Plasma Sterilization: New Epoch in Medical Textiles
NASA Astrophysics Data System (ADS)
Senthilkumar, P.; Arun, N.; Vigneswaran, C.
2015-04-01
Clothing is perceived to be second skin to the human body since it is in close contact with the human skin most of the times. In hospitals, use of textile materials in different forms and sterilization of these materials is an essential requirement for preventing spread of germs. The need for appropriate disinfection and sterilization techniques is of paramount importance. There has been a continuous demand for novel sterilization techniques appropriate for use on various textile materials as the existing sterilization techniques suffer from various technical and economical drawbacks. Plasma sterilization is the alternative method, which is friendlier and more effective on the wide spectrum of prokaryotic and eukaryotic microorganisms. Basically, the main inactivation factors for cells exposed to plasma are heat, UV radiation and various reactive species. Plasma exposure can kill micro-organisms on a surface in addition to removing adsorbed monolayer of surface contaminants. Advantages of plasma surface treatment are removal of contaminants from the surface, change in the surface energy and sterilization of the surface. Plasma sterilization aims to kill and/or remove all micro-organisms which may cause infection of humans or animals, or which can cause spoilage of foods or other goods. This review paper emphasizes necessity for sterilization, essentials of sterilization, mechanism of plasma sterilization and the parameters influencing it.
NASA Technical Reports Server (NTRS)
Liemohm, M. W.; Kozyra, J. U.; Thomsen, M. F.; Borovsky, J. E.; Gahurthakurta, Madulika (Technical Monitor)
2004-01-01
The goal of that proposal was to examine the relationship between solar wind drivers and ring current dynamics through data analysis and numerical simulations. The data analysis study was a statistical examination (via superposed epoch analyses) of a solar cycle's worth of storm data. Solar wind data, geophysical indices, and geosynchronous plasma data were collected for every time period with Dst< -50 nT from 1989 through 2002, and the storm list now exceeds 400 entries. This work was first conducted by a summer undergraduate student, Mr. John Vann (University of Kansas), with funding from the NSF Research Experience for Undergraduates program. It was then continued by a University of Michigan graduate student, Mr. Jichun Zhang. Mr. Zhang is now in his fourth year at U-M and is progressing very well toward a PhD in space science. His dissertation will be based on his data analysis and modeling efforts using this geomagnetic storm database. The results of the data analysis study have been the focus of several conference presentations, and the first manuscript has just been published. Two additional papers are presently being prepared, one on average (superposed) solar wind features for various storm subsets (e.g., intense storms at solar maximum), and another on geosynchronous plasma features for these same storm subsets. The latter result was highlighted by the TR&T program director in his presentation at the COSPAR meeting this summer.
Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet
NASA Technical Reports Server (NTRS)
Kistler, L. M.; Baumjohann, W.; Nagai, T.; Mobius, E.
1993-01-01
Using data from 41 substorm events in the near-Earth magnetotail, we have combined plasma, energetic ion, and magnetic field data from the AMPTE/IRM spacecraft to perform a superposed epoch analysis of changes in the total pressure and in the magnetic field configuration as a function of time relative to substorm onset. Unloading is evident in the total pressure profile; the pressure decreases by about 20 percent. Pressure changes during the growth phase are not as uniform for the different substorms as the pressure changes during the expansion phase. To study changes in the magnetic field configuration, we have determined the development of the plasma pressure profiles in z for an average of data from 15 to 19 R(E). At substorm onset, the field line dipolarization begins on the innermost field lines and then progresses to the outer field lines. The field lines map the closest to the Earth about 45 min after substorm onset, and then begin to stretch out again during the recovery phase of the substorm.
Theory of the unmagnetized plasma.
NASA Technical Reports Server (NTRS)
Montgomery, D. C.
1971-01-01
The Vlasov mathematical model of a plasma, which has come to be thought more useful than any other in describing the dynamical behavior of the majority of plasmas of interest, is first examined. Macroscopic variables and moment equations; linear electrostatics solutions; plasma oscillations, ion acoustic waves, and linear instabilities are treated, as well as external fields, 'test' charges, and nonlinear Vlasov phenomena. Plasmas are statistically described, and attention is given to the kinetic theory of the stable, uniform plasma and the Balescu-Lenard equation; two-time ensemble averages and fluctuation spectra in stable plasmas; the kinetic theory of the unstable plasma; and ensembles of Vlasov plasmas. Some illustrative experiments are described. Four appendixes deal with the electrostatic approximation and transverse waves; solution of the linearized Vlasov equation in a magnetic field; estimates of correlation functions from thermal equilibrium; and equivalence of spatially uniform BBGKY and Klimontovich correlations.
Plasma theory and simulation research
Birdsall, C.K.
1989-01-01
Our research group uses both theory and simulation as tools in order to increase the understanding of instabilities, heating, diffusion, transport and other phenomena in plasmas. We also work on the improvement of simulation, both theoretically and practically. Our focus has been more and more on the plasma edge (the sheath''), interactions with boundaries, leading to simulations of whole devices (someday a numerical tokamak).
Fusion Plasma Theory project summaries
Not Available
1993-10-01
This Project Summary book is a published compilation consisting of short descriptions of each project supported by the Fusion Plasma Theory and Computing Group of the Advanced Physics and Technology Division of the Department of Energy, Office of Fusion Energy. The summaries contained in this volume were written by the individual contractors with minimal editing by the Office of Fusion Energy. Previous summaries were published in February of 1982 and December of 1987. The Plasma Theory program is responsible for the development of concepts and models that describe and predict the behavior of a magnetically confined plasma. Emphasis is given to the modelling and understanding of the processes controlling transport of energy and particles in a toroidal plasma and supporting the design of the International Thermonuclear Experimental Reactor (ITER). A tokamak transport initiative was begun in 1989 to improve understanding of how energy and particles are lost from the plasma by mechanisms that transport them across field lines. The Plasma Theory program has actively-participated in this initiative. Recently, increased attention has been given to issues of importance to the proposed Tokamak Physics Experiment (TPX). Particular attention has been paid to containment and thermalization of fast alpha particles produced in a burning fusion plasma as well as control of sawteeth, current drive, impurity control, and design of improved auxiliary heating. In addition, general models of plasma behavior are developed from physics features common to different confinement geometries. This work uses both analytical and numerical techniques. The Fusion Theory program supports research projects at US government laboratories, universities and industrial contractors. Its support of theoretical work at universities contributes to the office of Fusion Energy mission of training scientific manpower for the US Fusion Energy Program.
NASA Astrophysics Data System (ADS)
Mendis, A.
2012-12-01
Ionized gases, contaminated with fine (nanometer to micrometer-sized) charged dust, loosely referred to a dusty plasmas, occur in a wide variety of cosmic and laboratory environments. In this topical review I will discuss the underlying theory of such plasmas, with emphasis on the space environment. Central to the discussion is the electrostatic charging of the dust grains by the various currents that they experience in the plasma and radiative environment in which they are immersed. This charging could lead to both physical and dynamical consequences for the dust as well as for the plasma. Among the physical effects for the dust are electrostatic disruption and electrostatic levitation from charged surfaces. The dynamics of the charged dust is affected by the Lorentz force they experience, since space plasmas are generally magnetized. The physical effects for plasma result from the fact that the dust can act both as a sink and as a source of electrons in different space environments. The dynamical effects on the plasma arise from the fact that the charged dust can alter the phase velocity of normal wave modes (e.g., the Ion acoustic mode) by changing the charge equilibrium in the plasma. Additionally the charged dust can also participate in the wave dynamics, leading, for example, to the very low frequency, novel, "dust-acoustic" wave that has been observed in the laboratory. Finally the possibility that charged dust in a space plasma, may indirectly influence the propagation of electromagnetic radiation through it, will also be, briefly, discussed.
Theory of beam plasma discharge
NASA Technical Reports Server (NTRS)
Papadopoulos, K.
1982-01-01
The general theory of beam plasma discharge (BPD) is discussed in relation to space and laboratory beam injection situations. An important concept introduced is that even when beam plasma instabilities are excited, there are two regime of BPD with radically different observational properties. They are described here as BPD with either classical or anomalous energy depositions. For high pressures or low altitudes, the classical is expected to dominate. For high altitudes and laboratory experiments, where the axial system size is less than lambda sub en, no BPD will be triggered unless the unstable waves are near the ambient plasma frequency and their amplitudes at saturation are large enough to create suprathermal tails by collapsing.
BOOK REVIEW: Kinetic theory of plasma waves, homogeneous plasmas
NASA Astrophysics Data System (ADS)
Porkolab, Miklos
1998-11-01
The linear theory of plasma waves in homogeneous plasma is arguably the most mature and best understood branch of plasma physics. Given the recently revised version of Stix's excellent Waves in Plasmas (1992), one might ask whether another book on this subject is necessary only a few years later. The answer lies in the scope of this volume; it is somewhat more detailed in certain topics than, and complementary in many fusion research relevant areas to, Stix's book. (I am restricting these comments to the homogeneous plasma theory only, since the author promises a second volume on wave propagation in inhomogeneous plasmas.) This book is also much more of a theorist's approach to waves in plasmas, with the aim of developing the subject within the logical framework of kinetic theory. This may indeed be pleasing to the expert and to the specialist, but may be too difficult to the graduate student as an `introduction' to the subject (which the author explicitly states in the Preface). On the other hand, it may be entirely appropriate for a second course on plasma waves, after the student has mastered fluid theory and an introductory kinetic treatment of waves in a hot magnetized `Vlasov' plasma. For teaching purposes, my personal preference is to review the cold plasma wave treatment using the unified Stix formalism and notation (which the author wisely adopts in the present book, but only in Chapter 5). Such an approach allows one to deal with CMA diagrams early on, as well as to provide a framework to discuss electromagnetic wave propagation and accessibility in inhomogeneous plasmas (for which the cold plasma wave treatment is perfectly adequate). Such an approach does lack some of the rigour, however, that the author achieves with the present approach. As the author correctly shows, the fluid theory treatment of waves follows logically from kinetic theory in the cold plasma limit. I only question the pedagogical value of this approach. Otherwise, I welcome this
Pylkkänen, Paavo
2015-12-01
The theme of phenomenology and quantum physics is here tackled by examining some basic interpretational issues in quantum physics. One key issue in quantum theory from the very beginning has been whether it is possible to provide a quantum ontology of particles in motion in the same way as in classical physics, or whether we are restricted to stay within a more limited view of quantum systems, in terms of complementary but mutually exclusive phenomena. In phenomenological terms we could describe the situation by saying that according to the usual interpretation of quantum theory (especially Niels Bohr's), quantum phenomena require a kind of epoché (i.e. a suspension of assumptions about reality at the quantum level). However, there are other interpretations (especially David Bohm's) that seem to re-establish the possibility of a mind-independent ontology at the quantum level. We will show that even such ontological interpretations contain novel, non-classical features, which require them to give a special role to "phenomena" or "appearances", a role not encountered in classical physics. We will conclude that while ontological interpretations of quantum theory are possible, quantum theory implies the need of a certain kind of epoché even for this type of interpretations. While different from the epoché connected to phenomenological description, the "quantum epoché" nevertheless points to a potentially interesting parallel between phenomenology and quantum philosophy.
Stability theory of Knudsen plasma diodes
Kuznetsov, V. I. Ender, A. Ya.
2015-11-15
A stability theory is developed for a plasma diode in which an electron beam supplied from the emitter propagates without collisions in the self-consistent electric field against the immobile ion background. An integral equation for the amplitude of the perturbed field is deduced using the Q,G method for the regime without electron reflection from a potential barrier. Analytic solutions to this equation are obtained for a number of important particular cases, and the plasma dispersion properties are examined.
Neutral Vlasov kinetic theory of magnetized plasmas
Tronci, Cesare; Camporeale, Enrico
2015-02-15
The low-frequency limit of Maxwell equations is considered in the Maxwell-Vlasov system. This limit produces a neutral Vlasov system that captures essential features of plasma dynamics, while neglecting radiation effects. Euler-Poincaré reduction theory is used to show that the neutral Vlasov kinetic theory possesses a variational formulation in both Lagrangian and Eulerian coordinates. By construction, the new model recovers all collisionless neutral models employed in plasma simulations. Then, comparisons between the neutral Vlasov system and hybrid kinetic-fluid models are presented in the linear regime.
Kinetic theory of relativistic plasmas
Gould, R.J.
1981-01-01
The thermalization of particle kinetic motion by binary collisions is considered for a plasma with kTapprox.(10--100) mc/sup 2/, where m is the electron mass. At this temperature, the principal mechanism for relaxation of electron motion is via radiationless electron-electron collisions (Moller scattering). Ions are nonrelativistic, but are energetic enough so that their Coulomb scattering can be treated in the Born approximation. Relaxation times are computed and Boltzmann-equation Fokker--Planck operators are derived for the various binary-collision processes. The expression for the rate of kinetic energy exchange between electron and ion gases is derived for the case where the gases are at different temperatures.
Kinetic theory of relativistic plasmas
NASA Technical Reports Server (NTRS)
Gould, R. J.
1981-01-01
The thermalization of particle kinetic motion by binary collisions is considered for a plasma with a Boltzmann constant-temperature product approximately equal to 10 to 100 times the product of the electron mass with the square of the speed of light. At this temperature, the principal mechanism for relaxation of electron motion is via radiationless electron-electron collisions (Moller scattering). Ions are nonrelativistic, but are energetic enough so that their Coulomb scattering can be treated in the Born approximation. Relaxation times are computed and Boltzmann-equation Fokker-Planck operators are derived for the various binary-collision processes. The expression for the rate of kinetic energy exchange between electron and ion gases is derived for the case where the gases are at different temperatures.
NASA Astrophysics Data System (ADS)
Kervalishvili, Guram; Lühr, Hermann
2016-04-01
This study presents results of a superposed epoch analysis (SEA) method applied to vertical plasma flow and large-scale field aligned currents (FACs) in the Northern Hemisphere cusp region. Our study is based on DMSP (F13 and F15) and CHAMP satellite observations during the years 2001-2005. Interplanetary magnetic field (IMF) data were taken from the NASA/GSFC's OMNI online database. The dependence on IMF By and Bx component orientation is investigated, while the absolute amplitude of IMF Bz is selected to be less than 2 nT. Seasonal variations are also investigated with seasons defined as follows: local winter (1 January ± 65 days), combined equinoxes (1 April and 1 October ± 32 days), and local summer (1 July ± 65 days). The reference time and location for the SEA method are taken from the vertical ion velocity peaks (> 100 m/s for upflow and <-100 m/s for downflow) detected by DMSP in the northern cusp region. Our analyses were performed in the magnetic latitude (MLat) and local time (MLT) coordinate system. In general the vertical plasma downflow is weaker than the upflow. This product, ion density times velocity, shows no dependence on the IMF By orientation, while its value increases towards local summer. The ion density is low in winter and increases towards local summer, while the vertical velocity is much higher in local winter than during equinoxes or local summer. The event number distribution (in MLat-MLT frame) of vertical ion velocity peaks shows no significant dependence on the given conditions. In case of large-scale FACs a clear dependence on IMF By orientation and local season emerges from SEA analysis. Similarly to the vertical plasma upflow, the amplitude of large-scale FACs is also increasing towards local summer. Large-scale FACs show an IMF By dependent regular pattern for upflow cases and no regular pattern for downflow cases in all considered cases.
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.
Beyond the standard plasma transport theory
NASA Astrophysics Data System (ADS)
Bird, T. M.; Candy, J. M.
2015-11-01
The standard approach to transport in strongly magnetized plasmas, based upon an expansion in the gyro-radius over magnetic field scale length, has an illustrious, and successful history. It is however not a complete theory for plasma transport, and a number of phenomena which fall outside of its purview have recently attracted interest. The assumptions needed to derive the entire transport theory have only recently been explicitly laid out. Many of these assumptions are likely not widely appreciated, and the consequences of using the standard tools of transport theory to address phenomena which do not obey them are rather unclear. We discuss the consequences of these assumptions, and then turn our attention to the task of overcoming them. An avant-garde approach to modifying the standard theory to incorporate new physics will be introduced and applied to the loss of thermal ions in the edge. We study how the plasma remains quasi-neutral in the presence of this non-ambipolar transport, and consider the collisional re-filling of the loss cone. We will also briefly discuss other phenomena of interest that could be addressed using these techniques. Work supported in part by US DOE under grant number DE-FC02-06ER54873.
Kinetic theory of electrical conductivity in plasmas
Boercker, D.B.
1981-04-01
A recently developed quantum kinetic theory for time-correlation functions is applied to the calculation of the electrical conductivity in dense, strongly coupled plasmas. In the weak-collision limit the theory generalizes the Ziman expression to finite temperatures while, for strong collisions, it generalizes the result of Gould and of Williams and DeWitt to include strong ion coupling. Numerical results which compare the effects that strong ion coupling, bound (core) electrons, and strong collisions have upon the collision frequency are also presented.
Theory and Simulations of Solar System Plasmas
NASA Technical Reports Server (NTRS)
Goldstein, Melvyn L.
2011-01-01
"Theory and simulations of solar system plasmas" aims to highlight results from microscopic to global scales, achieved by theoretical investigations and numerical simulations of the plasma dynamics in the solar system. The theoretical approach must allow evidencing the universality of the phenomena being considered, whatever the region is where their role is studied; at the Sun, in the solar corona, in the interplanetary space or in planetary magnetospheres. All possible theoretical issues concerning plasma dynamics are welcome, especially those using numerical models and simulations, since these tools are mandatory whenever analytical treatments fail, in particular when complex nonlinear phenomena are at work. Comparative studies for ongoing missions like Cassini, Cluster, Demeter, Stereo, Wind, SDO, Hinode, as well as those preparing future missions and proposals, like, e.g., MMS and Solar Orbiter, are especially encouraged.
Theory of plasma contractors for electrodynamic tethered satellite systems
NASA Technical Reports Server (NTRS)
Parks, D. E.; Katz, I.
1986-01-01
Recent data from ground and space experiments indicate that plasma releases from an object dramatically reduce the sheath impedance between the object and the ambient plasma surrounding it. Available data is in qualitative accord with the theory developed to quantify the flow of current in the sheath. Electron transport in the theory is based on a fluid model of a collisionless plasma with an effective collision frequency comparable to frequencies of plasma oscillations. The theory leads to low effective impedances varying inversely with the square root of the injected plasma density. To support such a low impedance mode of operation using an argon plasma source for example requires that only one argon ion be injected for each thirty electrons extracted from the ambient plasma. The required plasma flow rates are quite low; to extract one ampere of electron current requires a mass flow rate of about one gram of argon per day.
Theory of correlation effects in dusty plasmas
Avinash, K.
2015-03-15
A theory of correlation effects in dusty plasmas based on a suitably augmented Debye Huckel approximation is proposed. A model which takes into account the confinement of the dust within the plasma (by external fields) is considered. The dispersion relation of compressional modes with correlation effects is obtained. Results show that strong coupling effects may be subdominant even when Γ ≫ 1. Thus, in the limit Γ→0 and/or κ → ∞, one obtains the weakly coupled dust thermal mode. In the range of values of Γ ≫ 1, the strong coupling effects scale with κ instead of Γ; increasing Γ increases the dust acoustic waves phase velocity C{sub DAW} in this regime. In the limit Γ≫1,κ≪1, one obtains the weakly coupled dust acoustic wave. Only in the limit Γ≫1,κ≥1, one obtains strong coupling effects, e.g., the dust lattice waves (κ=a/λ{sub d}, a is the mean particle distance and λ{sub d} is the Debye length). Observations from a number of experiments are explained.
Plasma transport theory spanning weak to strong coupling
Daligault, Jérôme; Baalrud, Scott D.
2015-06-29
We describe some of the most striking characteristics of particle transport in strongly coupled plasmas across a wide range of Coulomb coupling strength. We then discuss the effective potential theory, which is an approximation that was recently developed to extend conventional weakly coupled plasma transport theory into the strongly coupled regime in a manner that is practical to evaluate efficiently.
Theory of edge plasma in a spheromak
Hooper, E.B., LLNL
1998-05-01
Properties of the edge plasma in the SSPX spheromak during the plasma formation and sustainment phases are discussed. For the breakdown and formation phase, the main emphasis is on the analysis of possible plasma contamination by impurities from the electrodes of the plasma gun (helicity injector). The issue of an azimuthally uniform breakdown initiation is also discussed. After the plasma settles down in the main vacuum chamber, one has to sustain the current between the electrodes, in order to continuously inject helicity. We discuss properties of the plasma on the field lines intersecting the electrodes. We conclude that the thermal balance of this plasma is maintained by Joule heating competing with parallel heat losses to the electrodes. The resulting plasma temperature is in the range of 15 - 30 eV. Under the expected operational conditions, the ``current`` velocity of the electrons is only slightly below their thermal velocity. Implications of this observation are briefly discussed.
Dust in fusion plasmas: theory and modeling
Smirnov, R. D.; Pigarov, A. Yu.; Krasheninnikov, S. I.; Mendis, D. A.; Rosenberg, M.; Rudakov, D.; Tanaka, Y.; Rognlien, T. D.; Soboleva, T. K.; Shukla, P. K.; Bray, B. D.; West, W. P.; Roquemore, A. L.; Skinner, C. H.
2008-09-07
Dust may have a large impact on ITER-scale plasma experiments including both safety and performance issues. However, the physics of dust in fusion plasmas is very complex and multifaceted. Here, we discuss different aspects of dust dynamics including dust-plasma, and dust-surface interactions. We consider the models of dust charging, heating, evaporation/sublimation, dust collision with material walls, etc., which are suitable for the conditions of fusion plasmas. The physical models of all these processes have been incorporated into the DUST Transport (DUSTT) code. Numerical simulations demonstrate that dust particles are very mobile and accelerate to large velocities due to the ion drag force (cruise speed >100 m/s). Deep penetration of dust particles toward the plasma core is predicted. It is shown that DUSTT is capable of reproducing many features of recent dust-related experiments, but much more work is still needed.
Final Report on The Theory of Fusion Plasmas
Steven C. Cowley
2008-06-17
Report describes theoretical research in the theory of fusion plasmas funded under grant DE-FG02-04ER54737. This includes work on: explosive instabilities, plasma turbulence, Alfven wave cascades, high beta (pressure) tokamaks and magnetic reconnection. These studies have lead to abetter understanding of fusion plasmas and in particular the future behavior of ITER. More than ten young researchers were involved in this research -- some were funded under the grant.
Experiments and Theory of Dusty Plasmas
Shukla, P. K.
2011-11-29
The purpose of this paper is to present the most important theoretical and experimental discoveries that have been made in the area of dusty plasma physics. We describe the physics and observations of the well celebrated dust acoustic wave (DAW) and the dust ion-acoustic wave (DIAW) in dusty plasmas with weakly coupled dust grains, as well as the dust Coulomb crystal and dust lattice oscillations (DLOs) in dusty plasmas with strongly coupled dust grains. In dusty plasmas, the dust charge fluctuation is a dynamical variable, which provides a novel collisionless damping of the DA and DIA waves. The latter and the DLOs are excited by external sources, which are here discussed. Besides the Debye-Hueckel short-range repulsive force between like charged dust grains, there are novel attractive forces (e.g. due to dipole-dipole dust particle interactions, overlapping Debye spheres, ion focusing and ion wakefields, dipole magnetic moments etc.), which provide unique possibilities for attracting charged dust particles of similar polarity. The dust particle attraction is responsible for the formation of dust Coulomb crystals in laboratory dusty plasmas, as well as for the formation of planets and large astrophysical bodies in the Milky Way galaxy and in interstellar media. Furthermore, the nonlinear DAW, DIAW, and DLOs also appear in the form of solitary and shock waves, the physics and observations of which are briefly discussed. Finally, we discuss possible applications of dust-in-plasmas and dusty plasmas in laboratory and space.
The Gaussian radial basis function method for plasma kinetic theory
NASA Astrophysics Data System (ADS)
Hirvijoki, E.; Candy, J.; Belli, E.; Embréus, O.
2015-10-01
Description of a magnetized plasma involves the Vlasov equation supplemented with the non-linear Fokker-Planck collision operator. For non-Maxwellian distributions, the collision operator, however, is difficult to compute. In this Letter, we introduce Gaussian Radial Basis Functions (RBFs) to discretize the velocity space of the entire kinetic system, and give the corresponding analytical expressions for the Vlasov and collision operator. Outlining the general theory, we also highlight the connection to plasma fluid theories, and give 2D and 3D numerical solutions of the non-linear Fokker-Planck equation. Applications are anticipated in both astrophysical and laboratory plasmas.
Testing THEMIS wave measurements against the cold plasma theory
NASA Astrophysics Data System (ADS)
Taubenschuss, Ulrich; Santolik, Ondrej; Le Contel, Olivier; Bonnell, John
2016-04-01
The THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission records a multitude of electromagnetic waves inside Earth's magnetosphere and provides data in the form of high-resolution electric and magnetic waveforms. We use multi-component measurements of whistler mode waves and test them against the theory of wave propagation in a cold plasma. The measured ratio cB/E (c is speed of light in vacuum, B is magnetic wave amplitude, E is electric wave amplitude) is compared to the same quantity calculated from cold plasma theory over linearized Faraday's law. The aim of this study is to get estimates for measurement uncertainties, especially with regard to the electric field and the cold plasma density, as well as evaluating the validity of cold plasma theory inside Earth's radiation belts.
Geometric perturbation theory and plasma physics
Omohundro, S.M.
1985-01-01
Modern differential geometric techniques are used to unify the physical asymptotics underlying mechanics, wave theory, and statistical mechanics. The approach gives new insights into the structure of physical theories and is suited to the needs of modern large-scale computer simulation and symbol manipulation systems. A coordinate-free formulation of non-singular perturbation theory is given, from which a new Hamiltonian perturbation structure is derived and related to the unperturbed structure in five different ways. The theory of perturbations in the presence of symmetry is developed, and the method of averaging is related to reduction by a circle-group action. The pseudo-forces and magnetic Poisson bracket terms due to reduction are given a natural asymptotic interpretation. Similar terms due to changing reference frames are related to the method of variation of parameters, which is also given a Hamiltonian formulation. These methods are used to answer a long-standing question posed by Kruskal about nearly periodic systems. The answer leads to a new secular perturbation theory that contains no adhoc elements, which is then applied to gyromotion. Eikonal wave theory is given a Hamiltonian formulation that generalizes Whitham's Lagrangian approach. The evolution of wave action density on ray phase space is given a Hamiltonian structure using a Lie-Poisson bracket. The relationship between dissipative and Hamiltonian systems is discussed. A theory motivated by free electron lasers gives new restrictions on the change of area of projected parallelepipeds under canonical transformations.
Theory of dust voids in plasmas.
Goree, J; Morfill, G E; Tsytovich, V N; Vladimirov, S V
1999-06-01
Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M=1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.
Geometric perturbation theory and plasma physics
Omohundro, S.M.
1985-04-04
Modern differential geometric techniques are used to unify the physical asymptotics underlying mechanics, wave theory and statistical mechanics. The approach gives new insights into the structure of physical theories and is suited to the needs of modern large-scale computer simulation and symbol manipulation systems. A coordinate-free formulation of non-singular perturbation theory is given, from which a new Hamiltonian perturbation structure is derived and related to the unperturbed structure. The theory of perturbations in the presence of symmetry is developed, and the method of averaging is related to reduction by a circle group action. The pseudo-forces and magnetic Poisson bracket terms due to reduction are given a natural asymptotic interpretation. Similar terms due to changing reference frames are related to the method of variation of parameters, which is also given a Hamiltonian formulation. These methods are used to answer a question about nearly periodic systems. The answer leads to a new secular perturbation theory that contains no ad hoc elements. Eikonal wave theory is given a Hamiltonian formulation that generalizes Whitham's Lagrangian approach. The evolution of wave action density on ray phase space is given a Hamiltonian structure using a Lie-Poisson bracket. The relationship between dissipative and Hamiltonian systems is discussed. A new type of attractor is defined which attracts both forward and backward in time and is shown to occur in infinite-dimensional Hamiltonian systems with dissipative behavior. The theory of Smale horseshoes is applied to gyromotion in the neighborhood of a magnetic field reversal and the phenomenon of reinsertion in area-preserving horseshoes is introduced. The central limit theorem is proved by renormalization group techniques. A natural symplectic structure for thermodynamics is shown to arise asymptotically from the maximum entropy formalism.
Nonlinear theory of a plasma Cherenkov maser
Choi, J.S.; Heo, E.G.; Choi, D.I.
1995-12-31
The nonlinear saturation state in a plasma Cherenkov maser (PCM) propagating the intense relativistic electron beam through a circular waveguide partially filled with a dense annular plasma, is analyzed from the nonlinear formulation based on the cold fluid-Maxwell equations. We obtain the nonlinear efficiency and the final operation frequency under consideration of the effects of the beam current, the beam energy and the slow wave structure. We show that the saturation mechanism of a PCM instablity is a close correspondence in that of the relativistic two stream instability by the coherent trapping of electrons in a single most-ustable wave. And the optimal conditions in PCM operation are also obtained from performing our nonliear analysis together with computer simulations.
Pliocene geomagnetic polarity epochs
Dalrymple, G.B.; Cox, A.; Doell, Richard R.; Gromme, C.S.
1967-01-01
A paleomagnetic and K-Ar dating study of 44 upper Miocene and Pliocene volcanic units from the western United States suggests that the frequency of reversals of the earth's magnetic field during Pliocene time may have been comparable with that of the last 3.6 m.y. Although the data are too limited to permit the formal naming of any new polarity epochs or events, four polarity transitions have been identified: the W10 R/N boundary at 3.7 ?? 0.1 m.y., the A12 N/R boundary at 4.9 ?? 0.1 m.y., the W32 N/R boundary at 9.0 ?? 0.2m.y., and the W36 R/N boundary at 10.8 ?? 0.3 - 1.0 m.y. The loss of absolute resolution of K-Ar dating in older rocks indicates that the use of well defined stratigraphic successions to identify and date polarity transitions will be important in the study of Pliocene and older reversals. ?? 1967.
Observing the epoch of galaxy formation
Steidel, Charles C.
1999-01-01
Significant observational progress in addressing the question of the origin and early evolution of galaxies has been made in the past few years, allowing for direct comparison of the epoch when most of the stars in the universe were forming to prevailing theoretical models. There is currently broad consistency between theoretical expectations and the observations, but rapid improvement in the data will provide much more critical tests of theory in the coming years. PMID:10200244
An analytical theory of corona discharge plasmas
Uhm, H.S.; Lee, W.M.
1997-09-01
In this paper we describe an analytical investigation of corona discharge systems. Electrical charge and the energy transfer mechanism are investigated based on the circuit analysis. Efficient delivery of electrical energy from the external circuit to the reactor chamber is a major issue in design studies. The optimum condition obtained in this paper ensures 100{percent} energy transfer. Second-order coupled differential equations are numerically solved. All the analytical results agree remarkably well with numerical data. The reactor capacitor plays a pivotal role in circuit performance. The voltage profile is dominated by the reactor capacitor. Corona discharge properties in the reactor chamber are also investigated, assuming that a specified voltage profile V(t) is fed through the inner conductor. The analytical description is based on the electron moment equation. Defining the plasma breakdown parameter u=V/R{sub c}p, plasma is generated for a high-voltage pulse satisfying u{gt}u{sub c}, where u{sub c} is the critical breakdown parameter defined by geometrical configuration. Here, u is in units of a million volts per m per atm, and R{sub c} is the outer conductor radius. It is found that the plasma density profile generated inside the reactor chamber depends very sensitively on the system parameters. A small change of a physical parameter can easily lead to a density change in one order of magnitude.
Microwave Plasma Window Theory and Experiments
NASA Astrophysics Data System (ADS)
McKelvey, Andrew; Zheng, Peng; Franzi, Matthew; Lau, Y. Y.; Gilgenbach, Ronald; Plasma, Pulsed Power,; Microwave Laboratory Team
2011-10-01
The microwave plasma window is an experiment designed to promote RF breakdown in a controlled vacuum-gas environment using a DC bias. Experimental data has shown that this DC bias will significantly reduce the RF power required to yield breakdown, a feature also shown in recent simulation. The cross-polarized conducting array is biased at (100's V) DC on the surface of a Lucite vacuum window. Microwave power is supplied to the window's surface by a single 1-kW magnetron operating at 2.45 GHz CW. The goal of this project is to establish controllable characteristics relating vacuum pressure, DC bias, RF power required for surface breakdown, as well as RF transmission after the formation of plasma. Experimental data will be compared with multipactor susceptibility curves generated using a Monte Carlo simulation which incorporates an applied DC bias and finite pressures of air and argon. Research supported by an AFOSR grant on the Basic Physics of Distributed Plasma Discharge, AFRL, L-3 Communications, and Northrop Grumman.
Toward a Fully Kinetic Theory of Turbulence in Magnetized Plasmas
Yoon, Peter H.
2010-12-30
This paper outlines the present status of the kinetic theory of turbulence in magnetized plasmas as being developed by the present author. The systematic program to formulate the theory of turbulence starting from the Vlasov-Klimontovich formalism began with the works by pioneers of modern plasma physics in the 1960s and 1970s. However, early efforts adopted the heuristic semi-classical method instead of the statistical mechanical formulation, which is necessary for a quantitative analysis. Recently, the present author picked up where the early pioneers left, and began to reformulate the kinetic turbulence theory of turbulence in magnetized plasmas from statistical mechanical formalism. This paper is a brief outline of the progress to date.
Theory of a beam-driven plasma antenna
NASA Astrophysics Data System (ADS)
Timofeev, I. V.; Volchok, E. P.; Annenkov, V. V.
2016-08-01
In this paper, we propose a theory describing generation of electromagnetic waves in a thin beam-plasma system with a characteristic transverse size comparable with the radiation wavelength. In fact, a thin plasma column with a longitudinal density modulation works like a plasma antenna in which an electron beam can excite a superluminal wave of electric current. It has previously been shown that, if the period of this modulation coincides with the wavelength of the most unstable beam-driven mode, radiation at a frequency slightly below the plasma frequency is emitted transversely to the plasma column and generated in thin boundary layers. For the plasma thickness comparable with the skin-depth, generation of the terahertz radiation can reach high efficiency ( ˜10 % ) in such a scheme, but the absolute power of this radiation cannot be increased by increasing the transverse plasma size. In this paper, we study whether the power of such an antenna can be increased in the regime of oblique emission when the magnetized plasma is transparent to the radiated electromagnetic waves and the whole plasma volume may be involved in their generation.
Theory of current drive in plasmas
NASA Astrophysics Data System (ADS)
Fisch, Nathaniel J.
1987-01-01
The continuous operation of a tokamak fusion reactor requires, among other things, a means of providing continuously the toroidal current. Such operation is preferred to the conventional pulsed operation, where the plasma current is induced by a time-varying magnetic field. A variety of methods have been proposed to provide continuous current, including methods that utilize particle beams or radio-frequency waves in any of several frequency regimes. Currents as large as half a mega-amp have now been produced in the laboratory by such means, and experimentation in these techniques has now involved major tokamak facilities worldwide.
Theory of current-drive in plasmas
Fisch, N.J.
1986-12-01
The continuous operation of a tokamak fusion reactor requires, among other things, a means of providing continuous toroidal current. Such operation is preferred to the conventional pulsed operation, where the plasma current is induced by a time-varying magnetic field. A variety of methods has been proposed to provide continuous current, including methods which utilize particle beams or radio frequency waves in any of several frequency regimes. Currents as large as half a mega-amp have now been produced in the laboratory by such means, and experimentation in these techniques has now involved major tokamak facilities worldwide.
Elements of Neoclassical Theory and Plasma Rotation in a Tokamak
NASA Astrophysics Data System (ADS)
Smolyakov, A.
2015-12-01
The following sections are included: * Introduction * Quasineutrality condition * Diffusion in fully ionized magnetized plasma and automatic ambipolarity * Toroidal geometry and neoclassical diffusion * Diffusion and ambipolarity in toroidal plasmas * Ambipolarity and equilibrium poloidal rotation * Ambipolarity paradox and damping of poloidal rotation * Neoclassical plasma inertia * Oscillatory modes of poloidal plasma rotation * Dynamics of the toroidal momentum * Momentum diffusion in strongly collisional, short mean free path regime * Diffusion of toroidal momentum in the weak collision (banana) regime * Toroidal momentum diffusion and momentum damping from drift-kinetic theory and fluid moment equations * Comments on non-axisymmetric effects * Summary * Acknowledgments * Appendix: Trapped (banana) particles and collisionality regimes in a tokamak * Appendix: Hierarchy of moment equations * Appendix: Plasma viscosity tensor in the magnetic field: parallel viscosity, gyroviscosity, and perpendicular viscosity * Appendix: Closure relations for the flux surface averaged parallel viscosity in neoclassical (banana and plateau) regimes * References
Quasi-neutral Vlasov theory of magnetized plasmas
NASA Astrophysics Data System (ADS)
Tronci, Cesare; Camporeale, Enrico
2015-11-01
The low-frequency limit of Maxwell equations is considered in the Maxwell-Vlasov system. This limit produces a quasi-neutral Vlasov system that captures essential features of plasma dynamics, while neglecting radiation effects. Euler-Poincaré reduction theory is used to show that the quasi-neutral Vlasov theory possesses a variational formulation in both Lagrangian and Eulerian coordinates. By construction, the new model recovers all collisionless neutral models employed in plasma simulations. Then, comparisons between the quasi-neutral Vlasov system and hybrid kinetic-fluid models are presented in the linear regime. Financial support by the Leverhulme Trust Research Project Grant 2014-112 is greatly acknowledged.
Modified Enskog kinetic theory for strongly coupled plasmas.
Baalrud, Scott D; Daligault, Jérôme
2015-06-01
Concepts underlying the Enskog kinetic theory of hard-spheres are applied to include short-range correlation effects in a model for transport coefficients of strongly coupled plasmas. The approach is based on an extension of the effective potential transport theory [S. D. Baalrud and J. Daligault, Phys. Rev. Lett. 110, 235001 (2013)] to include an exclusion radius surrounding individual charged particles that is associated with Coulomb repulsion. This is obtained by analogy with the finite size of hard spheres in Enskog's theory. Predictions for the self-diffusion and shear viscosity coefficients of the one-component plasma are tested against molecular dynamics simulations. The theory is found to accurately capture the kinetic contributions to the transport coefficients, but not the potential contributions that arise at very strong coupling (Γ≳30). Considerations related to a first-principles generalization of Enskog's kinetic equation to continuous potentials are also discussed.
Multispecies transport theory for axisymmetric rotating plasmas
Tessarotto, M.; White, R.B.
1992-01-01
A reduced gyrokinetic equation is derived for a multi-species toroidal axisymmetric plasma with arbitrary toroidal differential rotation speeds and in the presence of a finite induced electric field. The kinetic equation obtained, extending previous results obtained by Hinton and Wong and by Catto, Bernstein and Tessarotto, has a form suited for transport applications, via variational techniques; in particular it exhibits the feature that all source terms, including the Spitzer source term, carrying the contribution due to the inductive electric field, appear to be acted upon by the collision operator. Moreover, the equation displays a new contribution due to ``explicit`` velocity perturbations, here proven to be consistent with transport ordering, whose evaluation appears relevant for transport calculations. In addition, general expressions are obtained for the neoclassical fluxes in terms of a variational principle, as well as for the classical ones, retaining, in both cases, the contributions due to the Spitzer`s inductive terms.
Multispecies transport theory for axisymmetric rotating plasmas
Tessarotto, M. . Dipt. di Scienze Matematiche); White, R.B. . Plasma Physics Lab.)
1992-01-01
A reduced gyrokinetic equation is derived for a multi-species toroidal axisymmetric plasma with arbitrary toroidal differential rotation speeds and in the presence of a finite induced electric field. The kinetic equation obtained, extending previous results obtained by Hinton and Wong and by Catto, Bernstein and Tessarotto, has a form suited for transport applications, via variational techniques; in particular it exhibits the feature that all source terms, including the Spitzer source term, carrying the contribution due to the inductive electric field, appear to be acted upon by the collision operator. Moreover, the equation displays a new contribution due to explicit'' velocity perturbations, here proven to be consistent with transport ordering, whose evaluation appears relevant for transport calculations. In addition, general expressions are obtained for the neoclassical fluxes in terms of a variational principle, as well as for the classical ones, retaining, in both cases, the contributions due to the Spitzer's inductive terms.
Theories of radio emissions and plasma waves. [in Jupiter magnetosphere
NASA Technical Reports Server (NTRS)
Goldstein, M. L.; Goertz, C. K.
1983-01-01
The complex region of Jupiter's radio emissions at decameter wavelengths, the so-called DAM, is considered, taking into account the basic theoretical ideas which underly both the older and newer theories and models. Linear theories are examined, giving attention to direct emission mechanisms, parallel propagation, perpendicular propagation, and indirect emission mechanisms. An investigation of nonlinear theories is also conducted. Three-wave interactions are discussed along with decay instabilities, and three-wave up-conversio. Aspects of the Io and plasma torus interaction are studied, and a mechanism by which Io can accelerate electrons is reviewed.
Plasma confinement theory and transport simulation
NASA Astrophysics Data System (ADS)
Ross, D. W.
1989-06-01
An overview of the program has been given in the contract proposal. The principal objectives are: to provide theoretical interpretation and computer modelling for the TEXT tokamak, and to advance the simulation studies of tokamaks generally, functioning as a National Transport Center. We also carry out equilibrium and stability studies in support of the TEXT upgrade, and work has continued on Alfven waves and MFENET software development. The focus of the program is to lay the groundwork for detailed comparison with experiment of the various transport theories to improve physics understanding and confidence in predictions of future machine behavior. This involves: to collect, in retrievable form, the data from TEXT and other tokamaks; to make the data available through easy-to-use interfaces; to develop criteria for success in fitting models to the data; to maintain the Texas transport code CHAPO and make it available to users; to collect theoretical models and implement them in the transport code; and to carry out simulation studies and evaluate fits to the data. In the following we outline the progress made in fiscal year 1989. Of special note are the proposed participation of our data base project in the ITER program, and a proposed q-profile diagnostic based on our neutral transport studies.
Nonlinear theory of slow dissipative layers in anisotropic plasmas
Ballai, I.; Ruderman, M.S.; Erdelyi, R.
1998-01-01
The solar coronal plasma is a well-known example of a plasma with strongly anisotropic dissipative coefficients. The main dissipative processes in the solar corona are strongly anisotropic thermal conductivity and viscosity. Ruderman and Goossens [Astrophys. J. {bold 471}, 1015 (1996)] developed a linear theory of driven slow resonant waves in plasmas with strongly anisotropic viscosity and thermal conductivity. Linear theory shows that in the slow dissipative layer the amplitudes of oscillations become very large for high Reynolds and Pecklet numbers, so that nonlinearity may be important. In the present paper the nonlinear behavior of driven magnetohydrodynamic waves in the slow dissipative layer in plasmas with strongly anisotropic viscosity and thermal conductivity is studied. The nonlinear governing equation for wave variables in the dissipative layer is derived. The nonlinear connection formulae, which are extensions of the linear connection formulae first introduced in the theory of resonant magnetohydrodynamic waves by Sakurai, Goossens, and Hollweg [Solar Phys. {bold 133}, 127 (1991)], are derived. {copyright} {ital 1998 American Institute of Physics.}
Hydrodynamic theory of diffusion in two-temperature multicomponent plasmas
Ramshaw, J.D.; Chang, C.H.
1995-12-31
Detailed numerical simulations of multicomponent plasmas require tractable expressions for species diffusion fluxes, which must be consistent with the given plasma current density J{sub q} to preserve local charge neutrality. The common situation in which J{sub q} = 0 is referred to as ambipolar diffusion. The use of formal kinetic theory in this context leads to results of formidable complexity. We derive simple tractable approximations for the diffusion fluxes in two-temperature multicomponent plasmas by means of a generalization of the hydrodynamical approach used by Maxwell, Stefan, Furry, and Williams. The resulting diffusion fluxes obey generalized Stefan-Maxwell equations that contain driving forces corresponding to ordinary, forced, pressure, and thermal diffusion. The ordinary diffusion fluxes are driven by gradients in pressure fractions rather than mole fractions. Simplifications due to the small electron mass are systematically exploited and lead to a general expression for the ambipolar electric field in the limit of infinite electrical conductivity. We present a self-consistent effective binary diffusion approximation for the diffusion fluxes. This approximation is well suited to numerical implementation and is currently in use in our LAVA computer code for simulating multicomponent thermal plasmas. Applications to date include a successful simulation of demixing effects in an argon-helium plasma jet, for which selected computational results are presented. Generalizations of the diffusion theory to finite electrical conductivity and nonzero magnetic field are currently in progress.
Kinetic theory of Jeans instability of a dusty plasma.
Pandey, B P; Lakhina, G S; Krishan, V
1999-12-01
A kinetic theory of the Jeans instability of a dusty plasma has been developed in the present work. The effect of grain charge fluctuations due to the attachment of electrons and ions to the grain surface has been considered in the framework of Krook's collisional model. We demonstrate that the grain charge fluctuations alter the growth rate of the gravitational collapse of the dusty plasma. The Jeans length has been derived under limiting cases, and its dependence on the attachment frequency is shown. In the absence of gravity, we see that the damping rate of the dust acoustic mode is proportional to the electron-dust collision frequency. PMID:11970688
Theory and Modeling of the Plasma Liner Experiment (PLX)
NASA Astrophysics Data System (ADS)
Cassibry, J. T.; Stanic, M. D.; Awe, T. J.; Hanna, D. S.; Davis, J. S.; Hsu, S. C.; Witherspoon, F. D.
2010-11-01
High pressures and temperatures may be generated at the center an imploding plasma liner. These phenomena are being studied on the Plasma Liner Experiment (PLX) in which a spherical liner is formed via the merging of plasma jets. The basic physical processes include pulsed plasma acceleration, plasma jet propagation in a vacuum, plasma jet merging, liner formation, liner implosion, stagnation, and rarefaction. Each of these processes is dominated by different physics, requiring different models. For example, λei at the jet merging radius may be ˜1 cm, so that liner formation is partially collisionless, while liner implosion is collision dominated. Further, the liner transitions from optically thin to gray during the implosion. An overview of the theory and modeling plan in support of PLX will be given, which includes 1D rad-hydro, 3D hydro, 3D MHD, 2D PIC, and 2D hybrid codes. We will emphasize our recent 3D hydro modeling, which provides insights into liner formation, implosion, and effects of initial jet parameters on scaling of peak pressure.
Theory components of the VASIMR plasma propulsion concept
NASA Astrophysics Data System (ADS)
Arefiev, Alexey
2003-10-01
The talk presents a selection of theoretical problems all motivated by the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) concept [1]. The focus of the talk is on fundamental physics aspects of VASIMR operation, which are formulated as standalone physics problems. The VASIMR device has a magnetic mirror configuration and consists of three main components: a low energy helicon plasma source; an ion cyclotron-resonance heating (ICRH) section; and a magnetic nozzle, which forms a superalfvenic outgoing plasma flow. The ICRH conditions in VASIMR are fundamentally different from the conventional ICRH, because 1) each ion passes the resonance only once; 2) the ion motion is collisionless; 3) the ion energy gain in a single pass significantly exceeds ion energy in the incoming flow. A self-consistent nonlinear model for the rf-power deposition in the ion cyclotron frequency range into a steady-state plasma flow has been developed [3], which generalizes the linear magnetic beach problem solved by T. Stix. Despite the fact that helicon sources are routinely used for plasma production, the underlying physics mechanism is yet to be established. The talk presents a first-principle theory for light-gas helicon plasma sources with a self-consistent treatment of the particle balance [4], power balance, and rf-field structure [2]. A separation of scales among the particle confinement time, the energy confinement time, and the wave period allows one to consider all three constituents separately prior to combining them into an integrated description. The theory addresses the mystery of the high efficiency of helicon sources at frequencies below the typical helicon frequency. The magnetic nozzle transforms the ion rotational motion into the longitudinal motion and it also ensures plasma detachment from the rocket. The detachment occurs when the energy density of the magnetic field drops below the kinetic energy density of the plasma flow. Then the plasma breaks free
Epochal trace elements and evolution.
Pfeiffer, C C; Braverman, E R
1982-07-01
The use of some trace elements by plants and animals during the evolutionary process has resulted in epochal changes. Noteworthy is the fact that plants (but not animals) needed boron in order to grow stems and roots as they left the seas and became anchored on land. Iodine is plentiful in sea water but rare on land. Therefore, the iodination of tyrosine provided an iodine transport mechanism which allowed for the metamorphosis and the development of warm bloodedness--a great evolutionary advantage. Zinc from clay was needed for the formation of the first primitive nucleic acids and, later, the presence of zinc in the retina provide the enhanced night vision of the nocturnal predators--a natural advantage. Hence, boron, iodine and zinc can be termed epochal trace elements. Inquiry should be directed towards the possible roles of other trace elements, which may have been epochal in evolution. PMID:7136960
Spin damping correction to electrostatic modes in kinetic plasma theory
NASA Astrophysics Data System (ADS)
Asenjo, Felipe A.
2009-12-01
The effect of spin of particles is studied using a semi-classical kinetic theory for a magnetized plasma. No other quantum effects are included. We focus in the simple damping effects for the electrostatic wave modes. Besides Landau damping, we show that spin produces two new different effects of damping or instability which are proportional to ℏ. These corrections depend on the electromagnetic part of the wave that is coupled with the spin vector.
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
A Quantitative Kinetic Theory of Meteor Plasma Formation
NASA Astrophysics Data System (ADS)
Dimant, Yakov; Oppenheim, Meers
2014-10-01
Every second millions of small meteoroids hit the Earth from space, the vast majority too small to observe visually. Radars easily detect the plasma they generate and use the data they gather to characterize the meteoroids and the atmosphere in which they disintegrate. These diagnostics requires a detailed quantitative understanding of the formation of the meteor plasma and how it interacts with the Earth's atmosphere. Meteors become detectable to radars after they heat due to collisions with atmospheric molecules sufficiently that they begin to sublimate. The sublimated material then collides into atmospheric molecules and forms plasma around and behind the meteoroid. Reflection of radar pulses from the plasma around the descending meteoroid produces a localized signal called a head echo. This research applies kinetic theory to show that the meteoroid plasma develops over a length-scale close to the ion mean free path with a non-Maxwellian velocity distribution. This analytical model will serve as a basis for quantitative interpretation of the head echo radar measurements, the ionization efficiency (called the Beta parameter), and should help us calculate meteoroid and atmosphere parameters from radar head-echo observations. Work supported by NSF Grant AGS-1244842.
Relativistic warm plasma theory of nonlinear laser-driven electron plasma waves.
Schroeder, C B; Esarey, E
2010-05-01
A relativistic, warm fluid model of a nonequilibrium, collisionless plasma is developed and applied to examine nonlinear Langmuir waves excited by relativistically intense, short-pulse lasers. Closure of the covariant fluid theory is obtained via an asymptotic expansion assuming a nonrelativistic plasma temperature. The momentum spread is calculated in the presence of an intense laser field and shown to be intrinsically anisotropic. Coupling between the transverse and longitudinal momentum variances is enabled by the laser field. A generalized dispersion relation is derived for Langmuir waves in a thermal plasma in the presence of an intense laser field. Including thermal fluctuations in three-velocity-space dimensions, the properties of the nonlinear electron plasma wave, such as the plasma temperature evolution and nonlinear wavelength, are examined and the maximum amplitude of the nonlinear oscillation is derived. The presence of a relativistically intense laser pulse is shown to strongly influence the maximum plasma wave amplitude for nonrelativistic phase velocities owing to the coupling between the longitudinal and transverse momentum variances.
Relativistic warm plasma theory of nonlinear laser-driven electron plasma waves
Schroeder, Carl B.; Esarey, Eric
2010-06-30
A relativistic, warm fluid model of a nonequilibrium, collisionless plasma is developed and applied to examine nonlinear Langmuir waves excited by relativistically-intense, short-pulse lasers. Closure of the covariant fluid theory is obtained via an asymptotic expansion assuming a non-relativistic plasma temperature. The momentum spread is calculated in the presence of an intense laser field and shown to be intrinsically anisotropic. Coupling between the transverse and longitudinal momentum variances is enabled by the laser field. A generalized dispersion relation is derived for langmuir waves in a thermal plasma in the presence of an intense laser field. Including thermal fluctuations in three velocity-space dimensions, the properties of the nonlinear electron plasma wave, such as the plasma temperature evolution and nonlinear wavelength, are examined, and the maximum amplitude of the nonlinear oscillation is derived. The presence of a relativistically intense laser pulse is shown to strongly influence the maximum plasma wave amplitude for non-relativistic phase velocities owing to the coupling between the longitudinal and transverse momentum variances.
Plasma mitigation of shock wave: experiments and theory
NASA Astrophysics Data System (ADS)
Kuo, Spencer P.
2007-12-01
Two types of plasma spikes, generated by on-board 60 Hz periodic and pulsed dc electric discharges in front of two slightly different wind tunnel models, were used to demonstrate the non-thermal plasma techniques for shock wave mitigation. The experiments were conducted in a Mach 2.5 wind tunnel. (1) In the periodic discharge case, the results show a transformation of the shock from a well-defined attached shock into a highly curved shock structure, which has increased shock angle and also appears in diffused form. As shown in a sequence with increasing discharge intensity, the shock in front of the model moves upstream to become detached with increasing standoff distance from the model and is eliminated near the peak of the discharge. The power measurements exclude the heating effect as a possible cause of the observed shock wave modification. A theory using a cone model as the shock wave generator is presented to explain the observed plasma effect on shock wave. The analysis shows that the plasma generated in front of the model can effectively deflect the incoming flow; such a flow deflection modifies the structure of the shock wave generated by the cone model, as shown by the numerical results, from a conic shape to a curved one. The shock front moves upstream with a larger shock angle, matching well with that observed in the experiment. (2) In the pulsed dc discharge case, hollow cone-shaped plasma that envelops the physical spike of a truncated cone model is produced in the discharge; consequently, the original bow shock is modified to a conical shock, equivalent to reinstating the model into a perfect cone and to increase the body aspect ratio by 70%. A significant wave drag reduction in each discharge is inferred from the pressure measurements; at the discharge maximum, the pressure on the frontal surface of the body decreases by more than 30%, the pressure on the cone surface increases by about 5%, whereas the pressure on the cylinder surface remains
A Plasma Instability Theory of Gamma-Ray Burst Emission
NASA Technical Reports Server (NTRS)
Brainerd, Jerome J.
1999-01-01
A plasma instability theory is presented for the prompt radiation from gamma-ray bursts. In the theory, a highly relativistic shell interacts with the interstellar medium through the filamentation and the two-stream instabilities to convert bulk kinetic energy into electron thermal energy and magnetic field energy. The processes are not efficient enough to satisfy the Rankine-Hugoniot conditions, so a shock cannot form through this mechanism. Instead, the interstellar medium passes through the shell, with the electrons radiating during this passage. Gamma-rays are produced by synchrotron self-Compton emission. Prompt optical emission is also produced through this mechanism, while prompt radio emission is produced through synchrotron emission. The model timescales are consistent with the shortest burst timescales. To emit gamma-rays, the shell's bulk Lorentz factor must be $\\simg 10(exp 3)$. For the radiative processes to be efficient, the interstellar medium density must satisfy a lower limit that is a function of the bulk Lorentz factor. Because the limits operate as selection effects, bursts that violate them constitute new classes. In particular, a class of optical and ultraviolet bursts with no gamma-ray emission should exist. The lower limit on the density of the interstellar medium is consistent with the requirements of the Compton attenuation theory, providing an explanation for why all burst spectra appear to be attenuated. Several tests of the theory are discussed, as are the next theoretical investigations that should be conducted.
Some improvements in the theory of plasma relaxation
Hameiri, Eliezer
2014-04-15
Taylor's relaxation theory is extended to plasmas with mass flow by using the cross helicity as a conserved quantity, similar to the magnetic helicity. Indeed, it is shown that the conservation of the cross helicity in magnetohydrodynamics is the result of the conservation of two magnetic-like helicities in two-fluid plasmas. In addition, the usually ignored toroidal flux is also held to be conserved. We also view plasma relaxation as attaining a maximum entropy state rather than Taylor's minimum energy state, but prove that maximizing the entropy subject to a given amount of energy is equivalent to minimizing the energy subject to a given amount of entropy. The resulting relaxed state is similar to the one discussed by Finn and Antonsen [Phys. Fluids 26, 3540 (1983)], and involves flow parallel to the magnetic field and constant temperature, but non-constant pressure. We show how to construct an asymptotic solution to the relaxed state based on the smallness of the Alfven Mach number of the flow.
Diamagnetic boundary layers - A kinetic theory. [for collisionless magnetized plasmas
NASA Technical Reports Server (NTRS)
Lemaire, J.; Burlaga, L. F.
1976-01-01
A kinetic theory is presented for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma, such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers in which the current is carried by protons are discussed; in particular, cases are considered in which the magnetic-field intensity, direction, or both, changed across the layer. In every case, the thickness was of the order of a few proton gyroradii, and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. These results are consistent with observations of boundary layers in the solar wind near 1 AU.
Hyper-resistivity Theory in a Cylindrical Plasma
Berk, H L; Fowler, T K; LoDestro, L L; Pearlstein, L D
2001-02-27
A model is presented for determining the hyper-resistivity coefficient that arises due to the presence of magnetic structures that appear in plasma configurations such as the reversed field pinch and spheromak. Emphasis is placed on modeling cases where magnetic islands pass from non-overlap to overlap regimes. Earlier works have shown that a diffusion-based model can give realistic transport scalings when magnetic islands are isolated, and this formalism is extended to apply to the hyper-resistivity problem. In this case electrons may either be in long or short mean-free-path regimes and intuitively-based arguments are presented of how to extend previous theories to incorporate this feature in the presence of magnetic structures that pass from laminar to moderately chaotic regimes.
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.
Wakes in complex plasmas: A self-consistent kinetic theory.
Kompaneets, Roman; Morfill, Gregor E; Ivlev, Alexei V
2016-06-01
In ground-based experiments with complex (dusty) plasmas, charged microparticles are levitated against gravity by an electric field, which also drives ion flow in the parent gas. Existing analytical approaches to describe the electrostatic interaction between microparticles in such conditions generally ignore the field and ion-neutral collisions, assuming free ion flow with a certain approximation for the ion velocity distribution function (usually a shifted Maxwellian). We provide a comprehensive analysis of our previously proposed self-consistent kinetic theory including the field, ion-neutral collisions, and the corresponding ion velocity distribution. We focus on various limiting cases and demonstrate how the interplay of these factors results in different forms of the shielding potential.
Wakes in complex plasmas: A self-consistent kinetic theory
NASA Astrophysics Data System (ADS)
Kompaneets, Roman; Morfill, Gregor E.; Ivlev, Alexei V.
2016-06-01
In ground-based experiments with complex (dusty) plasmas, charged microparticles are levitated against gravity by an electric field, which also drives ion flow in the parent gas. Existing analytical approaches to describe the electrostatic interaction between microparticles in such conditions generally ignore the field and ion-neutral collisions, assuming free ion flow with a certain approximation for the ion velocity distribution function (usually a shifted Maxwellian). We provide a comprehensive analysis of our previously proposed self-consistent kinetic theory including the field, ion-neutral collisions, and the corresponding ion velocity distribution. We focus on various limiting cases and demonstrate how the interplay of these factors results in different forms of the shielding potential.
Wakes in complex plasmas: A self-consistent kinetic theory.
Kompaneets, Roman; Morfill, Gregor E; Ivlev, Alexei V
2016-06-01
In ground-based experiments with complex (dusty) plasmas, charged microparticles are levitated against gravity by an electric field, which also drives ion flow in the parent gas. Existing analytical approaches to describe the electrostatic interaction between microparticles in such conditions generally ignore the field and ion-neutral collisions, assuming free ion flow with a certain approximation for the ion velocity distribution function (usually a shifted Maxwellian). We provide a comprehensive analysis of our previously proposed self-consistent kinetic theory including the field, ion-neutral collisions, and the corresponding ion velocity distribution. We focus on various limiting cases and demonstrate how the interplay of these factors results in different forms of the shielding potential. PMID:27415371
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.
Plasma stability theory including the resistive wall effects
NASA Astrophysics Data System (ADS)
Pustovitov, V. D.
2015-12-01
> Plasma stabilization due to a nearby conducting wall can provide access to better performance in some scenarios in tokamaks. This was proved by experiments with an essential gain in and demonstrated as a long-lasting effect at sufficiently fast plasma rotation in the DIII-D tokamak (see, for example, Strait et al., Nucl. Fusion, vol. 43, 2003, pp. 430-440). The rotational stabilization is the central topic of this review, though eventually the mode rotation gains significance. The analysis is based on the first-principle equations describing the energy balance with dissipation in the resistive wall. The method emphasizes derivation of the dispersion relations for the modes which are faster than the conventional resistive wall modes, but slower than the ideal magnetohydrodynamics modes. Both the standard thin wall and ideal-wall approximations are not valid in this range. Here, these are replaced by an approach incorporating the skin effect in the wall. This new element in the stability theory makes the energy sink a nonlinear function of the complex growth rate. An important consequence is that a mode rotating above a critical level can provide a damping effect sufficient for instability suppression. Estimates are given and applications are discussed.
New approach to MHD spectral theory of stationary plasma flows
NASA Astrophysics Data System (ADS)
Goedbloed, Hans
2009-11-01
The basic equations of MHD spectral theory date back to 1958 for static plasmas (Bernstein et al.) and to 1960 for stationary plasma flows (Frieman and Rotenberg). The number of papers on the two subjects appears to be inversely proportional to their complexity, with the vast majority of contributions to MHD stability of tokamaks being restricted to static equilibria and stationary equilibrium flows mostly being discussed analytically for trivial equilibria or numerically for complicated geometries. The problem with the latter is not that numerical approaches are inaccurate, but that they suffer from lack of analytical guidance concerning the structure of the spectrum. One of the reasons is the usual misnomer of ``non-self adjointness'' of the stationary flow problem. In fact, self-adjointness of the two occurring operators was proved right away. Based on the two quadratic forms corresponding to these operators, (a) we constructed an effective method to compute the eigenvalues in the complex plane, (b) we found the counterpart of the oscillation theorem for eigenvalues of static equilibria (Goedbloed and Sakanaka, 1974) for the eigenvalues of stationary flows, enabling one to map out sequences of eigenvalues in the complex plane. Examples will be given for Rayleigh-Taylor, Kelvin-Helmholtz and magneto-rotational instabilities.
New approach to magnetohydrodynamics spectral theory of stationary plasma flows
NASA Astrophysics Data System (ADS)
(Hans Goedbloed, J. P.
2011-07-01
While the basic equations of MHD spectral theory date back to 1958 for static plasmas (Bernstein et al 1958 Proc. R. Soc. A 244 17) and to 1960 for stationary plasma flows (Frieman and Rotenberg 1960 Rev. Mod. Phys. 32 898), progress on the latter subject has been slow since it suffers from lack of analytical insight concerning the structure of the spectrum. One of the reasons is the usual misnomer of 'non-self adjointness' of the stationary flow problem. Actually, self-adjointness of the occurring operators, namely the generalized force operator and the Doppler-Coriolis gradient operator -iρv·∇, was proved right away by Frieman and Rotenberg. Based on the reality of the two quadratic forms corresponding to these operators, we here construct (a) an effective method to compute the solution paths in the complex ω plane on which the eigenvalues are situated, (b) the counterpart of the oscillation theorem for eigenvalues of static equilibria (Goedbloed and Sakanaka 1974 Phys. Fluids 17 908) for the eigenvalues of stationary flows, based on the monotonicity of the alternating ratio, or alternator, of the boundary values of the displacement ξ and the total pressure perturbation Π. This enables one to map out the complete spectrum of eigenvalues in the complex ω-plane. The intricate topology of the solution paths is discussed for the fundamental examples of Rayleigh-Taylor, Kelvin-Helmholtz and combined instabilities.
Lee, Hyo-Chang; Chung, Chin-Wook
2015-01-01
Hysteresis, which is the history dependence of physical systems, is one of the most important topics in physics. Interestingly, bi-stability of plasma with a huge hysteresis loop has been observed in inductive plasma discharges. Despite long plasma research, how this plasma hysteresis occurs remains an unresolved question in plasma physics. Here, we report theory, experiment, and modeling of the hysteresis. It was found experimentally and theoretically that evolution of the electron energy distribution (EED) makes a strong plasma hysteresis. In Ramsauer and non-Ramsauer gas experiments, it was revealed that the plasma hysteresis is observed only at high pressure Ramsauer gas where the EED deviates considerably from a Maxwellian shape. This hysteresis was presented in the plasma balance model where the EED is considered. Because electrons in plasmas are usually not in a thermal equilibrium, this EED-effect can be regarded as a universal phenomenon in plasma physics. PMID:26482650
Lee, Hyo-Chang; Chung, Chin-Wook
2015-10-20
Hysteresis, which is the history dependence of physical systems, is one of the most important topics in physics. Interestingly, bi-stability of plasma with a huge hysteresis loop has been observed in inductive plasma discharges. Despite long plasma research, how this plasma hysteresis occurs remains an unresolved question in plasma physics. Here, we report theory, experiment, and modeling of the hysteresis. It was found experimentally and theoretically that evolution of the electron energy distribution (EED) makes a strong plasma hysteresis. In Ramsauer and non-Ramsauer gas experiments, it was revealed that the plasma hysteresis is observed only at high pressure Ramsauer gas where the EED deviates considerably from a Maxwellian shape. This hysteresis was presented in the plasma balance model where the EED is considered. Because electrons in plasmas are usually not in a thermal equilibrium, this EED-effect can be regarded as a universal phenomenon in plasma physics.
NASA Astrophysics Data System (ADS)
Lee, Hyo-Chang; Chung, Chin-Wook
2015-10-01
Hysteresis, which is the history dependence of physical systems, is one of the most important topics in physics. Interestingly, bi-stability of plasma with a huge hysteresis loop has been observed in inductive plasma discharges. Despite long plasma research, how this plasma hysteresis occurs remains an unresolved question in plasma physics. Here, we report theory, experiment, and modeling of the hysteresis. It was found experimentally and theoretically that evolution of the electron energy distribution (EED) makes a strong plasma hysteresis. In Ramsauer and non-Ramsauer gas experiments, it was revealed that the plasma hysteresis is observed only at high pressure Ramsauer gas where the EED deviates considerably from a Maxwellian shape. This hysteresis was presented in the plasma balance model where the EED is considered. Because electrons in plasmas are usually not in a thermal equilibrium, this EED-effect can be regarded as a universal phenomenon in plasma physics.
Extended neoclassical transport theory for incompressible tokamak plasmas
NASA Astrophysics Data System (ADS)
Shaing, K. C.
1997-09-01
Conventional neoclassical transport theory is extended to include the effects of orbit squeezing, and to allow the effective poloidal Mach number UpM=[(V∥/vt)+(VEB/vtBp)] of the order of unity for incompressible tokamak plasmas. Here, V∥ is the parallel mass flow, vt is the ion thermal speed, VE is the poloidal E×B drift speed, B is the magnetic field strength, and Bp is the poloidal magnetic field strength. It is found that ion thermal conductivity is reduced from its conventional neoclassical value in both banana and plateau regimes if UpM>1 and S>1. Here, S=[1+cI2Φ''/(Ω0B0)] is the orbit squeezing factor with c the speed of light, I=RBt, R the major radius, Φ the electrostatic potential, B0 the magnetic field strength on the axis, Ω0=eB0/Mc, M the ion mass, e the ion charge, Φ''=d2Φ/dψ2, and ψ the poloidal flux function. However, there is an irreducible minimum for the ion thermal conductivity in the banana-plateau regime set by the conventional Pfirsch-Schlüter transport.
Contributions to the theory of magnetorotational instability and waves in a rotating plasma
Mikhailovskii, A. B.; Lominadze, J. G.; Churikov, A. P.; Tsypin, V. S.; Erokhin, N. N.; Erokhin, N. S.; Konovalov, S. V.; Pashitskii, E. A.; Stepanov, A. V.; Vladimirov, S. V.; Galvao, R. M. O.
2008-01-15
The one-fluid magnetohydrodynamic (MHD) theory of magnetorotational instability (MRI) in an ideal plasma is presented. The theory predicts the possibility of MRI for arbitrary {beta}, where {beta} is the ratio of the plasma pressure to the magnetic field pressure. The kinetic theory of MRI in a collisionless plasma is developed. It is demonstrated that as in the ideal MHD, MRI can occur in such a plasma for arbitrary {beta}. The mechanism of MRI is discussed; it is shown that the instability appears because of a perturbed parallel electric field. The electrodynamic description of MRI is formulated under the assumption that the dispersion relation is expressed in terms of the permittivity tensor; general properties of this tensor are analyzed. It is shown to be separated into the nonrotational and rotational parts. With this in mind, the first step for incorporation of MRI into the general theory of plasma instabilities is taken. The rotation effects on Alfven waves are considered.
Theory of electromagnetic fluctuations for magnetized multi-species plasmas
Navarro, Roberto E. Muñoz, Víctor; Araneda, Jaime; Moya, Pablo S.; Viñas, Adolfo F.; Valdivia, Juan A.
2014-09-15
Analysis of electromagnetic fluctuations in plasma provides relevant information about the plasma state and its macroscopic properties. In particular, the solar wind persistently sustains a small but detectable level of magnetic fluctuation power even near thermal equilibrium. These fluctuations may be related to spontaneous electromagnetic fluctuations arising from the discreteness of charged particles. Here, we derive general expressions for the plasma fluctuations in a multi-species plasma following arbitrary distribution functions. This formalism, which generalizes and includes previous works on the subject, is then applied to the generation of electromagnetic fluctuations propagating along a background magnetic field in a plasma of two proton populations described by drifting bi-Maxwellians.
On the theory of Langmuir waves in a quantum plasma
Kuzelev, M. V.
2010-04-15
Nonlinear quantum-mechanical equations are derived for Langmuir waves in an isotropic electron collisionless plasma. A general analysis of dispersion relations is carried out for complex spectra of Langmuir waves and van Kampen waves in a quantum plasma with an arbitrary electron momentum distribution. Quantum nonlinear collisionless Landau damping in Maxwellian and degenerate plasmas is studied. It is shown that collisionless damping of Langmuir waves (including zero sound) occurs in collisionless plasmas due to quantum correction in the Cherenkov absorption condition, which is a purely quantum effect. Solutions to the quantum dispersion equation are obtained for a degenerate plasma.
Zhang, H.; Wu, S. Z.; Zhou, C. T.; He, X. T.; Zhu, S. P.
2013-09-15
The dispersion relation of one-dimensional longitudinal plasma waves in relativistic homogeneous plasmas is investigated with both linear theory and Vlasov simulation in this paper. From the Vlasov-Poisson equations, the linear dispersion relation is derived for the proper one-dimensional Jüttner distribution. Numerically obtained linear dispersion relation as well as an approximate formula for plasma wave frequency in the long wavelength limit is given. The dispersion of longitudinal wave is also simulated with a relativistic Vlasov code. The real and imaginary parts of dispersion relation are well studied by varying wave number and plasma temperature. Simulation results are in agreement with established linear theory.
Extended neoclassical transport theory for incompressible tokamak plasmas
Shaing, K.C.
1997-09-01
Conventional neoclassical transport theory is extended to include the effects of orbit squeezing, and to allow the effective poloidal Mach number U{sub pM}=[(V{sub {parallel}}/v{sub t})+(V{sub E}B/v{sub t}B{sub p})] of the order of unity for incompressible tokamak plasmas. Here, V{sub {parallel}} is the parallel mass flow, v{sub t} is the ion thermal speed, V{sub E} is the poloidal {bold E{times}B} drift speed, B is the magnetic field strength, and B{sub p} is the poloidal magnetic field strength. It is found that ion thermal conductivity is reduced from its conventional neoclassical value in both banana and plateau regimes if U{sub pM}{gt}1 and S{gt}1. Here, S=[1+cI{sup 2}{Phi}{sup {prime}{prime}}/({Omega}{sub 0}B{sub 0})] is the orbit squeezing factor with c the speed of light, I=RB{sub t}, R the major radius, {Phi} the electrostatic potential, B{sub 0} the magnetic field strength on the axis, {Omega}{sub 0}=eB{sub 0}/Mc, M the ion mass, e the ion charge, {Phi}{sup {prime}{prime}}=d{sup 2}{Phi}/d{psi}{sup 2}, and {psi} the poloidal flux function. However, there is an irreducible minimum for the ion thermal conductivity in the banana-plateau regime set by the conventional Pfirsch{endash}Schl{umlt u}ter transport. {copyright} {ital 1997 American Institute of Physics.}
Theory of semicollisional drift-interchange modes in cylindrical plasmas
Hahm, T.S.; Chen, L.
1985-01-01
Resistive interchange instabilities in cylindrical plasmas are studied, including the effects of electron diamagnetic drift, perpendicular resistivity, and plasma compression. The analyses are pertinent to the semicollisional regime where the effective ion gyro-radius is larger than the resistive layer width. Both analytical and numerical results show that the modes can be completely stabilized by the perpendicular plasma transport. Ion sound effects, meanwhile, are found to be negligible in the semicollisional regime.
Linear Covariance Analysis and Epoch State Estimators
NASA Technical Reports Server (NTRS)
Markley, F. Landis; Carpenter, J. Russell
2014-01-01
This paper extends in two directions the results of prior work on generalized linear covariance analysis of both batch least-squares and sequential estimators. The first is an improved treatment of process noise in the batch, or epoch state, estimator with an epoch time that may be later than some or all of the measurements in the batch. The second is to account for process noise in specifying the gains in the epoch state estimator. We establish the conditions under which the latter estimator is equivalent to the Kalman filter.
Linear Covariance Analysis and Epoch State Estimators
NASA Technical Reports Server (NTRS)
Markley, F. Landis; Carpenter, J. Russell
2012-01-01
This paper extends in two directions the results of prior work on generalized linear covariance analysis of both batch least-squares and sequential estimators. The first is an improved treatment of process noise in the batch, or epoch state, estimator with an epoch time that may be later than some or all of the measurements in the batch. The second is to account for process noise in specifying the gains in the epoch state estimator. We establish the conditions under which the latter estimator is equivalent to the Kalman filter.
Hollow cathodes as electron emitting plasma contactors Theory and computer modeling
NASA Technical Reports Server (NTRS)
Davis, V. A.; Katz, I.; Mandell, M. J.; Parks, D. E.
1987-01-01
Several researchers have suggested using hollow cathodes as plasma contactors for electrodynamic tethers, particularly to prevent the Shuttle Orbiter from charging to large negative potentials. Previous studies have shown that fluid models with anomalous scattering can describe the electron transport in hollow cathode generated plasmas. An improved theory of the hollow cathode plasmas is developed and computational results using the theory are compared with laboratory experiments. Numerical predictions for a hollow cathode plasma source of the type considered for use on the Shuttle are presented, as are three-dimensional NASCAP/LEO calculations of the emitted ion trajectories and the resulting potentials in the vicinity of the Orbiter. The computer calculations show that the hollow cathode plasma source makes vastly superior contact with the ionospheric plasma compared with either an electron gun or passive ion collection by the Orbiter.
Introduction to quantum chromo transport theory for quark-gluon plasmas
Gyulassy, M.; Elze, H.Th.; Iwazaki, A.; Vasak, D.
1986-08-01
Upcoming heavy ion experiments at the AGS and SPS are aimed at producing and diagnosing a primordial form of matter, the quark-gluon plasma. In these lectures some recent developments on formulating a quantum transport theory for quark-gluon plasmas are introduced. 46 refs.
Plasma theory and simulation research. Final technical report, January 1, 1986--October 31, 1989
Birdsall, C.K.
1989-12-31
Our research group uses both theory and simulation as tools in order to increase the understanding of instabilities, heating, diffusion, transport and other phenomena in plasmas. We also work on the improvement of simulation, both theoretically and practically. Our focus has been more and more on the plasma edge (the ``sheath``), interactions with boundaries, leading to simulations of whole devices (someday a numerical tokamak).
Orbital-motion-limited theory of dust charging and plasma response
Tang, Xian-Zhu Luca Delzanno, Gian
2014-12-15
The foundational theory for dusty plasmas is the dust charging theory that provides the dust potential and charge arising from the dust interaction with a plasma. The most widely used dust charging theory for negatively charged dust particles is the so-called orbital motion limited (OML) theory, which predicts the dust potential and heat collection accurately for a variety of applications, but was previously found to be incapable of evaluating the dust charge and plasma response in any situation. Here, we report a revised OML formulation that is able to predict the plasma response and hence the dust charge. Numerical solutions of the new OML model show that the widely used Whipple approximation of dust charge-potential relationship agrees with OML theory in the limit of small dust radius compared with plasma Debye length, but incurs large (order-unity) deviation from the OML prediction when the dust size becomes comparable with or larger than plasma Debye length. This latter case is expected for the important application of dust particles in a tokamak plasma.
Theory and modelling of helium enrichment in plasma experiments with pump limiters
Prinja, A.K.; Conn, R.W.
1984-01-01
Helium enrichment in the exhaust gas stream flowing from a hydrogen-helium plasma is studied using an analytical theory and Monte Carlo simulations. To provide a sensitive experimental test in a tokamak, an unusual configuration, inverted from traditional designs, is proposed for a pump limiter. The principle can be tested in other plasma devices as well. The theory suggests that for typical plasma edge conditions in a confinement device, namely, n = 10/sup 13/cm/sup -3/ and T/sub i/ = T/sub e/ approx. = 5-30eV, helium enrichment in the neutral gas exhaust stream can be very high, in the range 5 to 7, relative to the helium-hydrogen ratio in the plasma. Such high enrichment factors are achieved by exploiting the difference between the ionization rates of hydrogen and helium and the negligible helium charge exchange rate at these plasma conditions. A limiter arrangement is proposed in which the natural curvature of the toroidal magnetic field is used to isolate, using the plasma itself, the point of plasma neutralization from the location of the gas exhaust. The plasma region then acts to preferentially screen the recycling hydrogen by the processes of ionization and of charge-exchange-induced losses at open boundaries. The theory and analysis suggests that an experiment can provide a sensitive test of modules used to describe the plasma edge and of atomic and surface physics data used in these models.
Similarity theory of nonlinear cold pair-plasma dynamics
Diver, D. A.; Laing, E. W.
2009-09-15
In this article the waves and dynamics of an inhomogeneous cold magnetized electron-positron plasma are investigated using similarity methods to study particular classes of plasma wave behavior. A cold two-fluid plasma model in a cylindrical geometry ({rho},{theta},z) and time t is assumed, but attention is restricted to ({rho},t) variations only. The application of similarity procedures reduces the set of partial differential equations which describe the spatial and temporal evolution of the plasma to a set of ordinary differential equations. This model has particular relevance to the description of the evolution of the electron-positron component of pulsar magnetospheres. Some typical solutions of these similarity equations are presented which characteristically have the property of blow-up phenomena.
A theory of the plasma torch for waste-treatment
Uhm, H.S.; Hong, S.H.
1997-12-31
Arc-plasma technology has broad applications to waste treatment processing including the safe disposal of hazardous and low-level radioactive wastes. The plasma torch could be useful to the development of an efficient, compact, lightweight, clean burning incinerator for industrial and municipal waste disposal in an environmentally beneficial way. The authors therefore develop a simple theoretical model describing physics of the plasma torch plume in connection with its applications to the arc-plasma waste-treatment system. The theoretical analysis is carried out by making use of Bernoulli`s pressure-balance equation, which provides a stable equilibrium solution of the gas density in the plume ejected from the torch into a high-pressure reactor chamber with 4{var_epsilon} < 1. The pressure depression parameter {var_epsilon} is proportional to the gas temperature and inversely proportional to the square of the chamber pressure. In a low-pressure chamber, characterized by 4{var_epsilon} > 1, there is no stable equilibrium solution satisfying Bernoulli`s equation. Therefore, it is expected that the observable plasma data may change abruptly as the chamber pressure crosses the borderline defined by 4{var_epsilon} = 1. Indeed most of the plasma data measured in an experiment change abruptly at the pressure borderline of 4{var_epsilon} = 1.
Energy branching in the Io plasma torus - The failure of neutral cloud theory
NASA Technical Reports Server (NTRS)
Shemansky, D. E.
1988-01-01
Model calculations are used to explore the energy source characteristics of the energy branching of the hot Io plasma torus. It is assumed that the energy is derived from the kinetic energy acquired by ions created in the rotating planetary magnetic field, and that Coulomb collisions with the electron gas control the flow of energy to the ionizing and radiative processes. The results show that neutral cloud theory is qualitatively inadequate. It is shown that neutral cloud theory can only support a dominantly singly ionized system (at the measured electron densities in the plasma torus) and that it fails to predict observed plasma properties relative to variations in number density.
Validating Laser-Induced Birefringence Theory with Plasma Interferometry
Chen, Cecilia
2015-09-02
Intense laser beams crossing paths in plasma is theorized to induce birefringence in the medium, resulting from density and refractive index modulations that affect the polarization of incoming light. The goal of the associated experiment, conducted on Janus at Lawrence Livermore’s Jupiter Laser Facility, was to create a tunable laser-plasma waveplate to verify the relationship between dephasing angle and beam intensity, plasma density, plasma temperature, and interaction length. Interferometry analysis of the plasma channel was performed to obtain a density map and to constrain temperature measured from Thomson scattering. Various analysis techniques, including Fast Fourier transform (FFT) and two variations of fringe-counting, were tried because interferograms captured in this experiment contained unusual features such as fringe discontinuity at channel edges, saddle points, and islands. The chosen method is flexible, semi-automated, and uses a fringe tracking algorithm on a reduced image of pre-traced synthetic fringes. Ultimately, a maximum dephasing angle of 49.6° was achieved using a 1200 μm interaction length, and the experimental results appear to agree with predictions.
Quasilinear theory of general electromagnetic fluctuations in unmagnetized plasmas
Schlickeiser, R. E-mail: yoonp@umd.edu; Yoon, P. H. E-mail: yoonp@umd.edu
2014-09-15
The general quasilinear Fokker-Planck kinetic equation for the plasma particle distribution functions in unmagnetized plasmas is derived, making no restrictions on the frequency of the electromagnetic fluctuations. The derived kinetic particle equation complements our earlier study of the general fluctuation's kinetic equation. For collective plasma eigenmodes and gyrotropic particle distribution functions, the two coupled kinetic equations describe the self-consistent dynamical evolution of the plasma. The limit of weakly damped collective modes correctly reproduces the well-known textbook kinetic particle equation with longitudinal Langmuir and ion-acoustic fluctuations, demonstrating, in particular, the resonant nature of parallel momentum diffusion of particles. In the limit of aperiodic modes, the Fokker-Planck equation contains the nonresonant diffusion of particles in momentum and the parallel and perpendicular momentum drag coefficients. As an application these drag and diffusion coefficients are calculated for extragalactic cosmic ray particles propagating in the unmagnetized intergalactic medium. Whereas for all cosmic rays, the perpendicular momentum diffusion in intergalactic aperiodic fluctuations is negligibly small; cosmic ray protons with energies below 10{sup 5 }GeV are affected by the plasma drag.
Electromagnetic fluctuations in magnetized plasmas. I. The rigorous relativistic kinetic theory
NASA Astrophysics Data System (ADS)
Schlickeiser, R.; Yoon, P. H.
2015-07-01
Using the system of the Klimontovich and Maxwell equations, the general linear fluctuation theory for magnetized plasmas is developed. General expressions for the electromagnetic fluctuation spectra (electric and magnetic fields) from uncorrelated plasma particles in plasmas with a uniform magnetic field are derived, which are covariantly correct within the theory of special relativity. The general fluctuation spectra hold for plasmas of arbitrary composition, arbitrary momentum dependences of the plasma particle distribution functions, and arbitrary orientations of the wave vector with respect to the uniform magnetic field. Moreover, no restrictions on the values of the real and the imaginary parts of the frequency are made. The derived fluctuation spectra apply to both non-collective fluctuations and collective plasma eigenmodes in magnetized plasmas. In the latter case, kinetic equations for the components of fluctuating electric and magnetic fields in magnetized plasmas are derived that include the effect of spontaneous emission and absorption. In the limiting case of an unmagnetized plasmas, the general fluctuation spectra correctly reduce to the unmagnetized fluctuation spectra derived before.
Electromagnetic fluctuations in magnetized plasmas. I. The rigorous relativistic kinetic theory
Schlickeiser, R. E-mail: yoonp@umd.edu; Yoon, P. H. E-mail: yoonp@umd.edu
2015-07-15
Using the system of the Klimontovich and Maxwell equations, the general linear fluctuation theory for magnetized plasmas is developed. General expressions for the electromagnetic fluctuation spectra (electric and magnetic fields) from uncorrelated plasma particles in plasmas with a uniform magnetic field are derived, which are covariantly correct within the theory of special relativity. The general fluctuation spectra hold for plasmas of arbitrary composition, arbitrary momentum dependences of the plasma particle distribution functions, and arbitrary orientations of the wave vector with respect to the uniform magnetic field. Moreover, no restrictions on the values of the real and the imaginary parts of the frequency are made. The derived fluctuation spectra apply to both non-collective fluctuations and collective plasma eigenmodes in magnetized plasmas. In the latter case, kinetic equations for the components of fluctuating electric and magnetic fields in magnetized plasmas are derived that include the effect of spontaneous emission and absorption. In the limiting case of an unmagnetized plasmas, the general fluctuation spectra correctly reduce to the unmagnetized fluctuation spectra derived before.
Baalrud, Scott D.; Daligault, Jérôme
2014-05-15
A method for extending traditional plasma transport theories into the strong coupling regime is presented. Like traditional theories, this is based on a binary scattering approximation, but where physics associated with many body correlations is included through the use of an effective interaction potential. The latter is simply related to the pair-distribution function. Modeling many body effects in this manner can extend traditional plasma theory to orders of magnitude stronger coupling. Theoretical predictions are tested against molecular dynamics simulations for electron-ion temperature relaxation as well as diffusion in one component systems. Emphasis is placed on the connection with traditional plasma theory, where it is stressed that the effective potential concept has precedence through the manner in which screening is imposed. The extension to strong coupling requires accounting for correlations in addition to screening. Limitations of this approach in the presence of strong caging are also discussed.
On the theory of dynamics of dust grain in plasma
Stepanenko, A. A.; Krasheninnikov, S. I.
2013-03-15
The dynamics of rotationally symmetric dust grains in plasma embedded in a magnetic field are of concern. The general expressions for forces and torques acting on dust are found. It is shown that dust spinning is determined by torques related to both the Lorentz force (dominant for relatively small grains) and the gyro-motion of plasma particles impinging the grain (which prevails for large grains). The stability of grain spinning is analyzed and it is shown that, for some cases (e.g., oblate spheroid), there is no stable dynamic equilibrium of grain spinning.
Theory and application of maximum magnetic energy in toroidal plasmas
Chu, T.K.
1992-02-01
The magnetic energy in an inductively driven steady-state toroidal plasma is a maximum for a given rate of dissipation of energy (Poynting flux). A purely resistive steady state of the piecewise force-free configuration, however, cannot exist, as the periodic removal of the excess poloidal flux and pressure, due to heating, ruptures the static equilibrium of the partitioning rational surfaces intermittently. The rupture necessitates a plasma with a negative q{prime}/q (as in reverse field pinches and spheromaks) to have the same {alpha} in all its force-free regions and with a positive q{prime}/q (as in tokamaks) to have centrally peaked {alpha}`s.
Theory and application of maximum magnetic energy in toroidal plasmas
Chu, T.K.
1992-02-01
The magnetic energy in an inductively driven steady-state toroidal plasma is a maximum for a given rate of dissipation of energy (Poynting flux). A purely resistive steady state of the piecewise force-free configuration, however, cannot exist, as the periodic removal of the excess poloidal flux and pressure, due to heating, ruptures the static equilibrium of the partitioning rational surfaces intermittently. The rupture necessitates a plasma with a negative q{prime}/q (as in reverse field pinches and spheromaks) to have the same {alpha} in all its force-free regions and with a positive q{prime}/q (as in tokamaks) to have centrally peaked {alpha}'s.
Kim, Kihong; Lee, Dong-Hun
2006-04-15
A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized, and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances, and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obtained. The dependencies of mode conversion phenomena on the magnitude of the external magnetic field, the incident angle, and the wave frequency are explored in detail.
TOWARD A THEORY OF ASTROPHYSICAL PLASMA TURBULENCE AT SUBPROTON SCALES
Boldyrev, Stanislav; Horaites, Konstantinos; Xia, Qian; Perez, Jean Carlos
2013-11-01
We present an analytical study of subproton electromagnetic fluctuations in a collisionless plasma with a plasma beta of the order of unity. In the linear limit, a rigorous derivation from the kinetic equation is conducted focusing on the role and physical properties of kinetic-Alfvén and whistler waves. Then, nonlinear fluid-like equations for kinetic-Alfvén waves and whistler modes are derived, with special emphasis on the similarities and differences in the corresponding plasma dynamics. The kinetic-Alfvén modes exist in the lower-frequency region of phase space, ω << k v{sub Ti} , where they are described by the kinetic-Alfvén system. These modes exist both below and above the ion-cyclotron frequency. The whistler modes, which are qualitatively different from the kinetic-Alfvén modes, occupy a different region of phase space, k v{sub Ti} << ω << k{sub z}v{sub Te} , and they are described by the electron magnetohydrodynamics (MHD) system or the reduced electron MHD system if the propagation is oblique. Here, k{sub z} and k are the wavenumbers along and transverse to the background magnetic field, respectively, and v{sub Ti} and v{sub Te} are the ion and electron thermal velocities, respectively. The models of subproton plasma turbulence are discussed and the results of numerical simulations are presented. We also point out possible implications for solar-wind observations.
Theory and observation of a dynamically evolviong negative ion plasma
Mendillo, M.; Forbes, J.
1982-10-01
As part of the Project Firefly ionospheric modification campaigns conducted during the early 1960's, sulfur hexafluoride (SF/sub 6/) was used to study the creation and consequences of artificially-induced electron depletion regions via the attachment process (SF/sub 6/+e..-->..SF/sub 6/). Since those early experiments, a great many advances have occurred in theoretical, laboratory, and diagnostic techniques related to negative ion plasmas. This study examines the full range of negative ion chemistry in the upper ionosphere by using current reaction rate data to investigate the many chemical paths SF/sub 6/ type injections might take in an F region environment. Particular attention is given to the conditions required to create heavy negative ions that persist long enough to affect the dynamical properties of the F region. The ambipolar diffusion characteristics of a three component plasma (O/sup +/, e/sup -/, SF/sub 6//sup -/) are described, and estimates of the incoherent scatter spectra obtained from such a plasma are presented. Model calculations using a first order chemical code are defined and tested to investigate the actual types of negative ion plasmas capable of being created under nighttime conditions. A versatile model for diffusion in an exponential atmosphere ws used to simulate the evolution of 10/sup 26/SF/sub 6/ molecules released at 222 km during a 1962 Firefly experiment. When examined in conjunction with the chemical model calculatins, the results suggest that the ionospheric perturbations recorded at the time probably resulted more from molecular and atomic ion neutralizations involving SF/sub 6//sup -/, SF/sub 5//sup +/, O/sup -/, O/sup +/, and epsilon/sup -/, rather than simple electron attachments, as had been expected. A similar use of SF/sub 6/ diffusion scenarios for high-altitude releases (h = 350-500 km) indicates that large-scale, long-lived negative ion plasmas could be produced by modest rocket or Shuttle-borne payloads to study
Geomagnetic polarity epochs: Sierra Nevada II
Cox, A.; Doell, Richard R.; Brent, Dalrymple G.
1963-01-01
Ten new determinations on volcanic extrusions in the Sierra Nevada with potassium-argon ages of 3.1 million years or less indicate that the remanent magnetizations fall into two groups, a normal group in which the remanent magnetization is directed downward and to the north, and a reversed group magnetized up and to the south. Thermomagnetic experiments and mineralogic studies fail to provide an explanation of the opposing polarities in terms of mineralogic control, but rather suggest that the remanent magnetization reflects reversals of the main dipole field of the earth. All available radiometric ages are consistent with this field-reversal hypothesis and indicate that the present normal polarity epoch (N1) as well as the previous reversed epoch (R1) are 0.9 to 1.0 million years long, whereas the previous normal epoch (N2) was at least 25 percent longer.
Geomagnetic Polarity Epochs: Sierra Nevada II.
Cox, A; Doell, R R; Dalrymple, G B
1963-10-18
Ten new determinations on volcanic extrusions in the Sierra Nevada with potassium-argon ages of 3.1 million years or less indicate that the remanent magnetizations fall into two groups, a normal group in which the remanent magnetization is directed downward and to the north, and a reversed group magnetized up and to the south. Thermomagnetic experiments and mineralogic studies fail to provide an explanation of the opposing polarities in terms of mineralogic control, but rather suggest that the remanent magnetization reflects reversals of the main dipole field of the earth. All available radiometric ages are consistent with this field-reversal hypothesis and indicate that the present normal polarity epoch (N1) as well as the previous reversed epoch (R1) are 0.9 to 1.0 million years long, whereas the previous normal epoch (N2) was at least 25 percent longer. PMID:17799480
Gyrokinetic stability theory of electron-positron plasmas
NASA Astrophysics Data System (ADS)
Helander, P.; Connor, J. W.
2016-06-01
> The linear gyrokinetic stability properties of magnetically confined electron-positron plasmas are investigated in the parameter regime most likely to be relevant for the first laboratory experiments involving such plasmas, where the density is small enough that collisions can be ignored and the Debye length substantially exceeds the gyroradius. Although the plasma beta is very small, electromagnetic effects are retained, but magnetic compressibility can be neglected. The work of a previous publication (Helander, Phys. Rev. Lett., vol. 113, 2014a, 135003) is thus extended to include electromagnetic instabilities, which are of importance in closed-field-line configurations, where such instabilities can occur at arbitrarily low pressure. It is found that gyrokinetic instabilities are completely absent if the magnetic field is homogeneous: any instability must involve magnetic curvature or shear. Furthermore, in dipole magnetic fields, the stability threshold for interchange modes with wavelengths exceeding the Debye radius coincides with that in ideal magnetohydrodynamics. Above this threshold, the quasilinear particle flux is directed inward if the temperature gradient is sufficiently large, leading to spontaneous peaking of the density profile.
Synchronization Phenomena and Epoch Filter of Electroencephalogram
NASA Astrophysics Data System (ADS)
Matani, Ayumu
Nonlinear electrophysiological synchronization phenomena in the brain, such as event-related (de)synchronization, long distance synchronization, and phase-reset, have received much attention in neuroscience over the last decade. These phenomena contain more electrical than physiological keywords and actually require electrical techniques to capture with electroencephalography (EEG). For instance, epoch filters, which have just recently been proposed, allow us to investigate such phenomena. Moreover, epoch filters are still developing and would hopefully generate a new paradigm in neuroscience from an electrical engineering viewpoint. Consequently, electrical engineers could be interested in EEG once again or from now on.
An effective field theory approach to the stabilization of 8Be in a QED plasma
NASA Astrophysics Data System (ADS)
Yao, Xiaojun; Mehen, Thomas; Müller, Berndt
2016-07-01
We use effective field theory to study the α –α resonant scattering in a finite-temperature QED plasma. The static plasma screening effect causes the resonance state 8Be to live longer and eventually leads to the formation of a bound state when {m}{{D}}≳ 0.3 {{MeV}}. We speculate that this effect may have implications on the rates of cosmologically and astrophysically relevant nuclear reactions involving α particles.
An effective field theory approach to the stabilization of 8Be in a QED plasma
NASA Astrophysics Data System (ADS)
Yao, Xiaojun; Mehen, Thomas; Müller, Berndt
2016-07-01
We use effective field theory to study the α -α resonant scattering in a finite-temperature QED plasma. The static plasma screening effect causes the resonance state 8Be to live longer and eventually leads to the formation of a bound state when {m}{{D}}≳ 0.3 {{MeV}}. We speculate that this effect may have implications on the rates of cosmologically and astrophysically relevant nuclear reactions involving α particles.
Kinetic Theory of Meteor Plasma in the Earth's atmosphere: Implications for Radar Head Echo
NASA Astrophysics Data System (ADS)
Dimant, Y. S.; Oppenheim, M. M.
2015-12-01
Every second millions of tiny meteoroids hit the Earth from space, vast majority too small to be observed visually. However, radars detect the plasma they generate and use the collected data to characterize the incoming meteoroids and the atmosphere in which they disintegrate. This diagnostics requires a detailed quantitative understanding of formation of the meteor plasma and how it interacts with the Earth's atmosphere. Fast-descending meteoroids become detectable to radars after they heat due to collisions with atmospheric molecules sufficiently and start ablating. The ablated material then collides into atmospheric molecules and forms plasma around the meteoroid. Reflection of radar pulses from this plasma produces a localized signal called a head echo often accompanied by a much longer non-specular trail (see the Figure). Using first principles, we have developed a consistent collisional kinetic theory of the near-meteoroid plasma responsible for the radar head echo. This theory produces analytic expressions describing the ion and neutral velocity distributions along with the detailed 3-D spatial structure of the near-meteoroid plasma. These expressions predict a number of unexpected features such as shell-like velocity distributions. This theory shows that the meteoroid plasma develops over a length-scale close to the ion mean free path with a strongly non-Maxwellian velocity distribution. The spatial distribution of the plasma density shows significant deviations from a Gaussian law usually employed in head-echo modeling. This analytical model will serve as a basis for a more accurate quantitative interpretation of radar measurements, estimates of the ionization efficiency, and should help calculate meteoroid and atmosphere parameters from radar head-echo observations. This theory could also help clarify the physical nature of electromagnetic pulses observed during recent meteor showers and associated with the passage of fast-moving meteors through the
Fokker Planck and Krook theory of energetic electron transport in a laser produced plasma
Manheimer, Wallace; Colombant, Denis
2015-09-15
Various laser plasma instabilities, such as the two plasma decay instability and the stimulated Raman scatter instability, produce large quantities of energetic electrons. How these electrons are transported and heat the plasma are crucial questions for laser fusion. This paper works out a Fokker Planck and Krook theory for such transport and heating. The result is a set of equations, for which one can find a simple asymptotic approximation for the solution, for the Fokker Planck case, and an exact solution for the Krook case. These solutions are evaluated and compared with one another. They give rise to expressions for the spatially dependent heating of the background plasma, as a function of the instantaneous laser and plasma parameters, in either planar or spherical geometry. These formulas are simple, universal (depending weakly only on the single parameter Z, the charge state), and can be easily be incorporated into a fluid simulation.
Kinetic theory of a two-dimensional magnetized plasma. II - Balescu-Lenard limit.
NASA Technical Reports Server (NTRS)
Vahala, G.
1972-01-01
The kinetic theory of a two-dimensional one-species plasma in a uniform dc magnetic field is investigated in the small plasma parameter limit. The plasma consists of charged rods interacting through the logarithmic Coulomb potential. Vahala and Montgomery earlier (1971) derived a Fokker-Planck equation for this system, but it contained a divergent integral, which had to be cut off on physical grounds. This cutoff is compared to the standard cutoff introduced in the two-dimensional unmagnetized Fokker-Planck equation. In the small plasma parameter limit, it is shown that the Balescu-Lenard collision term is zero in the long time average limit if only two-body interactions are considered. The energy transfer from a test particle to an equilibrium plasma is discussed and is also shown to be zero in the long time average limit. This supports the unexpected result of zero Balescu-Lenard collision term.
Fokker Planck and Krook theory of energetic electron transport in a laser produced plasma
NASA Astrophysics Data System (ADS)
Manheimer, Wallace; Colombant, Denis
2015-09-01
Various laser plasma instabilities, such as the two plasma decay instability and the stimulated Raman scatter instability, produce large quantities of energetic electrons. How these electrons are transported and heat the plasma are crucial questions for laser fusion. This paper works out a Fokker Planck and Krook theory for such transport and heating. The result is a set of equations, for which one can find a simple asymptotic approximation for the solution, for the Fokker Planck case, and an exact solution for the Krook case. These solutions are evaluated and compared with one another. They give rise to expressions for the spatially dependent heating of the background plasma, as a function of the instantaneous laser and plasma parameters, in either planar or spherical geometry. These formulas are simple, universal (depending weakly only on the single parameter Z, the charge state), and can be easily be incorporated into a fluid simulation.
Hydrodynamic theory for ion structure and stopping power in quantum plasmas.
Shukla, P K; Akbari-Moghanjoughi, M
2013-04-01
We present a theory for the dynamical ion structure factor (DISF) and ion stopping power in an unmagnetized collisional quantum plasma with degenerate electron fluids and nondegenerate strongly correlated ion fluids. Our theory is based on the fluctuation dissipation theorem and the quantum plasma dielectric constant that is deduced from a linearized viscoelastic quantum hydrodynamical (LVQHD) model. The latter incorporates the essential physics of quantum forces, which are associated with the quantum statistical pressure, electron-exchange, and electron-correlation effects, the quantum electron recoil effect caused by the dispersion of overlapping electron wave functions that control the dynamics of degenerate electron fluids, and the viscoelastic properties of strongly correlated ion fluids. Both degenerate electrons and nondegenerate strongly correlated ions are coupled with each other via the space charge electric force. Thus, our LVQHD theory is valid for a collisional quantum plasma at atomic scales with a wide range of the ion coupling parameter, the plasma composition, and plasma number densities that are relevant for compressed plasmas in laboratories (inertial confinement fusion schemes) and in astrophysical environments (e.g., warm dense matter and the cores of white dwarf stars). It is found that quantum electron effects and viscoelastic properties of strongly correlated ions significantly affect the features of the DISF and the ion stopping power (ISP). Unlike previous theories, which have studied ion correlations in terms of the ion coupling parameter, by neglecting the essential physics of collective effects that are competing among each other, we have here developed a method to evaluate the dependence of the plasma static and dynamical features in terms of individual parameters, like the Wigner-Seitz radius, the ion atomic number, and the ion temperature. It is found that due to the complex nature of charge screening in quantum plasmas, the ion
Hydrodynamic theory for ion structure and stopping power in quantum plasmas.
Shukla, P K; Akbari-Moghanjoughi, M
2013-04-01
We present a theory for the dynamical ion structure factor (DISF) and ion stopping power in an unmagnetized collisional quantum plasma with degenerate electron fluids and nondegenerate strongly correlated ion fluids. Our theory is based on the fluctuation dissipation theorem and the quantum plasma dielectric constant that is deduced from a linearized viscoelastic quantum hydrodynamical (LVQHD) model. The latter incorporates the essential physics of quantum forces, which are associated with the quantum statistical pressure, electron-exchange, and electron-correlation effects, the quantum electron recoil effect caused by the dispersion of overlapping electron wave functions that control the dynamics of degenerate electron fluids, and the viscoelastic properties of strongly correlated ion fluids. Both degenerate electrons and nondegenerate strongly correlated ions are coupled with each other via the space charge electric force. Thus, our LVQHD theory is valid for a collisional quantum plasma at atomic scales with a wide range of the ion coupling parameter, the plasma composition, and plasma number densities that are relevant for compressed plasmas in laboratories (inertial confinement fusion schemes) and in astrophysical environments (e.g., warm dense matter and the cores of white dwarf stars). It is found that quantum electron effects and viscoelastic properties of strongly correlated ions significantly affect the features of the DISF and the ion stopping power (ISP). Unlike previous theories, which have studied ion correlations in terms of the ion coupling parameter, by neglecting the essential physics of collective effects that are competing among each other, we have here developed a method to evaluate the dependence of the plasma static and dynamical features in terms of individual parameters, like the Wigner-Seitz radius, the ion atomic number, and the ion temperature. It is found that due to the complex nature of charge screening in quantum plasmas, the ion
Avetissian, H K; Ghazaryan, A G; Matevosyan, H H; Mkrtchian, G F
2015-10-01
The microscopic quantum theory of plasma nonlinear interaction with the coherent shortwave electromagnetic radiation of arbitrary intensity is developed. The Liouville-von Neumann equation for the density matrix is solved analytically considering a wave field exactly and a scattering potential of plasma ions as a perturbation. With the help of this solution we calculate the nonlinear inverse-bremsstrahlung absorption rate for a grand canonical ensemble of electrons. The latter is studied in Maxwellian, as well as in degenerate quantum plasma for x-ray lasers at superhigh intensities and it is shown that one can achieve the efficient absorption coefficient in these cases.
Ideal magnetohydrodynamic theory for localized interchange modes in toroidal anisotropic plasmas
NASA Astrophysics Data System (ADS)
Shi, Tonghui; Zheng, L. J.; Wan, B. N.; Sun, Y.; Shen, B.; Qian, J. P.
2016-08-01
Ideal magnetohydrodynamic theory for localized interchange modes is developed for toroidal plasmas with anisotropic pressure. The work extends the existing theories of Johnson and Hastie [Phys. Fluids 31, 1609 (1988)], etc., to the low n mode case, where n is the toroidal mode number. Also, the plasma compressibility is included, so that the coupling of the parallel motion to perpendicular one, i.e., the so-called apparent mass effect, is investigated in the anisotropic pressure case. The singular layer equation is obtained, and the generalized Mercier's criterion is derived.
Analysis of modern optimal control theory applied to plasma position and current control in TFTR
Firestone, M.A.
1981-09-01
The strong compression TFTR discharge has been segmented into regions where linear dynamics can approximate the plasma's interaction with the OH and EF power supply systems. The dynamic equations for these regions are utilized within the linear optimal control theory framework to provide active feedback gains to control the plasma position and current. Methods are developed to analyze and quantitatively evaluate the quality of control in a nonlinear, more realistic simulation. Tests are made of optimal control theory's assumptions and requirements, and the feasibility of this method for TFTR is assessed.
Theory of self-organized critical transport in tokamak plasmas
Kishimoto, Y.; Tajima, T.; Horton, W.; LeBrun, M.J.; Kim, J.Y. |
1995-07-01
A theoretical and computational study of the ion temperature gradient and {eta}{sub i} instabilities in tokamak plasmas has been carried out. In toroidal geometry the modes have a radially extended structure and their eigenfrequencies are constant over many rational surfaces that are coupled through toroidicity. These nonlocal properties of the ITG modes impose strong constraint on the drift mode fluctuations and the amciated transport, showing a self-organized characteristic. As any significant deviation away from marginal stability causes rapid temperature relaxation and intermittent bursts, the modes hover near marginality and exhibit strong kinetic characteristics. As a result, the temperature relaxation is self-semilar and nonlocal, leading to a radially increasing heat diffusivity. The nonlocal transport leads to the Bohm-like diffusion scaling. The heat input regulates the deviation of the temperature gradient away from marginality. The obtained transport scalings and properties are globally consistent with experimental observations of L-mode charges.
Scale-free transport in fusion plasmas: theory and applications
NASA Astrophysics Data System (ADS)
Sanchez, R.; Mier, J. A.; Newman, D. E.; Carreras, B. A.; Garcia, L.; Leboeuf, J. N.; Decyk, V.
2008-11-01
A novel approach to detect the existence of scale-free transport in turbulent flows, based on the characterization of its Lagrangian characteristics, is presented and applied to two situations relevant for tokamak plasmas. The first one, radial transport in the presence of near-critical turbulence, has been known for quite some time to yield scale-free, superdiffusive transport. We use it to test the method and illustrate its robustness with respect to other approaches. The second situation, radial transport across radially-sheared poloidal zonal flows driven by turbulence via the Reynold stresses, is examined for the first time in this manner. The result is rather surprising and different from the traditionally assumed diffusive behavior. Instead, radial transport behaves instead in a scale-free, subdiffusive manner, which may have implications for the modeling of transport across transport barriers.
Fusion Plasma Theory: Task 3, Auxiliary radiofrequency heating of tokamaks
Scharer, J.E.
1992-01-01
The research performed under this grant during the past year has been concentrated on the following several key tokamak ICRF (Ion Cyclotron Range of Frequencies) coupling, heating and current drive issues: Efficient coupling during the L- to H- mode transition by analysis and computer simulation of ICRF antennas; analysis of ICRF cavity-backed coil antenna coupling to plasma edge profiles including fast and ion Bernstein wave coupling for heating and current drive; benchmarking the codes to compare with current JET, D-IIID and ASDEX experimental results and predictions for advanced tokamaks such as BPX and SSAT (Steady-State Advanced Tokamak); ICRF full-wave field solutions, power conservation, heating analyses and minority ion current drive; and the effects of fusion alpha particle or ion tail populations on the ICRF absorption. Research progress, publications, and conference and workshop presentations are summarized in this report.
Kinetic theory of a two-dimensional magnetized plasma.
NASA Technical Reports Server (NTRS)
Vahala, G.; Montgomery, D.
1971-01-01
Several features of the equilibrium and nonequilibrium statistical mechanics of a two-dimensional plasma in a uniform dc magnetic field are investigated. The charges are assumed to interact only through electrostatic potentials. The problem is considered both with and without the guiding-center approximation. With the guiding-center approximation, an appropriate Liouville equation and BBGKY hierarchy predict no approach to thermal equilibrium for the spatially uniform case. For the spatially nonuniform situation, a guiding-center Vlasov equation is discussed and solved in special cases. For the nonequilibrium, nonguiding-center case, a Boltzmann equation, and a Fokker-Planck equation are derived in the appropriate limits. The latter is more tractable than the former, and can be shown to obey conservation laws and an H-theorem, but contains a divergent integral which must be cut off on physical grounds. Several unsolved problems are posed.
Theory of self-organized critical transport in tokamak plasmas
Kishimoto, Y.; Tajima, T.; Horton, W.; LeBrun, M.J.; Kim, J.Y.
1996-04-01
A theoretical and computational study of the ion temperature gradient (ITG) and {eta}{sub {ital i}} instabilities in tokamak plasmas has been carried out. In a toroidal geometry the modes have a radially extended structure and their eigenfrequencies are constant over many rational surfaces that are coupled through toroidicity. These nonlocal properties of the ITG modes impose a strong constraint on the drift mode fluctuations and the associated transport, showing self-organized criticality. As any significant deviation away from marginal stability causes rapid temperature relaxation and intermittent bursts, the modes hover near marginality and exhibit strong kinetic characteristics. As a result of this, the temperature relaxation is self-similar and nonlocal, leading to radially increasing heat diffusivity. The nonlocal transport leads to Bohm-like diffusion scaling. Heat input regulates the deviation of the temperature gradient away from marginality. We present a critical gradient transport model that describes such a self-organized relaxed state. Some of the important aspects in tokamak transport like Bohm diffusion, near marginal stability, radially increasing fluctuation energy and heat diffusivity, intermittency of the wave excitation, and resilient tendency of the plasma profile can be described by this model, and these prominent features are found to belong to one physical category that originates from the radially extended nonlocal drift modes. The obtained transport properties and scalings are globally consistent with experimental observations of low confinement mode (L-mode) discharges. The nonlocal modes can be disintegrated into smaller radial islands by a poloidal shear flow, suggesting that the transport changes from Bohm-like to near gyro-Bohm. {copyright} {ital 1996 American Institute of Physics.}
Theory of plasma waves in the auroral E region
NASA Technical Reports Server (NTRS)
Fejer, B. G.; Providakes, J.; Farley, D. T.
1984-01-01
A general theory is developed for both electrojet waves and ion cyclotron and current convective waves observed above 120 km altitude. Previously defined electrojet instability theories are extended to encompass the effects of the magnetic field on ions and the presence of field-aligned currents. The ion-cyclotron (E) waves are assumed produced by the two-stream instability in regions dominated by ion magnetization effects. Field-aligned and cross-field currents drive the E waves, which have displayed threshold drift velocities (TDV) sensitive to conditions at altitudes with effective electron/ion and anomalous electron collision frequencies. The electron density gradients in the region affect the magnitude of the TDV for waves on scales of tens of meters. Recombinational damping increases the TDV for marginal damping of two-stream E waves and establishes a TDV for excitation of large-scale gradient drift waves which propagate nearly perpendicularly to the magnetic field and may have only 10-20 m wavelengths.
Theory of spatially non-symmetric kinetic equilibria for collisionless plasmas
Cremaschini, Claudio; Tessarotto, Massimo
2013-01-15
The problem posed by the possible existence/non-existence of spatially non-symmetric kinetic equilibria has remained unsolved in plasma theory. For collisionless magnetized plasmas, this involves the construction of stationary solutions of the Vlasov-Maxwell equations. In this paper, the issue is addressed for non-relativistic plasmas both in astrophysical and laboratory contexts. The treatment is based on a Lagrangian variational description of single-particle dynamics. Starting point is a non-perturbative formulation of gyrokinetic theory, which allows one to construct 'a posteriori' with prescribed order of accuracy an asymptotic representation for the magnetic moment. In terms of the relevant particle adiabatic invariants generalized bi-Maxwellian equilibria are proved to exist. These are shown to recover, under suitable assumptions, a Chapman-Enskog form which permits an analytical treatment of the corresponding fluid moments. In particular, the constrained posed by the Poisson and the Ampere equations are analyzed, both for quasi-neutral and non-neutral plasmas. The conditions of existence of the corresponding non-symmetric kinetic equilibria are investigated. As a notable feature, both astrophysical and laboratory plasmas are shown to exhibit, under suitable conditions, a kinetic dynamo, whereby the equilibrium magnetic field can be self-generated by the equilibrium plasma currents.
Birdsall, C.K.
1989-12-31
This is a brief progress report, covering our research in general plasma theory and simulation, plasma-wall physics theory and simulation, and code development. Reports written in this period are included with this mailing. A publications list plus abstracts for two major meetings are included.
Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.
NASA Technical Reports Server (NTRS)
Canuto, V.; Ventura, J.
1972-01-01
A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.
Very high Mach number shocks - Theory. [in space plasmas
NASA Technical Reports Server (NTRS)
Quest, Kevin B.
1986-01-01
The theory and simulation of collisionless perpendicular supercritical shock structure is reviewed, with major emphasis on recent research results. The primary tool of investigation is the hybrid simulation method, in which the Newtonian orbits of a large number of ion macroparticles are followed numerically, and in which the electrons are treated as a charge neutralizing fluid. The principal results include the following: (1) electron resistivity is not required to explain the observed quasi-stationarity of the earth's bow shock, (2) the structure of the perpendicular shock at very high Mach numbers depends sensitively on the upstream value of beta (the ratio of the thermal to magnetic pressure) and electron resistivity, (3) two-dimensional turbulence will become increasingly important as the Mach number is increased, and (4) nonadiabatic bulk electron heating will result when a thermal electron cannot complete a gyrorbit while transiting the shock.
Theory and Fluid Simulations of Boundary Plasma Fluctuations
Cohen, R H; LaBombard, B; LoDestro, L L; Rognlien, T D; Ryutov, D D; Terry, J L; Umansky, M V; Xu, X Q; Zweben, S
2007-01-09
Theoretical and computational investigations are presented of boundary plasma microturbulence that take into account important effects of the geometry of diverted tokamaks--in particular, the effect of x-point magnetic shear and the termination of field lines on divertor plates. We first generalize our previous 'heuristic boundary condition' which describes, in a lumped model, the closure of currents in the vicinity of the x-point region to encompass three current-closure mechanisms. We then use this boundary condition to derive the dispersion relation for low-beta flute-like modes in the divertor-leg region under the combined drives of curvature, sheath impedance, and divertor tilt effects. The results indicate the possibility of strongly growing instabilities, driven by sheath boundary conditions, and localized in either the private or common flux region of the divertor leg depending on the radial tilt of divertor plates. We re-visit the issue of x-point effects on blobs, examining the transition from blobs terminated by x-point shear to blobs that extend over both the main SOL and divertor legs. We find that, for a main-SOL blob, this transition occurs without a free-acceleration period as previously thought, with x-point termination conditions applying until the blob has expanded to reach the divertor plate. We also derive propagation speeds for divertor-leg blobs. Finally, we present fluid simulations of the C-Mod tokamak from the BOUT edge fluid turbulence code, which show main-SOL blob structures with similar spatial characteristics to those observed in the experiment, and also simulations which illustrate the possibility of fluctuations confined to divertor legs.
Geomagnetic reversal in brunhes normal polarity epoch.
Smith, J D; Foster, J H
1969-02-01
The magnetic stratigraphly of seven cores of deep-sea sediment established the existence of a short interval of reversed polarity in the upper part of the Brunches epoch of normal polarity. The reversed zone in the cores correlates well with paleontological boundaries and is named the Blake event. Its boundaries are estimated to be 108,000 and 114,000 years ago +/- 10 percent. PMID:17750890
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
Profile of a low-Mach-number shock in two-fluid plasma theory
NASA Astrophysics Data System (ADS)
Gedalin, M.; Kushinsky, Y.; Balikhin, M.
2015-08-01
Magnetic profiles of low-Mach-number collisionless shocks in space plasmas are studied within the two-fluid plasma theory. Particular attention is given to the upstream magnetic oscillations generated at the ramp. By including weak resistive dissipation in the equations of motion for electrons and protons, the dependence of the upstream wave train features on the ratio of the dispersion length to the dissipative length is established quantitatively. The dependence of the oscillation amplitude and spatial damping scale on the shock normal angle θ is found.
Nonlinear theory of intense laser-plasma interactions modified by vacuum polarization effects
Chen, Wenbo; Bu, Zhigang; Li, Hehe; Luo, Yuee; Ji, Peiyong
2013-07-15
The classical nonlinear theory of laser-plasma interactions is corrected by taking account of the vacuum polarization effects. A set of wave equations are obtained by using the Heisenberg-Euler Lagrangian density and the derivative correction with the first-order quantum electrodynamic effects. A model more suitable to formulate the interactions of ultra-strong lasers and high-energy-density plasmas is developed. In the result, some environments in which the effects of vacuum polarization will be enhanced are discussed.
Superposed Epoch Analysis of Current Systems During Intense Magnetic Storms
NASA Astrophysics Data System (ADS)
Liemohn, M. W.; Katus, R. M.
2013-05-01
A statistical approach to investigating the intensity and timing of storm-time current systems is conducted and presented. The Hot Electron and Ion Drift Integrator (HEIDI) model was used to simulate all of the intense storms (Dstmin < -100 nT) from solar cycle 23 (1996-2005). Five different HEIDI input combinations were used to create a large collection of numerical results, varying the plasma outer boundary condition and electric field description in the model. The simulation results are then combined with a normalized superposed epoch analysis, where each phase of each storm is prorated to the average duration of that phase and then all of the storms are averaged together. The azimuthal currents in the HEIDI simulation domain are classified as westward and eastward symmetric ring current, partial ring current, banana current, and tail current. The average behavior of these current systems with respect to the HEIDI plasma and electric field boundary conditions are then presented and discussed. It is found that the Volland-Stern electric field produces an earlier increase in the inner magnetospheric current systems because of the usage of the 3-h Kp index. A self-consistent electric field develops the current systems a few hours later, but produces much stronger asymmetric current systems (partial, banana, and tail currents), especially in the main phase of the storm. Applying a nonuniform local time distribution for the plasma outer boundary condition slightly increases the magnitudes of the current systems, but this effect is smaller than the electric field influence.
NASA Astrophysics Data System (ADS)
Vinko, Sam
2014-10-01
An accurate description of the ionization potential depression (IPD) of ions in plasmas due to their interaction with the environment is a fundamental problem in plasma physics, playing a key role in determining the ionization balance, charge state distribution, opacity and plasma equation of state. Here I present the first experimental investigation of the IPD as a function of ionic charge state in a range of dense Mg, Al and Si plasmas, using the Linac Coherent Light Source X-ray free-electron laser. The measurements show significantly larger IPDs than are predicted by the most commonly used models, such as that of Stewart-Pyatt, or the ion-sphere model of Zimmerman-More. Instead, plasma simulations using finite-temperature density functional theory with excited-state projector augmented-wave potentials show excellent agreement with the experimental results and explain the stronger-than-expected continuum lowering through the electronic structure of the valence states in these strong-coupling conditions, which retain much of their atomic characteristics close to the ion core regions. These results have a profound impact on the understanding and modelling of plasmas over a wide range of warm- and hot-dense matter conditions.
Administering an epoch initiated for remote memory access
Blocksome, Michael A; Miller, Douglas R
2014-03-18
Methods, systems, and products are disclosed for administering an epoch initiated for remote memory access that include: initiating, by an origin application messaging module on an origin compute node, one or more data transfers to a target compute node for the epoch; initiating, by the origin application messaging module after initiating the data transfers, a closing stage for the epoch, including rejecting any new data transfers after initiating the closing stage for the epoch; determining, by the origin application messaging module, whether the data transfers have completed; and closing, by the origin application messaging module, the epoch if the data transfers have completed.
Administering an epoch initiated for remote memory access
Blocksome, Michael A; Miller, Douglas R
2012-10-23
Methods, systems, and products are disclosed for administering an epoch initiated for remote memory access that include: initiating, by an origin application messaging module on an origin compute node, one or more data transfers to a target compute node for the epoch; initiating, by the origin application messaging module after initiating the data transfers, a closing stage for the epoch, including rejecting any new data transfers after initiating the closing stage for the epoch; determining, by the origin application messaging module, whether the data transfers have completed; and closing, by the origin application messaging module, the epoch if the data transfers have completed.
Administering an epoch initiated for remote memory access
Blocksome, Michael A.; Miller, Douglas R.
2013-01-01
Methods, systems, and products are disclosed for administering an epoch initiated for remote memory access that include: initiating, by an origin application messaging module on an origin compute node, one or more data transfers to a target compute node for the epoch; initiating, by the origin application messaging module after initiating the data transfers, a closing stage for the epoch, including rejecting any new data transfers after initiating the closing stage for the epoch; determining, by the origin application messaging module, whether the data transfers have completed; and closing, by the origin application messaging module, the epoch if the data transfers have completed.
Application of linear response theory to magnetotransport properties of dense plasmas.
Adams, J R; Reinholz, H; Redmer, R
2010-03-01
Linear response theory, as developed within the Zubarev formalism, is a quantum statistical approach for describing systems out of but close to equilibrium, which has been successfully applied to a wide variety of plasmas in an external electric field and/or containing a temperature gradient. We present here an extension of linear response theory to include the effects of an external magnetic field. General expressions for the complete set of relevant transport properties are given. In particular, the Hall effect and the influence of a magnetic field on the dc electrical conductivity are discussed. Low-density limits including electron-electron scattering are presented as well as results for arbitrary degeneracy.
Application of linear response theory to magnetotransport properties of dense plasmas
Adams, J. R.; Redmer, R.; Reinholz, H.
2010-03-15
Linear response theory, as developed within the Zubarev formalism, is a quantum statistical approach for describing systems out of but close to equilibrium, which has been successfully applied to a wide variety of plasmas in an external electric field and/or containing a temperature gradient. We present here an extension of linear response theory to include the effects of an external magnetic field. General expressions for the complete set of relevant transport properties are given. In particular, the Hall effect and the influence of a magnetic field on the dc electrical conductivity are discussed. Low-density limits including electron-electron scattering are presented as well as results for arbitrary degeneracy.
Theory of type 3b solar radio bursts. [plasma interaction and electron beams
NASA Technical Reports Server (NTRS)
Smith, R. A.; Delanoee, J.
1975-01-01
During the initial space-time evolution of an electron beam injected into the corona, the strong beam-plasma interaction occurs at the head of the beam, leading to the amplification of a quasi-monochromatic large-amplitude plasma wave that stabilizes by trapping the beam particles. Oscillation of the trapped particles in the wave troughs amplifies sideband electrostatic waves. The sidebands and the main wave subsequently decay to observable transverse electromagnetic waves through the parametric decay instability. This process gives rise to the elementary striation bursts. Owing to velocity dispersion in the beam and the density gradient of the corona, the entire process may repeat at a finite number of discrete plasma levels, producing chains of elementary bursts. All the properties of the type IIIb bursts are accounted for in the context of the theory.
Robiche, J.; Rax, J.-M.; Bonnaud, G.; Gremillet, L.
2010-03-15
The collisional dynamics of a relativistic electron jet in a magnetized plasma are investigated within the framework of kinetic theory. The relativistic Fokker-Planck equation describing slowing down, pitch angle scattering, and cyclotron rotation is derived and solved. Based on the solution of this Fokker-Planck equation, an analytical formula for the root mean square spot size transverse to the magnetic field is derived and this result predicts a reduction in radial transport. Some comparisons with particle-in-cell simulation are made and confirm striking agreement between the theory and the simulation. For fast electron with 1 MeV typical kinetic energy interacting with a solid density hydrogen plasma, the energy deposition density in the transverse direction increases by a factor 2 for magnetic field of the order of 1 T. Along the magnetic field, the energy deposition profile is unaltered compared with the field-free case.
Two-dimensional finite element multigroup diffusion theory for neutral atom transport in plasmas
Hasan, M.Z.; Conn, R.W.
1986-02-01
Solution of the energy dependent diffusion equation in two dimensions is formulated by multigroup approximation of the energy variable and general triangular mesh, finite element discretization of the spatial domain. Finite element formulation is done by Galerkin's method. Based on this formulation, a two-dimensional multigroup finite element diffusion theory code, FENAT, has been developed for the transport of neutral atoms in fusion plasmas. FENAT solves the multigroup diffusion equation in X-Y cartesian and R-Z cylindrical/toroidal geometries. Use of the finite element method allows solution of problems in which the plasma cross-section has an arbitrary shape. The accuracy of FENAT has been verified by comparing results to those obtained using the two-dimensional discrete ordinate transport theory code, DOT-4.3. Results of application of FENAT to the transport of limiter-originated neutral atoms in a tokamak fusion machine are presented.
Bendib, A.
2008-09-23
The conference is devoted to the study of systems consisting of a large number of particles by using the kinetic theory. In a first part, we present a general overview of the kinetic theory. In particular, the role of the correlations between particles is shown and discussed through the main models reported in the literature. In a second part, we present three applications to the transport properties in plasmas and neutral gases. The first application is devoted to the transport in hot plasmas perturbed with respect to the global equilibrium. The quasi-static and collisionless distribution function and transport coefficients are established. The influence of relativistic effects is also discussed. The second application deals with strongly inhomogeneous magnetized plasmas. The transport coefficients of Braginskii are calculated numerically in the local and the weakly nonlocal approximations. New nonlocal transport coefficients are emphasized. Finally, we apply the kinetic theory to the neutral gases by calculating the semi-collisional dispersion relation of acoustic waves. In particular, the dispersion and the damping of these waves in rarefied gases are highlighted. The method used to solve the kinetic equations is compared with the conventional method of Chapman-Enskog.
Neoclassical transport theory in a tokamak plasma with large spatial gradients
Chang, C.S.
1996-12-31
Usual neoclassical theories assumed that the spatical inhomogeneity of the plasma was weak. Specifically, this included the following two strong assumptions: banana width was negligible compared to the radial gradient scale length and variation of any physical quantity along the field line was small. This led to the simplification that the spatial inhomogeneity itself did not affect the fundamental transport processes. However, there have been many experimental suggestions that the spatial inhomogeneity may not be small. Firstly, both H-mode and ERS mode experiments have indicated that the finite banana width effect may be important to understand the plasma transport processes. Secondly, the RF and auxiliary heating processes may be sufficiently localized in space so that we may need to consider a strongly inhomogeneous heating effect along the field lines. In the present work we develop a modified neoclassical theory, in parallel with the old theories, which can include the finite banana width effect and the inhomogeneous heating effect. Several new and significant transport terms have been identified, which can play important roles in the understanding of the fundamental transport processes in a tokamak plasma.
Geomagnetic polarity epochs: Nunivak Island, Alaska
Cox, A.; Dalrymple, G.B.
1967-01-01
New paleomagnetic and potassium-argon dating measurements have been made of basalt flows from Nunivak Island, Alaska, with the following results. (1) The best estimate of the age of the Brunhes/Matuyama polarity epoch boundary is found to be 0.694 m.y. (2) The best estimate of the age of the Gauss/Gilbert boundary is 3.32 m.y. (3) Three normally magnetized flows with ages from 0.93 to 0.88 m.y. are in accord with previous estimates of the age and duration of the Jaramillo normal event. (4) One normally magnetized flow with an age of 1.65 ?? 0.09 m.y. supplies additional evidence for the Gilsa?? normal event. (5) Two new normal events are identified within the Gilbert reversed epoch, the "Cochiti normal event" with an age of 3.7 m.y. and the "Nunivak normal event" with an age of 4.1 m.y. ?? 1967.
Galaxies in the Epoch of Reionization
NASA Astrophysics Data System (ADS)
Livermore, Rachael C.
2015-08-01
The CANDELS survey has revolutionized the study of galaxies in the epoch of reionization, with the wide field and near-infrared coverage enabling the discovery of candidates for the brightest galaxies in the crucial redshift range 6 < z < 9. I will present results from spectroscopic followup of these candidates with Keck/MOSFIRE and DEIMOS, and will discuss the implications for reionization of the rapid drop-off in detection of Lyman alpha emission between z~6 and z~7.Complementing the results from CANDELS, the Hubble Frontier Fields open up the faint end of the luminosity function with their combination of deep HST imaging and magnification from gravitational lensing. I will discuss methods of removing the foreground galaxies and intracluster light through modelling and wavelet decomposition. This enables us to detect the faintest high-redshift galaxies in the fields, and provides insight into the faint-end slope of the luminosity function at 6 < z < 9, revealing the galaxies believed to be responsible for the bulk of the energy contributing to reionization in this epoch.
The applications of Complexity Theory and Tsallis Non-extensive Statistics at Solar Plasma Dynamics
NASA Astrophysics Data System (ADS)
Pavlos, George
2015-04-01
As the solar plasma lives far from equilibrium it is an excellent laboratory for testing complexity theory and non-equilibrium statistical mechanics. In this study, we present the highlights of complexity theory and Tsallis non extensive statistical mechanics as concerns their applications at solar plasma dynamics, especially at sunspot, solar flare and solar wind phenomena. Generally, when a physical system is driven far from equilibrium states some novel characteristics can be observed related to the nonlinear character of dynamics. Generally, the nonlinearity in space plasma dynamics can generate intermittent turbulence with the typical characteristics of the anomalous diffusion process and strange topologies of stochastic space plasma fields (velocity and magnetic fields) caused by the strange dynamics and strange kinetics (Zaslavsky, 2002). In addition, according to Zelenyi and Milovanov (2004) the complex character of the space plasma system includes the existence of non-equilibrium (quasi)-stationary states (NESS) having the topology of a percolating fractal set. The stabilization of a system near the NESS is perceived as a transition into a turbulent state determined by self-organization processes. The long-range correlation effects manifest themselves as a strange non-Gaussian behavior of kinetic processes near the NESS plasma state. The complex character of space plasma can also be described by the non-extensive statistical thermodynamics pioneered by Tsallis, which offers a consistent and effective theoretical framework, based on a generalization of Boltzmann - Gibbs (BG) entropy, to describe far from equilibrium nonlinear complex dynamics (Tsallis, 2009). In a series of recent papers, the hypothesis of Tsallis non-extensive statistics in magnetosphere, sunspot dynamics, solar flares, solar wind and space plasma in general, was tested and verified (Karakatsanis et al., 2013; Pavlos et al., 2014; 2015). Our study includes the analysis of solar plasma time
Theory and computer simulation of a new type of plasma Cherenkov maser
Pointon, T.D.
1986-01-01
Theory and computer simulation of a new experimental high-power microwave generator is presented. In this device, a circular waveguide is partially filled with a dense annular plasma. When an intense relativistic electron-beam pulse passes through the central vacuum region, microwaves are emitted with high efficiency (less than or equal to 20%). The plasma creates slow (i.e., v/sub ph/ < c) TM modes in the waveguide. The radiation mechanism is stimulated Cherenkov emission of these slow TM waves by the beam electrons. The linear theory is analyzed first. A dispersion relation and field-structure equations are derived for the azimuthally symmetric TM modes of this system. Numerical solutions demonstrate the existence of the slow TM waves without the beam, and confirm that some are unstable in the presence of the beam. To analyze the nonlinear theory, a new particle-simulation code was developed. This code is described in detail, and results of simulations of the experimental device are presented. In these simulations, the system initially evolves in good quantitative agreement with linear theory, while the nonlinear saturation amplitudes are consistent with experimentally observed efficiencies. Saturation of linear instability is shown to be due to trapping of the beam electrons, and the saturation amplitudes agree quite well with a simple trapping model
NASA Astrophysics Data System (ADS)
Thomas, Johannes; Kostyukov, Igor Yu.; Pronold, Jari; Golovanov, Anton; Pukhov, Alexander
2016-05-01
We introduce a complete semi-analytical model for a cavitated electron wake driven by an electron beam in a radially inhomogeneous plasma. The electron response to the driver, dynamics of electrons in a thin sheath surrounding the cavity, as well as accelerating and focusing fields inside the cavity are calculated in the quasistatic approximation. Our theory holds for arbitrary radial density profiles and reduces to known models in the limit of a homogeneous plasma. A free-propagating blow-out in an evacuated channel experiences longitudinal squeezing, qualitatively the same as observed in particle-in-cell simulations for the laser pulse-driven case [Pukhov et al., Phys. Rev. Lett. 113, 245003 (2014)]. Our model also permits qualitative interpretation of the earlier observed cancellation of the focusing gradient in the cavity [Pukhov et al., Phys. Rev. Lett. 113, 245003 (2014)]. In this work, we show the underlying mechanism that causes the radial fields in the vacuum part of a channel to become defocussing.
PREFACE: Theory of Fusion Plasmas, 13th Joint Varenna-Lausanne International Workshop (2012)
NASA Astrophysics Data System (ADS)
Garbet, Xavier; Sauter, Olivier
2012-12-01
The 2012 joint Varenna-Lausanne international workshop on the theory of fusion plasmas has been very fruitful. A broad variety of topics were addressed, as usual covering turbulence, MHD, edge physic, RF wave heating and a taste of astrophysics. Moreover the scope of the meeting was extended this year to include the physics of materials and diagnostics for burning plasmas. This evolution reflects the complexity of problems at hand in fusion, in particular in the context of ITER construction. Long-standing problems without immediate consequences have sometimes become an urgent matter in that context. One may quote for instance the choice of plasma facing components or the design of control systems. Another characteristic of the meeting is the interplay between various domains of plasma physics. For instance MHD modes are now currently investigated with gyrokinetic codes, kinetic effects are more and more included in MHD stability analysis, and turbulence is now accounted for in wave propagation problems. This is the proof of cross-fertilization and it is certainly a healthy sign in our community. Finally introducing some novelty in the programme does not prevent us from respecting the traditions of the meeting. As usual a good deal of the presentations were dedicated to numerical simulations. Combining advanced numerical techniques with elaborated analytical theory is certainly a trademark of the Varenna-Lausanne conference, which was respected again this year. The quality and size of the scientific production is illustrated by the 26 papers which appear in the present volume of Journal of Physics: Conference Series, all refereed. We would also like to mention another set of 20 papers to be published in Plasma Physics and Controlled Fusion. We hope the readers will enjoy this special issue of JPCS and the one to come in PPCF. Xavier Garbet and Olivier Sauter October 26, 2012
Cremaschini, Claudio; Stuchlík, Zdeněk; Tessarotto, Massimo
2013-05-15
The problem of formulating a kinetic treatment for quasi-stationary collisionless plasmas in axisymmetric systems subject to the possibly independent presence of local strong velocity-shear and supersonic rotation velocities is posed. The theory is developed in the framework of the Vlasov-Maxwell description for multi-species non-relativistic plasmas. Applications to astrophysical accretion discs arising around compact objects and to plasmas in laboratory devices are considered. Explicit solutions for the equilibrium kinetic distribution function (KDF) are constructed based on the identification of the relevant particle adiabatic invariants. These are shown to be expressed in terms of generalized non-isotropic Gaussian distributions. A suitable perturbative theory is then developed which allows for the treatment of non-uniform strong velocity-shear/supersonic plasmas. This yields a series representation for the equilibrium KDF in which the leading-order term depends on both a finite set of fluid fields as well as on the gradients of an appropriate rotational frequency. Constitutive equations for the fluid number density, flow velocity, and pressure tensor are explicitly calculated. As a notable outcome, the discovery of a new mechanism for generating temperature and pressure anisotropies is pointed out, which represents a characteristic feature of plasmas considered here. This is shown to arise as a consequence of the canonical momentum conservation and to contribute to the occurrence of temperature anisotropy in combination with the adiabatic conservation of the particle magnetic moment. The physical relevance of the result and the implications of the kinetic solution for the self-generation of quasi-stationary electrostatic and magnetic fields through a kinetic dynamo are discussed.
Unification of Plasma Fluid and Kinetic Theory via Gaussian Radial Basis Functions
NASA Astrophysics Data System (ADS)
Candy, J. M.
2015-11-01
A fundamental macroscopic description of a magnetized plasma is the Vlasov equation supplemented by the nonlinear inverse-square force Fokker-Planck collision operator [Rosenbluth et al., Phys. Rev. 107, 1957]. The Vlasov part describes advection in a six-dimensional phase space whereas the collision operator contains friction and diffusion coefficients that are weighted velocity-space integrals of the particle distribution function. The Fokker-Planck collision operator is an integro-differential, nonlinear (bilinear) operator. Numerical discretization of the operator, in particular for collisions of unlike species, is extremely challenging. In this work, we describe a new approach to discretize the entire kinetic system based on an expansion in Gaussian Radial Basis functions (RBFs). This approach is particularly well-suited to treat the collision operator because the friction and diffusion coefficients can be analytically calculated. Although the RBF method is known to be a powerful scheme for the interpolation of scattered multidimensional data, Gaussian RBFs also have a deep physical interpretation in statistical mechanics and plasma physics as local thermodynamic equilibria. We outline the general theory, highlight the connection to plasma fluid theories, and also give 2D and 3D numerical solutions of the nonlinear Fokker-Planck equation. A broad spectrum of applications for the new method is anticipated in both astrophysical and laboratory plasmas. In particular, we believe that the RBF method may provide a new bridge between fluid and kinetic descriptions of magnetized plasma. Work supported in part by US DOE under DE-FG02-08ER54963.
Cremaschini, Claudio; Kovář, Jiří; Slaný, Petr; Stuchlík, Zdeněk; Karas, Vladimír
2013-11-01
The possible occurrence of equilibrium off-equatorial tori in the gravitational and electromagnetic fields of astrophysical compact objects has been recently proved based on non-ideal magnetohydrodynamic theory. These stationary structures can represent plausible candidates for the modeling of coronal plasmas expected to arise in association with accretion disks. However, accretion disk coronae are formed by a highly diluted environment, and so the fluid description may be inappropriate. The question is posed of whether similar off-equatorial solutions can also be determined in the case of collisionless plasmas for which treatment based on kinetic theory, rather than a fluid one, is demanded. In this paper the issue is addressed in the framework of the Vlasov-Maxwell description for non-relativistic, multi-species axisymmetric plasmas subject to an external dominant spherical gravitational and dipolar magnetic field. Equilibrium configurations are investigated and explicit solutions for the species kinetic distribution function are constructed, which are expressed in terms of generalized Maxwellian functions characterized by isotropic temperature and non-uniform fluid fields. The conditions for the existence of off-equatorial tori are investigated. It is proved that these levitating systems are admitted under general conditions when both gravitational and magnetic fields contribute to shaping the spatial profiles of equilibrium plasma fluid fields. Then, specifically, kinetic effects carried by the equilibrium solution are explicitly provided and identified here with diamagnetic energy-correction and electrostatic contributions. It is shown that these kinetic terms characterize the plasma equation of state by introducing non-vanishing deviations from the assumption of thermal pressure.
Into the Epoch of Galaxy Formation
NASA Astrophysics Data System (ADS)
2000-02-01
Infrared VLT Observations Identify Hidden Galaxies in the Early Universe Working with the ESO Very Large Telescope (VLT) at the Paranal Observatory , a group of European astronomers [1] has just obtained one of the deepest looks into the distant Universe ever made by an optical telescope. These observations were carried out in the near-infrared spectral region and are part of an attempt to locate very distant galaxies that have so far escaped detection in the visual bands. The first results are very promising and some concentrations of galaxies at very large distances were uncovered. Some early galaxies may be in hiding Current theories hypothesize that more than 80% of all stars ever formed were assembled in galaxies during the latter half of the elapsed lifetime of the Universe, i.e., during the past 7-8 billion years. However, doubts have arisen about these ideas. There are now observational indications that a significant number of those galaxies that formed during the first 20% of the age of the Universe, i.e. within about 3 billion years after the Big Bang, may not be visible to optical telescopes. In some cases, we do not see them, because their light is obscured by dust. Other distant galaxies may escape detection by optical telescopes because star formation in them has ceased and their light is mainly emitted in the red and infrared spectral bands. This is because, while very young galaxies mostly contain hot and blue stars, older galaxies have substantial numbers of cool and red stars. They are then dominated by an older, "evolved" stellar population that is cooler and redder. The large cosmic velocities of these galaxies further enhance this effect by causing their light to be "redshifted" towards longer wavelengths, i.e. into the near-infrared spectral region. Observations in the infrared needed Within the present programme, long exposures in near-infrared wavebands were made with the Infrared Spectrometer And Array Camera (ISAAC) , mounted on ANTU , the
Hydrogen Epoch of Reionization Array (HERA)
NASA Astrophysics Data System (ADS)
DeBoer, David R.; HERA
2015-01-01
The Hydrogen Epoch of Reionization Arrays (HERA - reionization.org) roadmap uses the unique properties of the neutral hydrogen (HI) 21cm line to probe our cosmic dawn: from the birth of the first stars and black holes, through the full reionization of the primordial intergalactic medium (IGM). HERA is a collaboration between the Precision Array Probing the Epoch of Reionization (PAPER - eor.berkeley.edu), the US-based Murchison Widefield Array (MWA - mwatelescope.org), and MIT Epoch of Reionization (MITEOR) teams along with the South African SKA-SA, University of KwaZulu Natal and the University of Cambridge Cavendish Laborabory. HERA has recently been awarded a National Science Foundation Mid-Scale Innovation Program grant to begin the next phase.HERA leverages the operation of the PAPER and MWA telescopes to explore techniques and designs required to detect the primordial HI signal in the presence of systematics and radio continuum foreground emission some four orders of magnitude brighter. With this understanding, we are now able to remove foregrounds to the limits of our sensitivity, culminating in the first physically meaningful upper limits. A redundant calibration algorithm from MITEOR improves the sensitivity of the approach.Building on this, the next stage of HERA incorporates a 14m diameter antenna element that is optimized both for sensitivity and for minimizing foreground systematics. Arranging these elements in a compact hexagonal grid yields an array that facilitates calibration, leverages proven foreground removal techniques, and is scalable to large collecting areas. HERA will be located in the radio quiet environment of the SKA site in the Karoo region of South Africa (where PAPER is currently located). It will have a sensitivity close to two orders of magnitude better than PAPER and the MWA to ensure a robust detection. With its sensitivity and broader frequency coverage, HERA can paint an uninterrupted picture through reionization, back to the
The applications of Complexity Theory and Tsallis Non-extensive Statistics at Solar Plasma Dynamics
NASA Astrophysics Data System (ADS)
Pavlos, George
2015-04-01
As the solar plasma lives far from equilibrium it is an excellent laboratory for testing complexity theory and non-equilibrium statistical mechanics. In this study, we present the highlights of complexity theory and Tsallis non extensive statistical mechanics as concerns their applications at solar plasma dynamics, especially at sunspot, solar flare and solar wind phenomena. Generally, when a physical system is driven far from equilibrium states some novel characteristics can be observed related to the nonlinear character of dynamics. Generally, the nonlinearity in space plasma dynamics can generate intermittent turbulence with the typical characteristics of the anomalous diffusion process and strange topologies of stochastic space plasma fields (velocity and magnetic fields) caused by the strange dynamics and strange kinetics (Zaslavsky, 2002). In addition, according to Zelenyi and Milovanov (2004) the complex character of the space plasma system includes the existence of non-equilibrium (quasi)-stationary states (NESS) having the topology of a percolating fractal set. The stabilization of a system near the NESS is perceived as a transition into a turbulent state determined by self-organization processes. The long-range correlation effects manifest themselves as a strange non-Gaussian behavior of kinetic processes near the NESS plasma state. The complex character of space plasma can also be described by the non-extensive statistical thermodynamics pioneered by Tsallis, which offers a consistent and effective theoretical framework, based on a generalization of Boltzmann - Gibbs (BG) entropy, to describe far from equilibrium nonlinear complex dynamics (Tsallis, 2009). In a series of recent papers, the hypothesis of Tsallis non-extensive statistics in magnetosphere, sunspot dynamics, solar flares, solar wind and space plasma in general, was tested and verified (Karakatsanis et al., 2013; Pavlos et al., 2014; 2015). Our study includes the analysis of solar plasma time
Mars - Epochal climate change and volatile history
NASA Technical Reports Server (NTRS)
Fanale, Fraser P.; Postawko, Susan E.; Pollack, James B.; Carr, Michael H.; Pepin, Robert O.
1992-01-01
The epochal climate change and volatile history of Mars are examined, with special attention given to evidence for and mechanisms of long-term climate change. Long-term climate change on Mars is indicated most directly by the presence, age, and distribution of the valley networks. They were almost certainly formed by running water, but it seems more likely that they were formed by groundwater sapping than by rainfall. It is argued to be physically plausible that a higher early intensity of surface insolation caused by a CO2 greenhouse effect could have overcompensated for an early weak sun and raised temperatures to the freezing point near the equator under favorable conditions of obliquity and eccentricity. This could account for the morphological changes.
LEDDB: LOFAR Epoch of Reionization Diagnostic Database
NASA Astrophysics Data System (ADS)
Martinez-Rubi, O.; Veligatla, V. K.; de Bruyn, A. G.; Lampropoulos, P.; Offringa, A. R.; Jelic, V.; Yatawatta, S.; Koopmans, L. V. E.; Zaroubi, S.
2013-10-01
One of the key science projects of the Low-Frequency Array (LOFAR) is the detection of the cosmological signal coming from the Epoch of Reionization (EoR). Here we present the LOFAR EoR Diagnostic Database (LEDDB) that is used in the storage, management, processing and analysis of the LOFAR EoR observations. It stores referencing information of the observations and diagnostic parameters extracted from their calibration. These stored data are used to ease the pipeline processing, monitor the performance of the telescope, and visualize the diagnostic parameters which facilitates the analysis of the several contamination effects on the signals. It is implemented with PostgreSQL and accessed through the psycopg2 Python module. We have developed a very flexible query engine, which is used by a web user interface to access the database, and a very extensive set of tools for the visualization of the diagnostic parameters through all their multiple dimensions.
Orion: The Final Epoch (OrionTFE)
NASA Astrophysics Data System (ADS)
Megeath, Tom; Allen, Tom; Arce, Hector; Booker, Joseph; Calvet, Nuria; Flaherty, Kevin; Furlan, Elise; Fischer, Will; Gonzales, Beatriz; Gutermuth, Rob; Hartman, Lee; Henning, Thomas; Hora, Joe; Karnath, Nicole; Kim, Kyoung Hee; Kounkel, Marina; Mazur, Brian; Offner, Stella; Osorio, Mayra; Pillitteri, Ignazio; Pipher, Judy; Prchlik, Jakub; Rebull, Luisa; Terebey, Susan; Tobin, John; Stanke, Thomas; Stutz, Amelia; Watson, Dan; Wolk, Scott
2016-08-01
The Orion molecular clouds are an essential laboratory for studying low mass star formation over the broad range of environments in which they form. Starting with the Spitzer survey of Orion in 2004, more than a decade of observations with Spitzer, WISE, HST and Herschel, have accumulated an unparalleled characterization of the young stellar object population in Orion. We propose a final epoch of observations divided into two separate, complementary observations: A repeat of the entire Orion molecular cloud survey to 1.) identify ejected stars from clusters, 2.) measure the bulk proper motions of groups and clusters of stars, 3.) constrain the rate of luminous, accretion driven outbursts from both protostars and pre-main sequence stars with disks and 4.) use proper motions of IR Herbig-Haro knots as a fossil record of previous accretion events. A high cadence variability survey of the L1641 cloud extending the YSOVAR variability survey of the Orion Nebula Cluster across the Orion A cloud with the goals of 1.) constraining the star formation history of Orion A, 2.) studying the evolution of mid-IR variability from the protostellar to pre-main sequence phase, 3.) searching for periodicities in (nearly) edge-on protostars and disks due to orbiting clumps and structures from orbiting planets, and 4.) assessing whether inner disk processes - as traced by variability - are affected by their birth environment. This program completes an unparalleled, > 12 year multi-epoch, mid-IR study of the nearest large molecular cloud complex with both a wide spatial coverage and a uniformity that will not be exceeded in the forseeable future. It will place unique constraints on the highly dynamic processes that control low mass star formation, serve as a pathfinder to molecular cloud surveys of WFIRST, and provide well characterized targets needed to study mass accretion and planet formation around young low mass stars with SOFIA and JWST.
Application of diffusion theory to neutral atom transport in fusion plasmas
Hasan, M.Z.; Conn, R.W.; Pomraning, G.C.
1986-05-01
It is found that energy dependent diffusion theory provides excellent accuracy in the modelling of transport of neutral atoms in fusion plasmas. Two reasons in particular explain the good accuracy. First, while the plasma is optically thick for low energy neutrals, it is optically thin for high energy neutrals and diffusion theory with Marshak boundary conditions gives accurate results for an optically thin medium even for small values of 'c', the ratio of the scattering to the total cross section. Second, the effective value of 'c' at low energy becomes very close to one due to the down-scattering via collisions of high energy neutrals. The first reason is proven both computationally and theoretically by solving the transport equation in a power series in 'c' and the diffusion equation with 'general' Marshak boundary conditions. The second reason is established numerically by comparing the results from a one-dimensional, general geometry, multigroup diffusion theory code, written for this purpose, with the results obtained using the transport code ANISN.
W.M. Tang
2005-01-03
The present lecture provides an introduction to the subject of gyrokinetic theory with applications in the area of magnetic confinement research in plasma physics--the research arena from which this formalism was originally developed. It was presented as a component of the ''Short Course in Kinetic Theory within the Thematic Program in Partial Differential Equations'' held at the Fields Institute for Research in Mathematical Science (24 March 2004). This lecture also discusses the connection between the gyrokinetic formalism and powerful modern numerical simulations. Indeed, simulation, which provides a natural bridge between theory and experiment, is an essential modern tool for understanding complex plasma behavior. Progress has been stimulated in particular by the exponential growth of computer speed along with significant improvements in computer technology. The advances in both particle and fluid simulations of fine-scale turbulence and large-scale dynamics have produced increasingly good agreement between experimental observations and computational modeling. This was enabled by two key factors: (i) innovative advances in analytic and computational methods for developing reduced descriptions of physics phenomena spanning widely disparate temporal and spatial scales and (ii) access to powerful new computational resources.
Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.
2015-07-15
The evolution of filamentation instability in a weakly ionized current-carrying plasma with nonextensive distribution was studied in the diffusion frequency region, taking into account the effects of electron-neutral collisions. Using the kinetic theory, Lorentz transformation formulas, and Bhatnagar-Gross-Krook collision model, the generalized dielectric permittivity functions of this plasma system were achieved. By obtaining the dispersion relation of low-frequency waves, the possibility of filamentation instability and its growth rate were investigated. It was shown that collisions can increase the maximum growth rate of instability. The analysis of temporal evolution of filamentation instability revealed that the growth rate of instability increased by increasing the q-parameter and electron drift velocity. Finally, the results of Maxwellian and q-nonextensive velocity distributions were compared and discussed.
A theory of two-beam acceleration of charged particles in a plasma waveguide
Ostrovsky, A.O.
1993-11-01
The progress made in recent years in the field of high-current relativistic electron beam (REB) generation has aroused a considerable interest in studying REB potentialities for charged particle acceleration with a high acceleration rate T = 100MeV/m. It was proposed, in particular, to employ high-current REB in two-beam acceleration schemes (TBA). In these schemes high current REB (driving beam) excites intense electromagnetic waves in the electrodynamic structure which, in their turn, accelerate particles of the other beam (driven beam). The TBA schemes can be divided into two groups. The first group includes the schemes, where the two beams (driving and driven) propagate in different electrodynamic structures coupled with each other through the waveguides which ensure the microwave power transmission to accelerate driven beam particles. The second group includes the TBA schemes, where the driving and driven beams propagate in one electrodynamic structure. The main aim of this work is to demonstrate by theory the possibility of realizing effectively the TBA scheme in the plasma waveguide. The physical model of the TBA scheme under study is formulated. A set of equations describing the excitation of RF fields by a high-current REB and the acceleration of driven beam electrons is also derived. Results are presented on the the linear theory of plasma wave amplification by the driving beam. The range of system parameters, at which the plasma-beam instability develops, is defined. Results of numerical simulation of the TBA scheme under study are also presented. The same section gives the description of the dynamics of accelerated particle bunching in the high-current REB-excited field. Estimates are given for the accelerating field intensities in the plasma and electron acceleration rates.
Theory of Collisional Two-Stream Plasma Instabilities in the Solar Chromosphere
NASA Astrophysics Data System (ADS)
Madsen, Chad Allen; Dimant, Yakov; Oppenheim, Meers; Fontenla, Juan
2014-06-01
The solar chromosphere experiences intense heating just above its temperature minimum. The heating increases the electron temperature in this region by over 2000 K. Furthermore, it exhibits little time variation and appears widespread across the solar disk. Although semi-empirical models, UV continuum observations, and line emission measurements confirm the existence of the heating, its source remains unexplained. Potential heating sources such as acoustic shocks, resistive dissipation, and magnetic reconnection via nanoflares fail to account for the intensity, persistence, and ubiquity of the heating. Fontenla (2005) suggested turbulence from a collisional two-stream plasma instability known as the Farley-Buneman instability (FBI) could contribute significantly to the heating. This instability is known to heat the plasma of the E-region ionosphere which bears many similarities to the chromospheric plasma. However, the ionospheric theory of the FBI does not account for the diverse ion species found in the solar chromosphere. This work develops a new collisional, two-stream instability theory appropriate for the chromospheric plasma environment using a linear fluid analysis to derive a new dispersion relationship and critical E x B drift velocity required to trigger the instability. Using a 1D, non-local thermodynamic equilibrium, radiative transfer model and careful estimates of collision rates and magnetic field strengths, we calculate the trigger velocities necessary to induce the instability throughout the chromosphere. Trigger velocities as low as 4 km s^-1 are found near the temperature minimum, well below the local neutral acoustic speed in that region. From this, we expect the instability to occur frequently, converting kinetic energy contained in neutral convective flows from the photosphere into thermal energy via turbulence. This could contribute significantly to chromospheric heating and explain its persistent and ubiquitous nature.
Purohit, Gunjan Rawat, Priyanka; Chauhan, Prashant; Mahmoud, Saleh T.
2015-05-15
This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxial region by expanding the eikonal and other relevant quantities up to the fourth power of r. The splitted profile of laser beam in the plasma is observed due to uneven focusing/defocusing of the axial and off-axial rays. The growths of ring ripple increase when the laser beam intensity increases. Furthermore, the intensity profile of ring rippled laser beam gets modified due to the contribution of growth rate.
Linearized kinetic theory of spin-1/2 particles in magnetized plasmas
Lundin, J.; Brodin, G.
2010-11-15
We have considered linear kinetic theory, including the electron-spin properties in a magnetized plasma. The starting point is a mean-field Vlasov-like equation, derived from a fully quantum-mechanical treatment, where effects from the electron-spin precession and the magnetic dipole force are taken into account. The general conductivity tensor is derived, including both the free current contribution and the magnetization current associated with the spin contribution. We conclude the paper with an extensive discussion of the quantum-mechanical boundary where we list parameter conditions that must be satisfied for various quantum effects to be influential.
Theory of a laser-plasma method for detecting terahertz radiation
Frolov, A. A.; Borodin, A. V.; Esaulkov, M. N.; Kuritsyn, I. I.; Shkurinov, A. P.
2012-06-15
A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation.
Theory for large-amplitude electrostatic ion shocks in quantum plasmas.
Akbari-Moghanjoughi, M; Shukla, P K
2012-12-01
We present a generalized nonlinear theory for large-amplitude electrostatic (ES) ion shocks in collisional quantum plasmas composed of mildly coupled degenerate electron fluid of arbitrary degeneracy and nondegenerate strongly correlated ion fluid with arbitrary atomic number. For our purposes, we use the inertialess electron momentum equation including the electrostatic force, pressure gradient, and relevant quantum forces, as well as a generalized viscoelastic ion momentum (GVIM) equation for strongly correlated nondegenerate ions. The ion continuity equation, in the quasineutral approximation, then closes our nonlinear system of equations. When the electric field force is eliminated from the GVIM equation by using the inertialess electron momentum equation, we then obtain a GVIM and ion continuity equations, which exhibit nonlinear couplings between the ion number density and the ion fluid velocity. The pair of nonlinear equations is numerically solved to study the dynamics of arbitrarily-large-amplitude planar and nonplanar ES shocks arising from a balance between harmonic generation nonlinearities and the ion fluid viscosity for a wide range of plasma mass densities and ion atomic numbers that are relevant for the cores of giant planets (viz., Jupiter) and compact stars (viz., white dwarfs). Our numerical results reveal that the ES shock density profiles strongly depend on the plasma number density and composition (the atomic-number) parameters. Furthermore, ion density perturbations propagate with Mach numbers which significantly depend on the studied plasma fractional parameters. It is concluded that the dynamics of the ES shocks in the superdense degenerate plasma is quite different in the core of a white dwarf star from that in the lower density crust region. PMID:23368053
Theory for large-amplitude electrostatic ion shocks in quantum plasmas.
Akbari-Moghanjoughi, M; Shukla, P K
2012-12-01
We present a generalized nonlinear theory for large-amplitude electrostatic (ES) ion shocks in collisional quantum plasmas composed of mildly coupled degenerate electron fluid of arbitrary degeneracy and nondegenerate strongly correlated ion fluid with arbitrary atomic number. For our purposes, we use the inertialess electron momentum equation including the electrostatic force, pressure gradient, and relevant quantum forces, as well as a generalized viscoelastic ion momentum (GVIM) equation for strongly correlated nondegenerate ions. The ion continuity equation, in the quasineutral approximation, then closes our nonlinear system of equations. When the electric field force is eliminated from the GVIM equation by using the inertialess electron momentum equation, we then obtain a GVIM and ion continuity equations, which exhibit nonlinear couplings between the ion number density and the ion fluid velocity. The pair of nonlinear equations is numerically solved to study the dynamics of arbitrarily-large-amplitude planar and nonplanar ES shocks arising from a balance between harmonic generation nonlinearities and the ion fluid viscosity for a wide range of plasma mass densities and ion atomic numbers that are relevant for the cores of giant planets (viz., Jupiter) and compact stars (viz., white dwarfs). Our numerical results reveal that the ES shock density profiles strongly depend on the plasma number density and composition (the atomic-number) parameters. Furthermore, ion density perturbations propagate with Mach numbers which significantly depend on the studied plasma fractional parameters. It is concluded that the dynamics of the ES shocks in the superdense degenerate plasma is quite different in the core of a white dwarf star from that in the lower density crust region.
Theory of waves in pair-ion plasmas: Natural explanation of backward modes
Kono, M.; Vranjes, J.; Batool, N.
2013-12-15
Backward waves observed in the experiments by Oohara and Hatakeyama (Phys. Rev. Lett. 91, 205005 (2003)) are identified to be ion cyclotron harmonic waves inherent to the kinetic theory. The derived dispersion equation is based on exact solutions of the characteristic equations of the Vlasov equation in a bounded cylindrical coordinate system; it is different from its counterpart in unbounded plasmas, and it provides all the branches of the dispersion relations observed in the experiment. Positive and negative ions respond to a potential in the same time scale and cooperate to expose kinetic orbital behaviors to the macroscopic propagation characteristics. In addition, the experimental setting of the large Larmor radius makes higher harmonic ion cyclotron backward/forward waves observable. The large Larmor radius effects are naturally treated by a kinetic theory.
Molecular hydrogen in the cosmic recombination epoch
Alizadeh, Esfandiar; Hirata, Christopher M.
2011-10-15
The advent of precise measurements of the CMB anisotropies has motivated correspondingly precise calculations of the cosmic recombination history. Cosmic recombination proceeds far out of equilibrium because of a ''bottleneck'' at the n=2 level of hydrogen: atoms can only reach the ground state via slow processes--two-photon decay or Lyman-{alpha} resonance escape. However, even a small primordial abundance of molecules could have a large effect on the interline opacity in the recombination epoch and lead to an additional route for hydrogen recombination. Therefore, this paper computes the abundance of the H{sub 2} molecule during the cosmic recombination epoch. Hydrogen molecules in the ground electronic levels X{sup 1}{Sigma}{sub g}{sup +} can either form from the excited H{sub 2} electronic levels B{sup 1}{Sigma}{sub u}{sup +} and C{sup 1}{Pi}{sub u} or through the charged particles H{sub 2}{sup +}, HeH{sup +}, and H{sup -}. We follow the transitions among all of these species, resolving the rotational and vibrational sublevels. Since the energies of the X{sup 1}{Sigma}{sub g}{sup +}-B{sup 1}{Sigma}{sub u}{sup +} (Lyman band) and X{sup 1}{Sigma}{sub g}{sup +}-C{sup 1}{Pi}{sub u} (Werner band) transitions are near the Lyman-{alpha} energy, the distortion of the CMB spectrum caused by escaped H Lyman-line photons accelerates both the formation and the destruction of H{sub 2} due to this channel relative to the thermal rates. This causes the populations of H{sub 2} molecules in X{sup 1}{Sigma}{sub g}{sup +} energy levels to deviate from their thermal equilibrium abundances. We find that the resulting H{sub 2} abundance is 10{sup -17} at z=1200 and 10{sup -13} at z=800, which is too small to have any significant influence on the recombination history.
Theory of plasma contactors in ground-based experiments and low Earth orbit
NASA Technical Reports Server (NTRS)
Gerver, M. J.; Hastings, Daniel E.; Oberhardt, M. R.
1990-01-01
Previous theoretical work on plasma contactors as current collectors has fallen into two categories: collisionless double layer theory (describing space charge limited contactor clouds) and collisional quasineutral theory. Ground based experiments at low current are well explained by double layer theory, but this theory does not scale well to power generation by electrodynamic tethers in space, since very high anode potentials are needed to draw a substantial ambient electron current across the magnetic field in the absence of collisions (or effective collisions due to turbulence). Isotropic quasineutral models of contactor clouds, extending over a region where the effective collision frequency upsilon sub e exceeds the electron cyclotron frequency omega sub ce, have low anode potentials, but would collect very little ambient electron current, much less than the emitted ion current. A new model is presented, for an anisotropic contactor cloud oriented along the magnetic field, with upsilon sub e less than omega sub ce. The electron motion along the magnetic field is nearly collisionless, forming double layers in that direction, while across the magnetic field the electrons diffuse collisionally and the potential profile is determined by quasineutrality. Using a simplified expression for upsilon sub e due to ion acoustic turbulence, an analytic solution has been found for this model, which should be applicable to current collection in space. The anode potential is low and the collected ambient electron current can be several times the emitted ion current.
Theory of isolated, small-scale magnetic islands in a high temperature tokamak plasma
Connor, J.W.; Wilson, H.R.
1995-12-01
A theory for the existence of noninteracting small-scale, ``drift`` magnetic islands in a high temperature tokamak plasma is presented. This situation contrasts with that discussed by Rebut and Hugon [Plasma Phys. Controlled Fusion {bold 33}, 1085 (1991)] which involves a background ``sea`` of magnetic turbulence caused by island overlap. The islands are driven by the effect of finite ion Larmor radius on the particle drifts and they propagate with a velocity comparable to the diamagnetic velocity. In contrast with the work of Smolyakov [Plasma Phys. Controlled Fusion {bold 35}, 657 (1993)] collisions are assumed to be rare. Although the saturated island size is independent of the collision frequency in the model discussed here, collisions play a crucial role in determining the frequency of the magnetic islands. An estimate is made of the anomalous heat transport which results from the fluctuations in the electrostatic potential associated with these magnetic islands. The predicted thermal diffusivity has several, but not all, of the characteristics of the Rebut--Lallia--Watkins transport model. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Mean-field theory of the glass transition in the one-component classical plasma
NASA Astrophysics Data System (ADS)
Cardenas, M.; Tosi, M. P.
2004-08-01
We study the supercooled-fluid region and the transition to an amorphous glassy state in the one-component classical plasma, within the replica-symmetry-breaking scenario developed by Franz and Parisi. This approach implements the slowing down of jumps of the disordered system between the minima in a rugged free-energy landscape by examining its correlations with a quenched replica as a function of their coupling expressed through a suitable short-range attractive potential. We carry out these calculations within a mean-field theory for the structure of a quenched-annealed mixture, using both the hypernetted chain approximation and a refinement to include an account of the bridge function. In both formulations our theoretical results demonstrate the existence of a glassy state for the plasma and yield an estimate of the phase-transition line, which has the form T∝ Z2n1/3 where n is the particle number density, T the temperature and Z the valence, with a numerical coefficient which is about one eighth of that for equilibrium freezing. The consequences for various types of ionic fluids (simple molten salts, colloidal dispersions, and astrophysical plasmas) are illustrated.
Parallax Results from Urat Epoch Data
NASA Astrophysics Data System (ADS)
Finch, Charlie T.; Zacharias, Norbert
2016-06-01
We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a three-year period from 2012 April to 2015 June covering the entire sky north of about -10^\\circ decl. We selected two samples: previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax ≥40 mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10 mas. This sample gives a significant (of the order of 50%) increase to the number of known systems having a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz-Kelker bias corrections). A few of these are found to be within 10 pc. Many of these new nearby stars display a total proper motion of less than 200 mas yr-1. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all signifigant parallax observations from URAT data is in preparation for CDS.
Parallax Results from Urat Epoch Data
NASA Astrophysics Data System (ADS)
Finch, Charlie T.; Zacharias, Norbert
2016-06-01
We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a three-year period from 2012 April to 2015 June covering the entire sky north of about -10^\\circ decl. We selected two samples: previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax ≥40 mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10 mas. This sample gives a significant (of the order of 50%) increase to the number of known systems having a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz–Kelker bias corrections). A few of these are found to be within 10 pc. Many of these new nearby stars display a total proper motion of less than 200 mas yr‑1. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all signifigant parallax observations from URAT data is in preparation for CDS.
Variational theory of average-atom and superconfigurations in quantum plasmas.
Blenski, T; Cichocki, B
2007-05-01
Models of screened ions in equilibrium plasmas with all quantum electrons are important in opacity and equation of state calculations. Although such models have to be derived from variational principles, up to now existing models have not been fully variational. In this paper a fully variational theory respecting virial theorem is proposed-all variables are variational except the parameters defining the equilibrium, i.e., the temperature T, the ion density ni and the atomic number Z. The theory is applied to the quasiclassical Thomas-Fermi (TF) atom, the quantum average atom (QAA), and the superconfigurations (SC) in plasmas. Both the self-consistent-field (SCF) equations for the electronic structure and the condition for the mean ionization Z* are found from minimization of a thermodynamic potential. This potential is constructed using the cluster expansion of the plasma free energy from which the zero and the first-order terms are retained. In the zero order the free energy per ion is that of the quantum homogeneous plasma of an unknown free-electron density n0 = Z* ni occupying the volume 1/ni. In the first order, ions submerged in this plasma are considered and local neutrality is assumed. These ions are considered in the infinite space without imposing the neutrality of the Wigner-Seitz (WS) cell. As in the Inferno model, a central cavity of a radius R is introduced, however, the value of R is unknown a priori. The charge density due to noncentral ions is zero inside the cavity and equals en0 outside. The first-order contribution to free energy per ion is the difference between the free energy of the system "central ion+infinite plasma" and the free energy of the system "infinite plasma." An important part of the approach is an "ionization model" (IM), which is a relation between the mean ionization charge Z* and the first-order structure variables. Both the IM and the local neutrality are respected in the minimization procedure. The correct IM in the TF case
Variational theory of average-atom and superconfigurations in quantum plasmas.
Blenski, T; Cichocki, B
2007-05-01
Models of screened ions in equilibrium plasmas with all quantum electrons are important in opacity and equation of state calculations. Although such models have to be derived from variational principles, up to now existing models have not been fully variational. In this paper a fully variational theory respecting virial theorem is proposed-all variables are variational except the parameters defining the equilibrium, i.e., the temperature T, the ion density ni and the atomic number Z. The theory is applied to the quasiclassical Thomas-Fermi (TF) atom, the quantum average atom (QAA), and the superconfigurations (SC) in plasmas. Both the self-consistent-field (SCF) equations for the electronic structure and the condition for the mean ionization Z* are found from minimization of a thermodynamic potential. This potential is constructed using the cluster expansion of the plasma free energy from which the zero and the first-order terms are retained. In the zero order the free energy per ion is that of the quantum homogeneous plasma of an unknown free-electron density n0 = Z* ni occupying the volume 1/ni. In the first order, ions submerged in this plasma are considered and local neutrality is assumed. These ions are considered in the infinite space without imposing the neutrality of the Wigner-Seitz (WS) cell. As in the Inferno model, a central cavity of a radius R is introduced, however, the value of R is unknown a priori. The charge density due to noncentral ions is zero inside the cavity and equals en0 outside. The first-order contribution to free energy per ion is the difference between the free energy of the system "central ion+infinite plasma" and the free energy of the system "infinite plasma." An important part of the approach is an "ionization model" (IM), which is a relation between the mean ionization charge Z* and the first-order structure variables. Both the IM and the local neutrality are respected in the minimization procedure. The correct IM in the TF case
Kim, Kihong; Lee, Dong-Hun
2005-06-15
This is the first of a series of papers devoted to the development of the invariant imbedding theory of mode conversion in inhomogeneous plasmas. A new version of the invariant imbedding theory of wave propagation in inhomogeneous media allows one to solve a wide variety of coupled wave equations exactly and efficiently, even in the cases where the material parameters change discontinuously at the boundaries and inside the inhomogeneous medium. In this paper, the invariant imbedding method is applied to the mode conversion of the simplest kind, that is, the conversion of p-polarized electromagnetic waves into electrostatic modes in cold, unmagnetized plasmas. The mode conversion coefficient and the field distribution are calculated exactly for linear and parabolic plasma density profiles and compared quantitatively with previous results.
Theory of ballooning-mirror instabilities for anisotropic pressure plasmas in the magnetosphere
Cheng, C.Z.; Qian, Q.
1993-09-01
This paper deals with a kinetic-MHD eigenmode stability analysis of low frequency ballooning-mirror instabilities for anisotropic pressure plasmas in the magnetosphere. The ballooning mode is a dominant transverse wave driven unstable by pressure gradient in the bad curvature region. The mirror mode with a dominant compressional magnetic field perturbation is excited when the product of plasma beta and pressure anisotropy is large. The field-aligned eigenmode equations take into account the coupling of the transverse and compressional components of the perturbed magnetic field and describe the coupled ballooning-mirror mode. Because the energetic trapped ions precess very rapidly across the {rvec B} field, their motion becomes very rigid with respect to low frequency MHD perturbations with symmetric structure of parallel perturbed magnetic field {delta}B{sub {parallel}} and electrostatic potential {Phi} along the north-south ambient magnetic field, and the symmetric ballooning-mirror mode is shown to be stable. On the other hand, the ballooning-mirror mode with antisymmetric {delta}B{sub {parallel}}, and {Phi} structure along the north-south ambient magnetic field is only weakly influenced by energetic trapped particle kinetic effects due to rapid trapped particle bounce motion and has the lowest instability threshold determined by MHD theory. With large plasma beta ({beta}{sub {parallel}} {ge} O(1)) and pressure anisotropy (P{sub {perpendicular}}/P{sub {parallel}} > 1) at equator the antisymmetric ballooning-mirror mode structures resemble the field-aligned wave structures of the multisatellite observations of a long lasting compressional Pc 5 wave event during November 14--15, 1979 [Takahashi et al.]. The study provides the theoretical basis for identifying the internal excitation mechanism of ULF (Pc 4-5) waves by comparing the plasma stability parameters computed from the satellite particle data with the theoretical values.
Refinement of the semiclassical theory of the Stark broadening of hydrogen spectral lines in plasmas
NASA Astrophysics Data System (ADS)
Oks, Eugene
2015-02-01
Stark broadening (SB) of hydrogen, deuterium, and tritium lines (H-lines) is an important diagnostic tool for many applications. The most "user-friendly" are semiclassical theories of the SB of H-lines: their results can be expressed analytically in a relatively simple form for any H-line. The simplest semiclassical theory is the so-called Conventional Theory (CT), which is frequently referred to as Griem's theory. While by now there are several significantly more advanced semiclassical "non-CT" theories of the SB, Griem's CT is still used by a number of groups performing laboratory experiments or astrophysical observations for the comparison with their experimental or observational results. In the present study we engage unexplored capabilities of the CT for creating analytically a more accurate CT. First, we take into account that the perturbing electrons actually do not move as free particles: rather they move in a dipole potential V=
Into the Epoch of Galaxy Formation
NASA Astrophysics Data System (ADS)
2000-02-01
Infrared VLT Observations Identify Hidden Galaxies in the Early Universe Working with the ESO Very Large Telescope (VLT) at the Paranal Observatory , a group of European astronomers [1] has just obtained one of the deepest looks into the distant Universe ever made by an optical telescope. These observations were carried out in the near-infrared spectral region and are part of an attempt to locate very distant galaxies that have so far escaped detection in the visual bands. The first results are very promising and some concentrations of galaxies at very large distances were uncovered. Some early galaxies may be in hiding Current theories hypothesize that more than 80% of all stars ever formed were assembled in galaxies during the latter half of the elapsed lifetime of the Universe, i.e., during the past 7-8 billion years. However, doubts have arisen about these ideas. There are now observational indications that a significant number of those galaxies that formed during the first 20% of the age of the Universe, i.e. within about 3 billion years after the Big Bang, may not be visible to optical telescopes. In some cases, we do not see them, because their light is obscured by dust. Other distant galaxies may escape detection by optical telescopes because star formation in them has ceased and their light is mainly emitted in the red and infrared spectral bands. This is because, while very young galaxies mostly contain hot and blue stars, older galaxies have substantial numbers of cool and red stars. They are then dominated by an older, "evolved" stellar population that is cooler and redder. The large cosmic velocities of these galaxies further enhance this effect by causing their light to be "redshifted" towards longer wavelengths, i.e. into the near-infrared spectral region. Observations in the infrared needed Within the present programme, long exposures in near-infrared wavebands were made with the Infrared Spectrometer And Array Camera (ISAAC) , mounted on ANTU , the
The effect of epoch length on estimated EEG functional connectivity and brain network organisation
NASA Astrophysics Data System (ADS)
Fraschini, Matteo; Demuru, Matteo; Crobe, Alessandra; Marrosu, Francesco; Stam, Cornelis J.; Hillebrand, Arjan
2016-06-01
Objective. Graph theory and network science tools have revealed fundamental mechanisms of functional brain organization in resting-state M/EEG analysis. Nevertheless, it is still not clearly understood how several methodological aspects may bias the topology of the reconstructed functional networks. In this context, the literature shows inconsistency in the chosen length of the selected epochs, impeding a meaningful comparison between results from different studies. Approach. The aim of this study was to provide a network approach insensitive to the effects that epoch length has on functional connectivity and network reconstruction. Two different measures, the phase lag index (PLI) and the amplitude envelope correlation (AEC) were applied to EEG resting-state recordings for a group of 18 healthy volunteers using non-overlapping epochs with variable length (1, 2, 4, 6, 8, 10, 12, 14 and 16 s). Weighted clustering coefficient (CCw), weighted characteristic path length (L w) and minimum spanning tree (MST) parameters were computed to evaluate the network topology. The analysis was performed on both scalp and source-space data. Main results. Results from scalp analysis show a decrease in both mean PLI and AEC values with an increase in epoch length, with a tendency to stabilize at a length of 12 s for PLI and 6 s for AEC. Moreover, CCw and L w show very similar behaviour, with metrics based on AEC more reliable in terms of stability. In general, MST parameters stabilize at short epoch lengths, particularly for MSTs based on PLI (1-6 s versus 4-8 s for AEC). At the source-level the results were even more reliable, with stability already at 1 s duration for PLI-based MSTs. Significance. The present work suggests that both PLI and AEC depend on epoch length and that this has an impact on the reconstructed network topology, particularly at the scalp-level. Source-level MST topology is less sensitive to differences in epoch length, therefore enabling the comparison of brain
The effect of epoch length on estimated EEG functional connectivity and brain network organisation
NASA Astrophysics Data System (ADS)
Fraschini, Matteo; Demuru, Matteo; Crobe, Alessandra; Marrosu, Francesco; Stam, Cornelis J.; Hillebrand, Arjan
2016-06-01
Objective. Graph theory and network science tools have revealed fundamental mechanisms of functional brain organization in resting-state M/EEG analysis. Nevertheless, it is still not clearly understood how several methodological aspects may bias the topology of the reconstructed functional networks. In this context, the literature shows inconsistency in the chosen length of the selected epochs, impeding a meaningful comparison between results from different studies. Approach. The aim of this study was to provide a network approach insensitive to the effects that epoch length has on functional connectivity and network reconstruction. Two different measures, the phase lag index (PLI) and the amplitude envelope correlation (AEC) were applied to EEG resting-state recordings for a group of 18 healthy volunteers using non-overlapping epochs with variable length (1, 2, 4, 6, 8, 10, 12, 14 and 16 s). Weighted clustering coefficient (CCw), weighted characteristic path length (L w) and minimum spanning tree (MST) parameters were computed to evaluate the network topology. The analysis was performed on both scalp and source-space data. Main results. Results from scalp analysis show a decrease in both mean PLI and AEC values with an increase in epoch length, with a tendency to stabilize at a length of 12 s for PLI and 6 s for AEC. Moreover, CCw and L w show very similar behaviour, with metrics based on AEC more reliable in terms of stability. In general, MST parameters stabilize at short epoch lengths, particularly for MSTs based on PLI (1–6 s versus 4–8 s for AEC). At the source-level the results were even more reliable, with stability already at 1 s duration for PLI-based MSTs. Significance. The present work suggests that both PLI and AEC depend on epoch length and that this has an impact on the reconstructed network topology, particularly at the scalp-level. Source-level MST topology is less sensitive to differences in epoch length, therefore enabling the comparison of
New Insight into the Cosmic Renaissance Epoch
NASA Astrophysics Data System (ADS)
2003-08-01
VLT Discovers a Group of Early Inhabitants and Find Signs of Many More [1] Summary Using the ESO Very Large Telescope (VLT) , two astronomers from Germany and the UK [2] have discovered some of the most distant galaxies ever seen . They are located about 12,600 million light-years away. It has taken the light now recorded by the VLT about nine-tenths of the age of the Universe to traverse this huge distance. We therefore observe those galaxies as they were at a time when the Universe was very young, less than about 10% of its present age . At this time, the Universe was emerging from a long period known as the "Dark Ages" , entering the luminous "Cosmic Renaissance" epoch. Unlike previous studies which resulted in the discovery of a few, widely dispersed galaxies at this early epoch, the present study found at least six remote citizens within a small sky area, less than five per cent the size of the full moon! This allowed understanding the evolution of these galaxies and how they affect the state of the Universe in its youth. In particular, the astronomers conclude on the basis of their unique data that there were considerably fewer luminous galaxies in the Universe at this early stage than 500 million years later. There must therefore be many less luminous galaxies in the region of space that they studied, too faint to be detected in this study. It must be those still unidentified galaxies that emit the majority of the energetic photons needed to ionise the hydrogen in the Universe at that particularly epoch. PR Photo 25a/03 : Colour-composite of the sky field with the distant galaxies. PR Photo 25b/03 : Close-Up images of some of the most distant galaxies known in the Universe. PR Photo 25c/03 : Spectra of these galaxies. From the Big Bang to the Cosmic Renaissance Nowadays, the Universe is pervaded by energetic ultraviolet radiation, produced by quasars and hot stars. The short-wavelength photons liberate electrons from the hydrogen atoms that make up the
Kinetic theory of electromagnetic plane wave obliquely incident on bounded plasma slab
NASA Astrophysics Data System (ADS)
Angus, J. R.; Krasheninnikov, S. I.; Smolyakov, A. I.
2010-10-01
The effects of electromagnetic plane waves obliquely incident on a warm bounded plasma slab of finite length L are studied by solving the coupled Vlasov-Maxwell set of equations. It is shown that the solution can be greatly simplified in the limit where thermal effects are most important by expanding in small parameters and introducing self-similar variables. These solutions reveal that the coupling of thermal effects with the angle of incidence is negligible in the region of bounce resonance and anomalous skin effect. In the region of the anomalous skin effect, the heating is shown to scale linearly with the anomalous skin depth δa when δa≪L, in agreement with previous authors. Furthermore, for δa≫L, the heating is shown to decay with 1/δa3. The transmission is found to be exponentially larger than that predicted from a local theory in the appropriate region of the anomalous skin effect.
Hamiltonian theory of the ion cyclotron minority heating dynamics in tokamak plasmas
Becoulet, A.; Gambier, D.J.; Samain, A. )
1991-01-01
The question of heating a tokamak plasma by means of electromagnetic waves in the ion cyclotron range of frequencies (ICRF) is considered in the perspective of large rf powers and in the low collisionality regime. In such a case, the quasilinear theory (QLT) is validated by the Hamiltonian dynamics of the wave--particle interaction which exceeds the threshold of the intrinsic stochasticity. The Hamiltonian dynamics is represented by the evolution of a set of three canonical action angle variables well adapted to the tokamak magnetic configuration. This approach allows derivation of the rf diffusion coefficient with very few assumptions. The distribution function of the resonant ions is written as a Fokker--Planck equation but the emphasis is put on the QL diffusion instead of on the usual diffusion induced by collisions. The Fokker--Planck equation is then given a variational form from which a solution is derived in the form of a semianalytical trial function of three parameters: the percentage of resonant particles contained in the tail, an isotropic width {Delta}{ital T}, and an anisotropic width {Delta}{ital P}. This solution is successfully tested against real experimental observations. It is shown that in the case of the JET tokamak (Plasma Phys. Controlled Fusion {bold 30}, 1467 (1988)) the distribution function is influenced by adiabatic barriers which in turn limit the Hamiltonian stochasticity domain within energy values typically in the MeV range. Consequently and for a given ICRF power, the tail energy excursion is lower and its concentration higher than that from a bounce-averaged prediction. This may actually be an advantage for machines like JET (Plasma Phys. Controlled Fusion {bold 30}, 1467 (1988)) considering the energy range required to simulate the {alpha}-particle behavior in a relevant fusion reactor.
Water Formation During the Epoch of First Metal Enrichment
NASA Astrophysics Data System (ADS)
Bialy, Shmuel; Sternberg, Amiel; Loeb, Abraham
2015-05-01
We demonstrate that high abundances of water vapor could have existed in extremely low metallicity (10-3 solar) partially shielded gas during the epoch of first metal enrichment of the interstellar medium of galaxies at high redshifts.
Sub-Daily Earth Rotation During Epoch '92
NASA Technical Reports Server (NTRS)
Freedman, A. P.; Ibanez-Meier, R.; Dickey, J. O.; Lichten, S. M.; Herring, T. A.
1994-01-01
Earth rotation data were obtained with GPS during the EPOCH '92 campaign in the summer of 1992. About 10 days of data were acquired from 25 globally distributed stations and a constellation of 17 GPS satellites.
Shear viscosity of the quark-gluon plasma in a kinetic theory approach
Puglisi, A.; Plumari, S.; Scardina, F.; Greco, V.
2014-05-09
One of the main results of heavy ions collision (HIC) at relativistic energy experiments is the very small shear viscosity to entropy density ratio of the Quark-Gluon Plasma, close to the conjectured lower bound η/s=1/4π for systems in the infinite coupling limit. Transport coefficients like shear viscosity are responsible of non-equilibrium properties of a system: Green-Kubo relations give us an exact expression to compute these coefficients. We compute shear viscosity numerically using Green-Kubo relation in the framework of Kinetic Theory solving the relativistic transport Boltzmann equation in a finite box with periodic boundary conditions. We investigate a system of particles interacting via anisotropic and energy dependent cross-section in the range of temperature of interest for HIC. Green-Kubo results are in agreement with Chapman-Enskog approximation while Relaxation Time approximation can underestimates the viscosity of a factor 2. The correct analytic formula for shear viscosity can be used to develop a transport theory with a fixed η/s and have a comparison with physical observables like elliptic flow.
Shear viscosity of the quark-gluon plasma in a kinetic theory approach
NASA Astrophysics Data System (ADS)
Puglisi, A.; Plumari, S.; Scardina, F.; Greco, V.
2014-05-01
One of the main results of heavy ions collision (HIC) at relativistic energy experiments is the very small shear viscosity to entropy density ratio of the Quark-Gluon Plasma, close to the conjectured lower bound η/s=1/4π for systems in the infinite coupling limit. Transport coefficients like shear viscosity are responsible of non-equilibrium properties of a system: Green-Kubo relations give us an exact expression to compute these coefficients. We compute shear viscosity numerically using Green-Kubo relation in the framework of Kinetic Theory solving the relativistic transport Boltzmann equation in a finite box with periodic boundary conditions. We investigate a system of particles interacting via anisotropic and energy dependent cross-section in the range of temperature of interest for HIC. Green-Kubo results are in agreement with Chapman-Enskog approximation while Relaxation Time approximation can underestimates the viscosity of a factor 2. The correct analytic formula for shear viscosity can be used to develop a transport theory with a fixed η/s and have a comparison with physical observables like elliptic flow.
NASA Astrophysics Data System (ADS)
Song, Yan; Lysak, Robert
2015-04-01
In Earth's auroral acceleration regions, the nonlinear interaction of incident and reflected Alfven wave packets can collectively create non-propagating electromagnetic plasma structures, such as the Transverse Alfvenic Double Layer (TA-DL) and Charge Hole (TA-CH). These structures, such as TA-DL, encompass localized strong electrostatic electric fields, nested in low density cavities and surrounded by a local dynamo. Such structures constitute powerful high energy particle accelerators causing auroral particle acceleration and creating both Alfvenic and quasi-static discrete auroras. Similar electromagnetic plasma structures should also be generated by Alfvenic interaction in other inhomogenous cosmic plasma regions, and would constitute effective high energy particle accelerators.
BRIGHTEST CLUSTER GALAXIES AT THE PRESENT EPOCH
Lauer, Tod R.; Postman, Marc; Strauss, Michael A.; Graves, Genevieve J.; Chisari, Nora E.
2014-12-20
We have obtained photometry and spectroscopy of 433 z ≤ 0.08 brightest cluster galaxies (BCGs) in a full-sky survey of Abell clusters to construct a BCG sample suitable for probing deviations from the local Hubble flow. The BCG Hubble diagram over 0 < z < 0.08 is consistent to within 2% of the Hubble relation specified by a Ω {sub m} = 0.3, Λ = 0.7 cosmology. This sample allows us to explore the structural and photometric properties of BCGs at the present epoch, their location in their hosting galaxy clusters, and the effects of the cluster environment on their structure and evolution. We revisit the L{sub m} -α relation for BCGs, which uses α, the log-slope of the BCG photometric curve of growth, to predict the metric luminosity in an aperture with 14.3 kpc radius, L{sub m} , for use as a distance indicator. Residuals in the relation are 0.27 mag rms. We measure central stellar velocity dispersions, σ, of the BCGs, finding the Faber-Jackson relation to flatten as the metric aperture grows to include an increasing fraction of the total BCG luminosity. A three-parameter ''metric plane'' relation using α and σ together gives the best prediction of L{sub m} , with 0.21 mag residuals. The distribution of projected spatial offsets, r{sub x} of BCGs from the X-ray-defined cluster center is a steep γ = –2.33 power law over 1 < r{sub x} < 10{sup 3} kpc. The median offset is ∼10 kpc, but ∼15% of the BCGs have r{sub x} > 100 kpc. The absolute cluster-dispersion normalized BCG peculiar velocity |ΔV {sub 1}|/σ {sub c} follows an exponential distribution with scale length 0.39 ± 0.03. Both L{sub m} and α increase with σ {sub c}. The α parameter is further moderated by both the spatial and velocity offset from the cluster center, with larger α correlated with the proximity of the BCG to the cluster mean velocity or potential center. At the same time, position in the cluster has little effect on L{sub m} . Likewise, residuals from the metric plane
[Demographic transition at the epoch of industrialization].
Billig, W
1984-01-01
The relationship between the early stages of industrialization and population factors in the United Kingdom, France, and the United States is analyzed from a Marxist perspective. The author attempts to associate successive phases of industrialization with phases of the demographic transition. He concludes that no comprehensive general theory concerning this relationship has been established. (summary in ENG, RUS) PMID:12266382
Thin current sheet embedded within a thicker plasma sheet: Self-consistent kinetic theory
NASA Astrophysics Data System (ADS)
Sitnov, M. I.; Zelenyi, L. M.; Malova, H. V.; Sharma, A. S.
2000-06-01
A self-consistent theory of thin current sheets, where the magnetic field line tension is balanced by the ion inertia rather than by the pressure gradient, is presented. Assuming that ions are the main current carriers and their dynamics is quasi-adiabatic, the Maxwell-Vlasov equations are reduced to the nonlocal analogue of the Grad-Shafranov equation using a new set of integrals of motion, namely, the particle energy and the sheet invariant of the quasi-adiabatic motion. It is shown that for a drifting Maxwellian distribution of ions outside the sheet the equilibrium equation can be reduced in the limits of strong and weak anisotropy to universal equations that determine families of equilibria with similar profiles of the magnetic field. In the region Bn/B0
Transport coefficients of Quark-Gluon Plasma in a Kinetic Theory approach
NASA Astrophysics Data System (ADS)
Puglisi, A.; Plumari, S.; Scardina, F.; Greco, V.
2014-07-01
One of the main results of heavy ions collision at relativistic energy experiments is the very small shear viscosity to entropy density ratio of the Quark-Gluon Plasma, close to the conjectured lower bound η/s = 1/4π for systems in the infinite coupling limit. Transport coefficients like shear viscosity are responsible of non-equilibrium properties of a system: Green- Kubo relations give us an exact expression to compute these coefficients. We computed shear viscosity numerically using Green-Kubo relation in the framework of Kinetic Theory solving the relativistic transport Boltzmann equation in a finite box with periodic boundary conditions. We investigated different cases of particles, for one component system (gluon matter), interacting via isotropic or anisotropic cross-section in the range of temperature of interest for HIC. Green-Kubo results are in agreement with Chapman-Enskog approximation while Relaxation Time approximation can underestimates the viscosity of a factor 2. Another transport coefficient of interest is the electric conductivity σel which determines the response of QGP to the electromagnetic fields present in the early stage of the collision. We study the σel dependence on microscopic details of interaction and we find also in this case that Relaxation Time Approximation is a good approximation only for isotropic cross-section.
Kinetic theory of electromagnetic plane wave obliquely incident on bounded plasma slab
Angus, J. R.; Krasheninnikov, S. I.; Smolyakov, A. I.
2010-10-15
The effects of electromagnetic plane waves obliquely incident on a warm bounded plasma slab of finite length L are studied by solving the coupled Vlasov-Maxwell set of equations. It is shown that the solution can be greatly simplified in the limit where thermal effects are most important by expanding in small parameters and introducing self-similar variables. These solutions reveal that the coupling of thermal effects with the angle of incidence is negligible in the region of bounce resonance and anomalous skin effect. In the region of the anomalous skin effect, the heating is shown to scale linearly with the anomalous skin depth {delta}{sub a} when {delta}{sub a}<
Modified gravity and the radiation dominated epoch
NASA Astrophysics Data System (ADS)
van de Bruck, Carsten; Sculthorpe, Gregory I.
2013-02-01
In this paper we consider scalar-tensor theories, allowing for both conformal and disformal couplings to a fluid with a general equation of state. We derive the effective coupling for both background cosmology and for perturbations in that fluid. As an application we consider the scalar degree of freedom to be coupled to baryons and study the dynamics of the tightly coupled photon-baryon fluid in the early Universe. We derive an expression for the effective speed of sound, which differs from its value in General Relativity. We apply our findings to the μ-distortion of the cosmic microwave background radiation, which depends on the effective sound-speed of the photon-baryon fluid, and show that the predictions differ from General Relativity. Thus, the μ-distortion provides further information about gravity in the very early Universe well before decoupling.
Shapiro, Paul R; Mao, Yi; Iliev, Ilian T; Mellema, Garrelt; Datta, Kanan K; Ahn, Kyungjin; Koda, Jun
2013-04-12
The 21 cm background from the epoch of reionization is a promising cosmological probe: line-of-sight velocity fluctuations distort redshift, so brightness fluctuations in Fourier space depend upon angle, which linear theory shows can separate cosmological from astrophysical information. Nonlinear fluctuations in ionization, density, and velocity change this, however. The validity and accuracy of the separation scheme are tested here for the first time, by detailed reionization simulations. The scheme works reasonably well early in reionization (≲40% ionized), but not late (≳80% ionized).
Hassanein, A.; Konkashbaev, I.
1999-11-08
Surface and structural damage to plasma-facing components (PFCs) due to the frequent loss of plasma confinement remains a serious problem for the tokamak reactor concept. The deposited plasma energy causes significant surface erosion, possible structural failure, and frequent plasma contamination. Surface damage consists of vaporization, spallation, and liquid splatter of metallic materials. Structural damage includes large temperature increases in structural materials and at the interfaces between surface coatings and structural members. To evaluate the lifetimes of plasma-facing materials and nearby components and to predict the various forms of damage that they experience, comprehensive models (contained in the HEIGHTS computer simulation package) are developed, integrated self-consistently, and enhanced. Splashing mechanisms such as bubble boiling and various liquid magnetohydrodynamic instabilities and brittle destruction mechanisms of nonmelting materials are being examined. The design requirements and implications of plasma-facing and nearby components are discussed, along with recommendations to mitigate and reduce the effects of plasma instabilities on reactor components.
Almeida, P. G. C.; Benilov, M. S.
2013-10-15
The work is aimed at advancing the multiple steady-state solutions that have been found recently in the theory of direct current (DC) glow discharges. It is shown that an account of detailed plasma chemistry and non-locality of electron transport and kinetic coefficients results in an increase of the number of multiple solutions but does not change their pattern. Multiple solutions are shown to exist for discharges in argon and helium provided that discharge pressure is high enough. This result indicates that self-organization in DC glow microdischarges can be observed not only in xenon, which has been the case until recently, but also in other plasma-producing gases; a conclusion that has been confirmed by recent experiments. Existence of secondary bifurcations can explain why patterns of spots grouped in concentric rings, observed in the experiment, possess in many cases higher number of spots in outer rings than in inner ones.
Declinations in the Almagest: accuracy, epoch, and observers
NASA Astrophysics Data System (ADS)
Brandt, John C.; Zimmer, Peter; Jones, Patricia B.
2014-11-01
Almagest declinations attributed to Timocharis, Aristyllos, Hipparchus, and Ptolemy are investigated through comparisons of the reported declinations with the declinations computed from modern positions translated to the earlier epochs. Consistent results indicate an observational accuracy of ≈ 0.1° and epochs of: Timocharis, c. 298 BC; Aristyllos, c. 256 BC, and Hipparchus, c. 128 BC.The ≈ 42-year difference between Aristyllos and Timocharis is confirmed to be statistically significant. The declinations attributed to Ptolemy were likely two distinct groups—observations taken c. AD 57 and observations taken c. AD 128. The later observations could have been taken by Ptolemy himself.
The Anthropocene: a new epoch of geological time?
Zalasiewicz, Jan; Williams, Mark; Haywood, Alan; Ellis, Michael
2011-03-13
Anthropogenic changes to the Earth's climate, land, oceans and biosphere are now so great and so rapid that the concept of a new geological epoch defined by the action of humans, the Anthropocene, is widely and seriously debated. Questions of the scale, magnitude and significance of this environmental change, particularly in the context of the Earth's geological history, provide the basis for this Theme Issue. The Anthropocene, on current evidence, seems to show global change consistent with the suggestion that an epoch-scale boundary has been crossed within the last two centuries.
Deformed matter bounce with dark energy epoch
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-09-01
We extend the loop quantum cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario," the Universe is contracting from an initial noncausal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, and thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential as what follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a rip singularity exists, where the scale factor and Hubble rate diverge; however, the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, first that the ordinary loop quantum cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Second, the fact that both the pressure and the density become complex probably indicates that the description of the cosmic evolution within the theoretical context of loop quantum cosmology ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be rip singularity. We describe the qualitative features of the model, and we also investigate how this cosmology could be realized by a viscous fluid in the context of loop quantum cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of loop quantum cosmology. Finally, we demonstrate how the model can be generated by a vacuum F (R ) gravity.
NASA Astrophysics Data System (ADS)
Zhdanov, V. M.; Stepanenko, A. A.
2016-03-01
In this paper we derive the set of general transport equations for multicomponent partially ionized reactive plasma in the presence of electric and magnetic fields taking into account the internal degrees of freedom and electronic excitation of plasma particles. Our starting point is a generalized Boltzmann equation with the collision integral in the Wang-Chang and Uhlenbeck form and a reactive collision integral. We obtain a set of conservation equations for such plasma and employ a linearized variant of Grad's moment method to derive the system of moment (or transport) equations for the plasma species nonequilibrium parameters. Full and reduced transport equations, resulting from the linearized system of moment equations, are presented, which can be used to obtain transport relations and expressions for transport coefficients of electrons and heavy plasma particles (molecules, atoms and ions) in partially ionized reactive plasma.
Theory and experiments characterizing hypervelocity impact plasmas on biased spacecraft materials
NASA Astrophysics Data System (ADS)
Lee, Nicolas; Close, Sigrid; Goel, Ashish; Lauben, David; Linscott, Ivan; Johnson, Theresa; Strauss, David; Bugiel, Sebastian; Mocker, Anna; Srama, Ralf
2013-03-01
Space weather including solar activity and background plasma sets up spacecraft conditions that can magnify the threat from hypervelocity impacts. Hypervelocity impactors include both meteoroids, traveling between 11 and 72 km/s, and orbital debris, with typical impact speeds of 10 km/s. When an impactor encounters a spacecraft, its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. In order to study this phenomenon, we conducted ground-based experiments to study hypervelocity impact plasmas using a Van de Graaff dust accelerator. Iron projectiles ranging from 10-16 g to 10-11 g were fired at speeds of up to 70 km/s into a variety of target materials under a range of surface charging conditions representative of space weather effects. Impact plasmas associated with bare metal targets as well as spacecraft materials were studied. Plasma expansion models were developed to determine the composition and temperature of the impact plasma, shedding light on the plasma dynamics that can lead to spacecraft electrical anomalies. The dependence of these plasma properties on target material, impact speed, and surface charge was analyzed. Our work includes three major results. First, the initial temperature of the impact plasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impact plasmas from glass targets, unlike that of impact plasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of spacecraft in order to mitigate future impact-related space weather
Antenna-plasma coupling theory for ICRF heating of large tokamaks
Ram, A.; Bers, A.
1982-03-01
The coupling characteristics of antenna structure are studied by analyzing a model where a thin current sheet is placed between a fully conducting wall and a sheet of anisotropic conductivity representing the screen. The inhomogeneous plasma in the shadow of the limiter is assumed to extend from the screen onwards away from the antenna. The excitation of the fields inside the plasma are found by analyzing the radiation properties of this current sheet antenna. We assume that the current distribution of the antenna is given and that the fields excited inside the plasma are absorbed in a single pass. In all experiments to-date the cross-sectional plasmas are relatively small so that the rf conductor is a half-loop around the plasma in the poloidal direction. However, for reactor size plasmas this cannot be done and the antenna dimensions will be small compared to the plasma cross-sections. We, thus, assume an antenna of finite poloidal and toroidal extent with dimensions small compared to the plasma minor radius. We further approximate the coupling geometry by a slab model. The x-axis is taken to be along the plasma inhomogeneity, the y-axis along the poloidal direction and the x-axis along the toroidal magnetic field.
The Utility of Shorter Epochs in Direct Motion Monitoring
ERIC Educational Resources Information Center
Dorsey, Karen; Herrin, Jeph; Krumholz, Harlan; Irwin, Melinda
2009-01-01
This cross-sectional study using direct motion monitoring evaluated whether short epochs increased estimates of moderate or vigorous physical activity (MPA or VPA) and enhanced differences in daily VPA comparing overweight (OW) and nonoverweight (NOW) children. Seventy-seven children (ages 8-10 years) wore accelerometers for 7 days. We calculated…
Sub-Daily Polar Motion During Epoch '92 with GPS
NASA Technical Reports Server (NTRS)
Ibanez-Meier, R.; Freedman, A. P.; Lichten, S. M.; Lindqwister, U. J.; Gross, R. S.; Herring, T. A.
1994-01-01
Data from a worldwide Global Positioning System (GPS) tracking network spanning six days during the EPOCH '92 campaign are used to estimate variations of the Earth's pole position every 30 minutes. The resulting polar motion time series is compared with estimates derived from very long baseline interferometry (VLBI) observations.
NASA Astrophysics Data System (ADS)
Martín, P.; Puerta, J.
The following topics were dealt with: general plasma theory, plasma confinement, shock waves and instabilities in plasma, plasma spectroscopy, astrophysical and space plasmas, pulse power experiments, plasma processing.
NASA Astrophysics Data System (ADS)
Gabet, Xavier; Sauter, Olivier
2013-07-01
The 2012 Joint Varenna-Lausanne International Workshop on the theory of fusion plasmas was very fruitful. A broad variety of topics was addressed, covering turbulence, magnetohydrodynamics (MHD), edge physics, and radio frequency (RF) wave heating. Moreover, the scope of the meeting was extended this year to include the physics of materials and diagnostics for burning plasmas. This evolution reflects the complexity of problems at hand in fusion, some of them triggered by the construction of ITER and JT-60SA. Long-standing problems without immediate consequences have sometimes become an urgent matter in that context. One may refer to, for instance, the choice of plasma facing components or the design of control systems. Another characteristic of these workshops is the interplay between various domains of plasma physics. For instance, MHD modes are currently investigated with gyrokinetic codes, kinetic effects are included in MHD stability analysis more and more, and turbulence is now accounted for in wave propagation problems. This is proof of cross-fertilization and is certainly a healthy sign for our community. Finally, introducing some novelty in the programme does not prevent from us respecting old traditions. As usual, many presentations were dedicated to numerical simulations. Combining advanced numerical techniques with elaborated analytical theory is certainly a trademark of the Varenna-Lausanne Workshop, which was respected again this year. The quality and size of the scientific output from this workshop is shown in this special issue of Plasma Physics and Controlled Fusion; a further 26 papers have already appeared in Journal of Physics: Conference Series in December 2012. We hope the readers will enjoy this special issue, and find therein knowledge and inspiration.
NASA Astrophysics Data System (ADS)
Xaplanteris, C. L.; Xaplanteris, S. C.
2016-05-01
In the present manuscript enough observations and interpretations of three issues of Plasma Physics are presented. The first issue is linked to the common experimental confirmation of plasma waves which appear to be repeated in a standard way while there are also cases where plasma waves change to an unstable state or even to chaotic state. The second issue is associated with a mathematical analysis of the movement of a charged particle using the perturbation theory; which could be used as a guide for new researchers on similar issues. Finally, the suitability and applicability of the perturbation theory or the chaotic theory is presented. Although this study could be conducted on many plasma phenomena (e.g. plasma diffusion) or plasma quantities (e.g. plasma conductivity), here it was decided this study to be conducted on plasma waves and particularly on drift waves. This was because of the significance of waves on the plasmatic state and especially their negative impact on the thermonuclear fusion, but also due to the long-time experience of the plasma laboratory of Demokritos on drift waves.
NASA Astrophysics Data System (ADS)
Das, Madhulita; Chaudhuri, Rajat K.; Chattopadhyay, Sudip; Sinha Mahapatra, Uttam; Mukherjee, P. K.
2011-08-01
Ionization potential and low lying 1S0\\longrightarrow1P1 excitation energies (EE) of highly stripped He-like ions C4 +, Al11 +, and Ar16 + embedded in plasma environment are calculated for the first time using the state-of-the-art coupled cluster (CC)-based linear response theory (LRT) with the four-component relativistic spinors and compared with available experimental data from laser plasma experiments. Debye's screening model is used to estimate the effect of plasma on the ions within the relativistic and non-relativistic framework. The transition energies computed at the CCLRT level using the Debye model agree well with experiment and with other available theoretical data. To our knowledge, no prior CCLRT calculations within the Dirac-Fock framework are available for these systems. Our calculated transition energies for helium-like ions are in accord with experiment; we trust that our predicted EE might be acceptably good for the systems considered. Our preliminary result indicates that CCLRT with the four-component relativistic spinors appears to be a valuable tool for studying the atomic systems where accurate treatments of correlation effects play a crucial role in shaping the spectral lines of ions subjected to plasma environment.
Ramos, J. J.
2010-08-15
A closed theoretical model to describe slow, macroscopic plasma processes in a fusion-relevant collisionality regime is set forward. This formulation is a hybrid one, with fluid conservation equations for particle number, momentum and energy, and drift-kinetic closures. Intended for realistic application to the core of a high-temperature tokamak plasma, the proposed approach is unconventional in that the ion collisionality is ordered lower than in the ion banana regime of neoclassical theory. The present first part of a two-article series concerns the electron system, which is still equivalent to one based on neoclassical electron banana orderings. This system is derived such that it ensures the precise compatibility among the complementary fluid and drift-kinetic equations, and the rigorous treatment of the electric field and the Fokker-Planck-Landau collision operators. As an illustrative application, the special limit of an axisymmetric equilibrium is worked out in detail.
Meade, Christina S; Wang, Jianping; Lin, Xiuyun; Wu, Hao; Poppen, Paul J
2010-04-01
Throughout the 1990s, many villagers in rural China were infected with HIV through commercial plasma/blood donation. These former plasma/blood donors (FPDs) experienced many HIV-related stressors. This study tested a cognitive appraisal model of stress and coping in a sample of HIV-positive adult FPDs. Participants (N = 207) from multiple villages completed a battery of questionnaires assessing HIV-related stress, HIV symptoms, cognitive appraisal, coping behaviors, and psychological distress. Participants reported high levels of HIV-related stress, depression, and anxiety. In a structural equation model, greater HIV-related stress, HIV symptoms, and threat appraisal were directly associated with psychological distress. HIV-related stress was also indirectly associated with psychological distress through threat appraisal. In a second model, coping was found to mediate the relationship between challenge appraisal and psychological distress. Results support the utility of cognitive appraisal theory. Stress management interventions targeting HIV-positive FPDs in China are indicated.
Misra, Shikha; Mishra, S. K.; Sodha, M. S.
2013-01-15
The authors have modified Chow's theory of secondary electron emission (SEE) to take account of the fact that the path length of a primary electron in a spherical particle varies between zero to the diameter or x{sub m} the penetration depth depending on the distance of the path from the centre of the particle. Further by including this modified expression for SEE efficiency, the charging kinetics of spherical grains in a Maxwellian plasma has been developed; it is based on charge balance over dust particles and number balance of electrons and ionic species. It is seen that this effect is more pronounced for smaller particles and higher plasma temperatures. Desirable experimental work has also been discussed.
Electron-ion energy partition when a charged particle slows in a plasma: theory.
Brown, Lowell S; Preston, Dean L; Singleton, Robert L
2012-07-01
The preceding paper [Brown, Preston, and Singleton Jr., Phys. Rev. E 86, 016406 (2012)] presented precise results for the partition of the initial energy E(0) of a fast particle into the ions and electrons--E(I)/E(0) and E(e)/E(0)--when the fast particle slows in a plasma whose ion and electron temperatures may differ. As emphasized in that paper, this is an important problem because nuclear fusion reactions, such as those that occur in an inertial confinement fusion capsule, involve ion temperatures that run away from the electron temperatures. As also noted in the preceding paper, a precise evaluation entails the use of a well-defined Fokker-Planck equation for the phase-space evolution of initially fast projectile particles. When the plasma has differing ion and electron temperatures, the projectiles must slow into a "schizophrenic" final ensemble of particles that has neither the electron nor the ion temperature. This is not a simple Maxwell-Boltzmann distribution since the electrons are not in thermal equilibrium with the ions. Thus, detailed calculations are required for the solution of the problem. These we provide here for a weakly to moderately coupled plasma. The Fokker-Planck equation holds to first subleading order in the dimensionless plasma coupling constant, which translates to computing to order n ln n (leading) and n (subleading) in the plasma density n. The energy partitions for a background plasma in thermal equilibrium have been previously computed, but the order n terms have not been calculated, only estimated. The "schizophrenic" final ensemble of slowed particles gives a new mechanism to bring the electron and ion temperatures together. The rate at which this new mechanism brings the electrons and ions in the plasma into thermal equilibrium will be computed. PMID:23005550
Epoch-based Entropy for Early Screening of Alzheimer's Disease.
Houmani, N; Dreyfus, G; Vialatte, F B
2015-12-01
In this paper, we introduce a novel entropy measure, termed epoch-based entropy. This measure quantifies disorder of EEG signals both at the time level and spatial level, using local density estimation by a Hidden Markov Model on inter-channel stationary epochs. The investigation is led on a multi-centric EEG database recorded from patients at an early stage of Alzheimer's disease (AD) and age-matched healthy subjects. We investigate the classification performances of this method, its robustness to noise, and its sensitivity to sampling frequency and to variations of hyperparameters. The measure is compared to two alternative complexity measures, Shannon's entropy and correlation dimension. The classification accuracies for the discrimination of AD patients from healthy subjects were estimated using a linear classifier designed on a development dataset, and subsequently tested on an independent test set. Epoch-based entropy reached a classification accuracy of 83% on the test dataset (specificity = 83.3%, sensitivity = 82.3%), outperforming the two other complexity measures. Furthermore, it was shown to be more stable to hyperparameter variations, and less sensitive to noise and sampling frequency disturbances than the other two complexity measures.
On zero frequency magnetic fluctuations in plasmas
Tajima, T.; Cable, S. . Inst. for Fusion Studies); Kulsrud, R.M. . Dept. of Astrophysical Sciences)
1992-01-01
A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy lost'' by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l angle}B{sup 2}{r angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.
On zero frequency magnetic fluctuations in plasmas
Tajima, T.; Cable, S.; Kulsrud, R.M.
1992-01-01
A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy ``lost`` by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l_angle}B{sup 2}{r_angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.
NASA Technical Reports Server (NTRS)
Gary, S. P.
1984-01-01
This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.
NASA Astrophysics Data System (ADS)
Zhdanov, V. M.; Stepanenko, A. A.
2016-11-01
The previously obtained in (Zhdanov and Stepanenko, 2016) general transport equations for partially ionized reactive plasma are employed for analysis of electron transport properties in molecular and atomic plasmas. We account for both elastic and inelastic interaction channels of electrons with atoms and molecules of plasma and also the processes of electron impact ionization of neutral particles and three-body ion-electron recombination. The system of scalar transport equations for electrons is discussed and the expressions for non-equilibrium corrections to electron ionization and recombination rates and the diagonal part of the electron pressure tensor are derived. Special attention is paid to analysis of electron energy relaxation during collisions with plasma particles having internal degrees of freedom and the expression for the electron coefficient of inelastic energy losses is deduced. We also derive the expressions for electron vector and tensorial transport fluxes and the corresponding transport coefficients for partially ionized reactive plasma, which represent a generalization of the well-known results obtained by Devoto (1967). The results of numerical evaluation of contribution from electron inelastic collisions with neutral particles to electron transport properties are presented for a series of molecular and atomic gases.
Phase-space description of plasma waves. Part 1. Linear theory
NASA Astrophysics Data System (ADS)
Biro, T.; Rönnmark, K.
1992-06-01
We develop an (r, k) phase-space description of waves in plasmas by introducing Gaussian window functions to separate short-scale oscillations from long-scale modulations of the wave fields and variations in the plasma parameters. To obtain a wave equation that unambiguously separates conservative dynamics from dissipation in an inhomogeneous and time-varying background plasma, we first discuss the proper form of the current response function. In analogy with the particle distribution function f(v, r, t), we introduce a wave density N(k, r, t) on phase space. This function is proved to satisfy a simple continuity equation. Dissipation is also included, and this allows us to describe the damping or growth of wave density along rays. Problems involving geometric optics of continuous media often appear simpler when viewed in phase space, since the flow of N in phase space is incompressible.
NASA Astrophysics Data System (ADS)
Schlickeiser, R.; Ganz, A.; Kolberg, U.; Yoon, P. H.
2015-10-01
Starting from the recently derived general expressions for the electromagnetic fluctuation spectra (electric and magnetic field) from uncorrelated plasma particles in plasmas with an uniform magnetic field, the case of strictly parallel ( k ⊥ = 0 ) oriented wave vectors with the respect to the uniform magnetic field direction is investigated. To derive fluctuation spectra valid in the entire complex frequency plane, the relevant dispersion functions and form factors are analytically continued to negative values of the imaginary part of the frequency for arbitrary gyrotropic plasma particle distribution functions. The generalized fluctuation-dissipation theorems for non-collective fluctuations in isotropic equal-temperature thermal distribution functions for general complex values of the frequency of the fluctuations with parallel wave vectors are derived.
Theory and observation of a dynamically evolving negative ion plasma. [in F region
NASA Technical Reports Server (NTRS)
Mendillo, M.; Forbes, J.
1982-01-01
The study described here examines the full range of negative-ion chemistry in the upper ionosphere by using current reaction rate data to investigate the many chemical paths SF6-type injections might take in an F region environment. Special attention is given to the conditions required to create heavy negative ions that persist long enough to affect the dynamical properties of the F region. The ambipolar diffusion characteristics of a three-component plasma are described, and estimates are given of the incoherent scatter spectra obtained from such a plasma. Model calculations using a first-order chemical code are defined and tested in order to investigate the actual types of negative-ion plasma capable of being created under nighttime conditions.
Krommes, J.A.
2000-01-18
Recent results and future challenges in the systematic analytical description of plasma turbulence are described. First, the importance of statistical realizability is stressed, and the development and successes of the Realizable Markovian Closure are briefly reviewed. Next, submarginal turbulence (linearly stable but nonlinearly self-sustained fluctuations) is considered and the relevance of nonlinear instability in neutral-fluid shear flows to submarginal turbulence in magnetized plasmas is discussed. For the Hasegawa-Wakatani equations, a self-consistency loop that leads to steady-state vortex regeneration in the presence of dissipation is demonstrated and a partial unification of recent work of Drake (for plasmas) and of Waleffe (for neutral fluids) is given. Brief remarks are made on the difficulties facing a quantitatively accurate statistical description of submarginal turbulence. Finally, possible connections between intermittency, submarginal turbulence, and self-organized criticality (SOC) are considered and outstanding questions are identified.
Theory of coherent transition radiation generated at a plasma-vacuum interface
Schroeder, Carl B.; Esarey, Eric; van Tilborg, Jeroen; Leemans, Wim P.
2003-06-26
Transition radiation generated by an electron beam, produced by a laser wakefield accelerator operating in the self-modulated regime, crossing the plasma-vacuum boundary is considered. The angular distributions and spectra are calculated for both the incoherent and coherent radiation. The effects of the longitudinal and transverse momentum distributions on the differential energy spectra are examined. Diffraction radiation from the finite transverse extent of the plasma is considered and shown to strongly modify the spectra and energy radiated for long wavelength radiation. This method of transition radiation generation has the capability of producing high peak power THz radiation, of order 100 (mu)J/pulse at the plasma-vacuum interface, which is several orders of magnitude beyond current state-of-the-art THz sources.
Physics of laser fusion. Vol. I. Theory of the coronal plasma in laser-fusion targets
Max, C.E.
1981-12-01
This monograph deals with the physics of the coronal region in laser fusion targets. The corona consists of hot plasma which has been evaporated from the initially solid target during laser heating. It is in the corona that the laser light is absorbed by the target, and the resulting thermal energy is conducted toward cold high-density regions, where ablation occurs. The topics to be discussed are theoretical mechanisms for laser light absorption and reflection, hot-electron production, and the physics of heat conduction in laser-produced plasmas. An accompanying monograph by H. Ahlstrom (Vol.II) reviews the facilities, diagnostics, and data from recent laser fusion experiments.
Theory of a Stationary Current-Free Double Layer in a Collisionless Plasma
Ahedo, Eduardo; Martinez Sanchez, Manuel
2009-09-25
Current-free double layers can develop in a collisionless, inertia-controlled plasma with two electron populations, expanding in a convergent-divergent nozzle. The double layer characteristics depend on whether they develop at the nozzle divergent side, convergent side, or throat. The divergent-geometry double layer describes faithfully the Hairapetian-Stenzel experiment [Phys. Rev. Lett. 65, 175 (1990)], whereas the two other types correspond with those studied in self-similar expansions and wall-collection models of similar plasmas.
Weakly relativistic quantum kinetic theory for electrostatic wave modes in magnetized plasmas
Hussain, Azhar; Stefan, Martin; Brodin, Gert
2014-03-15
We have derived the electrostatic dispersion relation in a magnetized plasma using a recently developed quantum kinetic model based on the Dirac equation. The model contains weakly relativistic spin effects such as Thomas precession, the polarization currents associated with the spin and the spin-orbit coupling. It turns out that for strictly electrostatic perturbations the non-relativistic spin effects vanish, and the modification of the classical dispersion relation is solely associated with the relativistic terms. Several new wave modes appear due the electron spin effects, and an example for astrophysical plasmas are given.
Zaginaylov, G. I.; Shcherbinin, V. I.; Schuenemann, K.
2007-08-15
The linear stage of electron cyclotron instability of quasi-TE modes in a waveguide filled with a magnetoactive plasma is studied using a kinetic approach. The dispersion relation of the instability is derived analytically. It is shown that the presence of the plasma can reduce both the linear instability growth rate and the instability region; in this case, the maximum of the growth rate is displaced toward lower frequencies. The results obtained are compared with the available experimental observations. They can be useful for optimizing the operating regimes of high-power continuous-wave gyrotrons.
NASA Astrophysics Data System (ADS)
Gatsonis, Nikolaos Achilleas
A study is presented of the electrodynamic interactions within the plasma environment induced around spacecraft in Low Earth Orbit. A fully three-dimensional theory and a computational model is developed for an artificial plasma cloud created by spacecraft with the potential of releasing neutrals and/or plasma into the ambient ionosphere. A fluid model for the plasma transport is derived. The forces included in the momentum balance are due to electric fields, pressure, gravity, drag due to collisions and perturbative inertia terms. The Flux Corrected Transport (FCT) scheme is used for the numerical solution of the hyperbolic continuity equations. This approach limits the artificial dissipation or dispersion arising in the numerical solution. The 3D -FCT algorithm, and the stability characteristics of the high and low order schemes used in the FCT are discussed. The equation for the electrostatic potential is a three-dimensional nonself-adjoint elliptic equation with highly dissimilar coefficients. The numerical solution of the resulting large, sparse, asymmetric system of equations is discussed. Initial time numerical simulations are performed. A water-bag plasma cloud model is used to demonstrate the current coupling process. For neutral densities higher than the ambient the plasma cloud develops a transverse drift of the order of the orbital velocity. Simulations of typical spacecraft operations are performed and the created water plasma cloud is studied. It is shown that the flow of neutrals is in the free molecular regime. The effects of altitude of the release, orientation of the thrust vector with regard to the magnetic field, and latitude are considered. It is shown that a large water ion cloud is formed with densities of the order of the ambient oxygen ions. The ultraviolet radiation emission is shown to modify the signature of the spacecraft. The model predicts qualitatively most of the observations. Quantitatively predictions are within the measured
O'Brien, K.J.
1985-01-01
It is demonstrated that the cold Vlasov beam, the circle-limit of the warm Vlasov beam, the spread-mass model, and the energy-group model of a relativistic electron beam undergoing linear hose instability, are all formally equivalent. Therefore, the circle-orbit beam is the natural starting point for a higher order theory. Introducing the next order in non-circularity the author makes contact with the adiabatic theory for warm beams. The adiabatic theory is founded upon the existence of transverse action invariants that remain sufficiently well-defined, despite the nonaxisymmetric potential and the coupling resonances driven by linear hose instability. The existence of action invariants enables the elimination of a fast variable, analogous to gyro-motion, called vortex-gyration. One problem with adiabatic beam theory is that coupling resonances between the degrees of freedom could destroy the adiabatic invariants upon which the theory rests. KAM theory is employed here to study the destruction of action invariants due to linear hose instability. Nonaxisymmetric adiabatic beams are defined to be those for which KAM tori exist in the transverse phase space. For hose deflections of the magnitude considered in linear theory, KAM tori persist, preventing the destruction of the invariants.
Phase-space description of plasma waves: Linear and nonlinear theory
NASA Astrophysics Data System (ADS)
Biro, Thomas
1992-11-01
A (r,k) phase description of waves in plasmas is developed by introducing Gaussian window functions to separate short scale oscillations from long scale modulations of the wave fields and variations in the plasma parameters. To obtain a wave equation that unambiguously separates conservative dynamics from dissipation also in an inhomogeneous and time varying background plasma, the proper form of the current response function, is discussed. On the analogy of the particle distribution function f(v,r,t), a wave density N(k,r,t) is introduced on phase space. This function is proven to satisfy a simple continuity equation. Dissipation is also included, and this allows the damping or growth of wave density along rays to be described. Problems involving geometric optics of continuous media often appear simpler when viewed in phase space, since the flow of N in phase space is incompressible. Within the phase space representation, a very general formula for the second order nonlinear current is obtained in terms of the vector potential. This formula is a convenient starting point for studies of coherent as well as turbulent nonlinear processes. Kinetic equations for weakly inhomogeneous and turbulent plasmas are derived, including the effects of inhomogeneous turbulence, wave convection and refraction.
Nonlinear theory of ionic sound waves in a hot quantum-degenerate electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Dubinov, A. E.; Sazonkin, M. A.
2010-11-01
A collisionless nonmagnetized e-p-i plasma consisting of quantum-degenerate gases of ions, electrons, and positrons at nonzero temperatures is considered. The dispersion equation for isothermal ionic sound waves is derived and analyzed, and an exact expression is obtained for the linear velocity of ionic sound. Analysis of the dispersion equation has made it possible to determine the ranges of parameters in which nonlinear solutions in the form of solitons should be sought. A nonlinear theory of isothermal ionic sound waves is developed and used for obtaining and analyzing the exact solution to the system of initial equations. Analysis has been carried out by the method of the Bernoulli pseudopotential. The ranges of phase velocities of periodic ionic sound waves and soliton velocities are determined. It is shown that in the plasma under investigation, these ranges do not overlap and that the soliton velocity cannot be lower than the linear velocity of ionic sound. The profiles of physical quantities in a periodic wave and in a soliton are constructed, as well as the dependences of the velocity of sound and the critical velocity on the ionic concentration in the plasma. It is shown that these velocities increase with the ion concentration.
Nonlinear theory of ionic sound waves in a hot quantum-degenerate electron-positron-ion plasma
Dubinov, A. E. Sazonkin, M. A.
2010-11-15
A collisionless nonmagnetized e-p-i plasma consisting of quantum-degenerate gases of ions, electrons, and positrons at nonzero temperatures is considered. The dispersion equation for isothermal ionic sound waves is derived and analyzed, and an exact expression is obtained for the linear velocity of ionic sound. Analysis of the dispersion equation has made it possible to determine the ranges of parameters in which nonlinear solutions in the form of solitons should be sought. A nonlinear theory of isothermal ionic sound waves is developed and used for obtaining and analyzing the exact solution to the system of initial equations. Analysis has been carried out by the method of the Bernoulli pseudopotential. The ranges of phase velocities of periodic ionic sound waves and soliton velocities are determined. It is shown that in the plasma under investigation, these ranges do not overlap and that the soliton velocity cannot be lower than the linear velocity of ionic sound. The profiles of physical quantities in a periodic wave and in a soliton are constructed, as well as the dependences of the velocity of sound and the critical velocity on the ionic concentration in the plasma. It is shown that these velocities increase with the ion concentration.
Goebel, Dan M.; Jameson, Kristina K.; Watkins, Ron M.; Katz, Ira; Mikellides, Ioannis G.
2005-12-01
A detailed study of the spatial variation of plasma density, temperature, and potential in hollow cathodes using miniature fast scanning probes has been undertaken in order to better understand the cathode operation and to provide benchmark data for the modeling of the cathode performance and life described in a companion paper. Profiles are obtained throughout the discharge and in the very high-density orifice region by pneumatically driven Langmuir probes, which are inserted directly into the hollow cathode orifice from either the upstream insert region inside the hollow cathode or from the downstream anode-plasma region. A fast transverse-scanning probe is also used to provide radial profiles of the cathode plume as a function of position from the cathode exit. The probes are extremely small to avoid perturbing the plasma; the ceramic tube insulator is 0.05 cm in diameter with a probe tip area of 0.002 cm{sup 2}. A series of current-voltage characteristics are obtained by applying a rapid sawtooth voltage wave form to the probe as it is scanned through the plasma at speeds of up to 2 m/s to produce the profiles with a spatial resolution of about 0.05 cm. At discharge currents of 10-25 A from the 1.5-cm-diameter hollow cathode, the plasma density inside the cathode is found to exceed 10{sup 14} cm{sup -3}, with the peak density occurring upstream of the orifice. The plasma potentials on axis inside the cathode are found to be in the 10-20 V range with electron temperatures of 2-5 eV, depending on the discharge current and gas flow rate. A potential discontinuity or double layer of less than 10 V is observed in the orifice region, and under certain conditions appears in the bright 'plasma ball' in front of the cathode. This structure tends to change location and magnitude with discharge current, gas flow, and orifice size. A potential maximum proposed in the literature to exist in or near the cathode orifice is not observed. Instead, the plasma potential increases
Yoon, P. H. E-mail: rsch@tp4.rub.de; Schlickeiser, R. E-mail: rsch@tp4.rub.de; Kolberg, U. E-mail: rsch@tp4.rub.de
2014-03-15
Any fully ionized collisionless plasma with finite random particle velocities contains electric and magnetic field fluctuations. The fluctuations can be of three different types: weakly damped, weakly propagating, or aperiodic. The kinetics of these fluctuations in general unmagnetized plasmas, governed by the competition of spontaneous emission, absorption, and stimulated emission processes, is investigated, extending the well-known results for weakly damped fluctuations. The generalized Kirchhoff radiation law for both collective and noncollective fluctuations is derived, which in stationary plasmas provides the equilibrium energy densities of electromagnetic fluctuations by the ratio of the respective spontaneous emission coefficient and the true absorption coefficient. As an illustrative example, the equilibrium energy densities of aperiodic transverse collective electric and magnetic fluctuations in an isotropic thermal electron-proton plasmas of density n{sub e} are calculated as |δB|=√((δB){sup 2})=2.8(n{sub e}m{sub e}c{sup 2}){sup 1/2}g{sup 1/2}β{sub e}{sup 7/4} and |δE|=√((δE){sup 2})=3.2(n{sub e}m{sub e}c{sup 2}){sup 1/2}g{sup 1/3}β{sub e}{sup 2}, where g and β{sub e} denote the plasma parameter and the thermal electron velocity in units of the speed of light, respectively. For densities and temperatures of the reionized early intergalactic medium, |δB|=6·10{sup −18}G and |δE|=2·10{sup −16}G result.
From liquid crystal models to the guiding-center theory of magnetized plasmas
NASA Astrophysics Data System (ADS)
Tronci, Cesare
2016-08-01
Upon combining Northrop's picture of charged particle motion with modern liquid crystal theories, this paper provides a new description of guiding center dynamics (to lowest order). This new perspective is based on a rotation gauge field (gyrogauge) that encodes rotations around the magnetic field. In liquid crystal theory, an analogue rotation field is used to encode the rotational state of rod-like molecules. Instead of resorting to sophisticated tools (e.g. Hamiltonian perturbation theory and Lie series expansions) that still remain essential in higher-order gyrokinetics, the present approach combines the WKB method with a simple kinematical ansatz, which is then replaced into the charged particle Lagrangian. The latter is eventually averaged over the gyrophase to produce the guiding-center equations. A crucial role is played by the vector potential for the gyrogauge field. A similar vector potential is related to liquid crystal defects and is known as wryness tensor in Eringen's micropolar theory.
Douglass, S.R.; Eddy, C. Jr.; Lampe, M.; Joyce, G.; Slinker, S.; Weber, B.V.
1995-12-31
The authors are currently investigating the mechanisms of microwave power absorption in an ECR plasma. The microwave electric field is detected with an antenna at the end of a shielded co-ax cable, connected to a bolometer for power measurements. Initial measurements have been 1-D along the axis of the plasma chamber. Later, 3-D profiles will be made of the microwave heating power distribution. A comparison of the experimental results with the theoretical microwave absorption are presented. A ray tracing analysis of the propagating right hand wave are given, including both collisional and collisionless absorption. Mode conversion effects are studied to explain why most of the power is absorbed at the entry window, especially the L wave power.
Microwave N{sub 2}-Ar plasma torch. II. Experiment and comparison with theory
Henriques, J.; Tatarova, E.; Dias, F. M.; Ferreira, C. M.
2011-01-15
Spatially resolved emission spectroscopy techniques have been used to determine the gas temperature, the electron, and N{sub 2}{sup +} ion densities and the relative emission intensities of radiative species in a microwave (2.45 GHz) plasma torch driven by a surface wave. The experimental results have been analyzed in terms of a two-dimensional theoretical model based on a self-consistent treatment of particles kinetics, gas dynamics, and wave electrodynamics. The measured spatial variations in the various quantities agree well with the model predictions. The radially averaged gas temperature is around 3000 K and varies only slowly along the discharge zone of the source but it drops sharply down to about 400 K in the postdischarge. The experimental wave dispersion characteristics nearly follow the theoretical ones, thus confirming that this plasma source is driven by a surface wave.
The development of a Krook model for nonlocal transport in laser produced plasmas I. Basic theory
NASA Astrophysics Data System (ADS)
Manheimer, Wallace; Colombant, Denis; Goncharov, Valeri
2008-11-01
We examine the Krook model as a means of quantifying the problem of nonlocal transport of electron energy in laser produced plasmas. The result is an expression for the nonlocal electron energy flux q. The roles of both flux limitation and preheat are clearly delineated. Furthermore, it develops a test for the validity of this model. This is a physics based ``first principles'' model that can be economically incorporated into a fluid simulation.
The development of a Krook model for nonlocal transport in laser produced plasmas. I. Basic theory
NASA Astrophysics Data System (ADS)
Manheimer, Wallace; Colombant, Denis; Goncharov, Valeri
2008-08-01
This paper examines the Krook model as a means of quantifying the problem of nonlocal transport of electron energy in laser produced plasmas. The result is an expression for the nonlocal electron energy flux q. The roles of both flux limitation and preheat are clearly delineated. Furthermore, it develops a test for the validity of this model. This is a physics based, "first principles" model that can be economically incorporated into a fluid simulation.
Closure and transport theory for high-collisionality electron-ion plasmas
NASA Astrophysics Data System (ADS)
Ji, Jeong-Young; Held, Eric D.
2013-04-01
Systems of algebraic equations for a high-collisionality electron-ion plasma are constructed from the general moment equations with linearized collision operators [J.-Y. Ji and E. D. Held, Phys. Plasmas 13, 102103 (2006) and J.-Y. Ji and E. D. Held, Phys. Plasmas 15, 102101 (2008)]. A systematic geometric method is invented and applied to solve the system of equations to find closure and transport relations. It is known that some closure coefficients of Braginskii [S. I. Braginskii, Reviews of Plasma Physics (Consultants Bureau, New York, 1965), Vol. 1] are in error up to 65% for some finite values of x (cyclotron frequency × electron-ion collision time) and have significant error in the large-x limit [E. M. Epperlein and M. G. Haines, Phys. Fluids 29, 1029 (1986)]. In this work, fitting formulas for electron coefficients are obtained from the 160 moment (Laguerre polynomial) solution, which converges with increasing moments for x ≤100 and from the asymptotic solution for large x-values. The new fitting formulas are practically exact (less than 1% error) for arbitrary x and Z (the ion charge number, checked up to Z = 100). The ion coefficients for equal electron and ion temperatures are moderately modified by including the ion-electron collision operator. When the ion temperature is higher than the electron temperature, the ion-electron collision and the temperature change terms in the moment equations must be kept. The ion coefficient formulas from 3 moment (Laguerre polynomial) calculations, precise to less than 0.4% error from the convergent values, are explicitly written.
New Release of the BSM Epoch Photometry Database
NASA Astrophysics Data System (ADS)
Henden, A.
2016-06-01
(Abstract only) The Bright Star Monitor (BSM) Epoch Photometry Database (EPD) is a searchable catalog of all observations made by one of the AAVSO's five BSM systems. The newest release of this database contains some 100 million datasets, from both northern and southern hemispheres, taken over the last six years. These have been calibrated by both nightly visits to Landolt standard fields as well as through the use of the Tycho2 photometric catalog. The paper will describe how the observations were made, how to access the catalog, and the limitations to the photometric accuracy. Some examples of well-studied fields will be shown.
Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go
2016-05-10
It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle's Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas.
Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go
2016-01-01
It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle’s Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas. PMID:27160346
Krommes, John A.
2015-09-21
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 functionmore » $${\\mathcal{D}}$$. Dupree’s method of using$${\\mathcal{D}}$$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$C$and an infinitesimal response function$R$, which subsumes$${\\mathcal{D}}$$. An important example is the direct-interaction approximation (DIA). It is shown how to use Novikov’s theorem to develop an$$\\boldsymbol{x}$$-space approach to the DIA that is complementary to the original$$\\boldsymbol{k}$$-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$${\\mathcal{D}}$$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$${\\mathcal{D}}$$). The role of$R$in the calculation of the symmetry-breaking (zonostrophic) instability of homogeneous turbulence to the generation of inhomogeneous mean flows is
Physics of the Intergalactic Medium During the Epoch of Reionization
NASA Astrophysics Data System (ADS)
Lidz, Adam
A major goal of observational and theoretical cosmology is to observe the largely unexplored time period in the history of our universe when the first galaxies form, and to interpret these measurements. Early galaxies dramatically impacted the gas around them in the surrounding intergalactic medium (IGM) by photoionzing the gas during the "Epoch of Reionization" (EoR). This epoch likely spanned an extended stretch in cosmic time: ionized regions formed and grew around early generations of galaxies, gradually filling a larger and larger fraction of the volume of the universe. At some time—thus far uncertain, but within the first billion years or so after the big bang—essentially the entire volume of the universe became filled with ionized gas. The properties of the IGM provide valuable information regarding the formation time and nature of early galaxy populations, and many approaches for studying the first luminous sources are hence based on measurements of the surrounding intergalactic gas. The prospects for improved reionization-era observations of the IGM and early galaxy populations over the next decade are outstanding. Motivated by this, we review the current state of models of the IGM during reionization. We focus on a few key aspects of reionization-era phenomenology and describe: the redshift evolution of the volume-averaged ionization fraction, the properties of the sources and sinks of ionizing photons, along with models describing the spatial variations in the ionization fraction, the ultraviolet radiation field, the temperature of the IGM, and the gas density distribution.
Moon-based Epoch of Reionization Imaging Telescope (MERIT)
NASA Astrophysics Data System (ADS)
Jones, D. L.; MacDowall, R. J.; Bale, S. D.; Demaio, L.; Kasper, J. C.; Weiler, K. W.
2005-05-01
Radio observations of emission and absorption from neutral Hydrogen during the Epoch of Reionization (EoR) can reveal how structure leading to the first stars, galaxies, and black holes formed in the intergalactic medium between redshifts of about 6 and at least 20. Ground-based low frequency radio arrays are under construction (LOFAR, PAST) or development (LWA, MWA) to detect and eventually image the EoR signal. The Moon-based Epoch of Reionization Imaging Telescope (MERIT) is a mission concept that is intended to extend ground-based observations of the EoR to the highest possible dynamic range and image fidelity. This can be accomplished by locating the MERIT array on the far side of the moon. The array is composed of 10-12 radial arms, each 1-2 km in length. Each arm has several hundred dipole antennas and feedlines printed on a very thin sheet of kapton with a total mass of about 300 kg. This provides a convenient way to deploy thousands of individual antennas, and a centrally condensed distribution of array baselines. The lunar farside provides shielding from terrestrial natural and technological radio interference, shielding (half the time) from strong solar radio emissions, and freedom from the corrupting influence of Earth's ionosphere. Various options for array deployment and data transmission to Earth will be described is this paper. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Sati, Priti; Tripathi, V. K.
2012-12-15
Parametric decay of a large amplitude electromagnetic wave into two electromagnetic modes in a rippled density plasma channel is investigated. The channel is taken to possess step density profile besides a density ripple of axial wave vector. The density ripple accounts for the momentum mismatch between the interacting waves and facilitates nonlinear coupling. For a given pump wave frequency, the requisite ripple wave number varies only a little w.r.t. the frequency of the low frequency decay wave. The radial localization of electromagnetic wave reduces the growth rate of the parametric instability. The growth rate decreases with the frequency of low frequency electromagnetic wave.
Quasilinear theory of the ordinary-mode electron-cyclotron resonance in plasmas
Arunasalam, V.; Efthimion, P.C.; Hosea, J.C.; Hsuan, H.; Taylor, G.
1983-11-01
A coupled set of equations, one describing the time evolution of the ordinary-mode wave energy and the other describing the time evolution of the electron distribution function is presented. The wave damping is mainly determined by T/sub parallel/ while the radiative equilibrium is mainly an equipartition with T/sub perpendicular/. The time rate of change of T/sub perpendicular/, T/sub parallel/, particle (N/sub 0/), and current (J/sub parellel/) densities are examined for finite k/sub parallel/ electron-cyclotron-resonance heating of plasmas.
Peeters, A. G.; Angioni, C.; Strintzi, D.
2009-03-15
The comment addresses questions raised on the derivation of the momentum pinch velocity due to the Coriolis drift effect [A. G. Peeters et al., Phys. Rev. Lett. 98, 265003 (2007)]. These concern the definition of the gradient, and the scaling with the density gradient length. It will be shown that the turbulent equipartition mechanism is included within the derivation using the Coriolis drift, with the density gradient scaling being the consequence of drift terms not considered in [T. S. Hahm et al., Phys. Plasmas 15, 055902 (2008)]. Finally the accuracy of the analytic models is assessed through a comparison with the full gyrokinetic solution.
Kinetic theory and simulation of multi-species plasmas in tokamaks excited with ICRF microwaves
Kerbel, G.D.; McCoy, M.G.
1984-12-21
This paper presents a description of a bounce-averaged Fokker-Planck quasilinear model for the kinetic description of tokamak plasmas. The non-linear collision and quasilinear resonant diffusion operators are represented in a form conducive to numerical solution with specific attention to the treatment of the boundary layer separating trapped and passing orbit regions of velocity space. The numerical techniques employed are detailed in so far as they constitute significant departure from those used in the conventional uniform magnetic field case. Examples are given to illustrate the combined effects of collisional and resonant diffusion.
Linear theory of low frequency magnetosonic instabilities in counterstreaming bi-Maxwellian plasmas
NASA Astrophysics Data System (ADS)
Vafin, S.; Schlickeiser, R.; Yoon, P. H.
2015-09-01
An effect of the bi-Maxwellian counterstreaming distribution function is analyzed with regard to the linear low frequency instabilities in magnetized homogeneous collisionless plasmas. New analytical marginal instability conditions for the firehose and the mirror modes have been obtained. Presence of counterstreams along the ambient magnetic field causes a huge effect on the instability conditions of those modes. The instability conditions very sensitively depend on the functional dependence of the counterstreaming parameter P. The theoretically predicted results might give a full potential explanation for the observed solar wind temperature anisotropy diagram in A- β∥ plane [S. D. Bale et al., Phys. Rev. Lett. 103, 211101 (2009)].
NASA Technical Reports Server (NTRS)
Barnes, A.
1979-01-01
An exact solution of the kinetic and electromagnetic equations for a large-amplitude plane magnetoacoustic wave propagating transverse to the magnetic field in a hot collisionless plasma is presented. The solution gives simple relations among the magnetic-field strength, density, stress tensor, and plasma velocity, all of which are measurable in the interplanetary plasma. These relations are independent of the electron and ion velocity distributions, subject to certain restrictions on 'high-velocity tails.' The magnetic field of the wave is linearly polarized. The wave steepens to form a shock much as the analogous waves of MHD theory do.
Lee, H. C.; Jiang, T. F.
2010-11-15
We analytically solve the relativistic equation of motion for an electron in ion plasma channels and calculate the corresponding trajectory as well as the synchrotron radiation. The relativistic effect on a trajectory is strong, i.e., many high-order harmonic terms in the trajectory, when the ratio of the initial transverse velocity (v{sub x0}) to the longitudinal velocity (v{sub z0}) of the electron injected to ion plasma channels is high. Interestingly, these high-order harmonic terms result in a quite broad and intense radiation spectrum, especially at an oblique angle, in contrast to an earlier understanding. As the initial velocity ratio (v{sub x0}:v{sub z0}) decreases, the relativistic effect becomes weak; only the first and second harmonic terms remain in the transverse and longitudinal trajectories, respectively, which coincides with the result of Esarey et al. [Phys. Rev. E 65, 056505 (2002)]. Our formalism also allows the description of electron's trajectory in the presence of an applied magnetic field. Critical magnetic fields for cyclotron motions are figured out and compared with semiclassical results. The cyclotron motion leads to more high-order harmonic terms than the trajectory without magnetic fields and causes an immensely broad spectrum with vastly large radiation amplitude for high initial velocity ratios (v{sub x0}:v{sub z0}). The radiation from hard x-ray to gamma-ray regions can be generated with a broad radiation angle, thus available for applications.
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.
Superposed epoch analysis of CIRs at 0. 3 and 1. 0 AU: A comparative study
Richter, A.K.; Luttrell, A.H.
1986-05-01
Applying the superposed epoch analysis technique to 16 and to 31 well-defined, nonshock-associated stream-stream interaction regions observed by the Helios spacecraft in the distance ranges 0.3 to 0.4 AU and 0.9 to 1.0 AU, respectively, we obtain the average azimuthal variation in the solar wind density, velocity and temperature, in the magnetic field strength, and in the total proton plasma plus magnetic field pressure across CIRs at these two radial distances separately. For the radial evolution of these interaction regions we find by comparison: (1) due to compressional and rarefactional effects the amplitudes of all parameters in question taken along the leading as well as along the trailing part of the CIR are steadily increasing with the most pronounced increase in the pressure; (2) at the same time even the leading portion of the velocity profile steepens; (3) simultaneously, the positions in azimuth of the overall maximum values of the solar wind density and temperature, of the magnetic field strength and of the plasma plus magnetic field pressure are getting steadily lined up in longitude; (4) at the same time the leading portions of all profiles are steepening into discontinuous, shocklike structures. Thus, this analysis provides observational evidence for the following results obtained earlier from numerical simulation studies. Stream steepening does occur within 1 AU, and the probability of corotating shocks to form is, on average, much higher beyond than at or within 1 AU.
Nekrasov, Anatoly K.; Shadmehri, Mohsen E-mail: mshadmehri@thphys.nuim.i
2010-12-01
We develop a general theory of buoyancy instabilities in the electron-ion plasma with the electron heat flux based not upon magnetohydrodynamic (MHD) equations, but using a multicomponent plasma approach in which the momentum equation is solved for each species. We investigate the geometry in which the background magnetic field is perpendicular to the gravity and stratification. General expressions for the perturbed velocities are given without any simplifications. Collisions between electrons and ions are taken into account in the momentum equations in a general form, permitting us to consider both weakly and strongly collisional objects. However, the electron heat flux is assumed to be directed along the magnetic field, which implies a weakly collisional case. Using simplifications justified for an investigation of buoyancy instabilities with electron thermal flux, we derive simple dispersion relations for both collisionless and collisional cases for arbitrary directions of the wave vector. Our dispersion relations considerably differ from that obtained in the MHD framework and conditions of instability are similar to Schwarzschild's criterion. This difference is connected with simplified assumptions used in the MHD analysis of buoyancy instabilities and with the role of the longitudinal electric field perturbation which is not captured by the ideal MHD equations. The results obtained can be applied to clusters of galaxies and other astrophysical objects.
Lorenzen, Sonja; Omar, Banaz; Zammit, Mark C; Fursa, Dmitry V; Bray, Igor
2014-02-01
To apply spectroscopy as a diagnostic tool for dense plasmas, a theoretical approach to pressure broadening is indispensable. Here, a quantum-statistical theory is used to calculate spectral line shapes of few-electron atoms. Ionic perturbers are treated quasistatically as well as dynamically via a frequency fluctuation model. Electronic perturbers are treated in the impact approximation. Strong electron-emitter collisions are consistently taken into account with an effective two-particle T-matrix approach. Convergent close-coupling calculations give scattering amplitudes including Debye screening for neutral emitters. For charged emitters, the effect of plasma screening is estimated. The electron densities considered reach up to n(e) = 10(27) m(-3). Temperatures are between T = 10(4) and 10(5) K. The results are compared with a dynamically screened Born approximation for Lyman lines of H and H-like Li as well as for the He 3889 Å line. For the last, a comprehensive comparison to simulations and experiments is given. For the H Lyman-α line, the width and shift are drastically reduced by the Debye screening. In the T-matrix approach, the line shape is notably changed due to the dependence on the magnetic quantum number of the emitter, whereas the difference between spin-scattering channels is negligible.
Three dimensional theory of helix PASOTRON, a plasma-filled, backward wave oscillator
NASA Astrophysics Data System (ADS)
Abu-Elfadl, Tamer Mostafa
PASOTRONs (Plasma Assisted Slow wave Oscillator) are new high power Cherenkov sources, working without the heavy magnetic field solenoids. Instead of the strong magnetic field, electron transportation in these devices is provided by plasma ions, which compensate the self space charge forces of the beam. The absence of strong guiding magnetic field, gives the electrons the freedom to move transversely by the RF fields besides the usual axial motion in these type of devices. The transverse motion greatly alter the operation of the Cherenkov device. The field intensity of the synchronous space harmonic is concentrated around the SWS. So, transverse motion can be beneficial in electron wave interaction, as electrons experience this strong field as they move transversely towards the SWS. This stimulated interests in theoretical analysis of these devices. For symmetrical slow wave structures (SWS), i.e. corrugated waveguide, employed in traveling wave tubes (TWT) and backward wave oscillator (BWO), filled with plasma, it is shown in this study that the operation of these devices can be enhanced by adding a small magnetic field. The small magnetic field helps avoid interception, while maintaining the preferable transverse motion. A 3D "amplifier" model describing the steady state operation of the helix PASOTRON BWO is presented. The results showed that electrons injected inside the helix are those that contribute most to the device efficiency over those electrons injected outside the helix. It is also shown that by reducing the beam size, high efficiencies up to 55% can be achieved. Such high efficiency, which is unachievable in conventional BWOs driven by linear electron beams, can be explained by a favorable effect of the transverse motion of electrons. Temporal study of the helix PASOTRON BWO is also presented. It is shown that for zero reflection device, there was no automodulation oscillations. This is attributed to the 3D electron motion together with the 90° phase
NASA Astrophysics Data System (ADS)
Garbet, X.; Sauter, O.
2011-05-01
The 2010 edition of the joint Varenna-Lausanne workshop on the theory of fusion plasmas was undoubtedly a great success. The programme encompasses a wide variety of topics, namely turbulence, MHD, edge physics and RF wave heating. The present PPCF issue is a collection of 19 outstanding papers, which cover these topics. It follows the publication of 22 refereed contributed papers in Journal of Physics: Conference Series 2010 260. There is no doubt that the production of articles was both abundant and of high scientific quality. This is why the Varenna-Lausanne meeting takes an important place in the landscape of conferences on fusion. Indeed this is the ideal forum for exchanging ideas on theory and modelling, and for substantiating the best results obtained in our field. The tradition of the meeting is to provide a forum for numerical modelling activities. This custom was clearly respected given the large fraction of papers in this special issue which address this subject. This feature reflects the revolution we have been living through for some years with the fast growth of high-performance computers. It also appears that analytical theory is flourishing. This is important for bringing new ideas and guidance to numerical simulations. Finally, code validation and comparison to experiments are well represented. We believe that this is good news given the complexity of the non-linear physics that is at stake in fusion devices. Another subject of satisfaction was the presence of many young scientists at the meeting. The encounter between young researchers and senior scientists is certainly a strong point of the Varenna-Lausanne conference. In conclusion, we anticipate a great success for this special issue of PPCF and we hope that the readers will find therein ideas and inspiration.
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.
Role of lipid-induced changes in plasma membrane in the biophysical shunt theory of psychopathology.
Naisberg, Y; Weizman, A
1997-04-01
The existence of a lipid factor that either causes faulty lipid metabolism or directly contributes to the emergence of a biophysical shunt in neuronal membrane ionic flow propagation is proposed. The neuronal membrane contains a remarkable amount of phospholipids, glycolipids and cholesterol. It is assumed that, under certain unfavorable intrinsic states, the plasma membrane's lipid order and composition and, consequently, its cholesterol-to-phospholipid ratio, may change. This, in turn, may significantly modify membrane fluidity, altering the essential physical properties in the affected portions of the membrane and causing a disarray in the adjacent ion channels, leading to the establishment of a biophysical shunt in a loop-like operation, forming the basis for a variety of mental disorders. The present model offers a diet-induced lipid correction for the relief of psychopathological problems.
Plasma Streaming and Explosive Events in the Solar Transition Region: Theory and Observations
NASA Astrophysics Data System (ADS)
Ryutova, M.; Tarbell, T.
1999-05-01
As shown by Tarbell et al. (ApJ, 514, L47, 1999 ) a sporadic excess of temperature and wide variety of plasma jets observed in the chromosphere and transition region overlying quiet sun regions may be explained by hydrodynamic cumulation resulted from the acoustic shocks generated by the reconnecting small scale network magnetic elements in the solar photosphere. Here we study magneto-hydrodynamic cumulation resulted from post-reconnection MHD shocks generated in complex magnetic field geometries typical to upper chromosphere and low corona. We present the results for the observed regularities obtained from simultaneous measurements taken by TRACE in chromospheric, transition region and coronal images and MDI on SOHO showing time series of high resolution magnetograms. We find that (1) All the essential features of the hydrodynamic cumulation remain in place: the MHD shocks driven by the post-reconnection sling-shot effect and self-focusing of these shocks lead to several well observed signatures of the energy release. (2) The evolution of generated flows depends on the geometry of intermittent magnetic fields and the height of jet formation. In regions of open magnetic structures plasma flows have tendency to accelerate and reach supersonic and super-Alfvenic velocities. Due to linear KH instability such flows may generate high frequency Alfven waves propagating along the magnetic structures. (3) In those regions where cumulative effects result in the predominant heating which is accompanied by generation of "moderate" (sub-Alfvenic) velocity jets, there are conditions when high velocity explosive events are driven. Our theoretical model shows that the explosive events proceeded by appearance of the bright transients are caused by the development of shear flow dissipative (nonlinear) instabilities. We also suggest that "non-bright"explosive events may be driven by rare effect of the cylindrical focusing of the MHD shocks (the Guderley's effect).
Zhang, J.; Peebles, W. A.; Crocker, N. A.; Carter, T. A.; Doyle, E. J.; Rhodes, T. L.; Wang, G.; Zeng, L.; Hyatt, A. W.
2013-10-15
Mueller-Stokes theory can be used to calculate the polarization evolution of an electromagnetic (EM) wave as it propagates through a magnetized plasma. Historically, the theory has been used to interpret polarimeter signals from systems operating on fusion plasmas. These interpretations have mostly employed approximations of Mueller-Stokes theory in regimes where either the Faraday rotation (FR) or the Cotton-Mouton (CM) effect is dominant. The current paper presents the first systematic comparison of polarimeter measurements with the predictions of full Mueller-Stokes theory where conditions transition smoothly from a FR-dominant (i.e., weak CM effect) plasma to one where the CM effect plays a significant role. A synthetic diagnostic code, based on Mueller-Stokes theory accurately reproduces the trends evident in the experimentally measured polarimeter phase over this entire operating range, thereby validating Mueller-Stokes theory. The synthetic diagnostic code is then used to investigate the influence of the CM effect on polarimetry measurements. As expected, the measurements are well approximated by the FR effect when the CM effect is predicted to be weak. However, the code shows that as the CM effect increases, it can compete with the FR effect in rotating the polarization of the EM-wave. This results in a reduced polarimeter response to the FR effect, just as observed in the experiment. The code also shows if sufficiently large, the CM effect can even reverse the handedness of a wave launched with circular polarization. This helps to understand the surprising experimental observations that the sensitivity to the FR effect can be nearly eliminated at high enough B{sub T} (2.0 T). The results also suggest that the CM effect on the plasma midplane can be exploited to potentially measure magnetic shear in tokamak plasmas. These results establish increased confidence in the use of such a synthetic diagnostic code to guide future polarimetry design and interpret
NASA Astrophysics Data System (ADS)
Zhang, J.; Peebles, W. A.; Crocker, N. A.; Carter, T. A.; Doyle, E. J.; Hyatt, A. W.; Rhodes, T. L.; Wang, G.; Zeng, L.
2013-10-01
Mueller-Stokes theory can be used to calculate the polarization evolution of an electromagnetic (EM) wave as it propagates through a magnetized plasma. Historically, the theory has been used to interpret polarimeter signals from systems operating on fusion plasmas. These interpretations have mostly employed approximations of Mueller-Stokes theory in regimes where either the Faraday rotation (FR) or the Cotton-Mouton (CM) effect is dominant. The current paper presents the first systematic comparison of polarimeter measurements with the predictions of full Mueller-Stokes theory where conditions transition smoothly from a FR-dominant (i.e., weak CM effect) plasma to one where the CM effect plays a significant role. A synthetic diagnostic code, based on Mueller-Stokes theory accurately reproduces the trends evident in the experimentally measured polarimeter phase over this entire operating range, thereby validating Mueller-Stokes theory. The synthetic diagnostic code is then used to investigate the influence of the CM effect on polarimetry measurements. As expected, the measurements are well approximated by the FR effect when the CM effect is predicted to be weak. However, the code shows that as the CM effect increases, it can compete with the FR effect in rotating the polarization of the EM-wave. This results in a reduced polarimeter response to the FR effect, just as observed in the experiment. The code also shows if sufficiently large, the CM effect can even reverse the handedness of a wave launched with circular polarization. This helps to understand the surprising experimental observations that the sensitivity to the FR effect can be nearly eliminated at high enough BT (2.0 T). The results also suggest that the CM effect on the plasma midplane can be exploited to potentially measure magnetic shear in tokamak plasmas. These results establish increased confidence in the use of such a synthetic diagnostic code to guide future polarimetry design and interpret the
Satellite- and Epoch Differenced Precise Point Positioning Based on a Regional Augmentation Network
Li, Haojun; Chen, Junping; Wang, Jiexian; Wu, Bin
2012-01-01
Precise Point Positioning (PPP) has been demonstrated as a simple and effective approach for user positioning. The key issue in PPP is how to shorten convergence time and improve positioning efficiency. Recent researches mainly focus on the ambiguity resolution by correcting residual phase errors at a single station. The success of this approach (referred to hereafter as NORM-PPP) is subject to how rapidly one can fix wide-lane and narrow-lane ambiguities to achieve the first ambiguity-fixed solution. The convergence time of NORM-PPP is receiver type dependent, and normally takes 15–20 min. Different from the general algorithm and theory by which the float ambiguities are estimated and the integer ambiguities are fixed, we concentrate on a differential PPP approach: the satellite- and epoch differenced (SDED) approach. In general, the SDED approach eliminates receiver clocks and ambiguity parameters and thus avoids the complicated residual phase modeling procedure. As a further development of the SDED approach, we use a regional augmentation network to derive tropospheric delay and remaining un-modeled errors at user sites. By adding these corrections and applying the Robust estimation, the weak mathematic properties due to the ED operation is much improved. Implementing this new approach, we need only two epochs of data to achieve PPP positioning converging to centimeter-positioning accuracy. Using seven days of GPS data at six CORS stations in Shanghai, we demonstrate the success rate, defined as the case when three directions converging to desired positioning accuracy of 10 cm, reaches 100% when the interval between the two epochs is longer than 15 min. Comparing the results of 15 min' interval to that of 10 min', it is observed that the position RMS improves from 2.47, 3.95, 5.78 cm to 2.21, 3.93, 4.90 cm in the North, East and Up directions, respectively. Combining the SDED coordinates at the starting point and the ED relative coordinates thereafter, we
NASA Astrophysics Data System (ADS)
Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June
2015-10-01
The developed kinetic theory for the stability of a magnetic-field-aligned (parallel) shear flow with inhomogeneous ion temperature [Mikhailenko et al., Phys. Plasmas 21, 072117 (2014)] predicted that a kinetic instability arises from the coupled reinforcing action of the flow velocity shear and ion temperature gradient in the cases where comparable ion and electron temperatures exist. In the present paper, the nonlinear theory was developed for the instability caused by the combined effects of ion-temperature-gradient and shear-flow (ITG-SF). The level of the electrostatic turbulence is determined for the saturation state of the instability on the basis of the nonlinear dispersion equation, which accounts for a nonlinear scattering of ions by the developed turbulence in a sheared flow. The renormalized quasilinear equation for the ion distribution function, which accounts for the turbulent scattering of ions by ITG-SF driven turbulence, was derived and employed for the estimation of the turbulent ion viscosity, the anomalous ion thermal conductivity, and anomalous ion heating rate at the saturation state of the instability.
Mikhailenko, V. V. Mikhailenko, V. S.; Lee, Hae June
2015-10-15
The developed kinetic theory for the stability of a magnetic-field-aligned (parallel) shear flow with inhomogeneous ion temperature [Mikhailenko et al., Phys. Plasmas 21, 072117 (2014)] predicted that a kinetic instability arises from the coupled reinforcing action of the flow velocity shear and ion temperature gradient in the cases where comparable ion and electron temperatures exist. In the present paper, the nonlinear theory was developed for the instability caused by the combined effects of ion-temperature-gradient and shear-flow (ITG–SF). The level of the electrostatic turbulence is determined for the saturation state of the instability on the basis of the nonlinear dispersion equation, which accounts for a nonlinear scattering of ions by the developed turbulence in a sheared flow. The renormalized quasilinear equation for the ion distribution function, which accounts for the turbulent scattering of ions by ITG–SF driven turbulence, was derived and employed for the estimation of the turbulent ion viscosity, the anomalous ion thermal conductivity, and anomalous ion heating rate at the saturation state of the instability.
EMHD theory and observations of electron solitary waves in magnetotail plasmas
NASA Astrophysics Data System (ADS)
Ji, Xiao-Fei; Wang, Xiao-Gang; Sun, Wei-Jie; Xiao, Chi-Jie; Shi, Quan-Qi; Liu, Jiang; Pu, Zu-Yin
2014-06-01
A new approach of electron magnetohydrodynamics (EMHD) is developed by including the anisotropy of the electron pressure tensor to take Biermann battery effect into account. Based on the model, the dispersion relation of slow and fast electron magnetosonic modes are derived. A Korteweg-de Vries equation is then obtained from the wave equation to get a solution of one-dimensional slow-mode soliton. Furthermore, according to measurements of Cluster and Time History of Events and Macroscale Interactions during Substorms, we find a good agreement between the theory and observations of magnetic field depression and perpendicular pressure increase.
Investigating the earliest epochs of the Milky Way halo
NASA Astrophysics Data System (ADS)
Starkenburg, Else; Starkenburg
2016-08-01
Resolved stellar spectroscopy can obtain knowledge about chemical enrichment processes back to the earliest times, when the oldest stars were formed. In this contribution I will review the early (chemical) evolution of the Milky Way halo from an observational perspective. In particular, I will discuss our understanding of the origin of the peculiar abundance patterns in various subclasses of extremely metal-poor stars, taking into account new data from our abundance and radial velocity monitoring programs, and their implications for our understanding of the formation and early evolution of both the Milky Way halo and the satellite dwarf galaxies therein. I conclude by presenting the ``Pristine'' survey, a program on the Canada-France-Hawaii Telescope to study this intriguing epoch much more efficiently.
Three epochs of EVN observations towards IRAS 23365+3604
NASA Astrophysics Data System (ADS)
Romero-Canizales, C.; Perez-Torres, M.; Alberdi, A.
The European VLBI Network (EVN) provides us with the necessary sensitivity and angular resolution to study the nuclear and circumnuclear regions in Luminous and Ultraluminous Infrared Galaxies. The high Star Formation Rates (SFR) inferred for these galaxies implies both the presence of a high number of massive stars and a dense surrounding medium. Therefore, bright radio SNe are expected to occur. With the aim of estimating the SFR in ULIRGs by means of Core Collapse supernova (CCSN) detections, we started an observing campaign with the EVN on a small sample of the brightest and farthest ULIRGs in the local Universe. We present here our results from three epochs of quasi-simultaneous observations with the EVN at 6 and 18 cm towards one of the objects in our sample: IRAS 23365+3604.
Doppler imaging of AR Lacertae at three epochs
NASA Technical Reports Server (NTRS)
Walter, Frederick M.; Neff, James E.; Linsky, Jeffrey L.; Rodono, Marcello
1988-01-01
Observations from IUE were used to study the structure of the lower chromosphere of AR Lacertae in the light of Mg II k. Sequences of LWR/P-HI images distributed around the binary period at three epochs were obtained. Discrete plage-like regions of enhanced Mg II surface flux in this system are identified. There are temporal variations in the Mg II flux on timescales of hours as well as substantial changes in chromospheric morphology on timescales of years. Even with the limited S/N attainable with the IUE, one can map the gross structures of active stellar atmospheres. With such information, one can begin to study the true 3-D structure of the atmospheres of late-type stars.
Sub-Daily Earth Rotation during the Epoch '92 Campaign
NASA Technical Reports Server (NTRS)
Freedman, A. P.; Ibanez-Meier, R.; Lichten, S. M.; Dickey, J. O.; Herring, T. A.
1993-01-01
Earth rotation measurements were obtained using Global Positioning System (GPS) data for 11 days during the Epoch '92 campaign in the Summer of 1992. Earth orientation was measured simultaneously with several very long baseline interferornetry (VLBI) networks. These data were processed to yield both GPS and VLBI estimates of UT1 with 3-hour time resolution, which were then compared and analyzed. The high frequency behavior of both data sets is similar, although drifts between the two series of approx.0,1 ms over 2-5 days are evident, Models for tidally induced UT1 variations and estimates of atmospheric angular momentum (AAM) at 6-hour intervals were also compared with the geodetic data, These studies indicate that most of the geodetic signal in the diurnal and semidiurnal frequency bands can be attributed to tidal processes, and that UT1 variations over a few days are mostly atmospheric in origin.
Subdaily Earth rotation during the Epoch '92 campaign
NASA Technical Reports Server (NTRS)
Freedman, A. P.; Ibanez-Meier, R.; Herring, T. A.; Lichten, S. M.; Dickey, J. O.
1994-01-01
Global Positioning System (GPS) data were used to estimate Earth rotation variations over an 11-day period during the Epoch '92 campaign in the summer of 1992. Earth orientation was measured simultaneously by several very long baseline interferometry (VLBI) networks. GPS and VLBI estimates of UT1 with 3-hour time resolution were then compared and analyzed. The high frequency behavior of both data sets is similar, although drifts between the two series of approximately 0.1 ms over 2-5 days are evident. The geodetic results were also compared with models for UT1 fluctuations at tidal periods and with estimates of atmospheric angular momentum made at 6-hour intervals. Most of the geodetic signal in the diurnal and semidiurnal frequency bands can be attributed to tidal processes, whereas UT1 variations over a few days are mostly atmospheric in origin.
Primary Effusion Lymphoma: Is Dose-Adjusted-EPOCH Worthwhile Therapy?
Jessamy, Kegan; Ojevwe, Fidelis O; Doobay, Ravi; Naous, Rana; Yu, John; Lemke, Sheila M
2016-01-01
Primary effusion lymphoma (PEL) is a rare condition, which accounts for approximately 4% of all human immunodeficiency virus (HIV)-associated non-Hodgkin lymphomas. PEL has a predilection for body cavities and occurs in the pleural space, pericardium, and peritoneum. Without treatment, the median survival is approximately 2-3 months, and with chemotherapy, the median survival is approximately 6 months. We describe the case of a 47-year-old male with HIV and Kaposi's sarcoma who presented with complaints of abdominal pain and distension and was subsequently diagnosed with PEL. Despite limited clinical data being available, chemotherapy with dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (EPOCH) has proven to increase survival rates in patients with this condition. PMID:27462227
Tomography of the Reionization Epoch with Multifrequency CMB Observations
NASA Astrophysics Data System (ADS)
Hernández-Monteagudo, Carlos; Verde, Licia; Jimenez, Raul
2006-12-01
We study the constraints that future multifrequency cosmic microwave background (CMB) experiments will be able to set on the metal enrichment history of the intergalactic medium at the epoch of reionization. We forecast the signal-to-noise ratio for the detection of the signal introduced into the CMB by resonant scattering off metals at the end of the cosmic dark ages. We take into account systematics associated with cross-channel calibration, errors in reconstruction of the point-spread function, and inaccurate foreground removal. We develop an algorithm to optimally extract the signal generated by metals during reionization and to accurately remove the contamination due to the thermal Sunyaev-Zel'dovich effect. Although demanding levels of foreground characterization and control of systematics are required, they are very distinct from those encountered in H I 21 cm studies and CMB polarization, and this fact encourages the study of resonant scattering off metals as an alternative way of conducting tomography of the reionization epoch. A realistic experiment, looking at clean regions of the sky, can detect changes of 3%-12% (95% confidence level) in the O III abundance (with respect to its solar value) in the redshift range z=12-22 for reionization redshift zre>10. However, for zre<10 one can only set upper limits on N II abundance increments of ~60% solar in the redshift range z=5.5-9 (95% c.l.). These constraints assume that cross-channel calibration is accurate to 1 part in 104, which constitutes the most critical technical requirement of this method but is still achievable with current technology.
Costa, A. A. da; Diver, D. A.; Laing, E. W.; Stark, C. R.; Teodoro, L. F. A.
2011-01-15
The classical modeling of radiation by accelerated charged particles in pulsars predicts a cutoff in photon energy at around 25 GeV. While this is broadly consistent with observations, the classical treatment is not self-consistent, and cannot be extended to explain the rare high-energy detections of photons in the 100s of GeV range. In this paper we revisit the theoretical modeling of high-energy radiation processes in very strong electromagnetic fields, in the context of both single particles and collective plasmas. There are no classical constraints on this description. We find that there is indeed a critical energy of around 50 GeV that arises naturally in this self-consistent treatment, but rather than being a cutoff, this critical energy signals a transition from radiation that is classical to a quasiquantum description, in which the particle is able to radiate almost its total energy in a single event. This new modeling therefore places pulsar radiation processes on a more secure physical basis, and admits the possibility of the production of TeV photons in a self-consistent way.
Correlation theory of a two-dimensional plasma turbulence with shear flow
Zhang, Y.Z.; Mahajan, S.M.
1992-09-01
When the ion sound effect is neglected, a wide class of electrostatic plasma turbulence can be modelled by a two-dimensional equation for the generalized exstrophy {Psi}, an inviscid constant of motion along the turbulent orbits. Under the assumption of a Gaussian stochastic electrostatic potential, an averaged Green's function method is used to rigorously derive equations for the N-particle correlation functions for a dissipative and sheared flow. This approach is equivalent to the cumulant expansion method used to study the Vlasov-Poisson system. For various cases of interest, appropriate equations are solved to obtain the absolute level as well as the detailed structure of the two-point correlation function C(r), and its Fourier transform, the exstrophy spectral function I(k). Uniformly valid analytical expressions are derived for the dissipative but shearless case resulting in a 'fluctuation-dissipation' theorem relating the total spectral intensity to classical viscosity. These self-consistent results show a strong logarithmic modification of the mixing length estimates for the turbulence levels.
Correlation theory of a two-dimensional plasma turbulence with shear flow
Zhang, Y.Z.; Mahajan, S.M.
1992-09-01
When the ion sound effect is neglected, a wide class of electrostatic plasma turbulence can be modelled by a two-dimensional equation for the generalized exstrophy {Psi}, an inviscid constant of motion along the turbulent orbits. Under the assumption of a Gaussian stochastic electrostatic potential, an averaged Green`s function method is used to rigorously derive equations for the N-particle correlation functions for a dissipative and sheared flow. This approach is equivalent to the cumulant expansion method used to study the Vlasov-Poisson system. For various cases of interest, appropriate equations are solved to obtain the absolute level as well as the detailed structure of the two-point correlation function C(r), and its Fourier transform, the exstrophy spectral function I(k). Uniformly valid analytical expressions are derived for the dissipative but shearless case resulting in a `fluctuation-dissipation` theorem relating the total spectral intensity to classical viscosity. These self-consistent results show a strong logarithmic modification of the mixing length estimates for the turbulence levels.
Introduction to statistical field theory: from a toy model to a one-component plasma
NASA Astrophysics Data System (ADS)
Frydel, Derek
2015-11-01
Working with a toy model whose partition function consists of a discrete summation, we introduce the statistical field theory methodology by transforming a partition function via a formal Gaussian integral relation (the Hubbard-Stratonovich transformation). We then consider Gaussian-type approximations, wherein correlational contributions enter as harmonic fluctuations around the saddle-point solution. This work focuses on how to arrive at a self-consistent, non-perturbative approximation without recourse to a standard variational construction based on the Gibbs-Bogolyubov-Feynman inequality that is inapplicable to a complex action. To address this problem, we propose a construction based on selective satisfaction of a set of exact relations generated by considering a dual representation of a partition function, in its original and transformed form.
Krommes, John A.
2015-09-21
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
Numerical study of chiral plasma instability within the classical statistical field theory approach
NASA Astrophysics Data System (ADS)
Buividovich, P. V.; Ulybyshev, M. V.
2016-07-01
We report on a numerical study of real-time dynamics of electromagnetically interacting chirally imbalanced lattice Dirac fermions within the classical statistical field theory approach. Namely, we perform exact simulations of the real-time quantum evolution of fermionic fields coupled to classical electromagnetic fields, which are in turn coupled to the vacuum expectation value of the fermionic electric current. We use Wilson-Dirac Hamiltonian for fermions, and noncompact action for the gauge field. In general, we observe that the backreaction of fermions on the electromagnetic field prevents the system from acquiring chirality imbalance. In the case of chirality pumping in parallel electric and magnetic fields, the electric field is screened by the produced on-shell fermions and the accumulation of chirality is hence stopped. In the case of evolution with initially present chirality imbalance, axial charge tends to transform to helicity of the electromagnetic field. By performing simulations on large lattices we show that in most cases this decay process is accompanied by the inverse cascade phenomenon, which transfers energy from short-wavelength to long-wavelength electromagnetic fields. In some simulations, however, we observe a very clear signature of inverse cascade for the helical magnetic fields that is not accompanied by the axial charge decay. This suggests that the relation between the inverse cascade and axial charge decay is not as straightforward as predicted by the simplest form of anomalous Maxwell equations.
Epochs of intrusion-related copper mineralization in the Andes
NASA Astrophysics Data System (ADS)
Sillitoe, R. H.
Seventy-four copper deposits and prospects related intimately to intrusive activity in the Andes have been dated radiometrically during the last 18 years by many different investigators, most of whom used the KAr method. The results are summarized and some of their local and regional implications are reviewed. A number of copper deposits, mainly of the porphyry type, were emplaced in, or near to, premineral volcanic sequences and (or) equigranular plutons. Such precursor volcanism lasted for as long as 9 Ma, and preceded mineralization by intervals of from less than 1 Ma to as much as 9 Ma. Precursor plutons were emplaced no more than 2 to 3 Ma prior to mineralization at several localities in Chile, but possibly as long as 10 to 30 Ma earlier in parts of Colombia and Peru. The time separating emplacement of progenitor stocks and hydrothermal alteration and accompanying copper mineralization, and the duration of alteration-mineralization sequences generally are both less than the analytical uncertainty of the KAr method. However, on the basis of a detailed study of the Julcani vein system in Peru and less clearcut evidence from elsewhere, it may be concluded that alteration and copper mineralization followed stock or dome emplacement by substantially less than 1 Ma and lasted for 0.5 to 2 Ma and, locally, possibly as long as 3 Ma. At several localities, post-mineral magmatic activity could not be separated by the KAr method from the preceding alteration-mineralization events. As many as nine epochs of copper mineralization, ranging in age from late Paleozoic to late Pliocene-Pleistocene, are recognizable in the central Andes of Chile, Peru, Bolivia, and Argentina, and at least four somewhat different epochs characterize the northern Andes of Colombia. Each epoch coincides with a discrete linear sub-belt, some of which extend for more than 2000 km along the length of the orogen. More than 90% of Andean copper resources, mainly as porphyry deposits, are
Krommes, John A.
2015-09-21
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
Accelerometry to Assess Preschooler's Free-Play: Issues with Count Thresholds and Epoch Durations
ERIC Educational Resources Information Center
Oliver, Melody; Schofield, Grant M.; Schluter, Philip J.
2009-01-01
This study examines the utility of current accelerometer threshold definitions and epoch durations for physical activity intensity classification in preschool-aged children. Using video footage of children engaged in active play, directly observed 1-sec epoch physical activity intensity scores were derived from a modified version of the Children's…
GRB 150101B/ Swift J123205.1-105602: Second epoch Chandra observations
NASA Astrophysics Data System (ADS)
Levan, A. J.; Hjorth, J.; Tanvir, N. R.; van der Horst, A. J.
2015-02-01
We obtained a second epoch of observations of the very short GRB 150101B/ Swift J123205.1-105602 (Cummings et al. GCN 17267) with Chandra. Observations began on 10 Feb 2015, 39 days after the burst, and 32 days after the first epoch of observations.
Plans for the Second Epoch of the Southern Proper-Motion Program
NASA Astrophysics Data System (ADS)
Lopez, C. E.; Lee, J. F.; van Altena, W.
The first photographs for the Yale-San Juan Southern Proper Motion program with respect to faint galaxies were taken with the collaboration of Columbia University in 1965. The first epoch photography was essentially completed in 1974 and plans are now under way to begin the second epoch observations in 1986.
Quasar feedback at the peak of the galaxy formation epoch
NASA Astrophysics Data System (ADS)
Alexandroff, Rachael; Zakamska, Nadia; Liu, Guilin; Greene, Jenny; Strauss, Michael
2014-08-01
Feedback from accreting supermassive black holes is now a standard ingredient in galaxy formation models. It is seen as necessary for limiting the maximal masses of galaxies and for establishing the black- hole / bulge correlations. Using Gemini GMOS, we demonstrated that powerful ionized gas winds are a ubiquitous feature in luminous obscured z=0.5 quasars. We now propose to extend this discovery to the epoch of peak galaxy formation and quasar activity - to the era at which feedback was most prominent and the galaxy / black hole correlations were established. We request 4.5 hours of Gemini-NIFS LGS adaptive- optics observations of an extremely luminous moderately obscured quasar at z=2.3 to map the morphology and kinematics of the ionized gas and to determine whether it exhibits the signs of black hole feedback in the form of an unbound ionized gas outflow. We will observe H(beta) and [OIII](lambda)5007Ain the H-band and H(alpha) and [NII](lambda)(lambda)6548,6583Ain the K-band on sub-galactic and galaxy-wide scales (spatial resolution 0.8 kpc, field of view 24 kpc). Obscured quasars likely constitute the majority of the quasar population and may represent the relatively early enshrouded phase of the black hole growth; thus, luminous obscured quasars are the most likely sites of quasar feedback, in agreement with our findings at low redshift.
Stable warm tropical climate through the Eocene Epoch
NASA Astrophysics Data System (ADS)
Pearson, Paul N.; van Dongen, Bart E.; Nicholas, Christopher J.; Pancost, Richard D.; Schouten, Stefan; Singano, Joyce M.; Wade, Bridget S.
2007-03-01
Earth's climate cooled from a period of extreme warmth in the early Eocene Epoch (ca. 50 Ma) to the early Oligocene (ca. 33 Ma), when a large ice cap first appeared on Antarctica. Evidence from the planktonic foraminifer oxygen isotope record in deep-sea cores has suggested that tropical sea-surface temperatures declined by 5-10 degrees over this interval, eventually becoming much cooler than modern temperatures. Here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine Crenarcheota from new drill cores in Tanzania that indicate a warm and generally stable tropical climate over this period. We reinterpret the previously published isotope records in the light of comparative textural analysis of the deep-sea foraminifer shells, which shows that in contrast to the Tanzanian material, they have been diagenetically recrystallized. We suggest that increasingly severe alteration of the deep-sea plankton shells through the Eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea-surface cooling trend. This implies that the long-term Eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes.
Exploring a Massive Starburst in the Epoch of Reionization
NASA Astrophysics Data System (ADS)
Marrone, Daniel; Aravena, M.; Chapman, S.; De Breuck, C.; Gonzalez, A.; Hezavehe, S.; Litke, K.; Ma, J.; Malkan, M.; Spilker, J.; Stalder, B.; Stark, D.; Strandet, M.; Tang, M.; Vieira, J.; Weiss, A.; Welikala, N.
2016-08-01
We request deep multi-band imaging of a unique dusty galaxy in the Epoch of Reionization (EoR), selected via its millimeter-wavelength dust emission in the 2500-square-degree South Pole Telescope survey. Spectroscopically confirmed to lie at z=6.900, this galaxy has a large dust mass and is likely one of the most rapidly star-forming objects in the EoR. Using Gemini-S, we have identified z-band emission from this object that could be UV continuum emission at z=6.9 or from a foreground lens. Interpretation of this object, and a complete understanding of its meaning for the census of star formation in the EoR, requires that we establish the presence or absence of gravitational lensing. The dust mass observed in this source is also unexpectedly large for its era, and measurements of the assembled stellar population, through the UV-continuum slope and restframe optical color, will help characterize the stellar mass and dust properties in this very early galaxy, the most spectacular galaxy yet discovered by the SPT.
The “Anthropocene” epoch: Scientific decision or political statement?
Finney, Stanley C.; Edwards, Lucy E.
2016-01-01
The proposal for the “Anthropocene” epoch as a formal unit of the geologic time scale has received extensive attention in scientific and public media. However, most articles on the Anthropocene misrepresent the nature of the units of the International Chronostratigraphic Chart, which is produced by the International Commission on Stratigraphy (ICS) and serves as the basis for the geologic time scale. The stratigraphic record of the Anthropocene is minimal, especially with its recently proposed beginning in 1945; it is that of a human lifespan, and that definition relegates considerable anthropogenic change to a “pre-Anthropocene.” The utility of the Anthropocene requires careful consideration by its various potential users. Its concept is fundamentally different from the chronostratigraphic units that are established by ICS in that the documentation and study of the human impact on the Earth system are based more on direct human observation than on a stratigraphic record. The drive to officially recognize the Anthropocene may, in fact, be political rather than scientific.
Large Scale Structure in the Epoch of Reionization
NASA Astrophysics Data System (ADS)
Koekemoer, Anton; Mould, Jeremy; Cooke, Jeffrey; Wyithe, Stuart; Lidman, Christopher; Trenti, Michele; Abbott, Tim; Kunder, Andrea; Barone-Nugent, Robert; Tescari, Edoardo; Katsianis, Antonios
2014-02-01
We propose to capitalize on the high red sensitivity and large field of view of DECam to detect the brightest and rarest galaxies at z=6-7. Our 2012 results show the signature of large scale structure with wavenumber of order 0.1 inverse Mpc in line with expectations of primordial non-gaussianity. But the signal to noise in one deep field from two nights' data is insufficient for a robust conclusion. Ten nights' data will do the job. These data will also constrain the galaxy contribution to reionization by enabling a tighter constraint on the full galaxy luminosity function, including the faint end. The observations will be executed with a cadence and depth that will enable the detection of super-luminous supernovae at z=6-7. Super-luminous supernovae are a recently observed class of supernovae that are 10-100x more luminous than typical supernovae. This class includes pair- instability supernovae that are a rare, third type of supernova explosion in which only 3 events are known. The proposed observations will greatly extend the current reach of supernovae research, examining their occurrence rate and properties near the epoch of reionization.
Phase-compensated averaging for analyzing electroencephalography and magnetoencephalography epochs.
Matani, Ayumu; Naruse, Yasushi; Terazono, Yasushi; Iwasaki, Taro; Fujimaki, Norio; Murata, Tsutomu
2010-05-01
Stimulus-locked averaging for electroencephalography and/or megnetoencephalography (EEG/MEG) epochs cancels out ongoing spontaneous activities by treating them as noise. However, such spontaneous activities are the object of interest for EEG/MEG researchers who study phase-related phenomena, e.g., long-distance synchronization, phase-reset, and event-related synchronization/desynchronization (ERD/ERS). We propose a complex-weighted averaging method, called phase-compensated averaging, to investigate phase-related phenomena. In this method, any EEG/MEG channel is used as a trigger for averaging by setting the instantaneous phases at the trigger timings to 0 so that cross-channel averages are obtained. First, we evaluated the fundamental characteristics of this method by performing simulations. The results showed that this method could selectively average ongoing spontaneous activity phase-locked in each channel; that is, it evaluates the directional phase-synchronizing relationship between channels. We then analyzed flash evoked potentials. This method clarified the directional phase-synchronizing relationship from the frontal to occipital channels and recovered another piece of information, perhaps regarding the sequence of experiments, which is lost when using only conventional averaging. This method can also be used to reconstruct EEG/MEG time series to visualize long-distance synchronization and phase-reset directly, and on the basis of the potentials, ERS/ERD can be explained as a side effect of phase-reset. PMID:20172813
Atrio-Barandela, F.; Kashlinsky, A. E-mail: Alexander.Kashlinsky@nasa.gov
2014-12-20
The epoch of first star formation and the state of the intergalactic medium (IGM) at that time are not directly observable with current telescopes. The radiation from those early sources is now part of the cosmic infrared background (CIB) and, as these sources ionize the gas around them, the IGM plasma would produce faint temperature anisotropies in the cosmic microwave background (CMB) via the thermal Sunyaev-Zeldovich (TSZ) effect. While these TSZ anisotropies are too faint to be detected, we show that the cross-correlation of maps of source-subtracted CIB fluctuations from Euclid, with suitably constructed microwave maps at different frequencies, can probe the physical state of the gas during reionization and test/constrain models of the early CIB sources. We identify the frequency-combined, CMB-subtracted microwave maps from space- and ground-based instruments to show that they can be cross-correlated with the forthcoming all-sky Euclid CIB maps to detect the cross-power at scales ∼5'-60' with signal-to-noise ratios (S/Ns) of up to S/N ∼ 4-8 depending on the contribution to the Thomson optical depth during those pre-reionization epochs (Δτ ≅ 0.05) and the temperature of the IGM (up to ∼10{sup 4} K). Such a measurement would offer a new window to explore the emergence and physical properties of these first light sources.
NASA Astrophysics Data System (ADS)
Atrio-Barandela, F.; Kashlinsky, A.
2014-12-01
The epoch of first star formation and the state of the intergalactic medium (IGM) at that time are not directly observable with current telescopes. The radiation from those early sources is now part of the cosmic infrared background (CIB) and, as these sources ionize the gas around them, the IGM plasma would produce faint temperature anisotropies in the cosmic microwave background (CMB) via the thermal Sunyaev-Zeldovich (TSZ) effect. While these TSZ anisotropies are too faint to be detected, we show that the cross-correlation of maps of source-subtracted CIB fluctuations from Euclid, with suitably constructed microwave maps at different frequencies, can probe the physical state of the gas during reionization and test/constrain models of the early CIB sources. We identify the frequency-combined, CMB-subtracted microwave maps from space- and ground-based instruments to show that they can be cross-correlated with the forthcoming all-sky Euclid CIB maps to detect the cross-power at scales ~5'-60' with signal-to-noise ratios (S/Ns) of up to S/N ~ 4-8 depending on the contribution to the Thomson optical depth during those pre-reionization epochs (Δτ ~= 0.05) and the temperature of the IGM (up to ~104 K). Such a measurement would offer a new window to explore the emergence and physical properties of these first light sources.
Atlas Basemaps in Web 2.0 Epoch
NASA Astrophysics Data System (ADS)
Chabaniuk, V.; Dyshlyk, O.
2016-06-01
The authors have analyzed their experience of the production of various Electronic Atlases (EA) and Atlas Information Systems (AtIS) of so-called "classical type". These EA/AtIS have been implemented in the past decade in the Web 1.0 architecture (e.g., National Atlas of Ukraine, Atlas of radioactive contamination of Ukraine, and others). One of the main distinguishing features of these atlases was their static nature - the end user could not change the content of EA/AtIS. Base maps are very important element of any EA/AtIS. In classical type EA/AtIS they were static datasets, which consisted of two parts: the topographic data of a fixed scale and data of the administrative-territorial division of Ukraine. It is important to note that the technique of topographic data production was based on the use of direct channels of topographic entity observation (such as aerial photography) for the selected scale. Changes in the information technology of the past half-decade are characterized by the advent of the "Web 2.0 epoch". Due to this, in cartography appeared such phenomena as, for example, "neo-cartography" and various mapping platforms like OpenStreetMap. These changes have forced developers of EA/AtIS to use new atlas basemaps. Our approach is described in the article. The phenomenon of neo-cartography and/or Web 2.0 cartography are analysed by authors using previously developed Conceptual framework of EA/AtIS. This framework logically explains the cartographic phenomena relations of three formations: Web 1.0, Web 1.0x1.0 and Web 2.0. Atlas basemaps of the Web 2.0 epoch are integrated information systems. We use several ways to integrate separate atlas basemaps into the information system - by building: weak integrated information system, structured system and meta-system. This integrated information system consists of several basemaps and falls under the definition of "big data". In real projects it is already used the basemaps of three strata: Conceptual
Seeking the epoch of maximum luminosity for dusty quasars
Vardanyan, Valeri; Weedman, Daniel; Sargsyan, Lusine E-mail: dweedman@isc.astro.cornell.edu
2014-08-01
Infrared luminosities νL{sub ν}(7.8 μm) arising from dust reradiation are determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4
A dusty, normal galaxy in the epoch of reionization.
Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy
2015-03-19
Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7.
Estimating Asteroid Thermal Inertia from Multi-epoch Observations
NASA Astrophysics Data System (ADS)
MacLennan, Eric M.; Emery, Joshua P.
2014-11-01
Granular material, or regolith, is observed to be ubiquitous on asteroid surfaces. To date, two feasible mechanisms of regolith generation have been proposed: recurrent impacts and thermal fracturing. By combining thermal infrared observations and a thermophysical model (TPM), the thermal inertia of an asteroid surface can be used to infer its physical properties, including the average regolith grain size. With the regolith properties of a large population of diverse asteroids (i.e. different spectral class, size, rotation period etc.), information regarding the details of regolith generation can be inferred.Traditional thermal inertia determination methods use a TPM with a previously derived asteroid shape model and spin axis for constraining the observed surface temperature distribution. TPMs invoke the heat diffusion equation to calculate surface temperatures for a rotating asteroid. An asteroid spin axis provide the boundary condition needed to calculate the surface energy balance in a TPM. However the limited amount of objects with a shape model and thermal infrared observations inhibit the number of thermal inertias that can potentially be calculated. Here, a technique using WISE (12 & 22 μm) observations taken before or after opposition is employed to derive thermal inertias of asteroids without using a shape model. By gathering thermal infrared data at multiple viewing geometries the temperature distribution, thus thermal inertia, is constrained.We first demonstrate the validity of this method on objects with a previously determined shape model and spin axis from the DAMIT website. Our analyses show that not knowing an asteroid’s shape does not significantly affect the resulting thermal inertia estimates. Additionally, we apply our TPM to WISE multi-epoch thermal observations to place estimates for the thermal inertia for more than 100 objects. The set of objects used samples many sizes, spectral classes and rotation periods, which may be important
Seeking the Epoch of Maximum Luminosity for Dusty Quasars
NASA Astrophysics Data System (ADS)
Vardanyan, Valeri; Weedman, Daniel; Sargsyan, Lusine
2014-08-01
Infrared luminosities νL ν(7.8 μm) arising from dust reradiation are determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4
On the Detection of Spectral Ripples from the Recombination Epoch
NASA Astrophysics Data System (ADS)
Sathyanarayana Rao, Mayuri; Subrahmanyan, Ravi; Udaya Shankar, N.; Chluba, Jens
2015-09-01
Photons emitted during cosmological hydrogen (500≲ z≲ 1600) and helium recombination (1600≲ z≲ 3500 for He ii \\to He i, 5000≲ z≲ 8000 for He iii \\to He ii) are predicted to appear as broad, weak spectral distortions of the cosmic microwave background. We present a feasibility study for a ground-based detection of these recombination lines, which would uniquely probe astrophysical cosmology beyond the last scattering surface and provide observational constraints on the thermal history of the universe. We find that including sufficient signal spectral structure and maximizing signal-to-noise ratio, an octave band in the 2-6 GHz window is optimal; in this band the predicted signal appears as an additive quasi-sinusoidal component with amplitude about 8 nK embedded in a sky spectrum some nine orders of magnitude brighter. We discuss algorithms to detect these tiny spectral fluctuations in the sky spectrum by foreground modeling and introduce a maximally smooth function capable of describing the foreground spectrum and distinguishing the signal of interest. We conclude that detection is in principle feasible in realistic observing times provided that radio frequency interference and instrument bandpass calibration are controlled in this band at the required level; using Bayesian tests and mock data, we show that 90% confidence detection is possible with an array of 128 radiometers observing for 255 days of effective integration time. We propose APSERa—Array of Precision Spectrometers for the Epoch of Recombination—a dedicated radio telescope to detect these recombination lines.
The epoch of reionization in the Rh = ct universe
NASA Astrophysics Data System (ADS)
Melia, Fulvio; Fatuzzo, Marco
2016-03-01
The measured properties of the epoch of reionization (EoR) show that reionization probably began around z ˜ 12-15 and ended by z = 6. In addition, a careful analysis of the fluctuations in the cosmic microwave background indicate a scattering optical depth τ ˜ 0.066 ± 0.012 through the EoR. In the context of Λ cold dark matter, galaxies at intermediate redshifts and dwarf galaxies at higher redshifts now appear to be the principal sources of UV ionizing radiation, but only for an inferred (ionizing) escape fraction fion ˜ 0.2, which is in tension with other observations that suggest a value as small as ˜0.05. In this paper, we examine how reionization might have progressed in the alternative Friedmann-Robertson Walker cosmology known as the Rh = ct universe, and determine the value of fion required with this different rate of expansion. We find that Rh = ct accounts quite well for the currently known properties of the EoR, as long as its fractional baryon density falls within the reasonable range 0.026 ≲ Ωb ≲ 0.037. This model can also fit the EoR data with fion ˜ 0.05, but only if the Lyman continuum photon production is highly efficient and Ωb ˜ 0.037. These results are still preliminary, however, given their reliance on a particular form of the star formation rate density, which is still uncertain at very high redshifts. It will also be helpful to reconsider the EoR in Rh = ct when complete structure formation models become available.
A dusty, normal galaxy in the epoch of reionization.
Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy
2015-03-19
Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7. PMID:25731171
The Galaxy UV Luminosity Function before the Epoch of Reionization
NASA Astrophysics Data System (ADS)
Mason, Charlotte A.; Trenti, Michele; Treu, Tommaso
2015-11-01
We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the assumption of a mass-dependent, but redshift-independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at z > 10 (lookback time ≲500 Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations (0 ≲ z ≲ 10). The significant drop in luminosity density of currently detectable galaxies beyond z ˜ 8 is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth τ ={0.056}-0.010+0.007, fully consistent with the latest Planck measurement, implying that the universe is fully reionized at z={7.84}-0.98+0.65. In addition, our model naturally produces smoothly rising star formation histories for galaxies with L ≲ L* in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at z > 10 we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope (α ˜ -3.5 at z ˜ 16). Finally, we construct forecasts for surveys with James Webb Space Telescope (JWST) and Wide-field Infrared Survey Telescope (WFIRST) and predict that galaxies out to z ˜ 14 will be observed. Galaxies at z > 15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.
Trajectory of the cosmic plasma through the quark matter phase diagram
NASA Astrophysics Data System (ADS)
McInnes, Brett
2016-02-01
Experimental studies of the quark-gluon plasma (QGP) focus on two, in practice distinct, regimes: one in which the baryonic chemical potential μB is essentially zero, the other in which it is of the same order of magnitude as the temperature. The cosmic QGP which dominates the early universe after reheating is normally assumed to be of the first kind, but recently it has been suggested that it might well be of the second: this is the case in the theory of "little inflation." If that is so, then it becomes a pressing issue to fix the trajectory of the Universe, as it cools, through the quark matter phase diagram: in particular, one wishes to know where in that diagram the plasma epoch ends, so that the initial conditions of the hadronic epoch can be determined. Here we combine various tools from strongly coupled QGP theory (the latest lattice results, together with gauge-gravity duality) in order to constrain that trajectory, assuming that little inflation did occur.
NASA Astrophysics Data System (ADS)
Bhattacharjee, Amitava
2015-11-01
In recent years, new developments in reconnection theory have challenged classical nonlinear reconnection models. One of these developments is the so-called plasmoid instability of thin current sheets that grows at super-Alfvenic growth rates. Within the resistive MHD model, this instability alters qualitatively the predictions of the Sweet-Parker model, leading to a new nonlinear regime of fast reconnection in which the reconnection rate itself becomes independent of S. This regime has also been seen in Hall MHD as well as fully kinetic simulations, and thus appears to be a universal feature of thin current sheet dynamics, including applications to reconnection forced by the solar wind in the heliosphere and spontaneously unstable sawtooth oscillations in tokamaks. Plasmoids, which can grow by coalescence to large sizes, provide a powerful mechanism for coupling between global and kinetic scales as well as an efficient accelerator of particles to high energies. In two dimensions, the plasmoids are characterized by power-law distribution functions followed by exponential tails. In three dimensions, the instability produces self-generated and strongly anisotropic turbulence in which the reconnection rate for the mean-fields remain approximately at the two-dimensional value, but the energy spectra deviate significantly from anisotropic strong MHD turbulence phenomenology. A new phase diagram of fast reconnection has been proposed, guiding the design of future experiments in magnetically confined and high-energy-density plasmas, and have important implications for explorations of the reconnection layer in the recently launched Magnetospheric Multiscale (MMS) mission. This research is supported by DOE, NASA, and NSF.
Liu, Chang; Dodin, Ilya Y.
2015-08-15
The nonlinear frequency shift is derived in a transparent asymptotic form for intense Langmuir waves in general collisionless plasma. The formula describes both fluid and kinetic effects simultaneously. The fluid nonlinearity is expressed, for the first time, through the plasma dielectric function, and the kinetic nonlinearity accounts for both smooth distributions and trapped-particle beams. Various known limiting scalings are reproduced as special cases. The calculation avoids differential equations and can be extended straightforwardly to other nonlinear plasma waves.
Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays
NASA Astrophysics Data System (ADS)
Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Rodriguez, L.; Janvier, M.
2016-08-01
Context. Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of Galactic cosmic rays (GCRs) decreases. Aims: The main aims of this paper are to find common plasma and magnetic properties of different ICME sub-structures and which ICME properties affect the flux of GCRs near Earth. Methods: We used a superposed epoch method applied to a large set of ICMEs observed in situ by the spacecraft ACE, between 1998 and 2006. We also applied a superposed epoch analysis on GCRs time series observed with the McMurdo neutron monitors. Results: We find that slow MCs at 1 AU have on average more massive sheaths. We conclude that this is because they are more effectively slowed down by drag during their travel from the Sun. Slow MCs also have a more symmetric magnetic field and sheaths expanding similarly as their following MC, while in contrast, fast MCs have an asymmetric magnetic profile and a sheath in compression. In all types of MCs, we find that the proton density and the temperature and the magnetic fluctuations can diffuse within the front of the MC due to 3D reconnection. Finally, we derive a quantitative model that describes the decrease in cosmic rays as a function of the amount of magnetic fluctuations and field strength. Conclusions: The obtained typical profiles of sheath, MC and GCR properties corresponding to slow, middle, and fast ICMEs, can be used for forecasting or modelling these events, and to better understand the transport of energetic particles in ICMEs. They are also useful for improving future operative space weather activities.
Organic Chemostratigraphic Markers Characteristic of the (Informally Designated) Anthropocene Epoch
NASA Astrophysics Data System (ADS)
Kruge, M. A.
2008-12-01
Recognizing the tremendous collective impact of humans on the environment in the industrial age, the proposed designation of the current time period as the Anthropocene Epoch has considerable merit. One of the signature activities during this time continues to be the intensive extraction, processing, and combustion of fossil fuels. While fossil fuels themselves are naturally-occurring, they are most often millions of years old and associated with deeply buried strata. They may be found at the surface, for example, as natural oil seeps or coal seam outcrops, but these are relatively rare occurrences. Fossil fuels and their myriad by- products become the source of distinctive organic chemostratigraphic marker compounds for the Anthropocene when they occur out of their original geological context, i.e., as widespread contaminants in sediments and soils. These persistent compounds have high long-term preservation potential, particularly when deposited under low oxygen conditions. Fossil fuels can occur as environmental contaminants in raw form (e.g., crude petroleum spilled during transport) or as manufactured products (e.g., diesel oil from a leaking storage facility, coal tar from a manufactured gas plant, plastic waste in a landfill, pesticides from petroleum feedstock in agricultural soils). Distinctive assemblages of hydrocarbon marker compounds including acyclic isoprenoids, hopanes, and steranes can be readily detected by gas chromatography/mass spectrometric analysis of surface sediments and soils. Polycyclic aromatic hydrocarbons (PAHs), along with sulfur-, oxygen-, and nitrogen-containing aromatic compounds, are also characteristic of fossil fuels and are readily detectable as well. More widespread is the airfall deposition of fossil fuel combustion products from vehicular, domestic and industrial sources. These occur in higher concentrations in large urban centers, but are also detected in remote areas. Parent (nonmethylated) PAHs such as phenanthrene
Discovery of a Giant Lya Emitter Near the Reionization Epoch
Ouchi, Masami; Ono, Yoshiaki; Egami, Eiichi; Saito, Tomoki; Oguri, Masamune; McCarthy, Patrick J.; Farrah, Duncan; Kashikawa, Nobunari; Momcheva, Ivelina; Shimasaku, Kazuhiro; Nakanishi, Kouichiro; Furusawa, Hisanori; Akiyama, Masayuki; Dunlop, James S.; Mortier, Angela M.J.; Okamura, Sadanori; Hayashi, Masao; Cirasuolo, Michele; Dressler, Alan; Iye, Masanori; Jarvis, Matt.J.
2008-08-01
We report the discovery of a giant Ly{alpha} emitter (LAE) with a Spitzer/IRAC counterpart near the reionization epoch at z = 6.595. The giant LAE is found from the extensive 1 deg{sup 2} Subaru narrow-band survey for z = 6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrow-band object with L(Ly{alpha}) = 3.9 {+-} 0.2 x 10{sup 43} erg s{sup -1} in our survey volume of 10{sup 6} Mpc{sup 3}, but also a spatially extended Ly{alpha} nebula with the largest isophotal area whose major axis is at least {approx_equal} 3-inches. This object is more likely to be a large Ly{alpha} nebula with a size of {approx}> 17-kpc than to be a strongly-lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is v{sub FWHM} = 251 {+-} 21 km s{sup -1}, and that the line-center velocity changes by {approx_equal} 60 km s{sup -1} in a 10-kpc range. The stellar mass and star-formation rate are estimated to be 0.9-5.0 x 10{sup 10}M{sub {circle_dot}} and > 34 M{sub {circle_dot}}yr{sup -1}, respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of inter-galactic medium.
Second Epoch Hubble Space Telescope Imaging of Kepler's Supernova Remnant
NASA Astrophysics Data System (ADS)
Sankrit, Ravi; Blair, William P.; Borkowski, Kazimierz J.; Long, Knox S.; Patnaude, Daniel; Raymond, John C.; Reynolds, Stephen P.; Williams, Brian J.
2015-01-01
We have obtained new HST/WFC3 images of Kepler's supernova remnant in H-alpha (F656N) and [N II] (F658N) emission line filters. The bright radiative shocks in dense clumps are detected in both filters, while non-radiative shocks are seen as faint filaments only in the H-alpha image. Most of these Balmer filaments lie around the periphery of the remnant where the blast wave encounters partially neutral interstellar gas. We compare the new images with HST/ACS images taken nearly 10 years previously, and find that these filaments tracing the forward shock have moved 0.6"-0.9" between the two epochs. Assuming a distance of 4 kpc to the remnant, these proper motions correspond to shock velocities of 1160-1740 km/s, which are consistent with the published values, 1550-2000 km/s (e.g. Blair et al. 1991, ApJ 366, 484). We also find a few Balmer filaments with highly non-radial proper motions. In one particularly interesting case in the projected interior of the remnant, SE of the center, the shock appears to have wrapped around a sharp density enhancement and moved about 0.3" in the period between the observations.The images allow us to study the evolution of the shock around an ejecta knot, which is punching through the remnant boundary in the northwest. The forward shock, visible as an arcuate Balmer filament, has moved about 1". At the trailing edges, the system of radiative knots formed by Rayleigh-Taylor instabilities have undergone significant changes - some knots have disappeared, new ones have appeared, and many have changed in brightness. Elsewhere in the remnant we find changes in the relative intensities of many small, bright knots over the 10 year baseline, indicating the short radiative lifetimes of these features.This work has been supported in part by grant HST-GO-12885 to the Universities Space Research Association.
Intracluster Supernovae in the Multi-epoch Nearby Cluster Survey
NASA Astrophysics Data System (ADS)
Sand, David J.; Graham, Melissa L.; Bildfell, Chris; Foley, Ryan J.; Pritchet, Chris; Zaritsky, Dennis; Hoekstra, Henk; Just, Dennis W.; Herbert-Fort, Stéphane; Sivanandam, Suresh
2011-03-01
The Multi-Epoch Nearby Cluster Survey has discovered 23 cluster Type Ia supernovae (SNe Ia) in the 58 X-ray-selected galaxy clusters (0.05 lsimzlsim 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. Although one of the candidates, Abell399_3_14_0, appears to be associated in projection with the outskirts of a nearby red sequence galaxy, its velocity offset of ~1000 km s-1 indicates that it is unbound and therefore an intracluster SN. Another of our candidates, Abell85_6_08_0, has a spectrum consistent with an SN1991bg-like object, suggesting that at least some portion of intracluster stars belong to an old stellar population. Deep image stacks at the location of the candidate intracluster SNe put upper limits on the luminosities of faint hosts, with Mr >~ -13.0 mag and Mg >~ -12.5 mag in all cases. For such limits, the fraction of the cluster luminosity in faint dwarfs below our detection limit is lsim0.1%, assuming a standard cluster luminosity function. All four events occurred within ~600 kpc of the cluster center (projected), as defined by the position of the brightest cluster galaxy, and are more centrally concentrated than the cluster SN Ia population as a whole. After accounting for several observational biases that make intracluster SNe easier to discover and spectroscopically confirm, we calculate an intracluster stellar mass fraction of 0.16+0.13 -0.09 (68% confidence limit) for all objects within R 200. If we assume that the intracluster stellar population is exclusively old, and the cluster galaxies themselves have a mix of stellar ages, we derive an upper limit on the intracluster stellar mass fraction of <0.47 (84% one-sided confidence limit). When combined with the intragroup SNe results of McGee & Balogh, we confirm the declining intracluster stellar mass fraction as a function of halo mass reported by Gonzalez and collaborators.
NASA Technical Reports Server (NTRS)
Zeng, X. C.; Stroud, D.
1989-01-01
The previously developed Ginzburg-Landau theory for calculating the crystal-melt interfacial tension of bcc elements to treat the classical one-component plasma (OCP), the charged fermion system, and the Bose crystal. For the OCP, a direct application of the theory of Shih et al. (1987) yields for the surface tension 0.0012(Z-squared e-squared/a-cubed), where Ze is the ionic charge and a is the radius of the ionic sphere. Bose crystal-melt interface is treated by a quantum extension of the classical density-functional theory, using the Feynman formalism to estimate the relevant correlation functions. The theory is applied to the metastable He-4 solid-superfluid interface at T = 0, with a resulting surface tension of 0.085 erg/sq cm, in reasonable agreement with the value extrapolated from the measured surface tension of the bcc solid in the range 1.46-1.76 K. These results suggest that the density-functional approach is a satisfactory mean-field theory for estimating the equilibrium properties of liquid-solid interfaces, given knowledge of the uniform phases.
NASA Astrophysics Data System (ADS)
Ratcliffe, H.; Brady, C. S.; Che Rozenan, M. B.; Nakariakov, V. M.
2014-12-01
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.
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.
Simultaneous single epoch satellite clock modelling in Global Navigation Satellite Systems
NASA Astrophysics Data System (ADS)
Thongtan, Thayathip
In order to obtain high quality positions from navigation satellites, range errors have to be identified and either modelled or estimated. This thesis focuses on satellite clock errors, which are needed to be known because satellite clocks are not perfectly synchronised with navigation system time. A new approach, invented at UCL, for the simultaneous estimation, in a single epoch, of all satellite clock offsets within a Global Navigation Satellite System (GNSS) from range data collected at a large number of globally distributed ground stations is presented. The method was originally tested using only data from a limited number of GPS satellites and ground stations. In this work a total of 50 globally distributed stations and the whole GPS constellation are used in order to investigate more fully the capabilities of the method, in terms of both accuracy and reliability. A number of different estimation models have been tested. These include those with different weighting schemes, those with and without tropospheric bias parameters and those that include assumptions regarding prior knowledge of satellite orbits. In all cases conclusions have been drawn based on formal error propagation theory. Accuracy has been assessed largely through the sizes of the predicted satellite clock standard deviations and, in the case of simultaneously estimating satellite positions, their error ellipsoids. Both internal and external reliability have been assessed as these are important contributors to integrity, something that is essential for many practical applications. It has been found that the accuracy and reliability of satellite clock offsets are functions of the number of known ground station clocks and distance from them, quality of orbits and quality of range measurement. Also the introduction of tropospheric zenith delay parameters into the model reduces both accuracy and reliability by amounts depending on satellite elevation angles. (Abstract shortened by UMI.)
The pulsar B2224+65 and its jets: a two epoch X-ray analysis
NASA Astrophysics Data System (ADS)
Johnson, S. P.; Wang, Q. D.
2010-10-01
We present an X-ray morphological and spectroscopic study of the pulsar B2224+65 and its apparent jet-like X-ray features based on two epoch Chandra observations. The main X-ray feature, which shows a large directional offset from the ram-pressure confined pulsar wind nebula (Guitar nebula), is broader in apparent width and shows evidence for spectral hardening (at 95 per cent confidence) in the second epoch compared to the first. Furthermore, the sharp leading edge of the feature is found to have a proper motion consistent with that of the pulsar (~180 mas yr-1). The combined data set also provides evidence for the presence of a counter feature, albeit substantially fainter and shorter than the main one. Additional spectral trends along the major and minor axes of the feature are only marginally detected in the two epoch data, including softening counter to the direction of proper motion. Possible explanations for the X-ray features include diffuse energetic particles being confined by an organized ambient magnetic field as well as a simple ballistic jet interpretation; however, the former may have difficulty in explaining observed spectral trends between epochs and along the feature's major axis, whereas the latter may struggle to elucidate its linearity. Given the low counting statistics available in the two epoch observations, it remains difficult to determine a physical production scenario for these enigmatic X-ray emitting features with any certainty.
Mason, Rod S
2010-04-21
A steady state chemical kinetic model is developed to describe the conduction of electrical current between two probes, of relatively large surface area, immersed in a fast flowing plasma by the mechanism of charge transfer through a gas of Rydberg atoms. It correctly predicts the shape of current-voltage profiles which are similar to those of Langmuir, or floating double probe measurements. The difference is that the plateau current at the probe reflects the transport limited ion current at the cathodic electrode, even when the probe is being scanned in the anodic region. The sharp gradient leading up to the plateau of the I-V curve is associated with the field dependence of the efficiency of Rydberg atom ionisation, not the electron temperature. This approach gives a good qualitative explanation of experimental behaviour over a wide range of probe bias voltages and includes the occurrence of electron impact ionisation at the anode. It also gives a value for the thermal rate coefficient of symmetrical charge transfer between Rydberg atoms of Ar (8.2 x 10(-7) molecule(-1) cm(3) s(-1), at 313 K; plasma density approximately = 10(10) atoms cm(-3), total pressure = 2.7 mbar).
NASA Astrophysics Data System (ADS)
Waltz, R. E.; Ferraro, N. M.
2013-10-01
The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, electric potential due to external resonant magnetic field perturbations (RMP) are obtained from the collisional two-fluid M3DC1 code. A newly developed RMPtran code computes the resulting quasilinear E × B and magnetic radial transport flows in all channels: ion and electron particle and energy, as well as toroidal angular momentum (TAM). The relative mix of ambipolar E × B and non-ambipolar magnetic particle transport and resulting J × B torque is of particular interest. Surprisingly much of the core RMP island J × B torque braking plasma rotation is returned to accelerate the plasma edge. Our main focus is on delineating the mechanisms for the RMP density pump-out where the radial convection of TAM is competitive with the magnetic braking of plasma rotation. Enhancement of the two-fluid crossfield resistivity, heat diffusivity, and viscosity represents the effects of turbulence on the low-n RMP transport. High-n turbulent transport is to be taken from the TGLF transport model. Supported by the US Department of Energy under DE-FG02-95ER54309.
NASA Astrophysics Data System (ADS)
Blum, L. W.; MacDonald, E.; Gary, S. P.; Thomsen, M. F.; Green, J. C.; Spence, H. E.
2009-12-01
There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. Using LANL Magnetospheric Plasma Analyzer (MPA) data from geosynchronous orbit, in conjunction with linear theory, we have developed a proxy for enhanced EMIC waves (Blum et al., 2009). We compare this proxy to in situ wave measurements from GOES high-resolution magnetometer data, and examine the presence of these waves as a function of both local time and storm epoch time. This enables broader understanding of the powerful applications of using plasma data to infer wave distributions in space.
D'yachkov, L. G. Khrapak, A. G.; Khrapak, S. A.
2008-01-15
The continuum approximation is used to analyze the effect of electron emission from the surface of a spherical dust grain immersed in a plasma on the grain charge by assuming negligible ionization and recombination in the disturbed plasma region around the grain. A parameter is introduced that quantifies the emission intensity regardless of the emission mechanism (secondary, photoelectric, or thermionic emission). An analytical expression for the grain charge Z{sub d} is derived, and a criterion for change in the charge sign is obtained. The case of thermionic emission is examined in some detail. It is shown that the long-distance asymptotic behavior of the grain potential follows the Coulomb law with a negative effective charge Z{sub eff}, regardless of the sign of Z{sub d}. Thus, the potential changes sign and has a minimum if Z{sub d} > 0, which implies that attraction is possible between positively charged dust grains.
NASA Astrophysics Data System (ADS)
Waltz, R. E.; Ferraro, N. M.
2015-04-01
The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, and electric potential from low-n external resonant magnetic field perturbations (RMPs) are obtained from the collisional two-fluid M3D-C1 code [N. M. Ferraro and S. C. Jardin, J. Comput. Phys. 228, 7742 (2009)]. A newly developed post-processing RMPtran code computes the resulting quasilinear E×B and magnetic (J×B) radial transport flows with respect to the unperturbed flux surfaces in all channels. RMPtran simulations focus on ion (center of mass) particle and transient non-ambipolar current flows, as well as the toroidal angular momentum flow. The paper attempts to delineate the RMP transport mechanisms that might be responsible for the RMP density pump-out seen in DIII-D [M. A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005)]. Experimentally, the starting high toroidal rotation does not brake to a significantly lower rotation after the pump-out suggesting that convective and E×B transport mechanisms dominate. The direct J×B torque from the transient non-ambipolar radial current expected to accelerate plasma rotation is shown to cancel much of the Maxwell stress J×B torque expected to brake the plasma rotation. The dominant E×B Reynolds stress accelerates rotation at the top of the pedestal while braking rotation further down the pedestal.
Haerendel, G.; Eccles, J.V.; Cakir, S. )
1992-02-01
Companion papers in this series present (1) the role of equatorial E region postsunset ionosphere, (2) the origin of horizontal plasma shear flow in the postsunset equatorial ionosphere (this paper), (3) the Colored Bubbles experiments results, and (4) computer simulations of artificial initiation of plasma density depletions (bubbles) in the equatorial ionosphere. Within this paper, equations describing the time evolution of the equatorial ionosphere are developed using flux tube integrated and flux tube weighted quantities which model the chemistry, dynamics, and electrodynamics of the equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial electric fields neglecting small-scale phenomena ({lambda} < 1 km). An immediate result derived from the integrated current equations is an equation describing the physics of the shear in the horizontal flow of the equatorial plasma during the evening hours. The profile of the horizontal flow has three important contributing terms relating to the neutral wind dynamo, Hall conduction, and the equatorial electrojet current divergence. Using a one-dimensional model of the velocity shear equation and the integrated ionosphere transport equations, a time history of the development of the shear feature during postsunset hours is presented. The one-dimensional model results are compared to the velocity shear measurements from the Colored Bubbles experiments.
Fundamentals of Plasma Physics
NASA Astrophysics Data System (ADS)
Bellan, Paul M.
2008-07-01
Preface; 1. Basic concepts; 2. The Vlasov, two-fluid, and MHD models of plasma dynamics; 3. Motion of a single plasma particle; 4. Elementary plasma waves; 5. Streaming instabilities and the Landau problem; 6. Cold plasma waves in a magnetized plasma; 7. Waves in inhomogeneous plasmas and wave energy relations; 8. Vlasov theory of warm electrostatic waves in a magnetized plasma; 9. MHD equilibria; 10. Stability of static MHD equilibria; 11. Magnetic helicity interpreted and Woltjer-Taylor relaxation; 12. Magnetic reconnection; 13. Fokker-Planck theory of collisions; 14. Wave-particle nonlinearities; 15. Wave-wave nonlinearities; 16. Non-neutral plasmas; 17. Dusty plasmas; Appendix A. Intuitive method for vector calculus identities; Appendix B. Vector calculus in orthogonal curvilinear coordinates; Appendix C. Frequently used physical constants and formulae; Bibliography; References; Index.
The Corporate University's Role in Managing an Epoch in Learning Organisation Innovation
ERIC Educational Resources Information Center
Dealtry, Richard
2006-01-01
Purpose: The purpose of this paper is to set the scene for some radical epochal thinking about the approach and future strategic directions in the management of organisational learning, following the author's earlier editorial theme concerning the need for exploration and innovation in organisational learning management.…
NASA Astrophysics Data System (ADS)
Enoki, Motohiro; Takahara, Fumio; Fujita, Yutaka
2001-07-01
We investigate statistical properties of galaxy clusters in the context of a hierarchical clustering scenario, taking into account their formation epoch distribution; this study is motivated by the recent finding by Fujita and Takahara that X-ray clusters form a fundamental plane in which the mass and the formation epoch are regarded as two independent parameters. Using the formalism that discriminates between major mergers and accretion, the epoch of a cluster formation is identified with that of the last major merger. Since tiny mass accretion following formation does not much affect the core structure of clusters, the properties of X-ray emission from clusters are determined by the total mass and density at their formation time. Under these assumptions, we calculate X-ray luminosity and temperature functions of galaxy clusters. We find that the behavior of the luminosity function differs from the model that does not take into account formation epoch distribution; the behavior of the temperature function, however, is not much different. In our model, the luminosity function is shifted to a higher luminosity and shows no significant evolution up to z~1, independent of cosmological models. The clusters are populated on the temperature-luminosity plane, with a finite dispersion. Since the simple scaling model in which the gas temperature is equal to the virial temperature fails to reproduce the observed luminosity-temperature relation, we also consider a model that takes into account the effects of preheating. The preheating model reproduces the observations much more accurately.
The Influence of Epoch Length on Physical Activity Patterns Varies by Child's Activity Level
ERIC Educational Resources Information Center
Nettlefold, Lindsay; Naylor, P. J.; Warburton, Darren E. R.; Bredin, Shannon S. D.; Race, Douglas; McKay, Heather A.
2016-01-01
Purpose: Patterns of physical activity (PA) and sedentary time, including volume of bouted activity, are important health indicators. However, the effect of accelerometer epoch length on measurement of these patterns and associations with health outcomes in children remain unknown. Method: We measured activity patterns in 308 children (52% girls,…
Examining Initial Sleep Onset in Primary Insomnia: A Case-Control Study Using 4-Second Epochs
Moul, Douglas E.; Germain, Anne; Cashmere, J. David; Quigley, Michael; Miewald, Jean M.; Buysse, Daniel J.
2007-01-01
Study Objectives: To explore the sleep onset process in primary insomnia patients, new rules for scoring 4-second epochs were implemented to score sleep and artifacts during initial sleep onset. Conventional scorings in 20-second and 60-second epochs were also obtained. Methods: The start of the initial 60-second epoch of stage 1 was used to define “time zero” (t0). Sleep onset periods from 11 patients and 11 individually age- and sex-matched controls spanned from 5 minutes before t0 through 29 minutes after t0. Using the new rules, the periods were scored blind to group assignment. This t0 time-referenced the data analysis to one plausible midpoint in the sleep onset process. In parallel, latencies were time-referenced from good night time. Results: Reliability in scoring sleep and artifacts was adequate (kappa = 0.68 & 0.63, respectively, p <0.001). Group differences in sleep latencies were marginal in 60-second and 20-second scoring but significant with a definition of 4-second sleep latency. Patients had more 4-second epochs scored as awake (Mantel-Haenszel χ2 = 271, d.f. = 1, p <0.001) and containing artifact (M-H χ2 = 143, p <0.001). Patients took longer to achieve 30 continuous 4-second epochs of NREM sleep (Breslow χ2 = 4.03, d.f. = 1, p = 0.045) after t0. Patients accumulated sleep more slowly with all 3 scoring rules after t0. A slower rate of accumulating sleep after t0 was detected only with the 4-second scoring (p = 0.047). Conclusions: Evidence was present for momentary state-switching instabilities in the patients during the initial sleep onset process. Using rules for scoring small epochs may reveal such instabilities more readily than traditional scoring methods. Citation: Moul DE; Germain A; Cashmere D; Quigley M; Miewald JM; Buysse DJ. Examining initial sleep onset in primary insomnia: a case-control study using 4-second epochs. J Clin Sleep Med 2007;3(5):479-488. PMID:17803011
NASA Astrophysics Data System (ADS)
Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June
2016-06-01
The temporal evolution of the kinetic ion temperature gradient driven instability and of the related anomalous transport of the ion thermal energy of plasma shear flow across the magnetic field is investigated analytically. This instability develops in a steady plasma due to the inverse ion Landau damping and has the growth rate of the order of the frequency when the ion temperature is equal to or above the electron temperature. The investigation is performed employing the non-modal methodology of the shearing modes which are the waves that have a static spatial structure in the frame of the background flow. The solution of the governing linear integral equation for the perturbed potential displays that the instability experiences the non-modal temporal evolution in the shearing flow during which the unstable perturbation becomes very different from a canonical modal form. It transforms into the non-modal structure with vanishing frequency and growth rate with time. The obtained solution of the nonlinear integral equation, which accounts for the random scattering of the angle of the ion gyro-motion due to the interaction of ions with ensemble of shearing waves, reveals similar but accelerated process of the transformations of the perturbations into the zero frequency structures. It was obtained that in the shear flow the anomalous ion thermal conductivity decays with time. It is a strictly non-modal effect, which originates from the temporal evolution of the shearing modes turbulence.
Bao, Junwei Lucas; Seal, Prasenjit; Truhlar, Donald G
2015-06-28
The growth of nanodusty particles, which is critical in plasma chemistry, physics, and engineering. The aim of the present work is to understand the detailed reaction mechanisms of early steps in this growth. The polymerization of neutral silane with the silylene or silyl anion, which eliminates molecular hydrogen with the formation of their higher homologues, governs the silicon hydride clustering in nanodusty plasma chemistry. The detailed mechanisms of these important polymerization reactions in terms of elementary reactions have not been proposed yet. In the present work, we investigated the initial steps of these polymerization reactions, i.e., the SiH4 + Si2H4(-)/Si2H5(-) reactions, and we propose a three-step mechanism, which is also applicable to the following polymerization steps. CM5 charges of all the silicon-containing species were computed in order to analyze the character of the species in the proposed reaction mechanisms. We also calculated thermal rate constant of each step using multi-structural canonical variational transition state theory (MS-CVT) with the small-curvature tunneling (SCT) approximation, based on the minimum energy path computed using M08-HX/MG3S electronic structure method.
STAR FORMATION IN ORION'S L1630 CLOUD: AN INFRARED AND MULTI-EPOCH X-RAY STUDY
Principe, David A.; Kastner, J. H.; Richmond, Michael; Grosso, Nicolas; Hamaguchi, Kenji
2014-07-01
X-ray emission is characteristic of young stellar objects (YSOs) and is known to be highly variable. We investigate, via an infrared and multi-epoch X-ray study of the L1630 dark cloud, whether and how X-ray variability in YSOs is related to protostellar evolutionary state. We have analyzed 11 Chandra X-Ray Observatory observations, obtained over the course of four years and totaling ∼240 ks exposure time, targeting the eruptive Class I YSO V1647 Ori in L1630. We used Two Micron All Sky Survey and Spitzer data to identify and classify IR counterparts to L1630 X-ray sources and identified a total of 52 X-ray-emitting YSOs with IR counterparts, including four Class I sources and one Class 0/I source. We have detected cool (<3 MK) plasma, possibly indicative of accretion shocks, in three classical T Tauri stars. A subsample of 27 X-ray-emitting YSOs were covered by 9 of the 11 Chandra observations targeting V1647 Ori and the vicinity. For these 27 YSOs, we have constructed X-ray light curves spanning approximately four years. These light curves highlight the variable nature of pre-main-sequence X-ray-emitting young stars; many of the L1630 YSOs vary by orders of magnitude in count rate between observations. We discuss possible scenarios to explain apparent trends between various X-ray spectral properties, X-ray variance, and YSO classification.
Stacey, W. M.; Bae, C.
2015-06-15
A systematic formalism for the calculation of rotation in non-axisymmetric tokamaks with 3D magnetic fields is described. The Braginskii Ωτ-ordered viscous stress tensor formalism, generalized to accommodate non-axisymmetric 3D magnetic fields in general toroidal flux surface geometry, and the resulting fluid moment equations provide a systematic formalism for the calculation of toroidal and poloidal rotation and radial ion flow in tokamaks in the presence of various non-axisymmetric “neoclassical toroidal viscosity” mechanisms. The relation among rotation velocities, radial ion particle flux, ion orbit loss, and radial electric field is discussed, and the possibility of controlling these quantities by producing externally controllable toroidal and/or poloidal currents in the edge plasma for this purpose is suggested for future investigation.
Scharer, J.E.
1992-12-31
The research performed under this grant during the past year has been concentrated on the following several key tokamak ICRF (Ion Cyclotron Range of Frequencies) coupling, heating and current drive issues: Efficient coupling during the L- to H- mode transition by analysis and computer simulation of ICRF antennas; analysis of ICRF cavity-backed coil antenna coupling to plasma edge profiles including fast and ion Bernstein wave coupling for heating and current drive; benchmarking the codes to compare with current JET, D-IIID and ASDEX experimental results and predictions for advanced tokamaks such as BPX and SSAT (Steady-State Advanced Tokamak); ICRF full-wave field solutions, power conservation, heating analyses and minority ion current drive; and the effects of fusion alpha particle or ion tail populations on the ICRF absorption. Research progress, publications, and conference and workshop presentations are summarized in this report.
Borovsky, Joseph E; Denton, Michael H
2009-01-01
A superposed-epoch analysis of ACE and OMNI2 measurements is performed on 27 corotating interaction regions (CIRs) in 2003-2008, with the zero epoch taken to be the stream interface as determined by the maximum of the plasma vorticity. The structure of CIRs is investigated. When the flow measurements are rotated into the local-Parker-spiral coordinate system the shear is seen to be abrupt and intense, with vorticities on the order of 10{sup -5}-10{sup -4} sec{sup -1}. Converging flows perpendicular to the stream interface are seen in the local-Parker-spiral coordinate system and about half of the CIRs show a layer of divergent rebound flow away from the stream interface. Arguments indicate that any spreading of turbulence away from the region where it is produced is limited to about 10{sup 6} km, which is very small compared with the thickness of a CrR. Analysis of the turbulence across the CrRs is performed. When possible, the effects of discontinuities are removed from the data. Fluctuation amplitudes, the Alfvenicity, and the level of Alfvenic correlations all vary smoothly across the CrR. The Alfven ratio exhibits a decrease at the shear zone of the stream interface. Fourier analysis of 4.5-hr subintervals of ACE data is performed and the results are superposed averaged as an ensemble of realizations. The spectral slopes of the velocity, magnetic-field, and total-energy fluctuations vary smoothly across the CIR. The total-energy spectral slope is {approx} 3/2 in the slow and fast wind and in the CrRs. Analysis of the Elsasser inward-outward fluctuations shows a smooth transition across the CrR from an inward-outward balance in the slow wind to an outward dominance in the fast wind. A number of signatures of turbulence driving at the shear zone are sought (entropy change, turbulence amplitude, Alfvenicity, Alfven ratio, spectral slopes, in-out nature): none show evidence of driving of turbulence by shear.
Plasma Physics: An Introductory Course
NASA Astrophysics Data System (ADS)
Dendy, R. O.
1995-03-01
Preface; Introduction R. O. Dendy; 1. Plasma particle dynamics R. J. Hastie; 2. Plasma kinetic theory J. A. Elliott; 3. Waves in plasmas J. P. Doughtery; 4. Magnetohydrodynamics K. I. Hopcraft; 5. Turbulence in fluids and fusion plasmas F. A. Haas; 6. Finite-dimensional dynamics and chaos T. J. Mullin; 7. Computational plasma physics J. W. Eastwood; 8. Tokomak experiments D. C. Robinson and M. R. O'Brien; 9. Magnetospheric plasmas: Part I Basic processes in the solar system D. A. Bryant; Part II Microprocesses R. L. Bingham; 10. Solar plasmas R. A. Hood; 11. Gravitational plasmas J. J. Binney; 12. Laser plasmas A. R. Bell; 13. Industrial plasmas P. C. Johnson; 14. Transport in magnetically confined plasmas T. E. Stringer; 15. Radio-frequency plasma heating R. A. Cairns; 16. Boundary plasmas G. McCracken; 17. How to build a tokomak T. N. Todd; 18. Survey of fusion plasma physics R. S. Pease; Index.
Tsytovich, Vadim; Gusein-zade, Namik; Ignatov, Alexander
2015-07-15
Dust structuring is a natural and universal process in complex plasmas. The scattering of electromagnetic waves by dust structures is governed by the factor of coherency, i.e., the total number of coherent electrons in a single structure. In the present paper, we consider how the factor of coherency changes due to additional pulse electron heating and show that it obeys a hysteresis. After the end of the pulse heating, the scattering intensity differs substantially from that before heating. There are three necessary conditions for scattering hysteresis: first, the radiation wavelength should be larger than the pattern (structure) size; second, the total number of coherent electrons confined by the structure should be large; and third, the heating pulse duration should be shorter than the characteristic time of dust structure formation. We present the results of numerical calculations using existing models of self-consistent dust structures with either positively or negatively charged dust grains. It is shown that, depending on the grain charge and the ionization rate, two types of hysteresis are possible: one with a final increase of the scattering and the other with a final decrease of the scattering. It is suggested that the hysteresis of coherent scattering can be used as a tool in laboratory experiments and that it can be a basic mechanism explaining the observed hysteresis in radar scattering by noctilucent clouds during active experiments on electron heating in mesosphere.
NASA Astrophysics Data System (ADS)
Kaurov, Alexander A.
2016-06-01
We explore a time-dependent energy dissipation of the energetic electrons in the inhomogeneous intergalactic medium (IGM) during the epoch of cosmic reionization. In addition to the atomic processes, we take into account the inverse Compton (IC) scattering of the electrons on the cosmic microwave background photons, which is the dominant channel of energy loss for electrons with energies above a few MeV. We show that: (1) the effect on the IGM has both local (atomic processes) and non-local (IC radiation) components; (2) the energy distribution between hydrogen and helium ionizations depends on the initial energy of an electron; (3) the local baryon overdensity significantly affects the fractions of energy distributed in each channel; and (4) the relativistic effect of the atomic cross-section becomes important during the epoch of cosmic reionization. We release our code as open source for further modification by the community.
THE EFFECTS OF POLARIZED FOREGROUNDS ON 21 cm EPOCH OF REIONIZATION POWER SPECTRUM MEASUREMENTS
Moore, David F.; Aguirre, James E.; Parsons, Aaron R.; Pober, Jonathan C.; Jacobs, Daniel C.
2013-06-01
Experiments aimed at detecting highly-redshifted 21 cm emission from the epoch of reionization (EoR) are plagued by the contamination of foreground emission. A potentially important source of contaminating foregrounds may be Faraday-rotated, polarized emission, which leaks into the estimate of the intrinsically unpolarized EoR signal. While these foregrounds' intrinsic polarization may not be problematic, the spectral structure introduced by the Faraday rotation could be. To better understand and characterize these effects, we present a simulation of the polarized sky between 120 and 180 MHz. We compute a single visibility, and estimate the three-dimensional power spectrum from that visibility using the delay spectrum approach presented in Parsons et al. Using the Donald C. Backer Precision Array to Probe the Epoch of Reionization as an example instrument, we show the expected leakage into the unpolarized power spectrum to be several orders of magnitude above the expected 21 cm EoR signal.
Li, W.; Thorne, R. M.; Bortnik, J.; Baker, D. N.; Reeves, G. D.; Kanekal, S. G.; Spence, H. E.; Green, J. C.
2015-09-07
In this study by determining preferential solar wind conditions leading to efficient radiation belt electron acceleration is crucial for predicting radiation belt electron dynamics. Using Van Allen Probes electron observations (>1 MeV) from 2012 to 2015, we identify a number of efficient and inefficient acceleration events separately to perform a superposed epoch analysis of the corresponding solar wind parameters and geomagnetic indices. By directly comparing efficient and inefficient acceleration events, we clearly show that prolonged southward Bz, high solar wind speed, and low dynamic pressure are critical for electron acceleration to >1 MeV energies in the heart of the outer radiation belt. We also evaluate chorus wave evolution using the superposed epoch analysis for the identified efficient and inefficient acceleration events and find that chorus wave intensity is much stronger and lasts longer during efficient electron acceleration events, supporting the scenario that chorus waves play a key role in MeV electron acceleration.
THE EPOCH OF ASSEMBLY OF TWO GALAXY GROUPS: A COMPARATIVE STUDY
Nichols, Matthew; Bland-Hawthorn, Joss
2013-10-01
Nearby galaxy groups of comparable mass to the Local Group show global variations that reflect differences in their evolutionary history. Satellite galaxies in groups have higher levels of gas deficiency as the distance to their host decreases. The well established gas-deficiency profile of the Local Group reflects an epoch of assembly starting at z ∼< 10. We investigate whether this gas-deficiency profile can be used to determine the epoch of assembly for other nearby groups. We choose the M81 group as this has the most complete inventory, both in terms of membership and multi-wavelength observations. We expand our earlier evolutionary model of satellite dwarf galaxies to not only confirm this result for the Local Group but also show that the more gas-rich M81 group is likely to have assembled at a later time (z ∼< 1-3) than the Local Group.
Period, epoch, and prediction errors of ephemerides from continuous sets of timing measurements
NASA Astrophysics Data System (ADS)
Deeg, H. J.
2015-06-01
Space missions such as Kepler and CoRoT have led to large numbers of eclipse or transit measurements in nearly continuous time series. This paper shows how to obtain the period error in such measurements from a basic linear least-squares fit, and how to correctly derive the timing error in the prediction of future transit or eclipse events. Assuming strict periodicity, a formula for the period error of these time series is derived, σP = σT (12 / (N3-N))1 / 2, where σP is the period error, σT the timing error of a single measurement, and N the number of measurements. Compared to the iterative method for period error estimation by Mighell & Plavchan (2013), this much simpler formula leads to smaller period errors, whose correctness has been verified through simulations. For the prediction of times of future periodic events, usual linear ephemeris were epoch errors are quoted for the first time measurement, are prone to an overestimation of the error of that prediction. This may be avoided by a correction for the duration of the time series. An alternative is the derivation of ephemerides whose reference epoch and epoch error are given for the centre of the time series. For long continuous or near-continuous time series whose acquisition is completed, such central epochs should be the preferred way for the quotation of linear ephemerides. While this work was motivated from the analysis of eclipse timing measures in space-based light curves, it should be applicable to any other problem with an uninterrupted sequence of discrete timings for which the determination of a zero point, of a constant period and of the associated errors is needed.
Dose-Adjusted EPOCH-Rituximab Therapy in Primary Mediastinal B-Cell Lymphoma
Dunleavy, Kieron; Pittaluga, Stefania; Maeda, Lauren S.; Advani, Ranjana; Chen, Clara C.; Hessler, Julie; Steinberg, Seth M.; Grant, Cliona; Wright, George; Varma, Gaurav; Staudt, Louis M.; Jaffe, Elaine S.; Wilson, Wyndham H.
2015-01-01
BACKGROUND Primary mediastinal B-cell lymphoma is a distinct subtype of diffuse large-B-cell lymphoma that is closely related to nodular sclerosing Hodgkin’s lymphoma. Patients are usually young and present with large mediastinal masses. There is no standard treatment, but the inadequacy of immunochemotherapy alone has resulted in routine consolidation with mediastinal radiotherapy, which has potentially serious late effects. We aimed to develop a strategy that improves the rate of cure and obviates the need for radiotherapy. METHODS We conducted a single-group, phase 2, prospective study of infusional dose-adjusted etoposide, doxorubicin, and cyclophosphamide with vincristine, prednisone, and rituximab (DA-EPOCH-R) and filgrastim without radiotherapy in 51 patients with untreated primary mediastinal B-cell lymphoma. We used results from a retrospective study of DA-EPOCH-R from another center to independently verify the outcomes. RESULTS The patients had a median age of 30 years (range, 19 to 52) and a median tumor diameter of 11 cm; 59% were women. During a median of 5 years of follow-up, the event-free survival rate was 93%, and the overall survival rate was 97%. Among the 16 patients who were involved in the retrospective analysis at another center, over a median of 3 years of follow-up, the event-free survival rate was 100%, and no patients received radiotherapy. No late morbidity or cardiac toxic effects were found in any patients. After follow-up ranging from 10 months to 14 years, all but 2 of the 51 patients (4%) who received DA-EPOCH-R alone were in complete remission. The 2 remaining patients received radiotherapy and were disease-free at follow-up. CONCLUSIONS Therapy with DA-EPOCH-R obviated the need for radiotherapy in patients with primary mediastinal B-cell lymphoma. (Funded by the National Cancer Institute; ClinicalTrials.gov number, NCT00001337.) PMID:23574119
Observations and Analysis of Three Field RR Lyrae Stars Selected Using Single-epoch SDSS Data
NASA Astrophysics Data System (ADS)
Powell, W. L., Jr.; Jameson, S. N.; De lee, N.; Wilhelm, R. J.
2015-08-01
We present the results of our Johnson B and V observations of three RR Lyrae candidate stars that we identified as likely variable stars using SDSS data. The stars were selected based upon a single epoch of photometry and spectroscopy. The stars were observed at McDonald Observatory to obtain full light curves. We present full light curves, measured periods, and amplitudes, as well as the results of our Fourier analysis of the light curves.
Fossil wood from the Miocene and Oligocene epoch: chemistry and morphology.
Bardet, Michel; Pournou, Anastasia
2015-01-01
Fossil wood is the naturally preserved remain of the secondary xylem of plants that lived before the Holocene epoch. Typically, fossil wood is preserved as coalified or petrified and rarely as mummified tissue. The process of fossilization is very complex and it is still unknown why in the same fossil record, wood can be found in different fossilisation forms. In 2007, a fossil forest was found in the Bükkábrány open-pit coal mine in Hungary. The non-petrified forest is estimated to be 7 million years old (Miocene epoch) and its trees were found standing in an upright position. This fossil assemblage is exceptionally rare because wood has been preserved as soft waterlogged tissue. This study aimed to investigate this remarkable way of fossil wood preservation, by examining its chemistry with (13)C CPMAS NMR and its morphology with light and electron microscopy. For comparison reasons, a petrified wood trunk from the Oligocene epoch (30 Myr) found in 2001 at Porrentruy region in Switzerland and two fresh wood samples of the modern equivalents of the Miocene sample were also examined. The results obtained showed that the outstanding preservation state of the Miocene fossil is not owed to petrification or coalification. Mummification is a potential mechanism that could explain Bükkábrány trunks' condition, however this fossilisation process is not well studied and therefore this hypothesis needs to be further investigated. PMID:25294390
Use of Apollo 17 Epoch Neutron Spectrum as a Benchmark in Testing LEND Collimated Sensor
NASA Technical Reports Server (NTRS)
Chin, Gordon; Sagdeev, R.; Milikh, G.
2011-01-01
The Apollo 17 neutron experiment LPNE provided a unique set of data on production of neutrons in the Lunar soil bombarded by Galactic Cosmic Rays (GCR). It serves as valuable "ground-truth" in the age of orbital remote sensing. We used the neutron data attributed to Apollo 17 epoch as a benchmark for testing the LEND's collimated sensor, as introduced by the geometry of collimator and efficiency of He3 counters. The latter is defined by the size of gas counter and pressure inside it. The intensity and energy spectrum of neutrons escaping the lunar surface are dependent on incident flux of Galactic Cosmic Rays (GCR) whose variability is associated with Solar Cycle and its peculiarities. We obtain first the share of neutrons entering through the field of view of collimator as a fraction of the total neutron flux by using the angular distribution of neutron exiting the Moon described by our Monte Carlo code. We computed next the count rate of the 3He sensor by using the neutron energy spectrum from McKinney et al. [JGR, 2006] and by consider geometry and gas pressure of the LEND sensor. Finally the neutron count rate obtained for the Apollo 17 epoch characterized by intermediate solar activity was adjusted to the LRO epoch characterized by low solar activity. It has been done by taking into account solar modulation potential, which affects the GCR flux, and in turn changes the neutron albedo flux.
The Time Evolution of HH 1 from Four Epochs of HST Images
NASA Astrophysics Data System (ADS)
Raga, A. C.; Reipurth, B.; Esquivel, A.; Bally, J.
2016-05-01
We present an analysis of four epochs of Hα and [S ii] λλ 6716/6731 Hubble Space Telescope (HST) images of HH 1. For determining proper motions, we explore a new method based on the analysis of spatially degraded images obtained convolving the images with wavelet functions of chosen widths. With this procedure, we are able to generate maps of proper motion velocities along and across the outflow axis, as well as (angularly integrated) proper motion velocity distributions. From the four available epochs, we find the time evolution of the velocities, intensities, and spatial distribution of the line emission. We find that over the last two decades HH 1 shows a clear acceleration. Also, the Hα and [S ii] intensities first dropped and then recovered in the more recent (2014) images. Finally, we show a comparison between the two available HST epochs of [O iii] λ 5007 (1994 and 2014), in which we see a clear drop in the value of the [O iii]/Hα ratio.
A 2 epoch proper motion catalogue from the UKIDSS Large Area Survey
NASA Astrophysics Data System (ADS)
Smith, Leigh; Lucas, Phil; Burningham, Ben; Jones, Hugh; Pinfield, David; Smart, Ricky; Andrei, Alexandre
2013-04-01
The UKIDSS Large Area Survey (LAS) began in 2005, with the start of the UKIDSS program as a 7 year effort to survey roughly 4000 square degrees at high galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of 2-epoch J band observations, with epoch baselines ranging from 2 to 7 years. We present a proper motion catalogue for the 1500 square degrees of the 2 epoch LAS data, which includes some 800,000 sources with motions detected above the 5σ level. We developed a bespoke proper motion pipeline which applies a source-unique second order polynomial transformation to UKIDSS array coordinates of each source to counter potential local non-uniformity in the focal plane. Our catalogue agrees well with the proper motion data supplied in the current WFCAM Science Archive (WSA) DR9 catalogue where there is overlap, and in various optical catalogues, but it benefits from some improvements. One improvement is that we provide absolute proper motions, using LAS galaxies for the relative to absolute correction. Also, by using unique, local, 2nd order polynomial tranformations, as opposed to the linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by their pipeline.
Plasma-based accelerator structures
Schroeder, Carl B.
1999-12-01
Plasma-based accelerators have the ability to sustain extremely large accelerating gradients, with possible high-energy physics applications. This dissertation further develops the theory of plasma-based accelerators by addressing three topics: the performance of a hollow plasma channel as an accelerating structure, the generation of ultrashort electron bunches, and the propagation of laser pulses is underdense plasmas.
Hones, E.W.
1992-01-01
The auroral motions and geomagnetic changes the characterize the substorm's expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.
Hones, E.W.
1992-05-01
The auroral motions and geomagnetic changes the characterize the substorm`s expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.
Hartigan, P.; Frank, A.; Foster, J. M.; Rosen, P. A.; Wilde, B. H.; Douglas, M.; Coker, R. F.; Blue, B. E.; Hansen, J. F.
2011-07-20
We present new, third-epoch Hubble Space Telescope H{alpha} and [S II] images of three Herbig-Haro (HH) jets (HH 1 and 2, HH 34, and HH 47) and compare the new images with those from previous epochs. The high spatial resolution, coupled with a time series whose cadence is of order both the hydrodynamic and radiative cooling timescales of the flow, allows us to follow the hydrodynamic/magnetohydrodynamic evolution of an astrophysical plasma system in which ionization and radiative cooling play significant roles. Cooling zones behind the shocks are resolved, so it is possible to identify which way material flows through a given shock wave. The images show that heterogeneity is paramount in these jets, with clumps dominating the morphologies of both bow shocks and their Mach disks. This clumpiness exists on scales smaller than the jet widths and determines the behavior of many of the features in the jets. Evidence also exists for considerable shear as jets interact with their surrounding molecular clouds, and in several cases we observe shock waves as they form and fade where material emerges from the source and as it proceeds along the beam of the jet. Fine structure within two extended bow shocks may result from Mach stems that form at the intersection points of oblique shocks within these clumpy objects. Taken together, these observations represent the most significant foray thus far into the time domain for stellar jets, and comprise one of the richest data sets in existence for comparing the behavior of a complex astrophysical plasma flow with numerical simulations and laboratory experiments.
NASA Astrophysics Data System (ADS)
Kubono, S.; Binh, Dam N.; Hayakawa, S.; Hashimoto, T.; Kahl, D. M.; Yamaguchi, H.; Wakabayashi, Y.; Teranishi, T.; Iwasa, N.; Komatsubara, T.; Kato, S.; Chen, A.; Cherubini, S.; Choi, S. H.; Hahn, I. S.; He, J. J.; Khiem, Le H.; Lee, C. S.; Kwon, Y. K.; Wanajo, S.; Janka, H.-T.
2013-05-01
Nucleosynthesis is one of the keys in studying the mechanism of core-collapse supernovae, which is an interesting challenge for modern science. The νp-process, which is similar to an explosive hydrogen burning process, has been proposed as the most probable process in the very early epoch of type II supernovae. Here, we discuss our experimental efforts for the νp-process, the first extensive direct measurements of the (α,p) reactions on bottle-neck proto-rich nuclei in light mass regions. Other challenges for the νp-process study are also discussed.
Joint US/UK Epoch World Magnetic Model 1995. Technical report
Quinn, J.M.; Coleman, R.J.; Shiel, D.L.
1995-04-01
This report contains a detailed summary of the data used, analyses performed, modeling techniques employed, and results obtained during the course of the 1995 Epoch World Magnetic Modeling effort. This report also contains the GEOMAG algorithm and describes its uses and limitations. Charts derived from the WMM-95 model and the GEOMAG algorithm for both the main geomagnetic field components and their secular variations are presented on Mercator and polar stereographic projections. Additionally, the numerical values of the main geomagnetic field components and their secular variations are tabulated on a 5-degree worldwide grid.
Lithographed spectrometers for tomographic line mapping of the Epoch of Reionization
NASA Astrophysics Data System (ADS)
O'Brient, R.; Bock, J. J.; Bradford, C. M.; Crites, A.; Duan, R.; Hailey-Dunsheath, S.; Hunacek, J.; LeDuc, R.; Shirokoff, E.; Staniszewski, Z.; Turner, A.; Zemcov, M.
2014-08-01
The Tomographic Ionized carbon Mapping Experiment (TIME) is a multi-phased experiment that will topographically map [CII] emission from the Epoch of Reionization. We are developing lithographed spectrometers that couple to TES bolometers in anticipation of the second generation instrument. Our design intentionally mirrors many features of the parallel SuperSpec project, inductively coupling power from a trunk-line microstrip onto half-wave resonators. The resonators couple to a rat-race hybrids that feeds TES bolometers. Our 25 channel prototype shows spectrally positioned lines roughly matching design with a receiver optical efficiency of 15-20%, a level that is dominated by loss in components outside the spectrometer.
The First Billion Years: The Growth of Galaxies in the Reionization Epoch
NASA Astrophysics Data System (ADS)
Illingworth, Garth
2015-08-01
Detection and measurement of the earliest galaxies in the first billion years only became possible after the Hubble Space Telescope was updated in 2009 with the infrared WFC3/IR camera during Shuttle servicing mission SM4. The first billion years is a fascinating epoch, not just because of the earliest galaxies known from about 450 Myr after the Big Bang, but also because it encompasses the reionization epoch that peaked around z~9, as Planck has recently shown, and ended around redshift z~6 at 900 Myr. Before 2009 just a handful of galaxies were known in the reionization epoch at z>6. But within the last 5 years, with the first HUDF09 survey, the HUDF12, CANDELS and numerous other surveys on the GOODS and CANDELS fields, as well as detections from the cluster lensing programs like CLASH and the Frontier Fields, the number of galaxies at redshifts 7-10 has exploded, with some 700 galaxies being found and characterized. The first billion years was a period of extraordinary growth in the galaxy population with rapid growth in the star formation rate density and global mass density in galaxies. Spitzer observations in the infrared of these Hubble fields are establishing masses as well as giving insights into the nature and timescales of star formation from the very powerful emission lines being revealed by the Spitzer IRAC data. I will discuss what we understand about the growth of galaxies in this epoch from the insights gained from remarkable deep fields like the XDF, as well as the wide-area GOODS/CANDELS fields, the detection of unexpectedly luminous galaxies at redshifts 8-10, the impact of early galaxies on reionization, confirmation of a number of galaxies at z~7-8 from ground-based spectroscopic measurements, and the indications of a change in the growth of the star formation rate around 500 Myr. The first billion years was a time of dramatic growth and change in the early galaxy population.
Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas.
Culfa, O; Tallents, G J; Rossall, A K; Wagenaars, E; Ridgers, C P; Murphy, C D; Dance, R J; Gray, R J; McKenna, P; Brown, C D R; James, S F; Hoarty, D J; Booth, N; Robinson, A P L; Lancaster, K L; Pikuz, S A; Faenov, A Ya; Kampfer, T; Schulze, K S; Uschmann, I; Woolsey, N C
2016-04-01
An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (10^{20}Wcm^{-2}) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μm). PMID:27176413
Guo, Hengxiao; Gu, Minfeng E-mail: gumf@shao.ac.cn
2014-09-01
In a sample of 60 quasars selected from the Sloan Digital Sky Survey with at least six-epoch spectroscopy, we investigate the variability of emission lines and continuum luminosity at various aspects. A strong anti-correlation between the variability and continuum luminosity at 2500 Å is found for the sample, which is consistent with previous works. In individual sources, we find that half of the sample objects follow the trend of being bluer when brighter, while the remaining half follow the redder-when-brighter (RWB) trend. Although the mechanism for RWB is unclear, the effects of host galaxy contribution due to seeing variations cannot be completely ruled out. As expected from the photoionization model, the positive correlations between the broad emission line and continuum luminosity are found in most individual sources, as well as for the whole sample. We confirm the Baldwin effect in most individual objects and the whole sample, while a negative Baldwin effect is also found in several quasars, which can be at least partly (if not all) due to the host galaxy contamination. We find positive correlations between the broad emission line luminosity and line width in most individual quasars, as well as the whole sample, implying a line base that is more variable than the line core.
The Hydrogen Epoch of Reionization Array Dish. I. Beam Pattern Measurements and Science Implications
NASA Astrophysics Data System (ADS)
Neben, Abraham R.; Bradley, Richard F.; Hewitt, Jacqueline N.; DeBoer, David R.; Parsons, Aaron R.; Aguirre, James E.; Ali, Zaki S.; Cheng, Carina; Ewall-Wice, Aaron; Patra, Nipanjana; Thyagarajan, Nithyanandan; Bowman, Judd; Dickenson, Roger; Dillon, Joshua S.; Doolittle, Phillip; Egan, Dennis; Hedrick, Mike; Jacobs, Daniel C.; Kohn, Saul A.; Klima, Patricia J.; Moodley, Kavilan; Saliwanchik, Benjamin R. B.; Schaffner, Patrick; Shelton, John; Taylor, H. A.; Taylor, Rusty; Tegmark, Max; Wirt, Butch; Zheng, Haoxuan
2016-08-01
The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen from the epoch of reionization (EOR). Drawing on lessons from the Murchison Widefield Array and the Precision Array for Probing the EOR, HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds. The dish not only determines overall sensitivity, but also affects the observed frequency structure of foregrounds in the interferometer. This is the first of a series of four papers characterizing the frequency and angular response of the dish with simulations and measurements. In this paper, we focus on the angular response (i.e., power pattern), which sets the relative weighting between sky regions of high and low delay and thus apparent source frequency structure. We measure the angular response at 137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a collecting area of 93 m2 in the optimal dish/feed configuration, implying that HERA-320 should detect the EOR power spectrum at z ˜ 9 with a signal-to-noise ratio of 12.7 using a foreground avoidance approach with a single season of observations and 74.3 using a foreground subtraction approach. Finally, we study the impact of these beam measurements on the distribution of foregrounds in Fourier space.
The Intricate Role of Cold Gas and Dust in Galaxy Evolution at Early Cosmic Epochs
NASA Astrophysics Data System (ADS)
Riechers, Dominik Alexander; Capak, Peter; Carilli, Christopher; Walter, Fabian
2015-08-01
Cold molecular and atomic gas plays a central role in our understanding of early galaxy formation and evolution. It represents the material that stars form out of, and its mass, distribution, excitation, and dynamics provide crucial insight into the physical processes that support the ongoing star formation and stellar mass buildup. We will discuss the most recent progress in studies of gas-rich galaxies out to the highest redshifts through detailed investigations with the most powerful facilities across the electromagnetic spectrum, with a particular focus on new observations obtained with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large (sub-) Millimeter Array (ALMA). These studies cover a broad range in galaxy properties, and provide a detailed comparison of the physical conditions in massive, dust-obscured starburst galaxies and star-forming active galactic nuclei hosts within the first billion years of cosmic time. Facilitating the impressive sensitivity of ALMA, this investigation also includes the first direct, systematic study of the star-forming interstellar medium, gas dynamics, and dust obscuration in (much less luminous and massive) "typical" galaxies at such early epochs. These new results show that "typical" z>5 galaxies are significantly metal-enriched, but not heavily dust-obscured, consistent with a decreasing contribution of dust-obscured star formation to the star formation history of the universe towards the earliest cosmic epochs.
Study of the star catalogue (epoch AD 1396.0) recorded in ancient Korean astronomical almanac
NASA Astrophysics Data System (ADS)
Jeon, Junhyeok; Lee, Yong Bok; Lee, Yong-Sam
2015-11-01
The study of old star catalogues provides important astrometric data. Most of the researches based on the old star catalogues were manuscript published in Europe and from Arabic/Islam. However, the old star catalogues published in East Asia did not get attention. Therefore, among the East Asian star catalogues we focus on a particular catalogue recorded in a Korean almanac. Its catalogue contains 277 stars that are positioned in a region within 10° of the ecliptic plane. The stars in the catalogue were identified using the modern Hipparcos catalogue. We identified 274 among 277 stars, which is a rate of 98.9 per cent. The catalogue records the epoch of the stars' positions as AD 1396.0. However, by using all of the identified stars we found that the initial epoch of the catalogue is AD 1363.1 ± 3.2. In conclusion, the star catalogue was compiled and edited from various older star catalogues. We assume a correlation with the Almagest by Ptolemaios. This study presents newly analysed results from the historically important astronomical data discovered in East Asia. Therefore, this star catalogue will become important data for comparison with the star catalogues published in Europe and from Arabic/Islam.
Li, W.; Thorne, R. M.; Bortnik, J.; Baker, D. N.; Reeves, G. D.; Kanekal, S. G.; Spence, H. E.; Green, J. C.
2015-09-07
In this study by determining preferential solar wind conditions leading to efficient radiation belt electron acceleration is crucial for predicting radiation belt electron dynamics. Using Van Allen Probes electron observations (>1 MeV) from 2012 to 2015, we identify a number of efficient and inefficient acceleration events separately to perform a superposed epoch analysis of the corresponding solar wind parameters and geomagnetic indices. By directly comparing efficient and inefficient acceleration events, we clearly show that prolonged southward Bz, high solar wind speed, and low dynamic pressure are critical for electron acceleration to >1 MeV energies in the heart of the outermore » radiation belt. We also evaluate chorus wave evolution using the superposed epoch analysis for the identified efficient and inefficient acceleration events and find that chorus wave intensity is much stronger and lasts longer during efficient electron acceleration events, supporting the scenario that chorus waves play a key role in MeV electron acceleration.« less
Contamination of the Epoch of Reionization power spectrum in the presence of foregrounds
NASA Astrophysics Data System (ADS)
Sims, Peter H.; Lentati, Lindley; Alexander, Paul; Carilli, Chris L.
2016-11-01
We construct foreground simulations comprising spatially correlated extragalactic and diffuse Galactic emission components and calculate the `intrinsic' (instrument-free) two-dimensional spatial power spectrum and the cylindrically and spherically averaged three-dimensional k-space power spectra of the Epoch of Reionization (EoR) and our foreground simulations using a Bayesian power spectral estimation framework. This leads us to identify a model-dependent region of optimal signal estimation for our foreground and EoR models, within which the spatial power in the EoR signal relative to the foregrounds is maximized. We identify a target field-dependent region, in k-space, of intrinsic foreground power spectral contamination at low k⊥ and k∥ and a transition to a relatively foreground-free intrinsic EoR window in the complement to this region. The contaminated region of k-space demonstrates that simultaneous estimation of the EoR and foregrounds is important for obtaining statistically robust estimates of the EoR power spectrum; biased results will be obtained from methodologies that ignore their covariance. Using simulated observations with frequency-dependent uv-coverage and primary beam, with the former derived for the Hydrogen Epoch of Reionization Array in 37-antenna and 331-antenna configuration, we recover instrumental power spectra consistent with their intrinsic counterparts. We discuss the implications of these results for optimal strategies for unbiased estimation of the EoR power spectrum.
OPENING THE 21 cm EPOCH OF REIONIZATION WINDOW: MEASUREMENTS OF FOREGROUND ISOLATION WITH PAPER
Pober, Jonathan C.; Parsons, Aaron R.; Ali, Zaki; Aguirre, James E.; Moore, David F.; Bradley, Richard F.; Carilli, Chris L.; DeBoer, Dave; Dexter, Matthew; MacMahon, Dave; Gugliucci, Nicole E.; Jacobs, Daniel C.; Klima, Patricia J.; Manley, Jason; Walbrugh, William P.; Stefan, Irina I.
2013-05-10
We present new observations with the Precision Array for Probing the Epoch of Reionization with the aim of measuring the properties of foreground emission for 21 cm epoch of reionization (EoR) experiments at 150 MHz. We focus on the footprint of the foregrounds in cosmological Fourier space to understand which modes of the 21 cm power spectrum will most likely be compromised by foreground emission. These observations confirm predictions that foregrounds can be isolated to a {sup w}edge{sup -}like region of two-dimensional (k , k{sub Parallel-To })-space, creating a window for cosmological studies at higher k{sub Parallel-To} values. We also find that the emission extends past the nominal edge of this wedge due to spectral structure in the foregrounds, with this feature most prominent on the shortest baselines. Finally, we filter the data to retain only this ''unsmooth'' emission and image its specific k{sub Parallel-To} modes. The resultant images show an excess of power at the lowest modes, but no emission can be clearly localized to any one region of the sky. This image is highly suggestive that the most problematic foregrounds for 21 cm EoR studies will not be easily identifiable bright sources, but rather an aggregate of fainter emission.
Signals from the epoch of cosmological recombination (Karl Schwarzschild Award Lecture 2008)
NASA Astrophysics Data System (ADS)
Sunyaev, R. A.; Chluba, J.
2009-07-01
The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of physical processes, still finding potentially measurable consequences for the energy spectrum and temperature anisotropies of the Cosmic Microwave Background (CMB). In this contribution we provide a short historical overview in connection with the cosmological recombination epoch and its connection to the CMB. Also we highlight some of the detailed physics that were studied over the past few years in the context of the cosmological recombination of hydrogen and helium. The impact of these considerations is two-fold: The associated release of photons during this epoch leads to interesting and unique deviations of the Cosmic Microwave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength and the Wien part of the CMB spectrum, may become observable in the near future. Despite the fact that the abundance of helium is rather small, it still contributes a sizeable amount of photons to the full recombination spectrum, leading to additional distinct spectral features. Observing the spectral distortions from the epochs of hydrogen and helium recombination, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium). Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. In this contribution we illustrate how the theoretical spectral template of the cosmological recombination spectrum may be utilized for this purpose. We also show that because hydrogen and helium recombine at very different epochs it is possible to address questions related to the thermal history of our Universe. In particular the cosmological recombination radiation may
More, R.M.
1986-01-01
Recent experiments with high-power pulsed lasers have strongly encouraged the development of improved theoretical understanding of highly charged ions in a dense plasma environment. This work examines the theory of dense plasmas with emphasis on general rules which govern matter at extreme high temperature and density. 106 refs., 23 figs.
Research in solar plasma theory
NASA Technical Reports Server (NTRS)
Vanhoven, Gerard
1992-01-01
The main thrust and significance of our research results are presented. The topics covered include: (1) coronal structure and dynamics; (2) coronal heating; (3) filament formation; and (4) flare energy release.
Chow, Clara K.; Lock, Karen; Madhavan, Manisha; Corsi, Daniel J.; Gilmore, Anna B.; Subramanian, S. V.; Li, Wei; Swaminathan, Sumathi; Lopez-Jaramillo, Patricio; Avezum, Alvaro; Lear, Scott A.; Dagenais, Gilles; Teo, Koon; McKee, Martin; Yusuf, Salim
2010-01-01
Background The environment in which people live is known to be important in influencing diet, physical activity, smoking, psychosocial and other risk factors for cardiovascular (CV) disease. However no instrument exists that evaluates communities for these multiple environmental factors and is suitable for use across different communities, regions and countries. This report describes the design and reliability of an instrument to measure environmental determinants of CV risk factors. Method/Principal Findings The Environmental Profile of Community Health (EPOCH) instrument comprises two parts: (I) an assessment of the physical environment, and (II) an interviewer-administered questionnaire to collect residents' perceptions of their community. We examined the inter-rater reliability amongst 3 observers from each region of the direct observation component of the instrument (EPOCH I) in 93 rural and urban communities in 5 countries (Canada, Colombia, Brazil, China and India). Data collection using the EPOCH instrument was feasible in all communities. Reliability of the instrument was excellent (Intraclass Correlation Coefficient - ICC>0.75) for 24 of 38 items and fair to good (ICC 0.4–0.75) for 14 of 38 items. Conclusion This report shows data collection with the EPOCH instrument is feasible and direct observation of community measures reliable. The EPOCH instrument will enable further research on environmental determinants of health for population studies from a broad range of settings. PMID:21170320
Light-cone anisotropy in the 21 cm signal from the epoch of reionization
NASA Astrophysics Data System (ADS)
Zawada, Karolina; Semelin, Benoît; Vonlanthen, Patrick; Baek, Sunghye; Revaz, Yves
2014-04-01
Using a suite of detailed numerical simulations, we estimate the level of anisotropy generated by the time evolution along the light cone of the 21 cm signal from the epoch of reionization. Our simulations include the physics necessary to model the signal during both the late emission regime and the early absorption regime, namely X-ray and Lyman band 3D radiative transfer in addition to the usual dynamics and ionizing UV transfer. The signal is analysed using correlation functions perpendicular and parallel to the line of sight. We reproduce general findings from previous theoretical studies: the overall amplitude of the correlations and the fact that the light-cone anisotropy is visible only on large scales (100 comoving Mpc). However, the detailed behaviour is different. We find that, at three different epochs, the amplitudes of the correlations along and perpendicular to the line of sight differ from each other, indicating anisotropy. We show that these three epochs are associated with three events of the global reionization history: the overlap of ionized bubbles, the onset of mild heating by X-rays in regions around the sources, and the onset of efficient Lyman α coupling in regions around the sources. We find that a 20 × 20 deg2 survey area may be necessary to mitigate sample variance when we use the directional correlation functions. On a 100 Mpc (comoving) scale, we show that the light-cone anisotropy dominates over the anisotropy generated by peculiar velocity gradients computed in the linear regime. By modelling instrumental noise and limited resolution, we find that the anisotropy should be easily detectable by the Square Kilometre Array, assuming perfect foreground removal, the limiting factor being a large enough survey size. In the case of the Low-Frequency Array for radio astronomy, it is likely that only one anisotropy episode (ionized bubble overlap) will fall in the observing frequency range. This episode will be detectable only if sample
Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch.
Inoue, Akio K; Tamura, Yoichi; Matsuo, Hiroshi; Mawatari, Ken; Shimizu, Ikkoh; Shibuya, Takatoshi; Ota, Kazuaki; Yoshida, Naoki; Zackrisson, Erik; Kashikawa, Nobunari; Kohno, Kotaro; Umehata, Hideki; Hatsukade, Bunyo; Iye, Masanori; Matsuda, Yuichi; Okamoto, Takashi; Yamaguchi, Yuki
2016-06-24
The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium. PMID:27312046
NASA Astrophysics Data System (ADS)
Tierney, J. E.; Oppo, D. W.; Legrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.
2012-10-01
Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preëminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.
Lyman horizons in the early phases of the epoch of reionization
NASA Astrophysics Data System (ADS)
Vonlanthen, P.; Semelin, B.
2011-12-01
It has been shown that the radial profile of the Lyman-α flux around light sources emitting in the Lyman band during the early phases of the epoch of reionization is characterized by a series of step-like discontinuities. This property originates in the fact that the neutral intergalactic medium is optically thick at the frequencies of all the Lyman-series lines. We show that, through unsaturated Wouthuysen-Field coupling, these spherical discontinuities are also present in the redshifted 21 cm signal of neutral hydrogen. We use realistic 3D numerical simulations with full radiative transfer calculation in the first five Lyman lines in order to study the properties of these discontinuities and the possibility for detection with the future Square Kilometre Array. Although challenging, these observations could provide a diagnostic tool to disentangle the cosmological signal and residuals from imperfect foreground removal.
Direct detection of projectile relics from the end of the lunar basin-forming epoch.
Joy, Katherine H; Zolensky, Michael E; Nagashima, Kazuhide; Huss, Gary R; Ross, D Kent; McKay, David S; Kring, David A
2012-06-15
The lunar surface, a key proxy for the early Earth, contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces. Surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the Earth-Moon system. In ancient [>3.4 billion years ago (Ga)] regolith breccias from the Apollo 16 landing site, we located mineral and lithologic relics of magnesian chondrules from chondritic impactors. These ancient impactor fragments are not nearly as diverse as those found in younger (3.4 Ga to today) regolith breccias and soils from the Moon or that presently fall as meteorites to Earth. This suggests that primitive chondritic asteroids, originating from a similar source region, were common Earth-Moon-crossing impactors during the latter stages of the basin-forming epoch. PMID:22604725
The Mars water cycle at other epochs: History of the polar caps and layered terrain
NASA Technical Reports Server (NTRS)
Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.
1992-01-01
The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.
NASA Technical Reports Server (NTRS)
Tierney, J.E.; Oppo, D. W.; LeGrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.
2012-01-01
Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preeminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.
Commissioning and Science Forecasts for the Hydrogen Epoch of Reionization Array (HERA)
NASA Astrophysics Data System (ADS)
Parsons, Aaron; HERA Collaboration
2016-01-01
The HERA is a low-frequency radio interferometer aiming to make precise measurements of the power spectrum of fluctuations in 21cm emission from the Epoch of Reionization at z=13—6. This project was recently awarded development funding under the 2014 cycle of the National Science Foundation's Mid-Scale Innovations Program (MSIP). We present initial results from the commissioning and testing of the 19-element HERA prototype in South Africa, including measurements of the performance of HERA's 14-m dish and feed via reflectometry, beam mapping, and on-sky commissioning tests. We then forecast the science results that HERA will deliver once it reaches its full size of 352 elements. These forecasts include constraints on the 21cm power spectrum, the impact of these constraints on parametrized models of ionization, and their relevance to cosmological models. Construction of HERA-352 is pending the outcome of the 2016 NSF MSIP cycle.
Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch
NASA Astrophysics Data System (ADS)
Inoue, Akio K.; Tamura, Yoichi; Matsuo, Hiroshi; Mawatari, Ken; Shimizu, Ikkoh; Shibuya, Takatoshi; Ota, Kazuaki; Yoshida, Naoki; Zackrisson, Erik; Kashikawa, Nobunari; Kohno, Kotaro; Umehata, Hideki; Hatsukade, Bunyo; Iye, Masanori; Matsuda, Yuichi; Okamoto, Takashi; Yamaguchi, Yuki
2016-06-01
The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium.
NASA Astrophysics Data System (ADS)
Shcherbakov, V. P.; Khokhlov, A. V.; Sycheva, N. K.
2014-03-01
The results of numerical modeling of the geomagnetic secular variation by the method of the Giant Gaussian Process (GGP) are presented and compared with the information derived from the presentday databases for paleointensity. The variances of the positions of the virtual geomagnetic pole (VGP) calculated from the synthetic and experimental data (Brunhes epoch, effusive rocks) are nearly similar, which supports the validity of the theoretical model. The average value of the virtual axial geomagnetic dipole (VADM) calculated from the PINT world database on paleointensity and the Sint-2000 model is lower than VADM calculated by the GGP model; at the same time, the estimates based on the archaeomagnetic data give the VADM value slightly above the model prediction. The largest difference is observed in the variances of VADM, which is for all the three databases noticeably higher than the value calculated from the GGP model. Most probably, this is due to the contribution of the neglected measurement errors of VADM.
NASA Technical Reports Server (NTRS)
Rhoads, James E.; Malhotra, Sangeeta; Stern, Daniel K.; Gardner, Jonathan P.; Dickinson, Mark; Pirzkal, Norbert; Spinrad, Hyron; Reddy, Naveen; Dey, Arjun; Hathi, Nimish; Grogin, Norman; Koekemoer, Anton; Peth, Michael A.; Cohen, Seth; Budavari, Tamas; Ferreras, Ignacio; Gronwall, Caryl; Haiman, Zoltan; Meurer, Gernhardt; Straughn, Amber N.
2013-01-01
Slitless grism spectroscopy from space offers dramatic advantages for studying high redshift galaxies: high spatial resolution to match the compact sizes of the targets, a dark and uniform sky background, and simultaneous observation over fields ranging from five square arcminutes (HST) to over 1000 square arcminutes (Euclid). Here we present observations of a galaxy at z = 6.57 the end of the reioinization epoch identified using slitless HST grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically) and reconfirmed with Keck + DEIMOS. This high redshift identification is enabled by the depth of the PEARS survey. Substantially higher redshifts are precluded for PEARS data by the declining sensitivity of the ACS grism at greater than lambda 0.95 micrometers. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms.
Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch.
Inoue, Akio K; Tamura, Yoichi; Matsuo, Hiroshi; Mawatari, Ken; Shimizu, Ikkoh; Shibuya, Takatoshi; Ota, Kazuaki; Yoshida, Naoki; Zackrisson, Erik; Kashikawa, Nobunari; Kohno, Kotaro; Umehata, Hideki; Hatsukade, Bunyo; Iye, Masanori; Matsuda, Yuichi; Okamoto, Takashi; Yamaguchi, Yuki
2016-06-24
The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium.
Persistent warmth across the Benguela upwelling system during the Pliocene epoch
NASA Astrophysics Data System (ADS)
Rosell-Melé, Antoni; Martínez-Garcia, Alfredo; McClymont, Erin L.
2014-01-01
A feature of Pliocene climate is the occurrence of “permanent El Niño-like” or “El Padre” conditions in the Pacific Ocean. From the analysis of sediment cores in the modern northern Benguela upwelling, we show that the mean oceanographic state off Southwest Africa during the warm Pliocene epoch was also analogous to that of a persistent Benguela “El Niño”. At present these events occur when massive southward flows of warm and nutrient-poor waters extend along the coasts of Angola and Namibia, with dramatic effects on regional marine ecosystems and rainfall. We propose that the persistent warmth across the Pliocene in the Benguela upwelling ended synchronously with the narrowing of the Indonesian seaway, and the early intensification of the Northern Hemisphere Glaciations around 3.0-3.5 Ma. The emergence of obliquity-related cycles in the Benguela sea surface temperatures (SST) after 3 Ma highlights the development of strengthened links to high latitude orbital forcing. The subsequent evolution of the Benguela upwelling system was characterized by the progressive intensification of the meridional SST gradients, and the emergence of the 100 ky cycle, until the modern mean conditions were set at the end of the Mid Pleistocene transition, around 0.6 Ma. These findings support the notion that the interplay of changes in the depth of the global thermocline, atmospheric circulation and tectonics preconditioned the climate system for the end of the warm Pliocene epoch and the subsequent intensification of the ice ages.
A Flux Scale for Southern Hemisphere 21 cm Epoch of Reionization Experiments
NASA Astrophysics Data System (ADS)
Jacobs, Daniel C.; Parsons, Aaron R.; Aguirre, James E.; Ali, Zaki; Bowman, Judd; Bradley, Richard F.; Carilli, Chris L.; DeBoer, David R.; Dexter, Matthew R.; Gugliucci, Nicole E.; Klima, Pat; MacMahon, Dave H. E.; Manley, Jason R.; Moore, David F.; Pober, Jonathan C.; Stefan, Irina I.; Walbrugh, William P.
2013-10-01
We present a catalog of spectral measurements covering a 100-200 MHz band for 32 sources, derived from observations with a 64 antenna deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. For transit telescopes such as PAPER, calibration of the primary beam is a difficult endeavor and errors in this calibration are a major source of error in the determination of source spectra. In order to decrease our reliance on an accurate beam calibration, we focus on calibrating sources in a narrow declination range from -46° to -40°. Since sources at similar declinations follow nearly identical paths through the primary beam, this restriction greatly reduces errors associated with beam calibration, yielding a dramatic improvement in the accuracy of derived source spectra. Extrapolating from higher frequency catalogs, we derive the flux scale using a Monte Carlo fit across multiple sources that includes uncertainty from both catalog and measurement errors. Fitting spectral models to catalog data and these new PAPER measurements, we derive new flux models for Pictor A and 31 other sources at nearby declinations; 90% are found to confirm and refine a power-law model for flux density. Of particular importance is the new Pictor A flux model, which is accurate to 1.4% and shows that between 100 MHz and 2 GHz, in contrast with previous models, the spectrum of Pictor A is consistent with a single power law given by a flux at 150 MHz of 382 ± 5.4 Jy and a spectral index of -0.76 ± 0.01. This accuracy represents an order of magnitude improvement over previous measurements in this band and is limited by the uncertainty in the catalog measurements used to estimate the absolute flux scale. The simplicity and improved accuracy of Pictor A's spectrum make it an excellent calibrator in a band important for experiments seeking to measure 21 cm emission from the epoch of reionization.
Tracing the Reionization Epoch with ALMA: [C II] Emission in z ˜ 7 Galaxies
NASA Astrophysics Data System (ADS)
Pentericci, L.; Carniani, S.; Castellano, M.; Fontana, A.; Maiolino, R.; Guaita, L.; Vanzella, E.; Grazian, A.; Santini, P.; Yan, H.; Cristiani, S.; Conselice, C.; Giavalisco, M.; Hathi, N.; Koekemoer, A.
2016-09-01
We present new results on [C ii]158 μ {{m}} emission from four galaxies in the reionization epoch. These galaxies were previously confirmed to be at redshifts between 6.6 and 7.15 from the presence of the Lyα emission line in their spectra. The Lyα emission line is redshifted by 100-200 km s-1 compared to the systemic redshift given by the [C ii] line. These velocity offsets are smaller than what is observed in z˜ 3 Lyman break galaxies (LBGs) with similar UV luminosities and emission line properties. Smaller velocity shifts reduce the visibility of Lyα and hence somewhat alleviate the need for a very neutral intergalactic medium at z˜ 7 to explain the drop in the fraction of Lyα emitters observed at this epoch. The galaxies show [C ii] emission with L[C ii] = 0.6 - 1.6× {10}8{L}⊙ : these luminosities place them consistently below the star formation rate (SFR)-L[C ii] relation observed for low-redshift star-forming and metal-poor galaxies and also below z = 5.5 LBGs with similar SFRs. We argue that previous undetections of [C ii] in z˜ 7 galaxies with similar or smaller SFRs are due to selection effects: previous targets were mostly strong Lyα emitters and therefore probably metal-poor systems, while our galaxies are more representative of the general high-redshift star-forming population.
NASA Astrophysics Data System (ADS)
Katus, Roxanne M.; Liemohn, Michael W.; Gallagher, Dennis L.; Ridley, Aaron; Zou, Shasha
2013-01-01