Tagged: Fusion technology Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 8:24 pm on November 17, 2014 Permalink | Reply
    Tags: , Fusion technology, LPPFusion   

    From LPP: “Physics of Plasmas Publishes LPPFusion’s Runaway Electron Theory” 

    lpp
    LPPFusion

    November 17, 2014
    No Writer Credit

    aip

    Physics of Plasmas, the leading journal in the field of plasma physics, has published LPPFusion’s new paper on Runaway electrons as a source of impurity and reduced fusion yield in the dense plasma focus. The paper, by Chief Scientist Eric J. Lerner and Chief Research Officer Hamid R. Yousefi, was published online October 22, 2014 less than a month after it was submitted for peer-review. Physics of Plasmas had published a previous LPPFusion paper on record-breaking ion energies in 2012.

    The new paper describes the evidence that runaway electrons are a key cause of vaporization of electrodes in the dense plasma focus device, an idea first reported on LPPFusion’s website in April of this year. Runaway electrons occur when very strong electric fields, such as in lightning bolts, accelerate electrons moving through a mainly neutral gas. If the field is strong enough the electrons gain more energy between each collision with an atom than they lose in the collision, thus speeding up to high energy.

    In FF-1, when the current pulse is just starting and the gas in the device is mostly neutral, very large fields build up as the electrons try to push their way through the resisting gas. With very few electrons able to move, the ones that do have to travel fast to carry a given current. The fast-moving runaway electrons gain as much as 3 keV of energy, slamming into the anode and depositing enough heat energy to vaporize some of the metal. This vaporized metal becomes a major impurity in the plasma, disrupting the formation of plasma filaments and leading to lower density in the plasmoid that the current generates. Lower density in turn leads to much lower fusion yield.

    This runaway mechanism is a second main source of impurities, the first being arcing between different pieces of the electrodes. While one-piece, monolithic electrodes will eliminate all arcing, more steps need to be taken to eliminate the runaway electrons. The most important is pre-ionization. In this technique a small current breaks down the plasma resistance before the main pulse passes through—smoothing the way, as it were. The small pulse has too little energy to cause runaway electrons, and by the time the main pulse comes through, there are lots of free electrons ready to move. With many electrons, the current can be carried with each electron moving slowly and thus having little energy. Thus runaway electrons don’t occur in the main pulse either. High pressure in the gas, which make collisions of electrons with atoms more common, can help to prevent runaways as well.

    Pre-ionization is a bit like deliberately creating a traffic jam. Runaway electrons are like cars on a highway at mid-day. There are fewer cars passing a given point but at a higher speed. These faster- moving cars, like the runaway electrons, are carrying more energy. At rush hour, there are far more cars passing a given point per minute, but they all move at a slower speed. Pre-ionization, by creating lots of free electrons, an electron ”rush hour”, allows a higher current with slower moving electrons, eliminating the fast runaways.

    The paper will be available for free download from Physics of Plasmas’ only until Nov.21, 2014.

    See this full article here.

    LPP and PPRC collaborate on pre-ionization experiments

    ero

    The FF-1 anode, which is plated with 0.001 inches of silver, shows a ring of erosion near the end of the insulator (which has been removed along with the cathode). On the right side, where deposits have been cleaned away, the copper color shows clearly where a ring of silver has been vaporized and measurements show about 0.12 grams eroded in 125 shots. On the left side, not cleaned, the copper is deposited lower on the anode, covering up silver below.

    LPP’s research team, having identified impurities vaporized from the electrodes as the main obstacle to higher yields, has been attempting to account theoretically for all sources of vaporization, so as to eliminate them. In January, the team looked more closely at the material eroded from around the anode near the insulator (see photo). Two things seemed surprising: the amount of material—about 1 mg per shot, or half of all the impurities in the plasma; and the fact that the vaporization occurred right at the start of the pulse, when the current flow is the weakest. No possible mechanism seemed to account for so much erosion so fast.

    However, a literature search turned up the answer: runaway electrons. Runaway electrons occur when very strong electric fields, such as in lightning bolts, accelerate electrons moving through a mainly neutral gas. If the field is strong enough the electrons gain more energy between each collision with an atom than they lose in the collision, thus speeding up to high energy. In FF-1, electrons gains as much as 3 keV of energy, slamming into the anode and depositing enough heat energy to vaporize the silver plating and some of the copper underneath. Once the plasma is fully ionized and its resistance drops, the high accelerating fields no longer exist, so the runaway electrons stop—But by then, the plasma has already been contaminated.

    There are two solutions to this problem. One is simply increasing the initial pressure of the gas, so more collisions occur. This will happen with FF-1 as it approaches peak current. But for now, an additional solution is needed: pre-ionization. In this technique a small current breaks down the plasma resistance before the main pulse passes through—smoothing the way, as it were. The small pulse has too little energy to cause runaway electrons, and by the time the main pulse comes through, the resistance that can sustain the large electric field is gone. Experiments by plasma focus groups in Pakistan and elsewhere had good results with pre-ionization.

    To directly test if pre-ionization can eliminate the “ring around the anode” erosion, LPP’s collaborators at the Plasma Physics Research Center (PPRC) in Tehran, Iran are conducting experiments using this technique on their 2-kJ DPF device. At the same time, LPP is doing preliminary tests of pre-ionization techniques on FF-1. Together, the experiments should be able to show how to eliminate this source of erosion prior to FF-1’s next round of experiments with tungsten electrodes.

    See this full article here.

    Please help promote STEM in your local schools

    stem

    STEM Education Coalition

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 2:29 pm on November 11, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “PPPL researchers present cutting edge results at APS Plasma Physics Conference” 


    PPPL

    November 10, 2014
    Kitta MacPherson
    Email: kittamac@pppl.gov
    Phone: 609-243-2755

    Some 135 researchers, graduate students, and staff members from PPPL joined 1,500 research scientists from around the world at the 56th annual meeting of the American Physical Society Division of Plasma Physics Conference from Oct. 27 to Oct. 31 in New Orleans. Topics in the sessions ranged from waves in plasma to the physics of ITER, the international physics experiment in Cadarache, France; to women in plasma physics. Dozens of PPPL scientists presented the results of their cutting-edge research into magnetic fusion and plasma science. There were about 100 invited speakers at the conference, more than a dozen of whom were from PPPL.

    sw
    Conceptual image of the solar wind from the sun encountering the Earth’s magnetosphere. No image credit

    The press releases in this issue are condensed versions of press releases that were prepared by the APS with the assistance of the scientists quoted and with background material written by John Greenwald and Jeanne Jackson DeVoe. The full text is available at the APS Virtual Pressroom 2014: http://www.aps.org/units/dpp/meetings/vpr/2014/index.cfm.

    How magnetic reconnection goes “Boom!”

    MRX research reveals how magnetic energy turns into explosive particle energy

    Paper by: M. Yamada, J. Yoo

    Magnetic reconnection, in which the magnetic field lines in plasma snap apart and violently reconnect, creates massive eruptions of plasma from the sun. But how reconnection transforms magnetic energy into explosive particle energy has been a major mystery.

    Now research conducted on the Magnetic Reconnection Experiment (MRX) at PPPL has taken a key step toward identifying how the transformation takes place, and measuring experimentally the amount of magnetic energy that turns into particle energy. The investigation showed that reconnection in a prototypical reconnection layer converts about 50 percent of the magnetic energy, with one-third of the conversion heating the electrons and two-thirds accelerating the ion in the plasma.

    “This is a major milestone for our research,” said Masaaki Yamada, the principal investigator for the MRX. “We can now see the entire picture of how much of the energy goes to the electrons and how much to the ions in a prototypical reconnection layer.”

    What a Difference a Magnetic Field Makes

    Experiments on MRX confirm the lack of symmetry in converging space plasmas

    Paper by: J. Yoo

    Spacecraft observing magnetic reconnection have noted a fundamental gap between most theoretical studies of the phenomenon and what happens in space. While the studies assume that the converging plasmas share symmetrical characteristics such as temperature, density and magnetic strength, observations have shown that this is hardly the case.

    PPPL researchers have now found the disparity in plasma density in experiments conducted on the MRX. The work, done in collaboration with the Space Science Center at the University of New Hampshire, marks the first laboratory confirmation of the disparity and deepens understanding of the mechanisms involved.

    Data from the MRX findings could help to inform a four-satellite mission—the Magnetospheric Multiscale Mission, or MMS—that NASA plans to launch next year to study reconnection in the magnetosphere. The probes could produce a better understanding of geomagnetic storms and lead to advanced warning of the disturbances and an improved ability to cope with them.

    Using radio waves to control density in fusion plasma

    Experiments show how heating electrons in the center of hot fusion plasma can increase turbulence, reducing the density in the inner core

    Paper by: D. Ernst, K. Burrell, W. Guttenfelder, T. Rhodes, A. Dimits

    Recent fusion experiments on the DIII-D tokamak at General Atomics in San Diego and the Alcator C-Mod tokamak at MIT show that beaming microwaves into the center of the plasma can be used to control the density in the center of the plasma. The experiments and analysis were conducted by a team of researchers as part of a National Fusion Science Campaign.

    The new experiments reveal that turbulent density fluctuations in the inner core intensify when most of the heat goes to electrons instead of plasma ions, as would happen in the center of a self-sustaining fusion reaction. Supercomputer simulations closely reproduce the experiments, showing that the electrons become more turbulent as they are more strongly heated, and this transports both particles and heat out of the plasma.

    “As we approached conditions where mainly the electrons are heated, pure trapped electrons begin to dominate,” said Walter Guttenfelder, who did the supercomputer simulations for the DIII-D experiments along with Andris Dimits of Lawrence Livermore National Laboratory. Guttenfelder was a co-leader of the experiments and simulations with Keith Burrell of General Atomics and Terry Rhoades of UCLA. Darin Ernst of MIT led the overall research.

    Calming the Plasma Edge: The Tail that Wags the Dog

    Lithium injections show promise for optimizing the performance of fusion plasmas

    Paper by: G.L. Jackson, R. Maingi, T. Osborne, Z. Yan, D. Mansfield, S.L. Allen

    Experiments on the DIII-D tokamak fusion reactor that General Atomics operates for the U.S. Department of Energy have demonstrated the ability of lithium injections to transiently double the temperature and pressure at the edge of the plasma and delay the onset of instabilities and other transients. Researchers conducted the experiments using a lithium-injection device developed at PPPL.

    Lithium can play an important role in controlling the edge region and hence the evolution of the entire plasma. In the present work, lithium diminished the frequency of instabilities known as “edge localized modes” (ELMs), which have associated heat pulses that can damage the section of the vessel wall used to exhaust heat in fusion devices.

    The tailored injections produced ELM-free periods of up to 0.35 seconds, while reference discharges without lithium showed no ELM-free periods above 0.03 sec. The lithium rapidly increased the width of the pedestal region—the edge of the plasma where temperature drops off sharply—by up to 100 percent and raised the electron pressure and total pressure in the edge by up to 100 percent and 60 percent respectively. These dramatic effects produced a 60 percent increase in total energy-confinement time.

    Scratching the surface of a material mystery

    Scientists shed new light on how lithium conditions the volatile edge of fusion plasmas

    Paper by: Angela Capece

    For fusion energy to fuel future power plants, scientists must find ways to control the interactions that take place between the volatile edge of fusion plasma and the physical walls that surround it in fusion facilities. Such interactions can profoundly affect conditions at the superhot core of the plasma in ways that include kicking up impurities that cool down the core and halt fusion reactions. Among the puzzles is how temperature affects the ability of lithium to absorb and retain the deuterium particles that stray from the fuel that creates fusion reactions.

    Answers are now emerging from a new surface-science laboratory at PPPL that can probe lithium coatings that are just three atoms thick. The experiments showed that the ability of ultrathin lithium films to retain deuterium drops as the temperature of the molybdenum substrate rises—a result that provides insight into how lithium affects the performance of tokamaks

    Experiments further showed that exposing the lithium to oxygen improved deuterium retention at temperatures below about 400 degrees Kelvin. But without exposure to oxygen, lithium films could retain deuterium at higher temperatures as a result of lithium-deuterium bonding during a PPPL experiment.

    Putting Plasma to Work Upgrading the U.S. Power Grid

    PPPL lends GE a hand in developing an advanced power-conversion switch

    Paper by: Johan Carlsson, Alex Khrabrov, Igor Kaganovich, Timothy Summerer

    When researchers at General Electric sought help in designing a plasma-based power switch, they turned to PPPL. The proposed switch, which GE is developing under contract with the DOE’s Advanced Research Projects Agency-Energy, could contribute to a more advanced and reliable electric grid and help lower utility bills.

    The switch would consist of a plasma-filled tube that turns current on and off in systems that convert the direct current coming from long-distance power lines to the alternating current that lights homes and businesses; such systems are used to reverse the process as well.

    To assist GE, PPPL used a pair of computer codes to model the properties of plasma under different magnetic configurations and gas pressures. GE also studied PPPL’s use of liquid lithium, which the laboratory employs to prevent damage to the divertor that exhausts heat in a fusion facility. The information could help GE develop a method for protecting the liquid-metal cathode—the negative terminal inside the tube—from damage from the ions carrying the current flowing through the plasma.

    Laser experiments mimic cosmic explosions

    Scientists bring plasma tsunamis into the lab

    Researchers are finding ways to understand some of the mysteries of space without leaving earth. Using high-intensity lasers at the University of Rochester’s OMEGA EP Facility focused on targets smaller than a pencil’s eraser, they conducted experiments to create colliding jets of plasma knotted by plasma filaments and self-generated magnetic fields.

    In two related experiments, researchers used powerful lasers to recreate a tiny laboratory version of what happens at the beginning of solar flares and stellar explosions, creating something like a gigantic plasma tsunami in space. Much of what happens in those situations is related to magnetic reconnection, which can accelerate particles to high energy and is the force driving solar flares towards earth.

    Laboratory experiment aims to identify how tsunamis of plasma called “shock waves” form in space

    By W. Fox, G. Fisksel (LLE), A. Bhattacharjee

    William Fox, a researcher at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory, and his colleague Gennady Fiksel, of the University of Rochester, got an unexpected result when they used lasers in the Laboratory to recreate a tiny version of a gigantic plasma tsunami called a “shock wave.” The shock wave is a thin area found at the boundary between a supernova and the colder material around it that has a turbulent magnetic field that sweeps up plasma into a steep tsunami-like wave of plasma.

    Fox and Fiksel used two very powerful lasers to zap two tiny pieces of plastic in a vacuum chamber to 10 million degrees and create two colliding plumes of extremely hot plasma. The researchers found something they had not anticipated that had not previously been seen in the laboratory: When the two plasmas merged they broke into clumps of long thin filaments due to a process called the “Weibel instability.” This instability could be causing the turbulent magnetic fields that form the shock waves in space. Their research could shed light on the origin of primordial magnetic fields that formed when galaxies were created and could help researchers understand how cosmic rays are accelerated to high energies.

    Magnetic reconnection in the laboratory

    By: G. Fiksel (LLE), W. Fox, A. Bhattacharjee

    Many plasmas in space already contain a strong magnetic field, so colliding plasmas there behave somewhat differently. Gennady Fiksel, of the University of Rochester, and William Fox continued their previous research by adding a magnetic field by pulsing current through very small wires. They then created the two colliding plumes of plasma as they did in an earlier experiment. When the two plasmas collided it compressed and stretched the magnetic field and a tremendous amount of energy accumulated in the field like a stretched rubber band. As the magnetic field lines pushed close together, the long lines broke apart and reformed like a single stretched rubber band, forming a slingshot that propels the plasma and releases the energy into the plasma, accelerating the plasma and heating it.

    The experiment showed that the reconnection process happens faster than theorists had previously predicted. This could help shed light on solar flares and coronal mass ejections, which also happen extremely quickly. Coronal mass ejections can trigger geomagnetic storms that can interfere with satellites and wreak havoc with cellphone service.

    The laser technique the scientists are using is new in the area of high energy density plasma and allows scientists to control the magnetic field to manipulate it in various ways.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 7:10 am on November 11, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “Hole in one: Technicians smoothly install the center stack in the NSTX-U vacuum vessel” 


    PPPL

    November 10, 2014
    John Greenwald

    With near-surgical precision, PPPL technicians hoisted the 29,000-pound center stack for the National Spherical Torus Experiment-Upgrade (NSTX-U) over a 20-foot wall and lowered it into the vacuum vessel of the fusion facility. The smooth operation on Oct. 24 capped more than two years of construction of the center stack, which houses the bundle of magnetic coils that form the heart of the $94 million upgrade.

    lift
    Closeup of the center stack being lowered into position by an overhead crane. (Photo by Elle Starkman/PPPL Office of Communications)

    “This was really a watershed moment,” said Mike Williams, the head of engineering and infrastructure at PPPL and associate director of the Laboratory. “The critical path [or key sequence of steps for the upgrade] was fabrication of the magnets, and that has now been done.”

    The lift team conducted the final steps largely in silence, attaching the bundled coils in their casing to an overhead crane and guiding the 21 foot-long center stack into place. The clearances were tiny: The bottom of the casing passed just inches over the shielding wall and the top of the vacuum vessel. Inserting the center stack into the vessel was like threading a needle, since the clearance at the opening was only about an inch. Guidance came chiefly from hand signals, with some radio communication at the end.

    more

    Key features

    The installation merged three key features of the upgrade that had been developed separately. These included the casing, the bundled coils and the work to ready the vacuum vessel for the center stack. Slipping the casing over the bundle was a highly precise task, with the space between them less than an inch. “The key word is ‘fit-up,’” said Ron Strykowsky, who heads the upgrade project. “We had a robust-enough design to handle all the very fine tolerances.”

    Installation of the center stack completed a key portion of the upgrade and opened another chapter. “For me, the burden is off our shoulders,” said Jim Chrzanowski, who led the coil project and retired on Oct. 31 after 39 years at PPPL. “We’ve delivered the center stack and are happy,” added Steve Raftopoulos, who worked alongside Chrzanowski and succeeds him as head of coil building. “This is my baby now,” said Raftopoulos, noting that he will be called on to resolve any problems that occur once the center stack is in operation.

    Praise for technicians

    The two leaders praised the many technicians who made the center stack possible. They ranged from a core of roughly a dozen workers who had been with the project from the beginning to technicians throughout the Laboratory who were called on to pitch in. “We drafted everyone,” Chrzanowski said.

    Their tasks included sanding, welding and applying insulation tape to each of the 36 copper conductors that went into the center stack, and sealing them all together through multiple applications of vacuum pressure impregnation — a potentially volatile process. Next came fabrication and winding of the ohmic heating coil that wraps around the conductors to put current into the hot, charged plasma that fuels fusion reactions.

    “Everyone who worked on this feels a lot of pride and ownership,” Raftopoulos said. “Steve and I were the conductors, but the technicians were the orchestra,” Chrzanowski said. “We’ve got to give credit to the guys who actually build the machines. They take our problems and make them go away.”

    Completion of the upgrade now rests with technicians working under engineer Erik Perry. Their jobs include connecting the center stack to the facility’s outer coils to complete a donut-shape magnetic field that will be used to confine the plasma. The work calls for installation of layers of custom-made electrical equipment plus hoses for water to cool the coils, all of which must fit around diagnostic and other equipment. Also ahead lies the task of connecting a second neutral beam injector for heating the plasma to the vacuum vessel. “It’s like a big puzzle,” said Perry. “Everything must fit together, and that’s what we excel at.”

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 6:52 pm on October 28, 2014 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “Bob Ellis designs a PPPL first: A 3D printed mirror for microwave launchers” 


    PPPL

    October 28, 2014
    John Greenwald

    When scientists at the Korea Supercomputing Tokamak Advanced Research (KSTAR) facility needed a crucial new component, they turned to PPPL engineer Bob Ellis. His task: Design a water-cooled fixed mirror that can withstand high heat loads for up to 300 seconds while directing microwaves beamed from launchers to heat the plasma that fuels fusion reactions.

    be
    Bob Ellis with a 3D-printed plastic prototype for a non-mirror part of the launcher. (Photo by Elle Starkman/PPPL Office of Communications)

    kstar
    KSTAR Tokamak

    Ellis, who had designed mirrors without coolant for shorter experiments, decided to try out a novel manufacturing process called 3D printing that produces components as unified wholes with minimal need for further processing. 3D printing would enable the mirror to be built for less cost than a non-water-cooled mirror produced by conventional manufacturing, Ellis said, “and that was a very nice thing to find out about.”

    The project marked a first for PPPL, which had previously used 3D printers to build plastic models but had not employed the process for creating metal parts. “Metal came into 3D printing about five years ago and was sort of exotic then,” said Phil Heitzenroeder, who heads the Mechanical Engineering Division at PPPL. “Now 3D is beginning to drift down into real-world metal products.”

    Ellis created a CAD-CAM model of the shoebox-size mirror system and delivered it to Imperial Machine & Tool Co. to produce the stainless steel and copper component through metal 3D printing. The process puts down hair-thin layers of stainless steel powder and fuses the powder in each layer with lasers. The parts are thus built from the bottom up layer by layer — another name for 3D printing is “additive manufacturing” — and follow every twist and turn of the CAD-CAM design.

    The stainless steel granules have the consistency of talcum powder before they are fused, said Christian M. Joest, president of the 70-year-old Columbia, N.J., machining and fabricating company. The 3D process took about 20 hours to complete, Joest said.

    The process proved ideal for the water-cooled mirror, which PPPL shipped to KSTAR in early October. The part consists of a thin sheet of polished copper mounted atop a stainless steel base, with serpentine channels for water winding through the base’s center. Conventional construction could have required the base to be built in multiple pieces so that the channels could be drilled, with the pieces then welded back together. “3D printing allows you to produce components in a single piece,” Ellis said, “and that’s a huge advantage.”

    Ellis now is designing a steerable mirror for KSTAR that can be controlled by computer to direct microwaves into different parts of the plasma. Ellis dubs this mirror, to be delivered next year, “Generation 2.0,” since it will have flat cooling channels rather than the round ones on the fixed mirror. The flat channels will increase the efficiency of the coolant, he said, which will be important for shedding heat from the constantly moving steerable mirror.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 3:35 pm on October 27, 2014 Permalink | Reply
    Tags: , , , Fusion technology, ,   

    From AAAS: “After Election 2014: FUSION RESEARCH” 

    AAAS

    AAAS

    ScienceInsider

    24 October 2014
    Adrian Cho

    Should we stay or should we go? Once the voters have spoken, that’s the question Congress will have to answer regarding the United States’ participation in ITER, the hugely overbudget fusion experiment under construction in Cadarache, France. Some lawmakers say it may be time for the United States to bow out, especially as the growing ITER commitment threatens to starve U.S.-based fusion research programs. The next Congress may have to decide the issue—if the current one doesn’t pull the plug first when it returns to Washington, D.C., for a 6-week lame-duck session.

    ITER Tokamak
    ITER Tokamak

    For those tired of the partisan squabbling on Capitol Hill, the ITER debate may provide curious relief. ITER appears to enjoy bipartisan support in the House of Representatives—and bipartisan opposition among key senators.

    ITER aims to prove that nuclear fusion is a viable source of energy, and the United States has agreed to build 9% of the reactor’s hardware, regardless of the cost. Recent estimates suggest the U.S. price tag could be $3.9 billion or more—nearly quadrupling original estimates and raising alarm among some lawmakers. In response, this past June a Senate appropriations subcommittee proposed a budget bill that would end U.S. participation in the project next year. In contrast, the next month the House passed a bill that would increase U.S. spending on ITER.

    Some observers think the current Congress will kick the issue to the next one by passing a stop-gap budget for fiscal year 2015, which began 1 October, that will keep U.S. ITER going. “I don’t think in the end they can come out and kill ITER based on what the Senate subcommittee did,” says Stephen Dean, president of Fusion Power Associates, a research and educational foundation in Gaithersburg, Maryland. Others say a showdown could come by year’s end.

    Trouble over ITER has been brewing for years. ITER was originally proposed in 1985 as a joint U.S.-Soviet Union venture. The United States backed out of the project in 1998 because of cost and schedule concerns—only to rejoin in 2003. At the time, ITER construction costs were estimated at $5 billion. That number had jumped to $12 billion by 2006, when the European Union, China, India, Japan, Russia, South Korea, and the United States signed a formal agreement to build the device. At the time, ITER was supposed to start running in 2016. By 2011, U.S. costs for ITER had risen to more than $2 billion, and the date for first runs had slid to 2020. But even that date was uncertain; U.S. ITER researchers did not have a detailed cost projection and schedule—or performance baseline—to go by.

    Then in 2013, the Department of Energy (DOE) argued in its budget request for the following year that U.S. ITER was not a “capital asset” and therefore did not have to go through the usual DOE review process for large construction projects—which requires a performance baseline. Even though DOE promised to limit spending on ITER to $225 million a year so as not to starve domestic fusion research efforts, that statement irked Senators Dianne Feinstein (D–CA) and Lamar Alexander (R–TN), the chair and ranking member of the Senate Appropriations Subcommittee on Energy and Water Development, respectively. They and other senators asked the Government Accountability Office (GAO) to investigate the U.S. ITER project.

    This year, things appeared to come to a head. This past April, researchers working on U.S. ITER released their new $3.9 billion cost estimate and moved back the date for first runs to 2024 or later. Two months later, GAO reported that even that new estimate was not reliable and that the cost to the United States could reach $6.5 billion. Based on that report, the Senate energy and water subcommittee moved to kill U.S. ITER in its markup of the proposed 2015 budget, giving it only $75 million for the year, half of what the White House had requested and just enough to wind things down. Alexander supported the move, even though the U.S. ITER office is based in his home state of Tennessee, at Oak Ridge National Laboratory.

    ITER still has friends in the House, however. In their version of the DOE budget for 2015, House appropriators gave ITER $225 million, $75 million more than the White House request. Moreover, the project seems to have bipartisan support in the House, as shown by a hearing of the energy subcommittee of the House Committee on Science, Space, and Technology. Usually deeply divided along party lines, the subcommittee came together to lavish praise on ITER, with representative Lamar Smith (R–TX), chair of the full committee, and Representative Eric Swalwell (D–CA), the ranking member on the subcommittee, agreeing that ITER was, in Swalwell’s words, “absolutely essential to proving that magnetically confined fusion can be a viable clean energy source.” Swalwell called for spending more than $225 million per year on ITER.

    When and how this struggle over ITER plays out depends on the answers to several questions. First, how will Congress deal with the already late budget for next year? The Senate, controlled by the Democrats, has yet to pass any of its 13 budget bills, including the one that would fund energy research. And if the House and Senate decide to simply continue the 2014 budget past the end of the year, then the decision on ITER will pass to the next Congress. If, on the other hand, Congress passes a last-minute omnibus budget for fiscal year 2015, then the fight over ITER could play out by year’s end.

    Second, how sincere is the Senate move to kill ITER? The Senate subcommittee’s move may have been meant mainly to send a signal to the international ITER organization that it needs to shape up, says one Democratic staffer in the House. The international ITER organization received scathing criticism in an independent review in October 2013. That review called for 11 different measures to overhaul the project’s management, and the Senate’s markup may have been meant primarily to drive home the message that those measures had to be taken to ensure continued U.S. involvement, the staffer says.

    Third, how broad is the House’s support for ITER? Over the past decade or so, the House has been more supportive of fusion in general, the Democratic staffer says. But some observers credit that support mainly to one person, Representative Rodney Frelinghuysen (R-NJ), a longtime member of the House Appropriations Committee. “Over the years he’s become a champion of fusion,” Dean says. “He protects it in the House.” Dean and others say that’s likely because the DOE’s sole dedicated fusion laboratory, the Princeton Plasma Physics Laboratory (PPPL), is in his home state of New Jersey (but not Frelinghuysen’s district).

    Indeed, observers say that Frelinghuysen has been instrumental in preventing cuts to the domestic fusion program proposed by DOE itself. For example, for fiscal 2014, DOE requested $458 million for its fusion energy sciences program, including $225 million for ITER. That meant cutting the domestic fusion program by about 20% to $233 million and closing one of three tokamak reactors in the United States. The Senate went along with those numbers, but House appropriators bumped the budget up to $506 million, the number that held sway in the final 2014 spending plan. But some observers speculate that Frelinghuysen might be willing to let ITER go if he could secure a brighter future for PPPL.

    PPPL Tokamak
    PPPL Tokamak

    PPPL NSTX
    PPPL National Spherical Torus Experiment

    Finally, the biggest question surrounding U.S. participation in ITER is: How will the international ITER organization respond to the calls for changes in its management structure? That should become clear within months. So far, officials with U.S. ITER have not been able to produce a baseline cost estimate and schedule in large measure, because the ITER project as a whole does not have a reliable schedule. The international ITER organization has said it will produce one by next July, the House staffer says. And if the international organization doesn’t produce a credible schedule, the staffer says, “the project will be very difficult to defend, even by its most ardent supporters.”

    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.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 8:13 am on October 11, 2014 Permalink | Reply
    Tags: , , Fusion technology,   

    From AAAS: “Z machine makes progress toward nuclear fusion” 

    AAAS

    AAAS

    10 October 2014
    Daniel Clery

    Scientists are reporting a significant advance in the quest to develop an alternative approach to nuclear fusion. Researchers at Sandia National Laboratories in Albuquerque, New Mexico, using the lab’s Z machine, a colossal electric pulse generator capable of producing currents of tens of millions of amperes, say they have detected significant numbers of neutrons—byproducts of fusion reactions—coming from the experiment. This, they say, demonstrates the viability of their approach and marks progress toward the ultimate goal of producing more energy than the fusion device takes in.

    z
    Z machine at Sandia

    Fusion is a nuclear reaction that releases energy not by splitting heavy atomic nuclei apart—as happens in today’s nuclear power stations—but by fusing light nuclei together. The approach is appealing as an energy source because the fuel (hydrogen) is plentiful and cheap, and it doesn’t generate any pollution or long-lived nuclear waste. The problem is that atomic nuclei are positively charged and thus repel each other, so it is hard to get them close enough together to fuse. For enough reactions to take place, the hydrogen nuclei must collide at velocities of up to 1000 kilometers per second (km/s), and that requires heating them to more than 50 million degrees Celsius. At such temperatures, gas becomes plasma—nuclei and electrons knocking around separately—and containing it becomes a problem, because if it touches the side of its container it will instantly melt it.

    Fusion scientists have been laboring for more than 60 years to find a way to contain superhot plasma and heat it till it fuses. Today, most efforts are focused on one of two approaches: Tokamak reactors, such as the international ITER fusion project in France, hold a diffuse plasma steady for seconds or minutes at a time while heating it to fusion temperature; laser fusion devices, such as the National Ignition Facility in California, take a tiny quantity of frozen hydrogen and crush it with an intense laser pulse lasting a few tens of billionths of a second to heat and compress it. Neither technique has yet reached “breakeven,” the point at which the amount of energy produced by fusion reactions exceeds that needed to heat and contain the plasma in the first place.

    ITER Tokamak
    ITER Tokamak

    LLNL NIF
    NIF at LLNL

    Sandia’s technique is one of several that fall into the middle ground between the extremes of laser fusion and the magnetically confined fusion of tokamaks. It crushes fuel in a fast pulse, as in laser fusion, but not as fast and not to such high density. Known as magnetized liner inertial fusion (MagLIF), the approach involves putting some fusion fuel (a gas of the hydrogen isotope deuterium) inside a tiny metal can 5 millimeters across and 7.5 mm tall. Researchers then use the Z machine to pass a huge current pulse of 19 million amps, lasting just 100 nanoseconds, through the can from top to bottom. This creates a powerful magnetic field that crushes the can inward at a speed of 70 km/s.

    While this is happening, the researchers do two other things: They preheat the fuel with a short laser pulse, and they apply a steady magnetic field, which acts as a straitjacket to hold the fusion fuel in place. Crushing the plasma also boosts the constraining magnetic field, from about 10 tesla to 10,000 tesla. This constraining field is key, because without it there is nothing to hold the superheated plasma in place other than its own inward inertia. Once the compression stops, it would fly apart before it has time to react.

    The Sandia researchers reported this week in Physical Review Letters that they had heated the plasma to about 35 million degrees Celsius and detected about 2 trillion neutrons coming from each shot. (One reaction of fusing two deuteriums produces helium-3 and a neutron.) Although the result shows that a substantial number of reactions is taking place—100 times as many as the team achieved a year ago—the group will need to produce 10,000 times as many to achieve breakeven. “It is good progress but just a beginning,” says Sandia senior scientist Mike Campbell. “We need to get more energy into the gas and increase the initial magnetic field and see if it scales in the right direction.”

    One significant aspect of the results is that the researchers also detected neutrons coming from the fusion of deuterium and tritium, another hydrogen isotope. The main reaction, deuterium with deuterium, or D-D, produces either helium-3 or tritium. Those reaction products would normally be traveling fast enough to fly out of the plasma without reacting again. But the intense constraining magnetic field forces the tritium to follow a tight helical path in which it is much more likely to collide with a deuterium and fuse again. The researchers detected 10 billion neutrons from deuterium-tritium (D-T) fusions. “To me, the most interesting data was the secondary D-T neutrons, which is very highly suggestive that the original [10 tesla] field was frozen in the plasma and reached values of [about 9000 tesla] at stagnation,” Campbell says.

    “It is great news,” says Glen Wurden, the magnetized plasma team leader at Los Alamos National Laboratory in New Mexico. He is impressed by “the fact that secondary D-T neutrons are observed … which means that at least some D-D–produced [tritium nuclei] are slowing down and reacting.” Simulations suggest that the Z machine’s maximum current of 27 million amps should be enough to reach breakeven. But the researchers are already setting their sights much higher. A hoped-for upgrade to 60 million amps, they say, would boost the power output into a “high gain” realm of 1000 times input—a giant step toward commercial viability.

    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.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 4:29 pm on September 29, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “PPPL successfully tests system for mitigating instabilities called ‘ELMs’ “ 


    PPPL

    September 29, 2014
    John Greenwald

    PPPL has successfully tested a Laboratory-designed device to be used to diminish the size of instabilities known as “edge localized modes (ELMs)” on the DIII–D tokamak that General Atomics operates for the U.S. Department of Energy in San Diego. Such instabilities can damage the interior of fusion facilities.

    DIII-D
    DIII–D

    The PPPL device injects granular lithium particles into tokamak plasmas to increase the frequency of the ELMs. The method aims to make the ELMs smaller and reduce the amount of heat that strikes the divertor that exhausts heat in fusion facilities.

    The system could serve as a possible model for mitigating ELMs on ITER, the fusion facility under construction in France to demonstrate the feasibility of fusion energy.

    iter tok
    ITER Tokamak

    “ELMs are a big issue for ITER,” said Mickey Wade, director of the DIII-D national fusion program at General Atomics. Large-scale ELMs, he noted, could melt plasma-facing components inside the ITER tokamak.

    General Atomics plans to install the PPPL-designed device, developed by physicist Dennis Mansfield and engineer Lane Roquemore, on DIII-D this fall. Previous experiments using deuterium-injection rather than lithium-injection have demonstrated the ability to increase the ELMs frequency on DIII-D, the ASDEX-Upgrade in Germany and the Joint European Torus in the United Kingdom.

    jet
    Joint European Torus

    Researchers at DIII-D now want to see how the results for lithium-injection compare with those obtained in the deuterium experiments on the San Diego facility. “We want to put them side-by-side,” Wade said.

    PPPL-designed systems have proven successful in mitigating ELMs on the EAST tokamak in Hefei, China, and have been used on a facility operated by the Italian National Agency for New Technologies in Frascati, Italy. A system also is planned for PPPL’s National Spherical Torus Experiment (NSTX), the Laboratory’s major fusion experiment, which is undergoing a $94 million upgrade.

    PPPL NSTX
    PPPL NSTX

    PPPL used salt grain-sized plastic pellets as proxies for lithium granules in testing the system for DIII-D. The pellets fell through a pinhole-sized opening inside a dropper to a rotating high-speed propeller that projected them onto a target precisely as planned.

    Joining Mansfield and Roquemore for the tests were physicists Erik Gilson and Alessandro Bortolon, a former University of Tennessee researcher now at PPPL who will begin an assignment to the DIII-D tokamak at General Atomics this fall. Also participating were Rajesh Maingi, the head of research on edge physics and plasma-facing components at PPPL, and engineer Alexander Nagy, who is on assignment to DIII-D.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 12:19 pm on July 15, 2014 Permalink | Reply
    Tags: , , , , Fusion technology,   

    From PPPL: “Experts assemble at PPPL to discuss mitigation of tokamak disruptions” 


    PPPL

    July 15, 2014
    John Greenwald

    Some 35 physicists from around the world gathered at PPPL last week for the second annual Laboratory-led workshop on improving ways to predict and mitigate disruptions in tokamaks. Avoiding or mitigating such disruptions, which occur when heat or electric current are suddenly reduced during fusion experiments, will be crucial for ITER the international experiment under construction in France to demonstrate the feasibility of fusion power.

    two
    Amitava Bhattacharjee, left, and John Mandrekas, a program manager in the U.S. Department of Energy’s office of Fusion Energy Sciences.(Photo by Elle Starkman/Princeton Office of
    Communications )

    PPPL Tokamak
    Tokamak at PPPL

    Presentations at the three-day session, titled “Theory and Simulation of Disruptions Workshop,” focused on the development of models that can be validated by experiment. “This is a really urgent task for ITER,” said Amitava Bhattacharjee, who heads the PPPL Theory Department and organized the workshop. The United States is responsible for designing disruption-mitigation systems for ITER, he noted, and faces a deadline of 2017.

    Speakers at the workshop included theorists and experimentalists from the ITER Organization, PPPL, General Atomics and several U.S. Universities, and from fusion facilities in the United Kingdom, China, Italy and India. Topics ranged from coping with the currents and forces that strike tokamak walls to suppressing runaway electrons that can be unleashed during experiments.

    Bringing together theorists and experimentalists is essential for developing solutions to disruptions, Bhattacharjee said. “I already see that major fusion facilities in the United States, as well as international tokamaks, are embarking on experiments that are ideal validation tools for theory and simulation,” he said. “And it is very important that theory and simulation ideas that can be validated with experimental results are presented and discussed in detail in focused workshops such as this one.”

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.


    ScienceSprings is powered by Maingear computers

     
  • richardmitnick 3:37 pm on July 14, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “PPPL’s dynamic diagnostic duo” 


    PPPL

    July 14, 2014
    John Greenwald

    Kenneth Hill and Manfred Bitter are scientific pioneers who have collaborated seamlessly for more than 35 years. Together they have revolutionized a key instrument in the quest to harness fusion energy — a device called an X-ray crystal spectrometer that is used around the world to reveal strikingly detailed information about the hot, charged plasma gas that fuels fusion reactions.

    two
    Kenneth Hill and Manfred Bitter inspect an X-ray crystal spectrometer to be used to study laser-produced plasmas. The vertically mounted silicon crystal has a thickness of 100 microns, about the average diameter of a human hair. (Photo by Elle Starkman/Princeton Office of Communications )

    sun
    The Sun is a natural fusion reactor.

    “Ken and Manfred are consummate diagnosticians,” said Michael Zarnstorff, deputy director for research at DOE’s Princeton Plasma Physics Laboratory(PPPL), where the duo has worked for nearly four decades. “Over the years they have developed highly innovative and uniquely capable tools for analyzing the results of fusion experiments.”

    These tools record key plasma parameters on fusion facilities in the United States, China, Japan and South Korea. They are being designed for a new German facility and will play a key role on ITER, the huge international experiment under construction in France to demonstrate the feasibility of fusion power.

    New applications for the spectrometers are rapidly expanding. Prospective new uses range from medical and industrial applications to the study of high energy-density physics. “An abundance of contexts is opening up,” Zarnstorff said.

    Low-key physicists

    Behind all these efforts are two low-key physicists. “I have known and worked with Ken and Manfred for over 30 years and have always admired their scientific work and polite demeanor,” said Philip Efthimion, who heads the Plasma Science and Technology Department at PPPL.

    The two divvy up tasks based on “whatever one of us is interested in and needs to do,” said Hill. “We have to try to check each other and make rational decisions instead of emotional ones.” Bitter puts it this way: “We are in this business together some 35 years. Everything that comes up is discussed between us.”

    The physicists first joined forces at PPPL in the late 1970s when the Princeton Large Torus, the Lab’s major experiment at the time, was reaching temperatures of more than 10 million degrees Celsius. That blistering heat stripped light-emitting electrons from the hydrogen atoms in the plasma, eliminating light as a source of information about the atomic nuclei, or ions, in the plasma and creating the need for a new diagnostic tool.

    Princeton Large Torus
    Princeton Large Torus

    Enter the X-ray crystal spectrometer, which gleans vital data from the X-rays that ions emit. At the heart of this tool is a hair-thin crystal that separates the X-rays into their wavelengths, or spectrum, and sends them to a detector. Shifts in the wavelengths reveal the temperature of the ions and other key data through a process called Doppler broadening — the same process that causes sirens to sound higher when speeding toward someone and lower when rushing away.

    Bitter and Hill worked on early X-ray spectrometers under Schweickhard von Goeler, who headed diagnostics and whom everyone called “Schwick.” Von Goeler and Hill introduced the first such device, whose lower resolution — or ability to distinguish between wavelengths in the spectra — was not yet sufficient to measure Doppler broadening. Responding to this challenge, von Goeler and Bitter built an improved spectrometer with higher resolution for Doppler measurements.

    Astonishing solar scientists

    The new PPPL device produced results that astonished solar scientists. The spectrometer revealed far more details of the X-ray spectrum for iron, an element used for diagnostic purposes in the plasma, than instruments aboard satellites that studied the spectra of iron in the sun had been able to show.

    But the new spectrometer, which PPPL also installed on the Tokamak Fusion Test Reactor (TFTR), the Laboratory’s key fusion experiment in the 1980s and 1990s, had a severe limitation. The cylindrically curved crystal provided only a single line of sight through the donut-shaped plasma and could record only the temperature of ions found at points along that line of sight. “What you really want to know is how hot it is at many points throughout the plasma,” said Hill.

    To increase the number of sightlines, PPPL put five X-ray spectrometers on TFTR. “They were large,” Hill said of the devices, “and you couldn’t imagine many more. So Manfred came up with the idea for a single crystal and a 2D [or two-dimensional] detector that would give you a continuous profile of the plasma.”

    Bitter’s concept, now a worldwide standard for fusion research, was simple and elegant. He envisioned a crystal whose spherically curved surface collected X-ray spectra from the entire plasma and imaged them onto a detector that recorded both the spectra and the location of the ions they came from. The revolutionary result: A complete picture of the plasma’s ion temperature, captured with just one X-ray spectrometer.

    Bitter and Hill first tested this design in 2003 on Alcator C-MOD, the fusion facility at MIT. While this trial showed that the concept worked, the 2D detector used at the time couldn’t record all the spectra that flowed in from the crystal. “The count-rate limit of this detector was very low,” recalled Hill. “You couldn’t see how the temperature evolved over time.”

    Like comparing an airplane to a bicycle

    This problem led to a search for a better detector, which Bitter found on a trip to Europe. While there in 2005, he learned of a device that the European Organization for Nuclear Research (CERN) had developed that could record spectral images in far greater detail than the detector he had been using. “It was like comparing an airplane to a bicycle,” Bitter said of the new detector, which made the spherically curved crystal spectrometer fully operational.

    MIT became the first to use the new spectrometer when the university’s Plasma Science and Fusion Center installed it on Alcator C-MOD in 2006 in a collaboration between MIT and PPPL. “It’s been a really great leap forward,” said John Rice, the principal research scientist at the MIT facility. “The original detector [on the 2003 spectrometer] had all sorts of problems and with this new system we can image the complete plasma.”

    Other fusion laboratories quickly followed. PPPL-designed spectrometers are now essential tools on the Korea Superconducting Tokamak Advanced Research (KSTAR) facility in Daejon, South Korea; the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, China; and the Large Helical Device (LHD) in Toki, Japan.

    Still to come are spectrometers planned for ITER in Cadarache, France; Wendelstein 7-X (W7-X) in Greifswald, Germany; and the upgraded National Spherical Torus Experiment (NSTX-U) at PPPL. For these projects, Bitter and Hill are providing expert guidance.

    “The highlight of my time here has been working with Ken and Manfred,” said physicist Novimir Pablant, who led the design of the LHD spectrometer and is developing the devices to be installed on ITER and W7-X. Joining Pablant on the ITER project is physicist Luis Delgado-Aparicio, who is developing the NSTX-U spectrometer and has likewise been inspired by Bitter and Hill. “They are incredible to work with,” said Delgado-Aparicio. “The degree of certainty to which they want to test their ideas is acute.”

    Bitter and Hill are still collaborating on new spectrometers. Among them are devices to study laser-produced plasmas at the University of Rochester and the Lawrence Livermore National Laboratory. What keeps the two scientists going? “X-ray spectrometry is a field that I find fascinating,” said Bitter. “It has so many applications and it’s very interesting to design new diagnostics.” Hill fully seconds those sentiments. “There’s just a lot of interesting physics in this field,” he said. “And there are broad applications and interest for this technology.”

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.


    ScienceSprings is powered by Maingear computers

     
  • richardmitnick 7:43 am on July 12, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From NERSC: “Hot Plasma Partial to Bootstrap Current” 

    NERSC Logo
    NERSC

    July 9, 2014
    Kathy Kincade, +1 510 495 2124, kkincade@lbl.gov

    Supercomputers at NERSC are helping plasma physicists “bootstrap” a potentially more affordable and sustainable fusion reaction. If successful, fusion reactors could provide almost limitless clean energy.

    In a fusion reaction, energy is released when two hydrogen isotopes are fused together to form a heavier nucleus, helium. To achieve high enough reaction rates to make fusion a useful energy source, hydrogen contained inside the reactor core must be heated to extremely high temperatures—more than 100 million degrees Celsius—which transforms it into hot plasma. Another key requirement of this process is magnetic confinement, the use of strong magnetic fields to keep the plasma from touching the vessel walls (and cooling) and compressing the plasma to fuse the isotopes.

    react
    A calculation of the self-generated plasma current in the W7-X reactor, performed using the SFINCS code on Edison. The colors represent the amount of electric current along the magnetic field, and the black lines show magnetic field lines. Image: Matt Landreman

    So there’s a lot going on inside the plasma as it heats up, not all of it good. Driven by electric and magnetic forces, charged particles swirl around and collide into one another, and the central temperature and density are constantly evolving. In addition, plasma instabilities disrupt the reactor’s ability to produce sustainable energy by increasing the rate of heat loss.

    Fortunately, research has shown that other, more beneficial forces are also at play within the plasma. For example, if the pressure of the plasma varies across the radius of the vessel, a self-generated current will spontaneously arise within the plasma—a phenomenon known as the “bootstrap” current.

    Now an international team of researchers has used NERSC supercomputers to further study the bootstrap current, which could help reduce or eliminate the need for an external current driver and pave the way to a more cost-effective fusion reactor. Matt Landreman, research associate at the University of Maryland’s Institute for Research in Electronics and Applied Physics, collaborated with two research groups to develop and run new codes at NERSC that more accurately calculate this self-generated current. Their findings appear in Plasma Physics and Controlled Fusion and Physics of Plasmas.

    “The codes in these two papers are looking at the average plasma flow and average rate at which particles escape from the confinement, and it turns out that plasma in a curved magnetic field will generate some average electric current on its own,” Landreman said. “Even if you aren’t trying to drive a current, if you take the hydrogen and heat it up and confine it in a curved magnetic field, it creates this current that turns out to be very important. If we ever want to make a tokamak fusion plant down the road, for economic reasons the plasma will have to supply a lot of its own current.”

    One of the unique things about plasmas is that there is often a complicated interaction between where particles are in space and their velocity, Landreman added.

    “To understand some of their interesting and complex behaviors, we have to solve an equation that takes into account both the position and the velocity of the particle,” he said. “That is the core of what these computations are designed to do.”

    Evolving Plasma Behavior

    int
    Interior of the Alcator C-Mod tokamak at the Massachusetts Institute of Technology’s Plasma Science and Fusion Center. Image: Mike Garrett

    The Plasma Physics and Controlled Fusion paper focuses on plasma behavior in tokamak reactors using PERFECT, a code Landreman wrote. Tokamak reactors, first introduced in the 1950s, are today considered by many to be the best candidate for producing controlled thermonuclear fusion power. A tokamak features a torus (doughnut-shaped) vessel and a combination of external magnets and a current driven in the plasma required to create a stable confinement system.

    In particular, PERFECT was designed to examine the plasma edge, a region of the tokamak where “lots of interesting things happen,” Landreman said. Before PERFECT, other codes were used to predict the flows and bootstrap current in the central plasma and solve equations that assume the gradients of density and temperature are gradual.

    “The problem with the plasma edge is that the gradients are very strong, so these previous codes are not necessarily valid in the edge, where we must solve a more complicated equation,” he said. “PERFECT was built to solve such an equation.”

    For example, in most of the inner part of the tokamak there is a fairly gradual gradient of the density and temperature. “But at the edge there is a fairly big jump in density and temperature—what people call the edge pedestal. What is different about PERFECT is that we are trying to account for some of this very strong radial variation,” Landreman explained.

    These findings are important because researchers are concerned that the bootstrap current may affect edge stability. PERFECT is also used to calculate plasma flow, which also may affect edge stability.

    “My co-authors had previously done some analytic calculations to predict how the plasma flow and heat flux would change in the pedestal region compared to places where radial gradients aren’t as strong,” Landreman said. “We used PERFECT to test these calculations with a brute force numerical calculation at NERSC and found that they agreed really well. The analytic calculations provide insight into how the plasma flow and heat flux will be affected by these strong radial gradients.”

    From Tokamak to Stellarator

    In the Physics of Plasmas study, the researchers used a second code, SFINCS, to focus on related calculations in a different kind of confinement concept: a stellarator. In a stellarator the magnetic field is not axisymmetric, meaning that it looks different as you circle around the donut hole. As Landreman put it, “A tokamak is to a stellarator as a standard donut is to a cruller.”

    hxt
    HSX stellarator

    First introduced in the 1950s, stellarators have played a central role in the German and Japanese fusion programs and were popular in the U.S. until the 1970s when many fusion scientists began favoring the tokamak design. In recent years several new stellarators have appeared, including the Wendelstein 7-X (W7-X) in Germany, the Helically Symmetric Experiment in the U.S. and the Large Helical Device in Japan. Two of Landreman’s coauthors on the Physics of Plasmas paper are physicists from the Max Planck Institute for Plasma Physics, where W7-X is being constructed.

    “In the W7-X design, the amount of plasma current has a strong effect on where the heat is exhausted to the wall,” Landreman explained. “So at Max Planck they are very concerned about exactly how much self-generated current there will be when they turn on their machine. Based on a prediction for this current, a set of components called the ‘divertor’ was located inside the vacuum vessel to accept the large heat exhaust. But if the plasma makes more current than expected, the heat will come out in a different location, and you don’t want to be surprised.”

    Their concerns stemmed from the fact that the previous code was developed when computers were too slow to solve the “real” 4D equation, he added.

    “The previous code made an approximation that you could basically ignore all the dynamics in one of the dimensions (particle speed), thereby reducing 4D to 3D,” Landreman said. “Now that computers are faster, we can test how good this approximation was. And what we found was that basically the old code was pretty darn accurate and that the predictions made for this bootstrap current are about right.”

    The calculations for both studies were run on Hopper and Edison using some additional NERSC resources, Landreman noted.

    “I really like running on NERSC systems because if you have a problem, you ask a consultant and they get back to you quickly,” Landreman said. “Also knowing that all the software is up to date and it works. I’ve been using NX lately to speed up the graphics. It’s great because you can plot results quickly without having to download any data files to your local computer.”

    See the full article here.

    The National Energy Research Scientific Computing Center (NERSC) is the primary scientific computing facility for the Office of Science in the U.S. Department of Energy. As one of the largest facilities in the world devoted to providing computational resources and expertise for basic scientific research, NERSC is a world leader in accelerating scientific discovery through computation. NERSC is a division of the Lawrence Berkeley National Laboratory, located in Berkeley, California. NERSC itself is located at the UC Oakland Scientific Facility in Oakland, California.

    More than 5,000 scientists use NERSC to perform basic scientific research across a wide range of disciplines, including climate modeling, research into new materials, simulations of the early universe, analysis of data from high energy physics experiments, investigations of protein structure, and a host of other scientific endeavors.

    The NERSC Hopper system, a Cray XE6 with a peak theoretical performance of 1.29 Petaflop/s. To highlight its mission, powering scientific discovery, NERSC names its systems for distinguished scientists. Grace Hopper was a pioneer in the field of software development and programming languages and the creator of the first compiler. Throughout her career she was a champion for increasing the usability of computers understanding that their power and reach would be limited unless they were made to be more user friendly.

    gh
    (Historical photo of Grace Hopper courtesy of the Hagley Museum & Library, PC20100423_201. Design: Caitlin Youngquist/LBNL Photo: Roy Kaltschmidt/LBNL)

    NERSC is known as one of the best-run scientific computing facilities in the world. It provides some of the largest computing and storage systems available anywhere, but what distinguishes the center is its success in creating an environment that makes these resources effective for scientific research. NERSC systems are reliable and secure, and provide a state-of-the-art scientific development environment with the tools needed by the diverse community of NERSC users. NERSC offers scientists intellectual services that empower them to be more effective researchers. For example, many of our consultants are themselves domain scientists in areas such as material sciences, physics, chemistry and astronomy, well-equipped to help researchers apply computational resources to specialized science problems.


    ScienceSprings is powered by MAINGEAR computers

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
Follow

Get every new post delivered to your Inbox.

Join 355 other followers

%d bloggers like this: