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  • richardmitnick 6:06 pm on May 10, 2016 Permalink | Reply
    Tags: , Fusion technology, LTX Tokamak,   

    From PPPL: “A major upgrade of the Lithium Tokamak Experiment at PPPL will explore liquid lithium as a first wall for hot plasmas” 


    PPPL

    May 10, 2016
    John Greenwald

    1
    View of the interior of the LTX prior to the upgrade. (Photo by Elle Starkman/Office of Communications)

    A promising experiment that encloses hot, magnetically confined plasma in a full wall of liquid lithium is undergoing a $2 million upgrade at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL). Engineers are installing a powerful neutral beam injector in the laboratory’s Lithium Tokamak Experiment (LTX), an innovative device used to test the liquid metal as a first wall that enhances plasma performance. The first wall material faces the plasma.

    PPPL LTX Lithium Tokamak Experiment

    “This will bring us one step closer to demonstrating this particular approach to fusion,” said Dick Majeski, principal investigator of the LTX. Funding comes from the DOE Office of Science.

    Energetic beams

    The neutral beam injector, a Russian-built device on loan from the Tri Alpha fusion firm in California, will shoot energetic beams into the small spherical tokamak to fuel the core of the plasma and increase its temperature and density — key factors in fusion reactions. “The beams will maintain the density and raise the temperature to a more fusion-relevant level,” said Philip Efthimion, PPPL head of the Plasma Science and Technology Department that includes the LTX.

    The experiment recently became the first device in the world to produce flat temperatures in a magnetically confined plasma. Such flatness reduces the loss of heat from the plasma that can halt fusion reactions. The LTX also has provided the first experimental evidence that coating a large area of walls with liquid lithium can produce high-performance plasmas.

    However, without fueling from the neutral beam the density of an LTX plasma tends to drop off fast. The beam upgrade will keep the density from dropping, and test whether the liquid lithium coating can continue to maintain flat temperatures in much hotter plasmas.

    A leader in use of liquid lithium

    PPPL has long been a leader in the use of liquid lithium to coat and protect the plasma-facing components inside tokamaks. The predecessor to LTX, the Current Drive Experiment-Upgrade (CDX-U), ran with a circular pool of liquid lithium at the bottom of the plasma. The CDX-U operated from 1999 to 2007 before it was disassembled for installation of heatable shells composed of thin stainless steel and thick sheets of copper that form the tokamak’s inner walls. LTX made its first plasma in 2008 and first used liquid coatings in 2010.

    Researchers have also explored the use of liquid lithium in the National Spherical Torus Experiment-Upgrade (NSTX-U), the laboratory’s flagship fusion experiment, prior to its recent upgrade. PPPL will continue to investigate use of the liquid metal in the revamped machine.

    The value of lithium as a first-wall material comes from its ability to sponge up particles that stray from the core of the plasma and keep them from recycling back and cooling down the edge and then the core. Lithium is a highly reactive material that combines with other elements and doesn’t let go.

    In LTX experiments, researchers use an electron beam to evaporate a pool of liquid lithium at the base of the tokamak. The evaporated metal then coats the shells. Keeping the temperature of the shells above the melting point of lithium sustains its liquid state.

    Differs sharply from a heavy metal first wall

    This approach differs sharply from the use of a heavy metal such as tungsten for a tokamak’s first wall. While tungsten resists erosion, has a high melting temperature and conducts heat well, heavy impurities kicked up by contact with the plasma can rapidly cool down the hot core. The Joint European Torus (JET) in the United Kingdom experiments with tungsten. ITER, the international tokamak under construction in France, also plans to use it.

    The LTX upgrade, scheduled for completion later this year, marks the latest PPPL format for studying the liquid metal. Experiments could resume next spring and plasma operations with the neutral beam by fall. The performance of the LTX upgrade could then provide new evidence of the ability of liquid lithium to serve as a first wall.

    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 (link is external).

    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.

     
  • richardmitnick 4:10 am on May 4, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “Scientists challenge conventional wisdom to improve predictions of the bootstrap current at the edge of fusion plasmas” 


    PPPL

    May 3, 2016
    John Greenwald

    1
    Simulation shows trapped electrons at left and passing electron at right that are carried in the bootstrap current of a tokamak. Credit: Kwan Liu-Ma, University of California, Davis.

    Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have challenged understanding of a key element in fusion plasmas. At issue has been an accurate prediction of the size of the “bootstrap current” — a self-generating electric current — and an understanding of what carries the current at the edge of plasmas in doughnut-shaped facilities called tokamaks. This bootstrap-generated current combines with the current in the core of the plasma to produce a magnetic field to hold the hot gas together during experiments, and can produce stability at the edge of the plasma.

    The recent work, published* in the April issue of the journal Physics of Plasmas, focuses on the region at the edge in which the temperature and density drop off sharply. In this steep gradient region — or pedestal — the bootstrap current is large, enhancing the confining magnetic field but also triggering instability in some conditions.

    The bootstrap current appears in a plasma when the pressure is raised. It was first discovered at the University of Wisconsin by Stewart Prager, now director of PPPL, and Michael Zarnstorff, now deputy director for research at PPPL. Prager was Zarnstorff’s thesis advisor at the time.

    Essential for predicting instabiities

    Physics understanding and accurate prediction of the size of the current at the edge of the plasma is essential for predicting its effect on instabilities that can diminish the performance of fusion reactors. Such understanding will be vital for ITER, the international tokamak under construction in France to demonstrate the feasibility of fusion power.

    ITER icon
    ITER Tokamak
    ITER Tokamak

    This work was supported by the DOE Office of Science.

    The new paper, by physicists Robert Hager and C.S. Chang, leader of the Scientific Discovery through Advanced Computing project’s Center for Edge Physics Simulation headquartered at PPPL, discovered that the bootstrap current in the tokamak edge is mostly carried by the “magnetically trapped” electrons that cannot travel as freely as the “passing” electrons in plasma. The trapped particles bounce between two points in the tokamak while the passing particles swirl all the way around it.

    Challenge to conventional understanding

    The discovery challenges conventional understanding and provides an explanation of how the bootstrap current can be so large at the tokamak edge, where the passing electron population is small. Previously, physicists thought that only the passing electrons carry the bootstrap current. “Correct modeling of the current enables accurate prediction of the instabilities,” said Hager, the lead author of the paper.

    The researchers performed the study by running an advanced global code called “XGCa” on the Mira supercomputer at the Argonne Leadership Computing Facility, a DOE Office of Science User Facility located at the Department’s Argonne National Laboratory.

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

    Researchers turned to the new global code, which models the entire plasma volume, because simpler local computer codes can become inadequate and inaccurate in the pedestal region.

    Numerous XGCa simulations led Hager and Chang to construct a new formula that greatly improves the accuracy of bootstrap current predictions. The new formula was found to fit well with all the XGCa cases studied and could easily be implemented into modeling or analysis codes.

    *Science paper:
    Gyrokinetic neoclassical study of the bootstrap current in the tokamak edge pedestal with fully non-linear Coulomb collisions

    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.

     
  • richardmitnick 11:20 am on May 2, 2016 Permalink | Reply
    Tags: , , Fusion technology, ,   

    From COSMOS: “Getting primed for fusion power” 

    Cosmos Magazine bloc

    COSMOS

    26 Apr 2016
    Cathal O’Connell

    Cracking fusion power would be one of the great technological achievements of the 21st century, providing almost limitless power with few drawbacks. With global efforts getting bigger and badder every year, Cathal O’Connell provides a primer to the basic technology.

    ITER Tokamak
    ITER Tokamak

    Fusion power is such a huge, potentially game-changing technology that it’s easy to get swept up in its utopian promise. Equally, it’s easy to dismiss the whole shebang as a wild fantasy that will never come to pass.

    Here’s what you need to know to help keep pace with developments in this global quest.

    What is nuclear fusion?

    Atoms are the really small bits from which we are all made. Inside each atom, when you strip away the shells of electrons, is an even smaller bit at the core – the nucleus.

    It turns out that when you join two small nuclei to make a bigger one, an enormous amount of energy is released – about 10 million times more energy than the puny chemical reactions that power most of our technology, such as burning oil, coal or the gasoline in your car.

    We know fusion works because it goes on in the core of the Sun. All the Sun’s heat and light are powered by fusion. The most important reaction is the fusion of two nuclei of hydrogen, which is the lightest atom, combine to form helium, the second lightest.

    How does it work?

    Igniting nuclear fusion is not as simple as starting a fire. It takes a lot of energy to get it going and typically, that means a temperature of millions of degrees Celsius.

    This is because atomic nuclei have a love-hate relationship. Each nucleus has a strong positive charge so they repel one another. To kickstart fusion, you have to overcome this repulsive barrier by ramming two nuclei together incredibly hard. That’s what happens in the core of the Sun, where the temperature is about 15 million °C and pressures are similarly insane.

    When the nuclei get close enough to touch, the nuclear strong force takes over – the strongest force in nature – and it’s the source of fusion energy.

    Fusion energy?

    The idea of fusion energy is to build power plants that generate energy by recreating the core of the Sun. Hundreds of research scale reactors have been built around the world.

    They are usually engineering marvels designed to containment hydrogen nuclei at a 100 million °C, or implode a nuclear pellet using massive lasers (see below).
    But I thought we already had nuclear power

    The nuclear power plants we have so far are based on a different process – nuclear fission, where you derive energy by splitting one big atom into two smaller atoms. That’s a much easier process and so fission reactors have been pumping power into the grid since the 1950s.

    Fusion reactors are much safer than traditional fission reactors because there is no chance of a runaway explosion and when the reaction is done, there’s no long-lived radioactive waste.

    Per kilogram of fuel, fusion releases four times more energy than fission and 10 million times more than coal.

    What’s the fuel?

    The first generations of fusion reactors will likely use two forms of hydrogen for the fuel – deuterium and tritium – because the fusion of these two nuclei is the easiest to achieve.

    Regular hydrogen is the smallest atom – just one electron orbiting a proton nucleus. Deuterium is a fatter version of hydrogen, where the nucleus contains a neutron as well as a proton. And tritium is the fattest hydrogen of all – its nucleus contains a proton and two neutrons.

    Deuterium is easily found in seawater, while tritium can be generated from lithium.

    The long-term goal is to switch to a deuterium-deuterium reaction, meaning all the world’s energy supply could one day be found in seawater.

    Has fusion ever been achieved?

    Humans first managed nuclear fusion on 1 November 1952 when the US exploded the first fusion bomb. Fusion bombs (also known as hydrogen bombs) are the most destructive weapons ever made. They typically use a fission-based atomic bomb to trigger a fusion reaction in the second stage.

    The challenge now is achieving fusion in a controlled manner.

    For more than 70 years researchers have been trialling different designs for containing the fusion reaction. Some of these designs (see below) have achieved fusion. The problem is releasing more energy than is put in, and doing it long enough to be useful. Nobody’s been able to do that yet.
    What’s been holding us back?

    Ah. The problem is the temperature. You have to heat the fuel to such a high temperature (100 million °C or so) that no material vessel could possibly contain it.

    The basic physics behind fusion has been known for decades. It’s the engineering that still needs to be worked out.

    What do fusion reactors look like?

    Fusion reactors come in all sorts of shapes and sizes.

    Most research has looked at containing the reaction within a sort of magnetic bottle. At the extreme temperatures of fusion, all of the electrons are stripped off the deuterium and tritium atoms, and what’s left is called a plasma.

    1
    How a tokamak, or toroidal magnetic confinement system, works.Credit: Encyclopaedia Britannica/UIG Via Getty Images

    The most common design is the toroidal chamber-magnetic (tokamak), which looks a bit like the inside of the Deathstar. Tokamaks form twisting donut-shapes called a torus. The plasma runs in rings and never touches the walls of the torus because it’s contained by the magnetic fields.

    Other variations confined the plasma in different geometries, such as the stellerator design which adds a twist with a different configuration of magnets. Other tokamak designs are spherical.
    But if fuel is squeezed in a magnetic field, how do you get the energy out?

    When deuterium fuses with tritium, an extra neutron is kicked out and receives a huge kick of energy. The neutron is a neutral particle, and so is not affected by the magnetic field – it can fly through the magnetic bottle and smash into a lithium blanket just inside the donut.

    The neutron collisions heat up the lithium. This heat is used to convert water into steam which drives turbines to generate electricity, just like in any other electric power-plant.
    What’s this about using lasers?

    Instead of using a magnetic field to contain a plasma, another idea is to ignite small fusion explosions by firing a powerful laser at a pellet.

    LLNL NIF
    LLNL/NIF

    At the National Ignition Facility at Lawrence Livermore National Laboratory in California, the world’s biggest laser (made of 192 laser beams) are fired simultaneously at a pellet of deuterium/tritium about the size of a pea.

    National Ignition Facility researchers have achieved fusion using this design, but the challenge is extracting more energy than is used to power the lasers. Their biggest problem is in constructing the pellet and its plastic container in the shape to absorb all the laser energy.

    And cold fusion?

    This is the idea to make a fusion reactor that works at close to room temperature. In 1989, British and American scientists seemed to achieve this a running a strong current through a platinum electrode in a thermos of heavy water (water where the hydrogen atoms are partially or completely replaced by deuterium) – but the experiment turned out to be flawed.

    Nowadays research into cold fusion is seen as an example of “pathological science”, like trying to build a perpetual motion machine.

    Best forget about this altogether. It’s not going to happen.

    What’s next for fusion?

    Despite the difficulties, progress in fusion power has actually been very rapid. Power output has increased by a factor of more than a million in 30 years.

    Much of the hope is centred on the ITER (Latin for “the way”) tokamak to be constructed in southern France by 2019.

    3
    ITER, the International Thermonuclear Experimental Reactor, is being designed to test the principles surrounding the generation of power from nuclear fusion, the energy source of stars. It comprises a toroidal chamber in which a plasma (pink) is contained by strong magnetic fields.Credit: MIKKEL JUUL JENSEN / SCIENCE PHOTO LIBRARY/Getty Images

    This design has been in the pipeline for two decades and is designed to be the first fusion reactor to produce more energy (about 10 times more) than it puts in. However, this 500-megawatt reactor is still only a proof-of-concept design, and no electricity will be generated.

    If ITER is successful, the next step is DEMO – which is designed to be the world’s first nuclear power plant to generate electricity, to be constructed by 2033.

    See the full article here .

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  • richardmitnick 4:29 pm on April 21, 2016 Permalink | Reply
    Tags: , , Fusion technology,   

    From AAAS: “ITER leader faces tough questions, even from relatively supportive U.S. House panel” 

    AAAS

    AAAS

    Apr. 21, 2016
    Adrian Cho

    1
    ITER construction is ramping up, even as the United States mulls its commitment to the project. ITER Organization

    For Bernard Bigot, director-general of ITER, the gargantuan fusion experiment under construction in Cadarache, France, a hearing in the U.S. House of Representatives was likely to be a relatively amicable event.

    ITER icon
    ITER Tokamak
    ITER Tokamak

    After all, even as budgetmakers in the Senate have tried repeatedly to pull the United States out of the troubled project, House appropriators have supported it and have prevailed in budget negotiations. Nevertheless, yesterday, in a hearing held by the energy subcommittee of the House Committee on Science, Space, and Technology, Bigot faced pointed questions from both Republican and Democratic representatives, suggesting some of them maybe losing patience with ITER.

    ITER aims to prove that a plasma of deuterium and tritium nuclei trapped in a magnetic field can produce more energy than it consumes as the nuclei fuse in a “burning plasma,” a process that mimics the inner workings of the sun. But ITER is running far over budget and at least 10 years behind its original schedule.

    In a tense exchange with Representative Dana Rohrabacher (R–CA), Bigot acknowledged that by the time ITER starts running late next decade its total cost will likely exceed $20 billion. That’s a big jump over the roughly $12 billion ITER was estimated to cost in 2006, when China, the European Union, India, Japan, Russia, South Korea, and the United States agreed to build the machine. The original plan also called for ITER to start running this year. More might have been done with the money slated for ITER if it had been spent instead on research involving more conventional nuclear energy, Rohrabacher said. “I still think that if we had put $20 billion into fission we would have done a lot more for humanity,” he said.

    The hearing opened an interesting fortnight for ITER and U.S. participation in it. Following a scathing external review in 2013, the international ITER organization revamped its management structure, including bringing in Bigot as director-general in November 2014. In November 2015, ITER officials presented a new baseline cost and schedule for the project. An independent committee will report on the reliability of that baseline on 27–28 April to ITER’s governing council. On 2 May, officials at the U.S. Department of Energy (DOE) are supposed report to Congress whether they think the United States should stay in ITER or leave. When pressed, Bigot agreed with Rohrabacher’s estimate that instead of the $1.1 billion originally envisioned, the U.S. contribution to ITER would likely total between $4 billion and $6 billion.

    Generally, subcommittee members seemed supportive of fusion research and ITER in particular. “I really appreciate the work that you’ve been doing, and from all that I’ve been hearing, ITER is in a much better place for your efforts,” Representative Randy Hultgren (R–IL) said to Bigot. “I do see how important this partnership is and I hope [the United States] can remain a reliable partner.”

    In fact, recently released budget numbers demonstrate exactly how much more supportive of fusion research and ITER the House is than the Senate. Earlier this week, the House appropriations committee passed its version of the bill that would fund DOE for fiscal year 2017, which starts 1 October. It includes $450 million for DOE’s fusion energy science (FES) program, a 2.7% bump up from this year’s budget. That sum includes $125 million for parts for ITER. In contrast, the Senate appropriations committee version of the bill would cut the FES budget by 36% to $280 million and would zero out ITER funding.

    Representative Bill Foster (D–IL) asked whether a U.S. withdrawal would be fatal to the ITER project. Bigot declined to answer the question directly, but said, “if the U.S. were to withdraw it would be a real drawback because it would be difficult to replace the expertise.”

    Another senior Democrat, Representative Alan Grayson (FL), expressed frustration with ITER. Fusion energy “is going to happen,” said Grayson, who is the ranking member of the subcommittee. However, he said, “it’s been 10 years already since the major governments signed off on the ITER project. We now have 11 years to go before we start the major experiments and there isn’t even a plan to generate net electricity from ITER, that’s not its design or its purpose.” He asked whether there was a way to achieve fusion on a 10-year timescale, but the witnesses—Bigot; Stewart Prager, the direct of DOE’s Princeton Plasma Physics Laboratory (PPPL) in New Jersey; and Scott Hsu, a fusion physicist at Los Alamos National Laboratory in New Mexico—cautioned that there was not.

    U.S. competitiveness

    The hearing aimed to assess more generally the United States’s fusion program. “Fusion energy research in Asia and Europe is escalating, and for the U.S. to contribute competitively in the face of larger investments elsewhere, we must focus on activity with breakthrough potential,” Prager said. PPPL researchers focus on four areas, Prager said: developing design for a “pilot plant” that might come after ITER and not only sustain a burning plasma, but generate a net gain in electricity; developing materials that can withstand the intense radiation in a fusion reactor; large-scale computer simulations; and physics related to ITER. Still, he said, U.S. fusion research is “resource limited.”

    PPPL NSTXII
    NSTX-U tokamak at PPPL, Princeton, NJ, USA

    Hsu testified that DOE currently supports only two types of fusion research: magnetic confinement fusion that uses devices called tokamaks such as ITER and PPPL’s National Spherical Torus Experiment; and inertial confinement fusion, which uses the powerful lasers at the National Ignition Facility at Lawrence Livermore National Laboratory in California (which is supported by DOE’s weapons program) to implode a fuel pellet.

    NIF Bloc
    LLNL NIF
    National Igniton Facility laser program at LLNL, Livermore, CA, USA

    DOE’s fusion energy science’s program used to spend $40 million a year on alternative fusion technologies, Hsu testified, but that money has dried up in recent years, even as nations such as China have pursued them.

    See the full article here .

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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  • richardmitnick 12:08 pm on April 15, 2016 Permalink | Reply
    Tags: , Fusion technology, ,   

    From PPPL: “Princeton graduate student Imène Goumiri creates computer program that helps stabilize fusion plasmas” 


    PPPL

    April 14, 2016
    John Greenwald
    Raphael Rosen

    1
    Imène Goumiri led the design of a controller. (Photo by Elle Starkman/Office of Communications)

    Imène Goumiri, a Princeton University graduate student, has worked with physicists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) to simulate a method for limiting instabilities that reduce the performance of fusion plasmas. The more instabilities there are, the less efficiently doughnut-shaped fusion facilities called tokamaks operate. The journal Nuclear Fusion published* results of this research in February 2016. The research was supported by the DOE’s Office of Science.

    The new method uses feedback from sensors for real-time control of the rotation of plasma that swirls within a tokamak and fuels fusion reactions. Goumiri, a student in the Princeton Department of Mechanical and Aerospace Engineering, led the design of a controller that employs two different kinds of actuators. The first provides a torque — or twisting force that causes rotation — by injecting high-energy neutral particles into the plasma. The second uses a tokamak’s three-dimensional coils to create a magnetic field that generates a torque by acting as a drag on the rotation and slowing it down.

    Goumiri built a model of plasma rotation from data collected from PPPL’s National Spherical Torus Experiment (NSTX) before it was upgraded, and used it to construct the program in MATLAB software.

    PPPL/NSTX
    PPPL/NSTX

    She then translated the program into a predictive model based on PPPL’s TRANSP code, the global standard for analyzing plasma performance. The TRANSP model found the new approach to be effective at controlling rotation.

    “This confirmed the validity of our model and the efficacy of the controller,” said Goumiri, the lead author of the paper. Coauthors included Clarence Rowley, Princeton professor of mechanical and aerospace engineering, and David Gates, principal research physicist at PPPL and stellarator physics leader, who served as her academic advisors; and Steve Sabbagh, senior research scientist and adjunct professor of applied physics at Columbia University on long-term assignment to PPPL, a member of her doctoral committee who served as a scientific advisor.

    “Shear” lessens instabilities

    The new program, which adapts quickly to feedback from the plasma, draws on the fact that rotating different sections of a plasma at different speeds creates a force called “shear” that lessens instabilities. Rotation can also disrupt transport, a process that leaks heat from the plasma and interferes with fusion reactions.

    A unique aspect of the new model is its use of three-dimensional magnetic fields to manipulate the torque produced by the neutral beam injector. The drag created by these magnetic fields, technically known as “neoclassical toroidal viscosity,” gives researchers more precise and continuous control of the plasma rotation.

    Looking ahead, researchers noted that the upgraded NSTX, called the National Spherical Torus Experiment-Upgrade (NSTX-U), has a second neutral beam injector that can affect a broader region toward the edge of the plasma. This broadened region could alter the shear and enable greater control of plasma instabilities.

    Researchers also noted that this new class of controllers can be developed from simulations based on experimental data, with no need for additional experiments for calibration. The new method could replace classical controllers like proportional-integral-derivative (PID) systems, which use experiments to tune their parameters. The new method would necessitate fewer experiments and would provide a way to predict requirements for adjusting plasma rotation in future fusion facilities.

    *Science paper:

    Modeling and control of plasma rotation for NSTX using neoclassical toroidal viscosity and neutral beam injection

    Science team:

    I.R. Goumiri1, C.W. Rowley1, S.A. Sabbagh2, D.A. Gates3, S.P. Gerhardt3, M.D. Boyer3, R. Andre3, E. Kolemen3 and K. Taira4

    Author affiliations

    1 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA

    2 Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA

    3 Princeton Plasma Physics Laboratory, Princeton, NJ 08544, USA

    4 Department of Mechanical Engineering, Florida State University, Tallahassee, FL 32310, USA

    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.

     
  • richardmitnick 10:35 am on March 22, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “Physicist Tyler Abrams models lithium erosion in tokamaks” 


    PPPL

    March 21, 2016
    Raphael Rosen

    1
    Physicist Tyler Abrams. (Photo by Tyler Abrams)

    The world of fusion energy is a world of extremes. For instance, the center of the ultrahot plasma contained within the walls of doughnut-shaped fusion machines known as tokamaks can reach temperatures well above the 15 million degrees Celsius core of the sun.

    PPPL NSTXII
    NSTX tokamak at PPPL

    And even though the portion of the plasma closer to the tokamak’s inner walls is 10 to 20 times cooler, it still has enough energy to erode the layer of liquid lithium that may be used to coat components that face the plasma in future tokamaks. Scientists thus seek to know how to prevent hot plasma particles from eroding the protective lithium coating.

    Physicist Tyler Abrams has led experiments on a facility in the Netherlands called Magnum-PSI that could provide an answer.

    1
    Side view of the 15 meter long Magnum-PSI experiment. To the far left, a cascade arc plasma source produces plasmas of Hydrogen, Deuterium or Argon. The vertical tubes guide lasers which determine the temperature and density of the plasma via Thomson scattering. In the center of the photo, the plasma beam impinges on the target plate. A movable arm can then retract the target into the target exchange and analysis chamber, a vacuum chamber for materials research without exposure to contamination in the air. The magnets which focus the plasma into a beam were not installed at the time of this picture. Photo: Bram Lamers

    The research, published in Nuclear Fusion in December 2015, found that combining lithium with the hydrogen isotope deuterium substantially reduced the erosion. Abrams conducted the research as a doctoral student in the Princeton Program in Plasma Physics substantially based at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL). He currently is a postdoctoral research fellow at General Atomics. The research was funded by the DOE Office of Science.

    “One potential issue with lithium is that it tends to erode off the chamber walls surfaces very quickly when it gets hot,” said Abrams. “In my research I was trying to determine exactly how much lithium actually comes off the wall under the conditions expected for fusion reactors.”

    Physicists have long known that in fusion devices with low levels of plasma flux, meaning that the flow of charged particles within them is relatively small, the rate at which lithium eroded depends on the plasma’s temperature. Physicists had not, however, studied what would happen to lithium coatings in high-flux plasmas with a greater flow of particles. That increased flow will occur in future tokamaks. Scientists had thought that erosion would be greater in such machines.

    But Abrams and the team found that the opposite was true while performing experiments at the Dutch Institute for Fundamental Energy Research. They found that the amount of lithium erosion in high-flux plasmas was much less than that in low-flux plasmas. The team conjectured that the difference stemmed from the chemical properties of lithium deuteride (LiD), a molecule created when deuterium atoms from plasma bond with the liquid lithium coating.

    To test the conjecture, Abrams and his colleague Dr. Mohan Chen, of Princeton University, created a computer program that modeled how deuterium combined with lithium. The new computer program indicated that the observed low rate of lithium erosion could stem from two factors. First, lithium deuteride molecules have a strong binding energy, meaning that incoming deuterium ions from the plasma have a hard time knocking lithium atoms loose from their bonds. Second, when deuterium ions in a plasma hit lithium deuteride molecules, they tend to knock the deuterium atoms out of the molecules and leave the lithium atoms in place.

    Once the computer program had been completed, Abrams and the other scientists performed experiments on Magnum-PSI. They shot streams of plasma at samples of lithium that were placed inside the machine and recorded how much lithium came off. The amount of lithium that was eroded was similar to the amount predicted by Abrams’ model. In addition, the simulations showed that a layer composed of lithium deuteride would erode 20 times more slowly than would a layer of pure lithium.

    “My results suggest that lithium is able to handle significantly higher amounts of plasma exposure and higher temperatures than others had previously expected,” said Abrams. “This suggests that liquid lithium will not erode too quickly if it is used on the walls of fusion reactors and will not contaminate the core plasma too much, making lithium coating a much more attractive alternative to solid metals walls.”

    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.

     
  • richardmitnick 4:17 pm on March 16, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From Princeton: “Compressing turbulence to improve inertial confinement fusion experiments (PRL)” 

    Princeton University
    Princeton University

    March 16, 2016
    John Greenwald

    Physicists have long regarded plasma turbulence as unruly behavior that can limit the performance of fusion experiments. But new findings by researchers associated with the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and the Department of Astrophysical Sciences at Princeton University indicate that turbulent swirls of plasma could benefit one of the two major branches of such research. The editors of Physical Review Letters highlighted these findings — a distinction given to one of every six papers per issue — when they published the results last week on March 11.

    Lead author Seth Davidovits, a Princeton University graduate student, and Professor of Astrophysical Sciences Nathaniel Fisch, his thesis adviser and Associate Director for Academic Affairs at PPPL, produced the findings. They modeled the compression of fluid turbulence, showing effects that suggested a surprising positive impact of turbulence on inertial confinement fusion (ICF) experiments.

    Stimulating this work were experiments conducted by Professor Yitzhak Maron at the Weizmann Institute of Science in Israel. Those experiments, on a Z-pinch inertial confinement machine, showed turbulence that contained a surprising amount of energy, which caught Fisch’s attention during a recent sabbatical at Weizmann.

    In a Z-pinch and other inertial confinement (ICF) machines, plasma is compressed to create fusion energy. The method contrasts with the research done at PPPL and other laboratories, which controls plasma with magnetic fields and heats it to fusion temperatures in doughnut-shaped devices called tokamaks.

    PPPL NSTXII
    PPPL NSTX-U tokamak

    The largest Z-pinch device in the United States is at the DOE’s Sandia National Laboratory. Other inertial confinement approaches are pursued at, among other places, the DOE’s Lawrence Livermore National Laboratory.

    Sandia Z machine
    Sandia Z machine

    LLNL NIF
    LLNL National Ignition Facility

    Present ICF approaches use compression to steadily heat the plasma. Methods range from squeezing plasma with magnetic fields at Sandia to firing lasers at capsules filled with plasma at Livermore’s National Ignition Facility. The presence of turbulence in the plasma is widely thought to increase the difficulty of achieving fusion.

    But there could be advantages to turbulence if handled properly, the authors point out, since energy contained in turbulence does not radiate away. This compares with hotter plasmas in which heat radiates away quickly, making fusion harder to achieve. By storing the energy of the compression in turbulence rather than temperature, the authors suppress the energy lost to radiation during the compression.

    The turbulent energy also does not immediately lead to fusion, which requires high temperature. This means a mechanism is needed to change the turbulence into the temperature required for fusion once the plasma has been compressed.

    Davidovits used a software code called Dedalus to show that turbulent energy is increased during the compression, but then suddenly transformed into heat. As external forces in his simulation compress the turbulence to increase the energy stored within it, they also gradually raise the temperature and viscosity of the plasma. The viscosity, which describes how “thick” or resistant to flow a fluid is, acts to slow the turbulence and convert its energy to temperature. The viscosity started small so that the turbulence was initially unhindered. The rapid compression then kept the viscosity growing until it suddenly catalyzed the transfer of energy from the turbulence to the temperature.

    In an experiment, this process would create the conditions for nuclear fusion in a plasma composed of the hydrogen isotopes deuterium and tritium. “This suggests a fundamentally different design for compression-based fusion experiments,” Davidovits said, “and a new paradigm for the inertial technique of producing fusion energy.”

    He warns, however, that the simulation includes caveats that could diminish the findings. For example, the model doesn’t consider any possible interaction between the plasma and the containing capsule, and highly energetic turbulence might mix parts of the capsule into the plasma and contaminate the fusion fuel.

    Nonetheless, the authors call the rapid transfer of turbulent energy into temperature during ICF experiments a “tantalizing” prospect that could benefit such research. And they note that their findings could lead to new understanding of the evolution of the relationship between the pressure, volume and temperature of a gas that is substantially turbulent. Determining this will be quite challenging, they say, “but the understanding will be important not only for the new fusion approach, but also for many situations involving the behavior of low viscosity compressible fluids and gases.”

    This research was initiated through a grant by the Defense Threat Reduction Agency, a unit of the U.S. Department of Defense, and has been supported also by the DOE’s National Nuclear Security Administration through a consortium with Cornell University. Recently, the National Science Foundation and the Israel Binational Science Foundation combined funding opportunities to ensure further experiments at Weizmann on this topic and continued collaboration with the Princeton researchers.

    See the full article here .

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    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 12:41 pm on March 10, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “PPPL engineers design and build state-of-the-art controller for AC to DC converter that manages plasma in upgraded fusion machine” 


    PPPL

    March 7, 2016
    Raphael Rosen

    The electric current that powers fusion experiments requires superb control. Without it, the magnetic coils the current drives cannot contain and shape the plasma that fuels experiments in doughnut-shaped tokamaks correctly.

    Now, engineers at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have developed an updated version of a key electronic component that helps regulate the current that powers the coils in PPPL’s recently completed National Spherical Torus Experiment-Upgrade (NSTX-U).

    PPPL NSTXII
    NSTX

    The device, known as a digital firing generator, replaces an analog device in the previous machine that was less accurate and harder to maintain.

    This upgrade will bring NSTX-U in line with other tokamaks around the world that employ the same kind of device. The engineers — Robert Mozulay, Weiguo Que, and Charles Neumeyer — presented their results at the 26th Symposium on Fusion Engineering in June 2015. This work was supported by the DOE Office of Science (Office of Fusion Energy Sciences).

    “The digital firing generator is very important for ensuring that NSTX-U operates effectively and reliably,” Neumeyer said. “These new generators extend the life of the power supplies that form the backbone of PPPL’s electrical power system, and provide the precise control necessary to drive currents in the NSTX-U magnet coil up to 140,000 amps — higher than any previous experiment at PPPL.”

    The ability to better manage the electric current flowing into NSTX-U, the world’s most advanced spherical tokamak, will provide new insights into how to control plasma, the soup of electrons and charged atomic nuclei that swirl within fusion facilities. With better control, scientists will be able to perform experiments on NSTX-U to advance the design of a working fusion reactor.

    The new generator links the computer that controls NSTX-U and a device called a “thyristor rectifier” that adjusts the voltage, and thus the current, for NSTX-U experiments. Through a computer command sent via fiber optic cables, the digital firing generator causes the AC (alternating current) that flows into PPPL to convert to DC (direct current) and deliver the amount requested for an experiment. The team also built the fiber optic links that make the conversion possible.

    “A single thyristor rectifier can generate up to 2,000 volts of DC current at 24,000 amps, for about three seconds,” Mozulay said. “That amount of voltage corresponds to 48 megawatts of power, which, during the three-second pulse, could power approximately 8,000 average-sized New Jersey homes.”

    NSTX-U has 32 pairs of thyristor rectifiers, each controlled by its own digital firing generator. These rectifiers help to double the heating power and magnetic field strength that the upgrade has made possible. “All of the firing generators were designed, built, and tested here at PPPL,” Mozulay said.

    Other advantages over their analog predecessors include a greater ability to coordinate the production of electric current and to shut down when sensing that a rapid change in current might damage components. This synchronized shut-off process is like applying the brakes in a car, Mozulay said.

    Engineers will also be able to adjust the digital firing generators much more easily than their analog predecessors. “Making changes in the future will mean making changes to the programming, not electronics,” Mozulay said. “A new program can be downloaded into the digital signal processors within the firing generators in minutes, thereby allowing fast, accurate updates.”

    Other PPPL staff members who helped design and build the digital firing generator include Jim Corl, Ed Bremen, Gary D’Amico, Westley Reese, Cindy Lasky, Gary Gibilisco, Alexis Sanchez, and Elliott Baer.

    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 1:04 pm on February 22, 2016 Permalink | Reply
    Tags: , Fusion technology, ,   

    From PPPL: “Developing the digital safeguard that protects the National Spherical Torus Experiment-Upgrade at PPPL” 


    PPPL

    February 22, 2016
    John Greenwald

    As the most powerful spherical tokamak in the world, the National Spherical Torus Experiment-Upgrade (NSTX-U) at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) produces magnetic forces that are far greater than what its predecessor could generate. Moreover, the power supply system that drives current in the fusion facility’s electromagnetic coils can potentially produce even higher forces unless properly constrained. To access the impressive operating capability planned for NSTX-U, while protecting the coils from accidental overload, a new Digital Coil Protection System (DCPS) was a key requirement.

    PPPL NSTXII
    NSTX

    At PPPL, engineers have successfully designed, built, tested and installed a state-of-the-art system that is up to the task. It replaces the analog system on the old NSTX that was too limited for the new operating levels. The new approach provides real-time computation of forces and stresses that result from the combined influence of current flowing in all the coils and in the plasma that fuels fusion reactions. This system is the first digital safeguard for a fusion device, said Charles Neumeyer, the engineer who defined its requirements, and could serve as a model for other labs, including ITER, the international experiment under construction in France. This work was supported by the DOE Office of Science.

    Lightning speed

    The safeguard consists of hardware, software and a network of fiber-optic cables that all work together at lightning speed. The system checks critical variables during each NSTX-U shot at a rate of 1,200 times every 200 microseconds and forces a shutdown if pre-set limits are approached.

    The team that developed the DCPS devoted four years of long hours to a project disrupted by tragedy when Ron Hatcher, a beloved engineer who led the work, suddenly died. “At our first meeting afterward I said to the team, ‘Ronnie’s gotten us this far, let’s finish it.’ And we did,” recalled engineer Tim Stevenson, who became leader of the project in 2014.

    The advanced system’s software consists of two identical codes that look at the same data and back each other up. The first code, located in the NSTX-U control room computer, is set more restrictively to trip first. The second code, which runs on a dedicated computer at the site of the NSTX-U, would respond and trip second. The two are independent and redundant and each is set to operate if the other one fails.

    This system is highly flexible. Engineers have already adjusted it to ensure that the ohmic heating coil that puts current in the plasma stays hotter than the coils that produce the magnetic field that encircles the plasma. This proved necessary when an intended air gap between the ohmic heating coil and the inner coils was not provided during the construction process.

    A project within a project

    Development of the DCPS “was a project within a project,” Stevenson noted, because it paralleled development of the NSTX-U “and was a real team effort.” Major contributors included engineers Keith Erickson, who designed the real-time computer and software system, and Hans Schneider, who built the hardware that ties the DCPS together with substantial assistance from Vince Mastrocola, Kevin Lamb, Gary Gibilisco and John Dong.

    Key contributions came also from engineers Gretchen Zimmer, who developed an auto-testing system for the software; Greg Tchilinguirian, who designed data management systems; Roman Rozenblat, who tested the software; John Lawson, who developed fiber-optic connections; and Paul Sichta, who provided input to the overall design. Engineer Peter Titus and members of the engineering analysis division derived protection algorithms for NSTX-U throughout the entire upgrade design process. Physicist Stefan Gerhardt, who heads experimental research operations for the NSTX-U, compiled these results into a format appropriate for the real-time protection system and verified the final results.

    The DCPS has proven vital to the NSTX-U. “The system has worked effectively,” Stevenson said. “It caught things it was supposed to catch and plays a critical role in protecting the upgraded facility.”

    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 5:49 pm on January 25, 2016 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “10 Facts You Should Know About Fusion Energy” 


    PPPL

    January 25, 2016
    PPPL Office of Communications
    Email: PPPL_OOC@pppl.gov
    Phone: 609-243-2755

    1.It’s natural. In fact, it’s abundant throughout the universe. Stars – and there are billions and billions of them – produce energy by fusion of light atoms.
    2.It’s safe. There are no dangerous byproducts. There is very little radioactive waste, and what waste there is requires only decades to decay, not thousands of years. Further, any byproducts are not suitable for production of nuclear weapons.
    3.It’s environmentally friendly. Fusion can help slow climate change. There are no carbon emissions so fusion will not contribute to a concentration of greenhouse gases that heat the Earth. And it helps keep the air clean.
    4.It’s conservation-friendly. Fusion helps conserve natural resources because it does not rely on traditional means of generating electricity, such as burning coal.
    5.It’s international. Fusion can help reduce conflicts among countries vying for natural resources due to fuel supply imbalances.
    6.It’s unlimited. Fusion fuel – deuterium and tritium – is available around the world. Deuterium can be readily extracted from ordinary water. Tritium can be produced from lithium, which is available from land deposits or from seawater.
    7.It’s industrial scale. Fusion can power cities 24 hours a day regardless of weather.
    8.It’s exciting. Fusion produces important scientific and engineering breakthroughs and spinoffs in its own and other fields.
    9.It’s achievable. Fusion is produced in laboratories around the world and research is devoted to making it practicable.
    10.It’s the Future. Fusion can transform the way the world produces energy.

    Two possible routes to fusion energy:

    PPPL NSTX
    PPPL NSTX tokamak

    Wendelstein 7-AS
    Wendelstein 7-x stellarator fusion reactor, Max Planck Institute for Plasma Physics

    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.

     
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