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  • richardmitnick 2:01 pm on January 3, 2019 Permalink | Reply
    Tags: "Nuno Loureiro: Understanding turbulence in plasmas", , , , , Tokamaks   

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

    MIT News
    MIT Widget

    From MIT News

    January 3, 2019
    Peter Dunn

    1
    “When we stimulate theoretically inclined minds by framing plasma physics and fusion challenges as beautiful theoretical physics problems, we bring into the game incredibly brilliant students,” says associate professor of nuclear science and engineering Nuno Loureiro. Photo: Gretchen Ertl

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .


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  • richardmitnick 10:33 am on June 21, 2018 Permalink | Reply
    Tags: "Knighthood in hand, astrophysicist prepares to lead U.S. fusion lab" Steven Cowley, , , , Tokamaks   

    From Science and PPPL: “Knighthood in hand, astrophysicist prepares to lead U.S. fusion lab” Steven Cowley 

    AAAS
    From Science Magazine

    and


    From PPPL

    1
    Steven Cowley, Princeton Plasma Physics Laboratory

    Jun. 19, 2018
    Daniel Clery

    It’s been quite a few weeks for Steven Cowley, the British astrophysicist who formerly headed the United Kingdom’s Culham Centre for Fusion Energy (CCFE). Last month, he was named as the new director of the Princeton Plasma Physics Laboratory (PPPL) in New Jersey, the United States’s premier fusion research lab. Then, last week he received a knighthood from the United Kingdom’s Queen Elizabeth II “for services to science and the development of nuclear fusion.”

    Cowley, or Sir Steven [in the U.K.], is now president of Corpus Christi College at the University of Oxford in the United Kingdom. He will take over his PPPL role on 1 July. He has a long track record in fusion research, having served as head of CCFE from 2008 to 2016 and as a staff scientist at PPPL from 1987 to 1993. PPPL is a Department of Energy (DOE)-funded national laboratory with a staff of more than 500 and an annual budget of $100 million. But in 2016, the lab took a knock when its main facility, the National Spherical Torus Experiment (NSTX), developed a series of disabling faults shortly after a $94 million upgrade.

    PPPL NSTX -U at Princeton Plasma Physics Lab, Princeton, NJ,USA

    PPPL’s then-director, Stewart Prager, resigned soon after. DOE is now considering a recovery plan for the NSTX, which is expected to cost tens of millions of dollars.

    During Cowley’s tenure at CCFE, that lab also started an upgrade of its rival to the NSTX, the Mega Amp Spherical Tokamak (MAST).

    Mega Ampere Spherical Tokamak. Credit Culham Centre for Fusion Energy

    Spherical tokamaks are a variation on the traditional doughnut-shaped tokamak design whose ultimate expression, the giant ITER device in France, is now under construction.

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

    The plan is for ITER to demonstrate a burning plasma, one where the fusion reactions themselves generate all or most of the heat required to sustain the burn. But once that is done, researchers hope spherical tokamaks, or some other variation, will provide a route to commercial reactors that are smaller, simpler, and cheaper than ITER. By upgrading the NSTX and the MAST, the labs hope to show that this type of compact reactor can achieve the same sort of performance as CCFE’s Joint European Torus (JET), the world’s largest tokamak right now and the record holder on fusion performance.

    The Joint European Torus tokamak generator based at the CCFE.

    “We have to push down the cost and scale of fusion reactors,” Cowley told ScienceInsider shortly after the 16 May announcement of his PPPL appointment. “I fully support ITER because we have to do a burning plasma. But commercial reactors will need to be smaller and cheaper. A JET-sized machine would be so much more appealing. MAST and NSTX will be a dynamic team going forward.”

    Despite the good food and well-stocked cellar on the Corpus Christi campus, Cowley says he is eager to return to the cut and thrust of laboratory life. “It’s too much fun. I was really feeling I missed the everyday discussions about physics and what was going on. I’m a fusion nut. We’re going to crack it one of these days and I want to be part of it,” he says. And PPPL, he adds, will be central to that effort. “Princeton is the place where much of what we know now was figured out. It’s a legendary lab in plasma physics. It’ll be fun to go and work with these people.”

    His first job there will be to get the NSTX back on track. “I’m confident we can solve this problem. They’ve understood how the faults arose and they’ve understood how to fix them. If the money comes through, we will get NSTX back online,” he says.

    Cowley says the key goal for spherical tokamaks and other variants is to reduce turbulent transport, the process that allows swirling plasma to move heat from the core of the device to the edge where it can escape. If designers can figure out how to retain the heat more effectively, the reactor doesn’t need to be so large. Spherical tokamaks do this by seeking to hold the plasma in the center of the device, close to the central column.

    Another way to solve the heat problem is to increase a device’s magnetic field strength overall by using superconducting magnets, an approach being followed by researchers at the Massachusetts Institute of Technology in Cambridge.

    MIT SPARC fusion reactor tokamak

    “That can push the scale down,” Cowley says, “but high field is not enough on its own. If there is a disruption [a sudden loss of confinement], that can be very damaging” to the machine.

    Cowley thinks future machines may take elements from more then one type of reactor—including stellarators, a reactor type that has a doughnut shape that is similar to tokamaks, but with bizarrely twisted magnets that can confine current without needing the flow of current around the loop that tokamaks rely on. “There are beautiful ideas coming from the stellarators community,” he says. Wendelstein 7-X, a “phenomenal” new stellarator in Germany, has been a major driver, he says.

    KIT Wendelstein 7-X, built in Greifswald, Germany

    What has changed dramatically in the past couple of decades has been “the ability to calculate what’s going on,” Cowley says. Advances in both theory and computing power means “we have all these new ideas and can explore the spaces in silicon. The field is driven more by science and less by intuition,” he says. “It’s quite a revolution.”

    Meanwhile, ITER construction trundles on despite numerous delays and price hikes. Cowley acknowledges that things have improved since the current director, Bernard Bigot, took over. “Bigot is an extremely good leader. He’s steadied the ship; he makes decisions,” Cowley says. “And they’ve got their team. It took time to find the right set of people.” Building ITER is “an amazingly tough thing to do. Assembly [of the tokamak] will be quite challenging and hard to stay on schedule. But when it is finished it will be a technological wonder.”

    But perhaps the biggest obstacle to progress is a shortage of funding, which has been stagnant in the United States for many years. President Donald Trump has requested $340 million for DOE’s fusion research programs in the 2019 fiscal year that begins 1 October, a 36% cut from current levels, but Congress is unlikely to approve that cut. “There’s real hope [the 2019 budget] will move up, but it’s not energizing the field,” Cowley says. “If we can get NSTX to produce spectacular physics results—on a par with the performance of JET—we will energize the community with science [Lotsa luck, pal].”

    See the full article here .


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    PPPL campus

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

     
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