPPL

    1
    Adam Cohen, at left, former deputy director for operations at PPPL, with Princeton Energy Scholars in the National Spherical Torus Experiment-Upgrade Control Room during a tour of PPPL in June 2014. (Photo by Elle Starkman/PPPL Office of Communications)

    Magnetic fusion has “enormous promise as a global energy source” if researchers are able to make “significant progress in several areas of science and technology” in the coming decades, according to a recent report published by Princeton University’s Andlinger Center for Energy and the Environment.

    The report was researched and written by 10 Ph.D. students who are part of the Princeton Energy Scholars graduate school honor society at the Princeton Environmental Institute. The students, supervised by Princeton University faculty mentor Robert Socolow, are from a variety of fields that include electrical engineering, psychology and public policy. The students visited the Princeton Plasma Physics Laboratory (PPPL ) in June 2014 and spoke with PPPL researchers, including former Deputy Director for Operations Adam Cohen now with the U.S. Department of Energy, as part of their research. Other PPPL staff whom the students consulted for technical information are: Nat Fisch, Rob Goldston, Greg Hammett, Dale Meade, Stewart Prager and Andrew Zwicker.

    “I am impressed with how well the students have captured essential elements of fusion from essentially a cold start,” said PPPL Director Stewart Prager. “The report is interesting reading and will be very useful to those wishing a lucid summary of fusion.”

    The report notes that the students recognized “a special challenge” to their objectivity arising from the fact that PPPL is a national Department of Energy (DOE) laboratory that is operated by Princeton University. “Although we consulted with several fusion experts at PPPL, this report was written independently of PPPL and does not represent its views,” the students wrote. “We have sought to write an impartial and rigorous assessment, the kind that we would most want to read ourselves.”

    Fusion energy offers unique advantages over current methods of generating electricity because its fuel is nearly inexhaustible, the report said. It could provide enough energy to meet global demand without producing carbon emissions that are linked to global warming. Fusion also avoids some of the issues of nuclear waste and potential danger to the environment associated with nuclear fission plants, according to the report.

    Another advantage: fusion energy power plants could be located in areas where renewable energy such as wind or solar would not work, the report said. Fusion plants also would not affect the health or environment of local communities.

    The nation’s newest magnetic fusion experiment is the NSTX-U (National Spherical Torus Experiment–Upgrade) at PPPL.

    PPPL NSTXII
    NSTX

    This spherical tokamak is designed to gather information over the next decade on how to inform the next generation of fusion devices, and perhaps lead to a fusion demonstration or pilot plant.

    But fusion energy faces several scientific and technological challenges to create, maintain, and manipulate a plasma at temperatures of up to 200 million degrees Celsius − far hotter than the sun, the report said.

    Those challenges go hand-in-hand with policy challenges regarding funding, the report said. Fusion scientists have formed international collaborations to overcome this challenge, most notably ITER, the massive international fusion experiment under construction in Cadarache, France.

    ITER Tokamak
    ITER Tokamak

    The report, or “distillate,” is divided into five sections that include an introduction and a discussion of four major issues. The full report can be downloaded here. (link is external)

    An executive summary (link is external), overview (link is external), and key concepts (link is external)
    Technology: (link is external) The report states that some of the major challenges in fusion energy include how to maintain a “burning plasma,” a plasma that sustains itself, which is the goal of ITER. Other key technological challenges include how to produce enough of the radioactive material tritium for fusion plants to operate.
    Economics (link is external): Fusion will be competitive if it can find a way to control instabilities that could damage components and thus avoid shutting down future power plants, the report said. Another challenge is finding materials that are strong enough to last without having to be frequently replaced. The report said a strong climate policy would help make fusion more competitive.
    Fusion and Fission (link is external): The report compares fusion and fission power. Fusion power plants do not use plutonium and highly enriched uranium, the materials used in nuclear fission plants. Thus they would not cause a nuclear meltdown in the event of an accident. Fusion power plants would not have the same issues of nuclear waste disposal as nuclear fission power plants and materials could not be used to create nuclear weapons.
    Politics and Progress (link is external): Countries that fund the ITER fusion experiment, which could begin operating in 2026 at a cost of more than $20 billion, find it challenging to also fund a strong domestic fusion research program, the report said. The next step would be to build a DEMO, a demonstration experiment that would be “a bridge between ITER and an eventual commercial reactor.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 12:59 pm on June 29, 2016 Permalink | Reply
    Tags: Anne White, , Fusion technology, ,   

    From MIT: Women in Science – “Anne White: A passion for plasma” 

    MIT News

    MIT Widget
    MIT News

    June 29, 2016
    David L. Chandler | MIT News Office

    Physicist has a fascination for the complexities of turbulence, and how to reduce it in fusion reactors.

    Turbulence is an everyday phenomenon that we see in the curls of smoke rising from a fire or in the cream we stir into our morning coffee. But despite centuries of research, the details of how turbulent flows behave are still something of a mystery to scientists. Turbulence is also one of the most critical challenges remaining in the quest to make fusion, potentially a clean and almost limitless source of electricity, practical for generating power.

    Anne White, the Cecil and Ida Green Associate Professor in Nuclear Engineering in MIT’s Plasma Fusion and Science Center, has been fascinated by the complexities of turbulence, and its critical role in sapping power from fusion reactors, since she was an undergraduate. Since coming to MIT, where she earned tenure last year, she has made important progress toward unraveling aspects of that mystery.

    1
    “When I started in graduate school I knew already that I wanted to work on turbulence in tokamaks,” says Anne White, the Cecil and Ida Green Associate Professor in Nuclear Engineering in MIT’s Plasma Fusion and Science Center. Photo: Bryce Vickmark

    White grew up in the parched desert landscape of Yuma, Arizona, and completed her undergraduate work at the University of Arizona, in Tucson, and her doctorate at the University of California at Los Angeles. When she arrived in Cambridge to join the MIT faculty in 2010 it was quite a change, she recalls, to be in a place “where leafy green plants grow and water often falls from the sky!”

    “When I started in graduate school I knew already that I wanted to work on turbulence in tokamaks,” she says, referring to the primary type of fusion reactor used in research, including MIT’s Alcator C-Mod, which is soon to be retired. In the donut-shaped cavities in these reactors, a soup of electrically charged atoms is heated and compressed by an intense magnetic field as it swirls around. This intense heat and pressure is needed to make atoms fuse together, providing the source of energy for fusion reactors, but turbulence in the form of hard-to-predict swirls and eddies can drain the heat away.

    Understanding exactly how this turbulence develops, and how to reduce it, has been one of the thorniest challenges in the last few decades of fusion research.

    But there have been “really exciting developments over the last two years,” White says. Her team has made use of three different fusion reactors, including MIT’s Alcator C-Mod, to understand the nature of the turbulence and associated transport. The combination of data and insights from multiple machines has made the conclusions much clearer than a single device could have provided, White says. “Right now our group has active projects on four tokamaks,” she says.

    White became interested in fusion while studying nonlinear dynamics as a math major at the University of Arizona. She was doing a lot of reading about how to tackle the problems of climate change and quickly decided that nuclear sources, fission and fusion, were key technologies for addressing the issue. Her undergraduate advisor, who had been at Princeton University and was familiar with its tokamak fusion reactor, the TFTR, encouraged her to pursue that goal.

    While in graduate school at UCLA, White first built devices called Langmuir probes and magnetic probes and inserted them in the edge of the tokamak plasma to study how properties of the plasma turbulence varied from the inboard to the outboard side of the tokamak. “This was a great experience, to jump into a research group, with little to no plasma physics knowledge and just start building instruments.” Likewise, White says she now encourages freshman or grad students to “just jump into” their Undergraduate Research Opportunities Programs (UROPs), or first year of research.

    Later in grad school, White worked on another edge-plasma turbulence project at the NSTX tokamak at the Princeton Plasma Physics Lab.

    PPPL NSTXII
    PPPL NSTX-II

    “I learned a great deal of plasma physics and also met a mentor and advocate, who has continued to be an inspiration to me,” she says. White encourages her own grad students to spend a summer away from the research group, perhaps doing an internship with another lab as a way to broaden their research and networking horizons.

    It was her third and final project in grad school that really defined her future research path in transport model validation, she says. White developed a radiometer-based instrument for measuring the turbulent fluctuations in the electron temperature in the core region — deep inside the plasma, very far from the edge and plasma boundary. White explains that fusion scientists had focused quite a bit on measuring turbulence in the density fluctuations, but less attention had been paid to temperature fluctuations: “It’s a harder measurement to make.” She provided the data to a collaborating group that could run very sophisticated simulations of the experimental set-up, which kick-started the ongoing theme of “transport model validation” in her research.

    Even as a kid, White reflects, “I loved tinkering.” Over the years she would take apart and rebuild dirt bikes, motorcycles, and cars. Her parents, both lawyers, were “very encouraging” of her mechanical inclinations, she says. Their household was full of books, and any time she had a question, they encouraged her to search out the answers on her own, an early lesson in research skills. “Now, I just pull out my phone and find everything” she says with a smile. But even now, she says, her house is “full of books.”

    As she did while growing up in a family given to outdoor activities, White enjoys hiking and backpacking, and says she’s now learning fly-fishing, “but I don’t catch a lot of fish yet.” She also enjoys amateur astrophotography, a hobby she picked up in Arizona, one of the country’s premier areas for astronomy. “Astrophotography is another way to remotely probe plasmas, since most of the objects we see up there are plasmas,” she says.

    Currently, she continues to push frontiers in her field, aiming to predict with high confidence the details of the turbulence in tokamaks, and to use these predictions to help winnow down the most promising possible new reactor system designs. A lot of past research in predictive models has involved “much trial and error,” she says, and finding formulas that can make truly useful predictions could be an important step on the long road toward practical, economical fusion power. White says she is excited about the ARC tokamak concept recently developed by MIT researchers, and how “theory-based predictive modeling can feed into new high magnetic field designs.”

    Though her work at MIT has expanded to include more theory and simulations, “I still like tinkering,” she says. “One of my favorite things is building instruments” to enable new or better measurements, “and analyzing experimental data.” And now, working with her graduate students and postdoc, she is developing systems to carry out measurements of turbulence and other factors at four different research reactors.

    White’s heavy emphasis on validation, and the synthesis of experiment and simulation work, continues to this day. “All my students get involved with transport model validation,” she says. She explains that validation is an ideal theme for the group, since it pushes more theory-minded students to learn about hardware, and more hands-on students to learn about the theory.

    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 3:16 pm on June 17, 2016 Permalink | Reply
    Tags: , Fusion technology, ,   

    From Physics Today: “NIF may never ignite, DOE admits” 

    Physics Today bloc

    Physics Today

    17 June 2016
    David Kramer

    More than three years after the deadline passed for obtaining a sustained, high-energy-yield nuclear fusion reaction at the National Ignition Facility (NIF), the US Department of Energy is still unsure whether the $3.5 billion laser can ever attain that milestone.

    NIF Bloc
    LLNL/NIF
    NIF

    Much as it did in 2012, the agency has established a new, less ambitious goal for NIF several years hence: to determine whether the machine can ever achieve its eponymous goal, and if not, why not.

    “The question is if the NIF will be able to reach ignition in its current configuration and not when it will occur,” states a May report prepared by DOE’s National Nuclear Security Administration (NNSA).

    NNSA

    The reassessment of progress toward ignition at the Lawrence Livermore National Laboratory facility was conducted three years after the NNSA suspended its formal two-year-long ignition campaign in September 2012. Ignition, the threshold at which more energy results from a fusion reaction than is required to spark it, is an essential determinant in whether inertial confinement fusion (ICF) could ever become a source of fusion power.

    Despite the report’s assurances that much progress has been made toward ignition since 2012, the NNSA appears no closer to committing to ignition on NIF than it was then. In a December 2012 report to Congress, the agency found “no compelling information suggesting that the [NIF’s] indirect-drive approach cannot achieve ignition.” Still, then-NNSA administrator Tom D’Agostino said it was “too early to say whether or not ignition can be achieved at the NIF.”

    In a new plan for the ICF program, the NNSA establishes a goal, with a deadline of 2020, to “determine the efficacy of reaching ignition on NIF.” That contrasts sharply with the virtual assurances of ignition that were made by proponents in 2009, when NIF began operating. Although ignition experiments continue at NIF, they have been interspersed with experiments designed to deepen understanding of other nuclear weapons–related phenomena, such as the behavior of materials under extreme pressures and densities.

    Since 2012 NIF’s 1.8 MJ laser has nearly doubled the frequency of shots, the machine’s diagnostics have been improved, and progress has been made on identifying key impediments to ignition, the new report states. NIF’s indirect-drive approach focuses 192 beams on a cylinder, or hohlraum, containing a tiny capsule of fusion fuel. The hohlraum converts the light to x rays, which implode the capsule.

    In the meantime, the University of Rochester’s Omega laser and Sandia National Laboratories’ Z machine—both also supported by the NNSA’s inertial confinement fusion program—continue research on alternative approaches to ignition.

    U Rochester Omega Laser
    U Rochester Omega Laser

    Sandia Z machine
    Sandia Z machine

    Omega, a glass laser like NIF, uses direct drive, which brings beams to impinge directly on targets; Z uses electromagnetic fields to produce implosions.

    The NNSA review says computer models and codes predicting that NIF would attain ignition conditions “are not capturing the necessary physics to make such predictions with confidence. A lack of appreciation for this, combined with a failed approach to scientific program management, led to the failures” in the ignition campaign.

    Although the performance of NIF’s targets containing fusion fuel continues to improve, “currently, there is no known configuration, specific target design, or approach that will guarantee ignition on the NIF,” says the review.

    Stephen Bodner, a former director of the plasma physics program at the US Naval Research Laboratory (NRL), has been a vocal critic of NIF since before its construction began. In a 1995 paper published in Plasma Physics and Controlled Fusion, Bodner predicted that the highly intense NIF laser would create instabilities in the plasma. That, plus the formation of unpredictable magnetic fields, would prevent the symmetrical implosions required for ignition.

    “Basically [the report] is confirmation of what I predicted in 1995,” Bodner says. “It took the community 21 years, and many billions of dollars, to vindicate my predictions. So sad.”

    Regardless of whether ignition is achieved, there are other compelling nuclear weapons stewardship questions concerning the properties of thermonuclear plasmas with multi-megajoule yields, the NNSA report says. Planned Russian and Chinese laser facilities may surpass NIF’s capabilities, it warns, and in an era without nuclear testing, a source capable of producing 500 MJ of fusion energy “will be essential for the health of the [weapons] program.” Such energy yields are unlikely to be achieved within the next decade but should be considered an ultimate goal, the report says.

    Bodner argues, however, that NIF’s regimes of temperature, ionization, pressure, density, and radiation spectrum are fundamentally different from those that occur in a nuclear weapon. “To extrapolate the regime in the laboratory that they’re using to anything in nuclear weapons would be outrageously irresponsible,” he says. “They should not be using any of that science in the nuclear weapons program.”

    David Crandall, a former NNSA scientist who helped oversee NIF, disagrees. He says the realization that the codes predicting ignition were wrong has instilled a new level of caution among weapons scientists about extrapolating from data sets of nuclear tests. “That piece of reality was extremely important to the weapons program,” he says. Further, Crandall says, new methods have been developed for using NIF-generated fast neutrons to test weapons codes. For those techniques, neutron yield is more important than ignition. Also, he explains, experiments at NIF have already provided important new information about the behavior of plutonium at high pressures.

    John Edwards, associate director for the NIF’s ICF program, declines to say whether he’s optimistic or pessimistic about ignition at NIF. Progress since 2012 includes the first ever laboratory demonstration of the alpha heating process, in which thermal energy is supplied by the helium nuclei that result from fusion. “But there are obstacles which we are quite open about,” Edwards acknowledges. Researchers think they can overcome the instabilities inside the hohlraums by making the cylinders larger; the question is whether NIF’s energy is sufficient to drive the larger targets, he says.

    Reconfiguring NIF to perform direct-drive experiments is being evaluated by a University of Rochester–led team. But that will require a major revamp costing several hundred million dollars.

    Bodner argues that solid-state lasers like NIF and Omega won’t work; he says the krypton fluoride gas laser—two of which he helped build while at the NRL—is the best option for an ignition driver. The KrF laser in a direct-drive mode produces a broader bandwidth beam that can be “smoothed” to eliminate asymmetric hot spots, he says. But the NNSA’s plan doesn’t include KrF lasers among its driver candidates.

    Stephen Dean, president of the nonprofit Fusion Power Associates, says DOE’s justification for NIF has shifted from the energy-relevant milestone of achieving ignition to a focus mainly on weapons research. “They don’t want to be held to ignition,” he says. Dean sees a parallel with DOE’s magnetic fusion program. In 1980 the project was sold as an energy program with a 2000 deadline for construction of a working fusion power plant; today it’s classified as a science program.

    “You have people working who were goal-oriented,” Dean says. “And when the program doesn’t accomplish those goals, there’s a scramble to do something to save it.”

    See the full article here .

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  • richardmitnick 8:53 am on June 14, 2016 Permalink | Reply
    Tags: , Diagnostic provides top-down view of neutrons, Fusion technology, ,   

    From LLNL: “Diagnostic provides top-down view of neutrons” 


    Lawrence Livermore National Laboratory

    Jun. 13, 2016
    Jeremy Thomas
    thomas244@llnl.gov

    1
    Target Diagnostics engineer Francisco Barbosa completes installation of the North Pole neutron Time of Flight (nTOF) diagnostic on the roof of the National Ignition Facility.

    A new diagnostic built on the National Ignition Facility’s (NIF) roof is giving researchers a clearer picture of the neutrons released during laser-driven implosions of target capsules containing deuterium or deuterium and tritium (DT).

    NIF Bloc
    LLNL/NIF
    LLNL/NIF

    Instruments inside the North Pole neutron Time of Flight (nTOF) enclosure, a structure slightly larger than an industrial shipping container, detect and record neutron arrival times, providing researchers with much-needed data in the northern hemisphere of the NIF Target Chamber.

    “It will give us a view of what we’ve been missing, and we believe a quieter one (with less interference) than what we’ve gotten so far,” said NIF Co-Target Diagnostic Manager Mark Jackson.

    The north pole system joins four other nTOF detectors — one located in the basement of the Target Bay (south pole), two on the Target Chamber equator, and one in the neutron alcove. The new nTOF is on the roof to provide a view of neutrons almost directly opposite from the south pole detector, enabling researchers to determine if the neutron source is moving coherently.

    “The detectors in the nTOF measure the time of flight of the thermonuclear neutrons from the implosion to the detector, and so their velocity,” said Joe Kilkenny, chief NIF experimentalist for measurements. “The north pole nTOF is close to opposite to NIF’s south pole nTOF. Importantly, this allows the Doppler shift of the neutrons due to motion of the compressed plasma — like the pitch of a train’s whistle changing as it approaches you and moves away from you—to be measured from the difference in the arrival times at the north and the south pole nTOFs.”

    As neutrons produced in the target chamber pass through the bibenzyl crystal housed in the North Pole nTOF enclosure, they induce scintillation light. The crystal’s scintillation light is collected by a fast photo-detector which in turn produces a voltage in proportion to the number of passing neutrons. This voltage signal is then digitized every 100 picoseconds (a tenth of a billionth of a second), producing a high-fidelity record of the neutron flux passing through the detector.

    The data collected by the devices will help researchers determine the shot’s yield, as well as interesting properties of the plasma producing the neutrons, including its temperature and velocity. Understanding those properties motivated constructing the north pole system opposite the existing south pole system.

    Construction crews began work on the enclosure last fall, cutting a 40-foot by 20-foot hole in the top of the NIF building down to the inner concrete ceiling of the facility. The precise alignment and the tricky angle of the three-inch-diameter line-of-sight flight path from target chamber center (TCC), projecting through a small hole in the floor of the structure, required an impressive feat of engineering. It also presented challenges from wind and seismic load, facility modification, and temperature control, Jackson said. About 30 LLNL employees worked on the project over the last year, about half of them from the Lab’s engineering staff.

    Behind the scintillators in the nTOF enclosure, preventing the neutrons from traveling further upward and outside the enclosure, is a three-foot thick concrete and steel block. The block is capable of fully stopping neutrons and photons, ensuring that any emissions are within the facility’s safety limits and reducing the risk of outside radiation exposure to a negligible level.

    The line-of-sight path is defined by a set of precision collimators that allow researchers to look at only the neutrons coming from the area around TCC.

    To allow for more efficient operation, and to minimize the time NIF employees will have to be on the roof, the detector can be operated by remote control.

    Not only is the newest detector a technological improvement over the others, said Perry Bell, NIF Co-Target Diagnostics manager, but the line of sight it affords is the best yet for researchers because there is limited mass around it to interfere with the measurement.

    NIF has more than 70 diagnostics in all, and Bell said two more diagnostics similar to the North Pole nTOF will be built to extend the facility’s diagnostic reach even further.

    “These detectors will provide additional insight into fusion ignition and will represent key diagnostics for the NIF program,” Bell added.

    The U.S. Department of Energy funded the construction and design of the diagnostic.

    See the full article here .

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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
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  • richardmitnick 10:34 am on June 6, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From MIT: “Kuang, Creely already contributing to fusion’s advancement” 


    MIT News

    1

    6.6.16
    No writer credit

    2
    No image caption. No image credit.

    PhD candidates thriving after first year at Plasma Science and Fusion Center

    This summer, nuclear fusion researchers at MIT and Germany’s Max Planck Institute will learn more about what’s going on inside their reactors, thanks in part to the accomplishments of two first-year Nuclear Science and Engineering doctoral students.

    Adam Kuang and Alex Creely work in separate groups at MIT’s interdisciplinary Plasma Science and Fusion Center (PSFC), helping advance the worldwide quest to harness fusion’s enormous potential as a low-cost, carbon-free energy source fueled by safe and readily available materials.

    Their contributions will help address two of fusion’s grand challenges: plasma turbulence, which affects the ability to create a self-sustaining “burning plasma” that produces more energy than it consumes, and the need to confine the plasma while safely extracting heat for electricity generation.

    Both young men have chosen to work in fusion research because it combines fascinatingly knotty technical challenges with the pursuit of an historic technological breakthrough. Creely, who earned his BS in mechanical engineering at Princeton University, explains, “Fusion is the most promising solution to the world’s challenges in energy and climate change. And working on fusion is the most worthwhile thing I can do to make a difference.”

    Or, as Kuang puts it, “we’re here to chase a dream — very few people today have a chance to do that.”

    Kuang became intrigued by fusion’s promise while earning undergraduate degrees in mechanical engineering and physics at Canterbury University in New Zealand. He chose MIT NSE for his graduate work because of its close engineering-physics ties, and now works on plasma boundaries and materials interactions with Senior Research Scientist Brian LaBombard.

    “One of the big problems is how to keep something hot, a 100 million degree plasma, away from things that don’t like to be hot, like reactor walls,” explains Kuang. “Ideally there would be a perfect step function at the plasma’s edge, but there’s always leakage, so you have to find ways to manage it and keep it from destroying the machine.”

    Kuang and research supervisor Dan Brunner spent the past academic year upgrading a multifunction metrology device originally designed by LaBombard for the PSFC’s Alcator C-Mod fusion experiment. They replaced its hydraulic mechanism with a linear electric drive that will allow faster, more precise, and more accurate temperature measurements, with reduced risk of probe damage. “It will tell us a lot more about what’s happening at the edge of the plasma,” he says.

    Creely works in a group under Associate Professor of Nuclear Science and Engineering Anne White, on one of the PSFC’s growing number of international collaborations, focused on Correlation Electron Cyclotron Emission (CECE) measurements of electron temperature through radiation. The diagnostic tool he built with fellow grad student Choongki Sung will be installed at the Max Planck Institute’s ASDEX-Upgrade fusion facility near Munich, where Creely and White will spend several weeks integrating it with density diagnostics.

    “Being able to measure temperature turbulence and density turbulence with the same system, which we haven’t been able to do before, is very relevant. It should help build understanding of how they’re coupled,” notes Creely.

    That understanding may help address the substantial gap between theoretical predictions of plasma behavior and observed results — a process that appeals to Creely’s enjoyment of experimental work, which was a prime motivator for him to join PSFC. He’s also spent time performing advanced analysis on existing turbulence data, extracting new insights into thermal diffusivity that he presented at this spring’s international Transport Task Force workshop.

    Both students intend to work in the fusion community after earning their doctorates. “Exactly what that will mean is anybody’s guess,” says Kuang. “But just providing some contribution to making fusion work, even if it takes until I’m 90, would feel like a justification — that’s what drives everyone.”

    Meanwhile, both are reveling in the collegial culture of MIT and the PSFC. “It’s cooperative — people are very open to helping, suggesting different tools you can use,” says Creely. He praises White’s accessibility and research acumen, as well as her interest in her students’ advancement, noting, “She really helped me get my materials together for my workshop presentation.”

    Kuang calls it “invigorating — the weekly science meetings are a very fun environment, and it feels like you can open any door and people will talk to you. I’ll stop in to ask [LaBombard] a quick question and walk out two hours later with material to keep me busy for a week.”

    See the full article here .

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  • richardmitnick 3:56 pm on June 1, 2016 Permalink | Reply
    Tags: , Fatima Ebrahimi, Fusion technology, , ,   

    From PPPL: “Physicist Fatima Ebrahimi conducts computer simulations that indicate the efficiency – Women in Science of an innovative fusion start-up technique” 


    PPPL

    May 31, 2016
    Raphael Rosen

    1
    Physicist Fatima Ebrahimi. (Photo by Elle Starkman / PPPL Office of Communications

    Physicist Fatima Ebrahimi at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University has for the first time performed computer simulations indicating the efficiency of a start-up technique for doughnut-shaped fusion machines known as tokamaks. The simulations show that the technique, known as coaxial helicity injection (CHI), could also benefit tokamaks that use superconducting magnets. The research was published* in March 2016, in Nuclear Fusion, and was supported by the DOE’s Office of Science.

    Physicists are interested in CHI because it could produce part of the complex web of magnetic fields that controls the superhot plasma within tokamaks. One component of that web is produced by large “D”-shaped magnets that surround the tokamak and pass through the hole in its center. The other component is produced by a central electromagnet known as a solenoid, which induces a current inside the plasma that creates another set of magnetic fields. These fields combine with the fields produced by the “D”-shaped magnets to form a twisting vortex that prevents the plasma from touching the tokamak’s walls.

    Future tokamaks — especially compact spherical tokamaks like NSTX-U — might not have enough room for solenoids, though.

    PPPL NSTXII
    PPPL NSTX-U

    CHI could be ideal for those tokamaks because it doesn’t require solenoids at all. During CHI, magnetic field lines, or loops, are inserted into the tokamak’s vacuum vessel through openings in the vessel’s floor. The field lines then expand to fill the vessel space, like a balloon inflating with air, until the loops undergo a process known as magnetic reconnection and snap closed. (Think of tying off that inflated balloon.) The newly formed closed field lines then induce current in the plasma.

    By performing simulations, Ebrahimi found that narrowing the part of the magnetic loop that extends up into the tokamak through the floor could cause 70 percent of the field lines to close, compared with 20 to 30 percent without such narrowing. “For the first time, we see a large volume of closure during computer simulations,” she said. The number of field lines that close is important because the more field lines that close, the greater the current flowing through the plasma, and the stronger the magnetic fields holding the plasma in place.

    “The findings help us figure out how we can get maximum start-up current in NSTX-U,” said Ebrahimi. “That is a direct application of the research. But now we also have insight into some basic physical phenomena: what are the physics behind the process of reconnection? How do the lines actually close?”

    The simulations also provide a boost to the advancement of fusion energy. “Can we create and sustain a big-enough magnetic bubble in a tokamak to support a strong electric current without a solenoid?” asks Ebrahimi. “The findings indicate that ‘yes, we can do it.'”

    *Science paper:
    Large-volume flux closure during plasmoid-mediated reconnection in coaxial helicity injection

    See the full article here .

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    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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