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  • richardmitnick 3:21 pm on September 8, 2017 Permalink | Reply
    Tags: , Breaking apart and snapping together of the magnetic field lines in plasma that occurs throughout the universe, Could lead to improved forecasts of space weather, Magnetic reconnection, , , Team led by graduate student at PPPL produces unique simulation of magnetic reconnection   

    From PPPL: “Team led by graduate student at PPPL produces unique simulation of magnetic reconnection” 


    September 8, 2017
    John Greenwald

    Northern lights in the night sky over Norway. (Photo by Jan R. Olsen)

    Jonathan Ng, a Princeton University graduate student at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), has for the first time applied a fluid simulation to the space plasma process behind solar flares northern lights and space storms. The model could lead to improved forecasts of space weather that can shut down cell phone service and damage power grids, as well as to better understanding of the hot, charged plasma gas that fuels fusion reactions.

    The new simulation captures the physics of magnetic reconnection, the breaking apart and snapping together of the magnetic field lines in plasma that occurs throughout the universe. The simulations approximate kinetic effects in a fluid code, which treats plasma as a flowing liquid, to create a more detailed picture of the reconnection process.

    Previous simulations used fluid codes to produce simplified descriptions of reconnection that takes place in the vastness of space, where widely separated plasma particles rarely collide. However, this collisionless environment gives rise to kinetic effects on plasma behavior that fluid models cannot normally capture.

    Estimation of kinetic behavior

    The new simulation estimates kinetic behavior. “This is the first application of this particular fluid model in studying reconnection physics in space plasmas,” said Ng, lead author of the findings reported in August in the journal Physics of Plasmas.

    Ng and coauthors approximated kinetic effects with a series of fluid equations based on plasma density, momentum and pressure. They concluded the process through a mathematical technique called “closure” that enabled them to describe the kinetic mixing of particles from non-local, or large-scale, regions. The type of closure involved was originally developed by PPPL physicist Greg Hammett and the late Rip Perkins in the context of fusion plasmas, making its application to the space plasma environment an example of fruitful cross-fertilization.

    The completed results agreed better with kinetic models as compared with simulations produced by traditional fluid codes. The new simulations could extend understanding of reconnection to whole regions of space such as the magnetosphere, the magnetic field that surrounds the Earth, and provide a more comprehensive view of the universal process.

    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

    Coauthoring the paper were physicists Ammar Hakim of PPPL and Amitava Bhattacharjee, head of the Theory Department at PPPL and a professor of astrophysical sciences at Princeton University, together with physicists Adam Stanier and William Daughton of Los Alamos National Laboratory. Support for this work comes from the DOE Office of Science, the National Science Foundation and NASA. Computation was performed at the National Energy Research Scientific Computer Center, a DOE Office of Science User Facility, and the University of New Hampshire.

    See the full article here .

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    PPPL campus

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

  • richardmitnick 8:36 pm on July 14, 2017 Permalink | Reply
    Tags: A high Mach number shock wave, High-energy plasma, , Magnetic reconnection, , The first high-energy shock waves in a laboratory setting, U Rochester OMEGA EP Laser System   

    From PPPL: “Scientists create first laboratory generation of high-energy shock waves that accelerate astrophysical particles” 


    July 14, 2017
    John Greenwald

    Physicist Derek Schaeffer. (Photo by Elle Starkman/Office of Communications).

    Throughout the universe, supersonic shock waves propel cosmic rays and supernova particles to velocities near the speed of light. The most high-energy of these astrophysical shocks occur too far outside the solar system to be studied in detail and have long puzzled astrophysicists. Shocks closer to Earth can be detected by spacecraft, but they fly by too quickly to probe a wave’s formation.

    No image credit or caption.

    Opening the door to new understanding

    Now a team of scientists has generated the first high-energy shock waves in a laboratory setting, opening the door to new understanding of these mysterious processes. “We have for the first time developed a platform for studying highly energetic shocks with greater flexibility and control than is possible with spacecraft,” said Derek Schaeffer, a physicist at Princeton University and the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), and lead author of a July paper in Physical Review Letters that outlines the experiments.

    Schaeffer and colleagues conducted their research on the Omega EP laser facility at the University of Rochester Laboratory for Laser Energetics.

    U Rochester OMEGA EP Laser System

    U Rochester Omega Laser

    Collaborating on the project was PPPL physicist Will Fox, who designed the experiment, and researchers from Rochester and the universities of Michigan and New Hampshire. “This lets you understand the evolution of the physical processes going on inside shock waves,” Fox said of the platform.

    To produce the wave, scientists used a laser to create a high-energy plasma — a form of matter composed of atoms and charged atomic particles — that expanded into a pre-existing magnetized plasma. The interaction created, within a few billionths of a second, a magnetized shock wave that expanded at a rate of more than 1 million miles per hour, congruent with shocks beyond the solar system. The rapid velocity represented a high “magnetosonic Mach number” and the wave was “collisionless,” emulating shocks that occur in outer space where particles are too far apart to frequently collide.

    Discovery by accident

    Discovery of this method of generating shock waves actually came about by accident. The physicists had been studying magnetic reconnection, the process in which the magnetic field lines in plasma converge, separate and energetically reconnect. To investigate the flow of plasma in the experiment, researchers installed a new diagnostic on the Rochester laser facility. To their surprise, the diagnostic revealed a sharp steepening of the density of the plasma, which signaled the formation of a high Mach number shock wave.

    To simulate the findings, the researchers ran a computer code called “PSC” on the Titan supercomputer, the most powerful U.S. computer, housed at the DOE’s Oak Ridge Leadership Computing Facility.

    ORNL Cray XK7 Titan Supercomputer

    The simulation utilized data derived from the experiments and results of the model agreed well with diagnostic images of the shock formation.

    Going forward, the laboratory platform will enable new studies of the relationship between collisionless shocks and the acceleration of astrophysical particles. The platform “complements present remote sensing and spacecraft observations,” the authors wrote, and “opens the way for controlled laboratory investigations of high-Mach number shocks.”

    Support for this research came from the DOE Office of Science, the DOE INCITE Leadership Computing program, and the National Nuclear Security Administration, a semi-autonomous agency within the DOE.

    See the full article here .

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    PPPL campus

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

  • richardmitnick 5:21 am on May 16, 2017 Permalink | Reply
    Tags: , , LLNL NIF, Magnetic reconnection, Particle acceleration, , Rochester’s Laboratory for Laser Energetics,   

    From ALCF: “Fields and flows fire up cosmic accelerators” 

    Argonne Lab
    News from Argonne National Laboratory

    ANL Cray Aurora supercomputer
    Cray Aurora supercomputer at the Argonne Leadership Computing Facility

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


    May 15, 2017
    John Spizzirri

    A visualization from a 3D OSIRIS simulation of particle acceleration in laser-driven magnetic reconnection. The trajectories of the most energetic electrons (colored by energy) are shown as the two magnetized plasmas (grey isosurfaces) interact. Electrons are accelerated by the reconnection electric field at the interaction region and escape in a fan-like profile. Credit: Frederico Fiuza, SLAC National Accelerator Laboratory/OSIRIS

    Every day, with little notice, the Earth is bombarded by energetic particles that shower its inhabitants in an invisible dusting of radiation, observed only by the random detector, or astronomer, or physicist duly noting their passing. These particles constitute, perhaps, the galactic residue of some far distant supernova, or the tangible echo of a pulsar. These are cosmic rays.

    But how are these particles produced? And where do they find the energy to travel unchecked by immense distances and interstellar obstacles?

    These are the questions Frederico Fiuza has pursued over the last three years, through ongoing projects at the Argonne Leadership Computing Facility (ALCF), a U.S. Department of Energy (DOE) Office of Science User Facility.

    A physicist at the SLAC National Accelerator Laboratory in California, Fiuza and his team are conducting thorough investigations of plasma physics to discern the fundamental processes that accelerate particles.

    The answers could provide an understanding of how cosmic rays gain their energy and how similar acceleration mechanisms could be probed in the laboratory and used for practical applications.

    While the “how” of particle acceleration remains a mystery, the “where” is slightly better understood. “The radiation emitted by electrons tells us that these particles are accelerated by plasma processes associated with energetic astrophysical objects,” says Fiuza.

    The visible universe is filled with plasma, ionized matter formed when gas is super-heated, separating electrons from ions. More than 99 percent of the observable universe is made of plasmas, and the radiation emitted from them creates the beautiful, eerie colors that accentuate nebulae and other astronomical wonders.

    The motivation for these projects came from asking whether it was possible to reproduce similar plasma conditions in the laboratory and study how particles are accelerated.

    High-power lasers, such as those available at the University of Rochester’s Laboratory for Laser Energetics or at the National Ignition Facility in the Lawrence Livermore National Laboratory, can produce peak powers in excess of 1,000 trillion watts.

    Rochester’s Laboratory for Laser Energetics

    At these high-powers, lasers can instantly ionize matter and create energetic plasma flows for the desired studies of particle acceleration.

    Intimate Physics

    To determine what processes can be probed and how to conduct experiments efficiently, Fiuza’s team recreates the conditions of these laser-driven plasmas using large-scale simulations. Computationally, he says, it becomes very challenging to simultaneously solve for the large scale of the experiment and the very small-scale physics at the level of individual particles, where these flows produce fields that in turn accelerate particles.

    Because the range in scales is so dramatic, they turned to the petascale power of Mira, the ALCF’s Blue Gene/Q supercomputer, to run the first-ever 3D simulations of these laboratory scenarios. To drive the simulation, they used OSIRIS, a state-of-the-art, particle-in-cell code for modeling plasmas, developed by UCLA and the Instituto Superior Técnico, in Portugal, where Fiuza earned his PhD.

    Part of the complexity involved in modeling plasmas is derived from the intimate coupling between particles and electromagnetic radiation — particles emit radiation and the radiation affects the motion of the particles.

    In the first phase of this project, Fiuza’s team showed that a plasma instability, the Weibel instability, is able to convert a large fraction of the energy in plasma flows to magnetic fields. They have shown a strong agreement in a one-to-one comparison of the experimental data with the 3D simulation data, which was published in Nature Physics, in 2015. This helped them understand how the strong fields required for particle acceleration can be generated in astrophysical environments.

    Fiuza uses tennis as an analogy to explain the role these magnetic fields play in accelerating particles within shock waves. The net represents the shockwave and the racquets of the two players are akin to magnetic fields. If the players move towards the net as they bounce the ball between each other, the ball, or particles, rapidly accelerate.

    “The bottom line is, we now understand how magnetic fields are formed that are strong enough to bounce these particles back and forth to be energized. It’s a multi-step process: you need to start by generating strong fields — and we found an instability that can generate strong fields from nothing or from very small fluctuations — and then these fields need to efficiently scatter the particles,” says Fiuza.


    NASA Magnetic reconnection, Credit: M. Aschwanden et al. (LMSAL), TRACE, NASA

    But particles can be energized in another way if the system provides the strong magnetic fields from the start.

    “In some scenarios, like pulsars, you have extraordinary magnetic field amplitudes,” notes Fiuza. “There, you want to understand how the enormous amount of energy stored in these fields can be directly transferred to particles. In this case, we don’t tend to think of flows or shocks as the dominant process, but rather magnetic reconnection.”

    Magnetic reconnection, a fundamental process in astrophysical and fusion plasmas, is believed to be the cause of solar flares, coronal mass ejections, and other volatile cosmic events. When magnetic fields of opposite polarity are brought together, their topologies are changed. The magnetic field lines rearrange in such a way as to convert magnetic energy into heat and kinetic energy, causing an explosive reaction that drives the acceleration of particles. This was the focus of Fiuza’s most recent project at the ALCF.

    Again, Fiuza’s team modeled the possibility of studying this process in the laboratory with laser-driven plasmas. To conduct 3D, first-principles simulations (simulations derived from fundamental theoretical assumptions/predictions), Fiuza needed to model tens of billions of particles to represent the laser-driven magnetized plasma system. They modeled the motion of every particle and then selected the thousand most energetic ones. The motion of those particles was individually tracked to determine how they were accelerated by the magnetic reconnection process.

    “What is quite amazing about these cosmic accelerators is that a very, very small number of particles carry a large fraction of the energy in the system, let’s say 20 percent. So you have this enormous energy in this astrophysical system, and from some miraculous process, it all goes to a few lucky particles,” he says. “That means that the individual motion of particles and the trajectory of particles are very important.”

    The team’s results, which were published in Physical Review Letters, in 2016, show that laser-driven reconnection leads to strong particle acceleration. As two expanding plasma plumes interact with each other, they form a thin current sheet, or reconnection layer, which becomes unstable, breaking into smaller sheets. During this process, the magnetic field is annihilated and a strong electric field is excited in the reconnection region, efficiently accelerating electrons as they enter the region.

    Fiuza expects that, like his previous project, these simulation results can be confirmed experimentally and open a window into these mysterious cosmic accelerators.

    This research is supported by the DOE Office of Science. Computing time at the ALCF was allocated through the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program.

    See the full article here .

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    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    About ALCF

    The Argonne Leadership Computing Facility’s (ALCF) mission is to accelerate major scientific discoveries and engineering breakthroughs for humanity by designing and providing world-leading computing facilities in partnership with the computational science community.

    We help researchers solve some of the world’s largest and most complex problems with our unique combination of supercomputing resources and expertise.

    ALCF projects cover many scientific disciplines, ranging from chemistry and biology to physics and materials science. Examples include modeling and simulation efforts to:

    Discover new materials for batteries
    Predict the impacts of global climate change
    Unravel the origins of the universe
    Develop renewable energy technologies

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

    Argonne Lab Campus

  • richardmitnick 2:42 pm on April 10, 2017 Permalink | Reply
    Tags: , , , , European Space Agency’s Cluster satellites, Magnetic reconnection   

    From AGU: “For Magnetic Reconnection Energy, O—not X—Might Mark the Spot” 

    AGU bloc

    American Geophysical Union

    Artist’s illustration of events on the Sun changing the conditions in near-Earth space. Credit: NASA

    Mark Zastrow

    Magnetic reconnection is one of the most important—and least understood—processes in all of space physics.

    NASA Magnetic reconnection, Credit: M. Aschwanden et al. (LMSAL), TRACE, NASA

    It happens at the boundaries of Earth’s magnetic field, where it meets the Sun’s, causing magnetic field lines to break and realign in an explosive manner that can generate hazardous radiation, especially during solar storms. Now a new study from Fu et al [Geophysical Research Lettersl . adds weight to suggestions that scientists have been looking for this energy in the wrong type of reconnection.

    For decades, the classic introductory textbook picture of magnetic reconnection has depicted two parallel lines that pull themselves together into an X shape, as if pinched together, until they finally touch at the center of the X line. Then, the field lines snap and realign. Like a rebounding rubber band, they fling plasma out from the center of the X, generating currents than can surge down into the Earth’s magnetic field. During high solar activity, this process generates the dangerous radiation that threatens power grids, satellite communications, and the health of astronauts.

    At reconnection O lines (usually referred to as magnetic islands or flux ropes in spacecraft data), there is strong current, turbulence, and energy dissipation. At reconnection X lines, there is no current, turbulence, or energy dissipation. Credit: Huishan Fu

    At least, that is the conventional wisdom. But that’s not what the authors’ analysis shows. Instead, the intense blasts of energy may come from a different kind of magnetic reconnection, one not as often shown in textbooks: so-called O lines, where the approaching field lines spiral and swirl together, as if caught in a whirlpool.

    The team analyzed data from the European Space Agency’s Cluster satellites, a quartet of spacecraft launched in 2000 that fly in formation—sometimes less than 10 kilometers apart—which allows them to make detailed measurements from within magnetic reconnection events.

    European Space Agency’s Cluster satellites

    In particular, the authors examined a pass through a magnetic storm on 9 October 2003, high over Earth’s nightside.

    During their pass through this storm, the craft flew within a few hundred kilometers of several potential sites of reconnection. The team used computer models to recreate the topology of the field lines, finding that two of them were X lines and the rest were O lines. But instead of seeing the highest current levels at X lines as expected, the team found most of the greatest current spikes to be near O lines. At the X lines, the current was almost nonexistent.

    The team writes that their results clearly show that O lines, not X lines, are responsible for energy dissipation in reconnection, a result that is likely to spark a great deal of discussion. (Geophysical Research Letters, https://doi.org/10.1002/2016GL071787, 2017)

    See the full post here .

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    The purpose of the American Geophysical Union is to promote discovery in Earth and space science for the benefit of humanity.

    To achieve this mission, AGU identified the following core values and behaviors.

    Core Principles

    As an organization, AGU holds a set of guiding core values:

    The scientific method
    The generation and dissemination of scientific knowledge
    Open exchange of ideas and information
    Diversity of backgrounds, scientific ideas and approaches
    Benefit of science for a sustainable future
    International and interdisciplinary cooperation
    Equality and inclusiveness
    An active role in educating and nurturing the next generation of scientists
    An engaged membership
    Unselfish cooperation in research
    Excellence and integrity in everything we do

    When we are at our best as an organization, we embody these values in our behavior as follows:

    We advance Earth and space science by catalyzing and supporting the efforts of individual scientists within and outside the membership.
    As a learned society, we serve the public good by fostering quality in the Earth and space science and by publishing the results of research.
    We welcome all in academic, government, industry and other venues who share our interests in understanding the Earth, planets and their space environment, or who seek to apply this knowledge to solving problems facing society.
    Our scientific mission transcends national boundaries.
    Individual scientists worldwide are equals in all AGU activities.
    Cooperative activities with partner societies of all sizes worldwide enhance the resources of all, increase the visibility of Earth and space science, and serve individual scientists, students, and the public.
    We are our members.
    Dedicated volunteers represent an essential ingredient of every program.
    AGU staff work flexibly and responsively in partnership with volunteers to achieve our goals and objectives.

  • richardmitnick 7:39 am on April 1, 2017 Permalink | Reply
    Tags: Magnetic reconnection, MPIPP,   

    From PPPL and Max Planck Institute of Plasma Physics via phys.org: “Physicists reveal experimental verification of a key source of fast reconnection of magnetic fields” 


    MPIPP bloc

    Max Planck Institute for Plasma Physics

    March 31, 2017

    Physicist Will Fox with Magnetic Reconnection Experiment. Credit: Elle Starkman/PPPL Office of Communications

    Magnetic reconnection, a universal process that triggers solar flares and northern lights and can disrupt cell phone service and fusion experiments, occurs much faster than theory says that it should. Now researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Germany’s Max Planck Institute of Plasma Physics have discovered a source of the speed-up in a common form of reconnection. Their findings could lead to more accurate predictions of damaging space weather and improved fusion experiments.

    Reconnection occurs when the magnetic field lines in plasma—the collection of atoms and charged electrons and atomic nuclei, or ions, that make up 99 percent of the visible universe—converge and forcefully snap apart. Electrons that exert a varying degree of pressure form an important part of this process as reconnection takes place.

    The research team found that variation in the electron pressure develops along the magnetic field lines in the region undergoing reconnection. This variation balances and keeps a strong electric current inside the plasma from growing out of control and halting the reconnection process. It is this balancing act that makes possible fast reconnection.

    “The main issue we addressed is how reconnection can take place so quickly,” said Will Fox, lead author of a paper that detailed the findings in March in the journal Physical Review Letters. “Here we’ve shown experimentally how electron pressure accelerates the process.”

    The physics team built a picture of the gradient and other parameters of reconnection from research conducted on the Magnetic Reconnection Experiment (MRX) at PPPL, the leading laboratory device for studying reconnection. The findings marked the first experimental confirmation of predictions made by earlier simulations performed by other researchers of the behavior of ions and electrons during reconnection. “The experiments demonstrate how the plasma can sustain a large electric field while preventing a large electric current from building up and halting the reconnection process,” said Fox.

    Among potential applications of the results:

    Predictions of space storms. Magnetic reconnection in the magnetosphere, the magnetic field that surrounds the Earth, can set off geomagnetic “substorms” that disable communications and global positioning satellites (GPS) and disrupt electrical grids. Improved understanding of fast reconnection can help locate regions where the process triggering storms is ready to take place.
    Mitigation of the impact. Advanced warning of reconnection and the disruptions that may follow can lead to steps to protect sensitive satellite systems and electric grids.
    Improvement of fusion facility performance. The process observed in MRX likely plays a key role in producing what are called “sawtooth” instabilities that can halt fusion reactions. Understanding the process could open the door to controlling it and limiting such instabilities. “How sawtooth happens so fast has been a mystery that this research helps to explain,” said Fox. “In fact, it was computer simulations of sawtooth crashes that first linked electron pressure to the source of fast reconnection.”

    See the full article here .

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    MPIPP campus

    The Max Planck Institute of Plasma Physics (Max-Planck-Institut für Plasmaphysik, IPP) is a physics institute for the investigation of plasma physics, with the aim of working towards fusion power. The institute also works on surface physics, also with focus on problems of fusion power.

    The IPP is an institute of the Max Planck Society, part of the European Atomic Energy Community, and an associated member of the Helmholtz Association.

    The IPP has two sites: Garching near Munich (founded 1960) and Greifswald (founded 1994), both in Germany.

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

  • richardmitnick 8:47 am on December 15, 2016 Permalink | Reply
    Tags: , , , Magnetic reconnection, Mystery of ultra-fast solar flares solved by plasma physics,   

    From Ethan Siegel: “Mystery of ultra-fast solar flares solved by plasma physics” 

    From Ethan Siegel


    A solar flare, visible at the right of the image, occurs when magnetic field lines split apart and reconnect, far more rapidly than prior theories have predicted. Image credit: NASA.

    Magnetic reconnection this fast shouldn’t be possible, yet we see it everywhere we look. Finally, we know why.

    Animated schematic of magnetic reconnection
    Date 4 August 2009
    Source Own work
    Author ChamouJacoN
    Permission (Reusing this file) “I, creator of this work, hereby release it into the public domain.”

    “We are inside this plasma,
    and plasma is inside everything. It is incandescent
    in the sun, and I am curious to know if you
    are able to stop orbiting yourself around it even for a second.”
    -Marieta Maglas

    Just like Earth and many other worlds, the Sun has a magnetic field that permeates throughout its interior and emerges far beyond its surface. The field is irregular over the surface, and oftentimes loops and other intricate structure can be seen. Plasma — the ionized matter found at the Sun’s edge and all throughout — often traces these magnetic structures. But every once in a while, these almost-always-tied-together field lines snap and rapidly reconnect, causing particles to stream outwards at incredible velocities. The reconnection speed has always been a mystery, occurring far more quickly than the equations would predict. Explanations have come and gone through the years; none has ever been satisfactory. But a new theoretical development, the science of plasmoid instability, appears have solved the puzzle at last.

    Magnetic reconnection between the Sun-Earth system. Image credit: NASA’s Goddard Space Flight Center/Duberstein/Magnetospheric Multiscale Mission.

    Magnetic reconnection doesn’t just happen on the Sun, but in a wide variety of astrophysical and terrestrial phenomena. When charged particles fly from the Sun towards our world and then flow down the Earth’s magnetic field to create aurorae, that’s due to magnetic reconnection. When turbulent plasmas exist in interstellar space,magnetic reconnection causes electron heating, and the same mechanism may even power gamma-ray bursts.

    Gamma-ray burst credit NASA SWIFT Cruz Dewilde
    Gamma-ray burst credit NASA SWIFT Cruz Dewilde

    And right here on Earth, we can perform laboratory-based experiments to not only study the phenomenon itself, but its consequences, such as causing the hot, central plasma to mix with the cooler, outer plasma closer to the wall in magnetic fusion reactors.

    The plasma in the center of this fusion reactor is so hot it doesn’t emit light; it’s only the cooler plasma located at the walls that can be seen. Hints of magnetic interplay between the hot and cold plasmas can be seen. Image credit: National Fusion Research Institute, Korea.


    Wendelstgein 7-X stellarator, built in Greifswald, Germany
    Wendelstgein 7-X stellarator, built in Greifswald, Germany

    The physics is pretty simple:

    Envision the magnetic field created by any number of bar magnets.
    Move those magnets around to different configurations relative to one another.
    Watch the lines disconnect from certain locations and reconnect in others as the fields change.

    That’s it! That’s magnetic reconnection. Thanks to a series of space-based explorers, we’ve been able to observe and confirm the phenomenon of magnetic reconnection quite robustly, both in the emission of solar flares and in the auroral phenomenon here on Earth.

    But, as with a great many things, the devil is in the details here.

    In astrophysics, one of the most important details of plasmas is electric currents. Because plasmas are made up of ionized atoms and free electrons, including bare atomic nuclei, electric and magnetic fields can separate, move and accelerate these particles at incredible speeds. Moving charged particles make electric currents, and in one of these magnetized environments, those currents get compressed into thin layers — or sheets — that wind up getting expelled from the plasma entirely. The largest such current in our Solar System arises from the Sun and is known as the heliospheric current sheet. At around 10,000 kilometers in thickness, it extends past the orbit of Pluto in all directions.

    Parker spiral.
    Date 9 April 2007 (original upload date)
    Source http://helios.gsfc.nasa.gov/solarmag.html.
    Author The original uploader was Miserlou at English Wikipedia

    The heliospheric current sheet results from the influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium (Solar Wind). Image credit: Werner Heil/NASA.

    It was thought, for a long time, that these thin current sheets needed to highly constrain the speed at which the magnetic field lines can split apart and reconnect; that’s what theoretical calculations predict. But physics is an experimental, measurable science for a reason, and our observations indicate unambiguously that the splitting and reconnection happens faster than that predicted speed. A team of physicists at the Princeton Plasma Physics Laboratory led by Luca Comisso performed a series of laboratory experiments that indicated the sought after solution was right in front of our faces the whole time: the plasma sheet isn’t a continuous, uniform entity, but rather can be broken up into small islands with their own unique magnetic properties. That’s what the “plasmoid instability” idea is.

    A hierarchy of interacting current sheets and islands arise in the plasmoid instability model of current sheets. Image credit: Phase Diagram for Magnetic Reconnection in Heliophysical, Astrophysical and Laboratory Plasmas — Ji, Hantao et al. Phys.Plasmas 18 (2011) 111207.

    The idea has been around for a few years, but the huge advance of Comisso’s team is that they were able — for the first time — to correctly determine the quantitative properties of the plasmoid instability that lead to fast magnetic reconnection in real situations. Ironically, it relied on one of the oldest physical principles of all, dating all the way back to Fermat (of Fermat’s last theorem) in the 1600s and the principle of least time. Here’s how this breaks down.

    1.A large current sheet behaves as the old, naïve model predicts: as a continuous, uniform entity where the magnetic field is mostly confined. In many ways, it’s like forming a thin sheet of plywood.
    2.Slight deviations from uniformity emerge, and plasmoid instabilities begin forming and growing at a uniform, linear rate. It’s like applying a small force to the plywood and watching it bend in response.
    3.As the outside magnetic properties continue to change — the Sun rotates, the Earth-Sun system switches from night to day, the field’s configuration shifts, etc. — the instabilities change less than they did before. It’s like increasing the force to the plywood and watching it bend less than you’d expect, as instead it just holds that tension in its material structure. This is an example of stored, potential energy.
    4.Finally, the magnetic properties have changed so much that the instabilities would be much more stably configured if the field lines rapidly shifted and reconnected. It’s here that the field lines break apart and reconnect, faster than any other model had predicted and in line with the observations. This is akin to the plywood simply snapping in two, and releasing that stored energy.

    Magnetic reconnection is imminent in this plasma current sheet, and the plasmoid instabilities are clearly visible. When the field lines snap, reconnection occurs. Image credit: Yi-Min Huang.

    The beauty of this research is twofold: in its newfound predictive power and in the surprising lessons that were learned. The predictions that can now be made? How long “phase 2” above lasts, how many plasmoid instabilities will form, and what their growth rate and ultimate size will be. Coming up with a model that physically reproduces what experiments and observations bear out is a tremendous advance. But the team has also uncovered some surprising lessons. There are four quantities that grow/change over time (like the number of plasmoids and how long they take to reach the critical, reconnection phase) and three quantities that they depend on (like the sizes of the initial imperfections). Unlike most physical laws, which are power laws (i.e., xis proportional to y to some power), these dependences aren’t! As the authors say:

    It is common in all realms of science to seek the existence of power laws, despite the fact that they are, sometimes, intrinsically simplistic. In contrast, we find that the scaling relations of the plasmoid instability are not true power laws — a result that has never been derived or predicted before.

    If you ever wondered where solar flares came from before and how they get ejected so quickly, the answer lies in magnetic reconnection. For the first time, we finally understand and can predict exactly how this phenomenon works, in not just a qualitative but a quantitative fashion.

    Reference: General Theory of the Plasmoid Instability, L. Comisso, M. Lingam, Y.-M. Huang, and A. Bhattacharjee, Phys. Plasmas 23, 100702 (2016). Preprint available at Arxiv.org.

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:31 pm on November 23, 2016 Permalink | Reply
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    From Princeton: “An explanation for the mysterious onset of a universal process (Physics of Plasmas)” 

    Princeton University
    Princeton University


    November 23, 2016
    John Greenwald, Princeton Plasma Physics Laboratory Communications

    Magnetic reconnection happens in solar flares on the surface in the sun, as well as in experimental fusion energy reactors here on Earth. Image credit: NASA.

    Scientists have proposed a groundbreaking solution to a mystery that has puzzled physicists for decades. At issue is how magnetic reconnection, a universal process that sets off solar flares, northern lights and cosmic gamma-ray bursts, occurs so much faster than theory says should be possible. The answer, proposed by researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University, could aid forecasts of space storms, explain several high-energy astrophysical phenomena, and improve plasma confinement in doughnut-shaped magnetic devices called tokamaks designed to obtain energy from nuclear fusion.

    Magnetic reconnection takes place when the magnetic field lines embedded in a plasma — the hot, charged gas that makes up 99 percent of the visible universe — converge, break apart and explosively reconnect. This process takes place in thin sheets in which electric current is strongly concentrated.

    According to conventional theory, these sheets can be highly elongated and severely constrain the velocity of the magnetic field lines that join and split apart, making fast reconnection impossible. However, observation shows that rapid reconnection does exist, directly contradicting theoretical predictions.

    Detailed theory for rapid reconnection

    Now, physicists at PPPL and Princeton University have presented a detailed theory for the mechanism that leads to fast reconnection. Their paper, published in the journal Physics of Plasmas in October, focuses on a phenomenon called “plasmoid instability” to explain the onset of the rapid reconnection process. Support for this research comes from the National Science Foundation and the DOE Office of Science.

    Plasmoid instability, which breaks up plasma current sheets into small magnetic islands called plasmoids, has generated considerable interest in recent years as a possible mechanism for fast reconnection. However, correct identification of the properties of the instability has been elusive.

    The Physics of Plasmas paper addresses this crucial issue. It presents “a quantitative theory for the development of the plasmoid instability in plasma current sheets that can evolve in time” said Luca Comisso, lead author of the study. Co-authors are Manasvi Lingam and Yi-Ming Huang of PPPL and Princeton, and Amitava Bhattacharjee, head of the Theory Department at PPPL and Princeton professor of astrophysical sciences.

    Pierre de Fermat’s principle

    The paper describes how the plasmoid instability begins in a slow linear phase that goes through a period of quiescence before accelerating into an explosive phase that triggers a dramatic increase in the speed of magnetic reconnection. To determine the most important features of this instability, the researchers adapted a variant of the 17th century “principle of least time” originated by the mathematician Pierre de Fermat.

    Use of this principle enabled the researchers to derive equations for the duration of the linear phase, and for computing the growth rate and number of plasmoids created. Hence, this least-time approach led to a quantitative formula for the onset time of fast magnetic reconnection and the physics behind it.

    The paper also produced a surprise. The authors found that such relationships do not reflect traditional power laws, in which one quantity varies as a power of another. “It is common in all realms of science to seek the existence of power laws,” the researchers wrote. “In contrast, we find that the scaling relations of the plasmoid instability are not true power laws – a result that has never been derived or predicted before.”

    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. The Laboratory is managed by Princeton 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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    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.

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  • richardmitnick 6:40 pm on May 16, 2016 Permalink | Reply
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    From Goddard via AGU: “Swept Up in the Solar Wind” 

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    NASA Goddard Space Flight Center

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    May 10, 2016
    Sarah Schlieder
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    This image from the ESA/NASA Solar and Heliospheric Observatory on June 15, 1999, shows streaks of bright light. This represents material streaming out from the sun (which is obscured in this picture by the central red disk so that it cannot overwhelm the image of the fainter material around it). Two other NASA spacecraft measured this material closer to Earth to better understand what causes this regular outflow, known as the solar wind, from the sun. Credits: NASA/SOHO


    A constant outflow of solar material streams out from the sun, depicted here in an artist’s rendering. This solar wind is always passing by Earth. Credits: NASA Goddard’s Conceptual Image Lab/Greg Shirah

    From our vantage point on the ground, the sun seems like a still ball of light, but in reality, it teems with activity. Eruptions called solar flares and coronal mass ejections explode in the sun’s hot atmosphere, the corona, sending light and high energy particles out into space. The corona is also constantly releasing a stream of charged particles known as the solar wind.

    But this isn’t the kind of wind you can fly a kite in.

    Even the slowest moving solar wind can reach speeds of around 700,000 mph. And while scientists know a great deal about solar wind, the source of the slow wind remains a mystery. Now, a team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has explored a detailed case study of the slow solar wind, using newly processed observations close to Earth to determine what in fact seeded that wind 93 million miles away, back on the sun. The team spotted tell-tale signs in the wind sweeping by Earth showing that it originated from a magnetic phenomenon known as magnetic reconnection. A paper* on these results was published April 22, 2016, in the journal Geophysical Research Letters.

    Knowing the source of the slow solar wind is important for understanding the space environment around Earth, as near-Earth space spends most of its time bathed in this wind. Just as it is important to know the source of cold fronts and warm fronts to predict terrestrial weather, understanding the source of the solar wind can help tease out space weather around Earth — where changes can sometimes interfere with our radio communications or GPS, which can be detrimental to guiding airline and naval traffic.

    Slow and Fast Solar Wind

    Fast solar wind — not surprisingly — can travel much faster than the slow wind at up to 1.7 million mph, but the most definitive difference between fast and slow solar wind is their composition. Solar wind is what’s known as a plasma, a heated gas made up of charged particles — primarily protons and electrons, with trace amounts of heavier elements such as helium and oxygen. The amount of heavy elements and their charge state, or number of electrons, differ between the two types of wind.

    “The composition and charge state of the slow solar wind is very different from that of fast solar wind,” said Nicholeen Viall, a solar scientist at Goddard. “These differences imply that they came from different places on the sun.”

    By studying its composition, scientists know that fast solar wind emanates from the interior of coronal holes — areas of the solar atmosphere where the corona is darker and colder. The slow solar wind, on the other hand, is associated with hotter regions around the equator, but just how the slow solar wind is released has not been clear.

    But the new results may have provided an answer.

    Tracking Down the Source: Magnetic Reconnection

    Magnetic reconnection can occur anywhere there are powerful magnetic fields, such as in the sun’s magnetic environment. Imagine a magnetic field line pointing in one direction and another field line nearby moving toward it pointing in the opposite direction. As they come together, the field lines will cancel and re-form, each performing a sort of U-turn and curving to move off in a perpendicular direction. The resulting new magnetic field lines create a large force — like a taut rubber band being released — that flings out plasma. This plasma is the slow solar wind.

    The team studied an interval of 90-minute periodic structures in the slow wind, and identified magnetic structures that are the telltale fingerprints of magnetic reconnection. They also found that each 90-minute parcel of slow wind showed an intriguing and repeating variability that could only be remnants of magnetic reconnection back at the sun.

    “We found that the density and charge state composition of the slow solar wind rises and falls every 90 minutes, varying from what is normally slow wind to what is considered fast,” Viall said. “But the speed was constant at a slow wind speed. This could only be created by magnetic reconnection at the sun, tapping into both fast and slow wind source regions.”

    Researchers first discovered the periodic density structures about 15 years ago using the Wind spacecraft — a satellite launched in 1994 to observe the space environment surrounding Earth. The scientists observed oscillations in the magnetic fields near Earth, known as the magnetosphere.

    The WIND Satellite launched on November 1, 1994. The first of NASA’s Global Geospace Science (GGS) program.

    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase
    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

    “It has been thought that the magnetosphere rang like a bell when the solar wind hit it with a sudden increase in pressure,” said Larry Kepko, a magnetospheric scientist at Goddard. “We went in for a closer look and found these periodicities in the solar wind. The magnetosphere was acting more like a drum than a bell.”

    But Wind only gave the researchers measurements of the slow solar wind’s density and velocity, and could not identify its source. For that, they needed composition data.

    Furthermore, in order to solve this problem, scientists from different disciplines needed to work together to come up with an explanation of the entire system. Kepko studies the magnetosphere, while Viall studies the sun. By observing what’s close to Earth and what’s happening at the sun, the team could determine the source of the slow solar wind.

    The scientists turned to NASA’s Advanced Composition Explorer. ACE launched in 1997 to study and measure the composition of several types of space material including the solar wind and cosmic rays. It can observe solar particles and helps researchers determine the elemental composition and speeds of solar wind.

    “Without the ACE data, we wouldn’t have been able to do this research,” Kepko said. “There’s no other instrument that gives us the information at the time resolution we needed.”

    The team is continuing to look at composition data to find other instances of the periodic density structures to determine if the source for all slow solar wind is magnetic reconnection. Their case study clearly shows that this particular event was the result of magnetic reconnection, but they wish to find other examples to show this is the most common mechanism for powering the slow solar wind.

    As the team gathers more information about magnetic reconnection and its effects near the sun, it will add to a growing body of knowledge about the phenomenon in general — because magnetic reconnection events take place throughout the universe.

    “If we can understand this phenomenon here, where we can actually measure the magnetic field, we can get a better handle on how these fundamental physics processes take place in other places in the universe,” Viall said.

    *Science paper: Geophysical Research Letters
    Implications of L1 observations for slow solar windformation by solar reconnection

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

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  • richardmitnick 3:19 pm on May 12, 2016 Permalink | Reply
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    From GIZMODO: “A Major Mystery About Earth’s Magnetic Field Has Just Been Solved” 

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    Maddie Stone


    NASA MMS in flight. University of Maryland

    For the first time, physicists have observed a mysterious process called magnetic reconnection—wherein opposing magnetic field lines join up, releasing a tremendous burst of energy. The discovery, published* today in Science, may help us unlock the secrets of space weather and learn about some of the weirdest, most magnetic objects in the universe.

    The magnetosphere, an invisible magnetic field surrounding our planet, is a critical shield for life on Earth.

    Magnetosphere of Earth
    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

    It protects us from all sorts of high energy particles emitted by the sun on a daily basis. When a particularly large burst of solar energy hits the edge of the magnetosphere (called the magnetopause), it can trigger space weather. This includes geomagnetic storms that light up the northern and southern skies with auroras, occasionally knocking out our satellites and power grids.

    A better understanding of space weather is key to helping us prepare for the next massive geomagnetic storm—a once-in-a-century event that could quite literally cause a global power surge. Magnetic reconnection is at the heart of the mystery, underlying both the formation of solar eruptions and how they interact with our planet.

    Access mp video here .
    Credits: NASA’s Goddard Space Flight Center/Duberstein

    “The process of space weather starts on the sun—reconnection there produces coronal mass ejections and solar flares, both of which lead to space weather at the Earth,” James Burch, a space weather scientist at the Southwest Research Institute told Gizmodo. “When the solar wind and its embedded magnetic field lines collide with Earth’s magnetosphere at a high angle, then you have a direct connection between the sun and the Earth.”

    Now, for the first time, Burch and his colleagues have observed that sun-Earth connection at the subatomic scale, using data collected by NASA’s Magnetospheric Multiscale (MMS) mission. This high-resolution physics laboratory consists of four identical spacecraft that fly in pyramid formation around Earth’s magnetopause, collecting precise information on tiny charged particles every 30 milliseconds.

    Artist’s concept of the four MMS satellites flying in formation. Image: University of Maryland

    Almost as soon as the mission launched in March of 2015, researchers started observing magnetic reconnection at unprecedented resolution. The most detailed of those is the subject of the new paper. “We hit the jackpot,” Roy Torbert, MMS deputy principal investigator said in a statement. “The spacecraft passed directly through the electron dissipation region, and we were able to perform the first-ever physics experiment in this environment.”

    The features of reconnection recorded in the data include a drop in the magnetic field to near zero, and a power spike generated by accelerating electrons. “We realized that the process of reconnection is really driven by electrons,” Burch said. “Before, all measurements had been made at much larger scales. People could see dramatic effects, but these are the result of reconnection, not the cause.”

    Burch and his colleagues are continuing to study five other instances of magnetic reconnection recently observed by the MMS, and they’re hopeful the mission will yield more events for years to come. In addition to shedding light on space weather, magnetic reconnection can help us understand exotic astronomical objects like magnetars, as well as the strong magnetic environments created by fusion reactors.

    “The quality of the MMS data is absolutely inspiring,” said James Drake, a physicist at the University of Maryland and a co-author on the study. “It’s not clear that there will ever be another mission quite like this one.”

    *Science paper:
    Electron-scale measurements of magnetic reconnection in space

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  • richardmitnick 11:23 am on April 6, 2016 Permalink | Reply
    Tags: , Magnetic reconnection,   

    From Physics- “Focus: Space Wave Gives Electrons a Shove” 

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    NASA’s MMS Formation Will Give Unique Look at Magnetic Reconnection


    April 5, 2016
    Michael Schirber

    A new satellite mission has observed electron acceleration by electric field waves moving along the magnetic boundary between the Earth and the solar wind.

    This artist’s drawing shows the four MMS spacecraft flying through the magnetopause, where the magnetic field of the solar wind (yellow-orange) confronts the Earth’s magnetic field (blue). At this boundary, magnetic field reconnection converts the field energy into particle energy. MMS has observed electric-field waves that likely play a role in this conversion.


    Charged particles around the Earth, Sun, and other astrophysical bodies appear to be accelerated to high energies in regions where magnetic fields break up and reconnect, but the exact mechanism is unclear. A recently launched multi-satellite mission has now flown through such a region and directly observed electron acceleration by fast-moving electric-field waves, suggesting a possible role for these waves in the production of high-energy particles. The new data may be an important step in unraveling the mysteries behind solar flares and other energetic cosmic events.

    To learn about the strong interactions between particles and magnetic fields that occur near many planets and stars, researchers study the magnetopause, where the solar wind meets the Earth’s magnetic field. The solar wind is a collection of mostly protons and electrons streaming out from the Sun, carrying with it the interplanetary magnetic field (IMF), which spirals outward from the Sun. Within the magnetopause, the IMF and the geomagnetic field often point in nearly opposite directions in a region called the X-line. The field misalignment forces the field lines to break and reconnect. This reconnection, which also occurs around the Sun and in other plasma regions, converts magnetic energy into kinetic energy for charged particles. Studying reconnection is important for understanding the generation of high-energy particles around the Earth (which endanger satellites and high-altitude airplane passengers) and also for explaining high-energy events like solar flares.

    Acceleration of electrons in a reconnection region has been much harder to measure than the acceleration of ions. Forrest Mozer of the University of California, Berkeley, and his colleagues now report on a direct observation of electron acceleration occurring in the magnetopause, using the Magnetospheric Multiscale (MMS) mission. Launched in the spring of 2015, MMS consists of four satellites flying in a tetrahedral formation. Each probe records electric and magnetic fields as well as the numbers of electrons and ions in various energy ranges. Compared with other multi-satellite missions, the MMS probes have a smaller separation (as little as 10 km), which affords them much higher spatial resolution for measuring localized acceleration mechanisms in reconnection regions.

    On October 5, 2015, the MMS flotilla was passing the X-line in the dayside magnetopause. Two of the probes recorded a set of sharp spikes in the electric field pointing parallel to the local magnetic field. The spikes were part of a traveling wave called a time domain structure (TDS). TDSs have been detected many times by satellite missions in other regions [1]. They have not generally been considered as acceleration mechanisms because the electric field in a spike has both positive (push) and negative (pull) peaks, giving a net electric potential of only 10 volts or less. “They were thought to be the result of some other processes rather than significant mechanisms on their own,” Mozer says.

    However, a TDS can accelerate particles because it acts like a fast-moving barrier that “bumps into slow-moving electrons,” Mozer explains. By comparing the spike arrival times at the two MMS spacecraft, he and his colleagues were able to directly measure the velocity of a TDS, whereas previous TDS observations could only infer the velocity. They found that the wave was moving away from the X-line at 4000 km/s. The MMS instruments confirmed that the wave led to particle acceleration by observing a 50% jump in the number of modestly-high-energy electrons after the wave’s passing. The TDS boosted electrons to around 200 eV, 40 times their initial energy.

    This is not the first detection of TDS-induced acceleration [2], but it is the first direct observation of electron acceleration by TDS within a reconnection region. Mozer admits that the energy gain is not enough to explain 100-keV electrons that have been observed in other reconnection zones. But he believes that faster moving TDSs may be observed in the future. “I think we are seeing just the tip of the iceberg,” Mozer says.

    The MMS observations are new and significant because they are “able to characterize TDSs and directly investigate the associated particle acceleration simultaneously,” says Daniel Graham of the Swedish Institute of Space Physics. James Drake of the University of Maryland says the acceleration “was more than you might expect for such a small electric field.” Still, the total energy gain is not very large, so other mechanisms may play a dominant role in accelerating electrons. Even so, Drake believes these new observations are important for providing benchmarks for computer simulations of reconnection regions.

    This research is published in Physical Review Letters.

    The science team:
    F. S. Mozer, O. A. Agapitov, A. Artemyev, J. L. Burch, R. E. Ergun, B. L. Giles, D. Mourenas, R. B. Torbert, T. D. Phan, and I. Vasko
    No affiliations given

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

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