Modeling Heliospheric Plasma Turbulence: A Critique of the Effects of Completeness, Realism and Size
NASA Astrophysics Data System (ADS)
Matthaeus, W. H.; Wan, M.; Parashar, T.; Shay, M. A.
2015-12-01
With the Solar Probe and Solar Orbiter missions approaching, and the highly capable instruments of MMS already in orbit, there is an upwelling of interest in understanding plasma turbulence and related effects at kinetic scales. Accordingly a variety of methods have been employed to study kinetic turbulence and in particular dissipation and cascade processes and their effects on protons, electrons and minor ions. Here we discuss the influence of system size, and the completeness and realism of the several kinetic physics models that are employed. One important issue is whether coherent structures such as current sheets can be properly represented and evolved in smaller systems; this is particular important when turbulence is intermittent and non-self similar, so that couplings become nonlocal in scale. Another factor is resolution, both spatial and statistical - what are the effects of counting statistics in PIC and velocity filamentation in Vlasov models? Also discussed is the efficacy and strategic use of models with reduced physics and/or dimensionality - hybrid, Reduced MHD and gyrokinetics, for example. It is suggested, using several example problems, how the cross comparison of models in the context of a framework such as Turbochallenge may have wide ranging conceptual impact.
Particle acceleration, transport and turbulence in cosmic and heliospheric physics
NASA Technical Reports Server (NTRS)
Matthaeus, W.
1992-01-01
In this progress report, the long term goals, recent scientific progress, and organizational activities are described. The scientific focus of this annual report is in three areas: first, the physics of particle acceleration and transport, including heliospheric modulation and transport, shock acceleration and galactic propagation and reacceleration of cosmic rays; second, the development of theories of the interaction of turbulence and large scale plasma and magnetic field structures, as in winds and shocks; third, the elucidation of the nature of magnetohydrodynamic turbulence processes and the role such turbulence processes might play in heliospheric, galactic, cosmic ray physics, and other space physics applications.
Slow Mode Waves in the Heliospheric Plasma Sheet
NASA Technical Reports Server (NTRS)
Smith, Edward. J.; Zhou, Xiaoyan
2007-01-01
We report the results of a search for waves/turbulence in the Heliospheric Plasma Sheet (HPS) surrounding the Heliospheric Current Sheet (HCS). The HPS is treated as a distinctive heliospheric structure distinguished by relatively high Beta, slow speed plasma. The data used in the investigation are from a previously published study of the thicknesses of the HPS and HCS that were obtained in January to May 2004 when Ulysses was near aphelion at 5 AU. The advantage of using these data is that the HPS is thicker at large radial distances and the spacecraft spends longer intervals inside the plasma sheet. From the study of the magnetic field and solar wind velocity components, we conclude that, if Alfven waves are present, they are weak and are dominated by variations in the field magnitude, B, and solar wind density, NP, that are anti-correlated.
Three-Dimensional Reconnection and Turbulence in the Outer Heliosphere
NASA Astrophysics Data System (ADS)
Gingell, P.; Burgess, D.; Matteini, L.
2015-12-01
In the outer heliosphere, close to the heliopause, we can expect the heliospheric current sheet to form a region of closely-packed, thin current sheets. These structures may be subject to an ion-kinetic tearing instability, and hence generate magnetic islands and hot populations of ions associated with magnetic reconnection. It has been suggested that reconnection processes in this environment have important implications for local particle transport, influencing the porosity of the sectored heliosheath, and for the generation of anomalous cosmic rays via acceleration at reconnection sites. We study this complex environment by means of three-dimensional hybrid simulations over long time scales, in order to capture the evolution of the system from linear growth of the tearing instability at early times, to a fully developed turbulent cascade at late times. Simulations are conducted using both force-free and Harris current sheet equilibria, with varying plasma beta and guide field angle. We discuss the evolution of the magnetic topology, and how changes in the initial conditions affect reconnection rates, particle acceleration, cross-boundary transport and magnetic spectra. We also examine the effect of including an energetic population of interstellar H+ pick-up ions. Finally, given the turbulent end state in the simulations, we also investigate the multiple current sheet system as a general scenario for driving turbulence, and as an alternative to the common methods for simulating decaying turbulence.
ION-SCALE TURBULENCE IN THE INNER HELIOSPHERE: RADIAL DEPENDENCE
Comisel, H.; Motschmann, U.; Büchner, J.; Narita, Y.; Nariyuki, Y.
2015-10-20
The evolution of the ion-scale plasma turbulence in the inner heliosphere is studied by associating the plasma parameters for hybrid-code turbulence simulations to the radial distance from the Sun via a Solar wind model based mapping procedure. Using a mapping based on a one-dimensional solar wind expansion model, the resulting ion-kinetic scale turbulence is related to the solar wind distance from the Sun. For this purpose the mapping is carried out for various values of ion beta that correspond to the heliocentric distance. It is shown that the relevant normal modes such as ion cyclotron and ion Bernstein modes will occur first at radial distances of about 0.2–0.3 AU, i.e., near the Mercury orbit. This finding can be used as a reference, a prediction to guide the in situ measurements to be performed by the upcoming Solar Orbiter and Solar Probe Plus missions. Furthermore, a radial dependence of the wave-vector anisotropy was obtained. For astrophysical objects this means that the spatial scales of filamentary structures in interstellar media or astrophysical jets can be predicted for photometric observations.
Pickup ion-mediated plasma physics of the outer heliosphere and very local interstellar medium
NASA Astrophysics Data System (ADS)
Zank, G. P.
2016-12-01
Observations of plasma and turbulence in the outer heliosphere (the distant supersonic solar wind and the subsonic solar wind beyond the heliospheric termination shock) made by the Voyager Interstellar Mission and the energetic neutral atom observations made by the IBEX spacecraft have revealed that the underlying plasma in the outer heliosphere and very local interstellar medium (VLISM) comprises distinct thermal proton and electron and suprathermal pickup ion (PUI) populations. Estimates of the appropriate collisional frequencies show that the multi-component plasma is not collisionally equilibrated in either the outer heliosphere or VLISM. Furthermore, suprathermal PUIs in these regions form a thermodynamically dominant component. We review briefly a subset of the observations that led to the realization that the solar wind-VLISM interaction region is described by a non-equilibrated multi-component plasma and summarizes the derivation of suitable plasma models that describe a PUI-mediated plasma.
Interplanetary magnetic field as a detector of turbulence in the inner heliosphere
NASA Astrophysics Data System (ADS)
Khabarova, O.
2013-12-01
Analysis of the interplanetary magnetic field (IMF) behavior at different scales may give a key for understanding of turbulence spatial evolution in the heliosphere. It has been known that the solar wind plasma becomes more and more turbulent with heliocentric distance. Recent multi-spacecraft investigations of the large-scale IMF [1] show unexpectedly fast lost of the regular sector structure of the solar wind in the inner heliosphere. In the ecliptic plane, it seems to be broken at 3-4 AU, much closer to the Sun than the Parker spiral gets perpendicular to the sunward direction. At the same time, the high-latitude solar wind remains more structured at the same heliocentric distances [2]. This fact may bear evidence of radial increase of turbulence and intermittency in the solar wind due to magnetic reconnection. The magnetic reconnection recurrently occurs at the large-scale heliospheric current sheet (HCS) as well as at smaller-scale current sheets during the solar wind expansion [3]. As a result, a significant part of the heliosphere is filled with secondary current sheets as well as with waves and accelerated particles in some vicinity of the HCS. Under averaging, it looks as a radial increase of turbulence, especially in low latitudes. It also can be considered as one of the main causes of the break of the expected IMF radial dependence law [1, 2]. Results of the consequent multi-spacecraft analysis of plasma and magnetic filed turbulence characteristics at different heliocentric distances and heliolatitudes will be discussed. 1. O. Khabarova, V. Obridko, Puzzles of the Interplanetary Magnetic Field in the Inner Heliosphere, 2012, Astrophysical Journal, 761, 2, 82, doi:10.1088/0004-637X/761/2/82, http://arxiv.org/pdf/1204.6672v2.pdf 2. O.V. Khabarova, The interplanetary magnetic field: radial and latitudinal dependences, Astronomy Reports, 2013, 57, 11, http://arxiv.org/ftp/arxiv/papers/1305/1305.1204.pdf 3. V. Zharkova, O. Khabarova, Particle Acceleration in
Turbulence transport modeling of the temporal outer heliosphere
Adhikari, L.; Zank, G. P.; Hu, Q.; Dosch, A.
2014-09-20
The solar wind can be regarded as a turbulent magnetofluid, evolving in an expanding solar wind and subject to turbulent driving by a variety of in situ sources. Furthermore, the solar wind and the drivers of turbulence are highly time-dependent and change with solar cycle. Turbulence transport models describing low-frequency magnetic and velocity fluctuations in the solar wind have so far neglected solar cycle effects. Here we consider the effects of solar cycle variability on a turbulence transport model developed by Zank et al. This model is appropriate for the solar wind beyond about 1 AU, and extensions have described the steady-state dependence of the magnetic energy density fluctuations, correlation length, and solar wind temperature throughout the outer heliosphere. We find that the temporal solar wind introduces a periodic variability, particularly beyond ∼10 AU, in the magnetic energy density fluctuations, correlation length, and solar wind temperature. The variability is insufficient to account for the full observed variability in these quantities, but we find that the time-dependent solutions trace the steady-state solutions quite well, suggesting that the steady-state models are reasonable first approximations.
Meridional plasma flow in the outer heliosphere
NASA Technical Reports Server (NTRS)
Lazarus, A. J.; Yedidia, B.; Villanueva, L.; Mcnutt, R. L., Jr.; Belcher, J. W.; Villante, U.; Burlaga, L. F.
1988-01-01
Voyager 2 observations made in the outer heliosphere near 25 AU and within 2 deg of the heliographic equatorial plane show periodic variations in the meridional (North/South) flow velocities that are much more prominent than the East/West variations. An autocorrelation analysis shows that the flow variation has a period of about 25.5 days in the latter half of 1986, in approximate agreement with the solar rotation period. The results suggest that increased pressure in interaction regions remains the best candidate for the driver of the nonradial flows.
Thickness of Heliospheric Current and Plasma Sheets: Dependence on Distance
NASA Astrophysics Data System (ADS)
Zhou, X.; Smith, E. J.; Winterhalter, D.; McComas, D. J.; Skoug, R. M.; Goldstein, B. E.; Smith, C. W.
2005-05-01
Heliospheric current sheets (HCS) are well defined structures that separate the interplanetary magnetic fields with inverse polarities. Surrounded by heliospheric plasma sheets (HPS), the current sheets stretch throughout the heliosphere. Interesting questions that still remain unanswered include how the thickness of these structures will change along the distance? And what determines the thickness of these structures? To answer these fundamental questions, we have carried out a study of the HCS and HPS using recent Ulysses data near 5 AU. When the results were compared with earlier studies at 1 AU using ISEE-3 data, they were surprising and unexplained. Although the plasma sheet grew thicker, the embedded current sheet grew thinner! Using data under the same (or very similar) circumstances, we have extended the analysis in two ways. First, the same current-plasma sheets studied at 5 AU have been identified at 1 AU using ACE data. Second, data obtained while Ulysses was en-route to Jupiter near 3 AU have been analyzed. This three-point investigation reveals the thickness variation along the distance and enables the examination of the controller of this variation.
Division E Commission 49: Interplanetary Plasma and Heliosphere
NASA Astrophysics Data System (ADS)
Mann, Ingrid; Manoharan, P. K.; Gopalswamy, Natchimuthuk; Briand, Carine; Chashei, Igor V.; Gibson, Sarah E.; Lario, David; Hanaoka, Yoichiro; Malandraki, Olga; Kontar, Eduard; Richardson, John D.
2016-04-01
After a little more than forty years of work related to the interplanetary plasma and the heliosphere the IAU's Commission 49 was formally discontinued in 2015. The commission started its work when the first spacecraft were launched to measure the solar wind in-situ away from Earth orbit, both inward and outward from 1 AU. It now hands over its activities to a new commission during an era of space research when Voyager 1 measures in-situ the parameters of the local interstellar medium at the edge of the heliosphere. The commission will be succeeded by C.E3 with a similar area of responsibility but with more focused specific tasks that the community intends to address during the coming several years. This report includes a short description of the motivation for this commission and of the historical context. It then describes work from 2012 to 2015 during the present solar cycle 24 that has been the weakest in the space era so far. It gave rise to a large number of studies on solar energetic particles and cosmic rays. Other studies addressed e.g. the variation of the solar wind structure and energetic particle fluxes on long time scales, the detection of dust in the solar wind and the Voyager measurements at the edge of the heliosphere. The research is based on measurements from spacecraft that are at present operational and motivated by the upcoming Solar Probe + and Solar Orbiter missions to explore the vicinity of the Sun. We also report here the progress on new and planned radio instruments and their importance for heliospheric studies. Contributors to this report are Carine Briand, Yoichiro Hanaoka, Eduard Kontar, David Lario, Ingrid Mann, John D. Richardson.
Electromagnetic strong plasma turbulence
Melatos, A.; Jenet, F. A.; Robinson, P. A.
2007-02-15
The first large-scale simulations of continuously driven, two-dimensional electromagnetic strong plasma turbulence are performed, for electron thermal speeds 0.01c{<=}v{<=}0.57c, by integrating the Zakharov equations for coupled Langmuir and transverse (T) waves near the plasma frequency. Turbulence scalings and wave number spectra are calculated, a transition is found from a mix of trapped and free T eigenstates for v{>=}0.1c to just free eigenstates for v{<=}0.1c, and wave energy densities are observed to undergo slow quasiperiodic oscillations.
Instabilities and Plasma Mixing at the Heliospheric Boundary
NASA Astrophysics Data System (ADS)
Avinash, K.; Zank, G. P.
2014-12-01
The stability of the heliopause (HP) that separates the tenuous heliosheath plasma from the relatively dense plasma of the local interstellar medium (LISM) is examined using a fully general model that includes all the important physical process pertaining to the heliosphere e.g., resonant charge exchange with neutral hydrogen, plasma flows and magnetic fields in the outer and inner heliosheath, and energetic neutral ENA) from the inner heliosheath. Charge exchange introduces Rayleigh Taylor (RT) like instability in the nose region of HP, the strong flow shear excites Kelvin-Helmholtz (KH) like instability in the flanks while mixed RT-KH modes are unstable in the shoulder region in between. ENA are found to be essential for the instability of flanks in the presence of magnetic field stabilization. Further, the mixing of the LISM plasma with solar wind (SW) plasma is across the HP caused by these instabilities is examined. The magnetic field in the OHS and IHS are oriented approximately parallel to each (on either side of HP). Such field lines normally do not experience reconnection However, we show that in the nonlinear phase, local mushroom like structures of RT and RT-KH mode will drag the OHS field lines across HP into the inner heliosheath. Driven by local plasma flows, these field lines will reconnect with magnetic field lines in the HIS. This reconnection of fields in OHS and IHS will greatly enhance the mixing of plasma across the HP. This scenario is examined using Sweet-Parker and Petscheck models of driven reconnection. The reconnection rates and mixing rates with collisional resistivity and anomalous resistivity are evaluated and compared with other mechanisms of mixing to assess the importance of reconnection in plasma mixing across HP.
ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE
Strumik, M.; Grzedzielski, S.; Czechowski, A.; Macek, W. M.; Ratkiewicz, R.
2014-02-10
We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP.
Self-consistent Simulations of Plasma-Neutral in a Partially Ionized Astrophysical Turbulent Plasma
NASA Astrophysics Data System (ADS)
Shaikh, Dastgeer; Zank, G. P.
2010-03-01
A local turbulence model is developed to study energy cascades in the heliosheath and outer heliosphere (OH) based on self-consistent two-dimensional fluid simulations. The model describes a partially ionized magnetofluid OH that couples a neutral hydrogen fluid with a plasma primarily through charge-exchange interactions. Charge-exchange interactions are ubiquitous in warm heliospheric plasma, and the strength of the interaction depends largely on the relative speed between the plasma and the neutral fluid. Unlike small-length scale linear collisional dissipation in a single fluid, charge-exchange processes introduce channels that can be effective on a variety of length scales that depend on the neutral and plasma densities, temperature, relative velocities, charge-exchange cross section, and the characteristic length scales. We find, from scaling arguments and nonlinear coupled fluid simulations, that charge-exchange interactions modify spectral transfer associated with large-scale energy-containing eddies. Consequently, the turbulent cascade rate prolongs spectral transfer among inertial range turbulent modes. Turbulent spectra associated with the neutral and plasma fluids are therefore steeper than those predicted by Kolmogorov's phenomenology. Our work is important in the context of the global heliospheric interaction, the energization and transport of cosmic rays, gamma-ray bursts, interstellar density spectra, etc. Furthermore, the plasma-neutral coupling is crucial in understanding the energy dissipation mechanism in molecular clouds and star formation processes.
An Unusual Heliospheric Plasma Sheet Crossing at 1 AU
NASA Astrophysics Data System (ADS)
Wu, C. C.; Liou, K.; Vourlidas, A.; Lepping, R. P.; Wang, Y. M.; Plunkett, S. P.; Socker, D. G.; Wu, S. T.
2014-12-01
At 11:46UT on September 9, 2011, the Wind spacecraft encountered an interplanetary (IP) fast forward shock. The shock was followed almost immediately (~5 minutes) by a short duration (~35 minutes), extremely large density pulse with a density peak of ~100 cm-3. While a sharp increase in the solar wind density is typical of an IP shock downstream, the unusual large density increase prompts a further investigation. After a close examination of other in situ data from Wind, we find the density pulse was associated with (1) a spike in the plasma beta (ratio of thermal to magnetic pressure), (2) multiple sign changes in the azimuthal angle of magnetic field, (3) depressed magnetic field, (4) a small radial component of magnetic field, and (5) a large (>90 degrees) pitch-angle change in suprathermal electrons (>200 eV) across the density pulse. We conclude that the density pulse is the heliospheric plasma sheet and the estimated thickness is ~820,000km. The unusually large density pulse is likely to be a result of the shock compression from behind. This view is supported by our 3D magnetohydrodynamic simulation. The detailed result and implications will be discussed. *This work is supported partially by ONR 6.1 program
Plasma wave generation near the inner heliospheric shock
NASA Technical Reports Server (NTRS)
Macek, W. M.; Cairns, I. H.; Kurth, W. S.; Gurnett, D. A.
1991-01-01
There is mounting evidence that the Voyager 1 and 2 and Pioneer 11 spacecraft may approach the inner (termination) heliospheric shock near the end of this century. It is argued here, by analogy with planetary bow shocks, that energetic electrons backstreaming from the heliospheric shock along the magnetic field should be unstable to the generation of Langmuir waves by the electron beam instability. Analytic expressions for the cutoff velocity, corresponding to the beam speed of the electrons backstreaming from the shock, are derived for a standard solar wind model. At the front side of the heliosphere the maximum beam velocity is expected to be at the meridian passing through the nose of the shock, which is assumed to be aligned with the Very Local Inter-Stellar Medium flow. This foreshock region and the associated Langmuir waves are relevant to both the expected in situ observations of the heliospheric boundaries, and to the low-frequency (2-3 kHz) radio emissions observed by the Voyager spacecraft in the outer heliosphere. Provided that these radio emissions are generated by Langmuir waves, the minimum Langmuir wave electric fields at the remote source are estimated to be greater than about 3 - 30 microV/m.
PLASMA HEATING DURING A CORONAL MASS EJECTION OBSERVED BY THE SOLAR AND HELIOSPHERIC OBSERVATORY
Murphy, N. A.; Raymond, J. C.; Korreck, K. E.
2011-07-01
We perform a time-dependent ionization analysis to constrain plasma heating requirements during a fast partial halo coronal mass ejection (CME) observed on 2000 June 28 by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO). We use two methods to derive densities from the UVCS measurements, including a density sensitive O V line ratio at 1213.85 and 1218.35 A, and radiative pumping of the O VI {lambda}{lambda}1032, 1038 doublet by chromospheric emission lines. The most strongly constrained feature shows cumulative plasma heating comparable to or greater than the kinetic energy, while features observed earlier during the event show plasma heating of order or less than the kinetic energy. SOHO Michelson Doppler Imager observations are used to estimate the active region magnetic energy. We consider candidate plasma heating mechanisms and provide constraints when possible. Because this CME was associated with a relatively weak flare, the contribution from flare energy (e.g., through thermal conduction or energetic particles) is probably small; however, the flare may have been partially behind the limb. Wave heating by photospheric motions requires heating rates to be significantly larger than those previously inferred for coronal holes, but the eruption itself could drive waves that heat the plasma. Heating by small-scale reconnection in the flux rope or by the CME current sheet is not significantly constrained. UVCS line widths suggest that turbulence must be replenished continually and dissipated on timescales shorter than the propagation time in order to be an intermediate step in CME heating.
1983-05-01
Ney, and J . F. Karczewski, Spae Sci. Instrum ., 4, 143 (1978). -- ’.. ...... .. " ’- -’ ... -,,, ,i, ,, - . --. : s v.-’ Z XW , - .. . Ř ’ - ’ " p...interactions with the able plasma theorists, Dr. J . R. Jasperse at the Air Force Geophysics Laboratory, Drs. B. Basu and J . Retterer of the Space Data Analysis...Drs. J . D. Winningham and J . Burch at the Southwest Research Institute, Dr. D. Klumpar of the University of Texas at Dallas, Dr. P. Kintner of the
Trajectory structures in turbulent plasmas
Vlad, Madalina; Spineanu, Florin
2006-11-03
Particle stochastic advection in two dimensional divergence free velocity fields is studied. The special statistical properties of this process (non-Gaussian distribution, memory effects and quasi-coherent behavior) are determined using a new approach, the nested subensemble method. The effect of the statistics of trajectories on the evolution of drift turbulence in magnetized plasmas is studied. It essentialy consists in the tendency of structure formation.
Electromagnetic scattering from turbulent plasmas
Resendes, D.G. Instituto Superior Tecnico, Rua Rovisco Pais, Lisboa )
1992-11-15
A self-consistent multiple-scattering theory of vector electromagnetic waves scattered from a turbulent plasma is presented. This approach provides a general and systematic treatment to all orders in turbulence of the scattering of electromagnetic waves in terms of the properties of the turbulent structure of the scattering system and is applicable in the full regime from underdense to overdense plasmas. To illustrate the theory, a plasma consisting of a finite number density of discrete scatterers with a simple geometry and statistical properties is chosen. In this approach the exact solution for a single scatterer is obtained first. From it the configuration-dependent solution for {ital N} scatterers is constructed. Rather than solving explicitly for this solution and then averaging, the averaging operation will be taken first in order to find an approximate equation obeyed by the mean or coherent field. The coherent and incoherent scattering are then determined in terms of the coherent field and the backscatter is evaluated. The coherent and incoherent scattering, our principal results, are expressed in a plane-wave basis in a form suitable for numerical computation. A number of interesting phenomena which may readily be incorporated into the theory are indicated.
Using Field-Particle Correlations to Diagnose the Collisionless Damping of Plasma Turbulence
NASA Astrophysics Data System (ADS)
Howes, Gregory; Klein, Kristropher
2016-10-01
Plasma turbulence occurs ubiquitously throughout the heliosphere, yet our understanding of how turbulence governs energy transport and plasma heating remains incomplete, constituting a grand challenge problem in heliophysics. In weakly collisional heliospheric plasmas, such as the solar corona and solar wind, damping of the turbulent fluctuations occurs due to collisionless interactions between the electromagnetic fields and the individual plasma particles. A particular challenge in diagnosing this energy transfer is that spacecraft measurements are typically limited to a single point in space. Here we present an innovative field-particle correlation technique that can be used with single-point measurements to estimate the energization of the plasma particles due to the damping of the electromagnetic fields, providing vital new information about this how energy transfer is distributed as a function of particle velocity. This technique has the promise to transform our ability to diagnose the kinetic plasma physical mechanisms responsible for not only the damping of turbulence, but also the energy conversion in both collisionless magnetic reconnection and particle acceleration. The work has been supported by NSF CAREER Award AGS-1054061, NSF AGS-1331355, and DOE DE-SC0014599.
Global Variation of Meteor Trail Plasma Turbulence
NASA Technical Reports Server (NTRS)
Dyrud, L. P.; Hinrichs, J.; Urbina, J.
2011-01-01
We present the first global simulations on the occurrence of meteor trail plasma irregularities. These results seek to answer the following questions: when a meteoroid disintegrates in the atmosphere will the resulting trail become plasma turbulent, what are the factors influencing the development of turbulence, and how do they vary on a global scale. Understanding meteor trail plasma turbulence is important because turbulent meteor trails are visible as non-specular trails to coherent radars, and turbulence influences the evolution of specular radar meteor trails, particularly regarding the inference of mesospheric temperatures from trail diffusion rates, and their usage for meteor burst communication. We provide evidence of the significant effect that neutral atmospheric winds and density, and ionospheric plasma density have on the variability of meteor trail evolution and the observation of nonspecular meteor trails, and demonstrate that trails are far less likely to become and remain turbulent in daylight, explaining several observational trends using non-specular and specular meteor trails.
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…
Turbulence modelling of thermal plasma flows
NASA Astrophysics Data System (ADS)
Shigeta, Masaya
2016-12-01
This article presents a discussion of the ideas for modelling turbulent thermal plasma flows, reviewing the challenges, efforts, and state-of-the-art simulations. Demonstrative simulations are also performed to present the importance of numerical methods as well as physical models to express turbulent features. A large eddy simulation has been applied to turbulent thermal plasma flows to treat time-dependent and 3D motions of multi-scale eddies. Sub-grid scale models to be used should be able to express not only turbulent but also laminar states because both states co-exist in and around thermal plasmas which have large variations of density as well as transport properties under low Mach-number conditions. Suitable solution algorithms and differencing schemes must be chosen and combined appropriately to capture multi-scale eddies and steep gradients of temperature and chemical species, which are turbulent features of thermal plasma flows with locally variable Reynolds and Mach numbers. Several simulations using different methods under different conditions show commonly that high-temperature plasma regions exhibit less turbulent structures, with only large eddies, whereas low-temperature regions tend to be more turbulent, with numerous small eddies. These numerical results agree with both theoretical insight and photographs that show the characteristics of eddies. Results also show that a turbulence transition of a thermal plasma jet through a generation-breakup process of eddies in a torch is dominated by fluid dynamic instability after ejection rather than non-uniform or unsteady phenomena.
Future heliospheric missions from Russian perspective
NASA Astrophysics Data System (ADS)
Petrukovich, Anatoli; Izmodenov, Vladislav; Zelenyi, Lev; Kuzin, Sergey; Kuznetsov, Vladimir; Eismont, Natan
Structure and plasma processes of the heliosphere will be in the focus of attention for the next decade with the launch of Solar Orbiter, Solar Probe Plus, Interhelioprobe and SPORT, as well as the continuing flight of Voyagers and New Horizons. We review possible scientific goals and technical challenges for even more distant projects which are under discussion now. The projects include high-ecliptic observations with the help of solar sail, remote observations of heliospheric outer boundaries with interstellar medium as well as local high resolution turbulence studies. A major future challenge for the space weather research is the support for manned spaceflight beyond low Earth orbit.
Using In Situ and Remote Sensing Data to Model the Plasma Flow throughout the Heliosphere
NASA Astrophysics Data System (ADS)
Kim, T. K.; Pogorelov, N. V.; Arge, C. N.; Jackson, B. V.; Kryukov, I.; Manoharan, P. K.; Tropf, D.; Yu, H. S.; Zank, G. P.
2015-12-01
The solar wind is a turbulent medium with physical properties fluctuating on multiple scales. We model three-dimensional solar wind plasma flow using our own software, Multi-Scale Fluid-Kinetic Simulation Suite, which, in addition to the thermal solar wind plasma, takes into account charge exchange of solar wind protons with interstellar neutral atoms and treats nonthermal ions (pickup ions, PUIs) born during this process as a separate fluid. Additionally, our model includes a description of turbulence generated by PUIs. For this investigation, we run our model using plasma and turbulence parameters from OMNI data as time-dependent boundary conditions at 1 AU for the Reynolds-averaged MHD equations and investigate the evolution of plasma and turbulent fluctuations along the trajectory of the New Horizons spacecraft, which recently passed by Pluto nearly ten years after launch. We also present solar wind simulations starting at 0.1 AU outwards using interplanetary scintillation data as boundary conditions. Simulations are compared with OMNI and STEREO data. The purpose of this study is to create a time-dependent solar wind model capable of reproducing the plasma flow, magnetic field, and turbulence along the trajectories of Solar Probe Plus and Solar Orbiter.
Development of turbulence in a dusty plasma
NASA Astrophysics Data System (ADS)
Schwabe, Mierk; Zhdanov, Sergey; Räth, Christoph
2016-10-01
Complex or dusty plasmas are low temperature plasmas which contain micrometer-sized particles (``dust''). The microparticles obtain high charges and interact with each other, effectively forming a solid, liquid or gas state in which the microparticles take over the role of molecules in conventional systems. Complex plasmas often are in a turbulent state, for instance when instabilities like the ``heartbeat'' instability or intense waves are present. The movement of the microparticles, the carriers of the turbulent interactions in complex plasmas, can be directly followed, unlike that of atoms and molecules in conventional experiments on turbulence. Here we present results of an experiment on the development of turbulence in a complex plasma in the PK-3 Plus laboratory on board the International Space Station. The microparticle cloud was first stabilized against an instability. Once the stabilization was turned off, the cloud became unstable, and the movement of the particles became turbulent. In the report, we show how the energy spectra evolve during the development of turbulence. In the case of fully developed turbulence, the spectra display multiple cascades explaining well the transport of turbulent energy and enstrophy.
Recent developments in plasma turbulence and turbulent transport
Terry, P.W.
1997-09-22
This report contains viewgraphs of recent developments in plasma turbulence and turbulent transport. Localized nonlinear structures occur under a variety of circumstances in turbulent, magnetically confined plasmas, arising in both kinetic and fluid descriptions, i.e., in either wave-particle or three-wave coupling interactions. These structures are non wavelike. They cannot be incorporated in the collective wave response, but interact with collective modes through their shielding by the plasma dielectric. These structures are predicted to modify turbulence-driven transport in a way that in consistent with, or in some cases are confirmed by recent experimental observations. In kinetic theory, non wavelike structures are localized perturbations of phase space density. There are two types of structures. Holes are self-trapped, while clumps have a self-potential that is too weak to resist deformation and mixing by ambient potential fluctuations. Clumps remain correlated in turbulence if their spatial extent is smaller than the correlation length of the scattering fields. In magnetic turbulence, clumps travel along stochastic magnetic fields, shielded by the plasma dielectric. A drag on the clump macro-particle is exerted by the shielding, inducing emission into the collective response. The emission in turn damps back on the particle distribution via Landau dampling. The exchange of energy between clumps and particles, as mediated by the collective mode, imposes constraints on transport. For a turbulent spectrum whose mean wavenumber along the equilibrium magnetic field is nonzero, the electron thermal flux is proportional to the ion thermal velocity. Conventional predictions (which account only for collective modes) are larger by the square root of the ion to electron mass ratio. Recent measurements are consistent with the small flux. In fluid plasma,s localized coherent structures can occur as intense vortices.
Observations of velocity shear driven plasma turbulence
NASA Technical Reports Server (NTRS)
Kintner, P. M., Jr.
1976-01-01
Electrostatic and magnetic turbulence observations from HAWKEYE-1 during the low altitude portion of its elliptical orbit over the Southern Hemisphere are presented. The magnetic turbulence is confined near the auroral zone and is similar to that seen at higher altitudes by HEOS-2 in the polar cusp. The electrostatic turbulence is composed of a background component with a power spectral index of 1.89 + or - .26 and an intense component with a power spectral index of 2.80 + or - .34. The intense electrostatic turbulence and the magnetic turbulence correlate with velocity shears in the convective plasma flow. Since velocity shear instabilities are most unstable to wave vectors perpendicular to the magnetic field, the shear correlated turbulence is anticipated to be two dimensional in character and to have a power spectral index of 3 which agrees with that observed in the intense electrostatic turbulence.
Boundary Plasma Turbulence Simulations for Tokamaks
Xu, X; Umansky, M; Dudson, B; Snyder, P
2008-05-15
The boundary plasma turbulence code BOUT models tokamak boundary-plasma turbulence in a realistic divertor geometry using modified Braginskii equations for plasma vorticity, density (ni), electron and ion temperature (T{sub e}; T{sub i}) and parallel momenta. The BOUT code solves for the plasma fluid equations in a three dimensional (3D) toroidal segment (or a toroidal wedge), including the region somewhat inside the separatrix and extending into the scrape-off layer; the private flux region is also included. In this paper, a description is given of the sophisticated physical models, innovative numerical algorithms, and modern software design used to simulate edge-plasmas in magnetic fusion energy devices. The BOUT code's unique capabilities and functionality are exemplified via simulations of the impact of plasma density on tokamak edge turbulence and blob dynamics.
Scaling laws in magnetized plasma turbulence
Boldyrev, Stanislav
2015-06-28
Interactions of plasma motion with magnetic fields occur in nature and in the laboratory in an impressively broad range of scales, from megaparsecs in astrophysical systems to centimeters in fusion devices. The fact that such an enormous array of phenomena can be effectively studied lies in the existence of fundamental scaling laws in plasma turbulence, which allow one to scale the results of analytic and numerical modeling to the sized of galaxies, velocities of supernovae explosions, or magnetic fields in fusion devices. Magnetohydrodynamics (MHD) provides the simplest framework for describing magnetic plasma turbulence. Recently, a number of new features of MHD turbulence have been discovered and an impressive array of thought-provoking phenomenological theories have been put forward. However, these theories have conflicting predictions, and the currently available numerical simulations are not able to resolve the contradictions. MHD turbulence exhibits a variety of regimes unusual in regular hydrodynamic turbulence. Depending on the strength of the guide magnetic field it can be dominated by weakly interacting Alfv\\'en waves or strongly interacting wave packets. At small scales such turbulence is locally anisotropic and imbalanced (cross-helical). In a stark contrast with hydrodynamic turbulence, which tends to ``forget'' global constrains and become uniform and isotropic at small scales, MHD turbulence becomes progressively more anisotropic and unbalanced at small scales. Magnetic field plays a fundamental role in turbulent dynamics. Even when such a field is not imposed by external sources, it is self-consistently generated by the magnetic dynamo action. This project aims at a comprehensive study of universal regimes of magnetic plasma turbulence, combining the modern analytic approaches with the state of the art numerical simulations. The proposed study focuses on the three topics: weak MHD turbulence, which is relevant for laboratory devices, the solar
NASA Technical Reports Server (NTRS)
Kabin, K.; Hansen, K. C.; Gombosi, T. I.; Combi, M. R.; Linde, T. J.; DeZeeuw, D. L.; Groth, C. P. T.; Powell, K. G.; Nagy, A. F.
2000-01-01
Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.
Transport phenomena in a turbulent plasma
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.; Silin, V. P.
1984-04-01
The results of a theory of ion-sound turbulence in a plasma which takes into account the electron quasilinear relaxation effect and the nonlinear wave interaction are presented. The transport coefficients characterizing the electrical current and heat flux in the plasma are obtained. A new point of view on the anomalous collision frequency is given.
Nusselt number scaling in tokamak plasma turbulence
Takeda, K.; Benkadda, S.; Hamaguchi, S.; Wakatani, M.
2005-05-15
Anomalous heat transport caused by ion temperature gradient (ITG) driven turbulence in tokamak plasmas is evaluated from numerical simulations of the two-dimensional (2D) partial-differential equations of the ITG model and of a reduced 1D version derived from a quasilinear approximation. In the strongly turbulent state, intermittent bursts of thermal transport are observed in both cases. In the strongly turbulent regime, the reduced model as well as the direct numerical simulation show that the Nusselt number Nu (normalized heat flux) scales with the normalized ion pressure gradient K{sub i} as Nu{proportional_to}K{sub i}{sup 1/3}. Since the Rayleigh number for ITG turbulence is proportional to K{sub i}, the Nusselt number scaling for ITG turbulence is thus similar to the classical thermal transport scaling for Rayleigh-Benard convections in neutral fluids.
The turbulent bremsstrahlung (plasma-maser) effect
Vladimirov, S. V.
2011-01-04
Because of nonlinear interaction between particles and waves, energy conversion between waves of large frequency difference can occur without particle population inversion or resonant wave-wave interaction. The effect involves the nonresonant interaction of the plasma particles with a pair of plasma modes of large frequency difference, and wave energy is converted into particle energy. This effect can appear in laboratory as well as astrophysical plasmas and is important in determining the transport properties of weakly turbulent plasmas. Here, the most important aspects of the plasma-maser theory is discussed.
Origin and turbulence spreading of plasma blobs
Manz, P.; Birkenmeier, G.; Stroth, U.; Ribeiro, T. T.; Scott, B. D.; Carralero, D.; Müller, S. H.; Müller, H. W.; Wolfrum, E.; Fuchert, G.
2015-02-15
The formation of plasma blobs is studied by analyzing their trajectories in a gyrofluid simulation in the vicinity of the separatrix. Most blobs arise at the maximum radial electric field outside the separatrix. In general, blob generation is not bound to one particular radial position or instability. A simple model of turbulence spreading for the scrape-off layer is derived. The simulations show that the blob dynamics can be represented by turbulence spreading, which constitutes a substantial energy drive for far scrape-off layer turbulence and is a more suitable quantity to study blob generation compared to the skewness.
Evolution of ion-acoustic plasma turbulence
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.
1986-03-01
The evolution of ion-acoustic turbulence is studied on the basis of a numerical solution of the nonstationary equation for in-acoustic waves. Consideration is given to conditions under which the excitation threshold of long-wave ion-acoustic oscillations is exceeded as the result of instability saturation due to quasi-linear relaxation of electrons on turbulent pulsations and the induced scattering of ions by the ion sound. Distributed spectra of ion-acoustic turbulence are established in the plasma under these conditions.
X-Ray Emission in the Heliosphere: Ion-Neutral Collisions as a Plasma Diagnostic
NASA Astrophysics Data System (ADS)
Cravens, Tom; Sibeck, David; Collier, MIchael
2015-04-01
The solar corona is the most powerful source of x-rays in the solar system but x-ray emission has also been observed from planets, including the Earth and Jupiter, from the Moon, from comets, and from interstellar gas entering the heliosphere. Astrophysical x-ray emission primarily comes from hot plasmas, such as in the million degree solar corona. The gas and plasma in planetary atmospheres are rather cold and the x-ray emission is driven by solar radiation and/or the solar wind. For example, x-rays from Venus come from the scattering and K-shell fluorescence of solar x-rays from the neutral atmosphere. Auroral x-ray emission at Earth and Jupiter is produced by energetic electron and ion precipitation from the magnetospheres into the atmospheres. Cometary and heliospheric x-ray emission is caused by charge transfer of high charge state solar wind ions (e.g., O7+, C6+,…) with neutral hydrogen and helium.An important source of solar system x-rays is the solar wind charge exchange (SWCX) mechanism. The solar wind originates in the hot solar corona and species heavier than helium (comprising about 0.1% of the gas) are highly-charged (e.g., O7+, C6+, Fe12+,….). Such ions undergo charge transfer collisions when they encounter neutral gas (e.g., cometary or interstellar gas or the Earth’s geocoronal hydrogen). The product ions are in highly-excited states and, subsequently, emit soft x-ray photons. The SWCX mechanism can explain the observed cometary x-ray emission and can also explain part of the soft x-ray background (the other part of which originates in the hot interstellar medium).The Earth has an extensive hot hydrogen exosphere, or geocorona, that is visible in scattered solar Lyman alpha. X-ray emission is produced in the magnetosheath due to the SWCX mechanism as the solar wind interacts with the exospheric gas. The most intense x-ray emission comes from the subsolar sheath region and from the cusp regions. Imaging of this emission by a spacecraft located
Plasma surrounding the global heliosphere at large distances controlled by the solar cycle
NASA Astrophysics Data System (ADS)
Dialynas, Konstantinos; Krimigis, Stamatios; Mitchell, Donald; Decker, Robert; Roelof, Edmond
2016-04-01
The past decade can be characterized by a series of key, groundbreaking remote energetic neutral atom (ENA) images (INCA, IBEX) and in-situ ion (Voyager 1 & 2) observations concerning the characteristics and interactions of the heliosphere with the Local Interstellar Medium (LISM). Voyagers 1 and 2 (V1, V2) discovered the reservoir of ions and electrons that constitute the heliosheath (HS) after crossing the termination shock (TS) 35deg north and 32deg south of the ecliptic plane at 94 and 84 astronomical units (1 AU= 1.5 x108 km), respectively. The in situ measurements by each Voyager were placed in a global context by remote sensing images using ENA obtained with the Ion and Neutral Camera (INCA) onboard Cassini orbiting Saturn. The ENA images contain a 5.2-55 keV hydrogen (H) ENA region (Belt) that loops through the celestial sphere and contributes to balancing the pressure of the interstellar magnetic field (ISMF). The success of any future mission with dedicated ENA detectors (e.g. the IMAP mission), highly depends on the antecedent understanding of the details of the plasma processes in the Heliosphere as revealed by remote sensing of the plasma environment characteristics. Therefore, we address here one of the remaining and most important questions: "Where do the 5-55 keV ENAs that INCA measures come from?". We analyzed INCA all-sky maps from 2003 to 2015 and compare the solar cycle (SC) variation of the ENAs in both the nose (upstream) and anti-nose (downstream) directions with the intensities of > 30 keV ions (source of ENA through charge exchange-CE with H) measured in-situ by V1 and V2, in overlapping energy bands ~30-55 keV. ENA intensities decrease during the declining phase of SC23 by ~x3 from 2003 to 2011 but recover through 2014 (SC24); similarly, V1 and V2 ion intensities also decrease and then recover through 2014. The similarity of time profiles of remotely sensed ENA and locally measured ions are consistent with (a) ENA originating in the HS
Magnetic Turbulence in colliding laser produced plasmas
NASA Astrophysics Data System (ADS)
Gekelman, Walter; Collette, Andrew
2006-10-01
We describe a series of experiments, which involve the collision of two dense (initially, δnlpp/n0>>1) laser-produced plasmas (llp) within an ambient, highly magnetized (Rci
Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations
NASA Astrophysics Data System (ADS)
Klein, K. G.; Howes, G. G.
2016-08-01
An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.
NASA Technical Reports Server (NTRS)
Hsieh, K. C.; Curtis, C. C.; Fan, C. Y.; Gruntman, M. A.
1992-01-01
A survey is conducted for state-of-the-art techniques for detecting energetic neutral atoms (ENAs) in the 100-300 keV range, in regions from the heliospheric boundary to the auroral zones where the solar wind plays a crucial role. While ENA spectrometry allows sampling of the mass and energy distributions of a distant plasma, ENA imaging gives a global view of the structures and dynamics of an extended plasma. The ENA instrument designs discussed share many components which exhibit excellent flight performance as elements in charged-particle analyzers for space missions.
Global simulations of plasma turbulence in laboratory plasmas
NASA Astrophysics Data System (ADS)
Ricci, P.; Fasoli, A.; Furno, I.; Jolliet, S.; Loizu, J.; Mosetto, A.; Rogers, B. N.; Theiler, C.
2012-04-01
The Global Braginskii Solver (GBS) code has been developed in the last few years to simulate plasma turbulence in laboratory plasmas [1]. By solving the drift-reduced Braginkii equation in magnetic configurations of increasing complexity, from linear devices to the Simple Magnetized Toroidal (SMT) configuration, GBS performs non-linear self-consistent global three-dimensional simulations of the plasma dynamics, as the result of the interplay among the plasma source, the turbulent transport, and the plasma losses at the vessel. This gradual approach has allowed gaining a deep understanding of the turbulence dynamics, by identifying the instabilities responsible for driving plasma turbulence and to estimate the turbulence saturation amplitude. In particular, simulation results have pointed out the need of global simulations to correctly represent the dynamics of laboratory plasmas, as well as the importance of not separating fluctuations and equilibrium quantities. A code validation development project has been conducted side by side with the GBS development [2]. Such validation project has lead to the establishment of a rigorous methodology to carry out experiment-simulation comparison, and has allowed quantifying precisely the level of agreement between the GBS results and the experimental data from the TORPEX experiment at CRPP. [1] P. Ricci, B.N. Rogers, S. Brunner, Phys. Rev. Lett. 100, 225002 (2008); P. Ricci and B. N. Rogers, Phys. Rev. Lett. 104, 145001 (2010); B. N. Rogers and P. Ricci, Phys. Rev. Lett. 104, 225002 (2010); B. Li et al., Phys. Rev. E 83, 056406 (2011). [2] P. Ricci et al, Phys. Plasmas 16, 055703 (2009); P. Ricci et al., Phys. Plasmas 18, 032109 (2011).
NASA Astrophysics Data System (ADS)
Bhattacharjee, A.; Huang, Y. M.
2015-12-01
It has been established that the Sweet-Parker current layer in high Lundquist number reconnection is unstable to the super-Alfvénic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime where the Sweet-Parker current layer changes into a chain of plasmoids connected by secondary current sheets, and the averaged reconnection rate becomes nearly independent of the Lundquist number. In this work, three-dimensional simulations with a guide field shows that the additional degree of freedom allows plasmoid instabilities to grow at oblique angles. We present a scenario in which large-scale oblique tearing modes overlap with each other, break flux surfaces, and stir up a spectrum of smaller-scale tearing modes, leading eventually to self-generated turbulent reconnection. The averaged reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfvén speed, which is similar to the two-dimensional result but is an order of magnitude lower than the fastest reconnection rate reported in recent studies of externally driven three-dimensional turbulent reconnection. Kinematic and magnetic energy fluctuations both form elongated eddies along the direction of local magnetic field, which is a signature of anisotropic magnetohydrodynamic turbulence. Both energy fluctuations satisfy power-law spectra in the inertial range. The anisotropy of turbulence eddies is found to be nearly scale-independent, in contrast with the prediction of the Goldreich-Sridhar (GS) theory for anisotropic turbulence in a homogeneous plasma permeated by a uniform magnetic field. The effect of varying the magnitude of the toroidal field on the critical balance condition underlying the GS theory is discussed.
Complexity and Intermittent Turbulence in Space Plasmas
NASA Technical Reports Server (NTRS)
Chang, Tom; Tam, Sunny W. Y.; Wu, Cheng-Chin
2004-01-01
Sporadic and localized interactions of coherent structures arising from plasma resonances can be the origin of "complexity" of the coexistence of non- propagating spatiotemporal fluctuations and propagating modes in space plasmas. Numerical simulation results are presented to demonstrate the intermittent character of the non-propagating fluctuations. The technique of the dynamic renormalization-group is introduced and applied to the study of scale invariance of such type of multiscale fluctuations. We also demonstrate that the particle interactions with the intermittent turbulence can lead to the efficient energization of the plasma populations. An example related to the ion acceleration processes in the auroral zone is provided.
Magnetic field amplification in turbulent astrophysical plasmas
NASA Astrophysics Data System (ADS)
Federrath, Christoph
2016-12-01
Magnetic fields play an important role in astrophysical accretion discs and in the interstellar and intergalactic medium. They drive jets, suppress fragmentation in star-forming clouds and can have a significant impact on the accretion rate of stars. However, the exact amplification mechanisms of cosmic magnetic fields remain relatively poorly understood. Here, I start by reviewing recent advances in the numerical and theoretical modelling of the turbulent dynamo, which may explain the origin of galactic and intergalactic magnetic fields. While dynamo action was previously investigated in great detail for incompressible plasmas, I here place particular emphasis on highly compressible astrophysical plasmas, which are characterised by strong density fluctuations and shocks, such as the interstellar medium. I find that dynamo action works not only in subsonic plasmas, but also in highly supersonic, compressible plasmas, as well as for low and high magnetic Prandtl numbers. I further present new numerical simulations from which I determine the growth of the turbulent (un-ordered) magnetic field component ( turb$ ) in the presence of weak and strong guide fields ( 0$ ). I vary 0$ over five orders of magnitude and find that the dependence of turb$ on 0$ is relatively weak, and can be explained with a simple theoretical model in which the turbulence provides the energy to amplify turb$ . Finally, I discuss some important implications of magnetic fields for the structure of accretion discs, the launching of jets and the star-formation rate of interstellar clouds.
Turbulent dynamo in a collisionless plasma
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-01-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981
Turbulent dynamo in a collisionless plasma
NASA Astrophysics Data System (ADS)
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-04-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
Mixing of the Interstellar and Solar Plasmas at the Heliospheric Interface
Pogorelov, N. V.; Borovikov, S. N.
2015-10-12
From the ideal MHD perspective, the heliopause is a tangential discontinuity that separates the solar wind plasma from the local interstellar medium plasma. There are physical processes, however, that make the heliopause permeable. They can be subdivided into kinetic and MHD categories. Kinetic processes occur on small length and time scales, and cannot be resolved with MHD equations. On the other hand, MHD instabilities of the heliopause have much larger scales and can be easily observed by spacecraft. The heliopause may also be a subject of magnetic reconnection. In this paper, we discuss mechanisms of plasma mixing at the heliopause in the context of Voyager 1 observations. Numerical results are obtained with a Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is a package of numerical codes capable of performing adaptive mesh refinement simulations of complex plasma flows in the presence of discontinuities and charge exchange between ions and neutral atoms. The flow of the ionized component is described with the ideal MHD equations, while the transport of atoms is governed either by the Boltzmann equation or multiple Euler gas dynamics equations. The code can also treat nonthermal ions and turbulence produced by them.
Mixing of the Interstellar and Solar Plasmas at the Heliospheric Interface
Pogorelov, N. V.; Borovikov, S. N.
2015-10-12
From the ideal MHD perspective, the heliopause is a tangential discontinuity that separates the solar wind plasma from the local interstellar medium plasma. There are physical processes, however, that make the heliopause permeable. They can be subdivided into kinetic and MHD categories. Kinetic processes occur on small length and time scales, and cannot be resolved with MHD equations. On the other hand, MHD instabilities of the heliopause have much larger scales and can be easily observed by spacecraft. The heliopause may also be a subject of magnetic reconnection. In this paper, we discuss mechanisms of plasma mixing at the heliopausemore » in the context of Voyager 1 observations. Numerical results are obtained with a Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is a package of numerical codes capable of performing adaptive mesh refinement simulations of complex plasma flows in the presence of discontinuities and charge exchange between ions and neutral atoms. The flow of the ionized component is described with the ideal MHD equations, while the transport of atoms is governed either by the Boltzmann equation or multiple Euler gas dynamics equations. The code can also treat nonthermal ions and turbulence produced by them.« less
Generation of quasistationary magnetic fields in a turbulent laser plasma
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.; Chokparova, G. A.
1984-07-01
A theory is derived for the generation of quasi-stationary magnetic fields in a laser plasma with well developed ion-acoustic turbulence. Qualitative changes are caused in the nature of the magnetic-field generation by an anomalous anisotropic transport in the turbulent plasma. The role played by turbulent diffusion and thermodiffusive transport in the magnetic-field saturation is discussed.
PLASMA EMISSION BY WEAK TURBULENCE PROCESSES
Ziebell, L. F.; Gaelzer, R.; Yoon, P. H.; Pavan, J. E-mail: rudi.gaelzer@ufrgs.br E-mail: joel.pavan@ufpel.edu.br
2014-11-10
The plasma emission is the radiation mechanism responsible for solar type II and type III radio bursts. The first theory of plasma emission was put forth in the 1950s, but the rigorous demonstration of the process based upon first principles had been lacking. The present Letter reports the first complete numerical solution of electromagnetic weak turbulence equations. It is shown that the fundamental emission is dominant and unless the beam speed is substantially higher than the electron thermal speed, the harmonic emission is not likely to be generated. The present findings may be useful for validating reduced models and for interpreting particle-in-cell simulations.
Multifractality in plasma edge electrostatic turbulence
NASA Astrophysics Data System (ADS)
Neto, C. Rodrigues; Guimarães-Filho, Z. O.; Caldas, I. L.; Nascimento, I. C.; Kuznetsov, Yu. K.
2008-08-01
Plasma edge turbulence in Tokamak Chauffage Alfvén Brésilien (TCABR) [R. M. O. Galvão et al., Plasma Phys. Contr. Fusion 43, 1181 (2001)] is investigated for multifractal properties of the fluctuating floating electrostatic potential measured by Langmuir probes. The multifractality in this signal is characterized by the full multifractal spectra determined by applying the wavelet transform modulus maxima. In this work, the dependence of the multifractal spectrum with the radial position is presented. The multifractality degree inside the plasma increases with the radial position reaching a maximum near the plasma edge and becoming almost constant in the scrape-off layer. Comparisons between these results with those obtained for random test time series with the same Hurst exponents and data length statistically confirm the reported multifractal behavior. Moreover, the persistence of these signals, characterized by their Hurst exponent, present radial profile similar to the deterministic component estimated from analysis based on dynamical recurrences.
Transport Bifurcation in Plasma Interchange Turbulence
NASA Astrophysics Data System (ADS)
Li, Bo
2016-10-01
Transport bifurcation and mean shear flow generation in plasma interchange turbulence are explored with self-consistent two-fluid simulations in a flux-driven system with both closed and open field line regions. The nonlinear evolution of interchange modes shows the presence of two confinement regimes characterized by the low and high mean flow shear. By increasing the input heat flux above a certain threshold, large-amplitude oscillations in the turbulent and mean flow energy are induced. Both clockwise and counter-clockwise types of oscillations are found before the transition to the second regime. The fluctuation energy is decisively transferred to the mean flows by large-amplitude Reynolds power as turbulent intensity increases. Consequently, a transition to the second regime occurs, in which strong mean shear flows are generated in the plasma edge. The peak of the spectrum shifts to higher wavenumbers as the large-scale turbulent eddies are suppressed by the mean shear flow. The transition back to the first regime is then triggered by decreasing the input heat flux to a level much lower than the threshold for the forward transition, showing strong hysteresis. During the back transition, the mean flow decreases as the energy transfer process is reversed. This transport bifurcation, based on a field-line-averaged 2D model, has also been reproduced in our recent 3D simulations of resistive interchange turbulence, in which the ion and electron temperatures are separated and the parallel current is involved. Supported by the MOST of China Grant No. 2013GB112006, US DOE Contract No. DE-FC02-08ER54966, US DOE by LLNL under Contract DE-AC52-07NA2734.
New Thermodynamical Force in Plasma Phase Space that Controls Turbulence and Turbulent Transport
Itoh, Sanae-I.; Itoh, Kimitaka
2012-01-01
Physics of turbulence and turbulent transport has been developed on the central dogma that spatial gradients constitute the controlling parameters, such as Reynolds number and Rayleigh number. Recent experiments with the nonequilibrium plasmas in magnetic confinement devices, however, have shown that the turbulence and transport change much faster than global parameters, after an abrupt change of heating power. Here we propose a theory of turbulence in inhomogeneous magnetized plasmas, showing that the heating power directly influences the turbulence. New mechanism, that an external source couples with plasma fluctuations in phase space so as to affect turbulence, is investigated. A new thermodynamical force in phase-space, i.e., the derivative of heating power by plasma pressure, plays the role of new control parameter, in addition to spatial gradients. Following the change of turbulence, turbulent transport is modified accordingly. The condition under which this new effect can be observed is also evaluated. PMID:23155481
Weak Turbulence Effects in Space Plasmas
NASA Astrophysics Data System (ADS)
Crabtree, Chris
2012-10-01
With the advent of multi-satellite missions such as Cluster and the Radiation Belt Storm Probes (RBSP) space plasmas have become a rich laboratory for the detailed and fundamental study of plasma turbulence. Space offers a diversity of plasma environments to directly test theory and simulation, from high-β plasmas in the solar-wind and the Earth's magnetotail, to low-β multi-species plasmas in the radiation belts and ionosphere. Recent theoretical work has demonstrated that by considering the effects of induced non-linear scattering (non-linear Landau damping, to be referred to as NL scattering) of electromagnetic waves leads to testable predictions in both storm-time radiation belt plasmas and the solar wind turbulent spectrum at scales below the ion gyroradius. In the radiation belts, VLF waves (with frequencies between the ion and electron gyrofrequencies) of sufficient amplitude may be nonlinearly scattered near the lower-hybrid surface inside the plasmasphere. Upon scattering a portion of these waves can return to the ionosphere where they may be reflected. This process can lead to the formation of a VLF wave cavity [1] that can efficiently resonate with the energetic (MeV) trapped electron population and quickly precipitate these particles into the ionosphere [2]. In the solar wind, the large-scale Alfvenic fluctuations can be shown to lead to a plateau in the electron distribution function that reduces the Landau damping of kinetic Alfven waves (KaWs). With the reduction of the linear damping the NL scattering of KAWs becomes important and leads to a non-local redistribution of energy in k-space and results in a steeper turbulent spectrum [3]. The edges of the plateaus are also unstable to electromagnetic left hand polarized ion cyclotron-Alfven waves as well as right hand polarized magnetosonic-whistler waves. These waves can pitch angle scatter the ion super-thermal velocity component to provide perpendicular ion heating [4]. [4pt] [1] C. Crabtree, L
Plasma Turbulence in the Local Bubble
NASA Astrophysics Data System (ADS)
Spangler, Steven R.
Turbulence in the Local Bubble could play an important role in the thermodynamics of the gas that is there. This turbulence could also determine the transport of cosmic rays and perhaps heat flow through this phase of the interstellar medium. The best astronomical technique for measuring turbulence in astrophysical plasmas is radio scintillation. Scintillation measurements yield information on the intensity and spectral characteristics of plasma turbulence between the source of the radio waves and the observer. Measurements of the level of scattering to the nearby pulsar B0950+08 by Philips and Clegg in 1992 showed a markedly lower value for the line-of-sight averaged turbulent intensity parameter
Plasma Turbulence in the Local Bubble
NASA Astrophysics Data System (ADS)
Spangler, Steven R.
2009-03-01
Turbulence in the Local Bubble could play an important role in the thermodynamics of the gas that is there. This turbulence could also determine the transport of cosmic rays and perhaps heat flow through this phase of the interstellar medium. The best astronomical technique for measuring turbulence in astrophysical plasmas is radio scintillation. Scintillation measurements yield information on the intensity and spectral characteristics of plasma turbulence between the source of the radio waves and the observer. Measurements of the level of scattering to the nearby pulsar B0950+08 by Philips and Clegg in 1992 showed a markedly lower value for the line-of-sight averaged turbulent intensity parameter < C {/N 2}> than is observed for other pulsars, qualitatively consistent with radio wave propagation through a highly rarefied plasma. In this paper, we discuss the observational progress that has been made since that time. The main development has been improved measurements of pulsar parallaxes with the Very Long Baseline Array. This provides better knowledge of the media along the lines of sight. At present, there are four pulsars (B0950+08, B1133+16, J0437-4715, and B0809+74) whose lines of sight seem to lie mainly within the local bubble. The mean densities and line of sight components of the interstellar magnetic field along these lines of sight are smaller than nominal values for pulsars, but not by as large a factor as might be expected. Three of the four pulsars also have measurements of interstellar scintillation. The value of the parameter < C {/N 2}> is smaller than normal for two of them, but is completely nominal for the third. This inconclusive status of affairs could be improved by measurements and analysis of “arcs” in “secondary spectra” of pulsars, which contain information on the location and intensity of localized screens of turbulence along the lines of sight. Similar data could be obtained from observations of highly compact extragalactic
Turbulent particle transport in magnetized fusion plasma
NASA Astrophysics Data System (ADS)
Bourdelle, C.
2005-05-01
Understanding the mechanisms responsible for particle transport is of the utmost importance for magnetized fusion plasmas. A peaked density profile is attractive to improve the fusion rate, which is proportional to the square of the density, and to self-generate a large fraction of non-inductive current required for continuous operation. Experiments in various tokamak devices (ASDEX Upgrade, DIII-D, JET, TCV, TEXT, TFTR) indicate the existence of a turbulent particle pinch. Recently, such a turbulent pinch has been unambiguously identified in Tore Supra very long discharges, in the absence of both collisional particle pinch and central particle source, for more than 4 min (Hoang et al 2003 Phys. Rev. Lett. 90 155002). This turbulent pinch is predicted by a quasilinear theory of particle transport (Weiland J et al 1989 Nucl. Fusion 29 1810), and confirmed by non-linear turbulence simulations (Garbet et al 2003 Phys. Rev. Lett. 91 035001) and general considerations based on the conservation of motion invariants (Baker et al 2004 Phys. Plasmas 11 992). Experimentally, the particle pinch is found to be sensitive to the magnetic field gradient in many cases (Hoang et al 2004 Phys. Rev. Lett. 93 135003, Zabolotsky et al 2003 Plasma Phys. Control. Fusion 45 735, Weisen et al 2004 Plasma Phys. Control. Fusion 46 751, Baker et al 2000 Nucl. Fusion 40 1003), to the temperature profile (Hoang et al 2004 Phys. Rev. Lett. 93 135003, Angioni et al 2004 Nucl. Fusion 44 827) and also to the collisionality that changes the nature of the microturbulence (Angioni et al 2003 Phys. Rev. Lett. 90 205003, Garzotti et al 2003 Nucl. Fusion 43 1829, Weisen et al 2004 31st EPS Conf. on Plasma Phys. (London) vol 28G (ECA) P-1.146, Lopes Cardozo N J 1995 Plasma Phys. Control. Fusion 37 799). The consistency of some of the observed dependences with the theoretical predictions gives us a clearer understanding of the particle pinch in tokamaks, allowing us to predict more accurately the density
NASA Astrophysics Data System (ADS)
Baranov, Vladimir
Under physical conditions of cosmic plasma the cyclotron frequency of electrons is almost always much greater than the frequency of their collisions. In particular, this inequality is fulfilled in the heliospheric interface. In this case the effect of magnetic field gives rise to the anisotropy of transport coefficients (viscosity, thermal-and electro-conductivities). It is shown in our presentation, that the most important dissipative process in the heliospheric interface is thermal conduction along the magnetic field lines because the Peclet number determining this process is quite small. It means that its effect has to be definitely taken into account in the energy equation at theoretical modelling. Hall currents, which arise due to the electro-conductivity anisotropy, determine the dispersion processes. The effect of Hall currents on the principle of the freezing-in magnetic field and on a wave propagation is discussed. In particular, it is shown that the interplanetary magnetic field can penetrate through the heliopause into the interstellar plasma even if it is the tangential discontinuity. The value of this penetration is estimated.
Weak turbulence theory for collisional plasmas
NASA Astrophysics Data System (ADS)
Yoon, P. H.; Ziebell, L. F.; Kontar, E. P.; Schlickeiser, R.
2016-03-01
Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.
Weak turbulence theory for collisional plasmas.
Yoon, P H; Ziebell, L F; Kontar, E P; Schlickeiser, R
2016-03-01
Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.
Visualization of plasma turbulence with laser-induced fluorescence (invited)
Levinton, Fred M.; Trintchouk, Fedor
2001-01-01
Turbulence is a key factor limiting the performance of fusion devices. Plasma edge turbulence determines the boundary values of the plasma density and temperature, which in turn determine the internal gradients and controls global plasma transport. In recent years, significant progress has been made in modeling turbulence behavior in plasmas and its effect on transport. Progress has also been made in diagnostics for turbulence measurement; however, there is still a large gap in our understanding of it. An approach to improve this situation is to experimentally visualize the turbulence, that is, a high resolution 2-D image of the plasma density. Visualization of turbulence can improve the connection to theory and help validate theoretical models. One method that has been successfully developed to visualize turbulence in gases and fluids is planar laser-induced fluorescence. We have recently applied this technique to visualize turbulence and structures in a plasma. This was accomplished using an Alexandrite laser that is tunable between 700 and 800 nm, and from 350 to 400 nm with second harmonic generation. The fluorescence light from an argon ion transition has been imaged onto an intensified charged coupled device camera that is gated in synchronization with the laser. Images from the plasma show a rotating structure at 30 kHz in addition to small scale turbulence.
The transport anisotropy effect in a turbulent plasma
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.; Silin, V. P.
1982-12-01
The theory of transport phenomena in a plasma with developed ion-acoustic turbulence is formulated. The transport anisotropy effect, caused by a temperature gradient, is observed. The corresponding fluxes across the effective force vector which generates the turbulence are substantially larger than longitudinal fluxes in a plasma with a comparatively low degree of nonisothermality. In a strongly nonisothermal plasma, the suppression of transverse fluxes occurs, corresponding to an increase in the thermal insulation of current-carrying plasma columns.
Validation metrics for turbulent plasma transport
NASA Astrophysics Data System (ADS)
Holland, C.
2016-06-01
Developing accurate models of plasma dynamics is essential for confident predictive modeling of current and future fusion devices. In modern computer science and engineering, formal verification and validation processes are used to assess model accuracy and establish confidence in the predictive capabilities of a given model. This paper provides an overview of the key guiding principles and best practices for the development of validation metrics, illustrated using examples from investigations of turbulent transport in magnetically confined plasmas. Particular emphasis is given to the importance of uncertainty quantification and its inclusion within the metrics, and the need for utilizing synthetic diagnostics to enable quantitatively meaningful comparisons between simulation and experiment. As a starting point, the structure of commonly used global transport model metrics and their limitations is reviewed. An alternate approach is then presented, which focuses upon comparisons of predicted local fluxes, fluctuations, and equilibrium gradients against observation. The utility of metrics based upon these comparisons is demonstrated by applying them to gyrokinetic predictions of turbulent transport in a variety of discharges performed on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], as part of a multi-year transport model validation activity.
Measuring plasma turbulence using low coherence microwave radiation
Smith, D. R.
2012-02-20
Low coherence backscattering (LCBS) is a proposed diagnostic technique for measuring plasma turbulence and fluctuations. LCBS is an adaptation of optical coherence tomography, a biomedical imaging technique. Calculations and simulations show LCBS measurements can achieve centimeter-scale spatial resolution using low coherence microwave radiation. LCBS measurements exhibit several advantages over standard plasma turbulence measurement techniques including immunity to spurious reflections and measurement access in hollow density profiles. Also, LCBS is scalable for 1-D profile measurements and 2-D turbulence imaging.
The heliosphere is a bubble that surrounds our entire solar system and is inflated by the outward solar wind, which pushes out and deflects the material from the part of the galactic medium through...
Interplanetary conditions during 3-kHz radio-wave detections in the outer heliosphere
NASA Technical Reports Server (NTRS)
Lanzerotti, L. J.; Maclennan, C. G.; Gold, R. E.
1985-01-01
Plasma waves detected by the Voyager 1 and 2 spacecraft beyond about 12 AU that may be associated with the turbulence expected at the heliopause are interpreted in terms of the characteristics of the interplanetary medium at large heliocentric distances. The low-energy charged-particle environment in the outer heliosphere during the observations of the unusual plasma-wave signals is addressed. The particle data suggest that the outer heliosphere was unusually stable and free of transient shock and particle events for the roughly eight months during the wave observations.
MULTIFRACTAL STRUCTURES DETECTED BY VOYAGER 1 AT THE HELIOSPHERIC BOUNDARIES
Macek, W. M.; Burlaga, L. F. E-mail: anna.wawrzaszek@cbk.waw.pl
2014-10-01
To better understand the dynamics of turbulent systems, we have proposed a phenomenological model based on a generalized Cantor set with two rescaling and one weight parameters. In this Letter, using recent Voyager 1 magnetic field data, we extend our two-scale multifractal analysis further in the heliosheath beyond the heliospheric termination shock, and even now near the heliopause, when entering the interstellar medium for the first time in human history. We have identified the scaling inertial region for magnetized heliospheric plasma between the termination shock and the heliopause. We also show that the degree of multifractality decreases with the heliocentric distance and is still modulated by the phases of the solar cycle in the entire heliosphere including the heliosheath. Moreover, we observe the change of scaling toward a nonintermittent (nonmultifractal) behavior in the nearby interstellar medium, just beyond the heliopause. We argue that this loss of multifractal behavior could be a signature of the expected crossing of the heliopause by Voyager 2 in the near future. The results obtained demonstrate that our phenomenological multifractal model exhibits some properties of intermittent turbulence in the solar system plasmas, and we hope that it could shed light on universal characteristics of turbulence.
A Concept of Cross-Ferroic Plasma Turbulence
Inagaki, S.; Kobayashi, T.; Kosuga, Y.; Itoh, S.-I.; Mitsuzono, T.; Nagashima, Y.; Arakawa, H.; Yamada, T.; Miwa, Y.; Kasuya, N.; Sasaki, M.; Lesur, M.; Fujisawa, A.; Itoh, K.
2016-01-01
The variety of scalar and vector fields in laboratory and nature plasmas is formed by plasma turbulence. Drift-wave fluctuations, driven by density gradients in magnetized plasmas, are known to relax the density gradient while they can generate flows. On the other hand, the sheared flow in the direction of magnetic fields causes Kelvin-Helmholtz type instabilities, which mix particle and momentum. These different types of fluctuations coexist in laboratory and nature, so that the multiple mechanisms for structural formation exist in extremely non-equilibrium plasmas. Here we report the discovery of a new order in plasma turbulence, in which chained structure formation is realized by cross-interaction between inhomogeneities of scalar and vector fields. The concept of cross-ferroic turbulence is developed, and the causal relation in the multiple mechanisms behind structural formation is identified, by measuring the relaxation rate and dissipation power caused by the complex turbulence-driven flux. PMID:26917218
Mass dependency of turbulent parameters in stationary glow discharge plasmas
Titus, J. B.; Alexander, A. B.; Wiggins, D. L.; Johnson, J. A. III
2013-05-15
A direct current glow discharge tube is used to determine how mass changes the effects of certain turbulence characteristics in a weakly ionized gas. Helium, neon, argon, and krypton plasmas were created, and an axial magnetic field, varied from 0.0 to 550.0 Gauss, was used to enhance mass dependent properties of turbulence. From the power spectra of light emission variations associated with velocity fluctuations, determination of mass dependency on turbulent characteristic unstable modes, energy associated with turbulence, and the rate at which energy is transferred from scale to scale are measured. The magnetic field strength is found to be too weak to overcome particle diffusion to the walls to affect the turbulence in all four types of plasmas, though mass dependency is still detected. Though the total energy and the rate at which the energy moves between scales are mass invariant, the amplitude of the instability modes that characterize each plasma are dependent on mass.
Comparing simulation of plasma turbulence with experiment
NASA Astrophysics Data System (ADS)
Ross, David W.; Bravenec, Ronald V.; Dorland, William; Beer, Michael A.; Hammett, G. W.; McKee, George R.; Fonck, Raymond J.; Murakami, Masanori; Burrell, Keith H.; Jackson, Gary L.; Staebler, Gary M.
2002-01-01
The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement.
A dynamical model of plasma turbulence in the solar wind
Howes, G. G.
2015-01-01
A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic plasma turbulence. It is argued that the linear and nonlinear dynamics of Alfvén waves are responsible, at a very fundamental level, for some of the key qualitative features of plasma turbulence that distinguish it from hydrodynamic turbulence, including the anisotropic cascade of energy and the development of current sheets at small scales. The first dynamical model of kinetic turbulence in the weakly collisional solar wind plasma that combines self-consistently the physics of Alfvén waves with the development of small-scale current sheets is presented and its physical implications are discussed. This model leads to a simplified perspective on the nature of turbulence in a weakly collisional plasma: the nonlinear interactions responsible for the turbulent cascade of energy and the formation of current sheets are essentially fluid in nature, while the collisionless damping of the turbulent fluctuations and the energy injection by kinetic instabilities are essentially kinetic in nature. PMID:25848075
A dynamical model of plasma turbulence in the solar wind.
Howes, G G
2015-05-13
A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic plasma turbulence. It is argued that the linear and nonlinear dynamics of Alfvén waves are responsible, at a very fundamental level, for some of the key qualitative features of plasma turbulence that distinguish it from hydrodynamic turbulence, including the anisotropic cascade of energy and the development of current sheets at small scales. The first dynamical model of kinetic turbulence in the weakly collisional solar wind plasma that combines self-consistently the physics of Alfvén waves with the development of small-scale current sheets is presented and its physical implications are discussed. This model leads to a simplified perspective on the nature of turbulence in a weakly collisional plasma: the nonlinear interactions responsible for the turbulent cascade of energy and the formation of current sheets are essentially fluid in nature, while the collisionless damping of the turbulent fluctuations and the energy injection by kinetic instabilities are essentially kinetic in nature.
Nondiffusive transport regimes for suprathermal ions in turbulent plasmas.
Bovet, A; Fasoli, A; Ricci, P; Furno, I; Gustafson, K
2015-04-01
The understanding of the transport of suprathermal ions in the presence of turbulence is important for fusion plasmas in the burning regime that will characterize reactors, and for space plasmas to understand the physics of particle acceleration. Here, three-dimensional measurements of a suprathermal ion beam in the toroidal plasma device TORPEX are presented. These measurements demonstrate, in a turbulent plasma, the existence of subdiffusive and superdiffusive transport of suprathermal ions, depending on their energy. This result stems from the unprecedented combination of uniquely resolved measurements and first-principles numerical simulations that reveal the mechanisms responsible for the nondiffusive transport. The transport regime is determined by the interaction of the suprathermal ion orbits with the turbulent plasma dynamics, and is strongly affected by the ratio of the suprathermal ion energy to the background plasma temperature.
A soliton gas model for astrophysical magnetized plasma turbulence
NASA Astrophysics Data System (ADS)
Spangler, S. R.; Sheerin, J. P.
1982-06-01
Plasma turbulence is considered as an ensemble of solitons. The derivation of the Alfven soliton by Spangler and Sheering (1981) is reviewed, and expressions are derived for the magnetic irregularity spectrum and the relationship between the magnetic and density irregularity power spectra. A derived expression also provides the answer to the question of the correlation between magnetic field and density enhancements. The properties of the turbulence model are compared with observations of plasma turbulence in the solar wind, and are found to reasonably account for them.
Turbulence studies in Tokamak boundary plasmas with realistic divertor geometry
Xu, X.Q.
1998-10-14
Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT [1] and the linearized shooting code BAL[2] to study turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant, resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the ExB drift speed, ion diamagnetism and finite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters.
The energetic coupling of scales in gyrokinetic plasma turbulence
NASA Astrophysics Data System (ADS)
Teaca, Bogdan; Navarro, Alejandro Bañón; Jenko, Frank
2014-07-01
In magnetized plasma turbulence, the couplings of perpendicular spatial scales that arise due to the nonlinear interactions are analyzed from the perspective of the free-energy exchanges. The plasmas considered here, with appropriate ion or electron adiabatic electro-neutrality responses, are described by the gyrokinetic formalism in a toroidal magnetic geometry. Turbulence develops due to the electrostatic fluctuations driven by temperature gradient instabilities, either ion temperature gradient (ITG) or electron temperature gradient (ETG). The analysis consists in decomposing the system into a series of scale structures, while accounting separately for contributions made by modes possessing special symmetries (e.g., the zonal flow modes). The interaction of these scales is analyzed using the energy transfer functions, including a forward and backward decomposition, scale fluxes, and locality functions. The comparison between the ITG and ETG cases shows that ETG turbulence has a more pronounced classical turbulent behavior, exhibiting a stronger energy cascade, with implications for gyrokinetic turbulence modeling.
The energetic coupling of scales in gyrokinetic plasma turbulence
Teaca, Bogdan; Jenko, Frank
2014-07-15
In magnetized plasma turbulence, the couplings of perpendicular spatial scales that arise due to the nonlinear interactions are analyzed from the perspective of the free-energy exchanges. The plasmas considered here, with appropriate ion or electron adiabatic electro-neutrality responses, are described by the gyrokinetic formalism in a toroidal magnetic geometry. Turbulence develops due to the electrostatic fluctuations driven by temperature gradient instabilities, either ion temperature gradient (ITG) or electron temperature gradient (ETG). The analysis consists in decomposing the system into a series of scale structures, while accounting separately for contributions made by modes possessing special symmetries (e.g., the zonal flow modes). The interaction of these scales is analyzed using the energy transfer functions, including a forward and backward decomposition, scale fluxes, and locality functions. The comparison between the ITG and ETG cases shows that ETG turbulence has a more pronounced classical turbulent behavior, exhibiting a stronger energy cascade, with implications for gyrokinetic turbulence modeling.
Toward the Theory of Turbulence in Magnetized Plasmas
Boldyrev, Stanislav
2013-07-26
The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a “condensate”, that is, concentration of magnetic and kinetic energy at small k{sub {parallel}}. A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model.
A weakened cascade model for turbulence in astrophysical plasmas
Howes, G. G.; TenBarge, J. M.; Dorland, W.
2011-10-15
A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong turbulence and the effect of nonlocal interactions on the nonlinear transfer of energy. The model describes the transition between weak and strong MHD turbulence and the complementary transition from strong kinetic Alfven wave (KAW) turbulence to weak dissipating KAW turbulence, a new regime of weak turbulence in which the effects of shearing by large scale motions and kinetic dissipation play an important role. The inclusion of the effect of nonlocal motions on the nonlinear energy cascade rate in the dissipation range, specifically the shearing by large-scale motions, is proposed to explain the nearly power-law energy spectra observed in the dissipation range of both kinetic numerical simulations and solar wind observations.
Nonlinear phenomena, turbulence and anomalous transport in fusion plasmas
Hidalgo, C.; Estrada, T.; Sanchez, E.; Branas, B.; Garcia-Cortes, I.; Van Milligen, B.P.; Balbin, R.; Pedrosa, M.A.; Sanchez, J.; Carreras, B.A.
1995-02-01
The nonlinear nature of the plasma turbulence, as measured by bicoherence analysis, has been studied in stellarator (ATF and W7AS) and tokamak (PBXM) devices. In ATF, little nonlinear interaction is found in the scrape-off layer region whereas the strength of the coupling is enhanced in the edge plasma region where the level of fluctuations is consistent with the theoretical expectations from resistive interchange modes. In W7AS the level of bicoherence is significantly smaller than in ATF. The comparison ATF/W7AS/PBXM suggest the important role of the magnetic shear to determine nonlinear behavior of the turbulence. The level of bicoherence also depends on the plasma conditions: in particular, it increases at the H-mode transition. The comparison between the nonlinear behavior of the turbulence in tokamaks and stellarators allows experimental verification of theoretical turbulence models.
A Field-Particle Correlation Technique to Explore the Collisionless Damping of Plasma Turbulence
NASA Astrophysics Data System (ADS)
Klein, Kristopher
2016-10-01
The nature of the dominant mechanisms which damp turbulent electromagnetic fluctuations remains an unanswered question in the study of a variety of collisionless plasma systems. Proposed damping mechanisms can be generally, but not exclusively, classified as resonant, e.g. Landau and cyclotron damping, non-resonant, e.g. stochastic ion heating, and intermittent, e.g. energization via current sheets or magnetic reconnection. To determine the role these mechanisms play in turbulent plasmas, we propose the application of field-particle correlations to time series of single spatial point observations of the type typically measured in the solar wind. This correlation, motivated by the form of the collisionless Vlasov equation, is the time averaged product of the factors comprising the nonlinear field-particle interaction term. The correlation both captures the secular transfer of energy between fields and perturbed plasma distributions by averaging out the conservative oscillatory energy transfer, and retains the velocity space structure of the secular transfer, allowing for observational characterization of the damping mechanism. Field-particle correlations are applied to a set of nonlinear kinetic numerical simulations of increasing complexity, including electrostatic, gyrokinetic, and hybrid Vlasov-Maxwell systems. These correlations are shown to capture the secular energy transfer between fields and particles and distinguish between the mechanisms accessible to the chosen system. We conclude with a discussion of the application of this general technique to data from current and upcoming spacecraft missions, including MMS, DSCOVR, Solar Probe Plus and THOR, which should help in determining which damping mechanisms operate in a variety of heliospheric plasmas. This work was performed in collaboration with Gregory Howes, Jason TenBarge, Nuno Loureiro, Ryusuke Numata, Francesco Valetini, Oreste Pezzi, Matt Kunz, Justin Kasper, and Chris Chen, with support from Grants
Reverse Energy Cascade in Turbulent Weakly Ionized Plasmas
NASA Technical Reports Server (NTRS)
Williams, Kyron; Appartaim, R.; Belay, K.; Johnson, J. A., III
1998-01-01
For systems far from equilibrium, the neglect of a role for viscous effects in turbulence may be generally inappropriate when the relaxation time for the molecular process approaches the local flow time (Orou et al. (1996)). Furthermore, for stationary collisional plasmas, the conventional Reynolds number is irrelevant under circumstances where the standard features of turbulence in ordinary gases are observed in the plasma (Johnson et al. (1987)). The current theoretical understanding of these turbulent phenomenon is particularly inadequate for turbulence associated with ionizing shock waves; generally speaking, thermodynamic, acoustic and pressure fluctuations are all seen as amplified across the shock wave followed by a dramatic decay (relaminarization) usually attributed to a lack of importance of viscosity in the turbulent regions. This decay would be accelerated when the flow speed is also reduced due to the importance usually given to the conventional Reynolds number (which is directly proportional to velocity) as a quality of turbulence index. However, evidence supporting this consensus is lacking. By contrast, recent evidence of vanishing triple correlations form De Silva et al. (1996) provides strong support for early theoretical speculation of inherently molecular effects in macroscopic turbulence in Tsuge (1974). This specifically suggests that the role of compressive effects ordinarily associated with the shock wave could be significantly muted by the existence of a strongly turbulent local environment. There is also more recent theoretical speculation (Frisch et al. (1984)) of an inherently and previously unsuspected non-dissipative nature to turbulence, with energy conservation being nurtured by reverse energy cascades in the turbulent fluctuation spectra. Furthermore, the role which might be played by fluctuations on quantum mechanical phenomena and variations in molecular parameters is completely unknown, especially of the sort which might be found
Status and Verification of Edge Plasma Turbulence Code BOUT
Umansky, M V; Xu, X Q; Dudson, B; LoDestro, L L; Myra, J R
2009-01-08
The BOUT code is a detailed numerical model of tokamak edge turbulence based on collisional plasma uid equations. BOUT solves for time evolution of plasma uid variables: plasma density N{sub i}, parallel ion velocity V{sub {parallel}i}, electron temperature T{sub e}, ion temperature T{sub i}, electric potential {phi}, parallel current j{sub {parallel}}, and parallel vector potential A{sub {parallel}}, in realistic 3D divertor tokamak geometry. The current status of the code, physics model, algorithms, and implementation is described. Results of verification testing are presented along with illustrative applications to tokamak edge turbulence.
MAGNETIZED JETS DRIVEN BY THE SUN: THE STRUCTURE OF THE HELIOSPHERE REVISITED
Opher, M.; Drake, J. F.; Zieger, B.; Gombosi, T. I.
2015-02-20
The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun’s travel through the interstellar medium (ISM) extending for thousands of astronomical units (AUs). Here, we show, based on magnetohydrodynamic (MHD) simulations, that the tension (hoop) force of the twisted magnetic field of the Sun confines the solar wind plasma beyond the termination shock and drives jets to the north and south very much like astrophysical jets. These jets are deflected into the tail region by the motion of the Sun through the ISM similar to bent galactic jets moving through the intergalactic medium. The interstellar wind blows the two jets into the tail but is not strong enough to force the lobes into a single comet-like tail, as happens to some astrophysical jets. Instead, the interstellar wind flows around the heliosphere and into the equatorial region between the two jets. As in some astrophysical jets that are kink unstable, we show here that the heliospheric jets are turbulent (due to large-scale MHD instabilities and reconnection) and strongly mix the solar wind with the ISM beyond 400 AU. The resulting turbulence has important implications for particle acceleration in the heliosphere. The two-lobe structure is consistent with the energetic neutral atom (ENA) images of the heliotail from IBEX where two lobes are visible in the north and south and the suggestion from the Cassini ENAs that the heliosphere is “tailless.”.
Gamayunov, Konstantin V.; Zhang Ming; Rassoul, Hamid K.; Pogorelov, Nikolai V.; Heerikhuisen, Jacob
2012-09-20
A self-consistent model of the interstellar pickup protons, the slab component of the Alfvenic turbulence, and core solar wind (SW) protons is presented for r {>=} 1 along with the initial results of and comparison with the Voyager 2 (V2) observations. Two kinetic equations are used for the pickup proton distribution and Alfvenic power spectral density, and a third equation governs SW temperature including source due to the Alfven wave energy dissipation. A fraction of the pickup proton free energy, f{sub D} , which is actually released in the waveform during isotropization, is taken from the quasi-linear consideration without preexisting turbulence, whereas we use observations to specify the strength of the large-scale driving, C{sub sh}, for turbulence. The main conclusions of our study can be summarized as follows. (1) For C{sub sh} Almost-Equal-To 1-1.5 and f{sub D} Almost-Equal-To 0.7-1, the model slab component agrees well with the V2 observations of the total transverse magnetic fluctuations starting from {approx}8 AU. This indicates that the slab component at low-latitudes makes up a majority of the transverse magnetic fluctuations beyond 8-10 AU. (2) The model core SW temperature agrees well with the V2 observations for r {approx}> 20 AU if f{sub D} Almost-Equal-To 0.7-1. (3) A combined effect of the Wentzel-Kramers-Brillouin attenuation, large-scale driving, and pickup proton generated waves results in the energy sink in the region r {approx}< 10 AU, while wave energy is pumped in the turbulence beyond 10 AU. Without energy pumping, the nonlinear energy cascade is suppressed for r {approx}< 10 AU, supplying only a small energy fraction into the k-region of dissipation by the core SW protons. A similar situation takes place for the two-dimensional turbulence. (4) The energy source due to the resonant Alfven wave damping by the core SW protons is small at heliocentric distances r {approx}< 10 AU for both the slab and the two-dimensional turbulent components
Study of edge turbulence in dimensionally similar laboratory plasmas
NASA Astrophysics Data System (ADS)
Stroth, Ulrich
2003-10-01
In recent years, the numerical simulation of turbulence has made considerable progress. Predictions are made for large plasma volumes taking into account realistic magnetic geometries. Because of diagnostic limitations, in fusion plasmas the means of experimental testing of the models are rather limited. Toroidal low-temperature plasmas offer the possibility for detailed comparisons between experiment and simulation. Due to the reduced plasma parameters, the relevant quantities can be measured in the entire plasma. At the same time, the relevant non-dimensional parameters can be comparable to those in the edge of fusion plasmas. This presentation reports on results from the torsatron TJ-K [1,2] operated with a low-temperature plasma. The data are compared with simulations using the drift-Alfven-wave code DALF3 [3]. Langmuir probe arrays with 64 tips are used to measure the spatial structure of the turbulence. The same analyses techniques are applied to experimental and numerical data. The measured properties of spectra and probability density functions are reproduced by the code. Although the plasma in experiment and simulation does not exhibit critical pressure gradients, the radial transport fluctuations are strongly intermittent in both cases. Using Hydrogen, Helium and Argon as working gases, the scale parameter ρs could be varied by more than a factor of ten. As predicted by theory, the size of the turbulent eddies increases with ρ_s. The measured cross-phase between density and potential fluctuations are small, indicating the importance of the drift-wave dynamics for the turbulence in toroidal plasmas. The wave number spectra decay with an exponent of -3 as one would expect for the enstrophy cascade in 2D turbulence. [1] N. Krause et al., Rev. Sci. Instr. 73, 3474 (2002) [2] C. Lechte et al., New J. of Physics 4, 34 (2002) [3] B. Scott, Plasma Phys. Contr. Fusion 39, 1635 (1997)
Tomography as a promising diagnostic tool for plasma turbulence
NASA Astrophysics Data System (ADS)
Fujisawa, A.; Nagashima, Y.; Inagaki, S.; Onchi, T.; Ohshima, S.; Shimizu, A.
2016-02-01
A system for plasma turbulence tomography has been developed in a linear cylindrical plasma as a prototype with aiming at future application on toroidal plasma of higher temperature. This paper describes the diagnostic system in both aspects of the soft- and hardware, and reports the first results of tomographic reconstruction that can successfully produce local emission and its fluctuations. In the reconstruction process, two dimensional view of plasma is obtained for approximately 0.6 ms in every sampling time of 1 μs using parallel processing of 120 cores with 10 personal computers. The results include the steady state analysis of local fluctuation power spectra using fast Fourier transform, analysis of temporal behavior of fluctuation power spectra with wavelet transform, and analyses of the structural deformation or pattern of local plasma emission, demonstrating that the success of tomography as a promising diagnostic tool for plasma turbulence.
Turbulent transport of alpha particles in reactor plasmas
Estrada-Mila, C.; Candy, J.; Waltz, R. E.
2006-11-15
A systematic study of the behavior of energetic ions in reactor plasmas is presented. Using self-consistent gyrokinetic simulations, in concert with an analytic asymptotic theory, it is found that alpha particles can interact significantly with core ion-temperature-gradient turbulence. Specifically, the per-particle flux of energetic alphas is comparable to the per-particle flux of thermal species (deuterium or helium ash). This finding opposes the conventional wisdom that energetic ions, because of their large gyroradii, do not interact with the turbulence. For the parameters studied, a turbulent modification of the alpha-particle density profile appears to be stronger than turbulent modification of the alpha-particle pressure profile. Crude estimates indicate that the alpha density modification, which is directly proportional to the core turbulence intensity, could be in the range of 15% at midradius in a reactor. The corresponding modification of the alpha-particle pressure profile is predicted to be smaller (in the 1% range)
BOOK REVIEW: Plasma and Fluid Turbulence: Theory and Modelling
NASA Astrophysics Data System (ADS)
Yoshizawa, A.; Itoh, S. I.; Itoh, K.
2003-03-01
The area of turbulence has been covered by many books over the years. This has, of course, mainly been fluid turbulence, while the area of plasma turbulence has been treated much less. This book by Yoshizawa et al covers both plasma and fluid turbulence, in a way that does justice to both areas at the same time as cross-disciplinary aspects are illuminated. The book should be useful to physicists working in both areas partly because it examines fundamental aspects in a pedagogical way, partly because it is up to date and partly because of the cross-disciplinary aspects which enrich both areas. It is written as an advanced textbook. The reader should have previous knowledge of at least one of the areas and also some background in statistical physics. The book starts with the very important and highly up to date area of structure formation which is relevant both to fluids and plasmas. Here, pipe flow of fluids is treated as an introduction to the area, then follows discussion of the generation of magnetic fields by turbulent motion in stellar objects and stucture formation in plasmas confined by a magnetic field. Also the concept of bifurcation is introduced. This part builds up knowledge from the simple fluid case to the problems of magnetic confinement of plasmas in a very pedagogical way. It continues by introducing the fundamentals of fluid turbulence. This is done very systematically and concepts useful for industrial applications like the K-e method and several ways of heuristic modelling are introduced. Also the two dimensional vortex equation, which is also relevant to magnetized plasmas is introduced. In chapter 5 the statistical theory of turbulence is treated. It starts with a very nice and easy to understand example of renormalization of a simple nonlinear equation where the exact solution is known. It introduces the method of partial renormalization, Greens functions and the direct interaction approximation (DIA). The book then continues with an
Remote sensing of plasma motion and turbulence near the Alfvén surface
NASA Astrophysics Data System (ADS)
DeForest, C. E.
2015-12-01
Despite a rich nearly-century-long history, Thomson scattering has not been fully exploited as a remote-sensing tool in the corona and nascent solar wind. In particular, stable deep-space coronagraphs such as SOHO/LASCO and STEREO/SECCHI enable time-dependent, photometric analyses that transcend basic feature tracking and brightness estimation. These techniques offer direct insight into the plasma conditions in the outer corona. In particular, fluctuations in the outer coronal brightness comprise both the familiar inhomogeneous "blobs" of material first tracked quantitatively with SOHO/LASCO, and also a recently-discovered compressive wave field that permits remote probing of the plasma even though individual wave fronts do not stand out visually. I will discuss recent and current measurements of this wave field in the outer corona as a means to probe outer coronal heating and wind acceleration near the transition from corona to heliosphere (known as the Alfvén surface); and present current results from a study of the transition from mostly smooth to mostly turbulent flow in the nascent solar wind.
Kinetic signatures and intermittent turbulence in the solar wind plasma.
Osman, K T; Matthaeus, W H; Hnat, B; Chapman, S C
2012-06-29
A connection between kinetic processes and intermittent turbulence is observed in the solar wind plasma using measurements from the Wind spacecraft at 1 A.U. In particular, kinetic effects such as temperature anisotropy and plasma heating are concentrated near coherent structures, such as current sheets, which are nonuniformly distributed in space. Furthermore, these coherent structures are preferentially found in plasma unstable to the mirror and firehose instabilities. The inhomogeneous heating in these regions, which is present in both the magnetic field parallel and perpendicular temperature components, results in protons at least 3-4 times hotter than under typical stable plasma conditions. These results offer a new understanding of kinetic processes in a turbulent regime, where linear Vlasov theory is not sufficient to explain the inhomogeneous plasma dynamics operating near non-Gaussian structures.
The Solar Wind in the Outer Heliosphere and Heliosheath
NASA Technical Reports Server (NTRS)
Richardson, J. D.; Burlaga, L. F.
2011-01-01
The solar wind environment has a large influence on the transport of cosmic rays. This chapter discusses the observations of the solar wind plasma and magnetic field in the outer heliosphere and the heliosheath. In the supersonic solar wind, interaction regions with large magnetic fields form barriers to cosmic ray transport. This effect, the "CR-B" relationship, has been quantified and is shown to be valid everywhere inside the termination shock (TS). In the heliosheath, this relationship breaks down, perhaps because of a change in the nature of the turbulence. Turbulence is compressive in the heliosheath, whereas it was non-compressive in the solar wind. The plasma pressure in the outer heliosphere is dominated by the pickup ions which gain most of the flow energy at the TS. The heliosheath plasma and magnetic field are highly variable on scales as small as ten minutes. The plasma flow turns away from the nose roughly as predicted, but the radial speeds at Voyager 1 are much less than those at Voyager 2, which is not understood. Despite predictions to the contrary, magnetic reconnection is not an important process in the inner heliosheath with only one observed occurrence to date.
Space-Time Localization of Plasma Turbulence Using Multiple Spacecraft Radio Links
NASA Technical Reports Server (NTRS)
Armstrong, John W.; Estabrook, Frank B.
2011-01-01
Space weather is described as the variability of solar wind plasma that can disturb satellites and systems and affect human space exploration. Accurate prediction requires information of the heliosphere inside the orbit of the Earth. However, for predictions using remote sensing, one needs not only plane-of-sky position but also range information the third spatial dimension to show the distance to the plasma disturbances and thus when they might propagate or co-rotate to create disturbances at the orbit of the Earth. Appropriately processed radio signals from spacecraft having communications lines-of-sight passing through the inner heliosphere can be used for this spacetime localization of plasma disturbances. The solar plasma has an electron density- and radio-wavelength-dependent index of refraction. An approximately monochromatic wave propagating through a thin layer of plasma turbulence causes a geometrical-optics phase shift proportional to the electron density at the point of passage, the radio wavelength, and the thickness of the layer. This phase shift is the same for a wave propagating either up or down through the layer at the point of passage. This attribute can be used for space-time localization of plasma irregularities. The transfer function of plasma irregularities to the observed time series depends on the Doppler tracking mode. When spacecraft observations are in the two-way mode (downlink radio signal phase-locked to an uplink radio transmission), plasma fluctuations have a two-pulse response in the Doppler. In the two-way mode, the Doppler time series y2(t) is the difference between the frequency of the downlink signal received and the frequency of a ground reference oscillator. A plasma blob localized at a distance x along the line of sight perturbs the phase on both the up and down link, giving rise to two events in the two-way tracking time series separated by a time lag depending the blob s distance from the Earth: T2-2x/c, where T2 is the
Plasma turbulence in the downstream ionosheath of Venus
NASA Technical Reports Server (NTRS)
Intriligator, D. S.; Scarf, F. L.
1982-01-01
Observations made by the Pioneer Venus Orbiter plasma analyzer and the plasma wave instrument in the Venus ionosheath are compared. Large increases in plasma wave turbulence levels appear to be connected with changing plasma distributions and interpenetrating plasma beams. Some of these plasma waves are identified as Doppler - shifted ion acoustic waves due to beam/beam interactions, but it is noted that different forms of instabilities are probably also operative. The changes in the temperature, intensity and energy of the peak in the PVO plasma distributions are similar to those observed by Venera 10 closer to the planet and appear to be evidence for rarefaction and compression in the downstream ionosheath. Some of the changes in the PVO plasma distributions may be related to the presence of a second ion population or the acceleration of protons.
Plasma Heating During Magnetic Reconnection: Implications for Turbulent Dissipation
NASA Astrophysics Data System (ADS)
Shay, M. A.; Parashar, T.; Matthaeus, W. H.; Haggerty, C. C.
2015-12-01
Current sheets and associated intermittency are known to be prevalent in many turbulent plasmas and have been shown to be correlated with heating in observations of solar wind turbulence [1] and dissipation in kinetic particle-in-cell simulations [5]. Most intriguing, recent PIC simulations have found that the relative ion to electron heating ratio is strongly dependent on the turbulence amplitude [3]. An important question is whether magnetic reconnection is an important mechanism responsible for this heating. Studies focused on laminar reconnection have made significant progress recently on the magnitude and physics responsible for heating during magnetic reconnection [2,4]. The ambient Alfven speed of plasma flowing into the reconnection region plays a critical role, with heating initially taking the form of counterstreaming beams generated by non-local acceleration mechanism. However, there are significant uncertainties with how to link this basic reconnection heating with generic heating in a turbulent plasma. In this presentation, our current understanding of heating due to reconnection will be reviewed, and the factors determining the applicability of this heating to turbulent dissipation and heating will be discussed. These ideas will be explored through the comparison of kinetic PIC simulations of turbulence with reconnection heating models. Key aspects that will be examined are the effect of differing turbulent conditions on the magnitude and anisotropy of the heating, as well as the ion to electron heating ratio. [1] Osman et al., ApJ Letters, 727, L11, 2011. [2] Phan, et al., GRL, 40, 50917, 2013. [3] Wu et al., ApJ Letters, 763, L30, 2013. [4] Shay et al., Phys. Plasmas, 21, 122902, 2014. [5] Wan et al., PRL, 114, 175002, 2015.
NASA Astrophysics Data System (ADS)
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel
2015-02-01
We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ~ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p ∥ and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ~ 0.3 langBrang in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ~ 0.1 langBrang, the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes.
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel E-mail: eliot@berkeley.edu
2015-02-10
We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ∼ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p {sub ∥} and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ∼ 0.3 (B) in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ∼ 0.1 (B), the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes.
Heliospheric Observations of Energetic Particles
NASA Technical Reports Server (NTRS)
Summerlin, Errol J.
2011-01-01
Heliospheric observations of energetic particles have shown that, on long time averages, a consistent v^-5 power-law index arises even in the absence of transient events. This implies an ubiquitous acceleration process present in the solar wind that is required to generate these power-law tails and maintain them against adiabatic losses and coulomb-collisions which will cool and thermalize the plasma respectively. Though the details of this acceleration process are being debated within the community, most agree that the energy required for these tails comes from fluctuations in the magnetic field which are damped as the energy is transferred to particles. Given this source for the tail, is it then reasonable to assume that the turbulent LISM should give rise to such a power-law tail as well? IBEX observations clearly show a power-law tail of index approximately -5 in energetic neutral atoms. The simplest explanation for the origins of these ENAs are that they are energetic ions which have charge-exchanged with a neutral atom. However, this would imply that energetic ions possess a v^-5 power-law distribution at keV energies at the source of these ENAs. If the source is presumed to be the LISM, it provides additional options for explaining the, so called, IBEX ribbon. This presentation will discuss some of these options as well as potential mechanisms for the generation of a power-law spectrum in the LISM.
Turbulent and directed plasma motions in solar flares
NASA Technical Reports Server (NTRS)
Fludra, A.; Bentley, R. D.; Lemen, J. R.; Jakimiec, J.; Sylwester, J.
1989-01-01
An improved method for fitting asymmetric soft X-ray line profiles from solar flares is presented. A two-component model is used where one component represents the total emission from directed upflow plasma and the other the emission from the plasma at rest. Unlike previous methods, the width of the moving component is independent from that of the stationary component. Time variations of flare plasma characteristics (i.e., temperature, emission measure of moving and stationary plasma, upflow and turbulent velocities) are derived from the Ca XIX and Fe XXV spectra recorded by the Bent Crystal Spectrometer on the Solar Maximum Mission. The fitting technique provides a statistical estimation for the uncertainties in the fitting parameters. The relationship between the directed and turbulent motions has been studied, and a correlation of the random and directed motions has been found in some flares with intensive plasma upflows. Mean temperatures of the upflowing and stationary plasmas are compared for the first time from ratios of calcium to iron X-ray line intensities. Finally, evidence for turbulent motions and the possibility of plasma upflow late into the decay phase is presented and discussed.
Simultaneous Multi-angle Measurements of Plasma Turbulence at HAARP
NASA Astrophysics Data System (ADS)
Watanabe, Naomi; Golkowski, Mark; Sheerin, James; University of Colorado Denver Team
2013-10-01
We report the results from a recent series of experiments employing the HAARP HF transmitter to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) located at HAARP, the Super DARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Short pulse, low duty cycle experiments demonstrate control and suppression of artificial field-aligned irregularities (AFAI). This allows the isolation of ponderomotive plasma turbulence effects. For the first time, plasma line spectra measured simultaneously in different spots of the interaction region displayed marked but contemporaneous differences dependent on the aspect angle of the HF pump beam and the pointing angle of the MUIR diagnostic radar. Outshifted Plasma Line (OPL) spectra, rarely observed in past experiments, occurred with sufficient regularity for experimentation. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.
Investigation of an Oscillating Surface Plasma for Turbulent Drag Reduction
NASA Technical Reports Server (NTRS)
Wilkinson, Stephen P.
2003-01-01
An oscillating, weakly ionized surface plasma has been investigated for use in turbulent boundary layer viscous drag reduction. The study was based on reports showing that mechanical spanwise oscillations of a wall can reduce viscous drag due to a turbulent boundary layer by up to 40%. It was hypothesized that the plasma induced body force in high electric field gradients of a surface plasma along strip electrodes could also be configured to oscillate the flow. Thin dielectric panels with millimeter-scale, flush- mounted, triad electrode arrays with one and two-phase high voltage excitation were tested. Results showed that while a small oscillation could be obtained, the effect was lost at a low frequency (less than 100Hz). Furthermore, a mean flow was generated during the oscillation that complicates the effect. Hot-wire and pitot probe diagnostics are presented along with phase-averaged images revealing plasma structure.
Simultaneous Multi-angle Measurements of Plasma Turbulence at HAARP
NASA Astrophysics Data System (ADS)
Watanabe, Naomi
We report the results from a recent series of experiments employing the HAARP HF transmitter to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the Super DARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Short pulse, low duty cycle experiments demonstrate control and suppression of artificial field-aligned irregularities (AFAI). This allows the isolation of ponderomotive plasma turbulence effects. For the first time, plasma line spectra measured simultaneously in different spots of the interaction region displayed marked but contemporaneous differences dependent on the aspect angle of the HF pump beam and the pointing angle of the MUIR diagnostic radar. Outshifted Plasma Line spectra, rarely observed in past experiments, occurred with sufficient regularity for experimentation. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.
RF wave propagation and scattering in turbulent tokamak plasmas
Horton, W. Michoski, C.; Peysson, Y.; Decker, J.
2015-12-10
Drift wave turbulence driven by the steep electron and ion temperature gradients in H-mode divertor tokamaks produce scattering of the RF waves used for heating and current drive. The X-ray emission spectra produced by the fast electrons require the turbulence broaden RF wave spectrum. Both the 5 GHz Lower Hybrid waves and the 170 GHz electron cyclotron [EC] RF waves experience scattering and diffraction by the electron density fluctuations. With strong LHCD there are bifurcations in the coupled turbulent transport dynamics giving improved steady-state confinement states. The stochastic scattering of the RF rays makes the prediction of the distribution of the rays and the associated particle heating a statistical problem. Thus, we introduce a Fokker-Planck equation for the probably density of the RF rays. The general frame work of the coupled system of coupled high frequency current driving rays with the low-frequency turbulent transport determines the profiles of the plasma density and temperatures.
Role of Plasma Elongation on Turbulent Transport in Magnetically Confined Plasmas
Angelino, P.; Garbet, X.; Ghendrih, Ph.; Grandgirard, V.; Sarazin, Y.; Dif-Pradalier, G.; Bottino, A.
2009-05-15
The theoretical study of plasma turbulence is of central importance to fusion research. Experimental evidence indicates that the confinement time results mainly from the turbulent transport of energy, the magnitude of which depends on the turbulent state resulting from nonlinear saturation mechanisms, in particular, the self-generation of coherent macroscopic structures and large scale flows. Plasma geometry has a strong impact on the structure and magnitude of these flows and also modifies the mode linear growth rates. Nonlinear global gyrokinetic simulations in realistic tokamak magnetohydrodynamic equilibria show how plasma shape can control the turbulent transport. Results are best described in terms of an effective temperature gradient. With increasing plasma elongation, the nonlinear critical effective gradient is not modified while the stiffness of transport is decreasing.
Turbulence in laboratory and natural plasmas: Connecting the dots
NASA Astrophysics Data System (ADS)
Jenko, Frank
2015-11-01
It is widely recognized that turbulence is an important and fascinating frontier topic of both basic and applied plasma physics. Numerous aspects of this paradigmatic example of self-organization in nonlinear systems far from thermodynamic equilibrium remain to be better understood. Meanwhile, for both laboratory and natural plasmas, an impressive combination of new experimental and observational data, new theoretical concepts, and new computational capabilities (on the brink of the exascale era) have become available. Thus, it seems fair to say that we are currently facing a golden age of plasma turbulence research, characterized by fundamental new insights regarding the role and nature of turbulent processes in phenomena like cross-field transport, particle acceleration and propagation, plasma heating, magnetic reconnection, or dynamo action. At the same time, there starts to emerge a more unified view of this key topic of basic plasma physics, putting it into the much broader context of complex systems research and connecting it, e.g., to condensed matter physics and biophysics. I will describe recent advances and future challenges in this vibrant area of plasma physics, highlighting novel insights into the redistribution and dissipation of energy in turbulent plasmas at kinetic scales, using gyrokinetic, hybrid, and fully kinetic approaches in a complementary fashion. In this context, I will discuss, among other things, the influence of damped eigenmodes, the importance of nonlocal interactions, the origin and nature of non-universal power law spectra, as well as the role of coherent structures. Moreover, I will outline exciting new research opportunities on the horizon, combining extreme scale simulations with basic plasma and fusion experiments as well as with observations from satellites.
Spontaneous emission of electromagnetic radiation in turbulent plasmas
Ziebell, L. F.; Yoon, P. H.; Simões, F. J. R.; Pavan, J.; Gaelzer, R.
2014-01-15
Known radiation emission mechanisms in plasmas include bremmstrahlung (or free-free emission), gyro- and synchrotron radiation, cyclotron maser, and plasma emission. For unmagnetized plasmas, only bremmstrahlung and plasma emissions are viable. Of these, bremmstrahlung becomes inoperative in the absence of collisions, and the plasma emission requires the presence of electron beam, followed by various scattering and conversion processes. The present Letter proposes a new type of radiation emission process for plasmas in a state of thermodynamic quasi-equilibrium between particles and enhanced Langmuir turbulence. The radiation emission mechanism proposed in the present Letter is not predicted by the linear theory of thermal plasmas, but it relies on nonlinear wave-particle resonance processes. The electromagnetic particle-in-cell numerical simulation supports the new mechanism.
Energy transfer and dual cascade in kinetic magnetized plasma turbulence.
Plunk, G G; Tatsuno, T
2011-04-22
The question of how nonlinear interactions redistribute the energy of fluctuations across available degrees of freedom is of fundamental importance in the study of turbulence and transport in magnetized weakly collisional plasmas, ranging from space settings to fusion devices. In this Letter, we present a theory for the dual cascade found in such plasmas, which predicts a range of new behavior that distinguishes this cascade from that of neutral fluid turbulence. These phenomena are explained in terms of the constrained nature of spectral transfer in nonlinear gyrokinetics. Accompanying this theory are the first observations of these phenomena, obtained via direct numerical simulations using the gyrokinetic code AstroGK. The basic mechanisms that are found provide a framework for understanding the turbulent energy transfer that couples scales both locally and nonlocally.
ECRH microwave beam broadening in the edge turbulent plasma
Sysoeva, E. V.; Gusakov, E. Z.; Popov, A. Yu.; Silva, F. da; Heuraux, S.
2014-02-12
The influence of turbulent plasma density fluctuations on angular and spatial beam width is treated analytically in the framework of WKB based eikonal method. Reasonable agreement of analytical and numerical treatment results is demonstrated within the domain of quasi-optical approximation validity. Significant broadening of microwave beams is predicted for future ECRH experiments at ITER.
NASA Astrophysics Data System (ADS)
Furno, I.; Avino, F.; Bovet, A.; Diallo, A.; Fasoli, A.; Gustafson, K.; Iraji, D.; Labit, B.; Loizu, J.; Müller, S. H.; Plyushchev, G.; Podestà, M.; Poli, F. M.; Ricci, P.; Theiler, C.
2015-06-01
The TORPEX basic plasma physics device at the Center for Plasma Physics Research (CRPP) in Lausanne, Switzerland is described. In TORPEX, simple magnetized toroidal configurations, a paradigm for the tokamak scrape-off layer (SOL), as well as more complex magnetic geometries of direct relevance for fusion are produced. Plasmas of different gases are created and sustained by microwaves in the electron-cyclotron (EC) frequency range. Full diagnostic access allows for a complete characterization of plasma fluctuations and wave fields throughout the entire plasma volume, opening new avenues to validate numerical codes. We detail recent advances in the understanding of basic aspects of plasma turbulence, including its development from linearly unstable electrostatic modes, the formation of filamentary structures, or blobs, and its influence on the transport of energy, plasma bulk and suprathermal ions. We present a methodology for the validation of plasma turbulence codes, which focuses on quantitative assessment of the agreement between numerical simulations and TORPEX experimental data.
The Heliospheric Magnetic Field
NASA Astrophysics Data System (ADS)
Owens, Mathew J.; Forsyth, Robert J.
2013-12-01
The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.
Magnetogenesis and magnetothermal equilibria in turbulent galaxy-cluster plasmas
NASA Astrophysics Data System (ADS)
Schekochihin, Alexander
2011-04-01
We do not know the exact mechanism of magnetic field generation in magnetised weakly collisional (or collisionless) turbulent plasma. We do know that large-scale MHD motions in such plasmas are subject to fast small-scale kinetic instabilities (mirror and firehose) triggered (at high beta) by pressure anisotropies and that these anisotropies will always arise in a turbulent plasma. Therefore, standard MHD equations cannot be used to describe the turbulent dynamo. I will argue that the likely scenario in such plasmas is explosively fast growth of magnetic fluctuations to dynamical levels. I will further argue that if an efficient turbulent dynamo is assumed, radiative cooling in such plasmas can be balanced in a thermally stable way by turbulent heating, whose rate is set by the condition that plasma locally remains in a marginal state with respect to the mirror and firehose instabilities. This thermal stability suggests that a cooling catastrophe is not inevitable, although whether this old problem is thus resolved depends on whether a number of assumptions about the nonlinear behaviour of the instabilities, strength of turbulence and efficiency of the dynamo are borne out by first- principles microphysical theory, simulations or plasma experiments.References:A. A. Schekochihin, M. Brueggen, L. Feretti, M. W. Kunz, and L. Rudnick, Space Sci. Rev., in preparation (2011)M. W. Kunz, A. A. Schekochihin, S. C. Cowley, J. J. Binney, and J. S. Sanders, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1003.2719]M. S. Rosin, A. A. Schekochihin, F. Rincon, and S. C. Cowley, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1002.4017]A. A. Schekochihin, S. C. Cowley, F. Rincon, and M. S. Rosin, Mon. Not. R. Astron. Soc. 405, 291 (2010) [e-print arXiv:0912.1359]A. A. Schekochihin, S. C. Cowley, R. M. Kulsrud, M. S. Rosin, and T. Heinemann, Phys. Rev. Lett. 100, 081301 (2008) [e-print arXiv:0709.3828]A. A. Schekochihin and S. C. Cowley, Phys. Plasmas 13, 056501
NASA Astrophysics Data System (ADS)
Jung, Young-Dae
2013-05-01
The effects of turbulence on the Thomson scattering process are investigated in turbulent plasmas. The Thomson scattering cross section in turbulent plasmas is obtained by the fluctuation-dissipation theorem and plasma dielectric function as a function of the diffusion coefficient, wave number, and Debye length. It is demonstrated that the turbulence effect suppresses the Thomson scattering cross section. It is also shown that the turbulence effect on the Thomson scattering process decreases with increasing thermal energy. The dependence of the wave number on the total Thomson scattering cross section including the turbulent structure factor is also discussed. This paper is dedicated to the late Prof. P. K. Shukla in memory of exciting and stimulating collaborations on effective interaction potentials in various astrophysical and laboratory plasmas.
Granular fluctuations in plasma turbulence and their role in transport
Terry, P.W.
1993-04-01
Three general types of granular or discrete fluctuations in plasma turbulence are reviewed, with emphasis placed on their unique role in fluctuation-induced transport. These fluctuations are clumps, holes, and vortices, and represent structures that are not part of the normal mode response, the basis of conventional descriptions of plasma turbulence and transport. These fluctuations interact with the normal mode response to produce profound modifications of transport. The self-consistent linking of fields and particle distributions through quasineutrality and Ampere's law is shown to be crucial in calculating these modifications. In particular, it is pointed out that collisionless electron motion along perturbed magnetic fields produces almost no transport of field aligned current across equilibrium surfaces. It is also shown that clumps are granular structures which are turbulently mixed, whereas holes and vortices avoid mixing and relaxation through strong self-binding effects. The distinction between structures that are mixed and those that are persistent is probed in an analysis of the interaction of an intense vortex and ambient turbulent fluctuations. It is shown that, above a critical amplitude, the shearing of eddies due to the differential rotation of the vortex suppresses the fluctuations that mix its vorticity, allowing it to achieve a lifetime greatly in excess of the turbulent interaction time scale.
Granular fluctuations in plasma turbulence and their role in transport
Terry, P.W.
1993-04-01
Three general types of granular or discrete fluctuations in plasma turbulence are reviewed, with emphasis placed on their unique role in fluctuation-induced transport. These fluctuations are clumps, holes, and vortices, and represent structures that are not part of the normal mode response, the basis of conventional descriptions of plasma turbulence and transport. These fluctuations interact with the normal mode response to produce profound modifications of transport. The self-consistent linking of fields and particle distributions through quasineutrality and Ampere`s law is shown to be crucial in calculating these modifications. In particular, it is pointed out that collisionless electron motion along perturbed magnetic fields produces almost no transport of field aligned current across equilibrium surfaces. It is also shown that clumps are granular structures which are turbulently mixed, whereas holes and vortices avoid mixing and relaxation through strong self-binding effects. The distinction between structures that are mixed and those that are persistent is probed in an analysis of the interaction of an intense vortex and ambient turbulent fluctuations. It is shown that, above a critical amplitude, the shearing of eddies due to the differential rotation of the vortex suppresses the fluctuations that mix its vorticity, allowing it to achieve a lifetime greatly in excess of the turbulent interaction time scale.
Plasma shaping effects on tokamak scrape-off layer turbulence
NASA Astrophysics Data System (ADS)
Riva, Fabio; Lanti, Emmanuel; Jolliet, Sébastien; Ricci, Paolo
2017-03-01
The impact of plasma shaping on tokamak scrape-off layer (SOL) turbulence is investigated. The drift-reduced Braginskii equations are written for arbitrary magnetic geometries, and an analytical equilibrium model is used to introduce the dependence of turbulence equations on tokamak inverse aspect ratio (ε ), Shafranov’s shift (Δ), elongation (κ), and triangularity (δ). A linear study of plasma shaping effects on the growth rate of resistive ballooning modes (RBMs) and resistive drift waves (RDWs) reveals that RBMs are strongly stabilized by elongation and negative triangularity, while RDWs are only slightly stabilized in non-circular magnetic geometries. Assuming that the linear instabilities saturate due to nonlinear local flattening of the plasma gradient, the equilibrium gradient pressure length {L}p=-{p}e/{{\
Strongly turbulent stabilization of electron beam-plasma interactions
NASA Technical Reports Server (NTRS)
Freund, H. P.; Haber, I.; Palmadesso, P.; Papadopoulos, K.
1980-01-01
The stabilization of electron beam interactions due to strongly turbulent nonlinearities is studied analytically and numerically for a wide range of plasma parameters. A fluid mode coupling code is described in which the effects of electron and ion Landau damping and linear growth due to the energetic electron beam are included in a phenomenological manner. Stabilization of the instability is found to occur when the amplitudes of the unstable modes exceed the threshold of the oscillating two-stream instability. The coordinate space structure of the turbulent spectrum which results clearly shows that soliton-like structures are formed by this process. Phenomenological models of both the initial stabilization and the asymptotic states are developed. Scaling laws between the beam-plasma growth rate and the fluctuations in the fields and plasma density are found in both cases, and shown to be in good agreement with the results of the simulation.
Universal probability distribution function for bursty transport in plasma turbulence.
Sandberg, I; Benkadda, S; Garbet, X; Ropokis, G; Hizanidis, K; del-Castillo-Negrete, D
2009-10-16
Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density fluctuations observed in plasma edge of several magnetic confinement devices and the remarkable scaling between their skewness S and kurtosis K. Similar statistical characteristics of variabilities have been also observed in other physical systems that are characterized by convection such as the x-ray fluctuations emitted by the Cygnus X-1 accretion disc plasmas and the sea surface temperature fluctuations.
Three-dimensional turbulence structure in space and astrophysical plasmas
NASA Astrophysics Data System (ADS)
Narita, Yasuhito; Comisel, Horia; Motschmann, Uwe
2016-04-01
Plasma turbulence appears in the solar wind and around the Earth bow shock, and serves as an ideal natural laboratory for studying turbulence structure, mechanisms of energy cascade and dissipation, and particle energization. Understanding dissipation mechanisms and particle energization is relevant to astrophysical applications such as accretion disks, interstellar medium, and supernova explosions. Our knowledge on turbulence structure and dissipation mechanisms has been advanced so much through the past decade thanks to multi-point measurements in space. Using the Cluster measurements in the solar wind, the three-dimensional filamentary structure of solar wind turbulence has experimentally been revealed from magnetohydrodynamic scales (at about 1,000 to 10,000 km) down to ion kinetic scales (at about 100 km). The filamentation process has also been confirmed by hybrid simulations of ion-kinetic turbulence. Based on a review of filamentation process, wave modes, spectral anisotropy models from the Cluster observations and the hybrid simulations, observational scenarios for understanding particle energization process for the THOR mission concept (Turbulence Heating Observer) are discussed.
GYROKINETIC PARTICLE SIMULATION OF TURBULENT TRANSPORT IN BURNING PLASMAS
Horton, Claude Wendell
2014-06-10
The SciDAC project at the IFS advanced the state of high performance computing for turbulent structures and turbulent transport. The team project with Prof Zhihong Lin [PI] at Univ California Irvine produced new understanding of the turbulent electron transport. The simulations were performed at the Texas Advanced Computer Center TACC and the NERSC facility by Wendell Horton, Lee Leonard and the IFS Graduate Students working in that group. The research included a Validation of the electron turbulent transport code using the data from a steady state university experiment at the University of Columbia in which detailed probe measurements of the turbulence in steady state were used for wide range of temperature gradients to compare with the simulation data. These results were published in a joint paper with Texas graduate student Dr. Xiangrong Fu using the work in his PhD dissertation. X.R. Fu, W. Horton, Y. Xiao, Z. Lin, A.K. Sen and V. Sokolov, “Validation of electron Temperature gradient turbulence in the Columbia Linear Machine, Phys. Plasmas 19, 032303 (2012).
Turbulent-driven intrinsic rotation in tokamak plasmas
NASA Astrophysics Data System (ADS)
Barnes, Michael; Parra, Felix; Lee, Jungpyo; Belli, Emily; Nave, Filomena; White, Anne
2013-10-01
Tokamak plasmas are routinely observed to rotate even in the absence of an externally applied torque. This ``intrinsic'' rotation exhibits several robust features, including rotation reversals with varying plasma density and current and rotation peaking at the transition from low confinement to high confinement regimes. Conservation of toroidal angular momentum dictates that the intrinsic rotation is determined by momentum redistribution within the plasma, which is dominated by turbulent transport. The turbulent momentum transport, and thus the intrinsic rotation profile, is driven by formally small effects that are usually neglected. We present a gyrokinetic theory that makes use of the smallness of the poloidal to total magnetic field ratio to self-consistently include the dominant effects driving intrinsic turbulent momentum transport in tokamaks. These effects (including slow radial profile variation, slow poloidal turbulence variation, and diamagnetic corrections to the equilibrium Maxwellian) have now been implemented in the local, delta-f gyrokinetic code GS2. We describe important features of the numerical implementation and show numerical results on intrinsic momentum transport that are qualitatively consistent with experimental rotation reversals.
Casanova, S.; Schlickeiser, R.
2012-02-01
Recently, a new transport theory of cosmic rays in magnetized space plasmas extending the quasilinear approximation to the particle orbit has been developed for the case of an axisymmetric incompressible magnetic turbulence. Here, we generalize the approach to the important physical case of a compressible plasma. As previously obtained in the case of an incompressible plasma, we allow arbitrary gyrophase deviations from the unperturbed spiral orbits in the uniform magnetic field. For the case of quasi-stationary and spatially homogeneous magnetic turbulence we derive, in the small Larmor radius approximation, gyrophase-averaged cosmic-ray Fokker-Planck coefficients. Upper limits for the perpendicular and pitch-angle Fokker-Planck coefficients and for the perpendicular and parallel spatial diffusion coefficients are presented.
Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas
Predebon, I.; Xanthopoulos, P.
2015-05-15
Turbulence induced by the ion temperature gradient (ITG) is investigated in the helical and axisymmetric plasma states of a reversed field pinch device by means of gyrokinetic calculations. The two magnetic configurations are systematically compared, both linearly and nonlinearly, in order to evaluate the impact of the geometry on the instability and its ensuing transport, as well as on the production of zonal flows. Despite its enhanced confinement, the high-current helical state demonstrates a lower ITG stability threshold compared to the axisymmetric state, and ITG turbulence is expected to become an important contributor to the total heat transport.
Anisotropy in solar wind plasma turbulence.
Oughton, S; Matthaeus, W H; Wan, M; Osman, K T
2015-05-13
A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.
A basic plasma test for gyrokinetics: GDC turbulence in LAPD
NASA Astrophysics Data System (ADS)
Pueschel, M. J.; Rossi, G.; Told, D.; Terry, P. W.; Jenko, F.; Carter, T. A.
2017-02-01
Providing an important step towards validating gyrokinetics under comparatively little-explored conditions, simulations of pressure-gradient-driven plasma turbulence in the Large Plasma Device (LAPD) are compared with experimental observations. The corresponding signatures confirm the existence of a novel regime of turbulence, based on the recently-discovered gradient-driven drift coupling (GDC) instability, which is thus confirmed as a candidate mechanism for turbulence in basic, space and astrophysical plasmas. Despite the limitations of flux-tube gyrokinetics for this scenario, when accounting for box size scaling by applying a scalar factor η =6, agreement between simulations and experiment improves to within a factor of two for key observables: compressional magnetic, density, and temperature fluctuations, both in amplitude and structure. Thus, a first, strong indication is presented that the GDC instability seen in gyrokinetics appears to operate in the experiment and that the essential instability physics is present in the numerical model. Overall, the gyrokinetic framework and its numerical implementation in the Gene code therefore perform well for LAPD plasmas very different from their brethren in fusion experiments.
Studies of Aspect Angle Dependence of Plasma Turbulence at HAARP
NASA Astrophysics Data System (ADS)
Adham, N.; Sheerin, J. P.; Wood, M. R.; Roe, R. G.; Gerres, J. M.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.; Selcher, C. A.
2010-12-01
We report the results from a recent series of campaigns employing the HAARP HF transmitter to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Short pulse, low duty cycle experiments demonstrate control and suppression of artificial field-aligned irregularities (AFAI). This allows the isolation of ponderomotive plasma turbulence effects. Plasma line spectra exhibit a marked dependence on the aspect angle of the HF pump beam and the pointing of the MUIR diagnostic radar. Refraction is shown to play an important role in the observed plasma line spectral density as a function of zenith angle including the discovery of a second region of strong turbulence displaced southward from the primary HF interaction region along the geomagnetic field line. Background ionospheric conditions are also observed to have a significant effect. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.
Turbulent transport of alpha particles in tokamak plasmas
NASA Astrophysics Data System (ADS)
Croitoru, A.; Palade, D. I.; Vlad, M.; Spineanu, F.
2017-03-01
We investigate the \\boldsymbol{E}× \\boldsymbol{B} diffusion of fusion born α particles in tokamak plasmas. We determine the transport regimes for a realistic model that has the characteristics of the ion temperature gradient (ITG) or of the trapped electron mode (TEM) driven turbulence. It includes a spectrum of potential fluctuations that is modeled using the results of the numerical simulations, the drift of the potential with the effective diamagnetic velocity and the parallel motion. Our semi-analytical statistical approach is based on the decorrelation trajectory method (DTM), which is adapted to the gyrokinetic approximation. We obtain the transport coefficients as a function of the parameters of the turbulence and of the energy of the α particles. According to our results, significant turbulent transport of the α particles can appear only at energies of the order of 100 KeV. We determine the corresponding conditions.
Hall MHD Stability and Turbulence in Magnetically Accelerated Plasmas
H. R. Strauss
2012-11-27
The object of the research was to develop theory and carry out simulations of the Z pinch and plasma opening switch (POS), and compare with experimental results. In the case of the Z pinch, there was experimental evidence of ion kinetic energy greatly in excess of the ion thermal energy. It was thought that this was perhaps due to fine scale turbulence. The simulations showed that the ion energy was predominantly laminar, not turbulent. Preliminary studies of a new Z pinch experiment with an axial magnetic field were carried out. The axial magnetic is relevant to magneto - inertial fusion. These studies indicate the axial magnetic field makes the Z pinch more turbulent. Results were also obtained on Hall magnetohydrodynamic instability of the POS.
Neoclassical diffusion in a turbulent plasma
Yushmanov, P. . Inst. Atomnoj Ehnergii Texas Univ., Austin, TX . Inst. for Fusion Studies)
1991-11-01
This work describes a new approach to plasma transport where the toroidal drift motion is considered as a perturbation to the fluctuating velocity. Percolation theory is used to determine the scaling of the diffusion coefficient. Several neoclassical phenomena should persist even when diffusion is enhanced from neoclassical predictions. Numerical simulation results support the theoretical scaling arguments.
Model of An Expanding Heliosphere
NASA Astrophysics Data System (ADS)
Song, P.; Vasyliunas, V. M.
2015-12-01
Conventional models of the heliosphere assume that the heliopause is formed, similarly to the magnetopause of a planet, at the location where the total pressure of the exterior (interstellar) medium is balanced by the total pressure of the interior (heliospheric) medium. The heliosphere, however, differs greatly from a planetary magnetosphere in being dominated by a continuous interior source of mass (present in some planetary magnetospheres, notably Jupiter and Saturn, but not to anything like the same extent), and it differs as well from systems with large interior mass sources such as comets (to which it has also been compared) in being threaded by magnetic flux from its central object (the Sun). The heliosphere must thus expand continually as more and more mass is put into it by the solar wind, with the heliopause marching into the interstellar medium at some non-zero speed while maintaining the plasma total (thermal plus magnetic) pressure equal to that of the interstellar medium. A steady state heliosphere is, strictly speaking, impossible unless and until the distinction between the heliospheric and the interstellar medium has disappeared. The geometry of the expansion can be visualized in different ways. Conventionally it is taken for granted that the expansion is deflected by interstellar flow sideways and channeled into an extended wake/tail region, the rest of the heliosphere being in apparently steady state. Even if this may occur, it would be at a distance much larger than commonly assumed. We explore the alternative possibility of a heliosphere expanding predominantly in the radial direction and describe some of its properties. The input from solar wind and interplanetary magnetic field during each solar cycle forms a shell, with subsequent cycles adding shells of alternating magnetic polarities. The ultimate extent of the heliosphere (in all directions) and the number of shells can be limited by the time until either the solar output or the
Stable Modes in Saturation of Instability-Driven Plasma Turbulence
NASA Astrophysics Data System (ADS)
Terry, P. W.
2016-10-01
Saturation of instability-driven plasma turbulence, apart from cases with quasilinear flattening, has been treated almost universally as an energy-transfer or wavenumber scattering process, with the Kolmogorov cascade as the idealized paradigm. This view is being modified by the realization that for a broad parameter range wavenumber transfer is subjected to heavy damping at the same scales as the instability through transfer to a separate space of stable modes. The densely populated, nonlinearly driven stable-mode space can be represented by roots of the linear dielectric or empirically extracted modes of a singular value decomposition. This new understanding of instability-driven turbulence brings to light fluctuation characteristics, transport processes, and saturation mechanisms that cannot be anticipated solely from analysis of the linear instability or the related quasilinear transport approximation. This tutorial describes key aspects of the new paradigm, including characterization of stable modes, quantitative measures of the branching ratio between wavenumber transfer and transfer to stable modes, simultaneity of transfer to stable modes as contrasted to wavenumber cascades, equipartition of energy dissipation rate among stable modes, and zonal-flow regulation of ion temperature gradient (ITG) turbulence by catalyzing transfer to stable modes. It is shown that ballooning-parity ITG turbulence creates a stochastic magnetic field by exciting a stable microtearing mode and that zonal-flow catalyzed transfer to stable modes yields a turbulence level proportional to zonal flow damping. In stellarator trapped electron mode turbulence, stable ion modes become energy driving sources via cross correlations between non orthogonal modes. Stable mode effects are shown to arise for a range of fusion plasmas systems and for astrophysically relevant Kelvin-Helmholtz instability. Supported by USDOE.
Magnetic Turbulence in Colliding Laser-Produced Plasmas
NASA Astrophysics Data System (ADS)
Collette, A.; Gekelman, W.; Vincena, S.
2007-05-01
The expansion and interaction of dense plasmas in the presence of a magnetized background plasma is important in many astrophysical processes, among them coronal mass ejections and the many examples of plasma jets from astrophotography. Turbulence is expected to be present in many such configurations. We describe a series of experiments which involve the collision of two dense (initially, n > 1015cm-3) laser-produced plasmas within an ambient, highly magnetized background plasma. The laser-produced plasmas form diamagnetic cavities in which a large percentage of the background magnetic field (600G) has been expelled. First-stage observations of these structures have been completed using a fast (3ns exposure) camera. The photographs indicate complicated structure at late times, in addition to coherent corrugated structures on the bubble surfaces. The data hint at the presence of turbulence in the interaction. The second stage of observation will consist of direct investigation of the magnetic field using probes. A novel diagnostic system composed of small (300-500 micron) 3-axis differential magnetic field probes in conjunction with a ceramic motor system capable of extremely fine (sub-micron) positioning accuracy is currently under development. An ensemble of magnetic field data from fixed and movable probes makes possible the calculation of the cross-spectral function. Initial data from photography and a prototype probe will be presented.
First 3-D simulations of meteor plasma dynamics and turbulence
NASA Astrophysics Data System (ADS)
Oppenheim, Meers M.; Dimant, Yakov S.
2015-02-01
Millions of small but detectable meteors hit the Earth's atmosphere every second, creating trails of hot plasma that turbulently diffuse into the background atmosphere. For over 60 years, radars have detected meteor plasmas and used these signals to infer characteristics of the meteoroid population and upper atmosphere, but, despite the importance of meteor radar measurements, the complex processes by which these plasmas evolve have never been thoroughly explained or modeled. In this paper, we present the first fully 3-D simulations of meteor evolution, showing meteor plasmas developing instabilities, becoming turbulent, and inhomogeneously diffusing into the background ionosphere. These instabilities explain the characteristics and strength of many radar observations, in particular the high-resolution nonspecular echoes made by large radars. The simulations reveal how meteors create strong electric fields that dig out deep plasma channels along the Earth's magnetic fields. They also allow researchers to explore the impacts of the intense winds and wind shears, commonly found at these altitudes, on meteor plasma evolution. This study will allow the development of more sophisticated models of meteor radar signals, enabling the extraction of detailed information about the properties of meteoroid particles and the atmosphere.
A Model of the Heliosphere with Jets
NASA Astrophysics Data System (ADS)
Drake, James; Swisdak, Marc; Opher, Merav
2015-11-01
The conventional picture of the heliosphere is that of a comet-shaped structure with an extended tail produced by the relative motion of the sun through the local interstellar medium. Recent magnetohydrodynamic (MHD) simulations of the heliosphere have revealed that the heliosphere drives magnetized jets to the north and south similar to those driven by the Crab Nebula. That the sun's magnetic field can drive such jets when β = 8 πP /B2 >> 1 in the outer heliosphere is a major surprise. An analytic model of the heliosheath (HS) is developed in the limit in which the interstellar flow and magnetic field are neglected. The heliosphere in this limit is axi-symmetric and the overall structure of the HS is controlled by the solar magnetic field even for very high β. The tension of the solar magnetic field produces a drop in the total pressure between the termination shock and the HP. This same pressure drop accelerates the plasma flow into the north and south directions to form two collimated jets. MHD simulations of the global heliosphere embedded in a stationary interstellar medium match well with the analytic model. Evidence from the distribution of energetic neutral atoms from the outer heliosphere from IBEX and CASSINI supports the picture of a heliosphere with jets.
Free energy and entropy flows in magnetised plasma turbulence
NASA Astrophysics Data System (ADS)
Schekochihin, A.; Cowley, S.; Dorland, W.; Howes, G. G.; Quataert, E.; Tatsuno, T.; Plunk, G.; TenBarge, J.; Mallet, A.; Kanekar, A.
2011-12-01
Just as fluid turbulence can be conceptualised as a cascade of kinetic energy from large to small scales, kinetic plasma turbulence is a cascade of free energy in the 6D phase space (position and velocity). I will discuss this as a general principle and then specialise to the case of magnetised plasma turbulence at kinetic (sub-ion-Larmor) scales. At these scales, the free energy flux arriving from the inertial range splits into two channels: the kinetic Alfven wave cascade destined to be dissipated into electron heat and the ion entropy cascade, resulting in ion heating. The phase-space nature of the cascade is particularly manifest in this case as the ion entropy cascade involves simultaneous generation of small spatial scales and small scales in velocity space, the latter via a nonlinear phase-mixing process due to ion gyromotion. I will also discuss how the electron Landau damping and the associated process of parallel phase mixing fit into this cascade picture and whether they represent an effective dissipation mechanism in a strongly turbulent nonlinear system.
Altitude characteristics of plasma turbulence excited with the Tromso superheater
Djuth, F.T.; Elder, J.H. ); Stubbe, P.; Kohl, H. ); Sulzer, M.P. ); Rietveld, M.T. )
1994-01-01
Langmuir/ion turbulence excited with the upgraded high-power (1.2-GW effective radiated power) HF heating facility at Tromso, Norway, has been recently studied with the European Incoherent Scatter VHF and UHF incoherent scatter radars. In this report the authors focus on the altitudinal development of the turbulence observed at the highest HF power levels available. Quite remarkably, the observed plasma turbulence plunges downward in altitude over timescales of tens of seconds following HF beam turn-on; the bottom altitude is generally reached after [approximately]30 s. This phenomenon has a well-defined HF power threshold. It is most likely caused by changes in the electron density profile brought about by HF heating of the electron gas. If this is the case, then the heat source must be nonlinearly dependent on HF power. Overall, the characteristics of the Tromso turbulence are quite distinctive when compared to similar high-resolution measurements made at Arecibo Observatory, Puerto Rico. After HF transmissions have been made for tens of seconds at Tromso, billowing altitude structures are often seen, in sharp contrast to layers of turbulence observed at Arecibo. 17 refs., 3 figs.
Transition to subcritical turbulence in a tokamak plasma
NASA Astrophysics Data System (ADS)
van Wyk, F.; Highcock, E. G.; Schekochihin, A. A.; Roach, C. M.; Field, A. R.; Dorland, W.
2016-12-01
Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.
Complexity Induced Anisotropic Bimodal Intermittent Turbulence in Space Plasmas
NASA Technical Reports Server (NTRS)
Chang, Tom; Tam, Sunny W. Y.; Wu, Cheng-Chin
2004-01-01
The "physics of complexity" in space plasmas is the central theme of this exposition. It is demonstrated that the sporadic and localized interactions of magnetic coherent structures arising from the plasma resonances can be the source for the coexistence of nonpropagating spatiotemporal fluctuations and propagating modes. Non-Gaussian probability distribution functions of the intermittent fluctuations from direct numerical simulations are obtained and discussed. Power spectra and local intermittency measures using the wavelet analyses are presented to display the spottiness of the small-scale turbulent fluctuations and the non-uniformity of coarse-grained dissipation that can lead to magnetic topological reconfigurations. The technique of the dynamic renormalization group is applied to the study of the scaling properties of such type of multiscale fluctuations. Charged particle interactions with both the propagating and nonpropagating portions of the intermittent turbulence are also described.
Anisotropy in solar wind plasma turbulence
Oughton, S.; Matthaeus, W. H.; Wan, M.; Osman, K. T.
2015-01-01
A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters. PMID:25848082
Trapped Electron Mode Turbulence Driven Intrinsic Rotation in Tokamak Plasmas
Wang, W. X.; Hahm, T. S.; Ethier, S.; Zakharov, L. E.
2011-02-07
Recent progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported with emphasis on electron thermal transport dominated regimes. The turbulence driven intrinsic torque associated with nonlinear residual stress generation by the fluctuation intensity and the intensity gradient in the presence of zonal flow shear induced asymmetry in the parallel wavenumber spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current. These results qualitatively reproduce empirical scalings of intrinsic rotation observed in various experiments. The origin of current scaling is found to be due to enhanced kll symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic torque on pressure gradient is that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving residual stress, increase with the strength of turbulence drive, which is R0/LTe and R0/Lne for the trapped electron mode. __________________________________________________
Kulsrud, R.M.; Sudan, R.N.
1981-04-01
The nonlinear damping in a strongly turbulent convecting plasma computed by Kraichnan's modified direct inteaction approximation and the power spectrum are rederived in a physically transparent form using Kolmogoroff's theory of turbulence.
Particle Energization throughout the Heliosphere: Opportunities with IMAP
NASA Astrophysics Data System (ADS)
Zank, Gary
2016-04-01
Understanding the radiation environment at the Earth and beyond is one of the critical elements in our developing Space Weather capabilities and strategy. Furthermore, the energization of charged particles in a collisionless plasma remains one of the compelling unsolved yet universal problems in space physics and astrophysics. The proposed instrumentation of IMAP enables two critical goals: 1) real-time monitoring of the radiation and plasma environment as part of a Space Weather capability, and 2) making coordinated simultaneous measurements of all the basic plasma parameters needed to develop a comprehensive and detailed understanding of fundamental particle energization processes. Since the session addresses the "Physics of particle acceleration", we will survey briefly the critical open problems associated with particle acceleration during quiet and active solar wind periods. At least three elements will be discussed. 1) Dissipative processes in the quiet solar wind and at shock waves. For the former, we discuss emerging ideas about the dissipation of turbulence via structures such as flux ropes and their role in possibly energizing charged particles during quiet times, especially in the vicinity of the heliospheric current sheet. In the latter, reflected ions play an essential role in dissipative processes at both quasi-perpendicular and quasi-parallel shocks. This in turn has consequences for the energization of particles, the generation of turbulence upstream and downstream of the shock, and the importance of a pre-existing suprathermal ion population. 2) What is the role of pre-existing energetic particles versus injection from a background thermal population of charged particles in the context of diffusive shock acceleration? Does the pre-existing suprathermal particle population play a fundamental role in the dissipation processes governing heliospheric shock, as suggested by the case of the heliospheric termination shock and pickup ions? 3) What is the
Low frequency turbulence in space plasmas with dust impurities
NASA Astrophysics Data System (ADS)
Atamaniuk, Barbara; Volokitin, Alexander S.; Rothkaehl, Hanna
2013-04-01
In order to enhance our understanding of the rich plasma physical processes that drive the solar-terrestrial space environment and to create the adequate and rich services for Space Weather Program, we need to increase our ability to perform multi-point measurements by means of different sensors. Moon as the natural spacecraft can be a target for localisation the radio receiver dedicated to monitoring Earth's space environment and obtain a much more complete picture of electromagnetic plasma turbulence in different space regions than those available hitherto. Moreover this diagnostic can give the information about the localisation and property of the plasmopause, magnetosheet, magnetopause, bow shock, solar wind and radio burst and CME. It is well known that even systems with a finite number of interacting waves can be realized in the turbulent state of the active media. At the same time the essential role of dissipation of the waves suggests that, at low threshold of instability, a typical perturbed state of the plasma can be described as a finite set of interacting waves, some of which are unstable and others are strongly damped. In such cases, the number of waves remains finite, but because of competition between the instability and damping of the waves when they interact, the dynamics of the amplitudes of the waves becomes stochastic in nature and the so-called few-mode turbulence. In analyzing the conditions of the various modes of instability of nonlinear low-frequency waves and discussed the transition from quasi-periodic regime to a few-mode turbulence, and then to the fully developed turbulence, depending on the density and composition of the dust component of the plasma. An important topic for lunar missions is understanding how the charged dust behaves, roles of dust transport, levitated dust and electrodynamics around the lunar surface . It could be essential for ensuring the continued safe operation of equipment and long-term exploration. Lunar dust is
Coherent structure and Intermittent Turbulence in the Solar Wind Plasma
NASA Astrophysics Data System (ADS)
Sondhiya, Deepak Kumar; Gwal, Ashok Kumar; Kasde, Satish Kumar
2016-07-01
We analyze the coherent structures and intermittent turbulence in the solar wind plasma using measurements from the Wind spacecraft. Previously established novel wavelet and higher order statistics are used in this work. We analyze the wavelet power spectrum of various solar wind plasma parameters. We construct a statistical significance level in the wavelet power spectrum to quantify the interference effects arising from filling missing data in the time series, allowing extraction of significant power from the measured data. We analyze each wavelet power spectra for transient coherency, and global periodicities resulting from the superposition of repeating coherent structures. Furthermore, these coherent structures are preferentially found in plasma unstable to the mirror and firehose instabilities. These results offer a new understanding of various processes in a turbulent regime. Finally, we discuss the implications of our results for current theories of solar wind generation and describe future work for determining the relationship between the coherent structures in our ionic composition data and the structure of the coronal magnetic field. Keywords: Wavelet Power Spectrum, Coherent structure and Solar wind plasma
Strong Turbulence in Alkali Halide Negative Ion Plasmas
NASA Astrophysics Data System (ADS)
Sheehan, Daniel
1999-11-01
Negative ion plasmas (NIPs) are charge-neutral plasmas in which the negative charge is dominated by negative ions rather than electrons. They are found in laser discharges, combustion products, semiconductor manufacturing processes, stellar atmospheres, pulsar magnetospheres, and the Earth's ionosphere, both naturally and man-made. They often display signatures of strong turbulence^1. Development of a novel, compact, unmagnetized alkali halide (MX) NIP source will be discussed, it incorporating a ohmically-heated incandescent (2500K) tantulum solenoid (3cm dia, 15 cm long) with heat shields. The solenoid ionizes the MX vapor and confines contaminant electrons, allowing a very dry (electron-free) source. Plasma densities of 10^10 cm-3 and positive to negative ion mass ratios of 1 <= fracm_+m- <= 20 are achievable. The source will allow tests of strong turbulence theory^2. 1 Sheehan, D.P., et al., Phys. Fluids B5, 1593 (1993). 2 Tsytovich, V. and Wharton, C.W., Comm. Plasma Phys. Cont. Fusion 4, 91 (1978).
Low-frequency instabilities and plasma turbulence
NASA Technical Reports Server (NTRS)
Ilic, D. B.
1973-01-01
A theoretical and experimental study is reported of steady-state and time-dependent characteristics of the positive column and the hollow cathode discharge (HCD). The steady state of a non-isothermal, cylindrical positive column in an axial magnetic field is described by three moment equations in the plasma approximation. Volume generation of electron-ion pairs by single-stage ionization, the presence of axial current, and collisions with neutrals are considered. The theory covers the range from the low pressure, collisionless regime to the intermediate pressure, collisional regime. It yields radial profiles of the charged particle velocities, density, potential, electron and ion temperatures, and demonstrates similarity laws for the positive column. The results are compared with two moment theories and with experimental data on He, Ar and Hg found in the literature for a wide range of pressures. A simple generalization of the isothermal theory for an infinitely long cylinder in an axial magnetic field to the case of a finite column with axial current flow is also demonstrated.
Fundamental Statistical Descriptions of Plasma Turbulence in Magnetic Fields
John A. Krommes
2001-02-16
A pedagogical review of the historical development and current status (as of early 2000) of systematic statistical theories of plasma turbulence is undertaken. Emphasis is on conceptual foundations and methodology, not practical applications. Particular attention is paid to equations and formalism appropriate to strongly magnetized, fully ionized plasmas. Extensive reference to the literature on neutral-fluid turbulence is made, but the unique properties and problems of plasmas are emphasized throughout. Discussions are given of quasilinear theory, weak-turbulence theory, resonance-broadening theory, and the clump algorithm. Those are developed independently, then shown to be special cases of the direct-interaction approximation (DIA), which provides a central focus for the article. Various methods of renormalized perturbation theory are described, then unified with the aid of the generating-functional formalism of Martin, Siggia, and Rose. A general expression for the renormalized dielectric function is deduced and discussed in detail. Modern approaches such as decimation and PDF methods are described. Derivations of DIA-based Markovian closures are discussed. The eddy-damped quasinormal Markovian closure is shown to be nonrealizable in the presence of waves, and a new realizable Markovian closure is presented. The test-field model and a realizable modification thereof are also summarized. Numerical solutions of various closures for some plasma-physics paradigms are reviewed. The variational approach to bounds on transport is developed. Miscellaneous topics include Onsager symmetries for turbulence, the interpretation of entropy balances for both kinetic and fluid descriptions, self-organized criticality, statistical interactions between disparate scales, and the roles of both mean and random shear. Appendices are provided on Fourier transform conventions, dimensional and scaling analysis, the derivations of nonlinear gyrokinetic and gyrofluid equations
Turbulent energy transfer in electromagnetic turbulence: hints from a Reversed Field Pinch plasma
NASA Astrophysics Data System (ADS)
Vianello, N.; Bergsaker, H.
2005-10-01
The relationship between electromagnetic turbulence and sheared plasma flow in a Reversed Field Pinch is addressed. ExB sheared flows and turbulence at the edge tends to organize themeselves near marginal stability, suggesting an underlying energy exchange process between turbulence and mean flow. In MHD this process is well described through the quantity P which represents the energy transfer (per mass and time unit) from turbulence to mean fields. In the edge region of RFP configuration, where magnetic field is mainly poloidal and the mean ExB is consequently toroidal, the quantity P results: P =[ -
Plasma turbulence and impulsive UV line emission in solar flares
NASA Technical Reports Server (NTRS)
Brown, John C.
1986-01-01
Observations show that hard X-ray burst and UV lines rise and fall simultaneously on time scales of seconds. Hydrodynamic simulations of beam-heated atmospheres, based on collisional transport, however, produce only a gradual fall in UV emission, when the beam flux falls, due to the long time scale of conductive relaxation. It is suggested that this discrepancy might be explained by onset of plasma turbulence driven by the strong heat flux or by the beam return current going unstable. Such turbulence greatly reduces electrical and thermal conductivities. Fall in electrical conductivity reduces the hard X-ray flux by enhanced ohmic dissipation of the return current, while fall in thermal conductivity may cause the UV line to fall by reducing the transition region thickness.
Solar system plasma Turbulence: Observations, inteRmittency and Multifractals
NASA Astrophysics Data System (ADS)
Echim, Marius M.
2016-04-01
The FP7 project STORM is funded by the European Commission to "add value to existing data bases through a more comprehensive interpretation". STORM targets plasma and magnetic field databases collected in the solar wind (Ulysses and also some planetary missions), planetary magnetospheres (Venus Express, Cluster, a few orbits from Cassini), cometary magnetosheaths (e.g. Haley from Giotto observations). The project applies the same package of analysis methods on geomagnetic field observations from ground and on derived indices (e.g. AE, AL, AU, SYM-H). The analysis strategy adopted in STORM is built on the principle of increasing complexity, from lower (like, e.g., the Power Spectral Density - PSD) to higher order analyses (the Probability Distribution Functions - PDFs, Structure Functions - SFs, Fractals and Multifractals - MFs). Therefore STORM targets not only the spectral behavior of turbulent fluctuations but also their topology and scale behavior inferred from advanced mathematical algorithms and geometrical-like analogs. STORM started in January 2013 and ended in December 2015. We will report on a selection of scientific and technical achievements and will highlight: (1) the radial evolution of solar wind turbulence and intermittency based on Ulysses data with some contributions from Venus Express and Cluster; (2) comparative study of fast and slow wind turbulence and intermittency at solar minimum; (3) comparative study of the planetary response (Venus and Earth magnetosheaths) to turbulent solar wind; (4) the critical behavior of geomagnetic fluctuations and indices; (5) an integrated library for non-linear analysis of time series that includes all the approaches adopted in STORM to investigate solar system plasma turbulence. STORM delivers an unprecedented volume of analysed data for turbulence. The project made indeed a systematic survey, orbit by orbit, of data available from ESA repositories and Principal Investigators and provides results ordered as a
Dynamics of Turbulence Suppression in a Helicon Plasma
NASA Astrophysics Data System (ADS)
Hayes, Tiffany; Gilmore, Mark
2012-10-01
Experiments are currently being conducted in the the Helicon-Cathode Device (HelCat) at the University of New Mexico. The goal is to the study in detail the transition from a turbulent to a non-turbulent state in the presence of flow shear. HelCat has intrinsic fluctuations that have been identified as drift-waves. Using simple electrode biasing, it has been found that these fluctuations can be completely suppressed. In some extreme cases, a different instability, possibly the Kelvin-Helmholtz instability, can be excited. Detailed studies are underway in order to understand the characteristics of each mode, and to elucidate the underlying physics that cause the change between an unstable plasma, and an instability-free plasma. Dynamics being observed include changes in flow profiles, both azimuthal and parallel, as well as changes in potential and temperature gradients. Further understanding is being sought using several computer codes developed at EPFL: a linear stability solver (LSS,footnotetextP. Ricci and B.N. Rogers (2009). Phys Plasmas 16, 062303. a one-dimensional PIC code/sheath solver, ODISEE,footnotetextJ. Loizu, P. Ricci, and C. Theiler (2011). Phys Rev E 83, 016406 and a global, 3D Braginski code, GBS.footnotetextRicci, Rogers (2009) A basic overview of results will be presented.
Observation of Pedestal Plasma Turbulence on EAST Tokamak
NASA Astrophysics Data System (ADS)
Gao, Xiang; Zhang, Tao; Han, Xiang; Zhang, Shoubiao; Wang, Yumin; Liu, Zixi; Yang, Yao; Liu, Shaocheng; Shi, Nan; Ling, Bili; Li, Jiangang; The EAST Team
2013-08-01
Pedestal plasma turbulence was experimentally studied by microwave reflectometry on EAST tokamak. The characteristics of edge pedestal turbulence during dithering L-H transition, ELM-free H-mode phase and inter-ELM phase have recently been studied on EAST. An edge spatial structure of density fluctuation and its dithering temporal evolution is observed for the first time on the EAST tokamak during the L-H transition phase. A coherent mode usually appears during the ELM-free phase prior to the first ELM on EAST tokamak. The mode frequency gradually decreases as the pedestal evolves. Analysis shows that the coherent mode is in the pedestal region inside the separatrix. In plasma with type-III ELMs, a precursor mode before ELM is usually observed. The frequency of the precursor was initially about 150 kHz and gradually decreased till the next ELM. The mode amplitude increases or shows saturation before ELM. In the plasma with compound ELMs composed of high and low frequency ELMs, the precursor was also observed before the high frequency ELM while the harmonic oscillations with frequencies of 20 kHz, 40 kHz and 60 kHz appear before the low frequency ELM.
Length of magnetic field lines in turbulent plasmas.
Nunez, Manuel
2002-06-01
An estimation of the length of any magnetic field line in a two-dimensional periodic magnetohydrodynamic problem is provided. This is done by using some classical function theory results on the analytic extension of the vector potential. The essential parameter, the maximum of this extension, may be analyzed in the case of turbulent plasmas by admitting the Iroshnikov-Kraichnan statistics, establishing in this way a relation between the length of any magnetic field line and the energy dissipation scale. (c) 2002 American Institute of Physics.
Turbulent boundary-layer control with plasma actuators.
Choi, Kwing-So; Jukes, Timothy; Whalley, Richard
2011-04-13
This paper reviews turbulent boundary-layer control strategies for skin-friction reduction of aerodynamic bodies. The focus is placed on the drag-reduction mechanisms by two flow control techniques-spanwise oscillation and spanwise travelling wave, which were demonstrated to give up to 45 per cent skin-friction reductions. We show that these techniques can be implemented by dielectric-barrier discharge plasma actuators, which are electric devices that do not require any moving parts or complicated ducting. The experimental results show different modifications to the near-wall structures depending on the control technique.
Transport equation for plasmas in a stationary-homogeneous turbulence
Wang, Shaojie
2016-02-15
For a plasma in a stationary homogeneous turbulence, the Fokker-Planck equation is derived from the nonlinear Vlasov equation by introducing the entropy principle. The ensemble average in evaluating the kinetic diffusion tensor, whose symmetry has been proved, can be computed in a straightforward way when the fluctuating particle trajectories are provided. As an application, it has been shown that a mean parallel electric filed can drive a particle flux through the Stokes-Einstein relation, independent of the details of the fluctuations.
NASA Astrophysics Data System (ADS)
Retinò, Alessandro
2016-04-01
The Universe is permeated by hot, turbulent magnetized plasmas. They are found in active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, as well as in the solar corona, the solar wind and the Earth's magnetosphere. Turbulent plasmas are also found in laboratory devices such as e.g. tokamaks. Our comprehension of the plasma Universe is largely based on measurements of electromagnetic radiation such as light or X-rays which originate from particles that are heated and accelerated as a result of energy dissipation in turbulent environments. Therefore it is of key importance to study and understand how plasma is energized by turbulence. Most of the energy dissipation occurs at kinetic scales, where plasma no longer behaves as a fluid and the properties of individual plasma species (electrons, protons and other ions) become important. THOR (Turbulent Heating ObserveR - http://thor.irfu.se/) is a space mission currently in Study Phase as candidate for M-class mission within the Cosmic Vision program of the European Space Agency. The scientific theme of the THOR mission is turbulent energy dissipation and particle energization in space plasmas, which ties in with ESA's Cosmic Vision science. The main focus is on turbulence and shock processes, however areas where the different fundamental processes interact, such as reconnection in turbulence or shock generated turbulence, are also of high importance. The THOR mission aims to address fundamental questions such as how plasma is heated and particles are accelerated by turbulent fluctuations at kinetic scales, how energy is partitioned among different plasma components and how dissipation operates in different regimes of turbulence. To reach the goal, a careful design of the THOR spacecraft and its payload is ongoing, together with a strong interaction with numerical simulations. Here we present the science of THOR mission and we discuss implications of THOR observations for space
Galactic Cosmic Rays in the Outer Heliosphere
NASA Technical Reports Server (NTRS)
Florinski, V.; Washimi, H.; Pogorelov, N. V.; Adams, J. H.
2010-01-01
We report a next generation model of galactic cosmic ray (GCR) transport in the three dimensional heliosphere. Our model is based on an accurate three-dimensional representation of the heliospheric interface. This representation is obtained by taking into account the interaction between partially ionized, magnetized plasma flows of the solar wind and the local interstellar medium. Our model reveals that after entering the heliosphere GCRs are stored in the heliosheath for several years. The preferred GCR entry locations are near the nose of the heliopause and at high latitudes. Low-energy (hundreds of MeV) galactic ions observed in the heliosheath have spent, on average, a longer time in the solar wind than those observed in the inner heliosphere, which would explain their cooled-off spectra at these energies. We also discuss radial gradients in the heliosheath and the implications for future Voyager observations
Dependence of Turbulence Spatial Correlation Lengths on Plasma Rotation
NASA Astrophysics Data System (ADS)
Parisi, Jason; Barnes, Michael; Parra, Felix I.; Roach, Colin M.
2015-11-01
We present the results from nonlinear gyrokinetic simulations in GS2 to investigate the parallel and perpendicular correlation lengths of electrostatic turbulence in tokamak plasmas with rotation. These correlation lengths are characterised for a range of parameters, including the E × B shear, γE. We observe that the correlation lengths decrease as γE increases. Simulation results are compared against scaling laws deduced from the critical balance conjecture, which states that nonlinear perpendicular decorrelation times and parallel streaming times are comparable at all spatial scales. This work received funding from Euratom grant agreement No 633053 and from the RCUK Energy Programme [grant number EP/I501045], and gyrokinetic calculations were performed on ARCHER via the Plasma HEC Consortium [EPSRC Grant No.EP/L000237/1].
Structures and turbulent relaxation in non-neutral plasmas
NASA Astrophysics Data System (ADS)
Romé, M.; Chen, S.; Maero, G.
2017-01-01
The transverse dynamics of a magnetized pure electron plasma confined in a Penning-Malmberg trap is analogous to that of a two-dimensional (2D) ideal fluid. The dynamics of a system in a regime of external forcing due to the application of time-dependent potentials on different azimuthal sectors of the confining circular wall is studied numerically by means of 2D particle-in-cell simulations. The evolution of turbulence starting from an annular initial density distribution is investigated for different kinds and parameters of forcing by means of wavelet-based multiresolution analysis. From an experimental point of view, the analyzed forcing technique is useful to excite or damp different diocotron perturbations and therefore for the control and manipulation of plasma evolution. Nonetheless, the numerical results indicate that even in a weak forcing regime the system evolution is sensitive to small initial density fluctuations.
Shear Alfvén waves in turbulent plasmas.
Núñez, Manuel
2002-03-01
The rate of decay of shear Alfvén waves along a magnetic field line of a diffusive plasma grows with the number of nodes of the initial perturbation. It is reasonable to think that the energy dissipation produced by this decay will be small if the perturbation was localized in a small set. This does not happen in turbulent plasmas: transport of the oscillation by the flow involves the whole domain. A general relation is obtained proving that the global energy dissipation is bounded below by an exponential of the number of nodes of any shear Alfvén wave along a segment of any field line of the average magnetic field.
Turbulent convective flows in the solar photospheric plasma
NASA Astrophysics Data System (ADS)
Caroli, A.; Giannattasio, F.; Fanfoni, M.; Del Moro, D.; Consolini, G.; Berrilli, F.
2015-10-01
> The origin of the 22-year solar magnetic cycle lies below the photosphere where multiscale plasma motions, due to turbulent convection, produce magnetic fields. The most powerful intensity and velocity signals are associated with convection cells, called granules, with a scale of typically 1 Mm and a lifetime of a few minutes. Small-scale magnetic elements (SMEs), ubiquitous on the solar photosphere, are passively transported by associated plasma flows. This advection makes their traces very suitable for defining the convective regime of the photosphere. Therefore the solar photosphere offers an exceptional opportunity to investigate convective motions, associated with compressible, stratified, magnetic, rotating and large Rayleigh number stellar plasmas. The magnetograms used here come from a Hinode/SOT uninterrupted 25-hour sequence of spectropolarimetric images. The mean-square displacement of SMEs has been modelled with a power law with spectral index . We found for times up to and for times up to . An alternative way to investigate the advective-diffusive motion of SMEs is to look at the evolution of the two-dimensional probability distribution function (PDF) for the displacements. Although at very short time scales the PDFs are affected by pixel resolution, for times shorter than the PDFs seem to broaden symmetrically with time. In contrast, at longer times a multi-peaked feature of the PDFs emerges, which suggests the non-trivial nature of the diffusion-advection process of magnetic elements. A Voronoi distribution analysis shows that the observed small-scale distribution of SMEs involves the complex details of highly nonlinear small-scale interactions of turbulent convective flows detected in solar photospheric plasma.
Plasma turbulence measured with fast frequency swept reflectometry in JET H-mode plasmas
NASA Astrophysics Data System (ADS)
Clairet, F.; Sirinelli, A.; Meneses, L.; Contributors, JET
2016-12-01
In this work we present recent achievements to provide precise measurements of turbulence on JET H-mode plasmas using frequency sweeping reflectometry diagnostic. The plasma density fluctuations retrieved from swept reflected signals, first initiated with the Tore Supra reflectometry (Heuraux et al 2003 Rev. Sci. Instrum. 74 1501, Vermare et al 2006 Nucl. Fusion 46 S743, Gerbaud et al 2006 Rev. Sci. Instrum. 77 10E928), provides a radial profile of the density fluctuation level and its spectral structure. Using the complete set of the JET X-mode fast sweeping heterodyne reflectometers we have determined the temporal dynamic of the density fluctuation profile from the edge to the center during an H-mode discharge. At the L-H transition, the turbulence reduction seems to occur, at first, simultaneously from the edge to the center then deepens at the edge at ρ ~ 0.95 and this deepening propagates toward the center with a steepening of the wavenumber spectra. During an edge localized mode (ELM) event, a substantial density fluctuations increase has been observed with a localized turbulent wave front propagating toward the center accompanying a particle transport. We also show that type-III ELMs sustain a steady and high level of plasma turbulence compare to type-I.
Plasma flow, turbulence and magnetic islands in TJ-II
NASA Astrophysics Data System (ADS)
Estrada, T.; Ascasíbar, E.; Blanco, E.; Cappa, A.; Hidalgo, C.; Ida, K.; López-Fraguas, A.; van Milligen, B. Ph
2016-02-01
The effect of magnetic islands on plasma flow and turbulence has been experimentally investigated in ohmically induced magnetic configuration scans at the stellarator TJ-II. This operational mode allows sweeping the radial position of a low order rational surface from the plasma core towards the edge in a controlled way, what reveals effects that are difficult to notice in scans performed on a shot to shot basis. The main diagnostic used in the present work is a two-channel Doppler reflectometer that allows the measurement of the perpendicular rotation velocity of the turbulence and density fluctuations with good spatial and temporal resolution. A characteristic signature of the n/m = 3/2 magnetic island as it crosses the measurement position is clearly detected: the perpendicular flow reverses at the center of the magnetic island and a flow shear develops at the island boundaries. Fluctuations of the perpendicular flow and density have been also measured along the 3/2 magnetic island. An increase in the low frequency flow oscillations is measured at the magnetic island boundaries together with a reduction in the density fluctuation level; the later being more pronounced at the inner island boundary. These observations could explain the link between magnetic islands and transport barriers observed in a number of fusion devices.
Transition of energy transfer from MHD turbulence to kinetic plasma
NASA Astrophysics Data System (ADS)
Yang, Yan; Matthaeus, William; Parashar, Tulasi; Shi, Yipeng; Wan, Minping; Chen, Shiyi
2016-11-01
The classical energy cascade scenario is of great importance in explaining the heating of corona and solar wind. One can envision that energy residing in large-scale fluctuations is transported to smaller scales where dissipation occurs and finally drives kinetic processes that absorb the energy flux and energize charged particles. Here we inquire how the cascade operates in a compressible plasma, and how the characteristics of energy transfer vary going from MHD to kinetic scales. When filtering MHD equations, we can get an apparent inertial range over which the conservative energy cascade occurs and the scale locality of energy transfer is similar to the cases of incompressible MHD turbulence. Pervasive shocks not only make a significant difference on energy cascade and magnetic amplification, but can also introduce considerable pressure dilation, a complement of viscous and ohmic dissipation that can trigger an alternative channel of the conversion between kinetic and internal energy. The procedure can also be applied to the Vlasov equation and kinetic simulation, in comparison with MHD turbulence, and is a good candidate to investigate the energy cascade process and the analogous role of the (tensor) pressure dilation in collisionless plasma.
A region of intense plasma wave turbulence on auroral field lines
NASA Technical Reports Server (NTRS)
Gurnett, D. A.; Frank, L. A.
1976-01-01
This report presents a detailed study of the plasma wave turbulence observed by HAWKEYE-1 and IMP-6 on high latitude auroral field lines and investigates the relationship of this turbulence to magnetic field and plasma measurements obtained in the same region.
Ion-cyclotron turbulence and diagonal double layers in a magnetospheric plasma
NASA Technical Reports Server (NTRS)
Liperovskiy, V. A.; Pudovkin, M. I.; Skuridin, G. A.; Shalimov, S. L.
1981-01-01
A survey of current concepts regarding electrostatic ion-cyclotron turbulence (theory and experiment), and regarding inclined double potential layers in the magnetospheric plasma is presented. Anomalous resistance governed by electrostatic ion-cyclotron turbulence, and one-dimensional and two-dimensional models of double electrostatic layers in the magnetospheric plasma are examined.
Virtual Energetic Particle Observatory for the Heliospheric Data Environment
NASA Technical Reports Server (NTRS)
Cooper, J. F.; Armstrong, T. P.; Hill, M. E.; Lal, N.; McGuire, R. E.; McKibben, R. B.; Narock, T. W.; Szabo, A.; Tranquille, C.
2007-01-01
The heliosphere is pervaded by interplanetary energetic particles, traditionally also called cosmic rays, from solar, internal heliospheric, and galactic sources. The particles species of interest to heliophysics extend from plasma energies to the GeV energies of galactic cosmic rays still measurably affected by heliospheric modulation and the still higher energies contributing to atmospheric ionization. The NASA and international Heliospheric Network of operational and legacy spacecraft measures interplanetary fluxes of these particles. Spatial coverage extends from the inner heliosphere and geospace to the heliosheath boundary region now being traversed by Voyager 1 and soon by Voyager 2. Science objectives include investigation of solar flare and coronal mass ejection events, acceleration and transport of interplanetary particles within the inner heliosphere, cosmic ray interactions with planetary surfaces and atmospheres, sources of suprathermal and anomalous cosmic ray ions in the outer heliosphere, and solar cycle modulation of galactic cosmic rays. The Virtual Energetic Particle Observatory (VEPO) will improve access and usability of selected spacecraft and sub-orbital NASA heliospheric energetic particle data sets as a newly approved effort within the evolving heliophysics virtual observatory environment. In this presentation, we will describe current VEPO science requirements, our initial priorities and an overview of our strategy to implement VEPO rapidly and at minimal cost by working within the high-level framework of the Virtual Heliospheric Observatory (VHO). VEPO will also leverage existing data services of NASA's Space Physics Data Facility and other existing capabilities of the U.S. and international heliospheric research communities.
Electromagnetic turbulence and transport in increased β LAPD Plasmas
NASA Astrophysics Data System (ADS)
Rossi, Giovanni; Carter, Troy; Pueschel, Mj; Jenko, Frank; Terry, Paul; Told, Daniel
2016-10-01
The new LaB6 plasma source in LAPD has enabled the production of magnetized, increased Î² plasmas (up to 15%). We report on the modifications of pressure-gradient-driven turbulence and transport with increased plasma Î². Density fluctuations decrease with increasing Î² while magnetic fluctuations increase. B ⊥ fluctuations saturate while parallel (compressional) magnetic fluctuations increase continuously with β. At the highest β values Î δ ||/ δ B ⊥ 2 and δ B/B 1%. The measurements are consistent with the excitation of the Gradient-driven Drift Coupling (GDC). This instability prefers k|| = 0 and grows in finite β plasmas due to density and temperature gradients through the production of parallel magnetic field fluctuations and resulting ⊥ B|| drifts. Comparisons between experimental measurements and theoretical predictions for the GDC will be shown. Direct measurements of electrostatic particle flux have been performed and show a strong reduction with increasing β. No evidence is found (e.g. density profile shape) of enhanced confinement, suggesting that other transport mechanisms are active. Preliminary measurements indicate that electromagnetic transport due to parallel magnetic field fluctuations at first increases with β but is subsequently suppressed at higher β values.
Perspectives of future observations on particle acceleration in the heliosphere
NASA Technical Reports Server (NTRS)
Moebius, Eberhard
1992-01-01
The development of the quantitative study of particle acceleration processes in the outer heliosphere into the foreseeable future is outlined. In the near future, the combination of spacecraft, new improved instrumentation, and powerful plasma simulations are expected to enhance the understanding of acceleration processes in the near-earth environment, on the sun, and in the outer heliosphere. The multispacecraft mission CLUSTER will allow the most detailed view of the bow shock, while spacecraft passing through various regions of the inner and outer heliosphere are to provide the large-scale view needed to understand the heliospheric boundary. Improvements in ionic charge resolution and collecting power are to elucidate fractionation processes.
Anisotropy of the energetic neutral atom flux in the heliosphere
NASA Technical Reports Server (NTRS)
Gruntman, Michael A.
1992-01-01
Characteristics of the energetic neutral atoms born at the heliospheric interface are considered for plasma flow structure resulting from a two-shock model of the interaction between the solar wind and the interstellar medium. The energy distributions of heliospheric energetic neutral atoms (HELENAs) are calculated and it is shown that the HELENA flux is highly anisotropic at the earth's orbit. The characteristics of the HELENA flux are highly sensitive to the size of the heliosphere. This supports the conclusion that measurements of HELENAs from the earth's orbit would provide an efficient tool to remotely study the heliosphere.
Shukla-Spatschek diffusion effects on surface plasma waves in astrophysical turbulent plasmas
NASA Astrophysics Data System (ADS)
Lee, Myoung-Jae; Jung, Young-Dae
2017-02-01
The effects of Shukla-Spatschek turbulent diffusion on a temporal mode of surface waves propagating at the interface of an astrophysical turbulent plasma are investigated. The damping rates for high and low modes of surface wave are kinetically derived by employing the Vlasov-Poisson equation and the specular reflection boundary condition. We found that the diffusion caused by the fluctuating electric fields leads to damping for both high and low modes of surface waves. The high-mode damping is enhanced with an increase of the wavenumber and the diffusion coefficient, but suppressed by an increase of electron thermal energy. By contrast, the low-mode damping is suppressed as the wavenumber and the thermal energy increase although it is enhanced as the diffusion increases. The variation of the damping rate due to the Shukla-Spatschek turbulent diffusion is also discussed.
Three-Fluid Magnetohydrodynamic Modeling of the Solar Wind in the Outer Heliosphere
NASA Technical Reports Server (NTRS)
Usmanov, Arcadi V.; Goldstein, Melvyn L.; Matthaeus, William H.
2011-01-01
We have developed a three-fluid, fully three-dimensional magnetohydrodynamic model of the solar wind plasma in the outer heliosphere as a co-moving system of solar wind protons, electrons, and interstellar pickup protons, with separate energy equations for each species. Our approach takes into account the effects of electron heat conduction and dissipation of Alfvenic turbulence on the spatial evolution of the solar wind plasma and interplanetary magnetic fields. The turbulence transport model is based on the Reynolds decomposition of physical variables into mean and fluctuating components and uses the turbulent phenomenologies that describe the conversion of fluctuation energy into heat due to a turbulent cascade. We solve the coupled set of the three-fluid equations for the mean-field solar wind and the turbulence equations for the turbulence energy, cross helicity, and correlation length. The equations are written in the rotating frame of reference and include heating by turbulent dissipation, energy transfer from interstellar pickup protons to solar wind protons, and solar wind deceleration due to the interaction with the interstellar hydrogen. The numerical solution is constructed by the time relaxation method in the region from 0.3 to 100 AU. Initial results from the novel model are presented.
Turbulence and bias-induced flows in simple magnetized toroidal plasmas
Li, B.; Rogers, B. N.; Ricci, P.; Gentle, K. W.; Bhattacharjee, A.
2011-05-15
Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three-dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows.These bias-induced vertical flows located in the gradient region appear to reduce the radial extent of turbulent structures,and thereby lower the radial plasma transport on the low field side.
Subgrid-scale modeling for the study of compressible magnetohydrodynamic turbulence in space plasmas
NASA Astrophysics Data System (ADS)
Chernyshov, A. A.; Karelsky, K. V.; Petrosyan, A. S.
2014-05-01
A state-of-the-art review is given of research by computing physics methods on compressible magnetohydrodynamic turbulence in space plasmas. The presence of magnetic fields and compressibility in this case makes space plasma turbulence much less amenable to direct numerical simulations than a neutral incompressible fluid. The large eddy simulation method is discussed, which was developed as an alternative to direct modeling and which filters the initial magnetohydrodynamic equations and uses the subgrid-scale modeling of universal small-scale turbulence. A detailed analysis is made of both the method itself and different subgrid-scale parametrizations for compressible magnetohydrodynamic turbulent flows in polytropic and heat-conducting plasmas. The application of subgrid-scale modeling to study turbulence in the local interstellar medium and the scale-invariant spectra of magnetohydrodynamic turbulence are discussed.
Effects of Plasma Shaping on Nonlinear Gyrokinetic Turbulence
E. A. Belli; Hammett, G. W.; Dorland, W.
2008-08-01
The effects of flux surface shape on the gyrokinetic stability and transport of tokamak plasmas are studied using the GS2 code [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. 88, 128 (1995); W. Dorland, F. Jenko, M. Kotschenreuther, and B.N. Rogers, Phys. Rev. Lett. 85, 5579 (2000)]. Studies of the scaling of nonlinear turbulence with shaping parameters are performed using analytic equilibria based on interpolations of representative shapes of the Joint European Torus (JET) [P.H. Rebut and B.E. Keen, Fusion Technol. 11, 13 (1987)]. High shaping is found to be a stabilizing influence on both the linear ion-temperature-gradient (ITG) instability and the nonlinear ITG turbulence. For the parameter regime studied here, a scaling of the heat flux with elongation of χ ~ κ^{-1.5} or κ^{-2.0}, depending on the triangularity, is observed at fixed average temperature gradient. While this is not as strong as empirical elongation scalings, it is also found that high shaping results in a larger Dimits upshift of the nonlinear critical temperature gradient due to an enhancement of the Rosenbluth-Hinton residual zonal flows.
Magnetorotational Turbulence and Dynamo in a Collisionless Plasma
NASA Astrophysics Data System (ADS)
Kunz, Matthew W.; Stone, James M.; Quataert, Eliot
2016-12-01
We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disk. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. These results have implications for the properties of low-collisionality accretion flows, such as that near the black hole at the Galactic center.
Magnetorotational Turbulence and Dynamo in a Collisionless Plasma.
Kunz, Matthew W; Stone, James M; Quataert, Eliot
2016-12-02
We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disk. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. These results have implications for the properties of low-collisionality accretion flows, such as that near the black hole at the Galactic center.
Two dimensional turbulence in inviscid fluids or guiding center plasmas
NASA Technical Reports Server (NTRS)
Seyler, C. E., Jr.; Salu, Y.; Montgomery, D.; Knorr, G.
1975-01-01
Analytic theory for two-dimensional turbulent equilibria for the inviscid Navier-Stokes equations is examined mathematically. Application of the technique to electrostatic guiding center plasma is discussed. A good fit is demonstrated for the approach to a predicted energy per Fourier mode obtained from a two-temperature canonical ensemble. Negative as well as positive temperature regimes are explored. Fluctuations about the mean energy per mode also compare well with theory. In the regime of alpha less than zero, beta greater than zero, with the minimum value of alpha plus beta times k squared near zero, contour plots of the stream function reveal macroscopic vortex structures similar to those seen previously in discrete vortex simulations. Eulerian direct interaction equations, which can be used to follow the approach to inviscid equilibrium, are derived.
Kinetic theory of weak turbulence in magnetized plasmas: Perpendicular propagation
Yoon, Peter H.
2015-08-15
The present paper formulates a weak turbulence theory in which electromagnetic perturbations are assumed to propagate in directions perpendicular to the ambient magnetic field. By assuming that all wave vectors lie in one direction transverse to the ambient magnetic field, the linear solution and second-order nonlinear solutions to the equation for the perturbed distribution function are obtained. Nonlinear perturbed current from the second-order nonlinearity is derived in general form, but the limiting situation of cold plasma temperature is taken in order to derive an explicit nonlinear wave kinetic equation that describes three-wave decay/coalescence interactions among X and Z modes. A potential application of the present formalism is also discussed.
MHD processes in the outer heliosphere
NASA Technical Reports Server (NTRS)
Burlaga, L. F.
1984-01-01
The magnetic field measurements from Voyager and the magnetohydrodynamic (MHD) processes in the outer heliosphere are reviewed. A bibliography of the experimental and theoretical work concerning magnetic fields and plasmas observed in the outer heliosphere is given. Emphasis in this review is on basic concepts and dynamical processes involving the magnetic field. The theory that serves to explain and unify the interplanetary magnetic field and plasma observations is magnetohydrodynamics. Basic physical processes and observations that relate directly to solutions of the MHD equations are emphasized, but obtaining solutions of this complex system of equations involves various assumptions and approximations. The spatial and temporal complexity of the outer heliosphere and some approaches for dealing with this complexity are discussed.
NASA Astrophysics Data System (ADS)
Opher, M.; Drake, J. F.; Zieger, B.; Michael, A.; Toth, G.; Swisdak, M.; Gombosi, T. I.
2015-12-01
Recently we proposed (Opher et al. 2015) that the structure of the heliosphere might be very different than we previously thought. The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun's travel through the interstellar medium (ISM) extending for thousands of astronomical units. We have shown, based on magnetohydrodynamic (MHD) simulations, that the tension force of the twisted magnetic field of the Sun confines the solar wind plasma beyond the termination shock and drives jets to the north and south very much like astrophysical jets. These heliospheric jets are deflected into the tail region by the motion of the Sun through the ISM. As in some astrophysical jets the interstellar wind blows the two jets into the tail but is not strong enough to force the lobes into a single comet-like tail. Instead, the interstellar wind flows around the heliosphere and into the equatorial region between the two jets. We show that the heliospheric jets are turbulent (due to large-scale MHD instabilities and reconnection) and strongly mix the solar wind with the ISM. The resulting turbulence has important implications for particle acceleration in the heliosphere. The two-lobe structure is consistent with the energetic neutral atom (ENA) images of the heliotail from IBEX where two lobes are visible in the north and south and the suggestion from the Cassini ENAs that the heliosphere is "tailless." The new structure of the heliosphere is supported by recent analytic work (Drake et al. 2015) that shows that even in high β heliosheath the magnetic field plays a crucial role in funneling the solar wind in two jets. Here we present these recent results and show that the heliospheric jets mediate the draping of the magnetic field and the conditions ahead of the heliopause. We show that reconnection between the interstellar and solar magnetic field both at the flanks of the jets and in between them twist the interstellar magnetic
Meinecke, Jena; Tzeferacos, Petros; Bell, Anthony; Bingham, Robert; Clarke, Robert; Churazov, Eugene; Crowston, Robert; Doyle, Hugo; Drake, R. Paul; Heathcote, Robert; Koenig, Michel; Kuramitsu, Yasuhiro; Kuranz, Carolyn; Lee, Dongwook; MacDonald, Michael; Murphy, Christopher; Notley, Margaret; Park, Hye-Sook; Pelka, Alexander; Ravasio, Alessandra; Reville, Brian; Sakawa, Youichi; Wan, Willow; Woolsey, Nigel; Yurchak, Roman; Miniati, Francesco; Schekochihin, Alexander; Lamb, Don; Gregori, Gianluca
2015-01-01
The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe. PMID:26100873
Meinecke, Jena; Tzeferacos, Petros; Bell, Anthony; Bingham, Robert; Clarke, Robert; Churazov, Eugene; Crowston, Robert; Doyle, Hugo; Drake, R Paul; Heathcote, Robert; Koenig, Michel; Kuramitsu, Yasuhiro; Kuranz, Carolyn; Lee, Dongwook; MacDonald, Michael; Murphy, Christopher; Notley, Margaret; Park, Hye-Sook; Pelka, Alexander; Ravasio, Alessandra; Reville, Brian; Sakawa, Youichi; Wan, Willow; Woolsey, Nigel; Yurchak, Roman; Miniati, Francesco; Schekochihin, Alexander; Lamb, Don; Gregori, Gianluca
2015-07-07
The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe.
Kobayashi, T.; Inagaki, S.; Sasaki, M.; Nagashima, Y.; Kasuya, N.; Fujisawa, A.; Itoh, S.-I.; Kosuga, Y.; Arakawa, H.; Yamada, T.; Miwa, Y.; Itoh, K.
2015-11-15
Fluctuation component in the turbulence regime is found to be azimuthally localized at a phase of the global coherent modes in a linear magnetized plasma PANTA. Spatial distribution of squared bicoherence is given in the azimuthal cross section as an indicator of nonlinear energy transfer function from the global coherent mode to the turbulence. Squared bicoherence is strong at a phase where the turbulence amplitude is large. As a result of the turbulence localization, time evolution of radial particle flux becomes bursty. Statistical features such as skewness and kurtosis are strongly modified by the localized turbulence component, although contribution to mean particle flux profile is small.
Interhelioprobe Mission for Solar and Heliospheric Studies
NASA Astrophysics Data System (ADS)
Kuznetsov, Vladimir; Zelenyi, Lev; Zimovets, Ivan
2016-07-01
A new concept has been adopted for the Interhelioprobe mission intended for studying the inner heliosphere and the Sun at short distances and from out-of-ecliptic positions. In accordance with this concept, two identical SC spaced by a quarter of a period on heliocentric orbits inclined to the ecliptic plane in different directions will orbit the Sun, thus ensuring continuous out-of-ecliptic solar observations and measurements in the heliosphere. The scientific payload will comprise instruments for remote observations of the Sun (Optical photometer, Magnetograph, Chemical Composition Analyzer, EUV Imager-Spectrometer, Coronagraph, X-ray Imager, Heliospheric Imager, X-ray Polarimeter, and Gamma-Spectrometers) and in-situ measurements in the heliosphere (Solar Wind Ion Analyzer, Solar Wind Electron Analyzer, Solar Wind Plasma Analyzers, Energetic Particle Telescope, Neutron Detector, Magnetic Wave Complex, Magnetometer, and Radio Spectrometer Detector). The instruments will study the structure and dynamics of the magnetic fields and plasma flows in the polar regions of the Sun, solar flares and mass ejections, the heating of the solar corona and solar wind acceleration, acceleration and propagation of energetic particles in the Sun and heliosphere, the solar wind, as well as disturbances and ejections that come from the Sun to the Earth and control space weather in the near-Earth space. The schedule of the mission and the development status of the instruments and the spacecraft are provided.
Weck, P J; Schaffner, D A; Brown, M R; Wicks, R T
2015-02-01
The Bandt-Pompe permutation entropy and the Jensen-Shannon statistical complexity are used to analyze fluctuating time series of three different turbulent plasmas: the magnetohydrodynamic (MHD) turbulence in the plasma wind tunnel of the Swarthmore Spheromak Experiment (SSX), drift-wave turbulence of ion saturation current fluctuations in the edge of the Large Plasma Device (LAPD), and fully developed turbulent magnetic fluctuations of the solar wind taken from the Wind spacecraft. The entropy and complexity values are presented as coordinates on the CH plane for comparison among the different plasma environments and other fluctuation models. The solar wind is found to have the highest permutation entropy and lowest statistical complexity of the three data sets analyzed. Both laboratory data sets have larger values of statistical complexity, suggesting that these systems have fewer degrees of freedom in their fluctuations, with SSX magnetic fluctuations having slightly less complexity than the LAPD edge I(sat). The CH plane coordinates are compared to the shape and distribution of a spectral decomposition of the wave forms. These results suggest that fully developed turbulence (solar wind) occupies the lower-right region of the CH plane, and that other plasma systems considered to be turbulent have less permutation entropy and more statistical complexity. This paper presents use of this statistical analysis tool on solar wind plasma, as well as on an MHD turbulent experimental plasma.
Whalley, Richard D.; Walsh, James L.
2016-01-01
Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence. PMID:27561246
Whalley, Richard D; Walsh, James L
2016-08-26
Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence.
NASA Astrophysics Data System (ADS)
Whalley, Richard D.; Walsh, James L.
2016-08-01
Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence.
The time evolution of turbulent parameters in reversed-field pinch plasmas
Titus, J. B.; Alexander, Brandon; Johnson, J. A. III
2013-04-28
Turbulence is abundant in fully ionized fusion plasmas, with unique turbulent characteristics in different phases of the discharge. Using Fourier and chaos-based techniques, a set of parameters have been developed to profile the time evolution of turbulence in high temperature, fusion plasmas, specifically in self-organized, reversed-field pinch plasma in the Madison Symmetric Torus. With constant density and plasma current, the turbulence profile is measured during ramp-up, magnetic reconnection, and increased confinement phases. During magnetic reconnection, a scan of plasma current is performed with a constant density. Analysis revealed that the energy associated with turbulence (turbulent energy) is found to increase when changes in magnetic energy occur and is correlated to edge ion temperatures. As the turbulent energy increases with increasing current, the rate at which this energy flow between scales (spectral index) and anti-persistence of the fluctuations increases (Hurst exponent). These turbulent parameters are then compared to the ramp-up phase and increased confinement regime.
Scattering of radio frequency waves by turbulence in fusion plasmas
NASA Astrophysics Data System (ADS)
Ram, Abhay K.
2016-10-01
In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments and incoherent fluctuations due to turbulence are routinely observed in the scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the scrape-off layer before reaching the core of the plasma. While the effect of fluctuations on RF waves has not been quantified experimentally, there are telltale signs, arising from differences between results from simulations and from experiments, that fluctuations can modify the spectrum of RF waves. Any effect on RF waves in the scrape-off layer can have important experimental consequences. For example, electron cyclotron waves are expected to stabilize the deleterious neoclassical tearing mode (NTM) in ITER. Spectral and polarization changes due to scattering will modify the spatial location and profile of the current driven by the RF waves, thereby affecting the control of NTMs. Pioneering theoretical studies and complementary computer simulations have been pursued to elucidate the impact of fluctuations on RF waves. From the full complement of Maxwell's equations for cold, magnetized plasmas, it is shown that the Poynting flux in the wake of filaments develops spatial structure due to diffraction and shadowing. The uniformity of power flow into the plasma is affected by side-scattering, modifications to the wave spectrum, and coupling to plasma waves other than the incident RF wave. The Snell's law and the Fresnel equations have been reformulated within the context of magnetized plasmas. They are distinctly different from their counterparts in scalar dielectric media, and reveal new and important physical insight into the scattering of RF waves. The Snell's law and Fresnel equations are the basis for the Kirchhoff approximation necessary to determine properties of the scattered waves. Furthermore, this theory is also relevant for studying back
Investigation of turbulence in reversed field pinch plasma by using microwave imaging reflectometry
Shi, Z. B.; Nagayama, Y.; Hamada, Y.; Yamaguchi, S.; Hirano, Y.; Kiyama, S.; Koguchi, H.; Sakakita, H.; Michael, C. A.; Yambe, K.
2011-10-15
Turbulence in the reversed field pinch (RFP) plasma has been investigated by using the microwave imaging reflectometry in the toroidal pinch experiment RX (TPE-RX). In conventional RFP plasma, the fluctuations are dominated by the intermittent blob-like structures. These structures are accompanied with the generation of magnetic field, the strong turbulence, and high nonlinear coupling among the high and low k modes. The pulsed poloidal current drive operation, which improves the plasma confinement significantly, suppresses the dynamo, the turbulence, and the blob-like structures.
Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators
NASA Astrophysics Data System (ADS)
Singh, Ashish; Little, Jesse
2016-11-01
A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).
Turbulent relaxation and meta-stable equilibrium states of an electron plasma
NASA Astrophysics Data System (ADS)
Rodgers, Douglas J.
A Malmberg-Penning electron trap allows for the experimental study of nearly ideal, two-dimensional (2D) inviscid (Euler) hydrodynamics. This is perhaps the simplest case of self organizing nonlinear turbulence, and is therefore a paradigm for dynamo theory, Taylor relaxation, selective decay and other nonlinear fluid processes. The dynamical relaxation of a pure electron plasma in the guiding-center-drift approximation is studied, comparing experiments, numerical simulations and statistical theories of weakly-dissipative 2D turbulence. The nonuniform metastable equilibrium states resulting from turbulent evolution are examined, and are well-described by a maximum entropy principle for constrained circulation, energy, and angular momentum. The turbulent decay of the system is also examined, and a similarity decay law is proposed which incorporates the substantial enstrophy trapped in the metastable equilibrium. This law approaches Batchelor's t-2 self-similar decay in the limit of strong turbulence, and is verified in turbulent evolution in the electron plasma experiment.
Simulation of turbulence in the divertor region of tokamak edge plasma
NASA Astrophysics Data System (ADS)
Umansky, M. V.; Rognlien, T. D.; Xu, X. Q.
2005-03-01
Results are presented for turbulence simulations with the fluid edge turbulence code BOUT [X.Q. Xu, R.H. Cohen, Contr. Plas. Phys. 36 (1998) 158]. The present study is focussed on turbulence in the divertor leg region and on the role of the X-point in the structure of turbulence. Results of the present calculations indicate that the ballooning effects are important for the divertor fluctuations. The X-point shear leads to weak correlation of turbulence across the X-point regions, in particular for large toroidal wavenumber. For the saturated amplitudes of the divertor region turbulence it is found that amplitudes of density fluctuations are roughly proportional to the local density of the background plasma. The amplitudes of electron temperature and electric potential fluctuations are roughly proportional to the local electron temperature of the background plasma.
Heliophysics' finding of the 'squashed' heliosphere when Voyager 1 and 2 crossed the bubble of solar wind at different distances from the sun. This led to a change in the way we see the shape of ou...
Heliophysics describes the study of the Sun, its atmosphere or the heliosphere, and the planets within it as a system. This visualization tours areas from the Sun to the boundary between the Sun an...
NASA Astrophysics Data System (ADS)
Davidovits, Seth; Fisch, Nat
2016-10-01
Turbulent plasma flow, amplified by rapid 3D compression, can be suddenly dissipated under continuing compression. This sudden dissipation comes about because the plasma viscosity is very sensitive to temperature, μ T 5 / 2 . We discuss approaches to constructing simple models to capture the turbulence energy growth and dissipation during rapid plasma compressions. Additionally, we explore the effects on compressing turbulence of plasma ionization during compression, to which the viscosity is also very sensitive. We show plasma ionization during compression enables larger turbulence growth, compared to when there is no plasma ionization. Further, ionization during compression can prevent the sudden dissipation effect, and can also make the difference between increasing and decreasing turbulence energy under compression. The influence exerted by ionization opens up the prospect for control of turbulence growth and sudden dissipation timing through choice of the plasma ion species. This work was supported by DOE through Contracts No. DE-AC02-09CH1-1466 and NNSA 67350-9960 (Prime # DOE DE-NA0001836), by DTRA HDTRA1-11-1-0037, and by NSF Contract No. PHY-1506122.
Report of the cosmic and heliospheric panel
NASA Technical Reports Server (NTRS)
Mewaldt, Richard A.; Mason, Glenn M.; Barnes, Aaron; Binns, W. Robert; Burlaga, Leonard F.; Cherry, Michael L.; Holzer, Thomas E.; Jokipii, J. R.; Jones, Vernon; Ling, James C.
1991-01-01
The Cosmic and Heliospheric Branch proposes a bold new program for the years 1995 to 2010 that is centered on the following two themes: (1) the global heliosphere and interstellar space; and (2) cosmic particle acceleration and the evolution of matter. Within these major themes are more specific goals that have been studied and continue to be examined for a better understanding of their processes. These include: origin, structure, and evolution of the solar wind; interaction of the heliosphere, the solar wind, and the interstellar medium; fundamental microscopic and macroscopic plasma processes; acceleration and transport of energetic particles; and the origin and evolution of matter. Finally, the report summarizes a wide variety of proposed small and large space missions.
The role of the plasma current in turbulence decrease during lower hybrid current drive
NASA Astrophysics Data System (ADS)
Antar, G.; Ekedahl, A.; Goniche, M.; Asghar, A.; Žàček, F.
2017-03-01
The interaction of radio frequency (RF) waves with edge turbulence has resurfaced after the results obtained on many tokamaks showing that edge turbulence decreases when the ion cyclotron frequency heating (ICRH) is switched on. Using the lower hybrid (LH) waves to drive current into tokamak plasmas, this issue presented contradicting results with some tokamaks (FTU & HT-7) showing a net decrease, similar to the ICRH results, and others (Tore Supra) did not. In this article, these apparent discrepancies among tokamaks and RF wave frequencies are removed. It is found that turbulence large-scale structures in the scrape-off layer decrease at high enough plasma currents (Ip) on the Tore Supra tokamak. We distinguish three regimes: At low Ip's, no modification is detected with statistical properties of turbulence similar to ohmic plasmas even with PLH reaching 4.8 MW. At moderate plasma currents, turbulence properties are modified only at a high LH power. At high plasma currents, turbulent large scales are reduced to values smaller than 1 cm, and this is accompanied by a net decrease in the level of turbulence of about 30% even with a moderate LH power.
Ricci, P. Riva, F.; Theiler, C.; Fasoli, A.; Furno, I.; Halpern, F. D.; Loizu, J.
2015-05-15
In the present work, a Verification and Validation procedure is presented and applied showing, through a practical example, how it can contribute to advancing our physics understanding of plasma turbulence. Bridging the gap between plasma physics and other scientific domains, in particular, the computational fluid dynamics community, a rigorous methodology for the verification of a plasma simulation code is presented, based on the method of manufactured solutions. This methodology assesses that the model equations are correctly solved, within the order of accuracy of the numerical scheme. The technique to carry out a solution verification is described to provide a rigorous estimate of the uncertainty affecting the numerical results. A methodology for plasma turbulence code validation is also discussed, focusing on quantitative assessment of the agreement between experiments and simulations. The Verification and Validation methodology is then applied to the study of plasma turbulence in the basic plasma physics experiment TORPEX [Fasoli et al., Phys. Plasmas 13, 055902 (2006)], considering both two-dimensional and three-dimensional simulations carried out with the GBS code [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. The validation procedure allows progress in the understanding of the turbulent dynamics in TORPEX, by pinpointing the presence of a turbulent regime transition, due to the competition between the resistive and ideal interchange instabilities.
Influence of Dupree diffusivity on the occurrence scattering time advance in turbulent plasmas
Lee, Myoung-Jae; Jung, Young-Dae
2015-12-15
The influence of Dupree diffusivity on the occurrence scattering time advance for the electron-ion collision is investigated in turbulent plasmas. The second-order eikonal method and the effective Dupree potential term associated with the plasma turbulence are employed to obtain the occurrence scattering time as a function of the diffusion coefficient, impact parameter, collision energy, thermal energy, and Debye length. The result shows that the occurrence scattering time advance decreases with an increase of the Dupree diffusivity. Hence, we have found that the influence of plasma turbulence diminishes the occurrence time advance in forward electron-ion collisions in thermal turbulent plasmas. The occurrence time advance shows that the propensity of the occurrence time advance increases with increasing scattering angle. It is also found that the effect of turbulence due to the Dupree diffusivity on the occurrence scattering time advance decreases with an increase of the thermal energy. In addition, the variation of the plasma turbulence on the occurrence scattering time advance due to the plasma parameters is also discussed.
Electromagnetic gyrokinetic turbulence in finite-beta helical plasmas
Ishizawa, A.; Watanabe, T.-H.; Sugama, H.; Nakajima, N.; Maeyama, S.
2014-05-15
A saturation mechanism for microturbulence in a regime of weak zonal flow generation is investigated by means of electromagnetic gyrokinetic simulations. The study identifies a new saturation process of the kinetic ballooning mode (KBM) turbulence originating from the spatial structure of the KBM instabilities in a finite-beta Large Helical Device (LHD) plasma. Specifically, the most unstable KBM in LHD has an inclined mode structure with respect to the mid-plane of a torus, i.e., it has a finite radial wave-number in flux tube coordinates, in contrast to KBMs in tokamaks as well as ion-temperature gradient modes in tokamaks and helical systems. The simulations reveal that the growth of KBMs in LHD is saturated by nonlinear interactions of oppositely inclined convection cells through mutual shearing as well as by the zonal flow. The saturation mechanism is quantitatively investigated by analysis of the nonlinear entropy transfer that shows not only the mutual shearing but also a self-interaction with an elongated mode structure along the magnetic field line.
Feedback control of plasma instabilities with charged particle beams and study of plasma turbulence
NASA Technical Reports Server (NTRS)
Tham, Philip Kin-Wah
1994-01-01
. A plasma instability is usually observed in its saturated state and appears as a single feature in the frequency spectrum with a single azimuthal and parallel wavenumbers. The physics of the non-zero spectral width was investigated in detail because the finite spectral width can cause "turbulent" transport. One aspect of the "turbulence" was investigated by obtaining the scaling of the linear growth rate of the instabilities with the fluctuation levels. The linear growth rates were measured with the established gated feedback technique. The research showed that the ExB instability evolves into a quasi-coherent state when the fluctuation level is high. The coherent aspects were studied with a bispectral analysis. Moreover, the single spectral feature was discovered to be actually composed of a few radial harmonics. The radial harmonics play a role in the nonlinear saturation of the instability via three-wave coupling.
Turbulent fluctuations in the main core of TFTR plasmas with negative magnetic shear
Mazzucato, E.; Beer, M.; Bell, M.G.
1997-04-01
Turbulent fluctuations in plasmas with reversed magnetic shear have been investigated in TFTR. Under intense auxiliary heating, these plasmas are observed to bifurcate into two states with different transport properties. In the state with better confinement, it has been found that the level of fluctuations is very small throughout most of the region with negative shear. By contrast, the state with lower confinement is characterized by large bursts of fluctuations which suggest a competition between the driving and the suppression of turbulence. These results are consistent with the suppression of turbulence by the ExB velocity shear.
Intermittency, avalanche statistics, and long-term correlations in a turbulent plasma
NASA Astrophysics Data System (ADS)
Castellanos, Omar; López, Juan M.; Sentíes, José M.; Anabitarte, Ernesto
2013-04-01
We study the turbulent dynamics of a helium plasma in a non-confining cylindrical configuration. Our experimental setup allows us to analyze particle transport in different plasma regions. We find that, whereas the transport is diffusive in the innermost regions of the plasma, distinctive non-diffusive features appear in regions away from the center. Indeed, at the plasma edge we find that particle flux exhibits a power-law distribution of avalanche durations, intermittency, and long-term correlations.
Plasma turbulence in the equatorial ionospheric F region
NASA Astrophysics Data System (ADS)
McDaniel, Rickey Dale
Equatorial spread F is a spectacular phenomenon in which the equatorial region ionosphere is reshaped after sunset. The plasma instabilities responsible for equatorial spread F are fascinating since they occur on time scales ranging from seconds to hours and length scales from centimeters to tens of kilometers. The plasma irregularities that occur in the F region also influence the performance and reliability of space borne and ground based electronic systems and may cause the disruption of satellite operations, communications, navigation, and electrical power distribution grids, leading to potentially broad economic losses. The ionospheric model equations that describe these plasma instabilities display different dynamical behavior based on the value of the ion-neutral collision frequency. The transition occurs at the so-called inertial regime of the ionosphere, where the model equations are similar to the Navier Stokes equations except applied to inhomogeneous fluids. A general analytic solution does not exist for these nonlinear equations; however, a numerical model is developed by maintaining charge neutrality in the vicinity of a circular bubble rising from the collisional to the inertial regime. Using this model, we are able to determine the location of the inertial regime as a function of local time, longitude, season, and solar cycle. The model results determine that the regime occurs generally from about 2000 and 2100 local time and 500-900 km apex height. Also, the model predicts that solar minimum periods are generally more conducive for inertial effects than solar maximum periods. Time series analysis performed on Dynamics Explorer II ion density data show that a turbulent cascade form in the inertial regime predicted by the model. Intermediate scale density power spectra all obey k-5/3 spectra scaling when measured in altitude and local time windows predicted by our model as failing within the inertial regime. Meanwhile, density power spectra for data
NASA Astrophysics Data System (ADS)
Furno, I.; Fasoli, A.; Avino, F.; Bovet, A.; Gustafson, K.; Iraji, D.; Labit, B.; Loizu, J.; Ricci, P.; Theiler, C.
2012-04-01
TORPEX is a toroidal device located at the CRPP-EPFL in Lausanne. In TORPEX, a vertical magnetic field superposed on a toroidal field creates helicoidal field lines with both ends terminating on the torus vessel. The turbulence driven by magnetic curvature and plasma gradients causes plasma transport in the radial direction while at the same time plasma is progressively lost along the field lines. The relatively simple magnetic geometry and diagnostic access of the TORPEX configuration facilitate the experimental study of low frequency instabilities and related turbulent transport, and make an accurate comparison between simulations and experiments possible. We first present a detailed investigation of electrostatic interchange turbulence, associated structures and their effect on plasma using high-resolution diagnostics of plasma parameters and wave fields throughout the whole device cross-section, fluid models and numerical simulations. Interchange modes nonlinearly develop blobs, radially propagating filaments of enhanced plasma pressure. Blob velocities and sizes are obtained from probe measurements using pattern recognition and are described by an analytical expression that includes ion polarization currents, parallel sheath currents and ion-neutral collisions. Then, we describe recent advances of a non-perturbative Li 6+ miniaturized ion source and a detector for the investigation of the interaction between supra thermal ions and interchange-driven turbulence. We present first measurements of the spatial and energy space distribution of the fast ion beam in different plasma scenarios, in which the plasma turbulence is fully characterized. The experiments are interpreted using two-dimensional fluid simulations describing the low-frequency interchange turbulence, taking into account the plasma source and plasma losses at the torus vessel. By treating fast ions as test particles, we integrate their equations of motion in the simulated electromagnetic fields, and
Applications of continuous and orthogonal wavelet transforms to MHD and plasma turbulence
NASA Astrophysics Data System (ADS)
Farge, Marie; Schneider, Kai
2016-10-01
Wavelet analysis and compression tools are presented and different applications to study MHD and plasma turbulence are illustrated. We use the continuous and the orthogonal wavelet transform to develop several statistical diagnostics based on the wavelet coefficients. We show how to extract coherent structures out of fully developed turbulent flows using wavelet-based denoising and describe multiscale numerical simulation schemes using wavelets. Several examples for analyzing, compressing and computing one, two and three dimensional turbulent MHD or plasma flows are presented. Details can be found in M. Farge and K. Schneider. Wavelet transforms and their applications to MHD and plasma turbulence: A review. Support by the French Research Federation for Fusion Studies within the framework of the European Fusion Development Agreement (EFDA) is thankfully acknowledged.
Low Frequency Turbulence as the Source of High Frequency Waves in Multi-Component Space Plasmas
NASA Technical Reports Server (NTRS)
Khazanov, George V.; Krivorutsky, Emmanuel N.; Uritsky, Vadim M.
2011-01-01
Space plasmas support a wide variety of waves, and wave-particle interactions as well as wavewave interactions are of crucial importance to magnetospheric and ionospheric plasma behavior. High frequency wave turbulence generation by the low frequency (LF) turbulence is restricted by two interconnected requirements: the turbulence should be strong enough and/or the coherent wave trains should have the appropriate length. These requirements are strongly relaxed in the multi-component plasmas, due to the heavy ions large drift velocity in the field of LF wave. The excitation of lower hybrid waves (LHWs), in particular, is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves, in particular those associated with LF turbulence, may generate LHW s in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We also argue that the described scenario can playa vital role in various parts of the outer magnetosphere featuring strong LF turbulence accompanied by LHW activity. Using the data from THEMIS spacecraft, we validate the conditions for such cross-scale coupling in the near-Earth "flow-braking" magnetotail region during the passage of sharp injection/dipolarization fronts, as well as in the turbulent outflow region of the midtail reconnection site.
A Model of the Heliosphere with Jets
NASA Astrophysics Data System (ADS)
Drake, J. F.; Swisdak, M.; Opher, M.
2015-12-01
The conventional picture of the heliosphere is that of a comet-shaped structure with an extended tail produced by the relative motion of the sun through the local interstellar medium (LISM). On the other hand, the measurements of energetic neutral atoms (ENAs) by IBEX and CASSINI produced some surprises. The CASSINI ENA fluxes from the direction of the nose and the tail were comparable, leading the CASSINI observers to conclude that the heliosphere was ``tailless''. The IBEX observations from the tail revealed that the hardest spectrum of ENAs were localized in two lobes at high latitude while the softest spectra were at low latitudes. Recent MHD simulations of the global heliosphere have revealed that the heliosphere drives magnetized jets to the north and south similar to those driven by the Crab Nebula and other astrophysical objects [1]. That the sun's magnetic field can drive such jets when the magnetic pressure in the outer heliosphere is small compared with the local plasma pressure (β=8∏ P/B2 >> 1) is a major surprise. An analytic model of the heliosheath (HS) between the termination shock (TS) and the heliopause (HP) is developed in the limit in which the interstellar flow and magnetic field are neglected [2]. The heliosphere in this limit is axisymmetric. The overall structure of the HS and HP are controlled by the solar magnetic field even in the limit of very high β because the large pressure in the HS is to lowest order balanced by the pressure of the LISM. The tension of the solar magnetic field produces a drop in the total pressure between the TS and the HP. This same pressure drop accelerates the plasma flow downstream of the TS into the north and south directions to form two collimated jets. The radii of these jets are controlled by the flow through the TS and the acceleration of this flow by the magnetic field -- a stronger solar magnetic field boosts the velocity of the jets and reduces the radii of the jets and the HP. Magnetohydrodynamic
Phase space structures in gyrokinetic simulations of fusion plasma turbulence
NASA Astrophysics Data System (ADS)
Ghendrih, Philippe; Norscini, Claudia; Cartier-Michaud, Thomas; Dif-Pradalier, Guilhem; Abiteboul, Jérémie; Dong, Yue; Garbet, Xavier; Gürcan, Ozgür; Hennequin, Pascale; Grandgirard, Virginie; Latu, Guillaume; Morel, Pierre; Sarazin, Yanick; Storelli, Alexandre; Vermare, Laure
2014-10-01
Gyrokinetic simulations of fusion plasmas give extensive information in 5D on turbulence and transport. This paper highlights a few of these challenging physics in global, flux driven simulations using experimental inputs from Tore Supra shot TS45511. The electrostatic gyrokinetic code GYSELA is used for these simulations. The 3D structure of avalanches indicates that these structures propagate radially at localised toroidal angles and then expand along the field line at sound speed to form the filaments. Analysing the poloidal mode structure of the potential fluctuations (at a given toroidal location), one finds that the low modes m = 0 and m = 1 exhibit a global structure; the magnitude of the m = 0 mode is much larger than that of the m = 1 mode. The shear layers of the corrugation structures are thus found to be dominated by the m = 0 contribution, that are comparable to that of the zonal flows. This global mode seems to localise the m = 2 mode but has little effect on the localisation of the higher mode numbers. However when analysing the pulsation of the latter modes one finds that all modes exhibit a similar phase velocity, comparable to the local zonal flow velocity. The consequent dispersion like relation between the modes pulsation and the mode numbers provides a means to measure the zonal flow. Temperature fluctuations and the turbulent heat flux are localised between the corrugation structures. Temperature fluctuations are found to exhibit two scales, small fluctuations that are localised by the corrugation shear layers, and appear to bounce back and forth radially, and large fluctuations, also readily observed on the flux, which are associated to the disruption of the corrugations. The radial ballistic velocity of both avalanche events if of the order of 0.5ρ∗c0 where ρ∗ = ρ0/a, a being the tokamak minor radius and ρ0 being the characteristic Larmor radius, ρ0 = c0/Ω0. c0 is the reference ion thermal velocity and Ω0 = qiB0/mi the reference
High density turbulent plasma processes from a shock tube. Final performance report
Johnson, J.A. III
1997-01-01
A broad-based set of measurements has begun on high density turbulent plasma processes. This includes determinations of new plasma physics and the initiation of work on new diagnostics for collisional plasmas as follows: (1) A transient increase is observed in both the spectral energy decay rate and the degree of chaotic complexity at the interface of a shock wave and a turbulent ionized gas. Even though the gas is apparently brought to rest by the shock wave, no evidence is found either of prompt relaminarization or of any systematic influence of end-wall material thermal conductivities on the turbulence parameters. (2) Point fluorescence emissions and averaged spectral line evolutions in turbulent plasmas produced in both the primary and the reflected shock wave flows exhibit ergodicity in the standard turbulence parameters. The data show first evidence of a reverse energy cascade in the collisional turbulent plasma. This suggests that the fully turbulent environment can be described using a stationary state formulation. In these same data, the author finds compelling evidence for a turbulent Stark effect on neutral emission lines in these data which is associated with evidence of large coherent structures and dominant modes in the Fourier analyses of the fluctuations in the optical spectra. (3) A neutral beam generator has been assembled by coupling a Colutron Ion Gun to a charge exchange chamber. Beam-target collisions where the target species is neutral and the beam is either singly charged or neutral have been performed using argon as the working gas. Spectral analysis of the emission shows specific radiative transitions characteristic of both Ar I and Ar II, indicating that some ionization of the target gas results. Gas and plasma parameters such as density, pressure, temperature and flow velocity and their fluctuations can now be followed in real time by spectroscopic analysis of carefully chosen radiative emissions.
HELCATS - Heliospheric Cataloguing, Analysis and Techniques Service
NASA Astrophysics Data System (ADS)
Harrison, Richard; Davies, Jackie; Perry, Chris; Moestl, Christian; Rouillard, Alexis; Bothmer, Volker; Rodriguez, Luciano; Eastwood, Jonathan; Kilpua, Emilia; Gallagher, Peter
2016-04-01
Understanding the evolution of the solar wind is fundamental to advancing our knowledge of energy and mass transport in the solar system, rendering it crucial to space weather and its prediction. The advent of truly wide-angle heliospheric imaging has revolutionised the study of both transient (CMEs) and background (SIRs/CIRs) solar wind plasma structures, by enabling their direct and continuous observation out to 1 AU and beyond. The EU-funded FP7 HELCATS project combines European expertise in heliospheric imaging, built up in particular through lead involvement in NASA's STEREO mission, with expertise in solar and coronal imaging as well as in-situ and radio measurements of solar wind phenomena, in a programme of work that will enable a much wider exploitation and understanding of heliospheric imaging observations. With HELCATS, we are (1.) cataloguing transient and background solar wind structures imaged in the heliosphere by STEREO/HI, since launch in late October 2006 to date, including estimates of their kinematic properties based on a variety of established techniques and more speculative, approaches; (2.) evaluating these kinematic properties, and thereby the validity of these techniques, through comparison with solar source observations and in-situ measurements made at multiple points throughout the heliosphere; (3.) appraising the potential for initialising advanced numerical models based on these kinematic properties; (4.) assessing the complementarity of radio observations (in particular of Type II radio bursts and interplanetary scintillation) in combination with heliospheric imagery. We will, in this presentation, provide an overview of progress from the first 18 months of the HELCATS project.
NASA Technical Reports Server (NTRS)
Sahraoui, Fouad; Goldstein, Melvyn
2008-01-01
Several observations in space plasmas have reported the presence of coherent structures at different plasma scales. Structure formation is believed to be a direct consequence of nonlinear interactions between the plasma modes, which depend strongly on phase synchronization of those modes. Despite this important role of the phases in turbulence, very limited work has been however devoted to study the phases as a potential tracers of nonlinearities in comparison with the wealth of literature on power spectra of turbulence where phases are totally missed. We present a method based on surrogate data to systematically detect coherent structures in turbulent signals. The new method has been applied successfully to magnetosheath turbulence (Sahraoui, Phys. Rev. E, 2008, in press), where the relationship between the identified phase coherence and intermittency (classically identified as non Gaussian tails of the PDFs) as well as the energy cascade has been studied. Here we review the main results obtained in that study and show further applications to small scale solar wind turbulence. Implications of the results on theoretical modelling of space turbulence (applicability of weak/wave turbulence, its validity limits and its connection to intermittency) will be discussed.
Probabilistic analysis of turbulent structures from two-dimensional plasma imaging
Mueller, S. H.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Plyushchev, G.; Podesta, M.; Poli, F. M.
2006-10-15
A method is presented to construct object-related structure observables, such as size, mass, shape, and trajectories from two-dimensional plasma imaging data. The probability distributions of these observables, deduced from measurements of many realizations, provide a robust framework in which the fluctuations, the turbulence, and the related transport are characterized. The results for imaging data recorded in the presence of drift-interchange instabilities and turbulence on the TORPEX toroidal plasma experiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)] are discussed.
Chang, C S; Ku, Seung-Hoe; Diamond, P. H.; Adams, Mark; Tchoua, Roselyne B; Chen, Yang; Cummings, J.; D'Azevedo, Ed F; Dif-Pradalier, Guilhem; Ethier, Stephane; Greengard, Leslie; Hahm, Taik Soo; Hinton, Fred; Keyes, David E; Klasky, Scott A; Lin, Z.; Lofstead, J.; Park, G.; Podhorszki, Norbert; Schwan, Karsten; Shoshani, A.; Silver, D.; Wolf, M.; Worley, Patrick H; Zorin, Denis
2009-01-01
Performance prediction for ITER is based upon the ubiquitous experimental observation that the plasma energy confinement in the device core is strongly coupled to the edge confinement for an unknown reason. The coupling time-scale is much shorter than the plasma transport time-scale. In order to understand this critical observation, a multi-scale turbulence-neoclassical simulation of integrated edge-core plasma in a realistic diverted geometry is a necessity, but has been a formidable task. Thanks to the recent development in high performance computing, we have succeeded in the integrated multiscale gyrokinetic simulation of the ion-temperature-gradient driven turbulence in realistic diverted tokamak geometry for the first time. It is found that modification of the self-organized criticality in the core plasma by nonlocal core-edge coupling of ITG turbulence can be responsible for the core-edge confinement coupling.
Chang, C S; Ku, Seung-Hoe; Diamond, Patrick; Adams, Mark; Tchoua, Roselyne B; Chen, Yang; Cummings, Julian; D'Azevedo, Eduardo; Dif-Pradalier, Guilhem; Ethier, Stephane; Greengard, Leslie; Hahm, Taik Soo; Hinton, Fred; Keyes, David E; Klasky, Scott A; Lin, Zhihong; Lofstead, J.; Park, G.; Parker, Scott; Podhorszki, Norbert; Schwan, Karsten; Shoshani, A.; Silver, D.; Weitzner, Harold; Wolf, M.; Worley, Patrick H; Yoon, E.; Zorin, Denis
2009-01-01
Performance prediction for ITER is based upon the ubiquitous experimental observation that the plasma energy confinement in the device core is strongly coupled to the edge confinement for an unknown reason. The coupling time-scale is much shorter than the plasma transport time-scale. In order to understand this critical observation, a multi-scale turbulence-neoclassical simulation of integrated edge-core plasma in a realistic diverted geometry is a necessity, but has been a formidable task. Thanks to the recent development in high performance computing, we have succeeded in the integrated multiscale gyrokinetic simulation of the ion-temperature-gradient driven turbulence in realistic diverted tokamak geometry for the first time. It is found that modification of the self-organized criticality in the core plasma by nonlocal core-edge coupling of ITG turbulence can be responsible for the core-edge confinement coupling.
Turbulence and atomic physics in magnetically confined plasmas
NASA Astrophysics Data System (ADS)
Marandet, Y.; Bufferand, H.; Ciraolo, G.; Nace, N.; Serre, E.; Tamain, P.; Valentinuzzi, M.
2017-03-01
An overview of issues related to the interplay between atomic process and turbulence in the peripheral regions of magnetically confined fusion devices is presented. Both atomic processes and turbulence play key roles for fusion, but have most of the time been treated separately. The effects of fluctuations on the time averaged ionization balance, on the transport of neutral particles (atoms and molecules) are discussed, using stochastic models to generate fluctuations with statistically relevant properties. Then applications to optical diagnostics of turbulence, namely gas puff imaging and beam emission spectroscopy are discussed.
Experimental Investigation of Active Feedback Control of Turbulent Transport in a Magnetized Plasma
Gilmore, Mark Allen
2013-07-07
A new and unique basic plasma science laboratory device - the HelCat device (HELicon-CAThode) - has been constructed and is operating at the University of New Mexico. HelCat is a 4 m long, 0.5 m diameter device, with magnetic field up to 2.2 kG, that has two independent plasmas sources - an RF helicon source, and a thermionic cathode. These two sources, which can operate independently or simultaneously, are capable of producing plasmas with a wide range of parameters and turbulence characteristics, well suited to a variety of basic plasma physics experiments. An extensive set of plasma diagnostics is also operating. Experiments investigating the active feedback control of turbulent transport of particles and heat via electrode biasing to affect plasma ExB flows are underway, and ongoing.
Cosmic rays in the heliosphere
NASA Technical Reports Server (NTRS)
Webber, William R.
1987-01-01
The different types of cosmic ray particles and their role in the heliosphere are briefly described. The rates of various energetic particles were examined as a function of time and used to derive various differential energy gradients. The Pioneer and Voyager cosmic ray observations throughout the heliosphere are indeed giving a perspective on the three-dimensional character and size of the heliosphere. Most clearly the observations are emphasizing the role that transient variations in the outer heliosphere, and most likely the heliospheric boundary shock, play in the 11 year solar cycle modulation of cosmic rays.
Turbulent fluctuations during pellet injection into a dipole confined plasma torus
NASA Astrophysics Data System (ADS)
Garnier, D. T.; Mauel, M. E.; Roberts, T. M.; Kesner, J.; Woskov, P. P.
2017-01-01
We report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly "stationary" such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wavenumber dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.
Multiple heliospheric current sheets and coronal streamer belt dynamics
NASA Technical Reports Server (NTRS)
Crooker, N. U.; Siscoe, G. L.; Shodhan, S.; Webb, D. F.; Gosling, J. T.; Smith, E. J.
1993-01-01
The occurrence of multiple directional discontinuities in the coronal streamer belt at sector boundary crossings in the heliosphere, often ascribed to waves or kinks in the heliospheric current sheet, may alternatively be attributed to a network of extended current sheets from multiple helmet streamers with a hierarchy of sizes at the base of the corona. Frequent transient outflows from these helmets can account for a variety of signatures observed at sector boundaries, including ordered field rotations, planar magnetic structures and sandwichlike plasma structure.
Solar wind eddies and the heliospheric current sheet
NASA Technical Reports Server (NTRS)
Suess, S. T.; Mccomas, D. J.; Bame, S. J.; Goldstein, B. E.
1995-01-01
Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.
From coherent structures to turbulence spectra
NASA Astrophysics Data System (ADS)
Lion, Sonny; Alexandrova, Olga; Zaslavsky, Arnaud
2016-04-01
Turbulence in the solar wind has been attracting attention since first in-situ measurements in the Heliosphere. Still a lot of open questions remain. In particular, the nature of turbulence around plasma kinetic scales, where self-similarity breaks down and no-power law behaviour of the turbulent spectrum is expected. It is known that approaching these small scales, Probability Distribution Functions (PDF) of magnetic fluctuations deviate strongly from the Gaussian distribution. This is called intermittency and is usually interpreted as presence of coherent structures. Here, using magnetic field waveforms and their wavelet coefficients, we study the nature of these intermittent events. We propose as well a universal description of magnetic fluctuations PDF using a four-parameter function and we describe the evolution of this parameters with increasing frequencies. Using two different approaches we establish the connection between intermittency and the evolution of the turbulent spectrum at ion scales. Finally the relationship between intermittency and ion temperature is discussed.
Dynamic properties of ionospheric plasma turbulence driven by high-power high-frequency radiowaves
NASA Astrophysics Data System (ADS)
Grach, S. M.; Sergeev, E. N.; Mishin, E. V.; Shindin, A. V.
2016-11-01
A review is given of the current state-of-the-art of experimental studies and the theoretical understanding of nonlinear phenomena that occur in the ionospheric F-layer irradiated by high-power high-frequency ground-based transmitters. The main focus is on the dynamic features of high-frequency turbulence (plasma waves) and low-frequency turbulence (density irregularities of various scales) that have been studied in experiments at the Sura and HAARP heating facilities operated in temporal and frequency regimes specially designed with consideration of the characteristic properties of nonlinear processes in the perturbed ionosphere using modern radio receivers and optical instruments. Experimental results are compared with theoretical turbulence models for a magnetized collisional plasma in a high-frequency electromagnetic field, allowing the identification of the processes responsible for the observed features of artificial ionospheric turbulence.
Symmetry breaking in MAST plasma turbulence due to toroidal flow shear
NASA Astrophysics Data System (ADS)
Fox, M. F. J.; van Wyk, F.; Field, A. R.; Ghim, Y.-c.; Parra, F. I.; Schekochihin, A. A.; the MAST Team
2017-03-01
The flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up–down symmetry of the magnetic equilibrium. Using experimental beam-emission-spectroscopy measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating density field. The tilt is a statistical expression of the ‘shearing’ of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the nonlinear stability threshold. Away from the threshold, the symmetry is effectively restored.
Generation of a magnetic island by edge turbulence in tokamak plasmas
Poyé, A.; Agullo, O.; Muraglia, M.; Benkadda, S.; Dubuit, N.; Garbet, X.; Sen, A.
2015-03-15
We investigate, through extensive 3D magneto-hydro-dynamics numerical simulations, the nonlinear excitation of a large scale magnetic island and its dynamical properties due to the presence of small-scale turbulence. Turbulence is induced by a steep pressure gradient in the edge region [B. D. Scott, Plasma Phys. Controlled Fusion 49, S25 (2007)], close to the separatrix in tokamaks where there is an X-point magnetic configuration. We find that quasi-resonant localized interchange modes at the plasma edge can beat together and produce extended modes that transfer energy to the lowest order resonant surface in an inner stable zone and induce a seed magnetic island. The island width displays high frequency fluctuations that are associated with the fluctuating nature of the energy transfer process from the turbulence, while its mean size is controlled by the magnetic energy content of the turbulence.
Dynamic properties of ionospheric plasma turbulence driven by high-power high-frequency radiowaves
NASA Astrophysics Data System (ADS)
Grach, S. M.; Sergeev, E. N.; Mishin, E. V.; Shindin, A. V.
2017-02-01
A review is given of the current state-of-the-art of experimental studies and the theoretical understanding of nonlinear phenomena that occur in the ionospheric F-layer irradiated by high-power high-frequency ground-based transmitters. The main focus is on the dynamic features of high-frequency turbulence (plasma waves) and low-frequency turbulence (density irregularities of various scales) that have been studied in experiments at the Sura and HAARP heating facilities operated in temporal and frequency regimes specially designed with consideration of the characteristic properties of nonlinear processes in the perturbed ionosphere using modern radio receivers and optical instruments. Experimental results are compared with theoretical turbulence models for a magnetized collisional plasma in a high-frequency electromagnetic field, allowing the identification of the processes responsible for the observed features of artificial ionospheric turbulence.
Regulating drift-wave plasma turbulence into spatiotemporal patterns by pinning coupling.
Liu, Panpan; Yang, Lei; Deng, Zhigang; Wang, Xingang
2011-07-01
Using the technique of pinning coupling in chaos control, we investigate how the two-dimensional drift-wave plasma turbulence described by the Hasegawa-Mima equation can be regulated into different spatiotemporal patterns. It is shown both analytically and numerically that, depending on the pattern structure of the target, the pinning strength necessary for regulating the turbulence could have a large variation. More specifically, with the increase of the wave number of the target, the critical pinning strength is found to be increased by a power-law scaling. Moreover, in both the transition and transient process of the pinning regulation, the modes of the turbulence are found to be suppressed in a hierarchical fashion, that is, by the sequence of mode wave number. The findings give insight into the dynamics of drift-wave turbulence, as well as indicative to the design of new control techniques for real-world turbulence.
Turbulent transport across shear layers in magnetically confined plasmas
Nold, B.; Ramisch, M.; Manz, P.; Birkenmeier, G.; Ribeiro, T. T.; Müller, H. W.; Scott, B. D.; Fuchert, G.; Stroth, U.
2014-10-15
Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatial-temporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process.
Route to Drift Wave Chaos and Turbulence in a Bounded Low-{beta} Plasma Experiment
Klinger, T.; Latten, A.; Piel, A.; Bonhomme, G.; Pierre, T.; Dudok de Wit, T.
1997-11-01
The transition scenario from stability to drift wave turbulence is experimentally investigated in a magnetized low-{beta} plasma with cylindrical geometry. It is demonstrated that the temporal dynamics is determined by the interaction and destabilization of spatiotemporal patterns, in particular, traveling waves. The analysis of the temporal and the spatiotemporal data shows that the bifurcations sequence towards weakly developed turbulence follows the Ruelle-Takens scenario. {copyright} {ital 1997} {ital The American Physical Society}
Closure of a kinetic model of plasma in strong turbulence by relaxation
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1978-01-01
A Fokker-Planck kinetic equation for a turbulent plasma is derived by a repeated cascade decomposition. Calculation of the propagator and the kinetic equation determine the transport coefficients (diffusivity and turbulent viscosity) by means of a closure based on a relaxation procedure governing the approach to equilibrium. The k to the minus third power spectral law is obtained, which governs the coupling between the velocity and the electrostatic field fluctuations.
Compressible sub-Alfvénic MHD turbulence in low-beta plasmas.
Cho, Jungyeon; Lazarian, A
2002-06-17
We present a model for compressible sub-Alfvénic isothermal magnetohydrodynamic (MHD) turbulence in low- beta plasmas and numerically test it. We separate MHD fluctuations into three distinct families: Alfvén, slow, and fast modes. We find that production of slow and fast modes by Alfvénic turbulence is suppressed. As a result, Alfvén modes in compressible regime exhibit scalings and anisotropy similar to those in incompressible regime. Slow modes passively mimic Alfvén modes. However, fast modes show isotropy and a scaling similar to acoustic turbulence.
Yordanova, E.; Vaivads, A.; Andre, M.; Buchert, S. C.; Voeroes, Z.
2008-05-23
We study the plasma turbulence, at scales larger than the ion inertial length scale, downstream of a quasiparallel bow shock using Cluster multispacecraft measurements. We show that turbulence is intermittent and well described by the extended structure function model, which takes into account the spatial inhomogeneity of the cascade rate. For the first time we use multispacecraft observations to characterize the evolution of magnetosheath turbulence, particularly its intermittency, as a function of the distance from the bow shock. The intermittency significantly changes over the distance of the order of 100 ion inertial lengths, being increasingly stronger and anisotropic away from the bow shock.
NASA Astrophysics Data System (ADS)
Ghasemi, Maede; Xu, Haitao; Pei, Xuekai; Lu, Xinpei
2016-09-01
Among variety of plasma applications, there is significant interest recently in the use of plasma as an actuator in flow control for aerodynamic applications in which the correlation between atmospheric pressure plasma jet (APPJ) and gas flow field is a crucial role. In this contribution, dynamic characterizations of the turbulent flow field in APPj are investigated by focusing on the effect of different parameters of APPJ, such as applied voltage, pulse repetition frequency, gas flow rate, and time duration of the pulse We utilized Schlieren photography and photomultiplier tubes (PMT) as a signal triggering of an intensified charge coupled device (ICCD) and also a high speed camera to examine the formation of the turbulent front and its dynamics. The results reveal that the turbulent front will appear earlier and closer to the tube nozzle by increasing the gas flow rate and applied voltage amplitude. It is found that the pulse time duration and repetition frequency cannot change the dynamics and formation of the turbulent front. Further investigation demonstrated that every pulse can excite one turbulent front which is created in a specific position in a laminar region and propagates downstream and the effect of increasing frequency results in the increasing of the number of turbulent front and expansion of their region of formation.
Sheared E×B flow and plasma turbulence viscosity in a Reversed Field Pinch
NASA Astrophysics Data System (ADS)
Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Regnoli, G.; Zuin, M.; Cavazzana, R.; Bergsåker, H.; Cecconello, M.; Drake, J. R.
2004-11-01
The relationship between electromagnetic turbulence and sheared plasma flow in Reversed Field Pinch configuration is addressed. The momentum balance equation for a compressible plasma is considered and the terms involved are measured in the outer region of Extrap-T2R RFP device. It results that electrostatic fluctuations determine the plasma flow through the electrostatic component of Reynolds Stress tensor. This term involves spatial and temporal scales comparable to those of MHD activity. The derived experimental perpendicular viscosity is consistent with anomalous diffusion, the latter being discussed in terms of electrostatic turbulence background and coherent structures emerging from fluctuations. The results indicate a dynamical interplay between turbulence, anomalous transport and mean E×B profiles. The momentum balance has been studied also in non-stationary condition during the application of Pulsed Poloidal Current Drive, which is known to reduce the amplitude of MHD modes.
Characterization of radial turbulent fluxes in the Santander linear plasma machine
Mier, J. A. Anabitarte, E.; Sentíes, J. M.; Sánchez, R.; Newman, D. E.; Castellanos, O. F.; Milligen, B. Ph. van
2014-05-15
It is shown that the statistical and correlation properties of the local turbulent flux measured at different radial locations of the cold, weakly ionized plasmas inside the Santander Linear Plasma Machine [Castellanos et al., Plasma Phys. Control. Fusion 47, 2067 (2005)] are consistent with diffusive-like transport dynamics. This is in contrast to the dynamical behavior inferred from similar measurements taken in hotter, fully ionized tokamak and stellarator edge plasmas, in which long-term correlations and other features characteristic of complex, non-diffusive transport dynamics have been reported in the past. These results may shed some light on a recent controversy regarding the possible universality of the dynamics of turbulent transport in magnetized plasmas.
Characterization of radial turbulent fluxes in the Santander linear plasma machine
NASA Astrophysics Data System (ADS)
Mier, J. A.; Sánchez, R.; Newman, D. E.; Castellanos, O. F.; Anabitarte, E.; Sentíes, J. M.; van Milligen, B. Ph.
2014-05-01
It is shown that the statistical and correlation properties of the local turbulent flux measured at different radial locations of the cold, weakly ionized plasmas inside the Santander Linear Plasma Machine [Castellanos et al., Plasma Phys. Control. Fusion 47, 2067 (2005)] are consistent with diffusive-like transport dynamics. This is in contrast to the dynamical behavior inferred from similar measurements taken in hotter, fully ionized tokamak and stellarator edge plasmas, in which long-term correlations and other features characteristic of complex, non-diffusive transport dynamics have been reported in the past. These results may shed some light on a recent controversy regarding the possible universality of the dynamics of turbulent transport in magnetized plasmas.
TURBULENT GENERAL MAGNETIC RECONNECTION
Eyink, G. L.
2015-07-10
Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian–Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.
Wang, W. X.; Hahm, T. S.; Ethier, S.; Rewoldt, G.; Tang, W. M.; Lee, W. W.; Diamond, P. H.
2011-03-20
Toroidal plasma flow driven by turbulent torque associated with nonlinear residual stress generation is shown to recover the observed key features of intrinsic rotation in experiments. Specifically, the turbulence-driven intrinsic rotation scales close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing empirical scalings obtained from a large experimental data base. The effect of magnetic shear on the symmetry breaking in the parallel wavenumber spectrum is identified. The origin of the current scaling is found to be the enhanced kll symmetry breaking induced by increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic rotation on the pressure gradient comes from the fact that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving the residual stress, are increased with the strength of the turbulence drives, which are R/LTe and R/Lne for the collisionless trapped electron mode (CTEM). Highlighted results also include robust radial pinches in toroidal flow, heat and particle transport driven by CTEM turbulence, which emerge "in phase", and are shown to play important roles in determining plasma profiles. Also discussed are experimental tests proposed to validate findings from these gyrokinetic simulations.
NASA Astrophysics Data System (ADS)
Lee, Myoung-Jae; Jung, Young-Dae
2016-05-01
The influence of non-thermal Dupree turbulence and the plasma shielding on the electron-ion collision is investigated in Lorentzian turbulent plasmas. The second-order eikonal analysis and the effective interaction potential including the Lorentzian far-field term are employed to obtain the eikonal scattering phase shift and the eikonal collision cross section as functions of the diffusion coefficient, impact parameter, collision energy, Debye length and spectral index of the astrophysical Lorentzian plasma. It is shown that the non-thermal effect suppresses the eikonal scattering phase shift. However, it enhances the eikonal collision cross section in astrophysical non-thermal turbulent plasmas. The effect of non-thermal turbulence on the eikonal atomic collision cross section is weakened with increasing collision energy. The variation of the atomic cross section due to the non-thermal Dupree turbulence is also discussed. This research was supported by Nuclear Fusion Research Program through NRF funded by the Ministry of Science, ICT & Future Planning (Grant No. 2015M1A7A1A01002786).
Turbulence, flows and edge localized mode (ELM) dynamics in limiter H-mode plasmas in TEXTOR
NASA Astrophysics Data System (ADS)
Soldatov, S.; Krämer-Flecken, A.; Kantor, M.; Unterberg, B.; Sun, Y.; Van Oost, G.; Reiter, D.; TEXTOR Team
2010-08-01
The turbulence, plasma flow and edge localized mode (ELM) dynamics in the limiter H-mode TEXTOR plasmas are investigated. Properties of both ambient turbulence within 0 < k⊥ < 4.2 cm-1 and coherent modes are studied on the ELM time scale in detail. The turbulence level near the pedestal is shown to evolve several times with the period of ELMs. Within the inter-ELM period the 'silent stage' is found which is characterized by an extremely low (below that for Ohmic plasmas) turbulence level and a phase growth in the reflectometry signal. The silent stage is associated with the quasi-steady state when the pedestal is formed and confinement is improved between two successive ELMs. Quasi-coherent density oscillations near the pedestal region with m ≈ 3, 5, 16 and 38 are measured with correlation reflectometry. Low-m modes are found to reveal the signatures of precursor mode. At first, the radial structure of the rotation shear and radial electric field Er in limiter H-mode in TEXTOR is presented. The characteristic negative electric field well with the sharp gradient ∇Er ≈ 250 V cm-2 at ≈2 cm inside separatrix is resolved. The Er × B rotation profile defines both the resulting plasma rotation in the electron diamagnetic drift direction and a significant rotation shear near the separatrix which exceeds the decorrelation rate of ambient turbulence by several times.
Jenet, F. A.; Melatos, A.; Robinson, P. A.
2007-10-15
Zakharov simulations of nonlinear wave collapse in continuously driven two-dimensional, electromagnetic strong plasma turbulence with electron thermal speeds v{>=}0.01c show that for v < or approx. 0.1c, dipole radiation occurs near the plasma frequency, mainly near arrest, but for v > or approx. 0.1c, a new mechanism applies in which energy oscillates between trapped Langmuir and transverse modes until collapse is arrested, after which trapped transverse waves are advected into incoherent interpacket turbulence by an expanding annular density well, where they detrap. The multipole structure, Poynting flux, source current, and radiation angular momentum are computed.
Reconnection AND Bursty Bulk Flow Associated Turbulence IN THE Earth'S Plasma Sheet
NASA Astrophysics Data System (ADS)
Voros, Z.; Nakamura, R.; Baumjohann, W.; Runov, A.; Volwerk, M.; Jankovicova, D.; Balogh, A.; Klecker, B.
2006-12-01
Reconnection related fast flows in the Earth's plasma sheet can be associated with several accompanying phenomena, such as magnetic field dipolarization, current sheet thinning and turbulence. Statistical analysis of multi-scale properties of turbulence facilitates to understand the interaction of the plasma flow with the dipolar magnetic field and to recognize the remote or nearby temporal and spatial characteristics of reconnection. The main emphasis of this presentation is on differentiating between the specific statistical features of flow associated fluctuations at different distances from the reconnection site.
Ion acoustic turbulence and transport in a plasma in a strong electric field
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.; Silin, V. P.
1984-01-01
A theory is derived for the nonlinear state which is established in a plasma when the ion acoustic instability is suppressed by nonlinear induced wave scattering by ions, and there is a quasi-linear relaxation of electrons among turbulent fluctuations. The behavior of the ion acoustic noise spectrum and of transport processes in strong fields, where the anomalous plasma resistance is a square-root function of the field intensity, is found. In this region of electric fields there is a universal distribution of the ion acoustic fluctuations in the magnitude of the wave vector and in angle for the turbulence spectrum.
Suppressed ion-scale turbulence in a hot high-β plasma
Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.
2016-01-01
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements. PMID:28000675
Suppressed ion-scale turbulence in a hot high-β plasma.
Schmitz, L; Fulton, D P; Ruskov, E; Lau, C; Deng, B H; Tajima, T; Binderbauer, M W; Holod, I; Lin, Z; Gota, H; Tuszewski, M; Dettrick, S A; Steinhauer, L C
2016-12-21
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.
Suppressed ion-scale turbulence in a hot high-β plasma
NASA Astrophysics Data System (ADS)
Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.
2016-12-01
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.
Vortices, Reconnection and Turbulence in High Electron-Beta Plasmas
Stenzel, R. L.
2004-08-31
Plasmas in which the kinetic energy exceeds the magnetic energy by a significant factor are common in space and in the laboratory. Such plasmas can convect magnetic fields and create null points in whose vicinity first the ions become unmagnetized, then the electrons. This project focuses on the detailed study of the transition regime of these plasmas.
The Self-Consistent Generation of Current Sheets in Astrophysical Plasma Turbulence
NASA Astrophysics Data System (ADS)
Howes, Gregory
2014-10-01
In space and astrophysical plasma turbulence, it has long been recognized that dissipation occurs predominantly in intermittent current sheets, with vigorous activity in the past few years focused on obtaining observational evidence for such localized dissipation in the near-Earth solar wind. The nature of these magnetic discontinuities and their associated current sheets measured in the solar wind remains unclear--are these discontinuities due to filamentary magnetic structure in the solar wind, or do they arise dynamically from turbulent interactions? Recent analytical solution, numerical validation, and experimental verification of the nonlinear energy transfer in Alfven wave collisions, the nonlinear interactions between counterpropagating Alfven waves, has established this interaction as the fundamental building block of astrophysical plasma turbulence. Here I will present first-principles analytical calculations and supporting numerical simulations that Alfven wave collisions in the strong turbulence limit naturally produce current sheets, providing the first theoretical unification of models of plasma turbulence mediated by Alfven waves with ideas on localized dissipation in current sheets. Supported by NSF CAREER Award AGS-1054061, NSF Grant PHY-10033446, and NASA Grant NNX10AC91G.
NASA Astrophysics Data System (ADS)
Roberts, T. Maximillian
2014-10-01
Turbulence in a dipole-confined plasma is dominated by interchange fluctuations with complex dynamics and short coherence. We report the first laboratory demonstration of the regulation of interchange turbulence in a plasma torus confined by an axisymmetric dipole magnet using active feedback. Feedback is performed by varying the bias to an electrode in proportion to the electric potential measured at other locations. The phase and amplitude of the bias to the electrode is adjusted with a linear circuit, forming a relatively broad-band current-collection feedback system. Changing the gain and phase of collection results in modification of turbulent fluctuations, observed as amplification or suppression of turbulent spectrum. Significantly, power can be either extracted from or injected into the turbulence. When the gain and phase are adjusted to suppress turbulence, the external circuit becomes a controlled load extracting power from the plasma. This is analogous to the regulation of magnetospheric convection by ionospheric currents. When the gain and phase of the external circuit is adjusted to amplify turbulence, the direction of power flow from the electrode reverses, enhancing the fluctuations. Although we observe significant changes to the intensity and spectrum of plasma fluctuations, these changes appear only on those magnetic field lines within a region near the current collector equal in size to the turbulent correlation length and shifted in the direction of the electron magnetic drift. We conclude that the effects of this feedback on turbulence in a dipole plasma torus is localized. The clear influence of current-collection feedback on interchange turbulence suggests the possibility of global regulation of turbulent motion using multiple sensor and electrode pairs as well as the ability to perform controlled tests of bounce-averaged gyrokinetic theory of turbulence in the geometry of a dipole plasma torus. Supported by NSF-DOE Partnership for Plasma
Experimental observation of electron-temperature-gradient turbulence in a laboratory plasma.
Mattoo, S K; Singh, S K; Awasthi, L M; Singh, R; Kaw, P K
2012-06-22
We report the observation of electron-temperature-gradient (ETG) driven turbulence in the laboratory plasma of a large volume plasma device. The removal of unutilized primary ionizing and nonthermal electrons from uniform density plasma and the imposition and control of the gradient in the electron temperature (T[Symbol: see text] T(e)) are all achieved by placing a large (2 m diameter) magnetic electron energy filter in the middle of the device. In the dressed plasma, the observed ETG turbulence in the lower hybrid range of frequencies ν = (1-80 kHz) is characterized by a broadband with a power law. The mean wave number k perpendicular ρ(e) = (0.1-0.2) satisfies the condition k perpendicular ρ(e) ≤ 1, where ρ(e) is the electron Larmor radius.
Interaction of neutral atoms and plasma turbulence in the tokamak edge region
NASA Astrophysics Data System (ADS)
Wersal, Christoph; Ricci, Paolo; Jorge, Rogerio; Morales, Jorge; Paruta, Paola; Riva, Fabio
2016-10-01
A novel first-principles self-consistent model that couples plasma and neutral atom physics suitable for the simulation of turbulent plasma behaviour in the tokamak edge region has been developed and implemented in the GBS code. While the plasma is modelled by the drift-reduced two fluid Braginskii equations, a kinetic model is used for the neutrals, valid in short and in long mean free path scenarios. The model includes ionization, charge-exchange, recombination, and elastic collisional processes. The model was used to study the transition form the sheath to the conduction limited regime, to include gas puffs in the simulations, and to investigate the interplay between neutral atoms and plasma turbulence.
NASA Astrophysics Data System (ADS)
Krommes, John A.
2015-12-01
> In honour of the 50th anniversary of the influential review/monograph on plasma turbulence by B. B. Kadomtsev as well as the seminal works of T. H. Dupree and J. Weinstock on resonance-broadening theory, an introductory tutorial is given about some highlights of the statistical-dynamical description of turbulent plasmas and fluids, including the ideas of nonlinear incoherent noise, coherent damping, and self-consistent dielectric response. The statistical closure problem is introduced. Incoherent noise and coherent damping are illustrated with a solvable model of passive advection. Self-consistency introduces turbulent polarization effects that are described by the dielectric function . Dupree's method of using to estimate the saturation level of turbulence is described; then it is explained why a more complete theory that includes nonlinear noise is required. The general theory is best formulated in terms of Dyson equations for the covariance and an infinitesimal response function , which subsumes . An important example is the direct-interaction approximation (DIA). It is shown how to use Novikov's theorem to develop an -space approach to the DIA that is complementary to the original -space approach of Kraichnan. A dielectric function is defined for arbitrary quadratically nonlinear systems, including the Navier-Stokes equation, and an algorithm for determining the form of in the DIA is sketched. The independent insights of Kadomtsev and Kraichnan about the problem of the DIA with random Galilean invariance are described. The mixing-length formula for drift-wave saturation is discussed in the context of closures that include nonlinear noise (shielded by ). The role of in the calculation of the symmetry-breaking (zonostrophic) instability of homogeneous turbulence to the generation of inhomogeneous mean flows is addressed. The second-order cumulant expansion and the stochastic structural stability theory are also discussed in that context. Various historical
Fluctuation-induced shear flow and energy transfer in plasma interchange turbulence
Li, B.; Sun, C. K.; Wang, X. Y.; Zhou, A.; Wang, X. G.; Ernst, D. R.
2015-11-15
Fluctuation-induced E × B shear flow and energy transfer for plasma interchange turbulence are examined in a flux-driven system with both closed and open magnetic field lines. The nonlinear evolution of interchange turbulence shows the presence of two confinement regimes characterized by low and high E × B flow shear. In the first regime, the large-scale turbulent convection is dominant and the mean E × B shear flow is at a relatively low level. By increasing the heat flux above a certain threshold, the increased turbulent intensity gives rise to the transfer of energy from fluctuations to mean E × B flows. As a result, a transition to the second regime occurs, in which a strong mean E × B shear flow is generated.
Energy Dissipation and Landau Damping in Two- and Three-dimensional Plasma Turbulence
NASA Astrophysics Data System (ADS)
Li, Tak Chu; Howes, Gregory G.; Klein, Kristopher G.; TenBarge, Jason M.
2016-12-01
Plasma turbulence is ubiquitous in space and astrophysical plasmas, playing an important role in plasma energization, but the physical mechanisms leading to dissipation of the turbulent energy remain to be definitively identified. Kinetic simulations in two dimensions (2D) have been extensively used to study the dissipation process. How the limitation to 2D affects energy dissipation remains unclear. This work provides a model of comparison between two- and three-dimensional (3D) plasma turbulence using gyrokinetic simulations; it also explores the dynamics of distribution functions during the dissipation process. It is found that both 2D and 3D nonlinear gyrokinetic simulations of a low-beta plasma generate electron velocity-space structures with the same characteristics as that of the linear Landau damping of Alfvén waves in a 3D linear simulation. The continual occurrence of the velocity-space structures throughout the turbulence simulations suggests that the action of Landau damping may be responsible for the turbulent energy transfer to electrons in both 2D and 3D, and makes possible the subsequent irreversible heating of the plasma through collisional smoothing of the velocity-space fluctuations. Although, in the 2D case where variation along the equilibrium magnetic field is absent, it may be expected that Landau damping is not possible, a common trigonometric factor appears in the 2D resonant denominator, leaving the resonance condition unchanged from the 3D case. The evolution of the 2D and 3D cases is qualitatively similar. However, quantitatively, the nonlinear energy cascade and subsequent dissipation is significantly slower in the 2D case.
NASA Technical Reports Server (NTRS)
Scarf, F. L.; Fredricks, R. W.; Green, I. M.
1972-01-01
Simultaneous observations of plasma waves from the electric field instruments on Pioneer 9 and OGO 5 are used to illustrate the difference between near-earth and deep space conditions. It is shown that the experimental study of true interplanetary wave-particle interactions is difficult to carry out from an earth orbiter because the earth provides significant fluxes of nonthermal particles that generate intense plasma turbulence in the upstream region.
IRIS Diagnoses of Man-Made and Naturally-Occurring Ionospheric Plasma Turbulence
2005-03-01
swept-frequency HF radar that operates between 1 and 20 MHz. Output ionograms are plots of radar reflection heights as functions of frequency...corresponding to the local ionospheric plasma density). Diffuse echoes on ionograms called spread F, indicate the presence of plasma turbulence in the... Ionograms were recorded every 5 minutes. The ionosonde and ISR operated simultaneously to monitor the occurrence of spread-F due to bottomside
Optical and electrical diagnostics for the investigation of edge turbulence in fusion plasmas
Cavazzana, R.; Scarin, P.; Serianni, G.; Agostini, M.; Degli Agostini, F.; Cervaro, V.; Lotto, L.; Yagi, Y.; Sakakita, H.; Koguchi, H.; Hirano, Y.
2004-10-01
A new, two dimensional and fast diagnostic system has been developed for studying the dynamic structure of plasma turbulence; it will be used in the edge of the reversed-field pinch devices TPE-RX and RFX. The system consists of a gas-puffing nozzle, 32 optical channels measuring H{sub {alpha}} emitted from the puffed gas (to study the optical emissivity of turbulent patterns and to analyze structures in two dimensions), and an array of Langmuir probes (to compare the turbulent pattern with the optical method and to measure the local plasma parameters). The signals can be acquired at 10 Msamples/s with 2 MHz band width. The design of the system, calibrations, and tests of the electronic circuitry and the optical sensors are presented.
Effect of driving frequency on excitation of turbulence in a kinetic plasma
Parashar, T. N.; Shay, M. A.; Matthaeus, W. H.; Servidio, S.; Breech, B.
2011-09-15
The effect of driving frequency on the efficiency of turbulence generation through magnetic forcing is studied using kinetic hybrid simulations with fully kinetic ions and fluid electrons. The efficiency of driving is quantified by examining the energy input into magnetic field as well as the thermal energy for various driving frequencies. The driving is efficient in exciting turbulence and heating the plasma when the time period of the driving is larger than the nonlinear time of the system. For driving at faster time scales, the energy input is weak and the steady state energy is much lower. The heating of the plasma is correlated with intermittent properties of the magnetic field, which are manifested as non-Gaussian statistics. Implications for turbulence in solar corona are discussed.
Observation of turbulent intermittency scaling with magnetic helicity in an MHD plasma wind tunnel.
Schaffner, D A; Wan, A; Brown, M R
2014-04-25
The intermittency in turbulent magnetic field fluctuations has been observed to scale with the amount of magnetic helicity injected into a laboratory plasma. An unstable spheromak injected into the MHD wind tunnel of the Swarthmore Spheromak Experiment displays turbulent magnetic and plasma fluctuations as it relaxes into a Taylor state. The level of intermittency of this turbulence is determined by finding the flatness of the probability distribution function of increments for magnetic pickup coil fluctuations B˙(t). The intermittency increases with the injected helicity, but spectral indices are unaffected by this variation. While evidence is provided which supports the hypothesis that current sheets and reconnection sites are related to the generation of this intermittent signal, the true nature of the observed intermittency remains unknown.
Turbulent transport and heating in the auroral plasma of the topside ionosphere
NASA Technical Reports Server (NTRS)
Ionson, J. A.; Ong, R. S. B.; Fontheim, E. G.
1979-01-01
Using plasma parameters from a typical stormtime ionospheric energy balance model, we have investigated the effects of plasma turbulence on the auroral magnetoplasma. The turbulence is assumed to be comprised of electrostatic ion cyclotron waves. These waves have been driven to a nonthermal level by a geomagnetic field-aligned, current-driven instability. The evolution of this instability is shown to proceed in two stages and indicates an anomalous increase in field-aligned electrical resistivity and cross-field ion thermal conductivity as well as a decrease in electron thermal conductivity along the geomagnetic field. In addition, this turbulence heats ions perpendicular to the geomagnetic field and hence leads to a significant ion temperature anisotropy.
Radio Emissions from the Outer Heliosphere
NASA Technical Reports Server (NTRS)
Gurnett, D. A.; Kurth, W. S.
1996-01-01
For nearly fifteen years the Voyager 1 and 2 spacecraft have been detecting an unusual radio emission in the outer heliosphere in the frequency range from about 2 to 3 kHz. Two major events have been observed, the first in 1983-84 and the second in 1992-93. In both cases the onset of the radio emission occurred about 400 days after a period of intense solar activity, the first in mid-July 1982, and the second in May-June 1991. These two periods of solar activity produced the two deepest cosmic ray Forbush decreases ever observed. Forbush decreases are indicative of a system of strong shocks and associated disturbances propagating outward through the heliosphere. The radio emission is believed to have been produced when this system of shocks and disturbances interacted with one of the outer boundaries of the heliosphere, most likely in the vicinity of the the heliopause. The emission is believed to be generated by the shock-driven Langmuir-wave mode conversion mechanism, which produces radiation at the plasma frequency (f(sub p)) and at twice the plasma frequency (2f(sub p)). From the 400-day travel time and the known speed of the shocks, the distance to the interaction region can be computed, and is estimated to be in the range from about 110 to 160 AU.
Effects of Bursty Bulk Flows on the Turbulence in the Plasma Sheet.
NASA Astrophysics Data System (ADS)
Stepanova, M. V.; Antonova, E. E.
2014-12-01
Recent studies have shown the importance of turbulent processes in the dynamics of the magnetosphere of the Earth, including plasma and energy transport and the plasma sheet stability. We studied the properties of the turbulent plasma sheet in the presence and in the absence of the bursty bulk flow events for different phases of geomagnetic substorms and for quiet geomagnetic conditions. The criteria used for the selection of BBFs are similar to ones established by Angelopoulos et al., (JGR, 1994). The classification of time intervals as quiet, expansion phase, and recovery phase was based on the variation of the AL-index (Stepanova et al., 2011). Statistical analysis was performed using the data of THEMIS probes during tail-science seasons. It was found that the plasma pressure is the parameter which experienced major variation if we compare the data for different substrom phases, and also in the presence and absence of BBFs: The radial plasma pressure profiles are steaper during the substorm expansion phase, the presence of BBFs smoothes this effect, especially during the recovery phase and the quiet time. Study of eddy diffusion showed that even in the absence of BBFs the plasma sheet is strongly turbulent. Analysis of bulk velocity data 20 minutes before and after a BBF showed that the BBFs could generate additional vorticity at the leading and trailing edges, but their contribution is not decisive.
Effects of Surface Wave Turbulence on the Steep Density Gradients in Laser-Produced Plasmas
NASA Astrophysics Data System (ADS)
Gradov, O. M.; Stenflo, L.
1984-01-01
We point out that the surface wave turbulence in the plasma region where the temperature and density have large gradients can reduce the thermal flux and consequently steepen the temperature and density profiles significantly. An expression for the resultant density gradient as a function of the stationary intensity of the excited surface modes is also calculated.
On the Nonlinear Conductivity Tensor for an Unmagnetized Relativistic Turbulent Plasma.
1982-02-01
New York (1977). (10) L. M. Al’tshul’ and V. I. Karpman , The Kinetics of Waves in a Weakly Turbulent Plasma, Zh. Eksp. Teor. Fiz., 47 (1964), 1552...LONTZ DEFENSE FOR RESEARCH & ENGINEERING ATTN B. D. GUENTHER DIR ENERGY TECHNOLOGY OFFICE ATTN TECH LIBRARY ATTN J. R. AIREY RESEARCH TRIANGLE PARK, NC
Theory of coherent electron-scale magnetic structures in space plasma turbulence
NASA Astrophysics Data System (ADS)
Jovanović, Dušan; Alexandrova, Olga; Maksimović, Milan
2015-08-01
Recent spacecraft observations in the solar wind and in the Earth’s magnetosheath indicate that the dissipation range of magnetic turbulence probably takes place at electron scales. Here, we derive nonlinear electron magnetohydrodynamic (EMHD) equations for warm plasma, i.e. with the ratio of thermodynamic and magnetic pressures, β ∼ 1. This model describes plasma turbulence under the solar wind and magnetosheath conditions on the electron spatial scales and with the characteristic frequency that does not exceed the electron gyrofrequency. We show that at electron scales and in the presence of a sufficiently large temperature anisotropy {T}{e\\perp }/{T}{e\\parallel }\\gt 1, there exist self-organized, coherent, nonlinear dipole vortex structures associated with obliquely propagating whistler waves. These can be visualized as pairs of counterstreaming helicoidal currents that produce both the compressional and torsional perturbations of the magnetic field. In contrast to the previously known long-range EMHD dipolar vortices in a cold plasma, this novel solution is an evanescent mode, strongly localized in space (with wave numbers {k}\\perp \\gg {k}\\parallel ). It can constitute a building block for the plasma turbulence at short scales and provide a possible scenario of turbulence dissipation at electron scales.
Turbulence and wave particle interactions in solar-terrestrial plasmas
NASA Technical Reports Server (NTRS)
Dulk, G. A.; Goldman, M. V.; Toomre, J.
1985-01-01
Activities in the following study areas are reported: (1) particle and wave processes in solar flares; (2) solar convection zone turbulence; and (3) solar radiation emission. To investigate the amplification of cyclotron maser radiation in solar flares, a radio frequency. (RF) heating model was developed for the corona surrounding the energy release site. Then nonlinear simulations of compressible convection display prominent penetration by plumes into regions of stable stratification at the base of the solar convection zone, leading to the excitation of internal gravity waves there. Lastly, linear saturation of electron-beam-driven Langmuir waves by ambient density fluctuations, nonlinear saturation by strong turbulence processes, and radiation emission mechanisms are examined. An additional section discusses solar magnetic fields and hydromagnetic waves in inhomogeneous media, and the effect of magnetic fields on stellar oscillation.
Evolution of solar wind turbulence and intermittency over the solar cycle
NASA Astrophysics Data System (ADS)
Väisänen, Pauli; Virtanen, Ilpo; Echim, Marius; Munteanu, Costel; Mursula, Kalevi
2016-04-01
Solar wind is a natural, near-by plasma physics laboratory, which offers possibilities to study plasma physical phenomena over a wide range of parameter values that are difficult to reach in ground-based laboratories. Accordingly, the solar wind is subject of many studies of, e.g., intermittency, turbulence and other nonlinear space plasma phenomena. Turbulence is an important feature of the solar wind dynamics, e.g., for the energy transfer mechanisms and their scale invariance, the solar wind evolution, the structure of the heliospheric magnetic field (HMF), the particle energization and heating, and for phenomena related to solar wind interaction with the planetary plasma systems. Here we analyse high resolution measurements of the solar wind and the heliospheric magnetic field provided by several ESA and NASA satellites, including ACE, STEREO, Ulysses and Cluster. This collection of satellites allows us to compile and study nearly 20 years of high-resolution solar wind and HMF measurements from the start of solar cycle 23 to the current declining phase of solar cycle 24. Long-term studies require homogeneity and, therefore, we pay great attention to the reliability and consistency of the data, in particular to instrumental defects like spin harmonics, the purity of the solar wind and its possible contamination in the foreshock by magnetospheric ions. We study how the different key-descriptors of turbulence like the slope of the power law of power spectral density and the kurtosis of the fluctuations of the heliospheric magnetic field vary over the solar cycle.
Seo, Janghoon; Choe, W.; Chang, C. S.; Ku, S.; Kwon, J. M.; Müller, Stefan H.
2014-09-15
Fluid Reynolds stress from turbulence has usually been considered to be responsible for the anomalous toroidal momentum transport in tokamak plasma. Experiment by Müller et al. [Phys. Rev. Lett. 106, 115001 (2011)], however, reported that neither the observed edge rotation profile nor the inward momentum transport phenomenon at the edge region of an H-mode plasma could be explained by the fluid Reynolds stress measured with reciprocating Langmuir-probe. The full-function gyrokinetic code XGC1 is used to explain, for the first time, Müller et al.'s experimental observations. It is discovered that, unlike in the plasma core, the fluid Reynolds stress from turbulence is not sufficient for momentum transport physics in plasma edge. The “turbulent neoclassical” physics arising from the interaction between kinetic neoclassical orbit dynamics and plasma turbulence is key in the tokamak edge region across the plasma pedestal into core.
Turbulence and selective decay in the SSX plasma wind tunnel
NASA Astrophysics Data System (ADS)
Gray, Tim; Brown, Michael; Dandurand, Dan; Fisher, Mike; Flanagan, Ken; Weinhold, Darren; Lukin, V.
2011-10-01
A helical, relaxed plasma state has been observed in a long cylindrical volume. The cylinder has dimensions L = 1 m and R = 0 . 08 m. The cylinder is long enough so that the predicted minimum energy state is a close approximation to the infinite cylinder solution. The plasma is injected at v >= 50 km/s by a coaxial magnetized plasma gun located at one end of the cylindrical volume. Typical plasma parameters are Ti = 25 eV, ne >=1015 cm-3, and B = 0 . 25 T. The relaxed state is rapidly attained in 1-2 axial Alfvén times after initiation of the plasma. Magnetic data is favorably compared with an analytical model. Magnetic data exhibits broadband fluctuations of the measured axial modes during the formation period. The broadband activity rapidly decays as the energy condenses into the lowest energy mode, which is in agreement to the minimum energy eigenstate of ∇ × B --> = λ B --> . While the global structure roughly corresponds to the minimum energy eigenstate for the wind tunnel geometry, the plasma is high beta (β = 0 . 5) and does not have a flat λ profile. Merging with plasma plumes injected from both ends of the cylinder will be compared to the non-merging plasmas. Supported by US DOE and NSF.
NASA Technical Reports Server (NTRS)
Tsurutani, Bruce T.; Glassmeier, K.-H.; Neubauer, F. M.
1995-01-01
We examine and intercompare the LF plasma wave turbulence at three comets: Grigg-Skjellerup (GS), Giacobini-Zinner (GZ), and Halley (H). All three have power spectral peaks at the local ion cyclotron frequency (the pump wave) at approx. 10(exp -2) Hz, and a power-law fall-off at higher frequencies that suggest the development of turbulent cascades. The power laws for the three comets are approximately f(exp -1.9), f(exp -1.9) and f(exp -2.1), respectively. However, other than the similarities in the power spectra, we find the magnetic field turbulence is considerably different at the three comets. Phase steepening is demonstrated to occur at the trailing edges of the GS waves. This is probably due to nonlinear steepening plus dispersion of the left-hand mode components. A coherency analysis of GZ turbulence indicates that it is primarily composed of righthanded mode components, i.e., the turbulence is 'whistlermode.' This too can be explained by nonlinear steepening plus dispersion of the magnetosonic waves. At the level of GS and GZ turbulence development when the spacecraft measurements were made, classical three-wave processes, such as the decay or modulation instabilities do not appear to play important roles. It is most likely that the nonlinear steepening and dispersive time scales are more rapid than three-wave processes, and the latter had not had time to develop for the relatively 'new' turbulence. The wave turbulence at Halley is linearly polarized. The exact nature of this turbulence is still not well understood at this time. Several possibilities are suggested, based on our preliminary analyses.
Radio Wave Scattering in the Outer Heliosphere: Preliminary Calculations
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
1995-01-01
Detailed first estimates are presented of angular broadening in the outer heliosphere due to scattering of radio waves by density irregularities. The application is to the 2-3 kHz radiation observed by Voyager. Two plausible turbulence models, which account very well for scattering within 1 AU, are extrapolated beyond 10 AU. Both models predict significant angular broadening in the outer heliosphere, accounting semi- quantitatively alone for the source sizes inferred from roll modulation data. Predictions are presented for radial variations in the apparent source size if scattering is important. Comparisons with available data argue that scattering is important (and indeed is the dominant contributor to the apparent source size) and that the radiation source is located in the outer heliosphere. Other evidence that scattering is important, such as the fluctuations in apparent source direction and intensity, are also identified. The effects of scattering should be included in future analyses of the 2-3 kHz emissions.
Turbulent reconnection and its implications
Lazarian, A.; Eyink, G.; Vishniac, E.; Kowal, G.
2015-01-01
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700–718 ()) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate this process to
Turbulent reconnection and its implications.
Lazarian, A; Eyink, G; Vishniac, E; Kowal, G
2015-05-13
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700-718 (doi:10.1086/307233)) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate
Development of Data Analysis Techniques to Provide Photometric Images for a Heliospheric Imager
2008-10-31
signed / / signed / JANET C. JOHNSTON...ejections Heliospheric plasma 3D tomography Zodiacal light Spaceborne optical instrument Janet C. Johnston UNCL UNCL UNCL...waves. The instrument evolved from the heliospheric imaging capability demonstrated by the zodiacal light photometers of the Helios spacecraft. A near
NASA Astrophysics Data System (ADS)
Tsurutani, B. T.; Hajra, R.; Tanimori, T.; Takada, A.; Bhanu, R.; Mannucci, A. J.; Lakhina, G. S.; Kozyra, J. U.; Shiokawa, K.; Lee, L. C.; Echer, E.; Reddy, R. V.; Gonzalez, W. D.
2016-10-01
A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High-density solar wind heliospheric plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon-sector outer-zone magnetospheric 10-100 keV protons. The betatron accelerated protons generate coherent electromagnetic ion cyclotron (EMIC) waves through a temperature anisotropy (T⊥/T|| > 1) instability. The waves in turn interact with relativistic electrons and cause the rapid loss of these particles to a small region of the atmosphere. A peak total energy deposition of 3 × 1020 ergs is derived for the precipitating electrons. Maximum energy deposition and creation of electron-ion pairs at 30-50 km and at < 30 km altitude are quantified. We focus the readers' attention on the relevance of this present work to two climate change mechanisms. Wilcox et al. (1973) noted a correlation between solar wind heliospheric current sheet (HCS) crossings and high atmospheric vorticity centers at 300 mb altitude. Tinsley et al. has constructed a global circuit model which depends on particle precipitation into the atmosphere. Other possible scenarios potentially affecting weather/climate change are also discussed.
Hornsby, W. A.; Peeters, A. G.; Snodin, A. P.; Casson, F. J.; Camenen, Y.; Szepesi, G.; Siccinio, M.; Poli, E.
2010-09-15
The interaction between small scale turbulence (of the order of the ion Larmor radius) and mesoscale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Despite the stabilizing effect of sheared plasma flows in and around the island, the net effect of the island is a degradation of the confinement. When density and temperature gradients inside the island are below the threshold for turbulence generation, turbulent fluctuations still persist through turbulence convection and spreading. The latter mechanisms then generate a finite transport flux and, consequently, a finite pressure gradient in the island. A finite radial temperature gradient inside the island is also shown to persist due to the trapped particles, which do not move along the field around the island. In the low collisionality regime, the finite gradient in the trapped population leads to the generation of a bootstrap current, which reduces the neoclassical drive.
Temporal and spatial turbulent spectra of MHD plasma and an observation of variance anisotropy
Schaffner, D. A.; Brown, M. R.; Lukin, V. S.
2014-08-01
The nature of magnetohydrodynamic (MHD) turbulence is analyzed through both temporal and spatial magnetic fluctuation spectra. A magnetically turbulent plasma is produced in the MHD wind tunnel configuration of the Swarthmore Spheromak Experiment. The power of magnetic fluctuations is projected into directions perpendicular and parallel to a local mean field; the ratio of these quantities shows the presence of variance anisotropy which varies as a function of frequency. Comparisons among magnetic, velocity, and density spectra are also made, demonstrating that the energy of the turbulence observed is primarily seeded by magnetic fields created during plasma production. Direct spatial spectra are constructed using multi-channel diagnostics and are used to compare to frequency spectra converted to spatial scales using the Taylor hypothesis. Evidence for the observation of dissipation due to ion inertial length scale physics is also discussed, as well as the role laboratory experiments can play in understanding turbulence typically studied in space settings such as the solar wind. Finally, all turbulence results are shown to compare fairly well to a Hall-MHD simulation of the experiment.
Gyrokinetic Particle Simulation of Compressible Electromagnetic Turbulence in High-β Plasmas
Lin, Zhihong
2014-03-13
Supported by this award, the PI and his research group at the University of California, Irvine (UCI) have carried out computational and theoretical studies of instability, turbulence, and transport in laboratory and space plasmas. Several massively parallel, gyrokinetic particle simulation codes have been developed to study electromagnetic turbulence in space and laboratory plasmas. In space plasma projects, the simulation codes have been successfully applied to study the spectral cascade and plasma heating in kinetic Alfven wave turbulence, the linear and nonlinear properties of compressible modes including mirror instability and drift compressional mode, and the stability of the current sheet instabilities with finite guide field in the context of collisionless magnetic reconnection. The research results have been published in 25 journal papers and presented at many national and international conferences. Reprints of publications, source codes, and other research-related information are also available to general public on the PI’s webpage (http://phoenix.ps.uci.edu/zlin/). Two PhD theses in space plasma physics are highlighted in this report.
Gary, S. Peter
2015-01-01
Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. Temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave–particle interactions which transfer particle kinetic energy to field fluctuation energy; the resulting enhanced fluctuations are typically narrowband in wavevector magnitude and direction. Whatever their sources, short-wavelength fluctuations are those at which charged particle kinetic, that is, velocity-space, properties are important; these are generally wavelengths of the order of or shorter than the ion inertial length or the thermal ion gyroradius. The purpose of this review is to summarize and interpret recent computational results concerning short-wavelength plasma turbulence, short-wavelength temperature anisotropy instabilities and relationships between the two phenomena. PMID:25848081
Gary, S. Peter
2015-04-06
Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. In addition, temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave–particle interactions which transfer particle kinetic energy to field fluctuation energy; the resulting enhanced fluctuations are typically narrowband in wavevector magnitude and direction. Whatever their sources, short-wavelength fluctuations are those at which charged particle kinetic, that is, velocity-space, properties are important; these are generally wavelengths of the order of or shorter than the ion inertial length or the thermal ion gyroradius.more » The purpose of this review is to summarize and interpret recent computational results concerning short-wavelength plasma turbulence, short-wavelength temperature anisotropy instabilities and relationships between the two phenomena.« less
Von-Karman scaling of proton and electron heating in turbulent plasma
NASA Astrophysics Data System (ADS)
Parashar, T. N.; Matthaeus, W. H.; Wan, M.; Shay, M. A.
2015-12-01
Abstract: A self consistent description of plasma dissipation requires fully kinetic treatment. In recent publications, we have addressed how proton heating depends on large scale parameters [1,2] and how the system size simulated affects the plasma energetics [3]. Here, we study the relative heating of protons and electrons as it depends on large scale parameters. We also discuss the dependence of this relative heating on von-Karman decay rates, along with implications for turbulent dissipation challenge. An interesting possibility is that turbulent heating and heating in reconnection might be understood in a unified way [4]. [1] Wu et al, PRL, 111,121105 (2013) [2] Matthaeus et al, ApJ, 790, 155 (2014) [3] Parashar et al, ApJ (under review)[4] Shay et al, Physics of Plasmas, 21, 122902 (2014)
Aleksey Kuritsyn; Fred M. Levinton
2004-04-27
A megahertz LIF-based diagnostic system for measuring ion density fluctuations in two spatial dimensions is described. Well resolved spatial and temporal 2D images of turbulent structures will be useful in understanding ion turbulence in magnetically confined plasmas which is a key factor in the performance of fusion experimental devices. A sheet beam of a megahertz repetition rate tunable Alexandrite laser is used to excite ion emission from argon plasma. The fluorescence emitted from the plane of the laser beam is detected with a narrow band interference filter and intensified ultra-fast CCD camera providing 2D images of relative ion density fluctuations every microsecond. It is expected that the edge plasma on fusion devices will be accessible to this technique.
Kuritsyn, Aleksey; Levinton, Fred M.
2004-10-01
A megahertz laser-induced fluorescence-based diagnostic system for measuring ion density fluctuations in two spatial dimensions is described. Well resolved spatial and temporal two-dimensional (2D) images of turbulent structures will be useful in understanding ion turbulence in magnetically confined plasmas which is a key factor in the performance of fusion experimental devices. A sheet beam of a megahertz repetition rate tunable Alexandrite laser is used to excite ion emission from argon plasma. The fluorescence emitted from the plane of the laser beam is detected with a narrow band interference filter and intensified ultrafast charge coupled device camera providing 2D images of relative ion density fluctuations every microsecond. It is expected that the edge plasma on fusion devices will be accessible to this technique.
Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Diamond, P.H.; Lin, Z.; Wang, W.; Horton, W.; Klasky, S.; Decyk, V.; Ma, K.-L.; Chames, J.; Adams, M.
2011-09-21
The three-year project GPS-TTBP resulted in over 152 publications and 135 presentations. This summary focuses on the scientific progress made by the project team. A major focus of the project was on the physics intrinsic rotation in tokamaks. Progress included the first ever flux driven study of net intrinsic spin-up, mediated by boundary effects (in collaboration with CPES), detailed studies of the microphysics origins of the Rice scaling, comparative studies of symmetry breaking mechanisms, a pioneering study of intrinsic torque driven by trapped electron modes, and studies of intrinsic rotation generation as a thermodynamic engine. Validation studies were performed with C-Mod, DIII-D and CSDX. This work resulted in very successful completion of the FY2010 Theory Milestone Activity for OFES, and several prominent papers of the 2008 and 2010 IAEA Conferences. A second major focus was on the relation between zonal flow formation and transport non-locality. This culminated in the discovery of the ExB staircase - a conceptually new phenomenon. This also makes useful interdisciplinary contact with the physics of the PV staircase, well-known in oceans and atmospheres. A third topic where progress was made was in the simulation and theory of turbulence spreading. This work, now well cited, is important for understanding the dynamics of non-locality in turbulent transport. Progress was made in studies of conjectured non-diffusive transport in trapped electron turbulence. Pioneering studies of ITB formation, coupling to intrinsic rotation and hysteresis were completed. These results may be especially significant for future ITER operation. All told, the physics per dollar performance of this project was quite good. The intense focus was beneficial and SciDAC resources were essential to its success.
New Constraints on Plasma Turbulence in the Solar Corona
NASA Astrophysics Data System (ADS)
Spangler, S. R.; Spitler, L. G.
2005-12-01
One suggestion for coronal heating invokes the dissipation of high frequency, Alfvén-ion cyclotron waves which are generated in the photosphere and chromosphere and propagate into the corona. As we have previously noted (Spangler and Mancuso 2000, ApJ 530, 491) the properties of such waves can be constrained by radioastronomical observations. The observational effect is Faraday screen depolarization, in which stochastic Faraday rotation randomizes the polarization position angle on scales smaller than the telescope beam. We present observations made with the NRAO Very Large Array on August 16 and 18, 2003, when the radio galaxy 3C228 was viewed through the corona at heliocentric distances of 6.7 and 5.2 R⊙, respectively. The depolarization parameter D ≡ (m)/(m0) was measured, where m is the fractional linear polarization measured through the corona, and m0 is the intrinsic degree of polarization. Measurements were available for both hot spots of 3C228, and on both days of observation. The measurements are consistent with D=1 for both components on both days. These results are in agreement with, but superior to, previous reports of no coronal screen depolarization. Equations from Spangler and Mancuso (2000) are used to constrain the dimensionless amplitude and outer scale of the coronal turbulence. Turbulence with a dimensionless amplitude of 50 % or greater, and outer scale larger than 1000-2000 km, would have produced depolarization close to, or in excess of our limits. Turbulence with smaller dimensionless amplitude and outer scale would not have been detected with these measurements. This research was supported by grant ATM-0354782 from the National Science Foundation.
Double Langmuir frequency radiation due to transformation processes in turbulent plasma
NASA Astrophysics Data System (ADS)
Pavlenko, V. N.; Panchenko, V. G.; Beloshenko, N. A.
2015-04-01
We investigate the transformation process of longitudinal Langmuir wave into the transverse electromagnetic wave in turbulent plasma subjected to an upper hybrid pump. The case, when upper hybrid pump wave decays into daughter and ion - sound waves is considered. The transformation of the Langmuir wave into electromagnetic one is considered as the possible mechanism of energy radiation from the plasma. It is shown that the frequency of such radiation is chosen to be near double electron Langmuir frequency 2ωpe . These results give us the possibility to explain the nature of radiation from the laboratory and cosmic plasmas (particularly, from the solar crown).
Low Frequency Plasma Turbulence as a Source of Clutter in Surveillance and Communication (Postprint)
2013-08-01
excited by plasma flows with velocity shear, whereas interchange or flute type oscillations in magnetized plasma are associated with Rayleigh-Taylor type...turbulence. Lower-hybrid type density irregularities are excited by plasma flows with velocity shear, whereas interchange or flute type oscillations...where is the frequency of the flute mode and 0zi i ZeB m c is the cyclotron frequency of the ion with charge Z and mass i pm m , with pm
Mechanisms for the convergence of time-parallelized, parareal turbulent plasma simulations
Reynolds-Barredo, J.; Newman, David E; Sanchez, R.; Samaddar, D.; Berry, Lee A; Elwasif, Wael R
2012-01-01
Parareal is a recent algorithm able to parallelize the time dimension in spite of its sequential nature. It has been applied to several linear and nonlinear problems and, very recently, to a simulation of fully-developed, two-dimensional drift wave turbulence. The mere fact that parareal works in such a turbulent regime is in itself somewhat unexpected, due to the characteristic sensitivity of turbulence to any change in initial conditions. This fundamental property of any turbulent system should render the iterative correction procedure characteristic of the parareal method inoperative, but this seems not to be the case. In addition, the choices that must be made to implement parareal (division of the temporal domain, election of the coarse solver and so on) are currently made using trial-and-error approaches. Here, we identify the mechanisms responsible for the convergence of parareal of these simulations of drift wave turbulence. We also investigate which conditions these mechanisms impose on any successful parareal implementation. The results reported here should be useful to guide future implementations of parareal within the much wider context of fully-developed fluid and plasma turbulent simulations.
Cosmic ray transport in astrophysical plasmas
Schlickeiser, R.
2015-09-15
Since the development of satellite space technology about 50 years ago the solar heliosphere is explored almost routinely by several spacecrafts carrying detectors for measuring the properties of the interplanetary medium including energetic charged particles (cosmic rays), solar wind particle densities, and electromagnetic fields. In 2012, the Voyager 1 spacecraft has even left what could be described as the heliospheric modulation region, as indicated by the sudden disappearance of low energy heliospheric cosmic ray particles. With the available in-situ measurements of interplanetary turbulent electromagnetic fields and of the momentum spectra of different cosmic ray species in different interplanetary environments, the heliosphere is the best cosmic laboratory to test our understanding of the transport and acceleration of cosmic rays in space plasmas. I review both the historical development and the current state of various cosmic ray transport equations. Similarities and differences to transport theories for terrestrial fusion plasmas are highlighted. Any progress in cosmic ray transport requires a detailed understanding of the electromagnetic turbulence that is responsible for the scattering and acceleration of these particles.
Theoretical and Numerical Study of Anomalous Turbulent Transport in Plasmas
1991-02-05
Robert Barker of AFOSR and our plasma laboratory was involved in the program during the period of the contract. The selected undergraduate students were...involved in the related research. They participated in a weekly plasma seminar with graduate students and presented their assigned topics at the...seminar. The names of undergraduate students and the titles of their final reports are listed here. From May 16 to August 31. 1987: 1. Theodore Christopher
NASA Astrophysics Data System (ADS)
Sasaki, M.; Kasuya, N.; Itoh, K.; Yagi, M.; Itoh, S.-I.
2014-11-01
Nonlinear competition of turbulent structures and their roles in transport are investigated by using three-dimensional simulation code of resistive drift wave turbulence in magnetized cylindrical plasmas. Selective formation of zonal flows and streamers has been obtained by controlling the strength of damping of the zonal flow. In addition, there is an energy path from the drift waves to a flute type structure, which is linearly stable, and it becomes effective just below the stability boundary of the zonal flow. The flute structure directly induces transport effectively, and affects the drift waves and the zonal flow. A large amplitude zonal flow is formed selectively even with existence of the flute structure. The property of the particle confinement is investigated by changing the particle source intensity, which controls the strength of driving of the drift waves. The characteristic of the particle confinement changes according to turbulent states, and an improved confinement regime is obtained in the zonal flow dominant state. Study on cylindrical plasmas reveals the fundamental mechanism of improved confinement in the magnetized plasma with influence of turbulent structural formation.
NASA Astrophysics Data System (ADS)
Sugama, H.; Nunami, M.; Nakata, M.; Watanabe, T.-H.
2017-02-01
A novel gyrokinetic formulation is presented by including collisional effects into the Lagrangian variational principle to yield the governing equations for background and turbulent electromagnetic fields and gyrocenter distribution functions, which can simultaneously describe classical, neoclassical, and turbulent transport processes in toroidal plasmas with large toroidal flows on the order of the ion thermal velocity. Noether's theorem modified for collisional systems and the collision operator given in terms of Poisson brackets are applied to derivation of the particle, energy, and toroidal momentum balance equations in the conservative forms, which are desirable properties for long-time global transport simulation.
Transitions to spatiotemporal chaos and turbulence of flute instabilities in a magnetized plasma.
Brochard, F; Gravier, E; Bonhomme, G
2006-03-01
The spatiotemporal transition scenario of flute instabilities from a regular to a turbulent state is experimentally investigated in the plasma column of a thermionic discharge. The same transition scenario, i.e., the Ruelle-Takens route to turbulence, is found for both the Kelvin-Helmholtz and the Rayleigh-Taylor instabilities. It is demonstrated that the transition can be more or less smooth, according to the discharge mode. In both cases, a strong radial dependence is observed, which is linked to the velocity shear layer in the case of the Kelvin-Helmholtz instability.
Brochard, F.; Gravier, E.; Bonhomme, G.
2006-03-15
The spatiotemporal transition scenario of flute instabilities from a regular to a turbulent state is experimentally investigated in the low-{beta} plasma column of a thermionic discharge. The same transition scenario, i.e., the Ruelle-Takens route to turbulence, is found for both the Kelvin-Helmholtz and the Rayleigh-Taylor instabilities. It is demonstrated that the transition can be more or less smooth, according to the discharge mode. In both cases, a strong radial dependence is observed, which is linked to the velocity shear layer in the case of the Kelvin-Helmholtz instability.
Flux tube train model for local turbulence simulation of toroidal plasmas
Watanabe, T.-H.; Sugama, H.; Ishizawa, A.; Nunami, M.
2015-02-15
A new simulation method for local turbulence in toroidal plasmas is developed by extending the conventional idea of the flux tube model. In the new approach, a train of flux tubes is employed, where flux tube simulation boxes are serially connected at each end along a field line so as to preserve a symmetry of the local gyrokinetic equations for image modes in an axisymmetric torus. Validity of the flux tube train model is confirmed against the toroidal ion temperature gradient turbulence for a case with a long parallel correlation of fluctuations, demonstrating numerical advantages over the conventional method in the time step size and the symmetry-preserving property.
Intermittency of solar system plasma turbulence near Venus and Earth
NASA Astrophysics Data System (ADS)
Teodorescu, Eliza; Echim, Marius; Chang, Tom
2016-04-01
We analyze magnetic field data from Venus Express (VEX) and CLUSTER to investigate the turbulent properties of the solar wind and the Earth's and Venus' magnetosheaths. A systematic study of the PDFs (Probability Distribution Functions) of the measured magnetic fluctuations and their fourth order moments (kurtosis) reveals numerous intermittent time series. The presence of intermittency is marked by non-Gaussian PDFs with heavy wings and a scale dependent kurtosis. Higher order analyses on the scale dependence of several moment orders of the PDFs, the structure functions, along with the scaling of the kurtosis allow for a selection of scales that pertain to different scaling regimes, governed by different physics. On such sub-ranges of scales we investigate the fractal structure of fluctuations through the Rank Ordered Multifractal Analysis - ROMA (Chang and Wu, 2008). ROMA is applied to a selection of intermittent magnetic field time series in the solar wind and planetary magnetosheaths and helps to quantify the turbulence properties through the estimation of a spectrum of local Hurst exponents. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS - UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.
Role of nonlinear localized structures and turbulence in magnetized plasma
NASA Astrophysics Data System (ADS)
Pathak, Neha; Yadav, Nitin; Uma, R.; Sharma, R. P.
2016-09-01
In the present study, we have analyzed the field localization of kinetic Alfvén wave (KAW) due to the presence of background density perturbation, which are assumed to be originated by the three dimensionally propagating low frequency KAW. These localized structures play an important role for energy transportation at smaller scales in the dispersion range of magnetic power spectrum. For the present model, governing dynamic equations of high frequency pump KAW and low frequency KAW has been derived by considering ponderomotive nonlinearity. Further, these coupled equations have been numerically solved to analyze the resulting localized structures of pump KAW and magnetic power spectrum in the magnetopause regime. Numerically calculated spectrum exhibits inertial range having spectral index of -3/2 followed by steeper scaling; this steepening in the turbulent spectrum is a signature of energy transportation from larger to smaller scales. In this way, the proposed mechanism, which is based on nonlinear wave-wave interaction, may be useful for understanding the particle acceleration and turbulence in magnetopause.
Propagation of Interplanetary Disturbances in the Outer Heliosphere
NASA Technical Reports Server (NTRS)
Wang, Chi
2005-01-01
Contents include the following: 1. We have developed a one-dimensional, spherically symmetric, multi-fluid MHD model that includes solar wind protons and electrons, pickup ions, and interstellar neutral hydrogen. This model advances the existing solar wind models for the outer heliosphere in two important ways: one is that it distinguishes solar wind protons from pickup ions, and the other is that it allows for energy transfer from pickup ions to the solar wind protons. Model results compare favorably with the Voyager 2 observations. 2. 2. Solar wind slowdown and interstellar neutral density. The solar wind in the outer heliosphere is fundamentally different from that in the inner heliosphere since the effects of interstellar neutrals become significant. 3. ICME propagation from the inner to outer heliosphere. Large coronal mass ejections (CMEs) have major effects on the structure of the solar wind and the heliosphere. The plasma and magnetic field can be compressed ahead of interplanetary CMEs. 4. During the current solar cycle (Cycle 23), several major CMEs associated with solar flares produced large transient shocks which were observed by widely-separated spacecraft such as Wind at Earth and Voyager 2 beyond 60 AU. Using data from these spacecraft, we use the multi-fluid model to investigate shock propagation and interaction in the heliosphere. Specifically, we studied the Bastille Day 2000, April 2001 and Halloween 2003 events. 5. Statistical properties of the solar wind in the outer heliosphere. In a collaboration with L.F. Burlaga of GSFC, it is shown that the basic statistical properties of the solar wind in the outer heliosphere can be well produced by our model. We studied the large-scale heliospheric magnetic field strength fluctuations as a function of distance from the Sun during the declining phase of a solar cycle, using our numerical model with observations made at 1 AU during 1995 as input. 6. Radial heliospheric magnetic field events. The
Experimental Investigation of Turbulent-driven Sheared Parallel Flows in the CSDX Plasma Device
NASA Astrophysics Data System (ADS)
Tynan, George; Hong, Rongjie; Li, Jiacong; Thakur, Saikat; Diamond, Patrick
2016-10-01
Parallel velocity and its radial shear is a key element for both accessing improved confinement regimes and controlling the impurity transport in tokamak devices. In this study, the development of radially sheared parallel plasma flows in plasmas without magnetic shear is investigated using laser induced fluorescence, multi-tip Langmuir and Mach probes in the CSDX helicon linear plasma device. Results show that a mean parallel velocity shear grows as the radial gradient of plasma density increased. The sheared flow onset corresponds to the onset of a finite parallel Reynolds stress that acts to reinforce the flow. As a result, the mean parallel flow gains energy from the turbulence that, in turn, is driven by the density gradient. This results in a flow away from the plasma source in the central region of the plasma and a reverse flow in far-peripheral region of the plasma column. The results motivate a model of negative viscosity induced by the turbulent stress which may help explain the origin of intrinsic parallel flow in systems without magnetic shear.
The heliospheric energy source
NASA Technical Reports Server (NTRS)
Parker, E. N.
1986-01-01
The solar wind and the heliosphere exist as a consequence of the heat input to the corona, particularly the coronal holes. The necessary energy input to coronal holes has been estimated to be 10 to the 6th erg/sq cm sec, requiring Alfven waves with rms fluid velocities of 100 km/sec. Observational upper limits on coronal fluid velocities are of the order of 25 km/sec, which may not apply to the transparent coronal hole. Alternatively it has been suggested that coronal holes may be heated by agitation from neighboring active regions, suggesting that the vigor of a coronal hole depends upon its location. The Ulysses Mission will provide a direct comparison of the strength of the high speed wind from coronal holes at low latitude and coronal holes at high latitude, from which the nature of the presently unknown energy sources of the coronal holes and the resulting structure of the heliosphere may be better judged. The question is fundamental to the dynamics of the windspheres of all stars.
HELCATS - Heliospheric Cataloguing, Analysis and Techniques Service
NASA Astrophysics Data System (ADS)
Barnes, D.; Harrison, R. A.; Davies, J. A.; Byrne, J.; Perry, C. H.; Moestl, C.; Rouillard, A. P.; Bothmer, V.; Rodriguez, L.; Eastwood, J. P.; Kilpua, E.; Odstrcil, D.; Gallagher, P.
2015-12-01
Understanding the evolution of the solar wind is fundamental to advancing our knowledge of energy and mass transport in the Solar System, making it crucial to space weather and its prediction. The advent of truly wide-angle heliospheric imaging has revolutionised the study of both transient (CMEs) and background (IRs) solar wind plasma structures, by enabling their direct and continuous observation out to 1 AU and beyond. The EU-funded FP7 HELCATS project combines European expertise in heliospheric imaging, built up in particular through lead involvement in NASA's STEREO mission, with expertise in solar and coronal imaging as well as in-situ and radio measurements of solar wind phenomena, in a programme of work that will enable a much wider exploitation and understanding of heliospheric imaging observations. The HELCATS project endeavors to catalogue transient and background solar wind structures imaged by STEREO/HI throughout the duration of the mission. This catalogue will include estimates of their kinematic properties using a variety of established and more speculative approaches, which are to be evaluated through comparisons with solar source and in-situ measurements. The potential for driving numerical models from these kinematic properties is to be assessed, as is their complementarity to radio observations, specifically Type II bursts and interplanetary scintillation. This presentation provides an overview of the HELCATS project and its progress in first 18 months of operations.
Complexity methods applied to turbulence in plasma astrophysics
NASA Astrophysics Data System (ADS)
Vlahos, L.; Isliker, H.
2016-09-01
In this review many of the well known tools for the analysis of Complex systems are used in order to study the global coupling of the turbulent convection zone with the solar atmosphere where the magnetic energy is dissipated explosively. Several well documented observations are not easy to interpret with the use of Magnetohydrodynamic (MHD) and/or Kinetic numerical codes. Such observations are: (1) The size distribution of the Active Regions (AR) on the solar surface, (2) The fractal and multi fractal characteristics of the observed magnetograms, (3) The Self-Organised characteristics of the explosive magnetic energy release and (4) the very efficient acceleration of particles during the flaring periods in the solar corona. We review briefly the work published the last twenty five years on the above issues and propose solutions by using methods borrowed from the analysis of complex systems. The scenario which emerged is as follows: (a) The fully developed turbulence in the convection zone generates and transports magnetic flux tubes to the solar surface. Using probabilistic percolation models we were able to reproduce the size distribution and the fractal properties of the emerged and randomly moving magnetic flux tubes. (b) Using a Non Linear Force Free (NLFF) magnetic extrapolation numerical code we can explore how the emerged magnetic flux tubes interact nonlinearly and form thin and Unstable Current Sheets (UCS) inside the coronal part of the AR. (c) The fragmentation of the UCS and the redistribution of the magnetic field locally, when the local current exceeds a Critical threshold, is a key process which drives avalanches and forms coherent structures. This local reorganization of the magnetic field enhances the energy dissipation and influences the global evolution of the complex magnetic topology. Using a Cellular Automaton and following the simple rules of Self Organized Criticality (SOC), we were able to reproduce the statistical characteristics of the
NASA Technical Reports Server (NTRS)
Tsurutani, Bruce T.
1995-01-01
As the lead-off presentation for the topic of nonlinear waves and their evolution, we will illustrate some prominent examples of waves in space plasmas. We will describe recent observations detected within planetary foreshocks, near comets and in interplanetary space. It is believed that the nonlinear LF plasma wave features discussed here are part of and may be basic to the development of plasma turbulence. In this sense, this is one area of space plasma physics that is fundamental, with applications to fusion physics and astrophysics as well. It is hoped that the reader(s) will be stimulated to study nonlinear wave development themselves, if he/she is not already involved.
NASA Astrophysics Data System (ADS)
Chakraborty Thakur, S.; Adriany, K.; Gosselin, J. J.; McKee, J.; Scime, E. E.; Sears, S. H.; Tynan, G. R.
2016-11-01
We report experimental measurements of the axial plasma flow and the parallel ion temperature in a magnetized linear plasma device. We used laser induced fluorescence to measure Doppler resolved ion velocity distribution functions in argon plasma to obtain spatially resolved axial velocities and parallel ion temperatures. We also show changes in the parallel velocity profiles during the transition from resistive drift wave dominated plasma to a state of weak turbulence driven by multiple plasma instabilities.
Turbulence, Waves and Instabilities in the Solar Plasma
NASA Astrophysics Data System (ADS)
Erdélyi, R.; Petrovay, K.; Roberts, B.; Aschwanden, M.
2003-12-01
Significant advances have been made recently in both the theoretical understanding and observation of small-scale turbulence in different layers of the Sun, and in the instabilities that give rise to them. The general development of solar physics, however, has led to such a degree of specialization as to hinder interaction between workers in the field. This book therefore presents studies of different layers and regions of the Sun, but from the same aspect, concentrating on the study of small-scale motions. The main emphasis is on the common theoretical roots of these phenomena, but the book also contains an extensive treatment of the observational aspects. Link: http://www.springer.com/east/home?SGWID=5-102-22-3362=5696-0&changeHeader=true
Comments on adiabatic modifications to plasma turbulence theory
Krommes, J.A.
1980-11-01
Catto earlier introduced an interesting and plausible modification of the usual resonance-broadening prescription for obtaining the nonlinear dielectric function. He argued reasonably that one should employ that prescription only for the nonadiabatic response, and that one should treat the adiabatic response essentially exactly. However, Misguich, in a recent Comment on Catto's work, found an apparent divergence in a form for the renormalized dielectric which he argued was equivalent to Catto's. Misguich was thus led to conclude that, at least for stationary turbulence, Catto's form was suspect, and that a more intricate renormalization might have to be used to obtain a sensible, convergent result. It is argued that this conclusion is incorrect, at least for the reasons Misguich gives.
Orszag Tang vortex - Kinetic study of a turbulent plasma
Parashar, T. N.; Servidio, S.; Shay, M. A.; Matthaeus, W. H.; Cassak, P. A.
2010-03-25
Kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations based on particle in cell ions and fluid electrons. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. An earlier study estimated the dissipation in the system. A comparison of MHD and hybrid simulations showed similar behavior at large scales but substantial differences at small scales. The hybrid magnetic energy spectrum shows a break at the scale where Hall term in the Ohm's law becomes important. The protons heat perpendicularly and most of the energy is dissipated through magnetic interactions. Here, the space time structure of the system is studied using frequency-wavenumber (k-omega) decomposition. No clear resonances appear, ruling out the cyclotron resonances as a likely candidate for the perpendicular heating. The only distinguishable wave modes present, which constitute a small percentage of total energy, are magnetosonic modes.
Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma
Parashar, T. N.; Shay, M. A.; Cassak, P. A.; Matthaeus, W. H.
2009-03-15
The kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. At large length scales, the evolution of the hybrid simulations is very similar to MHD, with magnetic power spectra displaying scaling similar to a Kolmogorov scaling of -5/3. At small scales, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field. The magnetic energy spectrum of the hybrid simulation shows a break where linear theory predicts that the Hall term in Ohm's law becomes significant, leading to dispersive kinetic Alfven waves. A key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy of the type observed in the corona and solar wind.
Continuum Gyrokinetic Simulations of Turbulence in Open-Field-Line Plasmas
NASA Astrophysics Data System (ADS)
Shi, E. L.; Hammett, G. W.; Stoltzfus-Dueck, T.; Hakim, A.
2016-10-01
We have performed our first 3D2V gyrokinetic simulations of electrostatic plasma turbulence in open-field-line geometries using the full-F discontinuous-Galerkin code Gkeyll. These simulations include the basic elements of a scrape-off layer: localized sources to model plasma outflow from the core, cross-field turbulent transport, parallel flow along magnetic field lines, and parallel losses at the limiter or divertor with sheath boundary conditions. The set of boundary conditions used in our model allows currents to flow through the walls and satisfies energy conservation. In addition to details of our numerical approach, we will present results from flux-tube simulations of devices containing straight-field lines (such as LAPD) and helical-field-lines (such as the TORPEX simple magnetized torus). Preliminary results show turbulent fluctuation levels similar to fluid simulations, which are comparable to the observed fluctuation level in LAPD but somewhat smaller than observed in TORPEX. This research was supported by the Max-Planck/Princeton Center for Plasma Physics, the SciDAC Center for the Study of Plasma Microturbulence, and U.S. DOE contract DE-AC02-09CH11466.
Development of a long pulse plasma gun discharge for magnetic turbulence studies
NASA Astrophysics Data System (ADS)
Schaffner, David
2016-10-01
A long pulse ( 300 μs) plasma gun discharge is in development at the Bryn Mawr College Plasma Laboratory for the production of sustained magnetized plasma injection for magnetohydrodynamic (MHD) turbulence studies. An array of eight 0.5mF parallel capacitors are used to create a pulse-forming-network (PFN) with a plateaued current output of 50kA for at least 200 of the 300 μs pulse. A 24cm inner diameter plasma gun provides stuffing flux fields at the stuffing threshold in order to allow for the continuous injection of magnetic helicity. Plasma is injected into a 24cm diameter flux-conserving aluminum chamber with a high density port array for fine spatial resolution diagnostic access. Fluctuations of magnetic field and saturation current are measured using pickup probes and Langmuir probes respectively.
Mean and oscillating plasma flows and turbulence interactions across the L-H confinement transition.
Conway, G D; Angioni, C; Ryter, F; Sauter, P; Vicente, J
2011-02-11
A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.
STATISTICS OF THE VELOCITY GRADIENT TENSOR IN SPACE PLASMA TURBULENT FLOWS
Consolini, Giuseppe; Marcucci, Maria Federica; Pallocchia, Giuseppe; Materassi, Massimo
2015-10-10
In the last decade, significant advances have been presented for the theoretical characterization and experimental techniques used to measure and model all of the components of the velocity gradient tensor in the framework of fluid turbulence. Here, we attempt the evaluation of the small-scale velocity gradient tensor for a case study of space plasma turbulence, observed in the Earth's magnetosheath region by the CLUSTER mission. In detail, we investigate the joint statistics P(R, Q) of the velocity gradient geometric invariants R and Q, and find that this P(R, Q) is similar to that of the low end of the inertial range for fluid turbulence, with a pronounced increase in the statistics along the so-called Vieillefosse tail. In the context of hydrodynamics, this result is referred to as the dissipation/dissipation-production due to vortex stretching.
Kolesnikov, R.A.; Krommes, J.A.
2005-09-22
The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for the model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.
Mean and Oscillating Plasma Flows and Turbulence Interactions across the L-H Confinement Transition
Conway, G. D.; Angioni, C.; Ryter, F.; Sauter, P.; Vicente, J.
2011-02-11
A complex interaction between turbulence driven ExB zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.
Self-regulation of E x B flow shear via plasma turbulence.
Vianello, N; Spada, E; Antoni, V; Spolaore, M; Serianni, G; Regnoli, G; Cavazzana, R; Bergsåker, H; Drake, J R
2005-04-08
The momentum balance has been applied to the ExB flow in the edge region of a reversed field pinch (RFP) configuration. All terms, including those involving fluctuations, have been measured in stationary condition in the edge region of the Extrap-T2R RFP experiment. It is found that the component of the Reynolds stress driven by electrostatic fluctuations is the term playing the major role in driving the shear of the ExB flow to a value marginal for turbulent suppression, so that the results are in favor of a turbulence self-regulating mechanism underlying the momentum balance at the edge. Balancing the sheared flow driving and damping terms, the plasma viscosity is found anomalous and consistent with the diffusivity due to electrostatic turbulence.
Self-Regulation of E×B Flow Shear via Plasma Turbulence
NASA Astrophysics Data System (ADS)
Vianello, N.; Spada, E.; Antoni, V.; Spolaore, M.; Serianni, G.; Regnoli, G.; Cavazzana, R.; Bergsåker, H.; Drake, J. R.
2005-04-01
The momentum balance has been applied to the E×B flow in the edge region of a reversed field pinch (RFP) configuration. All terms, including those involving fluctuations, have been measured in stationary condition in the edge region of the Extrap-T2R RFP experiment. It is found that the component of the Reynolds stress driven by electrostatic fluctuations is the term playing the major role in driving the shear of the E×B flow to a value marginal for turbulent suppression, so that the results are in favor of a turbulence self-regulating mechanism underlying the momentum balance at the edge. Balancing the sheared flow driving and damping terms, the plasma viscosity is found anomalous and consistent with the diffusivity due to electrostatic turbulence.
Resonance line radiation originating from a region with well-developed plasma turbulence
NASA Astrophysics Data System (ADS)
Kleiman, E. B.; Koulinich, V. V.
1994-10-01
This study considers the influence of the effects of scattering due to Langmuir turbulent pulsations in the transfer of radiation in the spectral lines. The transfer equation of radiation in spectral lines, by taking into account scattering due to Langmuir turbulent pulsations, is written in a form convenient for application by numerical methods. The profile's intensity for a plane-parallel finite isothermal slab of a turbulent plasma in the case of complete redistribution of scattering by an atom are obtained. Numerical studies show that in this case with the broadening of spectral lines and the decreasing of self-reversal, the Langmuir frequency nupe is of the same order as the electronic Doppler width delta nuDe. Creation of the line satellites when nupe is larger than the line width delta nu is shown with the aid of numerical methods.
Zhong, W L; Shen, Y; Zou, X L; Gao, J M; Shi, Z B; Dong, J Q; Duan, X R; Xu, M; Cui, Z Y; Li, Y G; Ji, X Q; Yu, D L; Cheng, J; Xiao, G L; Jiang, M; Yang, Z C; Zhang, B Y; Shi, P W; Liu, Z T; Song, X M; Ding, X T; Liu, Yong
2016-07-22
The impact of impurity ions on a pedestal has been investigated in the HL-2A Tokamak, at the Southwestern Institute of Physics, Chengdu, China. Experimental results have clearly shown that during the H-mode phase, an electromagnetic turbulence was excited in the edge plasma region, where the impurity ions exhibited a peaked profile. It has been found that double impurity critical gradients are responsible for triggering the turbulence. Strong stiffness of the impurity profile has been observed during cyclic transitions between the I-phase and H-mode regime. The results suggest that the underlying physics of the self-regulated edge impurity profile offers the possibility for an active control of the pedestal dynamics via pedestal turbulence.
Modelling for turbulent transport of nanoparticles growing around a thermal plasma jet
NASA Astrophysics Data System (ADS)
Shigeta, Masaya
2015-09-01
Modelling works for expressing the simultaneous processes of growth and transport of nanoparticles around a turbulent-like thermal plasma jet are presented. From the physical aspect, extending the previous model, a simple-but-consistent model which requires less computational costs is developed to describe the nanoparticles' birth and collective growth through homogeneous nucleation, heterogeneous condensation, and coagulation among themselves as well as transports by convection, diffusion, and thermophoresis. From the mathematical aspect, an original simulation code with higher accuracy is developed to express thermal plasma turbulence and to capture steep gradients in the spatial distribution of nanoparticles. As a base case, an argon thermal plasma jet is ejected at 1.5 slm from the nozzle, and iron vapor is supplied at 0.1 g/min with the plasma jet. The computation shows that the high-temperature plasma jet entrains the surrounding non-ionized gas because of Kelvin-Helmholtz instability at their interface. The instability waves grow up and then the interface rolls up to eddies. As the jet goes downstream, the eddies break to smaller ones, which lead to turbulence transition. This feature has also been reported in the experimental study. The iron vapor is transported with the plasma flow and simultaneously diffuses across the plasma's fringe where the vapor experiences the temperature decrease. As a result, the vapor changes its phase to nanoparticles through nucleation and condensation. The nanoparticles are also transported by convection and diffusion. The regions of large diameters coincide with those of low number densities of nanoparticles, because the size of nanoparticles increases through coagulation among themselves decreasing their own numbers.
Turbulent Transport in a Three-dimensional Solar Wind
NASA Astrophysics Data System (ADS)
Shiota, D.; Zank, G. P.; Adhikari, L.; Hunana, P.; Telloni, D.; Bruno, R.
2017-03-01
Turbulence in the solar wind can play essential roles in the heating of coronal and solar wind plasma and the acceleration of the solar wind and energetic particles. Turbulence sources are not well understood and thought to be partly enhanced by interaction with the large-scale inhomogeneity of the solar wind and the interplanetary magnetic field and/or transported from the solar corona. To investigate the interaction with background inhomogeneity and the turbulence sources, we have developed a new 3D MHD model that includes the transport and dissipation of turbulence using the theoretical model of Zank et al. We solve for the temporal and spatial evolution of three moments or variables, the energy in the forward and backward fluctuating modes and the residual energy and their three corresponding correlation lengths. The transport model is coupled to our 3D model of the inhomogeneous solar wind. We present results of the coupled solar wind-turbulence model assuming a simple tilted dipole magnetic configuration that mimics solar minimum conditions, together with several comparative intermediate cases. By considering eight possible solar wind and turbulence source configurations, we show that the large-scale solar wind and IMF inhomogeneity and the strength of the turbulence sources significantly affect the distribution of turbulence in the heliosphere within 6 au. We compare the predicted turbulence distribution results from a complete solar minimum model with in situ measurements made by the Helios and Ulysses spacecraft, finding that the synthetic profiles of the turbulence intensities show reasonable agreement with observations.
On-Off intermittency detected at the onset of turbulence in a magnetized plasma column
NASA Astrophysics Data System (ADS)
Pierre, Thiery
2016-10-01
The transition to turbulence is investigated in a rotating linear magnetized plasma column (MISTRAL device) and the role of the noise is emphasized. The destabilization is induced by injection of electrons on the axis of the device biasing the anode of the source plasma. Starting from a rotating plasma, that can be compared to a laminar regime in fluid dynamics, the slight increase of the potential of the source plasma leads to the onset of intermittent bursts in the edge corresponding to the expulsion of plasma blobs and to the transient destruction of the stable rotating plasma column. The statistical analysis of the time series of the density at the onset of the intermittency is performed. The distribution of the recurrence time of the turbulent bursts and the distribution of the duration of the laminar phases are analyzed. At the threshold, a power law is found for the distribution of the laminar duration with critical exponent -3/2. This dynamical behavior is similar to On-off intermittency (Platt, Spiegel, Tresser, PRL 70, 279,1993) induced by Gaussian noise superimposed on the control parameter. When the control parameter is increased, the distribution evolves towards an exponential decay law.
Runaway electrons and turbulence in a current-carrying stellarator plasma
Volkov, E.D.; Perepelkin, N.F.; Suprunenko, V.A.; Arsen'ev, A.V.; Burchenko, P.Y.; Vasil'ev, M.P.; Kotsubanov, V.D.; Kulaga, A.E.; Rubtsov, K.S.; Slavnyi, A.S.
1984-07-01
A disruption of the free acceleration of electrons in a magnetized, ohmically heated plasma in the Uragan-2 and Sirius stellarators has been observed and studied. Depending on the electric field and the ratio E/E/sub c//sub r/, the plasma heating in a stellarator may fall in one of three regimes associated with the appearance of a tail on the electron energy distribution: free acceleration (runaway) of electrons in a relatively cool plasma with a classical conductivity, at E<0.1E/sub c//sub r/; limited acceleration at Eapprox.(0.1--1.0)E/sub c//sub r/; and total disruption of the free acceleration in a hot plasma at E>E/sub c//sub r/. The behavior of the electron tail from one regime to another over the course of the discharge is related to the development of various stages of microinstabilities near the plasma frequency ..omega../sub pe/ and the ion plasma frequency ..omega../sub ..pi../. It appears that these instabilities stabilize the current drift velocity at various levels. The turbulent heating of electrons and ions at the anomalous resistance and the suppression of the free electron acceleration arise near a threshold Eapprox.E/sub c//sub r/. Results on the turbulent heating of ions carried out in various tokamaks and stellarators are compared.
Wang, W. X.; Ethier, S.; Ren, Y.; Kaye, S.; Chen, J.; Startsev, E.; Lu, Z.; Li, Z. Q.
2015-10-15
Highly distinct features of spherical tokamaks (ST), such as National Spherical Torus eXperiment (NSTX) and NSTX-U, result in a different fusion plasma regime with unique physics properties compared to conventional tokamaks. Nonlinear global gyrokinetic simulations critical for addressing turbulence and transport physics in the ST regime have led to new insights. The drift wave Kelvin-Helmholtz (KH) instability characterized by intrinsic mode asymmetry is identified in strongly rotating NSTX L-mode plasmas. While the strong E x B shear associated with the rotation leads to a reduction in KH/ion temperature gradient turbulence, the remaining fluctuations can produce a significant ion thermal transport that is comparable to the experimental level in the outer core region (with no "transport shortfall"). The other new, important turbulence source identified in NSTX is the dissipative trapped electron mode (DTEM), which is believed to play little role in conventional tokamak regime. Due to the high fraction of trapped electrons, long wavelength DTEMs peaking around k_{θρs} ~ 0.1 are destabilized in NSTX collisionality regime by electron density and temperature gradients achieved there. Surprisingly, the E x B shear stabilization effect on DTEM is remarkably weak, which makes it a major turbulence source in the ST regime dominant over collisionless TEM (CTEM). The latter, on the other hand, is subject to strong collisional and E x B shear suppression in NSTX. DTEM is shown to produce significant particle, energy and toroidal momentum transport, in agreement with experimental levels in NSTX H-modes. Furthermore, DTEM-driven transport in NSTX parametric regime is found to increase with electron collision frequency, providing one possible source for the scaling of confinement time observed in NSTX H-modes. Most interestingly, the existence of a turbulence-free regime in the collision-induced CTEM to DTEM transition, corresponding to a minimum plasma
NASA Astrophysics Data System (ADS)
Wang, W. X.; Ethier, S.; Ren, Y.; Kaye, S.; Chen, J.; Startsev, E.; Lu, Z.; Li, Z. Q.
2015-10-01
Highly distinct features of spherical tokamaks (ST), such as National Spherical Torus eXperiment (NSTX) and NSTX-U, result in a different fusion plasma regime with unique physics properties compared to conventional tokamaks. Nonlinear global gyrokinetic simulations critical for addressing turbulence and transport physics in the ST regime have led to new insights. The drift wave Kelvin-Helmholtz (KH) instability characterized by intrinsic mode asymmetry is identified in strongly rotating NSTX L-mode plasmas. While the strong E ×B shear associated with the rotation leads to a reduction in KH/ion temperature gradient turbulence, the remaining fluctuations can produce a significant ion thermal transport that is comparable to the experimental level in the outer core region (with no "transport shortfall"). The other new, important turbulence source identified in NSTX is the dissipative trapped electron mode (DTEM), which is believed to play little role in conventional tokamak regime. Due to the high fraction of trapped electrons, long wavelength DTEMs peaking around kθρs˜0.1 are destabilized in NSTX collisionality regime by electron density and temperature gradients achieved there. Surprisingly, the E ×B shear stabilization effect on DTEM is remarkably weak, which makes it a major turbulence source in the ST regime dominant over collisionless TEM (CTEM). The latter, on the other hand, is subject to strong collisional and E ×B shear suppression in NSTX. DTEM is shown to produce significant particle, energy and toroidal momentum transport, in agreement with experimental levels in NSTX H-modes. Moreover, DTEM-driven transport in NSTX parametric regime is found to increase with electron collision frequency, providing one possible source for the scaling of confinement time observed in NSTX H-modes. Most interestingly, the existence of a turbulence-free regime in the collision-induced CTEM to DTEM transition, corresponding to a minimum plasma transport in advanced ST
Wang, W. X.; Ethier, S.; Ren, Y.; ...
2015-10-15
Highly distinct features of spherical tokamaks (ST), such as National Spherical Torus eXperiment (NSTX) and NSTX-U, result in a different fusion plasma regime with unique physics properties compared to conventional tokamaks. Nonlinear global gyrokinetic simulations critical for addressing turbulence and transport physics in the ST regime have led to new insights. The drift wave Kelvin-Helmholtz (KH) instability characterized by intrinsic mode asymmetry is identified in strongly rotating NSTX L-mode plasmas. While the strong E x B shear associated with the rotation leads to a reduction in KH/ion temperature gradient turbulence, the remaining fluctuations can produce a significant ion thermal transportmore » that is comparable to the experimental level in the outer core region (with no "transport shortfall"). The other new, important turbulence source identified in NSTX is the dissipative trapped electron mode (DTEM), which is believed to play little role in conventional tokamak regime. Due to the high fraction of trapped electrons, long wavelength DTEMs peaking around kθρs ~ 0.1 are destabilized in NSTX collisionality regime by electron density and temperature gradients achieved there. Surprisingly, the E x B shear stabilization effect on DTEM is remarkably weak, which makes it a major turbulence source in the ST regime dominant over collisionless TEM (CTEM). The latter, on the other hand, is subject to strong collisional and E x B shear suppression in NSTX. DTEM is shown to produce significant particle, energy and toroidal momentum transport, in agreement with experimental levels in NSTX H-modes. Furthermore, DTEM-driven transport in NSTX parametric regime is found to increase with electron collision frequency, providing one possible source for the scaling of confinement time observed in NSTX H-modes. Most interestingly, the existence of a turbulence-free regime in the collision-induced CTEM to DTEM transition, corresponding to a minimum plasma transport in
Self-regulating Drift wave -- Zonal Flow turbulence in a linear plasma device
NASA Astrophysics Data System (ADS)
Xie, Jinlin; Chen, Ran; Hu, Guanghai; Jin, Xiaoli; Li, Hong; Liu, Wandong; Yu, Changxuan
2012-10-01
Here we report new and interesting results about the DW-ZF system in a linear plasma device with much better control environments to illustrate important Zonal flow physics: (1) The three-dimensional spectral features of the LFZF have been provided. In particular, it is identified that the LFZF damping is dominated by ion-neutral collision in our case. Also experimental evidence of the shearing effect of ZF on DW has been given. (2) A zonal flow dominated state of the DW-ZF system has been achieved. Theoretically, it has been predicted that a significant portion of the turbulence energy can be stored in the Zonal Flows for the case of low collisionality plasmas. In our experiments we achieve a zonal flow dominated state, in which the maximum ratio of the ZF energy to the total turbulence energy is about 80%, which seems to support the hypothesis of zonostropic state in geostrophic turbulence. (3) The self-regulating dynamics in the DW-ZF system is clearly elucidated. The evolution of the energy partition ratio of drift-wave turbulence and zonal flow is investigated with varying magnetic field strength, which is found consistent with the general prey-predator model.
NASA Astrophysics Data System (ADS)
Takamoto, Makoto; Lazarian, Alexandre
2016-11-01
In this Letter, we report compressible mode effects on relativistic magnetohydrodynamic (RMHD) turbulence in Poynting-dominated plasmas using three-dimensional numerical simulations. We decomposed fluctuations in the turbulence into 3 MHD modes (fast, slow, and Alfvén) following the procedure of mode decomposition in Cho & Lazarian, and analyzed their energy spectra and structure functions separately. We also analyzed the ratio of compressible mode to Alfvén mode energy with respect to its Mach number. We found the ratio of compressible mode increases not only with the Alfvén Mach number, but also with the background magnetization, which indicates a strong coupling between the fast and Alfvén modes. It also signifies the appearance of a new regime of RMHD turbulence in Poynting-dominated plasmas where the fast and Alfvén modes are strongly coupled and, unlike the non-relativistic MHD regime, cannot be treated separately. This finding will affect particle acceleration efficiency obtained by assuming Alfvénic critical-balance turbulence and can change the resulting photon spectra emitted by non-thermal electrons.
NASA Astrophysics Data System (ADS)
Frisch, Uriel
1996-01-01
Written five centuries after the first studies of Leonardo da Vinci and half a century after A.N. Kolmogorov's first attempt to predict the properties of flow, this textbook presents a modern account of turbulence, one of the greatest challenges in physics. "Fully developed turbulence" is ubiquitous in both cosmic and natural environments, in engineering applications and in everyday life. Elementary presentations of dynamical systems ideas, probabilistic methods (including the theory of large deviations) and fractal geometry make this a self-contained textbook. This is the first book on turbulence to use modern ideas from chaos and symmetry breaking. The book will appeal to first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, as well as professional scientists and engineers.
Hard X-ray generation in the turbulent plasma of solar flares
NASA Astrophysics Data System (ADS)
Charikov, Yu. E.; Shabalin, A. N.
2016-12-01
The influence of scattering of accelerated electrons in the turbulent plasma on the transformation of their distribution function is studied. The turbulence is connected with the emergence of magnetic inhomogeneities and ion-sound mode. The level of ion-sound turbulence is specified by the ratio W s/ nk B T e = 10-3, while the value of magnetic fluctuations is δB/B = 10-3. Different initial angular distributions of the function of accelerated-electron source are regarded: from isotropic to narrow directional distributions. For the chosen energy-density values of the ion-sound turbulence and the level of magnetic fluctuations, it is shown that both types of turbulence lead to a qualitative change in the hard X-ray brightness along the loop, moreover their influence was found to be different. Models with magnetic fluctuations and the ion sound can be distinguished not only by the difference in the hard X-ray distribution along the loop but also by the photon spectrum.
Self-Consistent Simulation of Turbulence and Transport in Tokamak Edge Plasmas
Rognlien, T D; Umansky, M V; Xu, X Q; Cohen, R H
2003-09-03
The status of coupling the fluid 3D turbulence code BOUT and the fluid plasma/neutral 2D transport code UEDGE is reported, where both codes simulate the edge region of diverted tokamaks from several cm inside the magnetic separatrix to the far scrape-off layer (SOL), thereby including the magnetic X-point. Because the characteristic time scale of the turbulence is short ({approx} 10{sup -5}-10{sup -4}s) and the profile evolution time scale can be long ({approx} 10{sup -2}-10{sup -1} s owing to recycling), an iterative scheme is used that relaxes the turbulent fluxes passed from BOUT to UEDGE and the profiles from UEDGE to BOUT over many coupling steps. Each code is run on its own characteristic time scale, yielding a statistically averaged steady state. For this initial study, the ion and neutral densities and parallel velocities are evolved, while the temperature profiles are stationary. Here the turbulence code is run in the electrostatic approximation. For this example of self-consistent coupling with strong L-mode-like turbulence, the ion flux to the main-chamber exceeds that to the divertor plates.
Schaffner, D A; Carter, T A; Rossi, G D; Guice, D S; Maggs, J E; Vincena, S; Friedman, B
2012-09-28
Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) has been achieved using a biasable limiter which has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and transport in the LAPD. The LAPD rotates spontaneously in the ion diamagnetic direction; positive limiter bias first reduces, then minimizes (producing a near-zero shear state), and finally reverses the flow into the electron diamagnetic direction. Degradation of particle confinement is observed in the minimum shearing state and a reduction in the turbulent particle flux is observed with increasing shearing in both flow directions. Near-complete suppression of the turbulent particle flux is observed for shearing rates comparable to the turbulent autocorrelation rate measured in the minimum shear state. Turbulent flux suppression is dominated by amplitude reduction in low-frequency (<10 kHz) density fluctuations. An increase in fluctuations for the highest shearing states is observed with the emergence of a coherent mode which does not lead to net particle transport. The variations of density fluctuations are fit well with power laws and compare favorably to simple models of shear suppression of transport.
A source of plasma turbulence at the ionopause of Venus
NASA Technical Reports Server (NTRS)
Daniell, R. E., Jr.
1981-01-01
The microscopic aspects of the interaction of the solar wind with the ionosphere of Venus are explored, in light of simultaneous suprathermal ion and low frequency electric field signal measurements by Pioneer Venus instruments which suggest that the two ionopause phenomena may be causally related. Both parallel and perpendicular propagating waves are examined for instability, in the presence of planetary ions added to the flowing ionosheath plasma, by linear Vlasov theory. While for the low beta plasma conditions of the ionopause neither electrostatic nor electromagnetic parallel propagating waves are found to be unstable, perpendicular propagating electrostatic waves are unstable and have the proper frequency-wavelength relation to be Doppler shifted into the observed 100-Hz channel.
Methods of Plasma Turbulence Analysis: Application to Shock Studies
Balikhin, M.A.; Walker, S.N.
2005-08-01
The availability of multisatellite observations (e.g. ISEE, AMPTE, and Cluster) has triggered the development of new methods of analysis to shed light on the complex dynamics inherent in the solar wind and magnetosphere. This paper looks at the results of two such methods. Firstly, the phase differencing method is used to determine the properties of waves observed upstream of a quasiperpendicular bow shock. The resulting dispersion relation is then interpreted as evidence that the waves are generated as a result of the dynamics of the shock front. The second, NARMAX, is used to investigate the linear and nonlinear processes if the plasma observed at a antiparallel shock. The results show that for a small amplitude whistler wavetrain, third order nonlinear interactions are only important at the interface between the shocklet and the wavetrain. For higher amplitude wavetrains, the phase of the linear term describing the plasma is shifted.
THIN CURRENT SHEETS AND ASSOCIATED ELECTRON HEATING IN TURBULENT SPACE PLASMA
Chasapis, A.; Retinò, A.; Sahraoui, F.; Canu, P.; Vaivads, A.; Khotyaintsev, Yu. V.; Sundkvist, D.; Greco, A.; Sorriso-Valvo, L.
2015-05-01
Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.
Michopoulos, Filippos; Edge, Antony M; Theodoridis, Georgios; Wilson, Ian D
2010-06-01
The use of turbulent flow chromatography (TFC) as a method for the rapid metabonomic LC-MS analysis of plasma as an alternative to solvent-based protein precipitation has been investigated. This comparison has shown that TFC can be effectively used in this application with the benefit that off-line sample handling is significantly reduced. However, analysis of the data obtained via TFC for human plasma reveals substantial differences in the overall metabolite profiles compared with methanol-precipitated HPLC-MS. This seems in part at least to be related to greatly reduced amounts of phospholipids (ca. 10 fold reduction) for the turbulent flow methodology compared with protein-precipitated samples. The significance of these differences with respect to metabolite profiles as a result of the sample preparation method used are discussed.
Plasma wave turbulence in the strong coupling region at comet Giacobini-Zinner
NASA Technical Reports Server (NTRS)
Coroniti, F. V.; Kennel, C. F.; Scarf, F. L.; Smith, E. J.; Tsurutani, B. T.; Bame, S. J.; Thomsen, M. F.; Hynds, R.; Wenzel, K. P.
1986-01-01
Within 100,000 km of comet Giacobini-Zinner's nucleus, strong plasma wave turbulence was detected by the ICE electric and magnetic field wave instruments. The spatial profiles of the wave amplitudes are compared with measurements of the heavy ion fluxes of cometary origin, the plasma electron density, and the magnetic field strength. The general similarity of the wave and heavy ion profiles suggest that the waves might be generated by free energy in the pick-up ion distribution function. However, the expected parallel streaming instability of electrostatic modes generates waves with frequencies that are too low to explain the observations. The observed low frequency magnetic turbulence is plausibly explained by the lower hybrid loss-cone instability of heavy ions.
Ricci, Paolo; Theiler, C.; Fasoli, A.; Furno, I.; Labit, B.; Mueller, S. H.; Podesta, M.; Poli, F. M.
2009-05-15
The methodology for plasma-turbulence code validation is discussed, with focus on the quantities to use for the simulation-experiment comparison, i.e., the validation observables, and application to the TORPEX basic plasma physics experiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. The considered validation observables are deduced from Langmuir probe measurements and are ordered into a primacy hierarchy, according to the number of model assumptions and to the combinations of measurements needed to form each of them. The lowest levels of the primacy hierarchy correspond to observables that require the lowest number of model assumptions and measurement combinations, such as the statistical and spectral properties of the ion saturation current time trace, while at the highest levels, quantities such as particle transport are considered. The comparison of the observables at the lowest levels in the hierarchy is more stringent than at the highest levels. Examples of the use of the proposed observables are applied to a specific TORPEX plasma configuration characterized by interchange-driven turbulence.
Steady State Turbulent Transport in Magnetic Fusion Plasmas
Lee, W. W.; Ethier, S.; Kolesnikov, R.; Wang, W. X.; Tang, W. M.
2007-12-20
For more than a decade, the study of microturbulence, driven by ion temperature gradient (ITG) drift instabilities in tokamak devices, has been an active area of research in magnetic fusion science for both experimentalists and theorists alike. One of the important impetus for this avenue of research was the discovery of the radial streamers associated the ITG modes in the early nineties using a Particle-In-Cell (PIC) code. Since then, ITG simulations based on the codes with increasing realism have become possible with the dramatic increase in computing power. The notable examples were the demonstration of the importance of nonlinearly generated zonal flows in regulating ion thermal transport and the transition from Bohm to GyroBoham scaling with increased device size. In this paper, we will describe another interesting nonlinear physical process associated with the parallel acceleration of the ions, that is found to play an important role for the steady state turbulent transport. Its discovery is again through the use of the modern massively parallel supercomputers.
Turbulent mixing of the solar wind with the interstellar medium
NASA Astrophysics Data System (ADS)
Veselovsky, Igor; Zeldovich, Maria; Verigin, Michael
We demonstrate both theoretically and using recent experimental data, that interaction of the solar wind with the interstellar medium is not laminar as supposed in many theoretical and numerical models, but essentially turbulent. Evidences favoring the latter scenario are based on "Voyager" spacecraft observations of plasma, magnetic field and energetic particle parameters, which are inconsistent with laminar theories. Inhomogeneous and time-variable solar wind streams often show variations with relative amplitudes of an order of one in magnetic fields, velocity, density, temperature and other plasma parameters at different time scales from minutes to years. This could bring to their non-linear submagnetosonic and supermagnetosonic interactions on the way in the heliosphere to its boundaries and beyond. The relative variations in energy and amount of supra-thermal and accelerated ions are orders of magnitude stronger. Another cause and free energy source of turbulent behavior with possible saw-tooth relaxation type oscillations at the boundary is due to instabilities of interacting solar wind and interstellar flows. As a consequence, the heliosphere should have a turbulent comet-like shape in the interstellar wind what can be established only based on future measurements. Nevertheless, one can not expect any universal scaling here because of different ranges of dimensionless parameters suggesting non-steady state situation with not-fully developed inhomogeneous and intermittent turbulence. Possible indications are discussed on the existence of traveling perturbations in the interstellar medium influencing the outer heliosphere. This study was supported by the RFBR grants 07-02-00147, 06-05-64500, INTAS 03-51-6202 and MSU Interdisciplinary Scientific Project. It is also fulfilled as a part of the Programs of the Russian Academy of Sciences: "Origin and evolution of stars and galaxies" (P-04), "Solar activity and physical processes in the Sun-Earth system" (P-16
Gyrokinetic simulations of collisionless reconnection in turbulent non-uniform plasmas
Kobayashi, Sumire; Rogers, Barrett N.; Numata, Ryusuke
2014-04-15
We present nonlinear gyrokinetic simulations of collisionless magnetic reconnection with non-uniformities in the plasma density, the electron temperature, and the ion temperature. The density gradient can stabilize reconnection due to diamagnetic effects but destabilize driftwave modes that produce turbulence. The electron temperature gradient triggers microtearing modes that drive rapid small-scale reconnection and strong electron heat transport. The ion temperature gradient destabilizes ion temperature gradient modes that, like the driftwaves, may enhance reconnection in some cases.
Efforts to Simulate Solar Wind Turbulence
NASA Technical Reports Server (NTRS)
Goldstein, Melvyn L.
2007-01-01
A three-dimensional integration of the MHD equations in spherical coordinates has been developed that attempts to simulate a variety of solar wind conditions. These include the interaction of Alfven wave packets and the development of a turbulent cascade, the role of the heliospheric current sheet, the role of quasi-two-dimensional fluctuations in determining how magnetic field lines meander throughout the heliosphere, and the role of interstellar pickup ions in perturbing the solar wind in the outer heliosphere.
Kelvin-Helmholtz turbulence associated with collisionless shocks in laser produced plasmas.
Kuramitsu, Y; Sakawa, Y; Dono, S; Gregory, C D; Pikuz, S A; Loupias, B; Koenig, M; Waugh, J N; Woolsey, N; Morita, T; Moritaka, T; Sano, T; Matsumoto, Y; Mizuta, A; Ohnishi, N; Takabe, H
2012-05-11
We report the experimental results of a turbulent electric field driven by Kelvin-Helmholtz instability associated with laser produced collisionless shock waves. By irradiating an aluminum double plane target with a high-power laser, counterstreaming plasma flows are generated. As the consequence of the two plasma interactions, two shock waves and the contact surface are excited. The shock electric field and transverse modulation of the contact surface are observed by proton radiography. Performing hydrodynamic simulations, we reproduce the time evolutions of the reverse shocks and the transverse modulation driven by Kelvin-Helmholtz instability.
2013-12-26
694/1/618 (2009). [2] P. H. Yoon and T.-M. Fang, Proton heating by parallel Alfven wave cascade, Physics of Plasmas 16, 062314, doi: 10.1063...ANSI Std Z39-18 [5] C. S. Wu, P. H. Yoon, and C. B. Wang, On non-resonant proton heating via intrinsic Alfvenic turbulence, Physics of Plasmas 16...interaction, J. Geophys. Res. 115, A01103, doi: 10.1029/2009JA014447 (2010). [10] J. Pavan, L. F. Ziebell, P. H. Yoon, and R. Gaelzer, Ionospheric ion
NASA Astrophysics Data System (ADS)
Pottelette, R.; Treumann, R.; Bauer, O. H.; Lebreton, J. P.
1985-01-01
Experimental results, obtained during the PORCUPINE experiment and dealing with the interaction of an artificial ion conic with the background auroral plasma, are presented. In addition, these results are compared to the measurements performed by the S3-3 satellite when natural ion conics are present. This comparison shows that the physical processes associated with the neutralization of conical ion distributions and with their interaction with the background plasma induce the same kind of electrostatic shocks and turbulence as those recorded by S3-3.
NASA Astrophysics Data System (ADS)
Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kühl, P.; Kopp, A.; Heber, B.; Kissmann, R.
2014-06-01
The transport of energetic particles such as cosmic rays is governed by the properties of the plasma being traversed. While these properties are rather poorly known for galactic and interstellar plasmas due to the lack of in situ measurements, the heliospheric plasma environment has been probed by spacecraft for decades and provides a unique opportunity for testing transport theories. Of particular interest for the three-dimensional (3D) heliospheric transport of energetic particles are structures such as corotating interaction regions, which, due to strongly enhanced magnetic field strengths, turbulence, and associated shocks, can act as diffusion barriers on the one hand, but also as accelerators of low energy CRs on the other hand as well. In a two-fold series of papers, we investigate these effects by modeling inner-heliospheric solar wind conditions with a numerical magnetohydrodynamic (MHD) setup (this paper), which will serve as an input to a transport code employing a stochastic differential equation approach (second paper). In this first paper, we present results from 3D MHD simulations with our code CRONOS: for validation purposes we use analytic boundary conditions and compare with similar work by Pizzo. For a more realistic modeling of solar wind conditions, boundary conditions derived from synoptic magnetograms via the Wang-Sheeley-Arge (WSA) model are utilized, where the potential field modeling is performed with a finite-difference approach in contrast to the traditional spherical harmonics expansion often utilized in the WSA model. Our results are validated by comparing with multi-spacecraft data for ecliptical (STEREO-A/B) and out-of-ecliptic (Ulysses) regions.
Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kühl, P.; Kopp, A.; Heber, B.; Kissmann, R.
2014-06-10
The transport of energetic particles such as cosmic rays is governed by the properties of the plasma being traversed. While these properties are rather poorly known for galactic and interstellar plasmas due to the lack of in situ measurements, the heliospheric plasma environment has been probed by spacecraft for decades and provides a unique opportunity for testing transport theories. Of particular interest for the three-dimensional (3D) heliospheric transport of energetic particles are structures such as corotating interaction regions, which, due to strongly enhanced magnetic field strengths, turbulence, and associated shocks, can act as diffusion barriers on the one hand, but also as accelerators of low energy CRs on the other hand as well. In a two-fold series of papers, we investigate these effects by modeling inner-heliospheric solar wind conditions with a numerical magnetohydrodynamic (MHD) setup (this paper), which will serve as an input to a transport code employing a stochastic differential equation approach (second paper). In this first paper, we present results from 3D MHD simulations with our code CRONOS: for validation purposes we use analytic boundary conditions and compare with similar work by Pizzo. For a more realistic modeling of solar wind conditions, boundary conditions derived from synoptic magnetograms via the Wang-Sheeley-Arge (WSA) model are utilized, where the potential field modeling is performed with a finite-difference approach in contrast to the traditional spherical harmonics expansion often utilized in the WSA model. Our results are validated by comparing with multi-spacecraft data for ecliptical (STEREO-A/B) and out-of-ecliptic (Ulysses) regions.
Hidalgo, C; Gonçalves, B; Silva, C; Pedrosa, M A; Erents, K; Hron, M; Matthews, G F
2003-08-08
The dynamical coupling between turbulent transport and parallel flows has been investigated in the plasma boundary region of the Joint European Torus tokamak. Experimental results show that there is a dynamical relationship between transport and parallel flows. As the size of transport events increases, parallel flows also increase. These results show that turbulent transport can drive parallel flows in the plasma boundary of fusion plasmas. This new type of measurement is an important element to unravel the overall picture connecting radial transport and flows in fusion plasmas.
A MODEL OF THE HELIOSPHERE WITH JETS
Drake, J. F.; Swisdak, M.; Opher, M. E-mail: swisdak@umd.edu
2015-08-01
An analytic model of the heliosheath (HS) between the termination shock (TS) and the heliopause (HP) is developed in the limit in which the interstellar flow and magnetic field are neglected. The heliosphere in this limit is axisymmetric and the overall structure of the HS and HP is controlled by the solar magnetic field even in the limit in which the ratio of the plasma to magnetic field pressure, β = 8πP/B{sup 2}, in the HS is large. The tension of the solar magnetic field produces a drop in the total pressure between the TS and the HP. This same pressure drop accelerates the plasma flow downstream of the TS into the north and south directions to form two collimated jets. The radii of these jets are controlled by the flow through the TS and the acceleration of this flow by the magnetic field—a stronger solar magnetic field boosts the velocity of the jets and reduces the radii of the jets and the HP. MHD simulations of the global heliosphere embedded in a stationary interstellar medium match well with the analytic model. The results suggest that mechanisms that reduce the HS plasma pressure downstream of the TS can enhance the jet outflow velocity and reduce the HP radius to values more consistent with the Voyager 1 observations than in current global models.
Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory
NASA Astrophysics Data System (ADS)
Sheerin, J. P.; Adham, N.; Roe, R. G. E.; Keith, M. R.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.; Selcher, C. A.
2010-11-01
High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.
Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory
NASA Astrophysics Data System (ADS)
Sheerin, J. P.; Adham, N.; Watanabe, N.; Watkins, B. J.; Bristow, W. A.; Selcher, C. A.; Bernhardt, P. A.
2011-10-01
High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.
NASA Astrophysics Data System (ADS)
Palmadesso, P. J.; Ganguli, G.
1992-05-01
The effects of electron trapping and plasma turbulence on the current-voltage relation for a positively charged high-voltage spherical probe in a magnetized plasma are studied. When the neutral density is low enough so that ionization can be ignored, the present results indicate that the sheath structure and the current-voltage relation of a charged sphere configured as the originally planned SPEAR I experiment would be substantially influenced by the combined action of trapped electrons and plasma instabilities. Reduced levels of current collection relative to Linson's (1969) model are found. Variation of the scattering parameter over the whole range of physically realizable values results in a range of predicted current collection values which is a small fraction of the interval between the Parker-Murphy and Langmuir-Blodgett limits.
Electrostatic turbulence and transport in a simple magnetized plasma
Fasoli, A.; Labit, B.; McGrath, M.; Mueller, S.H.; Plyushchev, G.; Podesta, M.; Poli, F.M.
2006-05-15
Gradient driven electrostatic instabilities are investigated in TORPEX [A. Fasoli, B. Labit, M. McGrath, S. H. Mueller, M. Podesta, and F. M. Poli, Bull. Am. Phys. Soc. 48, 119 (2003)], a toroidal device (R=1 m, a=0.2 m) in which plasmas are produced by microwaves (P{<=}20 kW) with f{sub rf}=2.45 GHz, in the electron cyclotron frequency range. Typical density and temperature are n{sub e}{<=}10{sup 17} m{sup -3} and T{sub e}{approx_equal}5 eV, respectively. The magnetic field is mainly toroidal ({<=}0.1 T), with a small vertical component ({<=}4 mT). Instabilities that can be generally identified as drift-interchange waves are observed and characterized for different levels of collisionality with neutrals. The frequency spectrum and the spatial profile of the fluctuation-induced flux are measured. An 86-tip probe is used to reconstruct the spatio-temporal evolution of density structures across the plasma cross section. The measured structures are characterized statistically, and related quantitative observables are constructed.
Completing a Ground Truth View of the Global Heliosphere: What Does IMAP Tell Us?
NASA Astrophysics Data System (ADS)
Matthaeus, W. H.
2014-12-01
Recent and planned advances in heliospheric research promise to provide for the first time a fairly complete picture of the processes that shape the Geospace environment and the Heliospheric envelope that defines the magnetic and plasma neighborhood of the Sun. The upcoming Solar Orbiter and Solar probe Plus missions will vastly extend our knowledge of the inner heliospheric drivers that impact the entire system. However to develop understanding of energy and particle transport that controls the Geospace plasma and radiation envirionment, it is necessary to maintain an accurate monitoring of the plasma and electromagnetic properties of the solar wind near 1 AU. To complete understanding of the Heliosphere we must also extend understanding of energy and plasma transport to regions beyond 1 AU and throughout the Heliosphere. This understanding will complete the connection between the the corona, the 1AU environment and the outer boundaries recently explored by the Voyagers and IBEX. This talk will focus on the linkages between inner heliosphere, the Geospace environment and the outer heliosphere, with an emphasis on what an L1 monitor such as IMAP can provde for the next decade of great discoveries in space physics.
NASA Astrophysics Data System (ADS)
Miki, Kenji
Plasma assisted combustion (PAC) is a promising alternative to hold or ignite a fuel and air mixture in a supersonic environment. Efficient supersonic combustion is of primary importance for SCRAMJET technology. The advantages of PAC is the addition of large amounts of energy to specific regions of the SCRAMJET flow-field for short periods of time, and as a result accelerate the fuel/air kinetic rates to achieve a self-sustaining condition. Moreover, the promise of enhancement of fuel-air mixing by magnetohydrodynamics (MHD) flow control offers significant improvement of combustion performance. The development of a numerical tool for investigating high-temperature chemistry and plasmadynamic effects of a discharge arc is desired to gain understanding of PAC technology and the potential improvement of the operational efficiency of SCRAMJET engines. The main objective of this research is to develop a comprehensive model with the capability of modeling both high Reynolds number and high magnetic Reynolds number turbulent flow for application to supersonic combustor. The development of this model can be divided into three categories: first, the development of a self-consistent MHD numerical model capable of modeling magnetic turbulence in high magnetic Reynolds number applications. Second, the development of a gas discharge model which models the interaction of externally applied fields in conductive medium. Third, the development of models necessary for studying supersonic combustion applications with plasma-assistance such the extension of chemical kinetics models to extremely high temperature and non-equilibrium phenomenon. Finally, these models are combined and utilized to model plasma assisted combustion in a SCRAMJET. Two types of plasmas are investigated: an equilibrium electrical discharge (arc) and a non-equilibrium plasma jet. It is shown that both plasmas significantly increase the concentration of radicals such as O, OH and H, and both have positive impact
Solar Orbiter Exploring the Sun-Heliosphere Connection
NASA Technical Reports Server (NTRS)
Mueller, Daniel; Marsden, Richard George; Cyr, O. C. St.; Gilbert, Holly Robin
2012-01-01
The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015 - 2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.
Solar Orbiter: Exploring the Sun-Heliosphere Connection
NASA Technical Reports Server (NTRS)
Mueller, D.; Marsden, R. G.; St.Cyr, O. C.; Gilbert, H. R.
2013-01-01
The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015 - 2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.
NASA Astrophysics Data System (ADS)
Angioni, C.; Bilato, R.; Casson, F. J.; Fable, E.; Mantica, P.; Odstrcil, T.; Valisa, M.; ASDEX Upgrade Team; Contributors, JET
2017-02-01
In tokamaks, the role of turbulent transport of heavy impurities, relative to that of neoclassical transport, increases with increasing size of the plasma, as clarified by means of general scalings, which use the ITER standard scenario parameters as reference, and by actual results from a selection of discharges from ASDEX Upgrade and JET. This motivates the theoretical investigation of the properties of the turbulent convection of heavy impurities by nonlinear gyrokinetic simulations in the experimentally relevant conditions of comparable ion and electron heat fluxes. These conditions also correspond to an intermediate regime between dominant ion temperature gradient turbulence and trapped electron mode turbulence. At moderate plasma toroidal rotation, the turbulent convection of heavy impurities, computed with nonlinear gyrokinetic simulations, is found to be directed outward, in contrast to that obtained by quasi-linear calculations based on the most unstable linear mode, which is directed inward. In this mixed turbulence regime, with comparable electron and ion heat fluxes, the nonlinear results of the impurity transport can be explained by the coexistence of both ion temperature gradient and trapped electron modes in the turbulent state, both contributing to the turbulent convection and diffusion of the impurity. The impact of toroidal rotation on the turbulent convection is also clarified.
Cosmic ray heliospheric transport study with neutron monitor data
NASA Astrophysics Data System (ADS)
Ahluwalia, H. S.; Ygbuhay, R. C.; Modzelewska, R.; Dorman, L. I.; Alania, M. V.
2015-10-01
Determining transport coefficients for galactic cosmic ray (GCR) propagation in the turbulent interplanetary magnetic field (IMF) poses a fundamental challenge in modeling cosmic ray modulation processes. GCR scattering in the solar wind involves wave-particle interaction, the waves being Alfven waves which propagate along the ambient field (B). Empirical values at 1 AU are determined for the components of the diffusion tensor for GCR propagation in the heliosphere using neutron monitor (NM) data. At high rigidities, particle density gradients and mean free paths at 1 AU in B can only be computed from the solar diurnal anisotropy (SDA) represented by a vector A (components Ar, Aϕ, and Aθ) in a heliospherical polar coordinate system. Long-term changes in SDA components of NMs (with long track record and the median rigidity of response Rm ~ 20 GV) are used to compute yearly values of the transport coefficients for 1963-2013. We confirm the previously reported result that the product of the parallel (to B) mean free path (λ||) and radial density gradient (Gr) computed from NM data exhibits a weak Schwabe cycle (11y) but strong Hale magnetic cycle (22y) dependence. Its value is most depressed in solar activity minima for positive (p) polarity intervals (solar magnetic field in the Northern Hemisphere points outward from the Sun) when GCRs drift from the polar regions toward the helioequatorial plane and out along the heliospheric current sheet (HCS), setting up a symmetric gradient Gθs pointing away from HCS. Gr drives all SDA components and λ|| Gr contributes to the diffusive component (Ad) of the ecliptic plane anisotropy (A). GCR transport is commonly discussed in terms of an isotropic hard sphere scattering (also known as billiard-ball scattering) in the solar wind plasma. We use it with a flat HCS model and the Ahluwalia-Dorman master equations to compute the coefficients α (=λ⊥/λ∥) and ωτ (a measure of turbulence in the solar wind) and transport
Starprobe - Coronal plasma turbulence effects on tracking and telemetry
NASA Technical Reports Server (NTRS)
Armstrong, J. W.; Woo, R.; Koerner, M.
1982-01-01
The telemetry and tracking problems expected for Starprobe, a solar flyby with a perihelion of 4 solar radii, are discussed. The Starprobe is intended to obtain measurements of the solar quadrupole moment within an accuracy of 1/100,000,000, allowing more accurate modelling of the solar interior. Obstacles are perceived for Doppler velocity measurements due to RF signal amplitude and phase scintillations created by the solar corona. Model calculations are presented for the propagation effects in the maximum disturbance area, and an open loop two-way Doppler system is described. The system comprises X-band and S-band uplinks and downlinks to eliminate the plasma-induced phase scintillations, means of correcting unfolding errors caused by S-band amplitude scintillations, and a new method of estimating the Doppler frequency.
SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Lin, Zhihong
2013-12-18
During the first year of the SciDAC gyrokinetic particle simulation (GPS) project, the GPS team (Zhihong Lin, Liu Chen, Yasutaro Nishimura, and Igor Holod) at the University of California, Irvine (UCI) studied the tokamak electron transport driven by electron temperature gradient (ETG) turbulence, and by trapped electron mode (TEM) turbulence and ion temperature gradient (ITG) turbulence with kinetic electron effects, extended our studies of ITG turbulence spreading to core-edge coupling. We have developed and optimized an elliptic solver using finite element method (FEM), which enables the implementation of advanced kinetic electron models (split-weight scheme and hybrid model) in the SciDAC GPS production code GTC. The GTC code has been ported and optimized on both scalar and vector parallel computer architectures, and is being transformed into objected-oriented style to facilitate collaborative code development. During this period, the UCI team members presented 11 invited talks at major national and international conferences, published 22 papers in peer-reviewed journals and 10 papers in conference proceedings. The UCI hosted the annual SciDAC Workshop on Plasma Turbulence sponsored by the GPS Center, 2005-2007. The workshop was attended by about fifties US and foreign researchers and financially sponsored several gradual students from MIT, Princeton University, Germany, Switzerland, and Finland. A new SciDAC postdoc, Igor Holod, has arrived at UCI to initiate global particle simulation of magnetohydrodynamics turbulence driven by energetic particle modes. The PI, Z. Lin, has been promoted to the Associate Professor with tenure at UCI.
NASA Astrophysics Data System (ADS)
Zank, G. P.
2015-09-01
The 14th Annual International Astrophysics Conference was held at the Sheraton Tampa Riverwalk Hotel, Tampa, Florida, USA, during the week of 19-24 April 2015. The meeting drew some 75 participants from all over the world, representing a wide range of interests and expertise in the energization of particles from the perspectives of theory, modelling and simulations, and observations. The theme of the meeting was "Linear and Nonlinear Particle Energization throughout the Heliosphere and Beyond." Energetic particles are ubiquitous to plasma environments, whether collisionless such as the supersonic solar wind, the magnetospheres of planets, the exospheres of nonmagnetized planets and comets, the heliospheric-local interstellar boundary regions, interstellar space and supernova remnant shocks, and stellar wind boundaries. Energetic particles are found too in more collisional regions such as in the solar corona, dense regions of the interstellar medium, accretion flows around stellar objects, to name a few. Particle acceleration occurs wherever plasma boundaries, magnetic and electric fields, and turbulence are present. The meeting addressed the linear and nonlinear physical processes underlying the variety of particle acceleration mechanisms, the role of particle acceleration in shaping different environments, and acceleration processes common to different regions. Both theory and observations were addressed with a view to encouraging crossdisciplinary fertilization of ideas, concepts, and techniques. The meeting addressed all aspects of particle acceleration in regions ranging from the Sun to the interplanetary medium to magnetospheres, exospheres, and comets, the boundaries of the heliosphere, and beyond to supernova remnant shocks, galactic jets, stellar winds, accretion flows, and more. The format of the meeting included 25-minute presentations punctuated by two 40-minute talks, one by Len Fisk that provided an historical overview of particle acceleration in the
NASA Astrophysics Data System (ADS)
Pochelon, Antoine
2010-11-01
Due to turbulence, core energy transport in tokamaks generally exceeds collisional transport by at least an order of magnitude. It is therefore crucial to understand the instabilities driving the turbulent state and to find ways to control them. Shaping the plasma is one of these fundamental tools. In low collisionality plasmas, such as in a reactor, changing triangularity from positive (delta=+0.4) to negative triangularity (delta=-0.4) is shown on TCV to reduce the energy transport by a factor two. This opens the possibility of having H-mode-like confinement time within an L-mode edge, or reduced ELMs. An optimum triangularity can be sought between steep edge barriers (delta>0), plagued by large ELMs, and improved core confinement (delta<0). Recent correlation ECE measurements show that the reduction of transport at negative delta is reflected in a reduction by a factor of two of both the amplitude of temperature fluctuations in the broadband frequency range 30-150 kHz, and the fluctuation correlation length, measured at mid-radius. In addition, the fluctuations amplitude is reduced with increasing collisionality, consistent with a reduction of the Trapped Electron Modes (TEM) drive. The effect of negative triangularity on turbulence and transport is compared to gyrokinetic code results: First, global linear simulations predict shorter radial TEM wavelength, consistent with the shorter radial turbulence correlation length observed. Second, at least close to the strongly shaped plasma boundary, local nonlinear simulations predict lower TEM induced transport with decreased triangularity. Calculations are now being extended to global nonlinear simulations.
The Magnetic Connectivity of the Sun to the Heliosphere
NASA Technical Reports Server (NTRS)
Antiochos, S. K.
2010-01-01
A prime research focus of the upcoming Solar Probe Plus and Solar Orbiter missions will be to determine how the heliospheric magnetic field and plasma connect to the Sun's corona and photosphere. For much of the heliosphere this connection appears to be well understood. The quasi-steady fast wind emanates from so-called coronal holes, which appear dark in X-rays and are predominantly unipolar at the photosphere. However, the connection to the Sun of the slow, non-steady wind is far from understood and remains a major mystery. We review the existing theories for the sources of the nonsteady wind and demonstrate that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A new theory is described in which this wind originates from the continuous opening and closing of narrow open field corridors in the corona, which gives rise to a web of separatrices (the S-Web) in the heliosphere. Note that in this theory the corona - heliosphere connection is intrinsically dynamic, at least, for this type of wind. We present numerical simulations of the model and describe observational tests. We discuss the implications of our results for the competing slow wind theories and for understanding the corona - heliosphere connection, in general.
The Transport of Density Fluctuations Throughout the Heliosphere
NASA Technical Reports Server (NTRS)
Zank, G. P.; Jetha, N.; Hu, Q.; Hunana, P.
2012-01-01
The solar wind is recognized as a turbulent magnetofluid, for which the properties of the turbulent velocity and magnetic field fluctuations are often described by the equations of incompressible magnetohydrodynamics (MHD). However, low-frequency density turbulence is also ubiquitous. On the basis of a nearly incompressible formulation of MHD in the expanding inhomogeneous solar wind, we derive the transport equation for the variance of the density fluctuations (Rho(exp 2)). The transport equation shows that density fluctuations behave as a passive scalar in the supersonic solar wind. In the absence of sources of density turbulence, such as within 1AU, the variance (Rho(exp 2)) approximates r(exp -4). In the outer heliosphere beyond 1 AU, the shear between fast and slow streams, the propagation of shocks, and the creation of interstellar pickup ions all act as sources of density turbulence. The model density fluctuation variance evolves with heliocentric distance within approximately 300 AU as (Rho(exp 2)) approximates r(exp -3.3) after which it flattens and then slowly increases. This is precisely the radial profile for the density fluctuation variance observed by Voyager 2. Using a different analysis technique, we confirm the radial profile for Rho(exp 2) of Bellamy, Cairns, & Smith using Voyager 2 data. We conclude that a passive scalar description for density fluctuations in the supersonic solar wind can explain the density fluctuation variance observed in both the inner and the outer heliosphere.
Examining Periodic Solar-Wind Density Structures Observed in the SECCHI Heliospheric Imagers
NASA Technical Reports Server (NTRS)
Viall, Nicholeen M.; Spence, Harlan E.; Vourlidas, Angelos; Howard, Russell
2010-01-01
We present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as approximately equals 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper analyzed the alpha-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.
Redd, A.J.; Kritz, A.H.; Bateman, G.; Horton, W.
1998-05-01
A drift wave transport model, recently developed by Ottaviani, Horton and Erba (OHE) [Ottaviani {ital et al.}, Plasma Phys. Controlled Fusion {bold 39}, 1461 (1997)], has been implemented and tested in a time-dependent predictive transport code. This OHE model assumes that anomalous transport is due to turbulence driven by ion temperature gradients and that the fully developed turbulence will extend into linearly stable regions, as described in the reference cited above. A multiplicative elongation factor is introduced in the OHE model and simulations are carried out for 12 discharges from major tokamak experiments, including both L- and H-modes (low- and high-confinement modes) and both circular and elongated discharges. Good agreement is found between the OHE model predictions and experiment. This OHE model is also used to describe the performance of the International Thermonuclear Experimental Reactor (ITER) [Putvinski {ital et al.}, in {ital Proceedings of the 16th IAEA Fusion Energy Conference}, Montr{acute e}al, Canada, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 2, p. 737.] A second version of the OHE model, in which the turbulent transport is not allowed to penetrate into linearly stable regions, has also been implemented and tested. In simulations utilizing this version of the model, the linear stability of the plasma core eliminates the anomalous thermal transport near the magnetic axis, resulting in an increase in the core temperatures to well above the experimental values. {copyright} {ital 1998 American Institute of Physics.}
NASA Technical Reports Server (NTRS)
Huba, J. D.; Chen, J.; Anderson, R. R.
1992-01-01
Attention is given to a mechanism to generate a broad spectrum of electrostatic turbulence in the quiet time central plasma sheet (CPS) plasma. It is shown theoretically that multiple-ring ion distributions can generate short-wavelength (less than about 1), electrostatic turbulence with frequencies less than about kVj, where Vj is the velocity of the jth ring. On the basis of a set of parameters from measurements made in the CPS, it is found that electrostatic turbulence can be generated with wavenumbers in the range of 0.02 and 1.0, with real frequencies in the range of 0 and 10, and with linear growth rates greater than 0.01 over a broad range of angles relative to the magnetic field (5-90 deg). These theoretical results are compared with wave data from ISEE 1 using an ion distribution function exhibiting multiple-ring structures observed at the same time. The theoretical results in the linear regime are found to be consistent with the wave data.
Distinct turbulence sources and confinement features in the spherical tokamak plasma regime
Wang, W. X.; Ethier, S.; Ren, Y.; ...
2015-10-30
New turbulence contributions to plasma transport and confinement in the spherical tokamak (ST) regime are identified through nonlinear gyrokinetic simulations. The drift wave Kelvin-Helmholtz (KH) mode characterized by intrinsic mode asymmetry is shown to drive significant ion thermal transport in strongly rotating national spherical torus experiment (NSTX) L-modes. The long wavelength, quasi-coherent dissipative trapped electron mode (TEM) is destabilized in NSTX H-modes despite the presence of strong E x B shear, providing a robust turbulence source dominant over collisionless TEM. Dissipative trapped electron mode (DTEM)-driven transport in the NSTX parametric regime is shown to increase with electron collision frequency, offeringmore » one possible source for the confinement scaling observed in experiments. There exists a turbulence-free regime in the collision-induced collisionless trapped electron mode to DTEM transition for ST plasmas. In conclusion, this predicts a natural access to a minimum transport state in the low collisionality regime that future advanced STs may cover.« less
Distinct turbulence sources and confinement features in the spherical tokamak plasma regime
Wang, W. X.; Ethier, S.; Ren, Y.; Kaye, S.; Chen, J.; Startsev, E.; Lu, Z.
2015-10-30
New turbulence contributions to plasma transport and confinement in the spherical tokamak (ST) regime are identified through nonlinear gyrokinetic simulations. The drift wave Kelvin-Helmholtz (KH) mode characterized by intrinsic mode asymmetry is shown to drive significant ion thermal transport in strongly rotating national spherical torus experiment (NSTX) L-modes. The long wavelength, quasi-coherent dissipative trapped electron mode (TEM) is destabilized in NSTX H-modes despite the presence of strong E x B shear, providing a robust turbulence source dominant over collisionless TEM. Dissipative trapped electron mode (DTEM)-driven transport in the NSTX parametric regime is shown to increase with electron collision frequency, offering one possible source for the confinement scaling observed in experiments. There exists a turbulence-free regime in the collision-induced collisionless trapped electron mode to DTEM transition for ST plasmas. In conclusion, this predicts a natural access to a minimum transport state in the low collisionality regime that future advanced STs may cover.
An Efficient Approximation of the Coronal Heating Rate for use in Global Sun-Heliosphere Simulations
NASA Astrophysics Data System (ADS)
Cranmer, Steven R.
2010-02-01
The origins of the hot solar corona and the supersonically expanding solar wind are still the subject of debate. A key obstacle in the way of producing realistic simulations of the Sun-heliosphere system is the lack of a physically motivated way of specifying the coronal heating rate. Recent one-dimensional models have been found to reproduce many observed features of the solar wind by assuming the energy comes from Alfvén waves that are partially reflected, then dissipated by magnetohydrodynamic turbulence. However, the nonlocal physics of wave reflection has made it difficult to apply these processes to more sophisticated (three-dimensional) models. This paper presents a set of robust approximations to the solutions of the linear Alfvén wave reflection equations. A key ingredient of the turbulent heating rate is the ratio of inward-to-outward wave power, and the approximations developed here allow this to be written explicitly in terms of local plasma properties at any given location. The coronal heating also depends on the frequency spectrum of Alfvén waves in the open-field corona, which has not yet been measured directly. A model-based assumption is used here for the spectrum, but the results of future measurements can be incorporated easily. The resulting expression for the coronal heating rate is self-contained, computationally efficient, and applicable directly to global models of the corona and heliosphere. This paper tests and validates the approximations by comparing the results to exact solutions of the wave transport equations in several cases relevant to the fast and slow solar wind.
NASA Astrophysics Data System (ADS)
Habash Krause, L.; Enloe, C. L.; McHarg, M. G.
2013-12-01
Observations of ionospheric plasma density and frequency-dependent broadband plasma turbulence made during the heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE) are presented. Rather than record high frequency time series data, the experiment was designed to record Power Spectral Distributions (PSDs) in five decadal frequency bins with upper limits ranging from 1.0 Hz to 10 kHz. Additionally, PLANE was designed distinguish turbulence in the ambient plasma from that local to the spacecraft. The instrument consists of two retarding potential analyzers (RPAs) connected together via a feedback loop to force one analyzer into the I-V trace retardation region at all times. Fluctuations in this measurement are believed to be ambient only as the RPA's voltage would be too high for locally turbulent plasma to surmount the potential barrier, which is nominally at ram energy. The instrument requires pointing along the spacecraft's ram velocity vector to make this measurement, thus requiring stabilization in pitch and yaw. During PLANE's heritage flight, though the satellite's attitude control system failed early in the mission, plasma data were collected during opportune times in which the instrument rotated into and out of the ram. Observations of plasma density and PSDs of high frequency plasma turbulence were recorded on several occasions. Additionally, a plasma source onboard the satellite was used to generate artificial plasma turbulence, and the PLANE data observed periodic structure presumably associated with the rotation of the spacecraft during these source firings. A brief comparison with other high frequency in situ plasma instruments is presented.
Development of electrostatic turbulence from drift-interchange instabilities in a toroidal plasma
Poli, F. M.; Podesta, M.; Fasoli, A.
2007-05-15
Electrostatic instabilities develop on TORPEX (TORoidal Plasma EXperiment) [A. Fasoli et al., Phys. of Plasmas, 13, 55902 (2006)] in the bad curvature region and propagate consistently with the drift wave dispersion relation. The wave number and frequency spectra are coherent at the location where the instabilities are generated, then broaden along the ExB convection. The phase coupling between spectral components at different frequencies, measured at different locations over the plasma cross section, indicates that the transition from a coherent to a turbulent spectrum is mainly due to three-wave interaction processes. Nonlinear interactions are measured between the linearly unstable mode and fluctuations with larger frequency, with transfer of energy away from the linearly unstable mode. The results are consistent with a nonlinearity induced by the convection of density fluctuations by the ExB fluctuating velocity.
Diagnosing collisionless energy transfer using field-particle correlations: Vlasov-Poisson plasmas
NASA Astrophysics Data System (ADS)
Howes, Gregory G.; Klein, Kristopher G.; Li, Tak Chu
2017-02-01
Turbulence plays a key role in the conversion of the energy of large-scale fields and flows to plasma heat, impacting the macroscopic evolution of the heliosphere and other astrophysical plasma systems. Although we have long been able to make direct spacecraft measurements of all aspects of the electromagnetic field and plasma fluctuations in near-Earth space, our understanding of the physical mechanisms responsible for the damping of the turbulent fluctuations in heliospheric plasmas remains incomplete. Here we propose an innovative field-particle correlation technique that can be used to measure directly the secular energy transfer from fields to particles associated with collisionless damping of the turbulent fluctuations. Furthermore, this novel procedure yields information about the collisionless energy transfer as a function of particle velocity, providing vital new information that can help to identify the dominant collisionless mechanism governing the damping of the turbulent fluctuations. Kinetic plasma theory is used to devise the appropriate correlation to diagnose Landau damping, and the field-particle correlation technique is thoroughly illustrated using the simplified case of the Landau damping of Langmuir waves in a 1D-1V (one dimension in physical space and one dimension in velocity space) Vlasov-Poisson plasma. Generalizations necessary to apply the field-particle correlation technique to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, highlighting several caveats. This novel field-particle correlation technique is intended to be used as a primary analysis tool for measurements from current, upcoming and proposed spacecraft missions that are focused on the kinetic microphysics of weakly collisional heliospheric plasmas, including the Magnetospheric Multiscale (MMS), Solar Probe Plus, Solar Orbiter and Turbulence Heating ObserveR (THOR) missions.
Ensemble Space-Time Correlation of Plasma Turbulence in the Solar Wind.
Matthaeus, W H; Weygand, J M; Dasso, S
2016-06-17
Single point measurement turbulence cannot distinguish variations in space and time. We employ an ensemble of one- and two-point measurements in the solar wind to estimate the space-time correlation function in the comoving plasma frame. The method is illustrated using near Earth spacecraft observations, employing ACE, Geotail, IMP-8, and Wind data sets. New results include an evaluation of both correlation time and correlation length from a single method, and a new assessment of the accuracy of the familiar frozen-in flow approximation. This novel view of the space-time structure of turbulence may prove essential in exploratory space missions such as Solar Probe Plus and Solar Orbiter for which the frozen-in flow hypothesis may not be a useful approximation.
Spolaore, M. Vianello, N.; Agostini, M.; Cavazzana, R.; De Masi, G.; Martines, E.; Momo, B.; Scaggion, A.; Scarin, P.; Spagnolo, S.; Spizzo, G.; Zuin, M.; Furno, I.; Avino, F.; Fasoli, A.; Theiler, C.; Carralero, D.; Alonso, J. A.; Hidalgo, C.
2015-01-15
Electromagnetic features of turbulent filaments, emerging from a turbulent plasma background, have been studied in four different magnetic configurations: the stellarator TJ-II, the Reversed Field Pinch RFX-mod, a device that can be operated also as a ohmic tokamak, and the Simple Magnetized Torus, TORPEX. By applying an analogous diagnostic concept in all cases, direct measurements of both field-aligned current density and vorticity were performed inside the filament. The inter-machine comparison reveals a clear dependence of the filament vorticity upon the local time-averaged E × B flow shear. Furthermore, a wide range of local beta was explored allowing concluding that this parameter plays a fundamental role in the appearance of filament electromagnetic features.
Structure of Plasma Heating in Gyrokinetic Alfvénic Turbulence
NASA Astrophysics Data System (ADS)
Navarro, Alejandro Bañón; Teaca, Bogdan; Told, Daniel; Groselj, Daniel; Crandall, Paul; Jenko, Frank
2016-12-01
We analyze plasma heating in weakly collisional kinetic Alfvén wave turbulence using high resolution gyrokinetic simulations spanning the range of scales between the ion and the electron gyroradii. Real space structures that have a higher than average heating rate are shown not to be confined to current sheets. This novel result is at odds with previous studies, which use the electromagnetic work in the local electron fluid frame, i.e., J .(E +ve×B ) , as a proxy for turbulent dissipation to argue that heating follows the intermittent spatial structure of the electric current. Furthermore, we show that electrons are dominated by parallel heating while the ions prefer the perpendicular heating route. We comment on the implications of the results presented here.
Kinetic Turbulence in Relativistic Plasma: From Thermal Bath to Nonthermal Continuum.
Zhdankin, Vladimir; Werner, Gregory R; Uzdensky, Dmitri A; Begelman, Mitchell C
2017-02-03
We present results from particle-in-cell simulations of driven turbulence in magnetized, collisionless, and relativistic pair plasmas. We find that the fluctuations are consistent with the classical k_{⊥}^{-5/3} magnetic energy spectrum at fluid scales and a steeper k_{⊥}^{-4} spectrum at sub-Larmor scales, where k_{⊥} is the wave vector perpendicular to the mean field. We demonstrate the development of a nonthermal, power-law particle energy distribution f(E)∼E^{-α}, with an index α that decreases with increasing magnetization and increases with an increasing system size (relative to the characteristic Larmor radius). Our simulations indicate that turbulence can be a viable source of energetic particles in high-energy astrophysical systems, such as pulsar wind nebulae, if scalings asymptotically become insensitive to the system size.
Ensemble Space-Time Correlation of Plasma Turbulence in the Solar Wind
NASA Astrophysics Data System (ADS)
Matthaeus, W. H.; Weygand, J. M.; Dasso, S.
2016-06-01
Single point measurement turbulence cannot distinguish variations in space and time. We employ an ensemble of one- and two-point measurements in the solar wind to estimate the space-time correlation function in the comoving plasma frame. The method is illustrated using near Earth spacecraft observations, employing ACE, Geotail, IMP-8, and Wind data sets. New results include an evaluation of both correlation time and correlation length from a single method, and a new assessment of the accuracy of the familiar frozen-in flow approximation. This novel view of the space-time structure of turbulence may prove essential in exploratory space missions such as Solar Probe Plus and Solar Orbiter for which the frozen-in flow hypothesis may not be a useful approximation.
Kinetic Turbulence in Relativistic Plasma: From Thermal Bath to Nonthermal Continuum
NASA Astrophysics Data System (ADS)
Zhdankin, Vladimir; Werner, Gregory R.; Uzdensky, Dmitri A.; Begelman, Mitchell C.
2017-02-01
We present results from particle-in-cell simulations of driven turbulence in magnetized, collisionless, and relativistic pair plasmas. We find that the fluctuations are consistent with the classical k⊥-5 /3 magnetic energy spectrum at fluid scales and a steeper k⊥-4 spectrum at sub-Larmor scales, where k⊥ is the wave vector perpendicular to the mean field. We demonstrate the development of a nonthermal, power-law particle energy distribution f (E )˜E-α, with an index α that decreases with increasing magnetization and increases with an increasing system size (relative to the characteristic Larmor radius). Our simulations indicate that turbulence can be a viable source of energetic particles in high-energy astrophysical systems, such as pulsar wind nebulae, if scalings asymptotically become insensitive to the system size.
Turbulent Dynamo Amplification of Magnetic Fields in Laser-Produced Plasmas
NASA Astrophysics Data System (ADS)
Tzeferacos, Petros
2016-10-01
Magnetic fields are ubiquitous in the Universe, as revealed by diffuse radio-synchrotron emission and Faraday rotation observations, with strengths from a few nG to tens of μG. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter in the Universe. The standard model for the origin of these intergalactic magnetic fields is through the amplification of seed fields via turbulent dynamo to the level consistent with current observations. We have conceived and conducted a series of experiments using high-power laser facilities to study the amplification of magnetic fields via turbulence. In these experiments, we characterize the properties of the fluid and the magnetic field turbulence using a comprehensive suite of plasma and magnetic field diagnostics. We describe the large-scale 3D simulations we performed with the radiation-MHD code FLASH on ANL's Mira to help design and interpret the experiments. We then discuss the results of the experiments, which indicate magnetic Reynolds numbers above the expected dynamo threshold are achieved and seed magnetic fields produced by the Biermann battery mechanism are amplified by turbulent dynamo. We relate our findings to processes occurring in galaxy clusters. We acknowledge funding and resources from the ERC (FP7/2007-2013, no. 256973 and 247039), and the U.S. DOE, Contract No. B591485 to LLNL, FWP 57789 to ANL, Grant No. DE-NA0002724 to the University of Chicago, and contract DE-AC02-06CH11357 to ALCF at ANL.
Falceta-Gonçalves, D.; Kowal, G.
2015-07-20
In this work we report on a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of the magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that (i) amplification of the magnetic field was efficient in firehose-unstable turbulent regimes, but not in the mirror-unstable models; (ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo; and (iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales and pressure anisotropy is confirmed by the numerical simulations. These results reinforce the idea that pressure anisotropies—driven naturally in a turbulent collisionless medium, e.g., the intergalactic medium, could efficiently amplify the magnetic field in the early universe (post-recombination era), previous to the collapse of the first large-scale gravitational structures. This mechanism, though fast for the small-scale fields (∼kpc scales), is unable to provide relatively strong magnetic fields at large scales. Other mechanisms that were not accounted for here (e.g., collisional turbulence once instabilities are quenched, velocity shear, or gravitationally induced inflows of gas into galaxies and clusters) could operate afterward to build up large-scale coherent field structures in the long time evolution.
Time-Dependent 2D Modeling of Magnetron Plasma Torch in Turbulent Flow
NASA Astrophysics Data System (ADS)
Li, Lincun; Xia, Weidong
2008-06-01
A theoretical model is presented to describe the electromagnetic, heat transfer and fluid flow phenomena within a magnetron plasma torch and in the resultant plume, by using a commercial computational fluid dynamics (CFD) code FLUENT. Specific calculations are presented for a pure argon system (i.e., an argon plasma discharging into an argon environment), operated in a turbulent mode. An important finding of this work is that the external axial magnetic field (AMF) may have a significant effect on the behavior of arc plasma and thus affects the resulting plume. The AMF impels the plasma to retract axially and expand radially. As a result, the plasma intensity distribution on the cross section of torch seems to be more uniform. Numerical results also show that with AMF, the highest plasma temperature decreases and the anode arc root moves upstream significantly, while the current density distribution at the anode is more concentrated with a higher peak value. In addition, the use of AMF then induces a strong backflow at the torch spout and its magnitude increases with the AMF strength but decreases with the inlet gas velocity.
NASA Astrophysics Data System (ADS)
Kowal, G.; Falceta-Gonçalves, D. A.; Lazarian, A.
2011-05-01
In recent years, we have experienced increasing interest in the understanding of the physical properties of collisionless plasmas, mostly because of the large number of astrophysical environments (e.g. the intracluster medium (ICM)) containing magnetic fields that are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions, a new class of kinetic instabilities arises, such as firehose and mirror instabilities, which have been studied extensively in the literature. Their role in the turbulence evolution and cascade process in the presence of pressure anisotropy, however, is still unclear. In this work, we present the first statistical analysis of turbulence in collisionless plasmas using three-dimensional numerical simulations and solving double-isothermal magnetohydrodynamic equations with the Chew-Goldberger-Low laws closure (CGL-MHD). We study models with different initial conditions to account for the firehose and mirror instabilities and to obtain different turbulent regimes. We found that the CGL-MHD subsonic and supersonic turbulences show small differences compared to the MHD models in most cases. However, in the regimes of strong kinetic instabilities, the statistics, i.e. the probability distribution functions (PDFs) of density and velocity, are very different. In subsonic models, the instabilities cause an increase in the dispersion of density, while the dispersion of velocity is increased by a large factor in some cases. Moreover, the spectra of density and velocity show increased power at small scales explained by the high growth rate of the instabilities. Finally, we calculated the structure functions of velocity and density fluctuations in the local reference frame defined by the direction of magnetic lines. The results indicate that in some cases the instabilities significantly increase the anisotropy of
Diffusion of Energetic Electrons in Turbulent Plasmas of the Solar Wind
NASA Astrophysics Data System (ADS)
Volokitin, A. S.; Krafft, C.
2016-12-01
A method of calculation of the diffusion coefficients { D }(v) of particles in velocity space, based on the statistical analysis of the motion of a great number of test electrons, is proposed. In the case of Langmuir turbulence developing in plasmas with fluctuating density inhomogeneities such as the solar wind, simulations provide coefficients { D }(v) which mainly depend on the Langmuir wave spectra and agree well with the analytical predictions {{ D }}{th}(v) of the quasilinear theory of weak turbulence. Nevertheless, some noticeable differences exist with this theory: in the range of phase velocity of the short waves where the main part of the wave energy is concentrated, { D }(v) is noticeably smaller than {{ D }}{th}(v), due to the scattering, the reflection, and the focusing effects encountered by the Langmuir waves when they interact with the plasma density inhomogeneities. Moreover, the probability of large velocity jumps in the particles’ trajectories essentially exceeds the probability of a Gaussian distribution. These large jumps, which are connected with the waves’ transformation processes, modify the nature of the particle diffusion, which is no more classical. These higher order effects cause the discrepancies observed with the quasilinear theory, which does not take them into account in its perturbative approach. The solar wind plasmas, which present fluctuating density inhomogeneities of noticeable average levels, are a very good laboratory to study such diffusion processes, which can eventually influence significantly on the development of essential physical phenomena, as electromagnetic radio emissions by type III solar radio bursts, for example.
Cyclokinetic models and simulations for high-frequency turbulence in fusion plasmas
NASA Astrophysics Data System (ADS)
Deng, Zhao; Waltz, R. E.; Wang, Xiaogang
2016-10-01
Gyrokinetics is widely applied in plasma physics. However, this framework is limited to weak turbulence levels and low drift-wave frequencies because high-frequency gyro-motion is reduced by the gyro-phase averaging. In order to test where gyrokinetics breaks down, Waltz and Zhao developed a new theory, called cyclokinetics [R. E. Waltz and Zhao Deng, Phys. Plasmas 20, 012507 (2013)]. Cyclokinetics dynamically follows the high-frequency ion gyro-motion which is nonlinearly coupled to the low-frequency drift-waves interrupting and suppressing gyro-averaging. Cyclokinetics is valid in the high-frequency (ion cyclotron frequency) regime or for high turbulence levels. The ratio of the cyclokinetic perturbed distribution function over equilibrium distribution function δf/ F can approach 1. This work presents, for the first time, a numerical simulation of nonlinear cyclokinetic theory for ions, and describes the first attempt to completely solve the ion gyro-phase motion in a nonlinear turbulence system. Simulations are performed [Zhao Deng and R. E. Waltz, Phys. Plasmas 22(5), 056101 (2015)] in a local flux-tube geometry with the parallel motion and variation suppressed by using a newly developed code named rCYCLO, which is executed in parallel by using an implicit time-advanced Eulerian (or continuum) scheme [Zhao Deng and R. E. Waltz, Comp. Phys. Comm. 195, 23 (2015)]. A novel numerical treatment of the magnetic moment velocity space derivative operator guarantee saccurate conservation of incremental entropy. By comparing the more fundamental cyclokinetic simulations with the corresponding gyrokinetic simulations, the gyrokinetics breakdown condition is quantitatively tested. Gyrokinetic transport and turbulence level recover those of cyclokinetics at high relative ion cyclotron frequencies and low turbulence levels, as required. Cyclokinetic transport and turbulence level are found to be lower than those of gyrokinetics at high turbulence levels and low- Ω* values
Imaging of turbulent structures and tomographic reconstruction of TORPEX plasma emissivity
Iraji, D.; Furno, I.; Fasoli, A.; Theiler, C.
2010-12-15
In the TORPEX [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], a simple magnetized plasma device, low frequency electrostatic fluctuations associated with interchange waves, are routinely measured by means of extensive sets of Langmuir probes. To complement the electrostatic probe measurements of plasma turbulence and study of plasma structures smaller than the spatial resolution of probes array, a nonperturbative direct imaging system has been developed on TORPEX, including a fast framing Photron-APX-RS camera and an image intensifier unit. From the line-integrated camera images, we compute the poloidal emissivity profile of the plasma by applying a tomographic reconstruction technique using a pixel method and solving an overdetermined set of equations by singular value decomposition. This allows comparing statistical, spectral, and spatial properties of visible light radiation with electrostatic fluctuations. The shape and position of the time-averaged reconstructed plasma emissivity are observed to be similar to those of the ion saturation current profile. In the core plasma, excluding the electron cyclotron and upper hybrid resonant layers, the mean value of the plasma emissivity is observed to vary with (T{sub e}){sup {alpha}}(n{sub e}){sup {beta}}, in which {alpha}=0.25-0.7 and {beta}=0.8-1.4, in agreement with collisional radiative model. The tomographic reconstruction is applied to the fast camera movie acquired with 50 kframes/s rate and 2 {mu}s of exposure time to obtain the temporal evolutions of the emissivity fluctuations. Conditional average sampling is also applied to visualize and measure sizes of structures associated with the interchange mode. The {omega}-time and the two-dimensional k-space Fourier analysis of the reconstructed emissivity fluctuations show the same interchange mode that is detected in the {omega} and k spectra of the ion saturation current fluctuations measured by probes. Small scale turbulent plasma structures can be
Futatani, S.; Del-Castillo-Negrete, Diego B; Garbet, X; Benkadda, S.; Dubuit, N.
2012-01-01
Self-consistent turbulent transport of high concentration impurities in magnetically confined fusion plasmas is studied using a three-dimensional nonlinear fluid global turbulence model which includes ion temperature gradient (ITG) and trapped electron mode (TEM) instabilities. It is shown that the impurity concentration can have a dramatic feedback in the turbulence and, as a result, it can significantly change the transport properties of the plasma. High concentration impurities can trigger strong intermittency, that manifests in non-Gaussian heavy tails of the pdfs of E B and the ion-temperature flux fluctuations. At the heart of this self-consistent coupling is the existence of inward propagating ion temperature fronts with a sharp gradient at the leading edge that give rise to instabilities and avalanche-like bursty transport. Numerical evidence of time non-locality in the turbulent transport of high concentration impurities is also presented.
The radial scale length of turbulent fluctuations in the main core of TFTR plasmas
Mazzucato, E.; Nazikian, R.
1993-07-01
A new theory of microwave reflectometry in tokamaks has been developed which accounts for all the major characteristics of waves reflected from strong fluctuations near the cutoff layer. The theory has been used for studying the turbulence in the main core of neutral beam heated plasmas of the TFTR tokamak in the supershot regime. The results indicate that the radial correlation length of density fluctuations is a weak decreasing function of beam power, from [approximately]4 cm in Ohmic to [approx]2 cm at 14 MW of heating power. This corresponds to the range of wavelengths k[sub [perpendicular
2014-01-10
Astrophys. J. 694, 618, doi: 10.1088/0004-637X/694/1/618 (2009). [2] P. H. Yoon and T.-M. Fang, Proton heating by parallel Alfven wave cascade, Physics...doi: 10.1088/0741-3335/51/9/095011 (2009). [5] C. S. Wu, P. H. Yoon, and C. B. Wang, On non-resonant proton heating via intrinsic Alfvenic...Gaelzer, Ionospheric ion-acoustic enhancements by turbulent counterstreaming electron beam-plasma interaction, J. Geophys. Res. 115, A02310 doi
Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Quataert, E.; Tatsuno, T.
2009-04-23
This paper presents a theoretical framework for understanding plasma turbulence in astrophysical plasmas. It is motivated by observations of electromagnetic and density fluctuations in the solar wind, interstellar medium and galaxy clusters, as well as by models of particle heating in accretion disks. All of these plasmas and many others have turbulentmotions at weakly collisional and collisionless scales. The paper focuses on turbulence in a strong mean magnetic field. The key assumptions are that the turbulent fluctuations are small compared to the mean field, spatially anisotropic with respect to it and that their frequency is low compared to the ion cyclotron frequency. The turbulence is assumed to be forced at some system-specific outer scale. The energy injected at this scale has to be dissipated into heat, which ultimately cannot be accomplished without collisions. A kinetic cascade develops that brings the energy to collisional scales both in space and velocity. The nature of the kinetic cascade in various scale ranges depends on the physics of plasma fluctuations that exist there. There are four special scales that separate physically distinct regimes: the electron and ion gyroscales, the mean free path and the electron diffusion scale. In each of the scale ranges separated by these scales, the fully kinetic problem is systematically reduced to a more physically transparent and computationally tractable system of equations, which are derived in a rigorous way. In the "inertial range" above the ion gyroscale, the kinetic cascade separates into two parts: a cascade of Alfvenic fluctuations and a passive cascade of density and magnetic-fieldstrength fluctuations. The former are governed by the Reduced Magnetohydrodynamic (RMHD) equations at both the collisional and collisionless scales; the latter obey a linear kinetic equation along the (moving) field lines associated with the Alfvenic component (in the collisional limit, these compressive fluctuations
NASA Astrophysics Data System (ADS)
Usmanov, Arcadi V.; Goldstein, Melvyn L.; Matthaeus, William H.
2014-06-01
We have developed a three-fluid, three-dimensional magnetohydrodynamic solar wind model that incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating. The solar wind plasma is described as a system of co-moving solar wind protons, electrons, and interstellar pickup protons, with separate energy equations for each species. Numerical steady-state solutions of Reynolds-averaged solar wind equations coupled with turbulence transport equations for turbulence energy, cross helicity, and correlation length are obtained by the time relaxation method in the corotating with the Sun frame of reference in the region from 0.3 to 100 AU (but still inside the termination shock). The model equations include the effects of electron heat conduction, Coulomb collisions, photoionization of interstellar hydrogen atoms and their charge exchange with the solar wind protons, turbulence energy generation by pickup protons, and turbulent heating of solar wind protons and electrons. The turbulence transport model is based on the Reynolds decomposition and turbulence phenomenologies that describe the conversion of fluctuation energy into heat due to a turbulent cascade. In addition to using separate energy equations for the solar wind protons and electrons, a significant improvement over our previous work is that the turbulence model now uses an eddy viscosity approximation for the Reynolds stress tensor and the mean turbulent electric field. The approximation allows the turbulence model to account for driving of turbulence by large-scale velocity gradients. Using either a dipole approximation for the solar magnetic field or synoptic solar magnetograms from the Wilcox Solar Observatory for assigning boundary conditions at the coronal base, we apply the model to study the global structure of the solar wind and its three-dimensional properties, including embedded turbulence, heating, and acceleration throughout the heliosphere. The model results are
Usmanov, Arcadi V.; Matthaeus, William H.; Goldstein, Melvyn L.
2014-06-10
We have developed a three-fluid, three-dimensional magnetohydrodynamic solar wind model that incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating. The solar wind plasma is described as a system of co-moving solar wind protons, electrons, and interstellar pickup protons, with separate energy equations for each species. Numerical steady-state solutions of Reynolds-averaged solar wind equations coupled with turbulence transport equations for turbulence energy, cross helicity, and correlation length are obtained by the time relaxation method in the corotating with the Sun frame of reference in the region from 0.3 to 100 AU (but still inside the termination shock). The model equations include the effects of electron heat conduction, Coulomb collisions, photoionization of interstellar hydrogen atoms and their charge exchange with the solar wind protons, turbulence energy generation by pickup protons, and turbulent heating of solar wind protons and electrons. The turbulence transport model is based on the Reynolds decomposition and turbulence phenomenologies that describe the conversion of fluctuation energy into heat due to a turbulent cascade. In addition to using separate energy equations for the solar wind protons and electrons, a significant improvement over our previous work is that the turbulence model now uses an eddy viscosity approximation for the Reynolds stress tensor and the mean turbulent electric field. The approximation allows the turbulence model to account for driving of turbulence by large-scale velocity gradients. Using either a dipole approximation for the solar magnetic field or synoptic solar magnetograms from the Wilcox Solar Observatory for assigning boundary conditions at the coronal base, we apply the model to study the global structure of the solar wind and its three-dimensional properties, including embedded turbulence, heating, and acceleration throughout the heliosphere. The model results are
Strumik, M.; Czechowski, A.; Grzedzielski, S.; Macek, W. M.; Ratkiewicz, R.
2013-08-20
We study processes related to magnetic reconnection and plasma turbulence occurring in the presence of the heliopause (HP) and the heliospheric current sheet. It is shown that the interaction of plasmoids initiated by magnetic reconnection may provide connections between the inner and outer heliosheath and lead to an exchange of particles between the interstellar medium and the solar wind plasma shocked at the heliospheric termination shock. The magnetic reconnection may also cause plasma density and magnetic field compressions in the proximity of the HP. We argue that these phenomena could possibly be detected by the Voyager spacecraft approaching and crossing the HP. These results could clarify the concepts of the ''magnetic highway'' and the ''heliosheath depletion region'' recently proposed to explain recent Voyager 1 observations.
NASA Astrophysics Data System (ADS)
Jo, Young Hyun; Lee, Hae June; Mikhailenko, Vladimir V.; Mikhailenko, Vladimir S.
2016-01-01
It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows. The levels of the drift--Alfven turbulence, resulted from the development of both instabilities, are determined from the renormalized nonlinear dispersion equation, which accounts for the nonlinear effect of the scattering of ions by the electromagnetic turbulence. The renormalized quasilinear equation for the ion distribution function, which accounts for the same effect of the scattering of ions by electromagnetic turbulence, is derived and employed for the analysis of the ion viscosity and ions heating, resulted from the interactions of ions with drift-Alfven turbulence. In the same way, the phenomena of the ion cyclotron turbulence and anomalous anisotropic heating of ions by ion cyclotron plasma turbulence has numerous practical applications in physics of the near-Earth space plasmas. Using the methodology of the shearing modes, the kinetic theory of the ion cyclotron turbulence of the plasma with transverse current with strong velocity shear has been developed.
Choi, Jeong Ryeol
2014-01-01
Quantum dynamics of light waves traveling through a time-varying turbulent plasma is investigated via the SU(1,1) Lie algebraic approach. Plasma oscillations that accompany time-dependence of electromagnetic parameters of the plasma are considered. In particular, we assume that the conductivity of plasma involves a sinusoidally varying term in addition to a constant one. Regarding the time behavior of electromagnetic parameters in media, the light fields are modeled as a modified CK (Caldirola-Kanai) oscillator that is more complex than the standard CK oscillator. Diverse quantum properties of the system are analyzed under the consideration of time-dependent characteristics of electromagnetic parameters. Quantum energy of the light waves is derived and compared with the counterpart classical energy. Gaussian wave packet of the field whose probability density oscillates with time like that of classical states is constructed through a choice of suitable initial condition and its quantum behavior is investigated in detail. Our development presented here provides a useful way for analyzing time behavior of quantized light in complex plasma. PMID:25363295
A coarse-grained transport model for neutral particles in turbulent plasmas
Mekkaoui, A.; Reiter, D.; Boerner, P.; Marandet, Y.; Genesio, P.; Rosato, J.; Capes, H.; Koubiti, M.; Godbert-Mouret, L.; Stamm, R.
2012-12-15
The transport of neutral particles in turbulent plasmas is addressed from the prospect of developing coarse-grained transport models which can be implemented in code suites like B2-EIRENE, currently used for designing the ITER divertor. The statistical properties of turbulent fluctuations are described by a multivariate Gamma distribution able to retain space and time correlations through a proper choice of covariance function. We show that in the scattering free case, relevant for molecules and impurity atoms, the average neutral particle density obeys a Boltzmann equation with an ionization rate renormalized by fluctuations. This result lends itself to a straightforward implementation in the EIRENE Monte Carlo solver for neutral particles. Special emphasis is put on the inclusion of time correlations, and in particular on the ballistic motion of coherent turbulent structures. The role of these time dependent effects is discussed for D{sub 2} molecules and beryllium atoms. The sensitivity of our results to the assumptions on the statistical properties of fluctuations is investigated.
Lu, Z. X.; Tynan, G.; Wang, W. X.; Ethier, S.; Diamond, P. H.; Gao, C.; Rice, J.
2015-05-15
Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (s{sup ^}) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s{sup ^}. Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s{sup ^} discharges and that the value of s{sup ^}{sub crit} is consistent with the experimental results s{sup ^}{sub crit}{sup exp}≈0.2∼0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s{sup ^} and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s{sup ^}.
Lu, Z. X.; Wang, W. X.; Diamond, P. H.; Tynan, G.; Ethier, S.; Gao, C.; Rice, J.
2015-05-04
We report that intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. Here we focus on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (sˆ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak sˆ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak sˆ discharges and that the value of sˆ _{crit} is consistent with the experimental results sˆ ^{exp}_{crit} [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. In conclusion, the consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive sˆ .
Solar and Heliospheric Observatory (SOHO) (1995)
NASA Technical Reports Server (NTRS)
Fleck, Bernhard; St. Cyr, O. Chris (Editor)
2014-01-01
SOHO is the most comprehensive space mission ever devoted to the study of the Sun and its nearby cosmic environment known as the heliosphere. It was launched in December 1995 and is currently funded at least through the end of 2016. SOHO's twelve instruments observe and measure structures and processes occurring inside as well as outside the Sun, and which reach well beyond Earth's orbit into the heliosphere. While designed to study the "quiet" Sun, the new capabilities and combination of several SOHO instruments have revolutionized space weather research. This article gives a brief mission overview, summarizes selected highlight results, and describes SOHO's contributions to space weather research. These include cotemporaneous EUV imaging of activity in the Sun's corona and white light imaging of coronal mass ejections in the extended corona, magnetometry in the Sun's atmosphere, imaging of far side activity, measurements to predict solar proton storms, and monitoring solar wind plasma at the L1 Lagrangian point, 1.5 million kilometers upstream of Earth.
Aspect ratio effects on limited scrape-off layer plasma turbulence
Jolliet, Sébastien Halpern, Federico D.; Loizu, Joaquim; Mosetto, Annamaria; Ricci, Paolo
2014-02-15
The drift-reduced Braginskii model describing turbulence in the tokamak scrape-off layer is written for a general magnetic configuration with a limiter. The equilibrium is then specified for a circular concentric magnetic geometry retaining aspect ratio effects. Simulations are then carried out with the help of the global, flux-driven fluid three-dimensional code GBS [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. Linearly, both simulations and simplified analytical models reveal a stabilization of ballooning modes. Nonlinearly, flux-driven nonlinear simulations give a pressure characteristic length whose trends are correctly captured by the gradient removal theory [Ricci and Rogers, Phys. Plasmas 20, 010702 (2013)], that assumes the profile flattening from the linear modes as the saturation mechanism. More specifically, the linear stabilization of ballooning modes is reflected by a 15% increase in the steady-state pressure gradient obtained from GBS nonlinear simulations when going from an infinite to a realistic aspect ratio.
NASA Astrophysics Data System (ADS)
Avino, Fabio; Bovet, Alexandre; Fasoli, Ambrogio; Furno, Ivo; Gustafson, Kyle; Loizu, Joaquim; Ricci, Paolo; Theiler, Christian
2012-10-01
TORPEX is a basic plasma physics toroidal device located at the CRPP-EPFL in Lausanne. In TORPEX, a vertical magnetic field superposed on a toroidal field creates helicoidal field lines with both ends terminating on the torus vessel. We review recent advances in the understanding and control of electrostatic interchange turbulence, associated structures and their effect on suprathermal ions. These advances are obtained using high-resolution diagnostics of plasma parameters and wave fields throughout the whole device cross-section, fluid models and numerical simulations. Furthermore, we discuss future developments including the possibility of generating closed field line configurations with rotational transform using an internal toroidal wire carrying a current. This system will also allow the study of innovative fusion-relevant configurations, such as the snowflake divertor.
Filamentation of magnetosonic wave and generation of magnetic turbulence in laser plasma interaction
Modi, K. V.; Tiwary, Prem Pyari; Singh, Ram Kishor Sharma, R. P.; Satsangi, V. R.
2014-10-15
This paper presents a theoretical model for the magnetic turbulence in laser plasma interaction due to the nonlinear coupling of magnetosonic wave with ion acoustic wave in overdense plasma. For this study, dynamical equations of magnetosonic waves and the ion acoustic waves have been developed in the presence of ponderomotive force due to the pump magnetosonic wave. Slowly converging and diverging behavior has been studied semi-analytically, this results in the formation of filaments of the magnetosonic wave. Numerical simulation has also been carried out to study nonlinear stage. From the results, it has been found that the localized structures become quite complex in nature. Further, power spectrum has been studied. Results show that the spectral index follows (∼k{sup −2.0}) scaling at smaller scale. Relevance of the present investigation has been shown with the experimental observation.
Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas
NASA Astrophysics Data System (ADS)
Happel, T.; Manz, P.; Ryter, F.; Hennequin, P.; Hetzenecker, A.; Conway, G. D.; Guimarais, L.; Honoré, C.; Stroth, U.; Viezzer, E.; The ASDEX Upgrade Team
2016-06-01
This letter shows for the first time a pronounced increase of extremely intermittent edge density turbulence behavior inside the confinement region related to the I-mode confinement regime in the ASDEX Upgrade tokamak. With improving confinement, the perpendicular propagation velocity of density fluctuations in the plasma edge increases together with the intermittency of the observed density bursts. Furthermore, it is shown that the weakly coherent mode, a fluctuation feature generally observed in I-mode plasmas, is connected to the observed bursts. It is suggested that the large amplitude density bursts could be generated by a non-linearity similar to that in the Korteweg-de-Vries equation which includes the radial temperature gradient.
NASA Technical Reports Server (NTRS)
Intriligator, Devrie S.; Intriligator, James; Miller, W. David; Webber, William R.; Decker, Robert B.
2010-01-01
We have found in the Voyager 2 (V2) plasma science data in the heliosheath (HS) near the termination shock (TS) high-energy ions (HEIs) in addition to the bulk plasma convective flow ions. The HEI detections temporally coincide with increased V2 plasma wave subsystem (PWS) activity in "event A"h of Gurnett and Kurth. Maxwellian fits to HEI detections indicate the HEIs are moving radially anti -Sunward with a proton speed of 600 km/s, a density of 10(exp -4) (exp -3), and a thermal speed of 10 km/s. The heliosheath bulk convective protons have a speed of 204 km/s, a density of 0.0029 cm(exp -3), and a thermal speed of 26.7 km/s. The HEI flux and ram pressure are approximately 10% and 30% of those of the bulk HS flow. Since the HEI speed is both close to twice the solar wind speed and independent of the heliosheath bulk plasma speed, the HEIs may be detections of pickup protons formed in the solar wind and convected through the TS. The HEIs also are reminiscent of the pickup protons upstream of the Mars bow shock where their energy also was independent of the bulk plasma speed and attributed to multiple reflections off the Mars bow shock. Gurnett and Kurth 's (2008) event A enhanced PWS activity may be generated by a two ]stream instability from the interaction of these HEIs with the heliosheath bulk plasma ions. We present our findings, discuss their implications, and also present alternative interpretations.
Turbulence Decorrelation via Controlled Ex B Shear in High-Performance Plasmas
NASA Astrophysics Data System (ADS)
McKee, G. R.
2015-11-01
Multi-scale spatiotemporal turbulence properties are significantly altered as toroidal rotation and resulting ExB shearing rate profile are systematically varied in advanced-inductive H-mode plasmas on DIII-D (βN ~ 2.7, q95=5.1). Density, electron and ion temperature profiles and dimensionless parameters (βN, q95, ν*, ρ*, and Te/Ti) are maintained nearly fixed during the rotation scan. Low-wavenumber turbulence (k⊥ρS < 1), measured with Beam Emission Spectroscopy, exhibits increased decorrelation rates (reduced eddy lifetime) as the ExB shear rises across the radial zone of maximum shearing rate (0.55 < ρ < 0 . 75), while the fluctuation amplitude undergoes little change. The poloidal wavenumber is reduced at higher shear, indicating a change in the wavenumber spectrum: eddies elongate in the direction orthogonal to shear and field. At both low and high shear, the 2D turbulence correlation function exhibits a tilted structure, consistent with flow shear. At mid-radius (ρ ~ 0.5), low-k density fluctuations show localized amplitude reduction, consistent with linear GYRO growth rates and ωExB shearing rates. Intermediate and high wavenumber fluctuations measured with Doppler Back-Scattering (k⊥ρS ~ 2.5-3.5) at ρ=0.7 and Phase Contrast Imaging (k⊥ρS > 5) exhibit decreasing amplitude at higher rotation. The energy confinement time increases from 105 ms to 150 ms as the toroidal Mach number (M=vTOR / vth , i) increases to Mo ~ 0.5, while transport decreases. TGLF calculations match the Ti profile with modest discrepancies in the Te and ne profiles. These results clarify the complex mechanisms by which ExB shear affects turbulence. Work supported in part by the US DOE under DE-FG02-08ER54999, DE-FC02-04ER54698.
Core turbulent transport in tokamak plasmas: bridging theory and experiment with QuaLiKiz
NASA Astrophysics Data System (ADS)
Bourdelle, C.; Citrin, J.; Baiocchi, B.; Casati, A.; Cottier, P.; Garbet, X.; Imbeaux, F.; Contributors, JET
2016-01-01
Nonlinear gyrokinetic codes allow for detailed understanding of tokamak core turbulent transport. However, their computational demand precludes their use for predictive profile modeling. An alternative approach is required to bridge the gap between theoretical understanding and prediction of experiments. A quasilinear gyrokinetic model, QuaLiKiz (Bourdelle et al 2007 Phys. Plasmas 14 112501), is demonstrated to be rapid enough to ease systematic interface with experiments. The derivation and approximation of this approach are reviewed. The quasilinear approximation is proven valid over a wide range of core plasma parameters. Examples of profile prediction using QuaLiKiz coupled to the CRONOS integrated modeling code (Artaud et al 2010 Nucl. Fusion 50 043001) are presented. QuaLiKiz is being coupled to other integrated modeling platforms such as ETS and JETTO. QuaLiKiz quasilinear gyrokinetic turbulent heat, particle and angular momentum fluxes are available to all users. It allows for extensive stand-alone interpretative analysis and for first principle based integrated predictive modeling.
A model for two-dimensional bursty turbulence in magnetized plasmas
Servidio, Sergio; Primavera, Leonardo; Carbone, Vincenzo; Noullez, Alain; Rypdal, Kristoffer
2008-01-15
The nonlinear dynamics of two-dimensional electrostatic interchange modes in a magnetized plasma is investigated through a simple model that replaces the instability mechanism due to magnetic field curvature by an external source of vorticity and mass. Simulations in a cylindrical domain, with a spatially localized and randomized source at the center of the domain, reveal the eruption of mushroom-shaped bursts that propagate radially and are absorbed by the boundaries. Burst sizes and the interburst waiting times exhibit power-law statistics, which indicates long-range interburst correlations, similar to what has been found in sandpile models for avalanching systems. It is shown from the simulations that the dynamics can be characterized by a Yaglom relation for the third-order mixed moment involving the particle number density as a passive scalar and the ExB drift velocity, and hence that the burst phenomenology can be described within the framework of turbulence theory. Statistical features are qualitatively in agreement with experiments of intermittent transport at the edge of plasma devices, and suggest that essential features such as transport can be described by this simple model of bursty turbulence.
NASA Technical Reports Server (NTRS)
Klimas, Alex; Uritsky, Vadim; Donovan, Eric
2010-01-01
We provide indirect evidence for turbulent reconnection in Earth's midtail plasma sheet by reexamining the statistical properties of bright, nightside auroral emission events as observed by the UVI experiment on the Polar spacecraft and discussed previously by Uritsky et al. The events are divided into two groups: (1) those that map to absolute value of (X(sub GSM)) < 12 R(sub E) in the magnetotail and do not show scale-free statistics and (2) those that map to absolute value of (X(sub GSM)) > 12 R(sub E) and do show scale-free statistics. The absolute value of (X(sub GSM)) dependence is shown to most effectively organize the events into these two groups. Power law exponents obtained for group 2 are shown to validate the conclusions of Uritsky et al. concerning the existence of critical dynamics in the auroral emissions. It is suggested that the auroral dynamics is a reflection of a critical state in the magnetotail that is based on the dynamics of turbulent reconnection in the midtail plasma sheet.
Non-inductive Hybrid Scenario-Transport and Turbulence at Reduced Plasma Torque
NASA Astrophysics Data System (ADS)
Thome, K. E.; Petty, C. C.; Pace, D. C.; Turco, F.; Rhodes, T. L.
2016-10-01
As the neutral beam injection (NBI) torque is lowered in steady-state hybrid plasmas via counter-beam injection, increased turbulence and thermal transport is observed, particularly in the ion channel. These discharges require Pco-NBI = 11 MW and PECH = 3 MW to achieve zero surface loop voltage. As the beam torque is reduced from 8.5 N-m to 4 N-m with βN 3 and q95 6 , the global confinement decreases from H 98 y , 2 of 1.5 to 1.2 . Local transport analysis using TRANSP shows that the lower torque discharges have increased ion thermal diffusivity across the whole profile and increased electron thermal diffusivity localized to the ρ = 0.7 region. Similarly, Doppler Backscattering shows increased density fluctuations at intermediate wavenumbers at the lower torque. However, fast-ion transport caused by off-axis fishbones favorably decreases from 0.7m2 /s to 0.1m2 /s as the torque is lowered, partially offsetting the thermal transport reduction. These measured changes in turbulence and transport are being compared to plasma simulations using TGLF/GYRO to better predict the confinement of future steady-state hybrids that will be primarily RF-heated. Work supported by the US DOE under DE-FC02-04ER54698.
Drift wave turbulence in the edge region of MST reversed field pinch plasmas
NASA Astrophysics Data System (ADS)
Thuecks, D. J.; Almagri, A. F.; Sarff, J. S.; Terry, P. W.
2016-10-01
Measurements of electric field fluctuations reveal activity consistent with drift waves in the edge region of standard-confinement MST plasmas. The fluctuations are broadband and strongly anisotropic, with a power spectral index that is steeper in the direction parallel to the mean magnetic field direction than it is in the perpendicular direction. The power in the fluctuating kinetic energy, 1/2 minivẼ×B0 2 , exceeds the power in magnetic fluctuation energy for frequencies above 80 kHz. At lower frequencies (20-40 kHz), magnetic energy associated with unstable global tearing modes dominates. A lack of equipartition in the turbulent cascade coincides with measured signatures of independent fluctuation activity broadly consistent with drift-wave fluctuations. Statistical coherence measurements reveal mode activity at high frequencies (>=80 kHz) that is compressive, has high coherence in regions of the plasma with strong density gradients, and has a phase speed comparable to the electron drift speed. Elevated coherency associated with this fluctuation feature of the drift wave fluctuations return more quickly following magnetic reconnection events than corresponding coherence associated with the tearing activity. This suggests the drift-wave fluctuations may be excited by the large edge-localized thermal pressure gradient, but they could also be excited nonlinearly in a turbulent cascade driven by the tearing modes. Work supported by DOE and NSF.
NASA Astrophysics Data System (ADS)
Huang, S. Y.; Sahraoui, F.; Yuan, Z. G.; He, J. S.; Zhao, J. S.; Le Contel, O.; Deng, X. H.; Zhou, M.; Fu, H. S.; Shi, Q. Q.; Lavraud, B.; Pang, Y.; Yang, J.; Wang, D. D.; Li, H. M.; Yu, X. D.; Pollock, C. J.; Giles, B. L.; Torbert, R. B.; Russell, C. T.; Goodrich, K. A.; Gershman, D. J.; Moore, T. E.; Ergun, R. E.; Khotyaintsev, Y. V.; Lindqvist, P.-A.; Strangeway, R. J.; Magnes, W.; Bromund, K.; Leinweber, H.; Plaschke, F.; Anderson, B. J.; Burch, J. L.
2017-02-01
We report on the observations of an electron vortex magnetic hole corresponding to a new type of coherent structure in the turbulent magnetosheath plasma using the Magnetospheric Multiscale mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 ρ i (∼30 ρ e) in the quasi-circular cross-section perpendicular to its axis, where ρ i and ρ e are respectively the proton and electron gyroradius. There are no clear enhancements seen in high-energy electron fluxes. However, there is an enhancement in the perpendicular electron fluxes at 90° pitch angle inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components V em and V en suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the cross-section in the M–N plane. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations.
Investigation of edge turbulence by means of optical and electrical diagnostics in RFP plasmas
NASA Astrophysics Data System (ADS)
Scarin, Paolo; Cavazzana, Roberto; Serianni, Gianluigi; Yagi, Yasuyuki; Sakakita, Hajime
2003-10-01
Electrostatic turbulence in the edge region of RFP is commonly observed with sets of Langmuir probes during low current operation and associated with electrostatic structures. A new diagnostic system is being developed for the investigation of electrostatic turbulence in the edge region of fusion plasmas, at high plasma currents and thermal loads and will be used in the TPE-RX and RFX devices. The system is composed of gas puff nozzle, a double radial array of Langmuir probes and a set of 32 optical chords measuring the HÑ fluctuations. The nozzle will allow the puffing of gas to increase the local optical emissivity; the optical sensors will permit to investigate the optical emissivity turbulent pattern and to perform a two-dimensional analysis of turbulent structures. The Langmuir probes will be used to visualise the floating potential turbulent pattern and to measure the electron density. After assessing the correspondence between the results of the two systems and characterising the properties of the local plasma, the Langmuir probes will be remotely removed and only the optical analysis will be continued at high plasma currents. The gas flow will be characterised so as not to perturb the investigated region, while at the same time increasing the local emissivity. The area of optical view is 60 mm wide (toroidal direction) and 4 mm high (poloidal direction). The fields of view of adjacent chords in the object plane are 5 mm toroidally apart from each other and their diameter is 4 mm. The focus along the line of sight is about 50 mm deep. Each chord views a cone centred on focal point in the outer edge and extending through the plasma. The contributions due to small-scale structures away from the focus will be spatially averaged and so should contribute mainly a constant level to the chord signal. The puffed cloud emission will be collected from 3 optical heads and transferred through 35 m long optical fibres to the detection system, for which standard
Basse, N.P.; Zoletnik, S.; Michelsen, P.K.
2005-01-01
Confinement transitions in the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)] can be induced by varying either the internal plasma current or the external magnetic field. In this paper we report on experiments where closely matched confinement states (good and bad) were constructed using the latter method. Analysis using the former scheme has been reported upon previously [S. Zoletnik et al., Plasma Phys. Controlled Fusion 44, 1581 (2002)]. The electron temperature, along with the major spectral characteristics of magnetic and small-scale electron density fluctuations, changes dramatically at the transition from good to bad confinement. The fluctuation power is intermittent, and core bursts traveling in the electron diamagnetic drift (DD) direction are correlated between the bottom and top of the plasma, especially during degraded confinement. A corresponding top-bottom correlation for the edge ion DD direction turbulence feature was not found. Strong correlations are observed both between the two density fluctuation signals and between magnetic and density fluctuations in bad compared to good confinement. The correlation time of the bursts is of order 100 {mu}s, similar to the lifetime observed during edge localized modes.
NASA Astrophysics Data System (ADS)
Basse, N. P.; Zoletnik, S.; Michelsen, P. K.; W7-As Team
2005-01-01
Confinement transitions in the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)] can be induced by varying either the internal plasma current or the external magnetic field. In this paper we report on experiments where closely matched confinement states (good and bad) were constructed using the latter method. Analysis using the former scheme has been reported upon previously [S. Zoletnik et al., Plasma Phys. Controlled Fusion 44, 1581 (2002)]. The electron temperature, along with the major spectral characteristics of magnetic and small-scale electron density fluctuations, changes dramatically at the transition from good to bad confinement. The fluctuation power is intermittent, and core bursts traveling in the electron diamagnetic drift (DD) direction are correlated between the bottom and top of the plasma, especially during degraded confinement. A corresponding top-bottom correlation for the edge ion DD direction turbulence feature was not found. Strong correlations are observed both between the two density fluctuation signals and between magnetic and density fluctuations in bad compared to good confinement. The correlation time of the bursts is of order 100μs, similar to the lifetime observed during edge localized modes.
On the phase shift between electric potential and plasma density fluctuations in the edge turbulence
Shchepetov, S. V. Kholnov, Yu. V.; Vasil'kov, D. G.
2013-02-15
In some cases, the phase shift between fluctuations of the electric potential and plasma density helps to identify the instability that governs the turbulent state. In this paper, the basic experimental and theoretical results that denote the possibility (or impossibility) of such identification are briefly discussed. The experimental data based on measurements of the phase shift between the floating potential and ion saturation current fluctuations in the L-2M stellarator-a system with externally imposed magnetic surfaces-are presented (Shchepetov, Kholnov, Fedyanin, et al., Plasma Phys. Controlled Fusion 50, 045001 (2008)). It is shown that the observed phase shift {Omega} varies in a wide range from {pi} to 0, gradually decreasing with deepening inside the plasma. A number of arguments are presented suggesting that {Omega} Almost-Equal-To {pi} can indicate that the process is nonlocal, i.e., oscillations at a given spatial point are driven and mainly determined by the processes localized outside of the observation point. We note that, within the framework of the magnetohydrodynamic theory, plasma was definitely unstable with respect to resistive interchange modes in all cases under study. It is demonstrated experimentally that the widespread notion that the phase shift {Omega} Almost-Equal-To {pi}/2 is characteristic of only resistive interchange modes is hardly universal. The experimental results are analyzed on the basis of analytical estimates.
Ilyasov, Askar A.; Chernyshov, Alexander A. Mogilevsky, Mikhail M.; Golovchanskaya, Irina V. Kozelov, Boris V.
2015-03-15
Inhomogeneities of plasma density and non-uniform electric fields are compared as possible sources of a sort of electrostatic ion cyclotron waves that can be identified with broadband extremely low frequency electrostatic turbulence in the topside auroral ionosphere. Such waves are excited by inhomogeneous energy-density-driven instability. To gain a deeper insight in generation of these waves, computational modeling is performed with various plasma parameters. It is demonstrated that inhomogeneities of plasma density can give rise to this instability even in the absence of electric fields. By using both satellite-observed and model spatial distributions of plasma density and electric field in our modeling, we show that specific details of the spatial distributions are of minor importance for the wave generation. The solutions of the nonlocal inhomogeneous energy-density-driven dispersion relation are investigated for various ion-to-electron temperature ratios and directions of wave propagation. The relevance of the solutions to the observed spectra of broadband extremely low frequency emissions is shown.
Physics of the inner heliosphere: Mechanisms, models and observational signatures
NASA Technical Reports Server (NTRS)
Withbroe, George L.
1987-01-01
Selected problems concerned with the important physical processes that occur in the corona and solar wind acceleration region, particularly time dependent phenomena were studied. Both the physics of the phenomena and the resultant effects on observational signatures, particularly spectroscopic signatures were also studied. Phenomena under study include: wave motions, particularly Alfven and fast mode waves; the formation of standing shocks in the inner heliosphere as a result of momentum and/or heat addition to the wind; and coronal transient phenomena where momentum and/or heat are deposited in the corona to produce transient plasma heating and/or mass ejection. The development of theoretical models for the inner heliosphere, the theoretical investigation of spectroscopic plasma diagnostics for this region, and the analysis of existing skylab and other relevant data are also included.
Mikkelsen, D. R. Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.
2015-06-15
Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.
NASA Astrophysics Data System (ADS)
Jabbari, S.; Brandenburg, A.
2014-12-01
Recent studies have suggested a new mechanism that can be used to explain the formation of magnetic spots or bipolar regions in highly stratified turbulent plasmas. According to this model, a large-scale magnetic field suppresses the turbulent pressure, which leads to a negative contribution of turbulence to the effective magnetic pressure. Direct numerical simulations (DNS) have confirmed that the negative contribution is large enough so that the effective magnetic pressure becomes negative and leads to a large-scale instability, which we refer to as negative effective magnetic pressure Instability (NEMPI). NEMPI was used to explain the formation of active regions and sunspots on the solar surface. One step toward improving this model was to combine dynamo in- stability with NEMPI. The dynamo is known to be responsible for the solar large-scale magnetic field and to play a role in solar activity. In this context, we studied stratified turbulent plasmas in spherical geometry, where the background field was generated by alpha squared dynamo. For NEMPI to be excited, the initial magnetic field should be in a proper range, so we used quenching function for alpha. Using the Pencil Code and mean field simulations (MFS), we showed that in the presence of dynamo-generated magnetic fields, we deal with a coupled system, where both instabilities, dynamo and NEMPI, work together and lead to the formation of magnetic structures (Jabbari et al. 2013). We also studied a similar system in plane geometry in the presence of rotation and confirmed that for slow rotation NEMPI works, but as the Coriolis number increases, the rotation suppresses NEMPI. By increasing the Coriolis number even further, the combination of fast rotation and high stratification excites a dynamo, which leads again to a coupled system of dynamo and NEMPI (Jabbari et al. 2014). Another important finding concerning NEMPI is the case where the instability is excited by a vertical magnetic field (Brandenburg et
NASA Technical Reports Server (NTRS)
Usmanov, Arcadi V.; Goldstein, Melvyn L.; Matthaeus, William H.
2012-01-01
To study the effects of interstellar pickup protons and turbulence on the structure and dynamics of the solar wind, we have developed a fully three-dimensional magnetohydrodynamic solar wind model that treats interstellar pickup protons as a separate fluid and incorporates the transport of turbulence and turbulent heating. The governing system of equations combines the mean-field equations for the solar wind plasma, magnetic field, and pickup protons and the turbulence transport equations for the turbulent energy, normalized cross-helicity, and correlation length. The model equations account for photoionization of interstellar hydrogen atoms and their charge exchange with solar wind protons, energy transfer from pickup protons to solar wind protons, and plasma heating by turbulent dissipation. Separate mass and energy equations are used for the solar wind and pickup protons, though a single momentum equation is employed under the assumption that the pickup protons are comoving with the solar wind protons.We compute the global structure of the solar wind plasma, magnetic field, and turbulence in the region from 0.3 to 100 AU for a source magnetic dipole on the Sun tilted by 0 deg - .90 deg and compare our results with Voyager 2 observations. The results computed with and without pickup protons are superposed to evaluate quantitatively the deceleration and heating effects of pickup protons, the overall compression of the magnetic field in the outer heliosphere caused by deceleration, and the weakening of corotating interaction regions by the thermal pressure of pickup protons.
Beam-plasma instability in the presence of low-frequency turbulence. [during type 3 solar emission
NASA Technical Reports Server (NTRS)
Goldman, M. V.; Dubois, D. F.
1982-01-01
General equations are derived for a linear beam-plasma instability in the presence of low-frequency turbulence. Within a 'quasi-linear' statistical approximation, these equations contain Langmuir wave scattering, diffusion, resonant and nonresonant anomalous absorption, and a 'plasma laser' effect. It is proposed that naturally occurring density irregularities in the solar wind may stabilize the beam-unstable Langmuir waves which occur during type III solar emissions.
NASA Astrophysics Data System (ADS)
Halpern, F. D.; Ricci, P.
2017-03-01
The narrow power decay-length ({λq} ), recently found in the scrape-off layer (SOL) of inner-wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two-fluid turbulence simulations. The formation of the steep plasma profiles is found to arise due to radially sheared \\mathbf{E}× \\mathbf{B} poloidal flows. A complex interaction between sheared flows and parallel plasma currents outflowing into the sheath regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. Analytical calculations suggest that the IWL {λq} is roughly equal to the turbulent correlation length.
Halpern, Federico D.; Ricci, Paolo
2016-12-19
The narrow power decay-length (λ_{q}), recently found in the scrape-off layer (SOL) of inner wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two fluid turbulence simulations. The formation of the steep plasma profiles is found to arise due to radially sheared E×B poloidal flows. A complex interaction between sheared flows and parallel plasma currents outflowing into the sheath regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. As a result, analytical calculations suggest that the IWL λ_{q} is roughly equal to the turbulent correlation length.
Halpern, Federico D.; Ricci, Paolo
2016-12-19
The narrow power decay-length (λq), recently found in the scrape-off layer (SOL) of inner wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two fluid turbulence simulations. The formation of the steep plasma profiles is found to arise due to radially sheared E×B poloidal flows. A complex interaction between sheared flows and parallel plasma currents outflowing into the sheath regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. As a result, analytical calculations suggest that the IWL λq is roughly equal tomore » the turbulent correlation length.« less
Ratcliffe, H. Brady, C. S.; Che Rozenan, M. B.; Nakariakov, V. M.
2014-12-15
Quasilinear theory has long been used to treat the problem of a weak electron beam interacting with plasma and generating Langmuir waves. Its extension to weak-turbulence theory treats resonant interactions of these Langmuir waves with other plasma wave modes, in particular, ion-sound waves. These are strongly damped in plasma of equal ion and electron temperatures, as sometimes seen in, for example, the solar corona and wind. Weak turbulence theory is derived in the weak damping limit, with a term describing ion-sound wave damping then added. In this paper, we use the EPOCH particle-in-cell code to numerically test weak turbulence theory for a range of electron-ion temperature ratios. We find that in the cold ion limit, the results agree well, but for increasing ion temperature the three-wave resonance becomes broadened in proportion to the ion-sound wave damping rate. Additionally, we establish lower limits on the number of simulation particles needed to accurately reproduce the electron and wave distributions in their saturated states and to reproduce their intermediate states and time evolution. These results should be taken into consideration in, for example, simulations of plasma wave generation in the solar corona of Type III solar radio bursts from the corona to the solar wind and in weak turbulence investigations of ion-acoustic lines in the ionosphere.
Hinode/XRT Measurements of Turbulent Velocities in Flare Plasma Sheets
NASA Astrophysics Data System (ADS)
McKenzie, David; Freed, Michael
2015-04-01
The turbulent, dynamic motions that we observe in the hot plasma surrounding current sheets very likely distort the embedded magnetic fields, resulting in reduced length scales and locally augmented resistivities. These conditions may help to accelerate and/or prolong the reconnection in solar flares. Although we cannot as yet measure directly the magnetic fields in the corona, the velocity fields within the flare plasma sheets provide a means to study the conditions that control the spatial and temporal scales of reconnection, in the locations and at the times that are relevant to structuring the magnetic fields.The plasma sheets are observable in many flares in soft X-ray and EUV wavelengths, due to their high temperatures. For two recent flares observed with the Hinode X-Ray Telescope (XRT), we have analyzed the velocity fields with a local correlation tracking technique, and compared to measurements from the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA).This work is supported by NASA under contract NNM07AB07C with the Smithsonian Astrophysical Observatory, and by grant NNX14AD43G.
Distribution of turbulent plasma in the magnetosphere estimated by the SWARM magnetic data.
NASA Astrophysics Data System (ADS)
Yokoyama, Y.; Iyemori, T.; Nakanishi, K.; Aoyama, T.
2015-12-01
LEO satellites observe the magnetic fluctuations with period from a few second to a few tens of seconds along their orbits in high-latitudes. It has been proposed that these are mainly caused by the spatial structures of the field-aligned currents(FACs). However, since LEO satellites before the SWARM were single, the studies still have theoretical assumptions. In this study, at first, we will show that these fluctuations are the manifestations of the spatial structures of the FACs by using the data obtained by SWARM-satellites during initial two months. Second, based on the above, we assume that these fluctuations mainly consist of the spatial variations, and apply spectral analysis to see the characteristics of the spatial structure of the FACs. From the above analyses, we confirm that the fluctuations with period from about 2 second to about 30 second can be regarded as the manifestations of the spatial structure of FACs. Then we project the area of fluctuations on the equatorial plane of magnetosphere, i.e., the plasma sheet, by using the Tsyganenko model, and estimate the characteristics of turbulence. We will also show the relations between these turbulent region and the substorm phase etc.
Hasegawa, Akira
2009-01-01
One important discovery in the twentieth century physics is the natural formation of a coherent or a well-ordered structure in continuous media, in contrary to degradation of the state as predicted earlier from the second law of thermodynamics. Here nonlinearity plays the essential role in its process. The discovery of soliton, a localized stable wave in a nonlinear and dispersive medium and the self-organization of fluid turbulence are of the major examples. A soliton is formed primarily in one-dimensional medium where the dispersion and nonlinearity play the essential role. Here the temporal evolution can be described by an infinite dimensional Hamiltonian system that is integrable. While a self-organization appears in an infinite dimensional non-Hamiltonian (or dissipative) system where more than two conservative quantities exist in the limit of no dissipation. In this manuscript, by showing examples of the optical soliton in dielectric fibers and self-organization of turbulence in a toroidal plasma in a magnetic field, we demonstrate these interesting discoveries. The manuscript is intended to describe these discoveries more on philosophical basis with some sacrifice on mathematical details so that the idea is conveyed to those in the wide area of sciences. PMID:19145067
The Link Between Shocks, Turbulence, and Magnetic Reconnection in Collisionless Plasmas
NASA Technical Reports Server (NTRS)
Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-01-01
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, 'stir' the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space, and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
Weak turbulence theory of ion temperature gradient modes for inverted density plasmas
Hahm, T.S.; Tang, W.M.
1989-09-01
Typical profiles measured in H-mode ( high confinement'') discharges from tokamaks such as JET and DIII-D suggest that the ion temperature gradient instability threshold parameter {eta}{sub i} ({equivalent to}dlnT{sub i}/dlnn{sub i}) could be negative in many cases. Previous linear theoretical calculations have established the onset conditions for these negative {eta}{sub i}-modes and the fact that their growth rate is much smaller than their real frequency over a wide range of negative {eta}{sub i} values. This has motivated the present nonlinear weak turbulence analysis to assess the relevance of such instabilities for confinement in H-mode plasmas. The nonlinear eigenmode equation indicates that the 3-wave coupling to shorter wavelength modes is the dominant nonlinear saturation mechanism. It is found that both the saturation level for these fluctuations and the magnitude of the associated ion thermal diffusivity are considerably smaller than the strong turbulence mixing length type estimates for the more conventional positive-{eta}{sub i}-instabilities. 19 refs., 3 figs.
Expansion of magnetic clouds in the outer heliosphere
NASA Astrophysics Data System (ADS)
Gulisano, A. M.; Démoulin, P.; Dasso, S.; Rodriguez, L.
2012-07-01
Context. A large amount of magnetized plasma is frequently ejected from the Sun as coronal mass ejections (CMEs). Some of these ejections are detected in the solar wind as magnetic clouds (MCs) that have flux rope signatures. Aims: Magnetic clouds are structures that typically expand in the inner heliosphere. We derive the expansion properties of MCs in the outer heliosphere from one to five astronomical units to compare them with those in the inner heliosphere. Methods: We analyze MCs observed by the Ulysses spacecraft using in situ magnetic field and plasma measurements. The MC boundaries are defined in the MC frame after defining the MC axis with a minimum variance method applied only to the flux rope structure. As in the inner heliosphere, a large fraction of the velocity profile within MCs is close to a linear function of time. This is indicative of a self-similar expansion and a MC size that locally follows a power-law of the solar distance with an exponent called ζ. We derive the value of ζ from the in situ velocity data. Results: We analyze separately the non-perturbed MCs (cases showing a linear velocity profile almost for the full event), and perturbed MCs (cases showing a strongly distorted velocity profile). We find that non-perturbed MCs expand with a similar non-dimensional expansion rate (ζ = 1.05 ± 0.34), i.e. slightly faster than at the solar distance and in the inner heliosphere (ζ = 0.91 ± 0.23). The subset of perturbed MCs expands, as in the inner heliosphere, at a significantly lower rate and with a larger dispersion (ζ = 0.28 ± 0.52) as expected from the temporal evolution found in numerical simulations. This local measure of the expansion also agrees with the distribution with distance of MC size, mean magnetic field, and plasma parameters. The MCs interacting with a strong field region, e.g. another MC, have the most variable expansion rate (ranging from compression to over-expansion).
The radial scale length of turbulent fluctuations in the main core of TFTR plasmas
Mazzucato, E.; Nazikian, R.
1993-07-01
A new theory of microwave reflectometry in tokamaks has been developed which accounts for all the major characteristics of waves reflected from strong fluctuations near the cutoff layer. The theory has been used for studying the turbulence in the main core of neutral beam heated plasmas of the TFTR tokamak in the supershot regime. The results indicate that the radial correlation length of density fluctuations is a weak decreasing function of beam power, from {approx}4 cm in Ohmic to {approx}2 cm at 14 MW of heating power. This corresponds to the range of wavelengths k{sub {perpendicular}}{rho}{sub i}{approx}0.1--0.3. Over the same interval of heating powers, the level of density fluctuations is observed to steadily increase with beam power by more than an order of magnitude. This trend is inconsistent with mixing length estimates of the fluctuation level.
NASA Astrophysics Data System (ADS)
Mikkelsen, D. R.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N.; Podpaly, Y.; Reinke, M.; Rice, J. E.; Hughes, J. W.; Ma, Y.; Candy, J.; Waltz, R. E.
2012-10-01
In nonlinear GYRO simulations of C-Mod plasmas, a turbulently driven pinch produces modest density peaking of all species. The ratio of density at r/a=0.44 and 0.74 is 1.2 for the majority and minority D & H (and electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.29 for neon, 1.36 for argon, 1.47 for molybdenum. Density peaking is only weakly affected when the ion temperature profile is varied to align the predicted heat flux to the experimental transport analysis. New simulations will extend the collisionality to the lower part of the experimentally accessible range in C-Mod to study the collisionality dependence of density peaking, and to establish whether much stronger peaking is predicted for lower collisionalities. Simulations based on measured I-mode ion and electron temperature profiles will also be presented.
Observation of electron hole, double layer, and turbulent heating in a laboratory plasma
NASA Astrophysics Data System (ADS)
Tsukishima, T.; Inuzuka, H.
1990-08-01
Nonlinear phenomena such as electron hole, double layer, and turbulent heating, which were observed in a linear mirror device, THE NU-II, are reviewed. Observations were carried out with a temporal resolution of 2 ns and a spatial resolution of 1 mm, respectively. Upon applying a voltage difference of the order of 10 kV between two electrodes inserted in the cylindrical plasma at a distance of 67 cm, the nonlinear phenomena evolved consecutively. In particular, a strong current limited double layer was formed, and its lifetime was found to satisfy a simple empirical law. One dimensional computer simulations based on a kinetic code were carried out with boundary conditions close to the experimental ones. The effect of magnetic field was taken into consideration in the simulations.
NASA Astrophysics Data System (ADS)
Wu, D. J.; Feng, H. Q.; Li, B.; He, J. S.
2016-08-01
The nature of turbulence, dissipation, and heating in plasma media has been an attractive and challenge problem in space physics as well as in basic plasma physics. A wide continuous spectrum of Alfvénic turbulence from large MHD-scale Alfvén waves (AWs) in the inertial turbulence regime to small kinetic-scale kinetic AWs (KAWs) in the dissipation turbulence regime is a typical paradigm of plasma turbulence. The incorporation of current remote observations of AWs in the solar atmosphere, in situ satellite measurements of Alfvénic turbulence in the solar wind, and experimental investigations of KAWs on large plasma devices in laboratory provides a chance synthetically to study the physics nature of plasma turbulence, dissipation, and heating. A session entitled "Nature of Turbulence, Dissipation, and Heating in Space Plasmas: From Alfvén Waves to Kinetic Alfvén Waves" was held as a part of the twelfth Asia Oceania Geosciences Society Annual Meeting, which took place in Singapore between 2 and 7 August 2015. This special section is organized based on the session.
Schuster, Eugenio
2014-05-02
The strong coupling between the different physical variables involved in the plasma transport phenomenon and the high complexity of its dynamics call for a model-based, multivariable approach to profile control where those predictive models could be exploited. The overall objective of this project has been to extend the existing body of work by investigating numerically and experimentally active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport can be monitored by an array of electrostatic probes, and Ex B flow profiles can be controlled via a set of biased concentric ring electrodes that terminate the plasma column. The goals of the proposed research have been threefold: i- to develop a predictive code to simulate plasma transport in the linear HELCAT (HELicon-CAThode) plasma device at the University of New Mexico (UNM), where the experimental component of the proposed research has been carried out; ii- to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles, iii- to investigate the fundamental nonlinear dynamics of turbulence and transport physics. Lehigh University (LU), including Prof. Eugenio Schuster and one full-time graduate student, has been primarily responsible for control-oriented modeling and model-based control design. Undergraduate students have also participated in this project through the National Science Foundation Research Experience for Undergraduate (REU) program. The main goal of the LU Plasma Control Group has been to study the feasibility of controlling turbulence-driven transport by shaping the radial poloidal flow profile (i.e., by controlling flow shear) via biased concentric ring electrodes.
NASA Astrophysics Data System (ADS)
Sujar-Garrido, P.; Benard, N.; Moreau, E.; Bonnet, J. P.
2015-04-01
The objective of these experiments was to determine the optimal forcing location and unsteady forcing actuation produced by a single dielectric barrier discharge plasma actuator for controlling the flow downstream of a backward-facing step. The investigated configuration is a 30-mm-height step mounted in a closed-loop wind tunnel. The flow velocity is fixed at 15 m/s, corresponding to a Reynolds number based on the step height equal to 3 × 104 ( Re θ = 1400). The control authority of the plasma discharge is highlighted by the time-averaged modification of the reattachment point and by the effects obtained on the turbulent dynamics of the reattached shear layer. Several locations of the device actuator are considered, and a parametric study of the input signal is investigated for each location. This procedure leads to the definition of an optimal control configuration regarding the minimization of the reattachment length. When the actuator—that produces an electrohydrodynamic force resulting in an electric wind jet—is located upstream the separation point, it can manipulate the first stages of the formation of the turbulent free shear layer and consequently to modify the flow dynamics. Maximum effects have been observed when the high voltage is burst modulated at a frequency f BM = 125 Hz with a duty-cycle of 50 %. This forcing corresponds to a Strouhal number based on the momentum thickness equal to 0.011, a value corresponding to the convective instability or Kelvin-Helmholtz instability of the separated shear layer.
Smirnova, T. V.; Shishov, V. I.; Popov, M. V.; Andrianov, A. S.; Kardashev, N. S.; Kovalev, Y. Y.; Soglasnov, V. A.; Zhuravlev, V. I.; Anderson, J. M.; Karuppusamy, R.; Kramer, M.; Zensus, J. A.; Bartel, N.; Deller, A.; Joshi, B. C.
2014-05-10
RadioAstron space-ground very long baseline interferometry observations of the pulsar B0950+08, conducted with the 10 m Space Radio Telescope in conjunction with the Arecibo 300 m telescope and the Westerbork Synthesis Radio Telescope at a frequency of 324 MHz were analyzed in order to investigate plasma inhomogeneities in the direction of this nearby pulsar. The observations were conducted at a spacecraft distance of 330,000 km, resulting in a projected baseline of 220,000 km, providing the greatest angular resolution ever achieved at meter wavelengths. Our analysis is based on fundamental behavior of structure and coherence functions. We find that the pulsar shows scintillation on two frequency scales, both much less than the observing frequency, but modulation is less than 100%. We infer that the scattering is weak, but a refracting wedge disperses the scintillation pattern. The refraction angle of this 'cosmic prism' is measured as θ{sub 0} = 1.1-4.4 mas, with the refraction direction being approximately perpendicular to the observer velocity. We show that the observed parameters of scintillation effects indicate that two plasma layers lie along the line of sight to the pulsar, at distances of 4.4-16.4 pc and 26-170 pc, and traveling in different directions relative to the line of sight. Spectra of turbulence for the two layers are found to follow a power law with the indices γ{sub 1} = γ{sub 2} = 3.00 ± 0.08, significantly different from the index expected for a Kolmogorov spectrum of turbulence, γ = 11/3.
Vacuum ultraviolet detection of the VLISM-heliosphere interaction. [very local interstellar medium
NASA Technical Reports Server (NTRS)
Judge, D. L.; Gangopadhyay, P.; Ogawa, H. S.; Blum, P.
1992-01-01
As the neutral components of the interstellar gas flow through the heliosphere their spatial distribution is modified by charge exchange with the solar plasma, photoionization, and radiation pressure. The deep space probes Pioneers 10/11 and Voyagers 1/2 have provided an opportunity to investigate this distribution through VUV observations of the heliospheric glow. Since the interactions of the inflowing neutrals with the heliosphere depend on both space and time it is particularly useful to have multiple spacecraft observations. Pioneer 10 is in the downstream region of the inflowing interstellar breeze at 50 AU while Pioneer 11 and Voyager 2 are upstream at about 30 AU. Voyager 1 is also upstream at about 40 AU but at a heliographic latitude of + 30 deg. Both temporal and spatial effects are expected to be quite different for the upstream and downstream regions. Some of the recent VUV data and its implications with respect to the heliospheric structure will be presented.
Cosmic Ray Modulation in the Outer Heliosphere During the Minimum of Solar Cycle 23/24
NASA Technical Reports Server (NTRS)
Adams, James H., Jr.; Florinski, V.; Washimi, H.; Pogorelov, N. V.
2011-01-01
We report a next generation model of galactic cosmic ray (GCR) transport in the three dimensional heliosphere. Our model is based on an accurate three-dimensional representation of the heliospheric interface. This representation is obtained by taking into account the interaction between partially ionized, magnetized plasma flows of the solar wind and the local interstellar medium. Our model reveals that after entering the heliosphere GCRs are stored in the heliosheath for several years. The preferred GCR entry locations are near the nose of the heliopause and at high latitudes. Low-energy (hundreds of MeV) galactic ions observed in the heliosheath have spent, on average, a longer time in the solar wind than those observed in the inner heliosphere, which would explain their cooled-off spectra at these energies. We also discuss radial gradients in the heliosheath and the implications for future Voyager observations.
Physics of the outer heliosphere
Gazis, P.R. )
1991-01-01
Major advances in the physics of the outer heliosphere are reviewed for the 1987-1990 time frame. Emphasis is placed on five broad topics: the detailed structure of the solar wind at large heliocentric distances, the global structure of the interplanetary field, latidudinal variations and meridional flows, radial and temporal variations, and the interaction of the solar wind with the local interstellar medium. 122 refs.
NASA Astrophysics Data System (ADS)
Gauthier, Serge; Keane, Christopher J.; Niemela, Joseph J.; Abarzhi, Snezhana I.
2013-07-01
Mixing and turbulent mixing are non-equilibrium processes that occur in a broad variety of processes in fluids, plasmas and materials. The processes can be natural or artificial, their characteristic scales can be astrophysical or atomistic, and energy densities can be low or high. Understanding the fundamental aspects of turbulent mixing is necessary to comprehend the dynamics of supernovae and accretion discs, stellar non-Boussinesq and magneto-convection, mantle-lithosphere tectonics and volcanic eruptions, atmospheric and oceanographic flows in geophysics, and premixed and non-premixed combustion. It is crucial for the development of the methods of control in technological applications, including mixing mitigation in inertial confinement and magnetic fusion, and mixing enhancement in reactive flows, as well as material transformation under the action of high strain rates. It can improve our knowledge of realistic turbulent processes at low energy density involving walls, unsteady transport, interfaces and vortices, as well as high energy density hydrodynamics including strong shocks, explosions, blast waves and supersonic flows. A deep understanding of mixing and turbulent mixing requires one to go above and beyond canonical approaches and demands further enhancements in the quality and information capacity of experimental and numerical data sets, and in the methods of theoretical analysis of continuous dynamics and kinetics. This has the added potential then of bringing the experiment, numerical modelling, theoretical analysis and data processing to a new level of standards. At the same time, mixing and turbulent mixing being one of the most formidable and multi-faceted problems of modern physics and mathematics, is well open for a curious mind. In this article we briefly review various aspects of turbulent mixing, and present a summary of over 70 papers that were discussed at the third International Conference on 'Turbulent Mixing and Beyond', TMB-2011, that
Center for Gyrokinetic Particle Simulations of Turbulent Transport in Burning Plasmas
Scott, Parker
2011-05-02
This is the Final Technical Report for University of Colorado's portion of the SciDAC project 'Center for Gyrokinetic Particle Simulation of Turbulent Transport.' This is funded as a multi-institutional SciDAC Center and W.W. Lee at the Princeton Plasma Physics Laboratory is the lead Principal Investigator. Scott Parker is the local Principal Investigator for University of Colorado and Yang Chen is a Co-Principal Investigator. This is Cooperative Agreement DE-FC02-05ER54816. Research personnel include Yang Chen (Senior Research Associate), Jianying Lang (Graduate Research Associate, Ph.D. Physics Student) and Scott Parker (Associate Professor). Research includes core microturbulence studies of NSTX, simulation of trapped electron modes, development of efficient particle-continuum hybrid methods and particle convergence studies of electron temperature gradient driven turbulence simulations. Recently, the particle-continuum method has been extended to five-dimensions in GEM. We find that actually a simple method works quite well for the Cyclone base case with either fully kinetic or adiabatic electrons. Particles are deposited on a 5D phase-space grid using nearest-grid-point interpolation. Then, the value of delta-f is reset, but not the particle's trajectory. This has the effect of occasionally averaging delta-f of nearby (in the phase space) particles. We are currently trying to estimate the dissipation (or effective collision operator). We have been using GEM to study turbulence and transport in NSTX with realistic equilibrium density and temperature profiles, including impurities, magnetic geometry and ExB shear flow. Greg Rewoldt, PPPL, has developed a TRANSP interface for GEM that specifies the equilibrium profiles and parameters needed to run realistic NSTX cases. Results were reported at the American Physical Society - Division of Plasma Physics, and we are currently running convergence studies to ensure physical results. We are also studying the effect of
Numerical Simulation of Heliospheric Transients Approaching Geospace
2009-12-01
12/15/08 – 12/14/09 Numerical Simulation of Heliospheric Transients Approaching Geospace Report by Dusan Odstrcil, University of Colorado...simulations of heliospheric transients approaching geospace . The project was supervised by Dr. Dusan Odstrcil at the University of Colorado (CU...plays a key role in the prediction accuracy of heliospheric transients approaching geospace . This report presents main results achieved within the
NASA Astrophysics Data System (ADS)
Porkolab, M.; Ennever, P.; Baek, S. G.; Creely, A. J.; Edlund, E. M.; Hughes, J.; Rice, J. E.; Rost, J. C.; White, A. E.; Reinke, M. L.; Staebler, G.; Candy, J.; Alcator C-Mod Team
2016-10-01
Recent experiments on C-Mod ohmic plasmas and gyrokinetic studies indicated that dilution of deuterium plasmas by injection of nitrogen decreased the ion diffusivity and may also alter the direction of intrinsic toroidal rotation. Simulations with TGLF and GYRO showed that dilution of deuterium ions in low density (LOC) plasmas increased the critical ion temperature gradient, while in high density (SOC) plasmas it decreased the stiffness. The density fluctuation spectrum measured in low q95 plasmas with Phase Contrast Imaging (PCI), and corroborated with spatially localized reflectometer measurements show a reduction of turbulence near r/a = 0.8 with kρs <= 1, in agreement with modeling predictions in this region where the ion turbulence is well above marginal stability. Measurements also indicate that reversal of the toroidal rotation direction near the SOC-LOC transition may depend on ion collisionality rather than that of electrons. New experiments with neon seeding, which may be more relevant to ITER than with nitrogen seeding, show similar results. The impact of dilution on Te turbulence as measured with CECE diagnostic will also be presented. Supported by US DOE Awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512.
Heliosphere Dimension and Cosmic Ray Modulation
NASA Astrophysics Data System (ADS)
Bobik, P.; Boschini, M. J.; Consolandi, C.; Della Torre, S.; Gervasi, M.; Grandi, D.; Kudela, K.; Noventa, F.; Pensotti, S.; Rancoita, P. G.; Rozza, D.
2012-08-01
The differential intensities of Cosmic Rays at Earth were calculated using a 2D stochastic Montecarlo diffusion code and compared with observation data. We evaluated the effect of stretched and compressed heliospheres on the Cosmic Ray intensities at the Earth. This was studied introducing a dependence of the diffusion parameter on the heliospherical size. Then, we found that the optimum value of the heliospherical radius better accounting for experimental data. We also found that the obtained values depends on solar activity. Our results are compatible with Voyager observations and with models of heliospherical size modulation.
NASA Astrophysics Data System (ADS)
Yi, Sumin; Jhang, Hogun; Kwon, J. M.
2016-10-01
We report the results of a gyrokinetic simulation study elucidating the characteristics of the current driven by electron temperature gradient (ETG) turbulence in toroidal geometry. We examined the amount of the ETG turbulence-driven current for different turbulence levels, which were obtained by varying the relative electron gyroradius ρ* = ρe/a. Simulations show that the amount of the ETG turbulence-driven current increases with ρ* due to the gyro-Bohm scaling of turbulence intensity. A perturbation of the equilibrium q-profile by the ETG turbulence-driven current becomes noticeable when ρ* > 1/4000. Even in a small ρ* case, the proportional relation between the ETG turbulence-driven current and turbulence intensity suggests that a considerable intrinsic current can be driven inside an edge pedestal where a steep gradient of the electron temperature profile can excite ETG turbulence in a narrow region.
Comparison of the ionospheric plasma turbulence over seismic and equatorial regions.
NASA Astrophysics Data System (ADS)
Kosciesza, M.; Blecki, J.; Parrot, M.; Wronowski, R.
2012-04-01
Many strong earthquakes which are objects of interest in investigations of the changes registered in the electric field in the ELF frequency range (1 Hz - 1250 Hz) in the ionospheric plasma, occurs in the equatorial region. In order to determine, if the observed disturbances are connected with the coupling between the ground and the ionosphere in the seismic active region, it is necessary to analyse and compare plasma instability phenomena occurring in the equatorial F-region ionosphere and are known as equatorial spread F (ESF) to changes before earthquakes because their character is very similar. The aim of this paper is the analysis of changes in the electromagnetic ELF field, registered by the French micro-satellite DEMETER over epicentres of three selected strong earthquakes with magnitude bigger than 6, which took place in: Sichuan, Chile and Haiti. A comparison between those cases and changes observed by the same satellite over the equatorial region in the similar time of year is presented. The analysis of the data, was conducted with the Fourier, wavelet and bispectral methods. The last one gives answer to question, whether the changes localized with the spectral analysis are nonlinear. Further processing consists the determination of the power spectrum and its slope, which allows to determine the type of turbulence which was inducted by the three wave interaction. The last stage of the presented research, was finding the characteristic remarks of changes, by calculation of the probability density function (PDF) and calculation of its characteristic values such as kurtosis and skewness.
Hamza, A.M.; Sudan, R.N.
1995-03-01
The equations governing the nonlinear evolution of density fluctuations in a low-pressure weakly ionized plasma driven unstable by the ExB or gradient-drift instability were derived by Sudan and Keskinen for addressing the electrostatic turbulence in the E and F regions of the Earth`s ionosphere. The authors have developed a subgrid model suitable for the numerical simulation of these equations which is closely related to renormalized diffusion caused by small-scale fluctuation spectrum. {open_quotes}Dynamical Renormalization Group{close_quotes} (RNG) methods are employed to obtain the renormalized diffusion. This procedure computes the long-wavelength, long-time behavior of density correlations generated by the evolution equation for the plasma stirred by a Gaussian random force characterized by a correlation function {proportional_to} k{sup m} where k is the wavenumber of the forcing function. The effect of small scales on the large-scale dynamics in the limit k{yields}0 and infinite Reynolds number can be expressed in the form of renormalized coefficients; in this case, renormalized diffusion. If one assumes the power spectra to be given by the Kolmogorov argument of cascading of energy through k space then one can derive a subgrid model based on the results of RNG. 27 refs.
H-mode Edge Turbulence and Pedestal Measurements in Pegasus Plasmas using Langmuir Probes
NASA Astrophysics Data System (ADS)
Kriete, D. M.; Bodner, G. M.; Bongard, M. W.; Fonck, R. J.; Thome, K. E.; Thompson, D. S.
2015-11-01
In Pegasus discharges, L-H mode transitions are induced using Ohmic heating and high-field-side fueling. H-mode plasmas have energy confinement consistent with the ITER98pb(y,2) scaling law, indications of increased electron and ion temperature, and an increase in core rotation compared to L-mode plasmas. Electron density and temperature profiles have been measured in the edge region using a scannable triple Langmuir probe on a shot-by-shot basis. In H-mode, a pressure pedestal that has a hyperbolic tangent shape and a ~ 2 cm ∇pe scale length is observed, in contrast to a linear shape in L-mode. Autopower spectra of the collected ion saturation current in H-mode discharges show a factor of ~ 3 reduction in fluctuations in the 50-200 kHz band with respect to L-mode. Two Langmuir probes with 8 cm poloidal separation have been installed on Pegasus. The turbulence correlation length in the edge will be measured by radially scanning the probes. Knowledge of the correlation length will be used to inform the design of a future 8-channel radial multiprobe array. This system will simultaneously measure the dynamic ne (R , t) , Te (R , t) , and Φ (R , t) profiles and fluctuations across the L-H mode transition and be used to investigate nonlinear ELM dynamics. Work supported by US DOE grant DE-FG02-96ER54375.
Mechanism for generation of 2-3 kHz radiation in the outer heliosphere
NASA Technical Reports Server (NTRS)
Macek, W. M.
1995-01-01
The question of how low-frequency non-thermal radio emissions at the boundary of the heliosphere might be generated is considered. The mechanism consists of two steps. First, the beam of energetic electrons generates a high level of electrostatic Langmuir plasma waves. Second, electromagnetic radiation results from the non-linear interaction between Langmuir waves. Intensity of radio emissions at 2 to 3 kHz detected by the Voyager plasma wave instrument in the outer heliosphere can be explained provided that the electron beams generating Langmuir waves exist also in the postshock plasma due to secondary shocks in the compressed solar wind beyond the termination shock. Modification of the heliospheric shocks by the cosmic ray pressure is also taken into account. The field strengths of Langmuir waves required to generate the second harmonic emissions are of 50 to 100 microvolts per meter. These waves may be observed in situ by Voyager 1 and 2 in the near future.
Investigation on the effect of pressure on turbulent transports of the IR-T1 Tokamak plasma
NASA Astrophysics Data System (ADS)
Alipour, Ramin; Meshkani, Sakineh; Elahi, Ahmad Salar; Ghoranneviss, Mahmood
2017-03-01
Investigation on the effects of limiter biasing and applying external electric fields (positive and negative voltage of 200 V) under various pressures of 1.9, 2.3 and 2.7 Torr on the IR-T1 Tokamak plasma parameters such as plasma current, loop voltage, radial electric field, poloidal electric field and Reynolds stress and turbulent transports, was done in this work. The results show that the ramp time of the plasma current decreased and the change rate of loop voltage raised by increasing plasma pressure. The power of radial electric field is more than the power of poloidal electric field. According to the applied positive voltage to the plasma, it is observed that the Reynolds stress of IR-T1 Tokamak plasma has experienced a more significant reduction at the pressure of 2.3 Torr than other pressures. The results Also show that the applying positive voltage of 200 V to the IR-T1 Tokamak plasma at the pressure of 2.3 Torr (compared to other pressures) has more effect on increases and decreases the poloidal and radial turbulent transport, respectively.
Computer Simulation of Motion of Heliospheric Termination Shock
NASA Technical Reports Server (NTRS)
Ratkiewicz, R. E.; Barnes, A.; Molvik, G. A.
1995-01-01
A time-dependent computer model is used to study a non-equilibrium structure of the heliosphere, resulting from the interaction between the solar wind and the interstellar plasma. An interaction of the heliospheric termination shock with various disturbances such as density or velocity jumps or interplanetary shocks in upstream solar wind as well as pressure jumps in local interstellar medium is investigated. Consequences of latitudinal variation in dynamic pressure are also discussed. The initial boundary conditions of unsteady calculations are given by the solar wind parameters as functions of time and/or latitude on an inner boundary, and/or by the local interstellar pressure as a function of time (roughly simulating the effect of the local interstellar medium) on an outer boundary.
Ulysses - The first high-latitude heliospheric mission
NASA Technical Reports Server (NTRS)
Wenzel, K.-P.; Marsden, R. G.; Page, D. E.; Smith, E. J.
1989-01-01
The Ulysses mission will, for the first time, explore the heliosphere within a few astronomical units of the sun over the full range of heliographic latitudes, thereby providing the first characterization of the uncharted third dimension. Highly sophisticated scientific instrumentation carried on board the spacecraft is designed to measure the properties of the solar wind, the sun/wind interface, the heliospheric magnetic field, solar radio bursts and plasma waves, solar X-rays, solar and galactic cosmic rays, and interplanetary/interstellar neutral gas and dust. This collaborative ESA/NASA mission, scheduled for launch in October 1990, will use a Jupiter gravity-assist to achieve a trajectory extending to high solar latitudes /1,2/.
Solar Orbiter - Exploring the Sun-Heliosphere Connection
NASA Astrophysics Data System (ADS)
Zouganelis, Ioannis; Mueller, Daniel; St. Cyr, Chris; Gilbert, Holly R.
2016-04-01
Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme, promises to deliver groundbreaking science with previously unavailable observational capabilities provided by a suite of in-situ and remote-sensing instruments in a unique orbit. The mission will address the central question of heliophysics: How does the Sun create and control the heliosphere? The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. In this talk, we highlight the scientific goals of Solar Orbiter, address the synergy between this joint ESA/NASA mission and other new space- and ground-based observatories, and present the mission's development status.
The photon-plasmon transitions and diagnostics of the space plasma turbulence
NASA Astrophysics Data System (ADS)
Glushkov, Alexander; Glushkov, Alexander; Khetselius, Olga
We present a new approach to treating the space plasma turbulence, based on using to make diagnostic data regarding the photon-plasmon transitions. The theoretical definition of characteristics for these transitions is caried out within consistent theoretical approach, based on the Gell-Mann and Low formalism (energy approach in QED theory).We apply it to calculation of such transitions (Ps) with emission of photon and Langmuir quanta. It is well known that the hfs states of positronium Ps Ps differ in spin S, life time t and mode of annihilation. As a rule, probabilities of the cascade radiation transitions are more than the annihilation probability. The ortho-Ps atom has a metastable state 23s1 and probability of two-photon radiation transition from this state into 13s1 state (1.8•10(-3) 1/s) is significantly less than probability of the three-photon annihilation directly from 23s1level 8.9•10(5) s(-1), i.e. it is usually supposed that the ortho-Ps annihilates from 23s1state. Another situation may take place in plasma, where it is arisen the competition process of destruction of the metastable level - the photonplasmon transition 23s1-13s1with emission of photon and Langmuir quanta. In this paper we carried out the calculation of the probability of the Ps photon-plasmon transition and propose tu use it for diagnostics of the space plasma (dusty one etc.).Standard S-matrix calculation with using an expression for tensor of dielectric permeability of the isotropic space plasma and dispersion relationships for transverse and Langmuir waves [3] allows getting the corresponding probability P(ph-pl). Numerical value of P(ph-pl) is 5.2•10(6)•UL(s-1), where UL is density of the Langmuir waves energy. Our value is correlated with estimate, available in literature [3]: P(phpl)= 6•10(6)•UL (s-1). Comparison of the obtained probability with the life time t(3) allows getting the condition of predominance of the photon-plasmon transition over three
NASA Astrophysics Data System (ADS)
Tang, William
2013-04-01
Advanced computing is generally recognized to be an increasingly vital tool for accelerating progress in scientific research in the 21st Century. The imperative is to translate the combination of the rapid advances in super-computing power together with the emergence of effective new algorithms and computational methodologies to help enable corresponding increases in the physics fidelity and the performance of the scientific codes used to model complex physical systems. If properly validated against experimental measurements and verified with mathematical tests and computational benchmarks, these codes can provide more reliable predictive capability for the behavior of complex systems, including fusion energy relevant high temperature plasmas. The magnetic fusion energy research community has made excellent progress in developing advanced codes for which computer run-time and problem size scale very well with the number of processors on massively parallel supercomputers. A good example is the effective usage of the full power of modern leadership class computational platforms from the terascale to the petascale and beyond to produce nonlinear particle-in-cell simulations which have accelerated progress in understanding the nature of plasma turbulence in magnetically-confined high temperature plasmas. Illustrative results provide great encouragement for being able to include increasingly realistic dynamics in extreme-scale computing campaigns to enable predictive simulations with unprecedented physics fidelity. Some illustrative examples will be presented of the algorithmic progress from the magnetic fusion energy sciences area in dealing with low memory per core extreme scale computing challenges for the current top 3 supercomputers worldwide. These include advanced CPU systems (such as the IBM-Blue-Gene-Q system and the Fujitsu K Machine) as well as the GPU-CPU hybrid system (Titan).
NASA Astrophysics Data System (ADS)
Benard, N.; Pons-Prats, J.; Periaux, J.; Bugeda, G.; Braud, P.; Bonnet, J. P.; Moreau, E.
2016-02-01
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated flows. Here, a nonthermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step ( U 0 = 15 m/s, Re h = 30,000, Re θ = 1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step (objective function #1) and also to measure the wall pressure fluctuation coefficients (objective function #2). An autonomous multi-variable optimization by genetic algorithm is implemented in an experiment for optimizing simultaneously the voltage amplitude, the burst frequency and the duty cycle of the high-voltage signal producing the surface plasma discharge. The single-objective optimization problems concern alternatively the minimization of the objective function #1 and the maximization of the objective function #2. The present paper demonstrates that when coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm can find the optimum forcing conditions in only a few generations. At the end of the iterative search process, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing process. The objective function #2 is maximized for an actuation at half the shear layer mode. In this specific forcing mode, time-resolved PIV shows that the vortex pairing is reduced and that the strong fluctuations of the wall pressure coefficients result from the periodic passages of flow structures whose size corresponds to the height of the step model.
Rognlien, T; Umansky, M; Xu, X; Cohen, R; LoDestro, L
2004-05-24
The edge-plasma profiles and fluxes to the divertor and walls of a divertor tokamak with a magnetic X-point are simulated by coupling a 2D transport code (UEDGE) and a 3D turbulence code (BOUT). An relaxed iterative coupling scheme is used where each code is run on its characteristic time scale, resulting in a statistical steady state. Plasma variables of density, parallel velocity, and separate ion and electron temperatures are included, together with a fluid neutral model for recycling neutrals at material surfaces. Results for the DIII-D tokamak parameters show that the turbulence is preferentially excited in the outer radial region of the edge where magnetic curvature is destabilizing and that substantial plasma particle flux is transported to the main chamber walls. These results are qualitatively consistent with some experimental observations. The coupled transport/turbulence simulation technique provides a strategy to understanding edge-plasma physics in more detailed than previously available and to significantly enhance the realism of predictions of the performance of future devices.
Rognlien, T; Umanksy, M; Xu, X; Cohen, R; LoDestro, L
2004-05-24
The edge-plasma profiles and fluxes to the divertor and walls of a divertor tokamak with a magnetic X-point are simulated by coupling a 2D transport code (UEDGE) and a 3D turbulence code (BOUT). An relaxed iterative coupling scheme is used where each code is run on its characteristic time scale, resulting in a statistical steady state. Plasma variables of density, parallel velocity, and separate ion and electron temperatures are included, together with a fluid neutral model for recycling neutrals at material surfaces. Results for the DIII-D tokamak parameters show that the turbulence is preferentially excited in the outer radial region of the edge where magnetic curvature is destabilizing and that substantial plasma particle flux is transported to the main chamber walls. These results are qualitatively consistent with some experimental observations. The coupled transport/turbulence simulation technique provides a strategy to understanding edge-plasma physics in more detailed than previously available and to significantly enhance the realism of predictions of the performance of future devices
NASA Astrophysics Data System (ADS)
Romé, M.; Lepreti, F.; Maero, G.; Pozzoli, R.; Vecchio, A.; Carbone, V.
2013-03-01
Highly magnetized, pure electron plasmas confined in a Penning-Malmberg trap allow one to perform experiments on the two-dimensional (2D) fluid dynamics under conditions where non-ideal effects are almost negligible. Recent results on the freely decaying 2D turbulence obtained from experiments with electron plasmas performed in the Penning-Malmberg trap ELTRAP are presented. The analysis has been applied to experimental sequences with different types of initial density distributions. The dynamical properties of the system have been investigated by means of wavelet transforms and Proper Orthogonal Decomposition (POD). The wavelet analysis shows that most of the enstrophy is contained at spatial scales corresponding to the typical size of the persistent vortices in the 2D electron plasma flow. The POD analysis allows one to identify the coherent structures which give the dominant contribution to the plasma evolution. The statistical properties of the turbulence have been investigated by means of Probability Density Functions (PDFs) and structure functions of spatial vorticity increments. The analysis evidences how the shape and evolution of the dominant coherent structures and the intermittency properties of the turbulence strongly depend on the initial conditions for the electron density.
Von Kármán energy decay and heating of protons and electrons in a kinetic turbulent plasma.
Wu, P; Wan, M; Matthaeus, W H; Shay, M A; Swisdak, M
2013-09-20
Decay in time of undriven weakly collisional kinetic plasma turbulence in systems large compared to the ion kinetic scales is investigated using fully electromagnetic particle-in-cell simulations initiated with transverse flow and magnetic disturbances, constant density, and a strong guide field. The observed energy decay is consistent with the von Kármán hypothesis of similarity decay, in a formulation adapted to magnetohydrodyamics. Kinetic dissipation occurs at small scales, but the overall rate is apparently controlled by large scale dynamics. At small turbulence amplitudes the electrons are preferentially heated. At larger amplitudes proton heating is the dominant effect. In the solar wind and corona the protons are typically hotter, suggesting that these natural systems are in the large amplitude turbulence regime.
NASA Astrophysics Data System (ADS)
Jabbari, Sarah
2015-08-01
We study a system of a highly stratified turbulent plasma. In such a system, when the magnetic Reynolds number is large enough and there is a background field of suitable strength, a new effect will play role in con- centrating magnetic fields such that it leads to the formation of magnetic spots and bipolar regions. This effect is due to the fact that the turbu- lent pressure is suppressed by the large-scale magnetic field, which adds a negative term to the total mean-field (effective) pressure. This leads to an instability, which is known as the negative effective magnetic pressure instability (NEMPI). Direct numerical simulations (DNS) of isothermally forced turbulence have shown that NEMPI leads to the formation of spots in the presence of an imposed field. Our main aim now is to use NEMPI to explain the formation of active regions and sunspots. To achieve this goal, we need to move progressively to more realistic models. Here we extend our model by allowing the magnetic field to be generated by a dy- namo. A dynamo plays an important role in solar activity. Therefore, it is of interest to investigate NEMPI in the presence of dynamo-generated magnetic fields. Mean-field simulations (MFS) of such systems in spheri- cal geometry have shown how these two instabilities work in concert. In fact NEMPI will be activated as long as the strength of the magnetic field generated by the dynamo is in a proper range (for more detail see Jab- bari et al. 2013). In our new study, we use DNS to investigate a similar system. The turbulence is forced in the entire spherical shell, but the forc- ing is made helical in the lower 30% of the shell, similar to the model of Mitra et al. (2014). We perform simulations using the Pencil Code for different density contrasts and other input parameters. We applied ver- tical field boundary conditions in the r direction. The results show that, when the stratification is high enough, intense bipolar regions form and as time passes, they expand
The Heliosphere as Resonant Cavity
NASA Technical Reports Server (NTRS)
Bames, Aaron
1999-01-01
If a disturbance in the supersonic solar wind reaches the heliospheric shock, a number of events ensue. First, the shock itself responds with inward or outward motion. Secondly, the disturbance propagates outward through the heliosheath as a sound or magnetoacoustic wave; eventually it reaches the heliopause and is (partially) reflected back toward the termination shock. The reflected wave can return to the shock, affecting the shock's motion, and be reflected yet again. The repetition of these processes can produce a 'ringing' in the heliosheath. This suggests that it may be useful to regard the heliosheath as a resonant acoustic cavity with inner and outer boundaries at the termination shock and heliopause, respectively. To evaluate this concept we have developed a simple model of small-amplitude resonant oscillations in an outwardly flowing gas, with appropriate boundary conditions (shock on the interior, tangential discontinuity on the exterior boundary). The fundamental mode of oscillation has a period of order T approx. 2D/C, where C is the speed of sound in the heliosheath and D is the distance between the two boundaries. Typical numerical models of the heliosphere give C approx. 200-500 km/s and D approx. 20 - 100 AU, giving T approx. 0.5 - 2.5 years. Hence we suggest that motions of the heliosheath and termination shock will occur with time scales of the order of a year, and are the consequence of the resonant nature of the heliospheric cavity rather than the history of variation at the Sun and/or in the solar wind. In particular, we suggest that the motion of the termination shock may be unrelated to solar variations over the time scale of the sunspot cycle.
NASA Astrophysics Data System (ADS)
Leddy, Jarrod; Dudson, Ben
2016-10-01
Understanding the transport processes in the low temperature plasma at the boundary region of magnetic confinement fusion (MCF) devices is crucial to the design and operation of future fusion reactor devices. It influences the divertor heat load, and probably the core confinement as well. The dominant source of this transport is turbulence, which serves to mix the high and low temperature regions of the plasma. The nature of this plasma turbulence is affected by not only the plasma parameters, but also the neutral species that also exist in these low temperature regions. The interaction of neutrals with the plasma turbulence is studied in linear device geometry (for its simplicity, yet similarity in plasma parameters), and the result is a strong interaction that impacts the local plasma and neutral densities, momenta and energies. The neutral gas is found to affect plasma edge turbulence primarily through momentum exchange, reducing the radial electric field and enhancing cross-field transport, with consequent implications for the SOL width and divertor heat loads. Therefore, turbulent plasma and fluid simulations have been performed in multiple tokamak geometries to more closely examine the effects of this interaction. These cases were chosen for the variety in configuration with ISTOK having a toroidal limiter (ie. no divertor), DIII-D having a standard divertor configuration, and MAST-U having a super-X divertor with extended outer divertor legs. Progress towards the characterization of neutral impact on detachment and edge behavior will be presented.
MHD Modeling of the Solar Wind with Turbulence Transport and Heating
NASA Technical Reports Server (NTRS)
Goldstein, M. L.; Usmanov, A. V.; Matthaeus, W. H.; Breech, B.
2009-01-01
We have developed a magnetohydrodynamic model that describes the global axisymmetric steady-state structure of the solar wind near solar minimum with account for transport of small-scale turbulence associated heating. The Reynolds-averaged mass, momentum, induction, and energy equations for the large-scale solar wind flow are solved simultaneously with the turbulence transport equations in the region from 0.3 to 100 AU. The large-scale equations include subgrid-scale terms due to turbulence and the turbulence (small-scale) equations describe the effects of transport and (phenomenologically) dissipation of the MHD turbulence based on a few statistical parameters (turbulence energy, normalized cross-helicity, and correlation scale). The coupled set of equations is integrated numerically for a source dipole field on the Sun by a time-relaxation method in the corotating frame of reference. We present results on the plasma, magnetic field, and turbulence distributions throughout the heliosphere and on the role of the turbulence in the large-scale structure and temperature distribution in the solar wind.
NASA Astrophysics Data System (ADS)
Lee, Jaehyun; Yun, Gunsu S.; Choi, Minjun J.; Kwon, Jae-Min; Jeon, Young-Mu; Lee, Woochang; Luhmann, Neville C.; Park, Hyeon K.
2016-08-01
The effect of static n =1 resonant magnetic perturbation (RMP) on the spatial structure and temporal dynamics of edge-localized modes (ELMs) and edge turbulence in tokamak plasma has been investigated. Two-dimensional images measured by a millimeter-wave camera on the KSTAR tokamak revealed that the coherent filamentary modes (i.e., ELMs) are still present in the edge region when the usual large scale collapse of the edge confinement, i.e., the ELM crash, is completely suppressed by n =1 RMP. Cross-correlation analyses on the 2D images show that (1) the RMP enhances turbulent fluctuations in the edge toward the ELM-crash-suppression phase, (2) the induced turbulence has a clear dispersion relation for wide ranges of wave number and frequency, and (3) the turbulence involves a net radially outward energy transport. Nonlinear interactions of the turbulent eddies with the coexisting ELMs are clearly observed by bispectral analysis, which implies that the exchange of energy between them may be the key to the prevention of large scale crashes.
Remote Sensing of Inner Heliospheric Plasmas
1992-12-15
Colloquium 133 held in Iguazu , Argentina 2-6 August, 1991, Z. Svestka, B.V. Jackson and M.E. Machado, eds. Springer-Verlag, Heidelberg, (1992) (pg. 322 - 328...Physics, 399, the proceedings of IAU Colloquium 133 held in Iguazu , Argentina 2-6 August, 1991, Z. Svestka, B.V. Jackson and M.E. Machado, eds...133 on Eruptive Solar Flares held in Iguazu , Argentina 2-6 Au- gust (1991). 9. Jackson, B.V. "Remote Sensing Observations of Mass Ejections and Shocks
Remote Sensing of Inner Heliospheric Plasmas
1993-11-14
Physics, 399, the proceedings of IAU Colloquium 133 held in Iguazu , Argentina 2-6 August, 1991, Z. gvestka, B.V. Jackson and M.E. Machado, eds. Springer...34, in Eruptive Solar Flares - Lecture Notes in Physics, 399, the proceedings of r ’ýU Colloquium 133 held in Iguazu , Argentina 2-6 August, 1991, Z...IAU Colloquium 133 held in Iguazu , Argentina 2-6 August, 1991, Z. Svestka, B.V. Jackson and M.E. Machado, eds. Springer-Verlag, Heidelberg (1992) (pg. 1
Remote Sensing of Inner Heliospheric Plasmas
1991-11-14
Solar Mass Ejection hnager in Low-Earth Orbit", in press in the IAU Colloquium 133 proceedings on Eruptive Solar Flares held in Iguazu , Argentina 2-6...Colloquium 133 proceedings on Eruptive Solar Flares held in Iguazu , Argentina 2-6 August (1991) (10 pages). + Work In Progress 1. Jackson, B.V. and H.R...34, presented at IAU Colloquium 133 on Eruptive Solar Flares held in Iguazu , Argentina 2-6 August (1991). 9. Jackson, B.V. "Remote Sensing Observations of
Lafouti, Mansoureh; Ghoranneviss, Mahmood; Meshkani, Sakineh; Salar Elahi, Ahmad
2013-05-01
In this paper, both Resonant Helical magnetic Field (RHF) and limiter biasing have been applied to the tokamak. We have investigated their effects on the turbulence and transport of the particles at the edge of the plasma. The biased limiter voltage has been fixed at 200 V and RHF has L = 2 and L = 3. Also, the effects of the time order of the application of RHF and biasing to the tokamak have been explored. The experiment has been performed under three conditions. At first, the biasing and RHF were applied at t = 15 ms and at t = 20 ms. In the next step, RHF and biasing were applied at t = 15 ms and t = 20 ms, respectively. Finally, both of them were turned on at t = 15 ms until the end of the shot. For this purpose, the ion saturation current (I(sat)) and the floating potential (V(f)) have been measured by the Langmuir probe at r/a = 0.9. Moreover, the power spectra of I(sat) and floating potential gradient (∇V(f)), the coherency, the phase between them, and the particle diffusion coefficient have been calculated. The density fluctuations of the particles have been measured by the Rake probe and they have been analyzed with the Probability Distribution Function (PDF) technique. Also the particle diffusion coefficient has been determined by the Fick's law. The results show that, when RHF and biasing were applied at the same time to the plasma (during flatness region of plasma current), the radial particle density gradient, the radial particle flux, and the particle diffusion coefficient decrease about 50%, 60%, and 55%, respectively, compared to the other conditions. For more precision, the average values of the particle flux and the particle density gradient were calculated in the work. When the time is less than 15 ms, the average values of the particle flux and the particle density gradient are identical under all conditions, but in the other time interval they change. They reduce with the simultaneous application of biasing and RHF. The same results obtain
NASA Technical Reports Server (NTRS)
Rowland, H. L.; Palmadesso, P. J.
1983-01-01
Large amplitude ion cyclotron waves have been observed on auroral field lines. In the presence of an electric field parallel to the ambient magnetic field these waves prevent the acceleration of the bulk of the plasma electrons leading to the formation of a runaway tail. It is shown that low-frequency turbulence can also limit the acceleration of high-velocity runaway electrons via pitch angle scattering at the anomalous Doppler resonance.
Particle Acceleration at the Sun and in the Heliosphere
NASA Technical Reports Server (NTRS)
Reames, Donald V.
1999-01-01
Energetic particles are accelerated in rich profusion at sites throughout the heliosphere. They come from solar flares in the low corona, from shock waves driven outward by coronal mass ejections (CMEs), from planetary magnetospheres and bow shocks. They come from corotating interaction regions (CIRs) produced by high-speed streams in the solar wind, and from the heliospheric termination shock at the outer edge of the heliospheric cavity. We sample all these populations near Earth, but can distinguish them readily by their element and isotope abundances, ionization states, energy spectra, angular distributions and time behavior. Remote spacecraft have probed the spatial distributions of the particles and examined new sources in situ. Most acceleration sources can be "seen" only by direct observation of the particles; few photons are produced at these sites. Wave-particle interactions are an essential feature in acceleration sources and, for shock acceleration, new evidence of energetic-proton-generated waves has come from abundance variations and from local cross-field scattering. Element abundances often tell us the physics the source plasma itself, prior to acceleration. By comparing different populations, we learn more about the sources, and about the physics of acceleration and transport, than we can possibly learn from one source alone.
Anisotropy and minimum variance directions of solar wind fluctuations in the outer heliosphere
NASA Technical Reports Server (NTRS)
Klein, Larry W.; Roberts, D. Aaron; Goldstein, Melvyn L.
1991-01-01
Voyager 2 magnetic field and plasma data are examined over time intervals of 1 to 12 hours in the heliospheric range of 1 to 10 AU to study the evolution of the anisotropy of solar wind fluctuations. Consistent with previous results, the directions of minimum variance vectors of magnetic fluctuations are found to be close to the mean magnetic field direction with an increasing component along the field at larger scales. At large radial distances there is more spread in the minimum variance directions than at smaller radial distances. The power in smaller-scale fluctuations in the magnetic field components perpendicular to the local mean field B(0) is in the ratio of about 5:1 near 1 AU at the scale of 1 hour but decreases to about 3:1 further out. No evidence for selective enhancement of out-of-the-ecliptic components of fluctuations is found. In contrast to results for field fluctuations, analysis of velocity fluctuations shows that the minimum variance direction systematically remains more radially oriented and becomes increasingly less oriented along B(0) with increasing heliocentric distance. The velocity fluctuations are generally more isotropic than the magnetic fluctuations. The observations cannot be explained by a superposed wave picture, and thus are consistent with the view that nonlinear turbulent evolution is responsible for the anisotropy in the fluctuations.
Time-dependent Processes in the Sheath Between the Heliospheric Termination Shock and the Heliopause
NASA Astrophysics Data System (ADS)
Pogorelov, N. V.; Borovikov, S. N.; Heerikhuisen, J.; Kim, T. K.; Zank, G. P.
2014-09-01
In this paper, we present the results of our numerical simulation of the solar wind (SW) interaction with the local interstellar medium (LISM). In particular, a solar cycle model based on Ulysses measurements allowed us to estimate the interrelationship between heliospheric asymmetries due to the action of the interstellar magnetic field and the decrease in the solar wind ram pressure. We evaluate the possibility to develop an improved approach to derive SW boundary conditions from interplanetary scintillation data. It is shown that solar cycle affects stability of the heliopause in a way favorable for the interpretation of Voyager 1 “early” penetration into the local interstellar medium. We also show that the heliotail is always a subject of violent Kelvin-Helmholtz instability, which ultimately should make the heliotail indistinguishable from the LISM. Numerical results are obtained with a Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is a package of numerical codes capable of performing adaptive mesh refinement simulations of complex plasma flows in the presence of discontinuities and charge exchange between ions and neutral atoms. The flow of the ionized component is described with the ideal MHD equations, while the transport of atoms is governed either by the Boltzmann equation or multiple Euler gas dynamics equations. We have enhanced the code with additional physical treatments for the transport of turbulence and acceleration of pickup ions in interplanetary space and at the termination shock.
Not Available
1993-12-01
The long-range goal of the Numerical Tokamak Project (NTP) is the reliable prediction of tokamak performance using physics-based numerical tools describing tokamak physics. The NTP is accomplishing the development of the most advanced particle and extended fluid model`s on massively parallel processing (MPP) environments as part of a multi-institutional, multi-disciplinary numerical study of tokamak core fluctuations. The NTP is a continuing focus of the Office of Fusion Energy`s theory and computation program. Near-term HPCC work concentrates on developing a predictive numerical description of the core plasma transport in tokamaks driven by low-frequency collective fluctuations. This work addresses one of the greatest intellectual challenges to our understanding of the physics of tokamak performance and needs the most advanced computational resources to progress. We are conducting detailed comparisons of kinetic and fluid numerical models of tokamak turbulence. These comparisons are stimulating the improvement of each and the development of hybrid models which embody aspects of both. The combination of emerging massively parallel processing hardware and algorithmic improvements will result in an estimated 10**2--10**6 performance increase. Development of information processing and visualization tools is accelerating our comparison of computational models to one another, to experimental data, and to analytical theory, providing a bootstrap effect in our understanding of the target physics. The measure of success is the degree to which the experimentally observed scaling of fluctuation-driven transport may be predicted numerically. The NTP is advancing the HPCC Initiative through its state-of-the-art computational work. We are pushing the capability of high performance computing through our efforts which are strongly leveraged by OFE support.
Ghosh, Sanjoy; Parashar, Tulasi N.
2015-04-15
The local k-space ratio of linear and nonlinear accelerations associated with a variety of initial conditions undergoing steady relaxation is investigated for the Hall–finite-Larmor-radius magnetohydrodynamics (MHD) system in the presence of a mean magnetic field. Building on a related study (Paper I) where it was shown that discrepancies exist between describing the global and local characterizations of the pure MHD system with mean magnetic field, we find regions of the Fourier space that are consistently dominated by linear acceleration and other regions that are consistently dominated by nonlinear acceleration, independent of the overall system's description as linear, weakly nonlinear, or turbulent. In general, dynamics within a certain angular range of the mean magnetic field direction are predominantly linear, while dynamics adjacent the Hall scales along the field-parallel direction and dynamics adjacent the finite Larmor radius scales in the field-perpendicular direction can become strongly nonlinear. The nonlinear influences are particularly significant as the plasma beta increases from unity to higher values.
Isliker, H.; Pisokas, Th.; Vlahos, L.; Strintzi, D.
2010-08-15
A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e., a heating process and a local diffusive process that sets on if a threshold in the normalized ITG R/L{sub T} is exceeded. The model reaches the SOC state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.
Upper-hybrid wave-driven Alfvenic turbulence in magnetized dusty plasmas
Misra, A. P.; Banerjee, S.
2011-03-15
The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs are solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos, due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths, which, in turn, results in the onset of Alfvenic turbulence in dusty magnetoplasmas. Such a scenario can occur in the vicinity of Saturn's magnetosphere as many electrostatic solitary structures have been observed there by the Cassini spacecraft.
Gyrokinetic GDC turbulence simulations: confirming a new instability regime in LAPD plasmas
NASA Astrophysics Data System (ADS)
Pueschel, M. J.; Rossi, G.; Told, D.; Terry, P. W.; Jenko, F.; Carter, T. A.
2016-10-01
Recent high-beta experiments at the LArge Plasma Device have found significant parallel magnetic fluctuations in the region of large pressure gradients. Linear gyrokinetic simulations show the dominant instability at these radii to be the gradient-driven drift coupling (GDC) mode, a non-textbook mode driven by pressure gradients and destabilized by the coupling of ExB and grad-B∥ drifts. Unlike in previous studies, the large parallel extent of the device allows for finite-kz versions of this instability in addition to kz = 0 . The locations of maximum linear growth match very well with experimentally observed peaks of B∥ fluctuations. Local nonlinear simulations reproduce many features of the observations fairly well, with the exception of Bperp fluctuations, for which experimental profiles suggest a source unrelated to pressure gradients. In toto, the results presented here show that turbulence and transport in these experiments are driven by the GDC instability, that important characteristics of the linear instability carry over to nonlinear simulations, and - in the context of validation - that the gyrokinetic framework performs surprisingly well far outside its typical area of application, increasing confidence in its predictive abilities. Supported by U.S. DOE.
Upper-hybrid wave-driven Alfvénic turbulence in magnetized dusty plasmas.
Misra, A P; Banerjee, S
2011-03-01
The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfvén waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs are solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos, due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths, which, in turn, results in the onset of Alfvénic turbulence in dusty magnetoplasmas. Such a scenario can occur in the vicinity of Saturn's magnetosphere as many electrostatic solitary structures have been observed there by the Cassini spacecraft.
First Results from the Physics-Based Forecasting-Targeted Inner Heliosphere Model Euhforia
NASA Astrophysics Data System (ADS)
Pomoell, J.
2015-12-01
In this work, we present the first results of the new physics-based forecasting-targeted inner heliosphere model Euhforia ('European heliospheric forecasting information asset') that we are developing. Euhforia consists of a coronal model and a magnetohydrodynamic (MHD) heliosphere model with CMEs. The aim of the baseline coronal model is to produce realistic plasma conditions at the interface radius r = 0.1 AU between the two models thus providing the necessary input to the time-dependent, three-dimensional MHD heliosphere model. It uses GONG synoptic line-of-sight magnetograms as input for a potential (PFSS) field extrapolation of the low-coronal magnetic field coupled to a current sheet (CS) model of the extended coronal magnetic field. The plasma variables at the interface radius are determined by employing semi-empirical considerations based on the properties of the PFSS+CS field such as the flux tube expansion factor and distance to nearest coronal hole. The heliosphere model computes the time-dependent evolution of the MHD variables from the interface radius typically up to 2 AU. Coronal mass ejections (CMEs) are injected at the interface radius using a hydrodynamic cone-like model using parameters constrained from fits to coronal imaging observations. In order to account for the modification of the heliosphere due to the presence of earlier CMEs, the standard run scenario includes CMEs launched five days prior to the start of the forecast, while the duration of the forecast extends up to seven days. In addition to presenting results of the modeling, we will highlight our on-going efforts to advance beyond the baseline in the forecasting pipeline. In particular we discuss our path towards using magnetized CMEs, application of a time-dependent coronal model as well as modeling the transport of solar energetic particles (SEPs) in the heliosphere.
NASA Astrophysics Data System (ADS)
McKee, G. R.; Yan, Z.; Holland, C.; Buttery, R. J.; Evans, T. E.; Moyer, R. A.; Mordijck, S.; Nazikian, R.; Rhodes, T. L.; Schmitz, O.; Wade, M. R.
2013-11-01
Long-wavelength turbulence increases dramatically in the outer regions of DIII-D plasmas with the application of resonant magnetic field perturbations (RMPs) that suppress edge-localized modes (ELMs). Correspondingly, transport increases and global energy confinement decreases in these low-collisionality RMP-ELM suppressed discharges. The core and pedestal density are sharply reduced, while ion and electron temperatures may change only slightly. Low wavenumber density turbulence (k⊥ρi < 1) in the range of 60-300 kHz, measured with beam emission spectroscopy, is modified and generally increases throughout the outer region (0.6 < ρ < 1.0) of the plasma in response to RMPs over a range of q95 values; ELM suppression, in contrast, occurs for a narrower range in q95. Radial magnetic field modulation experiments indicate that these turbulence modifications occur on a time scale of a few milliseconds or less near ρ = 0.85-0.95, significantly faster than transport time-scales and faster than the local pressure gradients and shearing rates evolve at these locations. As the internal coil current is modulated in a square-wave fashion from 3.2 to 4.2 kA, the turbulence magnitude varies in phase by 30% or more, while local density changes by only a few per cent. This dynamical behaviour suggests that the turbulence is directly affected by the RMP, which may partially or largely explain the resulting increased transport and stabilization of the pedestal against peeling-ballooning instabilities that are thought to drive ELMs.
NASA Astrophysics Data System (ADS)
Zhao, K. J.; Shi, Yuejiang; Liu, H.; Diamond, P. H.; Li, F. M.; Cheng, J.; Chen, Z. P.; Nie, L.; Ding, Y. H.; Wu, Y. F.; Chen, Z. Y.; Rao, B.; Cheng, Z. F.; Gao, L.; Zhang, X. Q.; Yang, Z. J.; Wang, N. C.; Wang, L.; Jin, W.; Xu, J. Q.; Yan, L. W.; Dong, J. Q.; Zhuang, G.; J-TEXT Team
2016-07-01
The acceleration of the co-current toroidal rotations around resonant surfaces by resonant magnetic perturbations (RMPs) through turbulence is presented. These experiments were performed using a Langmuir probe array in the edge plasmas of the J-TEXT tokamak. This study aims at understanding the RMP effects on edge toroidal rotations and exploring its control method. With RMPs, the flat electron temperature T e profile, due to magnetic islands, appears around resonant surfaces (Zhao et al 2015 Nucl. Fusion 55 073022). When the resonant surface is closer to the last closed flux surface, the flat T e profile vanishes with RMPs. In both cases, the toroidal rotations significantly increase in the direction of the plasma current around the resonant surfaces with RMPs. The characteristics of turbulence are significantly affected by RMPs around the resonant surfaces. The turbulence intensity profile changes and the poloidal wave vector k θ increases with RMPs. The power fraction of the turbulence components in the ion diamagnetic drift direction increases with RMPs. The measurements of turbulent Reynolds stresses are consistent with the toroidal flows that can be driven by turbulence. The estimations of the energy transfer between the turbulence and toroidal flows suggest that turbulence energy transfers into toroidal flows. The result has the implication of the intrinsic rotation being driven by RMPs via turbulence.
NASA Astrophysics Data System (ADS)
Somov, B. V.
If you want to learn not only the most fundamental things about the physics of turbulent plasmas but also the current state of the problem including the most recent results in theoretical and experimental investigations - and certainly many physicists and astrophysicists do - this series of three excellent monographs is just for you. The first volume "Physical Kinetics of Turbulent Plasmas" develops the kinetic theory of turbulence through a focus on quasi-particle models and dynamics. It discusses the concepts and theoretical methods for describing weak and strong fluid and phase space turbulence in plasma systems far from equilibrium. The core material includes fluctuation theory, self-similar cascades and transport, mean field theory, resonance broadening and nonlinear wave-particle interaction, wave-wave interaction and wave turbulence, strong turbulence theory and renormalization. The book gives readers a deep understanding of the fields under consideration and builds a foundation for future applications to multi-scale processes of self-organization in tokamaks and other confined plasmas. In spite of a short pedagogical introduction, the book is addressed mainly to well prepared readers with a serious background in plasma physics, to researchers and advanced graduate students in nonlinear plasma physics, controlled fusions and related fields such as cosmic plasma physics
NASA Astrophysics Data System (ADS)
Intriligator, D. S.; Sun, W.; Detman, T.; Miller, W. D.; Intriligator, J.; Dryer, M.; Webber, W.; Deehr, C.; Gloeckler, G.
2016-11-01
The Sun has been observed for many years to be a dynamic influence in the heliosphere, and as the Voyager missions have continued long after achieving their original goals of observing the major planets they have provided the first in situ observations of the effects of solar activity in the heliosheath (HS), and the nearest portions of the local Interstellar Medium (LISM). Comparing these observations with models provides key insights. We employ two three-dimensional (3D) time-dependent models that simulate the propagation of shocks, other specific features, and the background solar wind throughout the heliosphere, starting with the solar background and solar event boundary conditions near the Sun at 2.5 Rs. The Hybrid Heliospheric Modeling System with Pickup Protons (HHMS-PI) is a 3D time- dependent Magnetohydrodynamic (MHD) simulation. HAFSS (HAF Solar Surface) is a 3D time-dependent kinematic simulation. Comparing our models with the observations indicates that solar effects are seen in the heliosphere, the HS, and the LISM in in-situ spacecraft measurements of plasma, magnetic field, energetic particles, cosmic rays, and plasma waves. There is quantitative agreement (at ACE, Ulysses, VI, V2) with data (e.g., solar wind, IMF, Ulysses SWICS pickup protons (PUPs)). Propagating shocks are slowed due to PUPs. The 3D locations of solar events and of various spacecraft are key to understanding the 3D propagation and timing of shocks, other specific features, and gradients throughout the heliosphere, HS, and LISM.
NASA Astrophysics Data System (ADS)
von Papen, M.; Saur, J.; Alexandrova, O.
2013-12-01
We analyze the statistical properties of magnetic field fluctuations measured by the Cassini spacecraft inside Saturn's plasma sheet. We introduce Saturn's magnetosphere as a new laboratory for plasma turbulence, where the background magnetic field is strong (B0≤75nT) and the ion plasma βi=0.04-1 is low. We also show that the dissipation of these magnetic field fluctuations might play a crucial role for the energy budget of the magnetospheric plasma. In a case study of the second orbit of Cassini around Saturn we show that the power spectral densities of the fluctuations have a variable low frequency spectral range and a continously present power law in the high frequency range, which shows characteristics of a turbulent cascade. A spectral break that correlates with water group ion scales seperates the two frequency ranges. We carry out a statistical study of the high frequency fluctuations and find an average spectral slope of -2.6. The probability density functions of the fluctuations have increasingly non-gaussian tails with frequency resulting in a power law increase of the kurtosis, which indicates intermittency and a multifractal nature of the fluctuations. We estimate the energy flux, that is contained in the turbulent cascade as 30-50GW, which is on the same order of magnitude as needed to heat an adiabatically expanding plasma to the temperatures measured in Saturn's magnetosphere. We compare these results with heating rates estimated for Jupiter's magnetosphere. Superposition of 1136 PSD of 10min time series as function of k⊥ρW (gyro radius of water group ions). Histogram of spectral indices for k⊥ρW>2.
Self-organized zonal flow in the flute-mode turbulence of a plasma
Kodama, Y.; Pavlenko, V.P.
1988-04-11
Flute-mode turbulence has a forward spectral cascade unlike the case of drift-wave turbulence. Therefore the linear flute instability may be reduced by this energy cascading toward large wave numbers. As a consequence of three-wave cascade processes derivable from model equations including the effects of density gradient and finite ion Larmor radius the formation of zonal flows in flute mode turbulence is predicted.
Simulation of Ionospheric E-Region Plasma Turbulence with a Massively Parallel Hybrid PIC/Fluid Code
NASA Astrophysics Data System (ADS)
Young, M.; Oppenheim, M. M.; Dimant, Y. S.
2015-12-01
The Farley-Buneman (FB) and gradient drift (GD) instabilities are plasma instabilities that occur at roughly 100 km in the equatorial E-region ionosphere. They develop when ion-neutral collisions dominate ion motion while electron motion is affected by both electron-neutral collisions and the background magnetic field. GD drift waves grow when the background density gradient and electric field are aligned; FB waves grow when the background electric field causes electrons to E × B drift with a speed slightly larger than the ion acoustic speed. Theory predicts that FB and GD turbulence should develop in the same plasma volume when GD waves create a perturbation electric field that exceeds the threshold value for FB turbulence. However, ionospheric radars, which regularly observe meter-scale irregularities associated with FB turbulence, must infer kilometer-scale GD dynamics rather than observe them directly. Numerical simulations have been unable to simultaneously resolve GD and FB structure. We present results from a parallelized hybrid simulation that uses a particle-in-cell (PIC) method for ions while modeling electrons as an inertialess, quasi-neutral fluid. This approach allows us to reach length scales of hundreds of meters to kilometers with sub-meter resolution, but requires solving a large linear system derived from an elliptic PDE that depends on plasma density, ion flux, and electron parameters. We solve the resultant linear system at each time step via the Portable Extensible Toolkit for Scientific Computing (PETSc). We compare results of simulated FB turbulence from this model to results from a thoroughly tested PIC code and describe progress toward the first simultaneous simulations of FB and GD instabilities. This model has immediate applications to radar observations of the E-region ionosphere, as well as potential applications to the F-region ionosphere and the chromosphere of the Sun.
Origin of the warped heliospheric current sheet
NASA Astrophysics Data System (ADS)
Wilcox, J. M.; Hoeksema, J. T.; Scherrer, P. H.
1980-08-01
The warped heliospheric current sheet for early 1976 is calculated from the observed photospheric magnetic field by a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity for early 1976 obtained at several locations in the heliosphere by Helios 1, Helios 2, Pioneer 11, and at the earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large-scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field and that 'ballerina skirt' effects may add small scale ripples.