Dielectric and permeability effects in collisionless plasmas. [in collisionless plasmas
NASA Technical Reports Server (NTRS)
Cole, K. D.
1984-01-01
Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular + B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in geophysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j-asterisk), which includes the well-known polarization current, given by J-asterisk = d/dt (E x M) + (P x B) x B B(-2) where M and P are the magnetization and polarization vectors respectively.
Modeling combined collisional/collisionless plasma interpenetration
Thomas, V.A.
1997-04-01
This paper describes one technique by which multifluid modeling capability can be achieved within the context of a Lagrangean single-fluid model. This technique is applied to the interpenetration of laser-produced, substantially collisionless plasmas. A single-fluid model by itself cannot simulate the interpenetration of a collisionless plasma correctly, but must be augmented with some other tool. One tool that can calculate collisionless plasma interpenetration correctly is ISIS, a particle code for plasma simulations which includes appropriate collision models. However, ISIS does not have the necessary physics to do the laser deposition, the atomic physics, the radiation transport, and does not possess a realistic electron temperature model. With appropriate integration of the single-fluid code and ISIS, a new capability is achieved which allows simulation of the colliding plasma problem, a problem that neither code can properly simulate individually.
Is collisionless heating in capacitively coupled plasmas really collisionless?
NASA Astrophysics Data System (ADS)
Lafleur, T.; Chabert, P.
2015-08-01
By performing a combination of test-particle and particle-in-cell simulations, we investigate electron heating in single frequency capacitively coupled plasmas (CCPs). In agreement with previous theoretical considerations highlighted in Kaganovich et al (1996 Appl. Phys. Lett. 69 3818), we show that the level of true collisionless/stochastic heating in typical CCPs is significantly smaller than that due to collisional interactions; even at very low pressures and wide gap lengths. Fundamentally electron heating is a collisional phenomenon whereby particle collisions provide the vital phase randomization and stochastization mechanism needed to generate both a local (or ohmic) heating component, and a non-local (or hybrid) heating component.
Magnetic reconnection in collisionless plasmas - Prescribed fields
NASA Technical Reports Server (NTRS)
Burkhart, G. R.; Drake, J. F.; Chen, J.
1990-01-01
The structure of the dissipation region during magnetic reconnection in collisionless plasma is investigated by examining a prescribed two-dimensional magnetic x line configuration with an imposed inductive electric field E(y). The calculations represent an extension of recent MHD simulations of steady state reconnection (Biskamp, 1986; Lee and Fu, 1986) to the collisionless kinetic regime. It is shown that the structure of the x line reconnection configuration depends on only two parameters: a normalized inductive field and a parameter R which represents the opening angle of the magnetic x lines.
Thin-shell instability in collisionless plasma.
Dieckmann, M E; Ahmed, H; Doria, D; Sarri, G; Walder, R; Folini, D; Bret, A; Ynnerman, A; Borghesi, M
2015-09-01
Thin-shell instability is one process which can generate entangled structures in astrophysical plasma on collisional (fluid) scales. It is driven by a spatially varying imbalance between the ram pressure of the inflowing upstream plasma and the downstream's thermal pressure at a nonplanar shock. Here we show by means of a particle-in-cell simulation that an analog process can destabilize a thin shell formed by two interpenetrating, unmagnetized, and collisionless plasma clouds. The amplitude of the shell's spatial modulation grows and saturates after about ten inverse proton plasma frequencies, when the shell consists of connected piecewise linear patches.
Scattering of radiation in collisionless dusty plasmas
Tolias, P.; Ratynskaia, S.
2013-04-15
Scattering of electromagnetic waves in collisionless dusty plasmas is studied in the framework of a multi-component kinetic model. The investigation focuses on the spectral distribution of the scattered radiation. Pronounced dust signatures are identified in the coherent spectrum due to scattering from the shielding cloud around the dust grains, dust acoustic waves, and dust-ion acoustic waves. The magnitude and shape of the scattered signal near these spectral regions are determined with the aid of analytical expressions and its dependence on the dust parameters is investigated. The use of radiation scattering as a potential diagnostic tool for dust detection is discussed.
Collisionless Relaxation in Non-Neutral Plasmas
Levin, Yan; Pakter, Renato; Teles, Tarcisio N.
2008-02-01
A theoretical framework is presented which allows us to quantitatively predict the final stationary state achieved by a non-neutral plasma during a process of collisionless relaxation. As a specific application, the theory is used to study relaxation of charged-particle beams. It is shown that a fully matched beam relaxes to the Lynden-Bell distribution. However, when a mismatch is present and the beam oscillates, parametric resonances lead to a core-halo phase separation. The approach developed accounts for both the density and the velocity distributions in the final stationary state.
Nonlinear Gyroviscous Force in a Collisionless Plasma
Belova, E.V.
2001-05-23
Nonlinear gyroviscous forces in a collisionless plasma with temperature variations are calculated from the gyrofluid moments of the gyrokinetic Vlasov equation. The low-frequency gyrokinetic ordering and electrostatic perturbations are assumed, and an additional finite Larmor radius (FLR) expansion is performed. This approach leads naturally to an expression for the gyroviscous force in terms of the gyrocenter distribution function, thus including all resonant effects, and represents a systematic FLR expansion in a general form (no assumption of any closure is made). The expression for the gyroviscous force is also calculated in terms of the particle-fluid moments by making the transformation from the gyrocenter to particle coordinates. The calculated expression represents a modification of the Braginskii gyroviscosity for a collisionless plasma with nonuniform temperature. It is compared with previous calculations based on the traditional fluid approach. As a byproduct of the gyroviscosity calculations, we derive a set of nonlinear reduced gyrofluid (and a corresponding set of particle-fluid) moment equations with FLR corrections, which exhibit a generalized form of the ''gyroviscous cancellation.''
Weak collisionless shocks in laser-plasmas
NASA Astrophysics Data System (ADS)
Cairns, R. A.; Bingham, R.; Trines, R. G. M.; Norreys, P.
2015-04-01
We obtain a theory describing laminar shock-like structures in a collisionless plasma and examine the parameter limits, in terms of the ion sound Mach number and the electron/ion temperature ratio, within which these structures exist. The essential feature is the inclusion of finite ion temperature with the result that some ions are reflected from a potential ramp. This destroys the symmetry between upstream and downstream regions that would otherwise give the well-known ion solitary wave solution. We have shown earlier (Cairns et al 2014 Phys. Plasmas 21 022112) that such structures may be relevant to problems such as the existence of strong, localized electric fields observed in laser compressed pellets and laser acceleration of ions. Here we present results on the way in which these structures may produce species separation in fusion targets and suggest that it may be possible to use shock ion acceleration for fast ignition.
Turbulent dynamo in a collisionless plasma.
Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco
2016-04-12
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981
Turbulent dynamo in a collisionless plasma
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-01-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981
Turbulent dynamo in a collisionless plasma
NASA Astrophysics Data System (ADS)
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-04-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
Turbulent dynamo in a collisionless plasma.
Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco
2016-04-12
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
Kinetic model for the collisionless sheath of a collisional plasma
NASA Astrophysics Data System (ADS)
Tang, Xian-Zhu; Guo, Zehua
2016-08-01
Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.
Global Scale-Invariant Dissipation in Collisionless Plasma Turbulence
Kiyani, K. H.; Chapman, S. C.; Khotyaintsev, Yu. V.; Dunlop, M. W.; Sahraoui, F.
2009-08-14
A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.
How to Patch Active Plasma and Collisionless Sheath: Practical Guide
Kaganovich, Igor D.
2002-08-22
Most plasmas have a very thin sheath compared with the plasma dimension. This necessitates separate calculations of the plasma and sheath. The Bohm criterion provides the boundary condition for calculation of plasma profiles. To calculate sheath properties, a value of electric field at the plasma-sheath interface has to be specified in addition to the Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy are reported.
Shearing Box Simulations of the MRI in a Collisionless Plasma
Sharma, Prateek; Hammett, Gregory, W.; Quataert, Eliot; Stone, James, M.
2005-08-31
We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Galactic Center. The MHD version of ZEUS is modified to evolve an anisotropic pressure tensor. A fluid closure approximation is used to calculate heat conduction along magnetic field lines. The anisotropic pressure tensor provides a qualitatively new mechanism for transporting angular momentum in accretion flows (in addition to the Maxwell and Reynolds stresses). We estimate limits on the pressure anisotropy due to pitch angle scattering by kinetic instabilities. Such instabilities provide an effective ''collision'' rate in a collisionless plasma and lead to more MHD-like dynamics. We find that the MRI leads to efficient growth of the magnetic field in a collisionless plasma, with saturation amplitudes comparable to those in MHD. In the saturated state, the anisotropic stress is comparable to the Maxwell stress, implying that the rate of angular momentum transport may be moderately enhanced in a collisionless plasma.
Coupled electron and ion nonlinear oscillations in a collisionless plasma
Karimov, A. R.
2013-05-15
Dynamics of coupled electrostatic electron and ion nonlinear oscillations in a collisionless plasma is studied with reference to a kinetic description. Proceeding from the exact solution of Vlasov-Maxwell equations written as a function of linear functions in the electron and ion velocities, we arrive at the two coupled nonlinear equations which describe the evolution of the system.
Sheath structure in plasma with two species of positive ions and secondary electrons
NASA Astrophysics Data System (ADS)
Xiao-Yun, Zhao; Nong, Xiang; Jing, Ou; De-Hui, Li; Bin-Bin, Lin
2016-02-01
The properties of a collisionless plasma sheath are investigated by using a fluid model in which two species of positive ions and secondary electrons are taken into account. It is shown that the positive ion speeds at the sheath edge increase with secondary electron emission (SEE) coefficient, and the sheath structure is affected by the interplay between the two species of positive ions and secondary electrons. The critical SEE coefficients and the sheath widths depend strongly on the positive ion charge number, mass and concentration in the cases with and without SEE. In addition, ion kinetic energy flux to the wall and the impact of positive ion species on secondary electron density at the sheath edge are also discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11475220 and 11405208), the Program of Fusion Reactor Physics and Digital Tokamak with the CAS “One-Three-Five” Strategic Planning, the National ITER Program of China (Grant No. 2015GB101003), and the Higher Education Natural Science Research Project of Anhui Province, China (Grant No. 2015KJ009).
Collisionless Reconnection in an Electron-Positron Plasma
Bessho, N.; Bhattacharjee, A.
2005-12-09
Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity.
Multiple eigenmodes of geodesic acoustic mode in collisionless plasmas
Gao Zhe; Itoh, K.; Sanuki, H.; Dong, J. Q.
2006-10-15
We report a series of eigenmodes of the geodesic acoustic mode (GAM), which includes the standard GAM, a branch of low-frequency mode, and a series of ion sound wave-like modes. The case of T{sub i}>>T{sub e} is investigated, and eigenfrequencies of these modes are obtained analytically from a linear gyrokinetic model in collisionless plasmas with a rigid constant electrostatic potential around a magnetic surface.
MHD instabilities of collisionless space plasma with heat fluxes
NASA Astrophysics Data System (ADS)
Kuznetsov, V. D.; Dzhalilov, N. S.
2014-12-01
Properties of instabilities in a collisionless plasma are considered based on 16-moment MHD equations with allowance for differences between the heat fluxes along the magnetic field due to longitudinal and transverse thermal ion motions. It is shown that the increments and thresholds appreciably depend on these two heat fluxes for all compressible instabilities arising in the MHD approach (second compressible fire-hose, mirror, and thermal instabilities).
Intercomponent momentum transport and electrical conductivity of collisionless plasma
NASA Technical Reports Server (NTRS)
Wilhelm, H. E.
1973-01-01
Based on the Lenard-Balescu equation, the interaction integral for the intercomponent momentum transfer in a two-component, collisionless plasma is evaluated in closed form. The distribution functions of the electrons and ions are represented in the form of nonisothermal, displaced Maxwellians corresponding to the 5-moment approximation. As an application, the transport of electrical current in an electric field is discussed for infrasonic up to sonic electron-ion drift velocities.
Generation of collisionless shock in laser-produced plasmas
NASA Astrophysics Data System (ADS)
Fiuza, Frederico
2015-08-01
Collisionless shocks are ubiquitous in astrophysical environments and are tightly connected with magnetic-field amplification and particle acceleration. The fast progress in high-power laser technology is bringing the study of high Mach number shocks into the realm of laboratory plasmas, where in situ measurements can be made helping us understand the fundamental kinetic processes behind shocks. I will discuss the recent progress in laser-driven shock experiments at state-of-the-art facilities like NIF and Omega and how these results, together with ab initio massively parallel simulations, can impact our understanding of magnetic field amplification and particle acceleration in astrophysical plasmas.
Magneto-Hydro-Dynamic Waves In The Collisionless Space Plasma
NASA Astrophysics Data System (ADS)
Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J.
2007-12-01
The instability of magneto-hydro-dynamic (MHD) waves in an anisotropic, collisionless, rarefied hot plasma is studied. Anisotropy properties of such a plasma are caused by a strong magnetic field, when the thermal gas pressures across and along the field become unequal. Moreover, there appears an anisotropy of the thermal fluxes. The study of the anisotropy features of the plasma are motivated by observed solar coronal data. The 16 moments equations derived from the Boltzmann-Vlasov kinetic equation are used. These equations strongly differ from the usual isotropic MHD case. For linear disturbances the wave equations in homogenous anisotropic plasma are deduced. The general dispersion relation for the incompressible wave modes is derived, solved and analyzed. It is shown that a wide wave spectrum with stable and unstable behavior is possible, in contrast to the usual isotropic MHD case. The dependence of the instability on magnetic field, pressure anisotropy, and heat fluxes is investigated. The general instability condition is obtained. The results can be applied to the theory of solar and stellar coronal heating, to wind models and in other modeling, where the collisionless approximation is valid.
A mean field Ohm's law for collisionless plasmas
Biglari, H. ); Diamond, P.H. )
1993-11-01
A mean field Ohm's law valid for collisionless plasmas is derived kinetically. It is shown that contrary to conventional thinking, the resulting hyperresistivity is significantly smaller than its fluid counterpart due to the fact that the turbulent decorrelation rate is linked to the rapid electron ballistic motion rather than the slower nonlinear mixing time. Moreover, the off-diagonal contributions to the parallel electron momentum flux are shown to result in Ohm's law renormalizations that dwarf the current diffusivity and break radial parity symmetry.
Plasma waves downstream of weak collisionless shocks
NASA Technical Reports Server (NTRS)
Coroniti, F. V.; Greenstadt, E. W.; Moses, S. L.; Smith, E. J.; Tsurutani, B. T.
1993-01-01
In September 1983 the International Sun Earth Explorer 3 (ISEE 3) International Cometary Explorer (ICE) spacecraft made a long traversal of the distant dawnside flank region of the Earth's magnetosphere and had many encounters with the low Mach number bow shock. These weak shocks excite plasma wave electric field turbulence with amplitudes comparable to those detected in the much stronger bow shock near the nose region. Downstream of quasi-perpendicular (quasi-parallel) shocks, the E field spectra exhibit a strong peak (plateau) at midfrequencies (1 - 3 kHz); the plateau shape is produced by a low-frequency (100 - 300 Hz) emission which is more intense behind downstream of two quasi-perpendicular shocks show that the low frequency signals are polarized parallel to the magnetic field, whereas the midfrequency emissions are unpolarized or only weakly polarized. A new high frequency (10 - 30 kHz) emission which is above the maximum Doppler shift exhibit a distinct peak at high frequencies; this peak is often blurred by the large amplitude fluctuations of the midfrequency waves. The high-frequency component is strongly polarized along the magnetic field and varies independently of the lower-frequency waves.
Perpendicular diffusion of energetic particles in collisionless plasmas
Shalchi, A.
2015-01-15
A fundamental problem in plasma and astrophysics is the interaction between energetic particles and magnetized plasmas. In the current paper, we focus on particle diffusion across the guide magnetic field. It is shown that the perpendicular diffusion coefficient depends only on the parallel diffusion coefficient and the Kubo number. Therefore, one can find four asymptotic limits depending on the values of these two parameters. These regimes are the quasilinear limit, the Kadomtsev and Pogutse limit, the scaling of Rechester and Rosenbluth, and the scaling found by Zybin and Istomin. In the current article, we focus on the Rechester and Rosenbluth scenario because this was not discovered before in the context of collisionless plasmas. Examples and applications are discussed as well. We show that an energy independent ratio of perpendicular and parallel diffusion coefficients can be found and that this ratio can be very small but also close to unity. This is exactly what one observes in the solar wind.
Hybrid numerical model of shock waves in collisionless plasma
NASA Astrophysics Data System (ADS)
Vshivkova, L.; Dudnikova, G.; Vshivkov, K.
2016-10-01
We present a 2D hybrid numerical plasma model of generation and structure of collisionless shock waves in plasma and ion acceleration on their front considering physical processes in supernova remnant shock precursor. In modeling a shock wave is generated by sending a supersonic flow against a reflecting wall. The consequent interaction between incoming and reflected plasma flows lead to formation of waves, the structure of which depends on a flow velocity. The hybrid approach reduces the computational expenses relative to a fully kinetic one, and on the other hand, permits to model ions with a greater accuracy than the magnetohydrodynamics (MHD) allows. Also, another important advantage of the hybrid approach is the possibility to study the important instabilities on an ion time scale, neglecting the modes associated with electrons. In the current work a new computational scheme where stability condition allows carry out computations on more wide set of computational and physical parameters is presented.
Perpendicular diffusion of energetic particles in collisionless plasmas
NASA Astrophysics Data System (ADS)
Shalchi, A.
2015-01-01
A fundamental problem in plasma and astrophysics is the interaction between energetic particles and magnetized plasmas. In the current paper, we focus on particle diffusion across the guide magnetic field. It is shown that the perpendicular diffusion coefficient depends only on the parallel diffusion coefficient and the Kubo number. Therefore, one can find four asymptotic limits depending on the values of these two parameters. These regimes are the quasilinear limit, the Kadomtsev and Pogutse limit, the scaling of Rechester and Rosenbluth, and the scaling found by Zybin and Istomin. In the current article, we focus on the Rechester and Rosenbluth scenario because this was not discovered before in the context of collisionless plasmas. Examples and applications are discussed as well. We show that an energy independent ratio of perpendicular and parallel diffusion coefficients can be found and that this ratio can be very small but also close to unity. This is exactly what one observes in the solar wind.
Simplex-in-cell technique for collisionless plasma simulations
NASA Astrophysics Data System (ADS)
Kates-Harbeck, Julian; Totorica, Samuel; Zrake, Jonathan; Abel, Tom
2016-01-01
We extend the simplex-in-cell (SIC) technique recently introduced in the context of collisionless dark matter fluids [1,2] to the case of collisionless plasmas. The six-dimensional phase space distribution function f (x , v) is represented by an ensemble of three-dimensional manifolds, which we refer to as sheets. The electric potential field is obtained by solving the Poisson equation on a uniform mesh, where the charge density is evaluated by a spatial projection of the phase space sheets. The SIC representation of phase space density facilitates robust, high accuracy numerical evolution of the Vlasov-Poisson system using significantly fewer tracer particles than comparable particle-in-cell (PIC) approaches by reducing the numerical shot-noise associated with the latter. We introduce the SIC formulation and describe its implementation in a new code, which we validate using standard test problems including plasma oscillations, Landau damping, and two stream instabilities in one dimension. Merits of the new scheme are shown to include higher accuracy and faster convergence rates in the number of particles. We finally motivate and outline the efficient application of SIC to higher dimensional problems.
Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas
NASA Technical Reports Server (NTRS)
Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael
2015-01-01
Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.
Collisionless Plasma Modeling in an Arbitrary Potential Energy Distribution
NASA Technical Reports Server (NTRS)
Liemohn, M. W.; Khazanov, G. V.
1997-01-01
A new technique for calculating a collisionless plasma along a field line is presented. The primary feature of the new model is that it can handle an arbitrary (including nonmonotonic) potential energy distribution. This was one of the limiting constraints on the existing models in this class, and these constraints are generalized for an arbitrary potential energy composition. The formulation for relating current density to the field-aligned potential as well as formulas for density, temperature and energy flux calculations are presented for several distribution functions, ranging from a bi-Lorentzian with a loss cone to an isotropic Maxwellian. A comparison of these results with previous models shows that the formulation reduces.to the earlier models under similar assumptions.
Firehose, Mirror, and Magnetorotational Instabilities in a Collisionless Shearing Plasma
NASA Astrophysics Data System (ADS)
Kunz, Matthew; Schekochihin, Alexander; Stone, James; Melville, Scott; Quataert, Eliot
2015-11-01
Describing the large-scale behavior of weakly collisional magnetized plasmas, such as the solar wind, black-hole accretion flows, or the intracluster medium of galaxy clusters, necessitates a detailed understanding of the kinetic-scale physics governing the dynamics of magnetic fields and the transport of momentum and heat. This physics is complicated by the fact that such plasmas are expected to exhibit particle distribution functions with unequal thermal pressures in the directions parallel and perpendicular to the local magnetic field. This pressure anisotropy can trigger fast Larmor-scale instabilities - namely, firehose and mirror - which solar-wind observations suggest to be effective at regulating the pressure anisotropy to marginally stable levels. Results from weakly nonlinear theory and hybrid-kinetic particle-in-cell simulations that address how marginal stability is achieved and maintained in a plasma whose pressure anisotropy is driven by a shearing magnetic field are presented. Fluctuation spectra and effective collisionality are highlighted. These results are placed in the context of our ongoing studies of magnetorotational turbulence in collisionless astrophysical accretion disks, in which microscale plasma instabilities regulate angular-momentum transport.
Collision-less Coupling between Explosive Debris Plasma and Magnetized Ambient Plasma
NASA Astrophysics Data System (ADS)
Bondarenko, Anton Sergeivich
The explosive expansion of a dense debris plasma cloud into relatively tenuous, magnetized, ambient plasma characterizes a wide variety of astrophysical and space environments, including supernova remnants, interplanetary coronal mass ejections, and ionospheric explosions. In these and other related phenomena, collision-less electro-magnetic processes rather than Coulomb collisions typically mediate the transfer of momentum and energy from the debris plasma to the ambient plasma. In an effort to better understand the detailed physics of collision-less coupling mechanisms, compliment in situ measurements, and provide validation of previous computational and theoretical work, the present research utilizes a unique experimental platform at the University of California, Los Angeles (UCLA) to study the interaction of explosive debris plasma with magnetized ambient plasma in a reproducible laboratory setting. Specifically, by jointly employing the Large Plasma Device (LAPD) and the Phoenix laser facility, the super-Alfvenic, quasi-perpendicular expansion of laser-produced carbon (C) and hydrogen (H) debris plasma through preformed, magnetized helium (He) ambient plasma is investigated via a variety of sophisticated diagnostics, including emission spectroscopy, wavelength-filtered imaging, a magnetic flux probe, and a Langmuir probe. The key result is the direct observation of collision-less coupling via large Doppler shifts in a He II ion spectral line, which indicate that the ambient ions accelerate in response to the explosive debris plasma. Specifically, the He II ions accelerate along a trajectory that qualitatively corresponds to the large-scale laminar electric field generated by the debris expansion. A custom computational approach is utilized to simulate the initial He II ion response to the explosive debris plasma, and a synthetic Doppler-shifted wavelength spectrum constructed from the simulated ion velocities excellently reproduces the experimental
On the quasi-linear diffusion in collisionless plasmas (to say nothing about Landau damping)
Hellinger, Petr; Travnicek, Pavel M.
2012-06-15
General quasi-linear diffusion coefficients for nonrelativistic collisionless plasmas are derived for unstable modes and analytically continued to damped modes. Properties of the resulting diffusion are investigated and discussed.
Enhanced thermal self-focusing of a Gaussian laser beam in a collisionless plasma
Gupta, Devki Nandan; Suk, Hyyong
2011-12-15
Theory given by Wang-Zhou [Phys. Plasmas 18, 043101 (2011)] for the thermal self-focusing of a Gaussian laser beam in a collisionless plasma is revisited by including the effect of a localized upward plasma-density ramp. As the equilibrium electron density is an increasing function of the distance of propagation of the laser beam, the diffraction length decreases rapidly as the beam penetrates deeper into the plasma and the diffraction effect becomes reduced; thus, the laser becomes more focused. A significant enhancement in laser thermal self-focusing in a collisionless plasma is consequently observed if a localized plasma density ramp is introduced.
NASA Technical Reports Server (NTRS)
Matsuda, Y.
1974-01-01
A low-noise plasma simulation model is developed and applied to a series of linear and nonlinear problems associated with electrostatic wave propagation in a one-dimensional, collisionless, Maxwellian plasma, in the absence of magnetic field. It is demonstrated that use of the hybrid simulation model allows economical studies to be carried out in both the linear and nonlinear regimes with better quantitative results, for comparable computing time, than can be obtained by conventional particle simulation models, or direct solution of the Vlasov equation. The characteristics of the hybrid simulation model itself are first investigated, and it is shown to be capable of verifying the theoretical linear dispersion relation at wave energy levels as low as .000001 of the plasma thermal energy. Having established the validity of the hybrid simulation model, it is then used to study the nonlinear dynamics of monochromatic wave, sideband instability due to trapped particles, and satellite growth.
Constraints on fluid modeling of magnetized collisionless plasmas
NASA Astrophysics Data System (ADS)
Sulem, Pierre-Louis; Passot, Thierry; Laveder, Dimitri; Hunana, Peter; Henri, Pierre
2013-04-01
It is well known that a complete description of the solar wind requires a kinetic description and that, particularly at sub-proton scales, kinetic effects cannot be ignored. It is nevertheless usually assumed that, at scales significantly larger than the proton gyroscale, MHD or bifluid models with isotropic pressures provide a satisfactory description. We demonstrate that in order to accurately capture, even at large scales, the low-frequency dynamics of a collisionless plasma, a fluid model should actually include kinetic effects such as Landau damping and finite Larmor radius corrections. Indeed, the usual polytropic bi-fluid models strongly overestimate the magnetic compressibility of oblique Alfvén waves. Retaining pressure anisotropy and Landau damping partially corrects this deficiency, but an accurate description of the Alfvén wave polarization and of the mirror instability growth rate actually requires to take into account the finite-Larmor corrections to all the retained moments. These remarks lead us to use the so-called FLR Landau fluid model (Phys. Plasmas, 19, 082113, 2012), for which a three-dimensional parallel code has been developed. Preliminary simulations in the turbulent regime will be presented, showing the reduction of the fluid compressibility and the inhibition of the parallel energy transfer. We will also report on the development of temperature anisotropy, associated with non-resonant perpendicular ion heating and constrained by the onset of the mirror instability.
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.
The role of microturbulence on collisionless reconnection. [in magnetospheric plasmas
NASA Technical Reports Server (NTRS)
Papadopoulos, K.
1980-01-01
The linear, non-linear and anomalous transport properties associated with various microinstabilities driven by cross field currents in reconnecting geometries are reviewed. An assessment of their role in collisionless tearing based on analytic theory, computer simulations and experimental evidence, supports the dominant role of lower hybrid waves. The relevance of microturbulence on macroscopic stationary and time dependent models of merging is presented. It is concluded that a fluid-numerical simulation approach that includes (at each space and time step) the effects of anomalous transport in a self consistent manner, similar to the one used for laboratory collisionless shocks, represents the best method for studying and modeling the details of the reconnection process.
Some Basic Concepts of Wave-Particle Interactions in Collisionless Plasmas
NASA Technical Reports Server (NTRS)
Lakhina, Gurbax S.; Tsurutani, Bruce T.
1997-01-01
The physical concepts of wave-particle interactions in a collisionless plasma are developed from first principles. Using the Lorentz force, starting with the concepts of gyromotion, particle mirroring and the loss-cone, normal and anomalous cyclotron resonant interactions, pitch-angle scattering, and cross-field diffusion are developed.
Scaling laws for collisionless laser-plasma interactions of relevance for laboratory astrophysics
Ryutov, D D; Rermington, B A
2006-04-04
Scaling laws for interaction of ultra-intense laser beams with a collisionless plasmas are discussed. Special attention is paid to the problem of the collective ion acceleration. Symmetry arguments in application to the generation of the poloidal magnetic field are presented. A heuristic model for evaluating the magnetic field strength is proposed.
Reconnection properties in collisionless plasma with open boundary conditions
Sun, H. E.; Ma, Z. W.; Huang, J.
2014-07-15
Collisionless magnetic reconnection in a Harris current sheet with different initial thicknesses is investigated using a 21/2 -D Darwin particle-in-cell simulation with the magnetosonic open boundary condition. It is found that the thicknesses of the ion dissipation region and the reconnection current sheet, when the reconnection rate E{sub r} reaches its first peak, are independent of the initial thickness of the current sheet; while the peak reconnection rate depends on it. The peak reconnection rate increases with decrease of the current sheet thickness as E{sub r}∼a{sup −1/2}, where a is the initial current sheet half-thickness.
The expansion of a collisionless plasma into a plasma of lower density
Perego, M.; Gunzburger, M. D.; Howell, P. D.; Ockendon, J. R.; Allen, J. E.
2013-05-15
This paper considers the asymptotic and numerical solution of a simple model for the expansion of a collisionless plasma into a plasma of lower density. The dependence on the density ratio of qualitative and quantitative features of solutions of the well-known cold-ion model is explored. In the cold-ion limit, we find that a singularity develops in the ion density in finite time unless the density ratio is zero or close to unity. The classical cold-ion model may cease to be valid when such a singularity occurs and we then regularize the model by the finite ion-temperature Vlasov-Poisson system. Numerical evidence suggests the emergence of a multi-modal velocity distribution.
Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Myers, Clayton E.
2012-12-10
The ion dynamics in a collisionless magnetic reconnection layer are studied in a laboratory plasma. The measured in-plane plasma potential profile, which is established by electrons accelerated around the electron diffusion region, shows a saddle-shaped structure that is wider and deeper towards the outflow direction. This potential structure ballistically accelerates ions near the separatrices toward the outflow direction. Ions are heated as they travel into the high pressure downstream region.
Collisionless damping of geodesic acoustic mode in plasma with nonextensive distribution
Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing
2014-06-15
Geodesic acoustic mode (GAM) in collisionless toroidal plasmas with a constant electrostatic potential around a magnetic surface is investigated based on the linear gyrokinetic theory in context of nonextensive statistics mechanics. The damping rate of GAM is shown to be dependent on the nonextensive parameters of ions, and in the extensive limit, the result in Maxwellian distribution plasma is recovered. The damping rate is found to be enhanced as the nonextensive parameter of ion decreases.
Numerical study of an electrostatic plasma sheath containing two species of charged dust particles
Foroutan, G.; Akhoundi, A.
2012-10-01
A multi-fluid model is used to study the dynamics of a dusty plasma sheath consists of electrons, ions, and two species of charged dust particles, i.e., nano-size and micron-size particles. It is found that, when the sheath is dominated by the nano-size dust grains, spatially periodic fluctuations are developed in the profiles of the sheath potential, and the number density and velocity of the plasma and dust particles. Due to inertial effects, the fluctuations in the parameters of the micron-size grains are much lower than those of the other parameters. The competition between the electric and ion drag forces plays the primary role in development of the fluctuations. The spatial period of the fluctuations is approximately a few Debye lengths and their amplitude depends on the plasma and dust parameters. The fluctuations are reduced by the increase in the radius, mass density, and Mach number of the nano-size particles, as well as the density and Mach number of the ions. But, they are enhanced by the increase in the plasma number density and the electron temperature. The sheath thickness demonstrates a non-monotonic behavior against variation of the nanoparticle parameters, i.e., it first decreases quickly, shows a minimum, and then increases. However, the sheath width always decreases with the plasma number density and ion Mach number, while grows linearly with the electron temperature.
Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma
Parashar, T. N.; Shay, M. A.; Cassak, P. A.; Matthaeus, W. H.
2009-03-15
The kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. At large length scales, the evolution of the hybrid simulations is very similar to MHD, with magnetic power spectra displaying scaling similar to a Kolmogorov scaling of -5/3. At small scales, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field. The magnetic energy spectrum of the hybrid simulation shows a break where linear theory predicts that the Hall term in Ohm's law becomes significant, leading to dispersive kinetic Alfven waves. A key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy of the type observed in the corona and solar wind.
Low-frequency instabilities of collisionless plasma and the 16-moment approximation
Dzhalilov, N. S. Kuznetsov, V. D.
2013-12-15
Using the 16-moment equations that take into account heat fluxes in anisotropic collisionless plasma, the properties of magnetohydrodynamic (MHD) instabilities are investigated. For all instabilities occurring in the MHD approach (the normal incompressible firehose instability, the second compressible almost longitudinal firehose instability, and the almost transverse mirror instability of slow magnetosonic modes, as well as thermal instability caused by the heat flux directed along the magnetic field), their kinetic analogs are considered. The kinetic dispersion relation in the low-frequency range in the vicinity of the ion thermal velocity is analyzed. The flow of plasma ions along the magnetic field is taken into account. The thresholds and instability growth rates obtained in the MHD and kinetic approaches are found to be in good agreement. This indicates that the 16-moment MHD equations adequately describe the dynamics of collisionless plasma.
Studying counterstreaming high velocity plasma flows relevant to astrophysical collisionless shock
NASA Astrophysics Data System (ADS)
Ross, James Steven; Amendt, Peter; Divol, Laurent; Pollock, Brad; Remington, Bruce; Ryutov, Dmitri; rozmus, Wojciech; Turnbull, David; Froula, Dustin; morita, taichi; Sakawa, Youichi; Takabe, Hideke; Drake, R. Paul; Kuranz, Carolyn C.; Gregori, Gianluca; Meinecke, Jena; Koenig, Michel; Spitkovsky, Anatoly; Park, Hye-Sook
2015-08-01
In a broad range of low-density astrophysical plasmas the flow has a high Mach number, making the ion-ion collisional mean free path very large compared to the scale lengths of various observed astrophysical shocks. These shocks are believed to be “collisionless,” driven by plasma instabilities and self-generated magnetic fields. A series of experiments at the NIF and Omega laser facilities is underway to study the formation of collisionless shocks under scaled laboratory conditions, using high velocity counterstreaming and interpenetrating plasma flows. Double CH2, and CH/CD planar foils have been irradiated with a laser intensity of ~1016 W/cm2. The laser-ablated plasma between the two foils was characterized using a suite of diagnostics, including Thomson scattering and x-ray radiography. On the Omega laser facility clear interpenetration and instability growth are observed, although our experimental conditions reached only ~50 ion skin depths (c/wpi) and were insufficient to fully form a collisionless shock. Initial NIF experimental results using 50x more laser energy than the Omega experiments will be presented.
An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta
Allanson, O. Neukirch, T. Wilson, F. Troscheit, S.
2015-10-15
We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely, the force-free Harris sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.
NASA Astrophysics Data System (ADS)
Kugland, N. L.; Ross, J. S.; Chang, P.-Y.; Drake, R. P.; Fiksel, G.; Froula, D. H.; Glenzer, S. H.; Gregori, G.; Grosskopf, M.; Huntington, C.; Koenig, M.; Kuramitsu, Y.; Kuranz, C.; Levy, M. C.; Liang, E.; Martinez, D.; Meinecke, J.; Miniati, F.; Morita, T.; Pelka, A.; Plechaty, C.; Presura, R.; Ravasio, A.; Remington, B. A.; Reville, B.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Park, H.-S.
2013-05-01
Collisionless shocks are often observed in fast-moving astrophysical plasmas, formed by non-classical viscosity that is believed to originate from collective electromagnetic fields driven by kinetic plasma instabilities. However, the development of small-scale plasma processes into large-scale structures, such as a collisionless shock, is not well understood. It is also unknown to what extent collisionless shocks contain macroscopic fields with a long coherence length. For these reasons, it is valuable to explore collisionless shock formation, including the growth and self-organization of fields, in laboratory plasmas. The experimental results presented here show at a glance with proton imaging how macroscopic fields can emerge from a system of supersonic counter-streaming plasmas produced at the OMEGA EP laser. Interpretation of these results, plans for additional measurements, and the difficulty of achieving truly collisionless conditions are discussed. Future experiments at the National Ignition Facility are expected to create fully formed collisionless shocks in plasmas with no pre-imposed magnetic field.
Collisionless electron heating in periodic arrays of inductively coupled plasmas
Czarnetzki, U.; Tarnev, Kh.
2014-12-15
A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.
Shaw, A. K.; Kar, S.; Goswami, K. S.
2012-10-15
The properties of a magnetized multi-component (two species of positive ions, negative ions and electrons) plasma sheath with finite positive ion temperature are studied. By using three fluid hydrodynamic model and some dimensionless variables, the ion (both lighter and heavier positive ions, and negative ions) densities, the ion (only for positive ions) velocities, and electric potential inside the sheath are investigated. In addition, the absence and presence of magnetic field and the orientation of magnetic field are considered. It is noticed that, with increase of positive ion temperature, the lighter positive ion density peaks increase only at the sheath edge and shift towards the sheath edge for both absence and presence of magnetic field. For heavier positive ions, in the absence of magnetic field, the density peaks increase at the sheath edge. But in the presence of magnetic field, the density fluctuations increase at the sheath edge. For both the cases, the density peaks shift towards the sheath edge.
Similarity Laws for Collisionless Interaction of Superstrong Electromagnetic Fields with a Plasma
Ryutov, D D; Remington, B A
2005-10-18
Several similarity laws for the collisionless interaction of ultra-intense electromagnetic fields with a plasma of an arbitrary initial shape is presented. Both ultra-relativistic and non-relativistic cases are covered. The ion motion is included. A brief discussion of possible ways of experimental verification of scaling laws is presented. The results can be of interest for experiments and numerical simulations in the areas of particle acceleration, harmonic generation, and Coulomb explosion of clusters.
R.A. Kolesnikov; J.A. Krommes
2004-10-21
The transition to collisionless ion-temperature-gradient-driven plasma turbulence is considered by applying dynamical systems theory to a model with ten degrees of freedom. Study of a four-dimensional center manifold predicts a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows and establishes the exact value of that shift in terms of physical parameters. For insight into fundamental physical mechanisms, the method provides a viable alternative to large simulations.
Collisionless expansion of pulsed radio frequency plasmas. II. Parameter study
NASA Astrophysics Data System (ADS)
Schröder, T.; Grulke, O.; Klinger, T.; Boswell, R. W.; Charles, C.
2016-01-01
The plasma parameter dependencies of the dynamics during the expansion of plasma are studied with the use of a versatile particle-in-cell simulation tailored to a plasma expansion experiment [Schröder et al., J. Phys. D: Appl. Phys. 47, 055207 (2014); Schröder et al., Phys. Plasmas 23, 013511 (2016)]. The plasma expansion into a low-density ambient plasma features a propagating ion front that is preceding a density plateau. It has been shown that the front formation is entangled with a wave-breaking mechanism, i.e., an ion collapse [Sack and Schamel, Plasma Phys. Controlled Fusion 27, 717 (1985); Sack and Schamel, Phys. Lett. A 110, 206 (1985)], and the launch of an ion burst [Schröder et al., Phys. Plasmas 23, 013511 (2016)]. The systematic parameter study presented in this paper focuses on the influence on this mechanism its effect on the maximum velocity of the ion front and burst. It is shown that, apart from the well known dependency of the front propagation on the ion sound velocity, it also depends sensitively on the density ratio between main and ambient plasma density. The maximum ion velocity depends further on the initial potential gradient, being mostly influenced by the plasma density ratio in the source and expansion regions. The results of the study are compared with independent numerical studies.
A Hamiltonian fluid-kinetic model for a two-species non-neutral plasma
Tassi, E.; Chandre, C.; Romé, M.
2014-04-15
A model for describing the dynamics of a pure electron plasma in the presence of a population of massive charged particles is presented. The model couples the fluid dynamics of the pure electron plasma with the dynamics of the massive particle population, the latter being treated kinetically. The model is shown to possess a noncanonical Hamiltonian structure and to preserve invariants analogous to those of the two-dimensional (2D) Euler equation for an incompressible inviscid fluid, and of the Vlasov equation. The Hamiltonian structure of the model is used to derive a set of stability conditions for rotating coherent structures of the two-species system, in the case of negatively charged massive particles. According to these conditions, stability is attained if both the equilibrium distribution function of the kinetic species and the equilibrium density of the electron fluid are monotonically decreasing functions of the corresponding single-particle energies in the rotating frame. For radially confined equilibria near the axis, the stability condition corresponds to the existence of a finite interval of rotation frequencies for the reference frame, with the upper bound determined by the presence of the kinetic population.
Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations
NASA Astrophysics Data System (ADS)
Klein, K. G.; Howes, G. G.
2016-08-01
An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.
Measuring Collisionless Damping in Heliospheric Plasmas using Field–Particle Correlations
NASA Astrophysics Data System (ADS)
Klein, K. G.; Howes, G. G.
2016-08-01
An innovative field–particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field–particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov–Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.
Collisionless damping of dust-acoustic waves in a charge varying dusty plasma with nonextensive ions
Amour, Rabia; Tribeche, Mouloud
2014-12-15
The charge variation induced nonlinear dust-acoustic wave damping in a charge varying dusty plasma with nonextensive ions is considered. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust acoustic wave propagation to be described by a damped Korteweg-de Vries (dK-dV) equation the coefficients of which depend sensitively on the nonextensive parameter q. The damping term, solely due to the dust charge variation, is affected by the ion nonextensivity. For the sake of completeness, the possible effects of nonextensivity and collisionless damping on weakly nonlinear wave packets described by the dK-dV equation are succinctly outlined by deriving a nonlinear Schrödinger-like equation with a complex nonlinear coefficient.
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.
TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal
Xu, X; Xiong, Z; Nevins, W; McKee, G
2007-05-31
The fully nonlinear 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of geodesic-acoustic mode (GAM) and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.
TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal
Xu, X Q; Xiong, Z; Nevins, W M; McKee, G R
2007-05-30
The fully nonlinear (full-f) 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of GAM and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.
The role of electron equation of state in heating partition of protons in a collisionless plasma
Parashar, Tulasi N.; Vasquez, Bernard J.; Markovskii, Sergei A.
2014-02-15
One of the outstanding questions related to the solar wind is the heating of solar wind plasma. Addressing this question requires a self consistent treatment of the kinetic physics of a collisionless plasma. A hybrid code (with particle ions and fluid electrons) is one of the most convenient computational tools, which allows us to explore self consistent ion kinetics, while saving us computational time as compared to the full particle in cell codes. A common assumption used in hybrid codes is that of isothermal electrons. In this paper, we discuss the role that the equation of state for electrons could potentially play in determining the ion kinetics.
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.
Evans, T E; Moyer, R A; Burrell, K H; Fenstermacher, M E; Joseph, I; Leonard, A W; Osborne, T H; Porter, G D; Schaffer, M J; Snyder, P B; Thomas, P R; Watkins, J G; West, W P
2006-06-13
A critical issue for fusion plasma research is the erosion of the first wall of the experimental device due to impulsive heating from repetitive edge magneto-hydrodynamic (MHD) instabilities known as 'edge-localized modes' (ELMs). Here, we show that the addition of small resonant magnetic field perturbations completely eliminates ELMs while maintaining a steady-state high-confinement (H-mode) plasma. These perturbations induce a chaotic behavior in the magnetic field lines, which reduces the edge pressure gradient below the ELM instability threshold. The pressure gradient reduction results from a reduction in particle content of the plasma, rather than an increase in the electron thermal transport. This is inconsistent with the predictions of stochastic electron heat transport theory. These results provide a first experimental test of stochastic transport theory in a highly rotating, hot, collisionless plasma and demonstrate a promising solution to the critical issue of controlling edge instabilities in fusion plasma devices.
Collisionless expansion of pulsed radio frequency plasmas. I. Front formation
NASA Astrophysics Data System (ADS)
Schröder, T.; Grulke, O.; Klinger, T.; Boswell, R. W.; Charles, C.
2016-01-01
The dynamics during plasma expansion are studied with the use of a versatile particle-in-cell simulation with a variable neutral gas density profile. The simulation is tailored to a radio frequency plasma expansion experiment [Schröder et al., J. Phys. D: Appl. Phys. 47(5), 055207 (2014)]. The experiment has shown the existence of a propagating ion front. The ion front features a strong electric field and features a sharp plasma potential drop similar to a double layer. However, the presented results of a first principle simulation show that, in general, the ion front does not have to be entangled with an electric field. The propagating electric field reflects the downstream ions, which stream with velocities up to twice as high as that of the ion front propagation. The observed ion density peak forms due to the accumulation of the reflected ions. The simulation shows that the ion front formation strongly depends on the initial ion density profile and is subject to a wave-breaking phenomenon. Virtual diagnostics in the code allow for a direct comparison with experimental results. Using this technique, the plateau forming in the wake of the plasma front could be indirectly verified in the expansion experiment. Although the simulation considers profiles only in one spatial dimensional, its results are qualitatively in a very good agreement with the laboratory experiment. It can successfully reproduce findings obtained by independent numerical models and simulations. This indicates that the effects of magnetic field structures and tangential inhomogeneities are not essential for the general expansion dynamic. The presented simulation will be used for a detailed parameter study dealt with in Paper II [Schröder et al., Phys. Plasma 23, 013512 (2016)] of this series.
Formation of collisional sheath in electronegative plasma with two species of positive ions
Moulick, R. Goswami, K. S.
2015-03-15
Sheath formation is investigated for electronegative plasma in presence of two species of positive ions in collisional environment. The gas under consideration is a mixture of oxygen and argon. Argon is the considered as having fixed volume and impact of collision is studied with increasing pressure of oxygen. Fluid equations are solved for three species namely, the two positive ions and a negative ion. Electrons are considered to follow Boltzmann distribution. Collision is modeled by constant mean free path model and has been used as a parameter. It has been found that collision enhances the sheath formation. The negative ion core is nearly unaffected by the presence of collision and is governed by the electric potential. The negative flux field is, however, affected by the presence of collision and shows a steady behavior in front of the wall. The two positive ions are heavily affected by the presence of collision and the modeling is such that their equilibrium densities can be estimated by solving simultaneous cubic equations.
NASA Astrophysics Data System (ADS)
Stawarz, Julia E.
Turbulence is a ubiquitous phenomenon that occurs throughout the universe, in both neutral fluids and plasmas. For collisionless plasmas, kinetic effects, which alter the nonlinear dynamics and result in small-scale dissipation, are still not well understood in the context of turbulence. This work uses direct numerical simulations (DNS) and observations of Earth's magnetosphere to study plasma turbulence. Long-time relaxation in magnetohydrodynamic (MHD) turbulence is examined using DNS with particular focus on the role of magnetic and cross helicity and symmetries of the initial configurations. When strong symmetries are absent or broken through perturbations, flows evolve towards states predicted by statistical mechanics with an energy minimization principle, which features two main regimes; one magnetic helicity dominated and one with quasi-equipartition of kinetic and magnetic energy. The role of the Hall effect, which contributes to the dynamics of collisionless plasmas, is also explored numerically. At scales below the ion inertial length, a transition to a magnetically dominated state, associated with advection becoming subdominant to dissipation, occurs. Real-space current, vorticity, and electric fields are examined. Strong current structures are associated with alignment between the current and magnetic field, which may be important in collisionless plasmas where field-aligned currents can be unstable. Turbulence within bursty bulk flow braking events, thought to be associated with near-Earth magnetotail reconnection, are then studied using the THEMIS spacecraft. It is proposed that strong field-aligned currents associated with turbulent intermittency destabilize into double layers, providing a collisionless dissipation mechanism for the turbulence. Plasma waves may also radiate from the region, removing energy from the turbulence and potentially depositing it in the aurora. Finally, evidence for turbulence in the Kelvin-Helmholtz instability (KHI) on the
Hassanein, A.; Konkashbaev, I.
1999-03-15
The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of a plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker-Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte-Carlo methods. The analytical solutions provide an insight to the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters.
Collisional relaxation of a strongly magnetized two-species pure ion plasma
Chim, Chi Yung; O’Neil, Thomas M.; Dubin, Daniel H.
2014-04-15
The collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ω{sub 1},Ω{sub 2}≫|Ω{sub 1}−Ω{sub 2}|≫v{sup ¯}{sub ij}/b{sup ¯} and v{sup ¯}{sub ⊥j}/Ω{sub j}≪b{sup ¯}, where Ω{sub 1} and Ω{sub 2} are two cyclotron frequencies, v{sup ¯}{sub ij}=√(T{sub ∥}/μ{sub ij}) is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b{sup ¯}=2e{sup 2}/T{sub ∥} is the classical distance of closest approach for such collisions, and v{sup ¯}{sub ⊥j}/Ω{sub j}=√(2T{sub ⊥j}/m{sub j})/Ω{sub j} is the characteristic cyclotron radius for particles of species j. Here, μ{sub ij} is the reduced mass for the two particles, and T{sub ∥} and T{sub ⊥j} are temperatures that characterize velocity components parallel and perpendicular to the magnetic field. For this ordering, the total cyclotron action for the two species, I{sub 1}=∑{sub i∈1}m{sub 1}v{sub ⊥i}{sup 2}/(2Ω{sub 1}) and I{sub 2}=∑{sub i∈2}m{sub 2}v{sub ⊥i}{sup 2}/(2Ω{sub 2}) are adiabatic invariants that constrain the collisional dynamics. On the timescale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions I{sub 1} and I{sub 2}, yielding a modified Gibbs distribution of the form exp[−H/T{sub ∥}−α{sub 1}I{sub 1}−α{sub 2}I{sub 2}]. Here, the α{sub j}’s are related to T{sub ∥} and T{sub ⊥j} through T{sub ⊥j}=(1/T{sub ∥}+α{sub j}/Ω{sub j}){sup −1}. Collisional relaxation to the usual Gibbs distribution, exp[−H/T{sub ∥}], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b{sup ¯2}Ω{sub 1}{sup 2}/v{sup ¯}{sub 11}{sup 2})exp(5[3π(b{sup ¯}|Ω{sub 1}−Ω{sub 2}|/v{sup ¯}{sub 12})]{sup 2/5}/6), the two
Sheath energy transmission in a collisional plasma with collisionless sheath
Tang, Xian-Zhu Guo, Zehua
2015-10-15
Sheath energy transmission governs the plasma energy exhaust onto a material surface. The ion channel is dominated by convection, but the electron channel has a significant thermal conduction component, which is dominated by the Knudsen layer effect in the presence of an absorbing wall. First-principle kinetic simulations reveal a robustly supersonic sheath entry flow. The ion sheath energy transmission and the sheath potential are accurately predicted by a sheath model of truncated bi-Maxwellian electron distribution. The electron energy transmission is further enhanced by a parallel heat flux of the perpendicular degrees of freedom.
NASA Astrophysics Data System (ADS)
Grosskopf, M. J.; Drake, R. P.; Kuranz, C. C.; Rutter, E. M.; Ross, J. S.; Kugland, N. L.; Plechaty, C.; Remington, B. A.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C. D.; Meinecke, J.; Reville, B.; Sakawa, Y.; Kuramitsu, Y.; Takabe, H.; Froula, D. H.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Liang, E.; Fu, W.; Woolsey, N.; Park, H.-S.
2013-03-01
Experiments investigating the physics of interpenetrating, collisionless, ablated plasma flows have become an important area of research in the high-energy-density field. In order to evaluate the feasibility of designing experiments that will generate a collisionless shock mediated by the Weibel instability on the National Ignition Facility (NIF) laser, computer simulations using the Center for Radiative Shock Hydrodynamics (CRASH) radiation-hydrodynamics model have been carried out. This paper reports assessment of whether the experiment can reach the required scale size while maintaining the low interflow collisionality necessary for the collisionless shock to form. Comparison of simulation results with data from Omega experiments shows the ability of the CRASH code to model these ablated systems. The combined results indicate that experiments on the NIF are capable of reaching the regimes necessary for the formation of a collisionless shock in a laboratory experiment.
Electric and magnetic contributions to spatial diffusion in collisionless plasmas
Smets, R.; Belmont, G.; Aunai, N.
2012-10-15
We investigate the role played by the different self-consistent fluctuations for particle diffusion in a magnetized plasma. We focus especially on the contribution of the electric fluctuations and how it combines with the (already investigated) magnetic fluctuations and with the velocity fluctuations. For that issue, we compute with a hybrid code the value of the diffusion coefficient perpendicular to the mean magnetic field and its dependence on the particle velocity. This study is restricted to small to intermediate level of electromagnetic fluctuations and focuses on particle velocities on the order of few times the Alfven speed. We briefly discuss the consequences for cosmic ray modulation and for the penetration of thermal solar wind particles in the Earth magnetosphere.
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2015-12-30
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron–positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power law ${\\gamma }^{-\\alpha }$, with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. As a result, for large L and σ, the power-law index α approaches about 1.2.
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2015-12-30
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron–positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power lawmore » $${\\gamma }^{-\\alpha }$$, with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. As a result, for large L and σ, the power-law index α approaches about 1.2.« less
Tempest Simulations of Collisionless Damping of the Geodesic-Acoustic Mode in Edge-Plasma Pedestals
Xu, X. Q.; Xiong, Z.; Nevins, W. M.; Gao, Z.; McKee, G. R.
2008-05-30
The fully nonlinear (full-f) four-dimensional TEMPEST gyrokinetic continuum code correctly produces the frequency and collisionless damping of geodesic-acoustic modes (GAMs) and zonal flow, with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon} scan and the tokamak safety factor q scan in homogeneous plasmas. TEMPEST simulations show that the GAMs exist in the edge pedestal for steep density and temperature gradients in the form of outgoing waves. The enhanced GAM damping may explain experimental beam emission spectroscopy measurements on the edge q scaling of the GAM amplitude.
Tempest Simulations of Collisionless Damping of the Geodesic-Acoustic Mode in Edge-Plasma Pedestals
NASA Astrophysics Data System (ADS)
Xu, X. Q.; Xiong, Z.; Gao, Z.; Nevins, W. M.; McKee, G. R.
2008-05-01
The fully nonlinear (full-f) four-dimensional TEMPEST gyrokinetic continuum code correctly produces the frequency and collisionless damping of geodesic-acoustic modes (GAMs) and zonal flow, with fully nonlinear Boltzmann electrons for the inverse aspect ratio γ scan and the tokamak safety factor q scan in homogeneous plasmas. TEMPEST simulations show that the GAMs exist in the edge pedestal for steep density and temperature gradients in the form of outgoing waves. The enhanced GAM damping may explain experimental beam emission spectroscopy measurements on the edge q scaling of the GAM amplitude.
NASA Astrophysics Data System (ADS)
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2016-01-01
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron-positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power law {γ }-α , with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. For large L and σ, the power-law index α approaches about 1.2.
NASA Technical Reports Server (NTRS)
Klimas, Alexander J.
1987-01-01
The solution of filtered Vlasov-Maxwell equations, rather than the Vlasov-Maxwell equations themselves, is shown to ameliorate the velocity space filamentation problem in collisionless plasma models. Exact field solutions and filtered velocity distribution functions are obtained without introducing errors. Proper selection of the filter width is demonstrated to inhibit development of velocity space filamentation and, it is conjectured, position space filamentation. The results of sample calculations of both filtered and nonfiltered field solutions illustrate a high degree of agreement between both solutions, with significant savings in computational time and memory requirements with the filtered solutions.
NASA Astrophysics Data System (ADS)
Ross, James; Park, H.-S.; Huntington, C.; Ryutov, D.; Drake, R. P.; Froula, D.; Gregori, G.; Levy, M.; Lamb, D.; Fiuza, F.; Petrasso, R.; Li, C.; Zylastra, A.; Rinderknecht, H.; Sakawa, Y.; Spitkovsky, A.
2015-11-01
Shock formation from high-Mach number plasma flows is observed in many astrophysical objects such as supernova remnants and gamma ray bursts. These are collisionless shocks as the ion-ion collision mean free path is much larger than the system size. It is believed that seed magnetic fields can be generated on a cosmologically fast timescale via the Weibel instability when such environments are initially unmagnetized. Here we present laboratory experiments using high-power lasers whose ultimate goal is to investigate the dynamics of collisionless shock formation in two interpenetrating plasma streams. Particle-in-cell numerical simulations have confirmed that the strength and structure of the generated magnetic field are consistent with the Weibel mediated electromagnetic nature and that the inferred magnetization level could be as high as ~ 1%. This paper will review recent experimental results from various laser facilities as well as the simulation results and the theoretical understanding of these observations. Taken together, these results imply that electromagnetic instabilities can be significant in both inertial fusion and astrophysical conditions. We will present results from initial NIF experiments, where we observe the neutrons and x-rays generated from the hot plasmas at the center of weakly collisional, counterstreaming flows. Prepared by LLNL under Contract DE-AC52-07NA27344.
Quasilinear wave-particle scattering rate in high-beta turbulent collisionless plasmas
NASA Astrophysics Data System (ADS)
Santos de Lima, Reinaldo; Yan, Huirong; Lazarian, Alex; de Gouveia Dal Pino, Elisabete
2015-08-01
Collisionless or weakly collisional plasmas, like the plasma of the intracluster medium of galaxies, are subject to electromagnetic instabilities driven by temperature anisotropy, which naturally arise in the presence of turbulence. These instabilities produce anomalous collisionality via wave-particle scattering, then reducing the mean-free-path of the particles by several orders of magnitude. This reduction affects directly the transport properties of the plasma and makes its large scale dynamics to behave similar to collisional MHD. In particular, it allows the turbulence to amplify the magnetic fields via the small-scale dynamo. Using the quasilinear theory, we calculate the scattering rate of ions due to the kinetic instabilities ion-cyclotron, mirror, and firehose. Using these results we estimate the average scattering rate of ions consistent with data cubes of high-beta MHD turbulence which represent the intracluster medium.
Thoma, C.; Welch, D. R.; Hsu, S. C.
2013-08-15
We describe numerical simulations, using the particle-in-cell (PIC) and hybrid-PIC code lsp[T. P. Hughes et al., Phys. Rev. ST Accel. Beams 2, 110401 (1999)], of the head-on merging of two laboratory supersonic plasma jets. The goals of these experiments are to form and study astrophysically relevant collisionless shocks in the laboratory. Using the plasma jet initial conditions (density ∼10{sup 14}–10{sup 16} cm{sup −3}, temperature ∼ few eV, and propagation speed ∼20–150 km/s), large-scale simulations of jet propagation demonstrate that interactions between the two jets are essentially collisionless at the merge region. In highly resolved one- and two-dimensional simulations, we show that collisionless shocks are generated by the merging jets when immersed in applied magnetic fields (B∼0.1–1 T). At expected plasma jet speeds of up to 150 km/s, our simulations do not give rise to unmagnetized collisionless shocks, which require much higher velocities. The orientation of the magnetic field and the axial and transverse density gradients of the jets have a strong effect on the nature of the interaction. We compare some of our simulation results with those of previously published PIC simulation studies of collisionless shock formation.
NASA Technical Reports Server (NTRS)
Barnes, A.
1983-01-01
An exact nonlinear solution is found to the relativistic kinetic and electrodynamic equations (in their hydromagnetic limit) that describes the large-amplitude fast-mode magnetoacoustic wave propagating normal to the magnetic field in a collisionless, previously uniform plasma. It is pointed out that a wave of this kind will be generated by transverse compression of any collisionless plasma. The solution is in essence independent of the detailed form of the particle momentum distribution functions. The solution is obtained, in part, through the method of characteristics; the wave exhibits the familiar properties of steepening and shock formation. A detailed analysis is given of the ultrarelativistic limit of this wave.
NASA Astrophysics Data System (ADS)
Falceta-Gonçalves, D.; Kowal, G.
2015-07-01
In this work we report on a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of the magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that (i) amplification of the magnetic field was efficient in firehose-unstable turbulent regimes, but not in the mirror-unstable models (ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo and (iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales and pressure anisotropy is confirmed by the numerical simulations. These results reinforce the idea that pressure anisotropies—driven naturally in a turbulent collisionless medium, e.g., the intergalactic medium, could efficiently amplify the magnetic field in the early universe (post-recombination era), previous to the collapse of the first large-scale gravitational structures. This mechanism, though fast for the small-scale fields (∼kpc scales), is unable to provide relatively strong magnetic fields at large scales. Other mechanisms that were not accounted for here (e.g., collisional turbulence once instabilities are quenched, velocity shear, or gravitationally induced inflows of gas into galaxies and clusters) could operate afterward to build up large-scale coherent field structures in the long time evolution.
Optical pyrometer system for collisionless shock experiments in high-power laser-produced plasmas.
Morita, T; Sakawa, Y; Kuramitsu, Y; Dono, S; Ide, T; Shibata, S; Aoki, H; Tanji, H; Sano, T; Shiroshita, A; Waugh, J N; Gregory, C D; Woolsey, N C; Takabe, H
2012-10-01
A temporally and spatially resolved optical pyrometer system has been fielded on Gekko XII experiments. The system is based on the self-emission measurements with a gated optical imager (GOI) and a streaked optical pyrometer (SOP). Both detectors measure the intensity of the self-emission from laser-produced plasmas at the wavelength of 450 nm with a bandpass filter with a width of ~10 nm in FWHM. The measurements were calibrated with different methods, and both results agreed with each other within 30% as previously reported [T. Morita et al., Astrophys. Space Sci. 336, 283 (2011)]. As a tool for measuring the properties of low-density plasmas, the system is applicable for the measurements of the electron temperature and density in collisionless shock experiments [Y. Kuramitsu et al., Phys. Rev. Lett. 106, 175002 (2011)]. PMID:23126856
Optical pyrometer system for collisionless shock experiments in high-power laser-produced plasmas
Morita, T.; Sakawa, Y.; Kuramitsu, Y.; Sano, T.; Takabe, H.; Dono, S.; Ide, T.; Tanji, H.; Shiroshita, A.; Shibata, S.; Aoki, H.; Waugh, J. N.; Woolsey, N. C.; Gregory, C. D.
2012-10-15
A temporally and spatially resolved optical pyrometer system has been fielded on Gekko XII experiments. The system is based on the self-emission measurements with a gated optical imager (GOI) and a streaked optical pyrometer (SOP). Both detectors measure the intensity of the self-emission from laser-produced plasmas at the wavelength of 450 nm with a bandpass filter with a width of {approx}10 nm in FWHM. The measurements were calibrated with different methods, and both results agreed with each other within 30% as previously reported [T. Morita et al., Astrophys. Space Sci. 336, 283 (2011)]. As a tool for measuring the properties of low-density plasmas, the system is applicable for the measurements of the electron temperature and density in collisionless shock experiments [Y. Kuramitsu et al., Phys. Rev. Lett. 106, 175002 (2011)].
NASA Technical Reports Server (NTRS)
Hairapetian, G.; Stenzel, R. L.
1991-01-01
The expansion of a two-electron-population, collisionless plasma into vacuum has been examined in detail. Plasma density, plasma potential, electric field, and particle disribution functions have been measured in situ. It is demonstrated that the presence of a low-pressure (P not less than 2 x 10 to the -5th torr) background neutral gas modifies the expansion of the plasma. A new plasma source creating dense, pulsed discharge plasma with a low background pressure (P not greater than 2 x 10 to the -6th torr) has been developed to perform in situ measurements of the temporal and spatial plasma evolution during its expansion into vacuum.
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.
Collisionless plasma expansion into vacuum: two new twists on an old problem
NASA Astrophysics Data System (ADS)
Arefiev, Alexey
2008-11-01
Plasma expansion into vacuum is a generic problem with a broad range of applications. Of particular interest are those regimes where the expanding plasma consists of energetic electrons and cold ions. The expansion is then caused by electron pressure and serves as an energy transfer mechanism from electrons to ions. Collisional plasma expansion is similar to the gas-dynamic expansion, with the fluid description applicable, whereas collisionless plasma expansion requires a kinetic treatment, especially for the energetic electrons. The collisionless expansion is often described under the assumption that the electron distribution is Maxwellian [1]. However, this assumption is not universally relevant, since the expansion may lead to a significant distortion of the electron distribution function. Also, non-Maxwellian electrons may force the quasineutrality condition to break down. This talk presents two problems [2,3] which illustrate the above kinetic effects. The first one is the problem of a magnetic nozzle that transforms an incoming subsonic plasma flow into a supersonic jet. The second is the problem of an expanding nanoplasma (cluster) with a two-component electron distribution. In the nozzle problem, a magnetic mirror, together with the expanding plasma boundary, generates a trapped electron population downstream. This population is decoupled from the plasma source and, consequently, it undergoes adiabatic cooling. The resulting distortion of the electron distribution function is a new element not captured by the usually used Boltzmann relation. In the cluster problem, the key feature is the initial two-component electron distribution with a cold majority and a hot minority both occupying the same volume prior to the expansion. The cluster problem exhibits a breakdown of quasineutrality manifested by a double-layer inside the flow. Both problems are illustrated with closed-form analytical solutions [2,3]. This work was supported by the US DOE NNSA under
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.
The Link Between Shocks, Turbulence, and Magnetic Reconnection in Collisionless Plasmas
NASA Technical Reports Server (NTRS)
Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-01-01
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, 'stir' the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space, and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
The link between shocks, turbulence, and magnetic reconnection in collisionless plasmas
Karimabadi, H.; Omelchenko, Y. A.; Roytershteyn, V.; Vu, H. X.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-06-15
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence, and magnetic reconnection. In particular, collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These “wavefronts” maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, “stir” the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence, and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
Dependence of Langmuir probe data on distance from the axis of a collisionless plasma
Knappmiller, Scott; Robertson, Scott
2007-03-15
A cylindrical Langmuir probe in a low-density, collisionless plasma (density {approx}10{sup 8} cm{sup -3}, electron temperature 0.2 eV) has been scanned radially through the presheath region to determine the effect of distance from the axis on the current-voltage characteristic. In the ion part of the probe characteristic, the collected ion current decreases with distance from the axis as a consequence of ion acceleration by the presheath. The part of the ion current from charge-exchange collisions remains relatively constant. In the electron part of the probe characteristic, the collected current decreases with distance from the axis, consistent with the existence of a small potential barrier from the presheath between the axis and the probe. The electron temperature from the slope of the probe characteristic is nearly constant across the presheath region. The plasma potential from the Langmuir probe characteristic is also nearly constant, indicating that the probe analysis finds the plasma potential on the axis, even when the probe is not on the axis. The plasma potential from an emissive probe shows an approximately parabolic profile. The plasma potential from the emissive probe and the Boltzmann relation give nearly the same density profile in the presheath that is obtained from the Langmuir probe data.
Intense laser driven collision-less shock and ion acceleration in magnetized plasmas
NASA Astrophysics Data System (ADS)
Mima, K.; Jia, Q.; Cai, H. B.; Taguchi, T.; Nagatomo, H.; Sanz, J. R.; Honrubia, J.
2016-05-01
The generation of strong magnetic field with a laser driven coil has been demonstrated by many experiments. It is applicable to the magnetized fast ignition (MFI), the collision-less shock in the astrophysics and the ion shock acceleration. In this paper, the longitudinal magnetic field effect on the shock wave driven by the radiation pressure of an intense short pulse laser is investigated by theory and simulations. The transition of a laminar shock (electro static shock) to the turbulent shock (electromagnetic shock) occurs, when the external magnetic field is applied in near relativistic cut-off density plasmas. This transition leads to the enhancement of conversion of the laser energy into high energy ions. The enhancement of the conversion efficiency is important for the ion driven fast ignition and the laser driven neutron source. It is found that the total number of ions reflected by the shock increases by six time when the magnetic field is applied.
NASA Astrophysics Data System (ADS)
Melville, Scott; Schekochihin, Alexander A.; Kunz, Matthew W.
2016-07-01
The non-linear state of a high-beta collisionless plasma is investigated where an imposed shear amplifies or diminishes a uniform mean magnetic field, driving pressure anisotropies and, therefore, firehose or mirror instabilities. To mimic the local behaviour of a macroscopic flow, the shear is switched off or reversed after one shear time, so a new macroscale configuration is superimposed on previous microscale state. A threshold plasma beta is found: when β ≪ Ω/S (ion cyclotron frequency/shear rate), the emergence/disappearance of firehose or mirror fluctuations is quasi-instantaneous compared to the shear time (lending some credence to popular closures that assume this). This follows from the free decay of these fluctuations being constrained by the same marginal-stability conditions as their growth in the unstable regime, giving the decay time ˜β/Ω ≪ S-1. In contrast, when β ≳ Ω/S, the old microscale state only disappears on the shear time-scale. In this `ultra-high-beta' regime, driven firehose fluctuations grow secularly to order-unity amplitudes, compensating for the decrease of the mean field and thus pinning the pressure anisotropy at marginal stability without scattering particles - unlike what happens at moderate β. After the shear reverses, the shearing away of these fluctuations compensates for the increase of the mean field and thus prevents growth of the pressure anisotropy, so the system stays close to the firehose threshold, does not go mirror-unstable, the total magnetic energy barely changing at all. Implications for various astrophysical situations, especially the origin of cosmic magnetism, are discussed: collisionless effects appear mostly beneficial to fast magnetic-field generation.
NASA Astrophysics Data System (ADS)
Ginzburg, S. L.; Dyachenko, V. F.; Orlov, Yu. N.; Fimin, N. N.; Chechetkin, V. M.
2016-09-01
The evolution of a collisionless electron-proton plasma in the self-consistent approximation is investigated. The plasma is assumed to move initially as a whole in a vacuum with the Lorentz factor. The behavior of the dynamical system is analyzed by applying a three-dimensional model based on the Vlasov-Maxwell equations with allowance for retarded potentials. It is shown that the analysis of the solution to the problem is not valid in the "center-of-mass frame" of the plasmoid (since it cannot be correctly defined for a relativistic plasma interacting via an electromagnetic field) and the transition to a laboratory frame of reference is required. In the course of problem solving, a chaotic electromagnetic field is generated by the plasma particles. As a result, the particle distribution functions in the phase space change substantially and differ from their Maxwell-Juttner form. Computations show that the kinetic energies of the electron and proton components and the energy of the self-consistent electromagnetic field become identical. A tendency to the isotropization of the particle momentum distribution in the direction of the initial plasmoid motion is observed.
Cremaschini, Claudio; Tessarotto, Massimo
2011-11-15
A largely unsolved theoretical issue in controlled fusion research is the consistent kinetic treatment of slowly-time varying plasma states occurring in collisionless and magnetized axisymmetric plasmas. The phenomenology may include finite pressure anisotropies as well as strong toroidal and poloidal differential rotation, characteristic of Tokamak plasmas. Despite the fact that physical phenomena occurring in fusion plasmas depend fundamentally on the microscopic particle phase-space dynamics, their consistent kinetic treatment remains still essentially unchallenged to date. The goal of this paper is to address the problem within the framework of Vlasov-Maxwell description. The gyrokinetic treatment of charged particles dynamics is adopted for the construction of asymptotic solutions for the quasi-stationary species kinetic distribution functions. These are expressed in terms of the particle exact and adiabatic invariants. The theory relies on a perturbative approach, which permits to construct asymptotic analytical solutions of the Vlasov-Maxwell system. In this way, both diamagnetic and energy corrections are included consistently into the theory. In particular, by imposing suitable kinetic constraints, the existence of generalized bi-Maxwellian asymptotic kinetic equilibria is pointed out. The theory applies for toroidal rotation velocity of the order of the ion thermal speed. These solutions satisfy identically also the constraints imposed by the Maxwell equations, i.e., quasi-neutrality and Ampere's law. As a result, it is shown that, in the presence of nonuniform fluid and EM fields, these kinetic equilibria can sustain simultaneously toroidal differential rotation, quasi-stationary finite poloidal flows and temperature anisotropy.
Cremaschini, Claudio Stuchlík, Zdeněk; Tessarotto, Massimo
2014-03-15
The kinetic description of relativistic plasmas in the presence of time-varying and spatially non-uniform electromagnetic (EM) fields is a fundamental theoretical issue both in astrophysics and plasma physics. This refers, in particular, to the treatment of collisionless and strongly-magnetized plasmas in the presence of intense radiation sources. In this paper, the problem is investigated in the framework of a covariant gyrokinetic treatment for Vlasov–Maxwell equilibria. The existence of a new class of kinetic equilibria is pointed out, which occur for spatially-symmetric systems. These equilibria are shown to exist in the presence of non-uniform background EM fields and curved space-time. In the non-relativistic limit, this feature permits the determination of kinetic equilibria even for plasmas in which particle energy is not conserved due to the occurrence of explicitly time-dependent EM fields. Finally, absolute stability criteria are established which apply in the case of infinitesimal symmetric perturbations that can be either externally or internally produced.
Ou, Jing; Wu, Guojiang; Li, Xinxia
2014-07-15
Distribution of the intrinsic rotation due to collisionless ion orbit loss near the tokamak edge region is studied by using an analytical model based on ion guiding center orbit approximation. A peak of the averaged ion orbit loss momentum fraction is found very near inside the separatrix region in a double null divertor configuration but is not found inside the last closed flux surface region in an outer limiter configuration. For the double null divertor configuration, the intrinsic rotation due to ion orbit loss depends on the plasma shape. With the increase in elongation and triangularity, the peak of the averaged ion orbit loss momentum fraction increases and it moves inward for the lower plasma current.
Magnetic mirror effects on a collisionless plasma in a convergent geometry
NASA Astrophysics Data System (ADS)
Martínez-Sánchez, Manuel; Ahedo, Eduardo
2011-03-01
Several plasma thruster concepts, as well as ion engine chambers, use magnetic cusps to protect walls and to throttle electron flow to anodes. We present a kinetic model of the plasma in the vicinity of one cusp. Electrons, strongly confined by the electrostatic presheath and sheath, are assumed isotropic. Collisionless ions are either magnetically guided or completely nonmagnetized, thus bracketing conditions of interest. For magnetized ions, electrostatic and magnetic mirror forces compete, and the resulting self-consistent potential is found by imposing quasineutrality. A similar competition occurs for nonmagnetized ions, this time as a result of the convergence of equipotential lines. Analytical solutions are found for monoenergetic ions, and these are generalized to the case of an initially Maxwellian population, for which some numerical iteration is required. The presheath potential drop is in all cases of the order of 0.6-0.75 times the electron temperature, and ions enter the sheath at a sonic velocity, according to Bohm's criterion. Contrary to intuition, the cusp does not reduce the ion flux (per unit area) to the wall, only the size of the wall area section that carries this flux by virtue of its connection to the distant plasma. These kinetic results are verified by checking the conservation of relevant moments of the ion distribution, including two new quantities that generalize the average magnetic moment and the total ion enthalpy by accounting for the nonzero ion heat fluxes.
Magnetic loop generation by collisionless gravitationally bound plasmas in axisymmetric tori.
Cremaschini, Claudio; Stuchlík, Zdeněk
2013-04-01
Current-carrying string loops are adopted in astrophysics to model the dynamics of isolated flux tubes of magnetized plasma expected to arise in the gravitational field of compact objects, such as black holes. Recent studies suggest that they could provide a framework for the acceleration and collimation of jets of plasma observed in these systems. However, the problem remains of the search of physical mechanisms which can consistently explain the occurrence of such plasma toroidal structures characterized by nonvanishing charge currents and are able to self-generate magnetic loops. In this paper, the problem is addressed in the context of Vlasov-Maxwell theory for nonrelativistic collisionless plasmas subject to both gravitational and electromagnetic fields. A kinetic treatment of quasistationary axisymmetric configurations of charged particles exhibiting epicyclic motion is obtained. Explicit solutions for the species equilibrium phase-space distribution function are provided. These are shown to have generally a non-Maxwellian character and to be characterized by nonuniform fluid fields and temperature anisotropy. Calculation of the relevant fluid fields and analysis of the Ampere equation then show the existence of nonvanishing current densities. As a consequence, the occurrence of a kinetic dynamo is proved, which can explain the self-generation of both azimuthal and poloidal magnetic fields by the plasma itself. This mechanism can operate in the absence of instabilities, turbulence, or accretion phenomena and is intrinsically kinetic in character. In particular, several kinetic effects contribute to it, identified here with finite Larmor radius, diamagnetic and energy-correction effects together with temperature anisotropy, and non-Maxwellian features of the equilibrium distribution function. PMID:23679535
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.
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.
Oblique firehose instability in hot collisionless plasmas - interplay between protons and electrons
NASA Astrophysics Data System (ADS)
Maneva, Yana; Lazar, Marian; Vinas, Adolfo; Poedts, Stefaan
2016-04-01
We solve the linearized kinetic Vlasov-Maxwell dispersion relation for oblique wave propagation in a homogeneous highly anisotropic hot electron-proton plasma. We assume bi-Maxwellian velocity distributions for both species, charge neutrality and current conservation, and consider no differential streaming between the ions and the electrons. We calculate the growth rate of the parallel and oblique proton firehose instabilities for various angles of wave propagation and varios electron plasma properties. We study the transition from stable to unstable scales with increasing electron temperature and temperature anisotropies. We find that for highly anisotropic hot plasma both the oscillatory parallel and the aperiodic oblique proton firehose branches may easily couple to the parallel and oblique electron firehose branches. In other words our work demonstrates the interplay between the proton and electron firehose instabilities, whose scales become fully mixed in hot collisionless plasma when the protons and the electrons are simultaneously anisotropic. In the case of parallel wave propagation both left and right-hand polarized waves are simultaneously excited. As we increase the angle of propagation the electron firehose starts to dominate with excitation of large-amplitude aperiodic fluctuations over a large range of wave-numbers, starting at the protons scales and extending up to the smaller electron scales. Whereas the maximum growth rate of the parallel proton firehose branch remains always at the proton scales, the maximum growth rate for the oblique proton firehose extends down to the electron scales. The observed electron-proton scale mixing can have significant implications for the observed plasma properties and instability thresholds in hot colissionless solar wind streams.
NASA Astrophysics Data System (ADS)
Verscharen, Daniel; Chandran, Benjamin D. G.; Klein, Kristopher G.; Quataert, Eliot
2016-11-01
Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in {β }\\parallel {{p}}\\equiv 8π {n}{{p}}{k}{{B}}{T}\\parallel {{p}}/{B}2 and in {R}{{p}}\\equiv {T}\\perp {{p}}/{T}\\parallel {{p}}, where {T}\\perp {{p}} and {T}\\parallel {{p}} are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and {n}{{p}} is the proton density. If the amplitude of the compressive fluctuations is large enough, {R}{{p}} crosses one or more instability thresholds for anisotropy-driven microinstabilities. The enhanced field fluctuations from these microinstabilities scatter the protons so as to reduce the anisotropy of the pressure tensor. We propose that this scattering drives the average value of {R}{{p}} away from the marginal stability boundary until the fluctuating value of {R}{{p}} stops crossing the boundary. We model this “fluctuating-anisotropy effect” using linear Vlasov–Maxwell theory to describe the large-scale compressive fluctuations. We argue that this effect can explain why, in the nearly collisionless solar wind, the average value of {R}{{p}} is close to unity.
Shaw, A. K.; Goswami, K. S.; Saikia, B. J.; Kar, S.
2012-01-15
The effect of ion temperature, magnitude of magnetic field and its orientation on a magnetized plasma sheath consisting of electrons and two species of positive ions are investigated. Using three-fluid hydrodynamic model and some dimensionless variables, the dimensionless equations are obtained and solved numerically. It is found that with the increase of the ion temperature and magnetic field strength there is a significant change in ion densities and energies in the sheath. It is also noticed that increase of magnetic field angle enhances the ion density near the sheath edge for a constant ion temperature. With increase in ion temperature and magnetic field angle, the lighter ion density near the sheath edge enhances and reverses for the heavier ion species.
NASA Astrophysics Data System (ADS)
Moser, Auna L.; Hsu, Scott C.
2015-05-01
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.
Moser, Auna L. Hsu, Scott C.
2015-05-15
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.
Turbulent energization of ions in warm collisionless plasmas - hybrid simulation study
NASA Astrophysics Data System (ADS)
Maneva, Yana; Vinas, Adolfo; Poedts, Stefaan
2016-04-01
Turbulent waves and structures are ubiquitous and indispensable part of the solar wind throughout the Heliosphere and have crucial contribution to the energization of particles in the warm collisionless plasma near the Earth, especially in regions where strong wave activity is observed. Wave-based turbulent energization of protons and minor ions in the undisturbed solar wind can occur through resonant and non-resonant wave-particle interactions and related wave absorption, particle scattering and diffusion in phase space. The efficiency of the ion heating depends on the characteristics of the waves carrying energy at the ion scales, such as polarization, direction of propagation and spectral properties of the fluctuations. The observed solar wind turbulence includes different types of waves at all scales, starting from the large-scale fluid regime and reaching towards the small electron scales, where the magnetic fluctuations are ultimately dissipated. Although the spatial and temporal scales of these fluctuation are separated by few orders of magnitudes, they can still exchange energy due to large and small-scales turbulent cascades. Trying to model part of the solar wind turbulence at the ion scales we assume a superposition of non-resonant Alfvén waves, which follow Kolmogorov-type spectral slope by construction. Such waves are frequently observed in situ in the solar wind, and yet their specific role for the energization of minor ions remains unclear. We perform 2.5D hybrid simulations with fluid electrons, kinetic ions and minor ions to study the effects of turbulent energization of minor ions by initial broad-band spectra, consisting of parallel and oblique forward propagating Alfvén waves. The numerical model is driven by observations of the solar wind plasma parameters at 1AU and takes into account the differential streaming between the protons and the minor ions. For the chosen spectral range of the external initial wave spectra we observe preferential
NASA Astrophysics Data System (ADS)
Gao, Dong-Ning; Qi, Xin; Hong, Xue-Ren; Yang, Xue; Duan, Wen-Shan; Yang, Lei; Yang
2014-06-01
Numerical and theoretical investigations are carried out for the stability of the dust acoustic waves (DAWs) under the transverse perturbation in a two-ion temperature magnetized and collisionless dusty plasma. The Zakharov-Kuznetsov (ZK) equation, modified ZK equation, and Extended ZK (EZK) equation of the DAWs are given by using the reductive perturbation technique. The cut-off frequency is obtained by applying higher-order transverse perturbations to the soliton solution of the EZK equation. The propagation velocity of solitary waves, the real cut-off frequency, as well as the growth rate of the higher-order perturbation to the solitary wave are obtained.
NASA Astrophysics Data System (ADS)
Hosseinpour, M.; Mohammadi, M. A.; Biabani, S.; Biabani
2013-10-01
Collisionless magnetic reconnection via tearing instability in non-relativistic electron-positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < r L ). This condition is satisfied when β > d 2 (d = c/ω p is the particle skin-depth with the electron/positron frequency ω p and β = 8πP (0)/B 0 2 << 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of dx. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτ A ) ~ d.
NASA Astrophysics Data System (ADS)
Vencels, Juris; Delzanno, Gian Luca; Manzini, Gianmarco; Markidis, Stefano; Peng, Ivy Bo; Roytershteyn, Vadim
2016-05-01
We present the design and implementation of a spectral code, called SpectralPlasmaSolver (SPS), for the solution of the multi-dimensional Vlasov-Maxwell equations. The method is based on a Hermite-Fourier decomposition of the particle distribution function. The code is written in Fortran and uses the PETSc library for solving the non-linear equations and preconditioning and the FFTW library for the convolutions. SPS is parallelized for shared- memory machines using OpenMP. As a verification example, we discuss simulations of the two-dimensional Orszag-Tang vortex problem and successfully compare them against a fully kinetic Particle-In-Cell simulation. An assessment of the performance of the code is presented, showing a significant improvement in the code running-time achieved by preconditioning, while strong scaling tests show a factor of 10 speed-up using 16 threads.
NASA Astrophysics Data System (ADS)
Ji, H.; Yamada, M.; Prager, S.; Daughton, W.; Roytershteyn, V.
2009-11-01
Magnetic reconnection, a topological change in magnetic field in plasmas, often occurs explosively leading to rapid conversion of magnetic energy to plasma particle energy in space, astrophysical and laboratory fusion plasmas. The Magnetic Reconnection Experiment (MRX, http://mrx.pppl.gov) is a primary dedicated experiment to study reconnection in a controlled environment. However, further critical understanding and contributions to space and astrophysical plasmas are limited by the parameters achievable in MRX and other dedicated experiments. The MRX plasmas are relatively collisional (Lundquist numbers S ˜10^3) and effectively small (plasma size normalized by ion skin depth or ion sound radius ˜10). In this paper, we discuss plans for a next-generation reconnection experiment based on MRX. By a combination of larger physical size, stronger magnetic field, and higher heating power, we aim to increase S by a factor of 100 and effective size by a factor of 10, representing a very large jump in the laboratory capabilities. Kinetic simulations in realistic boundaries will be used to guide the experimental design. Research topics include: (1) transition of collisional to collisionless reconnection and its scaling with collisionality and size, (2) interacting multiple reconnections as a possible cause of explosive phenomena, (3) particle energization by reconnection, (4) relation between local reconnection and global magnetic self-organization in 3D realistic geometry and boundary.
Moser, Auna L.; Hsu, Scott C.
2015-05-01
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease inmore » the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.« less
NASA Astrophysics Data System (ADS)
Benzekka, Moufida; Tribeche, Mouloud
2016-07-01
The aim of the present communication is to investigate the charge variation induced nonlinear dust acoustic wave damping in a charge varying electronegative dusty plasma with nonthermal ions. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust acoustic wave propagation to be described by a damped Korteweg-de Vries equation (dK-dV). The latter is significantly modified by the nonthermal negative ions effects. It may be useful to note that we consider nonthermal negative ions because of the role of their distribution into the formation and dynamics of nonlinear dust acoustic structures. Moreover, the observation of nonthermal ion distributions made by Phobos and Nozomi motivated us to consider non- Maxwellian ions.
NASA Astrophysics Data System (ADS)
Egedal, Jan; Le, Ari; Daughton, William
2013-06-01
From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, βe∞, the pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for
NASA Astrophysics Data System (ADS)
Bonde, J.; Vincena, S. T.; Gekelman, W. N.
2015-12-01
The collisionless coupling of an expanding diamagnetic cavity to a magnetized, ambient plasma is studied in a laboratory environment using a laser-produced plasma (LPP). The seed LPP rapidly expands with velocities up to the background Alfvén speed, vexp ≤ vA. The boundary layer of the expansion is characterized with in situ diagnostics as a cylindrical version of the Ferraro-Rosenbluth current sheath. Maintenance of quasi-neutrality in this sheath forms an electric field opposing the cross-field expansion which simultaneously drives the electron current that forms the diamagnetic cavity, decelerates the LPP ions to stagnation, and accelerates ambient ions inward. The field topology across the background magnetic field is identical to that described by Bernhardt, et al. [1] for the AMPTE magnetotail barium releases. The boundary along the magnetic field, however, is shown to contain an electric field with E·B ≠ 0, which is absent in simple fluid models of diamagnetic cavities. The electric fields at this boundary help explain previous observations in the experiment of the ejection of suprathermal electrons and return currents that generated whistler- and Alfvén-wave radiation in the ambient plasma. Magnetic loops and an emissive probe measure the magnetic field and electrostatic potential along 3 dimensions while a laser-induced fluorescence scheme measures the cross-field flow of the ambient argon ions as they penetrate the diamagnetic cavity. Particle orbit solvers employing the measured fields corroborate the flow diagnostic and predict strong outflows of ambient ions with higher charge to mass ratios after diamagnetic cavity collapse. This experiment was conducted in the Large Plasma Device at the Basic Plasma Science Facility and funded by grants from the US Department of Energy and the National Science Foundation. [1] P.A. Bernhardt, R.A. Roussel-Dupre, M.B. Pongratz, J. Geophys. Res. 92, 57777 (1987).
NASA Astrophysics Data System (ADS)
Sardar, Sankirtan; Bandyopadhyay, Anup; Das, K. P.
2016-07-01
A three-dimensional KP (Kadomtsev Petviashvili) equation is derived here describing the propagation of weakly nonlinear and weakly dispersive dust ion acoustic wave in a collisionless unmagnetized plasma consisting of warm adiabatic ions, static negatively charged dust grains, nonthermal electrons, and isothermal positrons. When the coefficient of the nonlinear term of the KP-equation vanishes an appropriate modified KP (MKP) equation describing the propagation of dust ion acoustic wave is derived. Again when the coefficient of the nonlinear term of this MKP equation vanishes, a further modified KP equation is derived. Finally, the stability of the solitary wave solutions of the KP and the different modified KP equations are investigated by the small-k perturbation expansion method of Rowlands and Infeld [J. Plasma Phys. 3, 567 (1969); 8, 105 (1972); 10, 293 (1973); 33, 171 (1985); 41, 139 (1989); Sov. Phys. - JETP 38, 494 (1974)] at the lowest order of k, where k is the wave number of a long-wavelength plane-wave perturbation. The solitary wave solutions of the different evolution equations are found to be stable at this order.
HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR
L. YIN; D. WINSKE; ET AL
2001-05-01
In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.
Plasma Waves Around Separatrix in Collisionless Magnetic Reconnection with Weak Guide Field
NASA Astrophysics Data System (ADS)
Chen, Y.; Fujimoto, K.; Xiao, C.; Ji, H.
2015-12-01
Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven Whistler instability. The localization of the Whistler waves is attributed to the non-uniformity of the out-of-plane magnetic field By. The Whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
Experimental study of collisionless super-Alfvénic interaction of interpenetrating plasma flows
Shaikhislamov, I. F. Zakharov, Yu. P.; Posukh, V. G.; Melekhov, A. V.; Boyarintsev, E. L.; Ponomarenko, A. G.; Terekhin, V. A.
2015-05-15
An experiment on the interaction between an expanding super-Alfvénic laser-produced plasma flow and a magnetized background plasma under conditions in which the ion gyroradius is comparable with the characteristic scale length of magnetic field displacement is described. The depletion of the background plasma in a substantial volume and the formation of a large-amplitude compression pulse propagating with a super-Alfvénic velocity are revealed. The efficiency of energy conversion into perturbations of the background plasma was found to be 25%. Combined data from magnetic, electric, and plasma measurements indicate that the interaction occurs via the magnetic laminar mechanism.
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.
Measurement of the ion drag force in a collisionless plasma with strong ion-grain coupling
Nosenko, V.; Fisher, R.; Merlino, R.; Khrapak, S.; Morfill, G.; Avinash, K.
2007-10-15
The ion drag force acting on dust grains was measured experimentally in a low-pressure Ar plasma in the regime of strong ion-grain coupling. Argon ions were drifting in the axial ambipolar electric field naturally present in a hot-filament dc discharge plasma. Following the method of Hirt et al. [Phys. Plasmas 11, 5690 (2004)], hollow glass microspheres were dropped into the plasma and allowed to fall due to gravity. The ion drag force was derived from the particle trajectory deflection from the vertical direction. The result is in reasonable agreement with a theoretical model that takes strong ion-grain coupling into account.
A collisionless shock wave experiment
Winske, D.; Jones, M.E.; Sgro, A.G.; Thomas, V.A.
1995-04-01
Collisionless shock waves are a very important heating mechanism for plasmas and are commonly found in space and astrophysical environments. Collisionless shocks were studied in the laboratory more than 20 years ago, and more recently in space via in situ satellite measurements. The authors propose a new laboratory shock wave experiment to address unresolved issues related to the differences in the partition of plasma heating between electrons and ions in space and laboratory plasmas, which can have important implications for a number of physical systems.
Ilgisonis, V. I.; Sorokina, E. A.; Yurchenko, E. I.
2010-01-15
The density of the noninductive current generated due to collisionless motion of {alpha}-particles in the tokamak magnetic field is calculated. The analysis is based on fully three-dimensional calculations of charged particle trajectories without simplifying assumptions typical for drift and neoclassical approaches. The current is calculated over the entire cross section of the plasma column, including the magnetic axis. It is shown that the current density is not a function of a magnetic surface and is strongly polarized over the poloidal angle. The current density distribution in the tokamak poloidal cross section is obtained, and the current density as a function of the safety factor, the tokamak aspect ratio, and the ratio of the particle Larmor radius on the axis to the tokamak minor radius is determined. It is shown that, when the source of {alpha}-particles is spatially nonuniform, the current density in the center of the tokamak is nonzero due to asymmetry of the phase-space boundary between trapped and passing particles. The current density scaling in the tokamak center differs from the known approximations for the bootstrap current and is sensitive to the spatial distribution of {alpha}-particles.
NASA Astrophysics Data System (ADS)
Kuramitsu, Y.; Mizuta, A.; Sakawa, Y.; Tanji, H.; Ide, T.; Sano, T.; Koenig, M.; Ravasio, A.; Pelka, A.; Takabe, H.; Gregory, C. D.; Woolsey, N.; Moritaka, T.; Matsukiyo, S.; Matsumoto, Y.; Ohnishi, N.
2016-09-01
We report experimental results on Kelvin–Helmholtz (KH) instability and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KH instability is excited. We observe the spatial and temporal evolution of plasmas and shocks with time-resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures, and circular features, which are interpreted as the KH instability and resultant vortices. The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreement with experimental results. Shocks, and thus the contact surfaces, are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.
NASA Astrophysics Data System (ADS)
Kuramitsu, Y.; Mizuta, A.; Sakawa, Y.; Tanji, H.; Ide, T.; Sano, T.; Koenig, M.; Ravasio, A.; Pelka, A.; Takabe, H.; Gregory, C. D.; Woolsey, N.; Moritaka, T.; Matsukiyo, S.; Matsumoto, Y.; Ohnishi, N.
2016-09-01
We report experimental results on Kelvin-Helmholtz (KH) instability and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KH instability is excited. We observe the spatial and temporal evolution of plasmas and shocks with time-resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures, and circular features, which are interpreted as the KH instability and resultant vortices. The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreement with experimental results. Shocks, and thus the contact surfaces, are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.
Self-consistent solution for a collisionless plasma slab in motion across a magnetic field
Echim, Marius M.; Lemaire, Joseph F.; Roth, Michel
2005-07-15
The problem of the dynamics of a plasma slab moving across a magnetic field is treated in the framework of the kinetic theory. A velocity distribution function (VDF) is found for each plasma species, electrons and protons, in terms of the constants of motion defined by the geometry of the problem. The zero- and first-order moments of the VDF are introduced into the right-hand side term of Maxwell's equations to compute the electric and magnetic vector potentials and corresponding fields. The solutions are found numerically. We obtain a region of plasma convection--the slab proper--where the plasma moves with a uniform velocity, V{sub x}=V{sub 0}=(ExB/B{sup 2}){sub x}. At the core margins two plasma 'wings' are formed, each being the result of a pair of interpenetrated boundary layers with different transition lengths. Inside these wings, the plasma velocity is not uniform, V{sub x}{ne}(ExB/B{sup 2}){sub x}. It decreases from the maximum value obtained in the core to a minimum value in the central region of the wings where a flow reversal is found with the plasma convecting in the opposite direction to the core motion. There is also an asymmetry of the velocity gradient at the borders of the core, which results in a corresponding asymmetry in the thickness of the wings. Furthermore, it is found that the reversed plasma flow in the thinner wing is larger than that in the broader wing. For a fixed direction of the magnetic field the two plasma wings interchange position with respect to the center of the slab when the plasma bulk velocity reverses sign.
Diffusion and radiation in magnetized collisionless plasmas with small-scale Whistler turbulence
NASA Astrophysics Data System (ADS)
Keenan, Brett D.; Medvedev, Mikhail V.
2016-04-01
> Magnetized high-energy-density plasmas can often have strong electromagnetic fluctuations whose correlation scale is smaller than the electron Larmor radius. Radiation from the electrons in such plasmas - which markedly differs from both synchrotron and cyclotron radiation - is tightly related to their energy and pitch-angle diffusion. In this paper, we present a comprehensive theoretical and numerical study of particle transport in cold, `small-scale' Whistler-mode turbulence and its relation to the spectra of radiation simultaneously produced by these particles. We emphasize that this relation is a superb diagnostic tool of laboratory, astrophysical, interplanetary and solar plasmas with a mean magnetic field and strong small-scale turbulence.
Nonlinear Collisionless Magnetic Reconnection
Grasso, D.; Tassi, E.; Borgogno, D.; Pegoraro, F.
2008-10-15
We review some recent results that have been obtained in the investigation of collisionless reconnection in two and three dimensional magnetic configurations with a strong guide field in regimes of interest for laboratory plasmas. First, we adopt a two-field plasma model where two distinct regimes, laminar and turbulent, can be identified. Then, we show that these regimes may combine when we consider a more general four-field model, where perturbation of the magnetic and velocity fields are allowed also along the ignorable coordinate.
A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, Seiji; Kuznetova, Masha; Klimas, Alex
2011-01-01
A set of conservation equations is utilized to derive balance equations in the reconnection diffusion region of a symmetric pair plasma. The reconnection electric field is assumed to have the function to maintain the current density in the diffusion region, and to impart thermal energy to the plasma by means of quasi-viscous dissipation. Using these assumptions it is possible to derive a simple set of equations for diffusion region parameters in dependence on inflow conditions and on plasma compressibility. These equations are solved by means of a simple, iterative, procedure. The solutions show expected features such as dominance of enthalpy flux in the reconnection outflow, as well as combination of adiabatic and quasi-viscous heating. Furthermore, the model predicts a maximum reconnection electric field of E(sup *)=0.4, normalized to the parameters at the inflow edge of the diffusion region.
Transport of a multiple-ion species plasma in a collisionless regime in a bumpy torus
Hastings, D.E.
1984-04-01
The ion neoclassical transport coefficient in a multiple ion species plasma in a bumpy torus are calculated in the low-collisionality regime. The poloidal electric field is calculated self-consistently with collisional electrons. Both pitch angle and energy scattering are included in the collision operator.
Nonlinear shielding of a point-like charge in a collisionless plasma
NASA Astrophysics Data System (ADS)
Krasovsky, Victor
A simple formulation of the problem related to the shielding phenomenon presumes instantaneous appearance of an external point-like charge in a uniform isotropic plasma. Corresponding asymptotic solution of the problem leads to well-known Debye formula for spatial dependence of electrostatic potential at long times. To determine dielectric constant of the plasma, such an approach implies linearization of Vlasov equation. At the same time, according to the Debye expression, the electric field intensity can take very high values in the vicinity of the external charge, i.e. the result of the calculation is in obvious contradiction with the condition for applicability of the linear theory. It follows from here that rejection of the perturbation theory methods is necessary in order to solve the problem correctly. Although the same initial-value problem becomes too difficult for analytical treatment beyond the scope of the linear approximation, analysis of the asymptotic equilibrium state of the disturbed plasma is still not hopeless effort. This study presents a solution of the nonlinear problem of the shielding of a positive point-like charge under simplifying assumption of immobile ions. The disturbed electron number density is calculated on the basis of kinetic theory, and the corresponding Poisson equation is solved numerically. The found spatial profiles of the electrostatic potential are confronted with the Debye formula. Particular attention is given to trapped electrons executing a spatially limited motion on finite orbits. It is shown that these particles contribute significantly to the disturbance of the plasma density and thereby affect essentially the structure of the disturbed region and the behavior of the self-consistent electric field. The major conclusion of the developed theory consists in weakening of the nonlinear shielding in comparison with the result of the linear analysis. Although the consideration of the point-like charge is probably one of the
The effects of plasma shape control on the edge collisionless ion orbit loss
Wu, G. J.; Zhang, X. D.; Li, Y. D.; Sun, P. J.; Cao, G. M.
2013-10-15
Double null magnetic configurations with different elongation κ and triangularity δ are constructed by using an analytical solution of the Grad–Shafranov equation. The ion orbit losses in plasma edge region are calculated by solving the ion guiding center orbit equation for different values of κ and δ. It is found that the ion orbit loss is larger for a smaller value of κ or δ. The variation of the ion orbit loss fraction on the magnetic surface is also studied.
NASA Technical Reports Server (NTRS)
Schindler, K.; Birn, J.; Hesse, M.
2012-01-01
Localized plasma structures, such as thin current sheets, generally are associated with localized magnetic and electric fields. In space plasmas localized electric fields not only play an important role for particle dynamics and acceleration but may also have significant consequences on larger scales, e.g., through magnetic reconnection. Also, it has been suggested that localized electric fields generated in the magnetosphere are directly connected with quasi-steady auroral arcs. In this context, we present a two-dimensional model based on Vlasov theory that provides the electric potential for a large class of given magnetic field profiles. The model uses an expansion for small deviation from gyrotropy and besides quasineutrality it assumes that electrons and ions have the same number of particles with their generalized gyrocenter on any given magnetic field line. Specializing to one dimension, a detailed discussion concentrates on the electric potential shapes (such as "U" or "S" shapes) associated with magnetic dips, bumps, and steps. Then, it is investigated how the model responds to quasi-steady evolution of the plasma. Finally, the model proves useful in the interpretation of the electric potentials taken from two existing particle simulations.
Reversible collisionless magnetic reconnection
Ishizawa, A.; Watanabe, T.-H.
2013-10-15
Reversible magnetic reconnection is demonstrated for the first time by means of gyrokinetic numerical simulations of a collisionless magnetized plasma. Growth of a current-driven instability in a sheared magnetic field is accompanied by magnetic reconnection due to electron inertia effects. Following the instability growth, the collisionless reconnection is accelerated with development of a cross-shaped structure of current density, and then all field lines are reconnected. The fully reconnected state is followed by the secondary reconnection resulting in a weakly turbulent state. A time-reversed simulation starting from the turbulent state manifests that the collisionless reconnection process proceeds inversely leading to the initial state. During the reversed reconnection, the kinetic energy is reconverted into the original magnetic field energy. In order to understand the stability of reversed process, an external perturbation is added to the fully reconnected state, and it is found that the accelerated reconnection is reversible when the deviation of the E × B streamlines due to the perturbation is comparable with or smaller than a current layer width.
NASA Astrophysics Data System (ADS)
Sánchez-Arriaga, G.
2013-10-01
The existence of discontinuities within the double-adiabatic Hall-magnetohydrodynamics (MHD) model is discussed. These solutions are transitional layers where some of the plasma properties change from one equilibrium state to another. Under the assumption of traveling wave solutions with velocity C and propagation angle θ with respect to the ambient magnetic field, the Hall-MHD model reduces to a dynamical system and the waves are heteroclinic orbits joining two different fixed points. The analysis of the fixed points rules out the existence of rotational discontinuities. Simple considerations about the Hamiltonian nature of the system show that, unlike dissipative models, the intermediate shock waves are organized in branches in parameter space, i.e., they occur if a given relationship between θ and C is satisfied. Electron-polarized (ion-polarized) shock waves exhibit, in addition to a reversal of the magnetic field component tangential to the shock front, a maximum (minimum) of the magnetic field amplitude. The jumps of the magnetic field and the relative specific volume between the downstream and the upstream states as a function of the plasma properties are presented. The organization in parameter space of localized structures including in the model the influence of finite Larmor radius is discussed.
Towards Closures for Multi-Fluid Moment Simulations of Collisionless Plasmas
NASA Astrophysics Data System (ADS)
Hakim, A.
2015-12-01
Fluid simulation remain an efficient and valuable tool to understand the global behavior of plasmas. However, as it wellknown, fluid models require a closure approximation to yield a closed set of equations. Designing closures that capture correctkinetic behavior in asymptotic regimes, specially in the presence of weak guide fields, remains a challenge. We present anapproach to developing such closures in the context of multi-fluid moment models. In these, each fluid is treated independently, with higher-order moments (pressure tensor, heat-flux tensor) evolved self-consistently with time-dependent equations. Electromagnetic fields are evolved with Maxwell equations, retaining displacement currents. The validity of these closures is determined by comparison with PIC simulations. A brief overview of the numerical schemes, implemented in the open-source computational framework Gkeyll, will also be presented.
A robust method for handling low density regions in hybrid simulations for collisionless plasmas
Amano, Takanobu Higashimori, Katsuaki; Shirakawa, Keisuke
2014-10-15
A robust method to handle vacuum and near vacuum regions in hybrid simulations for space and astrophysical plasmas is presented. The conventional hybrid simulation model dealing with kinetic ions and a massless charge-neutralizing electron fluid is known to be susceptible to numerical instability due to divergence of the whistler-mode wave dispersion, as well as division-by-density operation in regions of low density. Consequently, a pure vacuum region is not allowed to exist in the simulation domain unless some ad hoc technique is used. To resolve this difficulty, an alternative way to introduce finite electron inertia effect is proposed. Contrary to the conventional method, the proposed one introduces a correction to the electric field rather than the magnetic field. It is shown that the generalized Ohm's law correctly reduces to Laplace's equation in a vacuum which therefore does not involve any numerical problems. In addition, a variable ion-to-electron mass ratio is introduced to reduce the phase velocity of high frequency whistler waves at low density regions so that the stability condition is always satisfied. It is demonstrated that the proposed model is able to handle near vacuum regions generated as a result of nonlinear self-consistent development of the system, as well as pure vacuum regions set up at the initial condition, without losing the advantages of the standard hybrid code.
NASA Astrophysics Data System (ADS)
Zelenyi, Lev M.; Artemyev, Anton V.
2016-02-01
In this paper we revisit the paradigm of space science turbulent dissipation traditionally considered as myth (Coroniti, Space Sci. Rev., vol. 42, 1985, pp. 399-410). We demonstrate that due to approach introduced by Pitaevskii (Sov. J. Expl Theor. Phys., vol. 44, 1963, pp. 969-979 (in Russian)) (the effect of a finite Larmor radius on a classical collision integral) dissipation induced by effective interaction with microturbulence produces a significant effect on plasma dynamics, especially in the vicinity of the reconnection region. We estimate the multiplication factor of collision frequency in the collision integral for short wavelength perturbations. For waves propagating transverse to the background magnetic field, this factor is approximately ρekx)2 an electron gyroradius and where kx a transverse wavenumber. We consider recent spacecraft observations in the Earth's magnetotail reconnection region to the estimate possible impact of this multiplication factor. For small-scale reconnection regions this factor can significantly increase the effective collision frequency produced both by lower-hybrid drift turbulence and by kinetic Alfvén waves. We discuss the possibility that the Pitaevskii's effect may be responsible for the excitation of a resistive electron tearing mode in thin current sheets formed in the outflow region of the primary X-line.
Computation on collisionless steady-state plasma flow past a charged disk
NASA Technical Reports Server (NTRS)
Parker, L. W.
1976-01-01
A computer method is presented using the 'inside-out' approach, for predicting the structure of the disturbed zone near a moving body in space. The approach uses fewer simplifying assumptions than other available methods, and is applicable to large ranges of the values of body and plasma parameters. Two major advances concerning 3-dimensional bodies are that thermal motions of ions as well as of electrons are treated realistically by following their trajectories in the electric field, and the technique for achieving self-consistency is promising for very large bodies. Three sample solutions were obtained for a disk-shaped body, charged negatively to a potential 4kT/e. With ion Mach number 4, and equal ion and electron temperatures, the wakes of a relatively small body (radius 5 Debye lengths) and a relatively large body (radius 100 Debye lengths) both begin to fill up between 2 and 3 body radii downstream. For the large body there is in addition a potential well (about 6kT/e deep) behind the body. Increasing the ion Mach number to 8 for the large body causes the potential well to become wider and longer but not deeper. For the large body, the quasineutrality assumption is validated outside of a cone-shaped region in the very near wake. For the large as well as the small body, the disturbed zone behind the body extends transversely no more than 2 or 3 body radii, a result of significance for the design of spacecraft boom instrumentation.
Nanda, Vikas; Kant, Niti
2014-07-15
The effect of plasma density ramp on self-focusing of cosh-Gaussian laser beam considering ponderomotive nonlinearity is analyzed using WKB and paraxial approximation. It is noticed that cosh-Gaussian laser beam focused earlier than Gaussian beam. The focusing and de-focusing nature of the cosh-Gaussian laser beam with decentered parameter, intensity parameter, magnetic field, and relative density parameter has been studied and strong self-focusing is reported. It is investigated that decentered parameter “b” plays a significant role for the self-focusing of the laser beam as for b=2.12, strong self-focusing is seen. Further, it is observed that extraordinary mode is more prominent toward self-focusing rather than ordinary mode of propagation. For b=2.12, with the increase in the value of magnetic field self-focusing effect, in case of extraordinary mode, becomes very strong under plasma density ramp. Present study may be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, and x-ray lasers. Moreover, plasma density ramp plays a vital role to enhance the self-focusing effect.
Moser, Auna L.; Hsu, Scott C.
2015-05-01
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.
Ruyer, C. Gremillet, L.; Bonnaud, G.
2015-08-15
We present a particle-in-cell simulation of the generation of a collisionless strong shock in a dense plasma driven by an ultra-intense, plane-wave laser pulse. A linear theory analysis, based on a multi-waterbag model of the particle distributions, highlights the role of the laser-heated electrons in triggering the Weibel-like instability causing shock formation. It is demonstrated that the return-current electrons play a major role in the instability development as well as in the determination of the saturated magnetic field. By contrast, the ions are found of minor importance in driving the instability and the magnetic field fluctuations responsible for their isotropization. Finally, we show that a Weibel-mediated shock can also be generated by a focused laser pulse of large enough spot size.
NASA Technical Reports Server (NTRS)
Khabibrakhmanov, I. KH.; Galeev, A. A.; Galinskii, V. L.
1993-01-01
Consideration is given to a collisionless parallel shock based on solitary-type solutions of the modified derivative nonlinear Schroedinger equation (MDNLS) for parallel Alfven waves. The standard derivative nonlinear Schroedinger equation is generalized in order to include the possible anisotropy of the plasma distribution and higher-order Korteweg-de Vies-type dispersion. Stationary solutions of MDNLS are discussed. The anisotropic nature of 'adiabatic' reflections leads to the asymmetric particle distribution in the upstream as well as in the downstream regions of the shock. As a result, nonzero heat flux appears near the front of the shock. It is shown that this causes the stochastic behavior of the nonlinear waves, which can significantly contribute to the shock thermalization.
Porkolab, Miklos; Egedal, Jan
2007-11-30
The Grant DE-FG-02-00ER54712, ?Experimental Studies of Collisionless Reconnection Processes in Plasmas?, financed within the DoE/NSF, spanned a period from September , 2003 to August, 2007. It partly supported an MIT Research scientist, two graduate students and material expenses. The grant enabled the operation of a basic plasma physics experiment (on magnetic reconnection) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. A strong educational component characterized this work throughout, with the participation of a large number of graduate and undergraduate students and interns to the experimental activities. The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF). The first configuration is characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed [7]. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail [9]. The second configuration was developed to be specifically relevant to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection [12
Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma
Hirota, M.; Hattori, Y.; Morrison, P. J.
2015-05-15
A mechanism for explosive magnetic reconnection is investigated by analyzing the nonlinear evolution of a collisionless tearing mode in a two-fluid model that includes the effects of electron inertia and temperature. These effects cooperatively enable a fast reconnection by forming an X-shaped current-vortex layer centered at the reconnection point. A high-resolution simulation of this model for an unprecedentedly small electron skin depth d{sub e} and ion-sound gyroradius ρ{sub s}, satisfying d{sub e}=ρ{sub s}, shows an explosive tendency for nonlinear growth of the tearing mode, where it is newly found that the explosive widening of the X-shaped layer occurs locally around the reconnection point with the length of the X shape being shorter than the domain length and the wavelength of the linear tearing mode. The reason for the onset of this locally enhanced reconnection is explained theoretically by developing a novel nonlinear and nonequilibrium inner solution that models the local X-shaped layer, and then matching it to an outer solution that is approximated by a linear tearing eigenmode with a shorter wavelength than the domain length. This theoretical model proves that the local reconnection can release the magnetic energy more efficiently than the global one and the estimated scaling of the explosive growth rate agrees well with the simulation results.
Niemann, Christoph; Gekelman, W.; Winske, D.; Larsen, D.
2012-12-14
We have performed several thousand high-energy laser shots in the LAPD to investigate the dynamics of an exploding laser-produced plasma in a large ambient magneto-plasma. Debris-ions expanding at super-Alfvenic velocity (up to MA=1.5) expel the ambient magnetic field, creating a large (> 20 cm) diamagnetic cavity. We observed field compressions of up to B/B{sub 0} = 1.5 at the edge of the bubble, consistent with the MHD jump conditions, as well as localized electron heating at the edge of the bubble. Two-dimensional hybrid simulations reproduce these measurements well and show that the majority of the ambient ions are energized by the magnetic piston to super-Alfvenic speeds and swept outside the bubble volume. Nonlinear shear-Alfven waves ({delta}B/B{sub 0} > 25%) are radiated from the cavity with a coupling efficiency of 70% from magnetic energy in the bubble to the wave. While the data is consistent with a weak magneto-sonic shock, the experiments were severely limited by the low ambient plasma densities (10{sup 12} cm{sup -3}). 2D hybrid simulations indicate that future experiments with the new LAPD plasma source and densities in excess of 10{sup 13} cm{sup -3} will drive full-blown collisionless shocks with MA>10 over several c/wpi and shocked Larmor radii. In a separate experiment at the LANL Trident laser facility we have performed a proof-of-principle experiment at higher densities to demonstrate key elements of collisionless shocks in laser-produced magnetized plasmas with important implications to NIF. Simultaneously we have upgraded the UCLA glass-laser system by adding two large amplitude disk amplifiers from the NOVA laser and boost the on-target energy from 30 J to up to 1 kJ, making this one of the world’s largest university-scale laser systems. We now have the infrastructure in place to perform novel and unique high-impact experiments on collision-less shocks at the LAPD.
NASA Astrophysics Data System (ADS)
Allanson, O.; Wilson, F.; Neukirch, T.
2016-09-01
We calculate exact one-dimensional collisionless plasma equilibria for a continuum of flux tube models, for which the total magnetic field is made up of the "force-free" Gold-Hoyle magnetic flux tube embedded in a uniform and anti-parallel background magnetic field. For a sufficiently weak background magnetic field, the axial component of the total magnetic field reverses at some finite radius. The presence of the background magnetic field means that the total system is not exactly force-free, but by reducing its magnitude, the departure from force-free can be made as small as desired. The distribution function for each species is a function of the three constants of motion; namely, the Hamiltonian and the canonical momenta in the axial and azimuthal directions. Poisson's equation and Ampère's law are solved exactly, and the solution allows either electrically neutral or non-neutral configurations, depending on the values of the bulk ion and electron flows. These equilibria have possible applications in various solar, space, and astrophysical contexts, as well as in the laboratory.
Phukan, Ananya Goswami, K. S.; Bhuyan, P. J.
2014-08-15
The electric potential near a wall for a multi-species plasma with volume produced negative ions in presence of axially varying magnetic field is studied following an analytical-numerical approach. A constant negative ion source is assumed throughout the plasma volume, along with finite temperature positive ions and Boltzmann electrons. The particles are assumed to be guided by an open magnetic field that has its maximum at the centre, and field strength decreasing towards the walls. The one dimensional (1D) Poisson equation is derived using an analytical approach, and then solved numerically to study the potential profiles. Effect of (a) negative ion production rate, (b) magnetic field profile, and (c) negative ion temperature on the potential profile has been investigated. A potential peak appears near the wall when the negative ion temperature and density are sufficiently high. Also, the presence of negative ions further decreases the potential in the plasma region for a finite Debye Length (λ{sub D})
Khrapak, S. A.; Nosenko, V.; Morfill, G. E.; Merlino, R.
2009-04-15
We point out a deficiency in our previous analytic calculation of the ion drag force for conditions of the experiment by Nosenko et al. [Phys. Plasmas 14, 103702 (2007)]. An inaccurate approximation is corrected and the ion drag force is recalculated. The improved model yields better overall agreement with the experimental results as compared to the original calculation.
Krasovsky, V. L.
2013-06-15
The structure of the plasma disturbance near a spherical charged body is analyzed with allowance for the boundedness of the region of finite particle motion. The significance of the outer radius of the spherical region in which trapped particles can exist is demonstrated. The radius of the trapping sphere is determined by the boundary condition imposed on Poisson's equation. The important role played by the boundary of the trapping region in the general analysis and solution of the problem is illustrated by simple examples.
Transition from Collisionless to Collisional MRI
Prateek Sharma; Gregory W. Hammett; Eliot Quataert
2003-07-24
Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.
Chen, Guangye; Chacon, Luis; Knoll, Dana Alan; Barnes, Daniel C
2015-07-31
A multi-rate PIC formulation was developed that employs large timesteps for slow field evolution, and small (adaptive) timesteps for particle orbit integrations. Implementation is based on a JFNK solver with nonlinear elimination and moment preconditioning. The approach is free of numerical instabilities (ω_{pe}Δt >>1, and Δx >> λ_{D}), and requires many fewer dofs (vs. explicit PIC) for comparable accuracy in challenging problems. Significant gains (vs. conventional explicit PIC) may be possible for large scale simulations. The paper is organized as follows: Vlasov-Maxwell Particle-in-cell (PIC) methods for plasmas; Explicit, semi-implicit, and implicit time integrations; Implicit PIC formulation (Jacobian-Free Newton-Krylov (JFNK) with nonlinear elimination allows different treatments of disparate scales, discrete conservation properties (energy, charge, canonical momentum, etc.)); Some numerical examples; and Summary.
Valentini, F. . E-mail: valentin@fis.unical.it; Travnicek, P.; Califano, F.; Hellinger, P.; Mangeney, A.
2007-07-01
We present a numerical scheme for the integration of the Vlasov-Maxwell system of equations for a non-relativistic plasma, in the hybrid approximation, where the Vlasov equation is solved for the ion distribution function and the electrons are treated as a fluid. In the Ohm equation for the electric field, effects of electron inertia have been retained, in order to include the small scale dynamics up to characteristic lengths of the order of the electron skin depth. The low frequency approximation is used by neglecting the time derivative of the electric field, i.e. the displacement current in the Ampere equation. The numerical algorithm consists in coupling the splitting method proposed by Cheng and Knorr in 1976 [C.Z. Cheng, G. Knorr, J. Comput. Phys. 22 (1976) 330-351.] and the current advance method (CAM) introduced by Matthews in 1994 [A.P. Matthews, J. Comput. Phys. 112 (1994) 102-116.] In its present version, the code solves the Vlasov-Maxwell equations in a five-dimensional phase space (2-D in the physical space and 3-D in the velocity space) and it is implemented in a parallel version to exploit the computational power of the modern massively parallel supercomputers. The structure of the algorithm and the coupling between the splitting method and the CAM method (extended to the hybrid case) is discussed in detail. Furthermore, in order to test the hybrid-Vlasov code, the numerical results on propagation and damping of linear ion-acoustic modes and time evolution of linear elliptically polarized Alfven waves (including the so-called whistler regime) are compared to the analytical solutions. Finally, the numerical results of the hybrid-Vlasov code on the parametric instability of Alfven waves are compared with those obtained using a two-fluid approach.
Physics of collisionless phase mixing
Tsiklauri, D.; Haruki, T.
2008-11-15
Previous studies of phase mixing of ion cyclotron (IC), Alfvenic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5 D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: (i) Using the generalized Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20%, respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to be independent of plasma beta, while the fraction of accelerated electrons strongly increases with the decrease of plasma beta (for plasma beta of 0.0001 the fraction of accelerated electrons can be as large as 47%). (iii) In the collisionless regime IC wave dissipation length (that is defined as the distance over which the wave damps) variation with the driving frequency shows a deviation from the analytical MHD result, which we attribute to a possible frequency dependence of the effective resistivity. (iv) Effective anomalous resistivity, inferred from our numerical simulations, is at least four orders of magnitude larger than the classical Spitzer value.
Lessons on collisionless reconnection from quantum fluids
NASA Astrophysics Data System (ADS)
Narita, Yasuhito; Baumjohann, Wolfgang
2014-12-01
Magnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.
Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock
Hietala, H.; Vainio, R.; Laitinen, T. V.; Vaivads, A.; Andreeova, K.; Palmroth, M.; Pulkkinen, T. I.; Koskinen, H. E. J.; Lucek, E. A.; Reme, H.
2009-12-11
The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.
Driving Weibel-mediated collisionless shocks with NIF
NASA Astrophysics Data System (ADS)
Fiuza, Frederico; Spitkovsky, Anatoly; Ryutov, Dmitri; Ross, Steven; Huntington, Channing; Mori, Warren; Silva, Luis; Park, Hye-Sook; Remington, Bruce
2013-10-01
Collisionless shocks are ubiquitous in astrophysical plasmas and are known to be responsible for particle acceleration; however, the microphysics underlying shock formation and particle acceleration is not yet fully understood. High-power lasers are bringing the study of collisionless shocks into the realm of laboratory experiments. In particular, the National Ignition Facility allows for the generation of collisionless plasma flows that are hundreds of ion skin-depths long and provides ideal conditions for the study of Weibel-mediated shocks. We have performed detailed 2D and 3D particle-in-cell simulations with OSIRIS to explore the laboratory conditions associated with counter-streaming high-velocity plasma flows for realistic profiles. We have modeled the proton radiography of the interaction for self-consistent fields and determined the experimental signatures of the generation of Weibel B-fields and collisionless shocks. We will discuss the importance of modeling realistic ion to electron mass ratios and of taking into account Biermann battery B-fields. Our work identifies the conditions for the formation of collisionless shocks in laboratory, both in unmagnetized and magnetized scenarios, showing the possibility of observing for the first time Weibel-mediated shocks in near future experiments.
ICPP: Collisionless shock and supernova remnant simulation experiments on VULCAN.
NASA Astrophysics Data System (ADS)
Woolsey, Nigel C.
2000-10-01
The VULCAN laser at the Central Laser Facility is used for laboratory-based simulations of collisionless shocks. One of the most difficult aspects of collisionless shock behaviour, the role of the magnetic field, is to be tested directly against experiment. Preliminary experiments to generate strong magnetic fields using a laser-driven mm-scale Helmholtz coil, and the formation of collisionless colliding plasmas using two counter-streaming exploding foil plasmas will be discussed. We consider the scaling of the hydrodynamics and magnetic field of the these experiments to those in supernova remnants (SNR) impacting the interstellar medium (ISM). This is achieved by ensuring the experiment and the SNR-ISM exhibit similar values of key dimensionless parameters. Work supported in part by EPSRC, CLF Direct Access, CEC-ERB FMR XCT 980168, Euratom and the UK DTI.
In situ detection of collisionless reconnection in the Earth's magnetotail.
Oieroset, M; Phan, T D; Fujimoto, M; Lin, R P; Lepping, R P
2001-07-26
Magnetic reconnection is the process by which magnetic field lines of opposite polarity reconfigure to a lower-energy state, with the release of magnetic energy to the surroundings. Reconnection at the Earth's dayside magnetopause and in the magnetotail allows the solar wind into the magnetosphere. It begins in a small 'diffusion region', where a kink in the newly reconnected lines produces jets of plasma away from the region. Although plasma jets from reconnection have previously been reported, the physical processes that underlie jet formation have remained poorly understood because of the scarcity of in situ observations of the minuscule diffusion region. Theoretically, both resistive and collisionless processes can initiate reconnection, but which process dominates in the magnetosphere is still debated. Here we report the serendipitous encounter of the Wind spacecraft with an active reconnection diffusion region, in which are detected key processes predicted by models of collisionless reconnection. The data therefore demonstrate that collisionless reconnection occurs in the magnetotail.
Collisionless Reconnection and Electron Demagnetization
NASA Astrophysics Data System (ADS)
Scudder, J. D.
Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.
PARTICLE ACCELERATION DURING MAGNETOROTATIONAL INSTABILITY IN A COLLISIONLESS ACCRETION DISK
Hoshino, Masahiro
2013-08-20
Particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk was investigated by using a particle-in-cell simulation. We discuss the important role that magnetic reconnection plays not only on the saturation of MRI but also on the relativistic particle generation. The plasma pressure anisotropy of p > p{sub ||} induced by the action of MRI dynamo leads to rapid growth in magnetic reconnection, resulting in the fast generation of nonthermal particles with a hard power-law spectrum. This efficient particle acceleration mechanism involved in a collisionless accretion disk may be a possible model to explain the origin of high-energy particles observed around massive black holes.
NASA Technical Reports Server (NTRS)
Goodrich, C. C.; Scudder, J. D.
1984-01-01
The adiabatic energy gain of electrons in the stationary electric and magnetic field structure of collisionless shock waves was examined analytically in reference to conditions of the earth's bow shock. The study was performed to characterize the behavior of electrons interacting with the cross-shock potential. A normal incidence frame (NIF) was adopted in order to calculate the reversible energy change across a time stationary shock, and comparisons were made with predictions made by the de Hoffman-Teller (HT) model (1950). The electron energy gain, about 20-50 eV, is demonstrated to be consistent with a 200-500 eV potential jump in the bow shock quasi-perpendicular geometry. The electrons lose energy working against the solar wind motional electric field. The reversible energy process is close to that modeled by HT, which predicts that the motional electric field vanishes and the electron energy gain from the electric potential is equated to the ion energy loss to the potential.
Haque, Q.
2015-08-15
The plasma density non-uniformity gives rise to the coupling of transverse magnetic electron drift vortex (MEDV) mode with the longitudinal perturbations in dissipative and non-dissipative electron plasmas. This coupling produces partially transverse and partially longitudinal low frequency instabilities in classical un-magnetized laser plasmas. The MEDV mode couples with the ion acoustic wave, when the ion dynamics is also included. Both the modes have frequencies of the same order of magnitude and couple to give rise to electromagnetic instabilities in un-magnetized plasmas.
Collisionless shock experiments with lasers and observation of Weibel instabilitiesa)
NASA Astrophysics Data System (ADS)
Park, H.-S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.
2015-05-01
Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ˜1% [C. M. Huntington et al., "Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows," Nat. Phys. 11, 173-176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.
Collisionless shock experiments with lasers and observation of Weibel instabilities
Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.
2015-05-13
Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.
Exploring the nature of collisionless shocks under laboratory conditions
Stockem, A.; Fiuza, F.; Bret, A.; Fonseca, R. A.; Silva, L. O.
2014-01-01
Collisionless shocks are pervasive in astrophysics and they are critical to understand cosmic ray acceleration. Laboratory experiments with intense lasers are now opening the way to explore and characterise the underlying microphysics, which determine the acceleration process of collisionless shocks. We determine the shock character – electrostatic or electromagnetic – based on the stability of electrostatic shocks to transverse electromagnetic fluctuations as a function of the electron temperature and flow velocity of the plasma components, and we compare the analytical model with particle-in-cell simulations. By making the connection with the laser parameters driving the plasma flows, we demonstrate that shocks with different and distinct underlying microphysics can be explored in the laboratory with state-of-the-art laser systems. PMID:24488212
Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities
Bret, A.; Stockem, A.; Fiuza, F.; Silva, L. O.; Narayan, R.
2013-04-15
Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.
Collisionless shock experiments with lasers and observation of Weibel instabilities
Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; et al
2015-05-13
Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagneticmore » in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.« less
Evidence for Collisionless Magnetic Reconnection at Mars
NASA Astrophysics Data System (ADS)
Brain, D.; Eastwood, J.; Halekas, J.; Drake, J.; Phan, T.; Oieroset, M.; Mitchell, D.; Lin, R.; Acuna, M.
2007-12-01
Magnetic reconnection is a fundamental plasma process that enables the rapid conversion of magnetic to particle energy and is important in astrophysics as well as solar, space and planetary physics. Using data from the Mars Global Surveyor (MGS) spacecraft in combination with simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion that uniquely indicate the reconnection process. These are the first such in- situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars" recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.
Collisionless magnetic reconnection under anisotropic MHD approximation
NASA Astrophysics Data System (ADS)
Hirabayashi, Kota; Hoshino, Masahiro
We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{⊥}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{⊥})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.
The microphysics of collisionless shock waves
NASA Astrophysics Data System (ADS)
Marcowith, A.; Bret, A.; Bykov, A.; Dieckman, M. E.; O'C Drury, L.; Lembège, B.; Lemoine, M.; Morlino, G.; Murphy, G.; Pelletier, G.; Plotnikov, I.; Reville, B.; Riquelme, M.; Sironi, L.; Stockem Novo, A.
2016-04-01
Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.
The microphysics of collisionless shock waves.
Marcowith, A; Bret, A; Bykov, A; Dieckman, M E; Drury, L O'C; Lembège, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem
2016-04-01
Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics. PMID:27007555
Neoclassical Transport Caused by Collisionless Scattering across an Asymmetric Separatrix
Dubin, Daniel H. E.; Driscoll, C. F.; Tsidulko, Yu. A.
2010-10-29
Plasma loss due to apparatus asymmetries is a ubiquitous phenomenon in magnetic plasma confinement. When the plasma equilibrium has locally trapped particle populations partitioned by a separatrix from one another and from passing particles, the asymmetry transport is enhanced. The trapped and passing particle populations react differently to the asymmetries, leading to the standard 1/{nu} and {radical}({nu}) transport regimes of superbanana orbit theory as particles collisionally scatter from one orbit type to another. However, when the separatrix is itself asymmetric, particles can collisionlessly transit from trapped to passing and back, leading to enhanced transport.
NASA Astrophysics Data System (ADS)
Schamel, Hans; Eliasson, Bengt
2016-05-01
Quantum statistics and electron trapping have a decisive influence on the propagation characteristics of coherent stationary electrostatic waves. The description of these strictly nonlinear structures, which are of electron hole type and violate linear Vlasov theory due to the particle trapping at any excitation amplitude, is obtained by a correct reduction of the three-dimensional Fermi-Dirac distribution function to one dimension and by a proper incorporation of trapping. For small but finite amplitudes, the holes become of cnoidal wave type and the electron density is shown to be described by a ϕ ( x ) 1 / 2 rather than a ϕ ( x ) expansion, where ϕ ( x ) is the electrostatic potential. The general coefficients are presented for a degenerate plasma as well as the quantum statistical analogue to these steady state coherent structures, including the shape of ϕ ( x ) and the nonlinear dispersion relation, which describes their phase velocity.
Time-dependent closure relations for relativistic collisionless fluid equations
Bendib-Kalache, K.; Bendib, A.; El Hadj, K. Mohammed
2010-11-15
Linear fluid equations for relativistic and collisionless plasmas are derived. Closure relations for the fluid equations are analytically computed from the relativistic Vlasov equation in the Fourier space ({omega},k), where {omega} and k are the conjugate variables of time t and space x variables, respectively. The mathematical method used is based on the projection operator techniques and the continued fraction mathematical tools. The generalized heat flux and stress tensor are calculated for arbitrary parameter {omega}/kc where c is the speed of light, and for arbitrary relativistic parameter z=mc{sup 2}/T, where m is the particle rest mass and T, the plasma temperature in energy units.
Time-dependent closure relations for relativistic collisionless fluid equations.
Bendib-Kalache, K; Bendib, A; El Hadj, K Mohammed
2010-11-01
Linear fluid equations for relativistic and collisionless plasmas are derived. Closure relations for the fluid equations are analytically computed from the relativistic Vlasov equation in the Fourier space (ω,k), where ω and k are the conjugate variables of time t and space x variables, respectively. The mathematical method used is based on the projection operator techniques and the continued fraction mathematical tools. The generalized heat flux and stress tensor are calculated for arbitrary parameter ω/kc where c is the speed of light, and for arbitrary relativistic parameter z=mc²/T , where m is the particle rest mass and T, the plasma temperature in energy units.
Tether-Induced Airglow: Collisionless Effects
NASA Technical Reports Server (NTRS)
Mishin, E. V.; Khazanov, G. V.
2006-01-01
Martinez-Sanchez and Sanmartin [1997] showed that a bare conducting tether can be used as a source of an energetic electron beam. Interacting with the E region atmosphere, the beam should produce airglow thus making possible to deduce the neutral density on a continuous basis. Fujii et al. [2005] suggested that this idea be tested in a specially-designed sounding rocket experiment. We show that collisionless beam-plasma interactions (BPI) complement direct impact, leading to appreciable green-line (557.7 nm) emissions in the F region. In the E region, BPI develops near the entry in the valley, resulting in a narrow layer of strongly-elevated and airglow. Besides, neutralizing electric currents carried by ionospheric electrons in the valley can become unstable or even insufficient to compensate the beam current. Developing plasma waves inhibit neutralizing currents. In the extreme case, the beam might be locked in the valley (the 'virtual cathode'). In addition to optical observations, these effects can also be observed by radiophysical means.
Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks
Medvedev, Mikhail M.
2008-08-31
This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general.
Vlasov simulations of collisionless magnetic reconnection without background density
NASA Astrophysics Data System (ADS)
Schmitz, H.; Grauer, R.
2008-02-01
A standard starting point for the simulation of collisionless reconnection is the Harris equilibrium which is made up of a current sheet that separates two regions of opposing magnetic field. Magnetohydrodynamic simulations of collisionless reconnection usually include a homogeneous background density for reasons of numerical stability. While, in some cases, this is a realistic assumption, the background density may introduce new effects both due to the more involved structure of the distribution function or due to the fact that the Alfvèn speed remains finite far away from the current sheet. We present a fully kinetic Vlasov simulation of the perturbed Harris equilibrium using a Vlasov code. Parameters are chosen to match the Geospace Environment Modeling (GEM) Magnetic Reconnection Challenge but excluding the background density. This allows to compare with earlier simulations [Schmitz H, Grauer R. Kinetic Vlasov simulations of collisionless magnetic reconnection. Phys Plasmas 2006;13:092309] which include the background density. It is found that the absence of a background density causes the reconnection rate to be higher. On the other hand, the time until the onset of reconnection is hardly affected. Again the off diagonal elements of the pressure tensor are found to be important on the X-line but with modified importance for the individual terms.
Collisionless absorption in sharp-edged plasmas
Gibbon, P. ); Bell, A.R. )
1992-03-09
The absorption of subpicosecond, obliquely incident laser light is studied using a 11/2D particle-in-cell code. Density scale lengths from {ital L}/{lambda}=0.01 to 2 and laser irradiances between {ital I}{lambda}{sup 2}=10{sup 14} and 10{sup 18} W cm{sup {minus}2} {mu}m{sup 2} are considered. Vacuum heating'' (F. Brunel, Phys. Rev. Lett. 59, 52 (1987)) dominates over resonance absorption for scale lengths {ital L}/{lambda}{lt}0.1, and is most efficient when {ital v}{sub osc}/{ital c}{congruent}3.1({ital L}/{lambda}){sup 2}. Absorbed energy is carried mainly by a superhot'' electron population with {ital U}{sub hot}{similar to}({ital I}{lambda}{sup 2}){sup 1/3--1/2}.
Laboratory astrophysical collisionless shock experiments on Omega and NIF
NASA Astrophysics Data System (ADS)
Park, Hye-Sook; Ross, J. S.; Huntington, C. M.; Fiuza, F.; Ryutov, D.; Casey, D.; Drake, R. P.; Fiksel, G.; Froula, D.; Gregori, G.; Kugland, N. L.; Kuranz, C.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R.; Plechaty, C.; Remington, B.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Zylstra, A. B.
2016-03-01
We are performing scaled astrophysics experiments on Omega and on NIF. Laser driven counter-streaming interpenetrating supersonic plasma flows can be studied to understand astrophysical electromagnetic plasma phenomena in a controlled laboratory setting. In our Omega experiments, the counter-streaming flow plasma state is measured using Thomson scattering diagnostics, demonstrating the plasma flows are indeed super-sonic and in the collisionless regime. We observe a surprising additional electron and ion heating from ion drag force in the double flow experiments that are attributed to the ion drag force and electrostatic instabilities. [1] A proton probe is used to image the electric and magnetic fields. We observe unexpected large, stable and reproducible electromagnetic field structures that arise in the counter-streaming flows [2]. The Biermann battery magnetic field generated near the target plane, advected along the flows, and recompressed near the midplane explains the cause of such self-organizing field structures [3]. A D3He implosion proton probe image showed very clear filamentary structures; three-dimensional Particle-In-Cell simulations and simulated proton radiography images indicate that these filamentary structures are generated by Weibel instabilities and that the magnetization level (ratio of magnetic energy over kinetic energy in the system) is ∼0.01 [4]. These findings have very high astrophysical relevance and significant implications. We expect to observe true collisionless shock formation when we use >100 kJ laser energy on NIF.
The role of entropy in collisionless evolution
NASA Astrophysics Data System (ADS)
Barnes, Eric
2011-04-01
Understanding the path to mechanical equilibria for collisionless systems is a topic with a rich history. We are investigating the part that entropy plays in determining the outcome of collisionless evolution. I will discuss some previous work that lays a foundation for our current studies. With that framework in place, I will explain a modification to the entropy maximization procedure and compare the results to previous ideas. It is possible that entropy maxima are not achievable, and we argue that entropy production rates can influence collisionless system evolution. This work has been supported by NASA ATP grant NNX07AG86G.
Dispersion discontinuities of strong collisionless shocks
NASA Technical Reports Server (NTRS)
Coroniti, F. V.
1970-01-01
Linear fluid equations are used to estimate wave train properties of strong collisionless shocks. Fast shocks exhibit several dispersion changes with increasing Mach number. For perpendicular propagation into a finite-beta plasma, an ion cyclotron radius trailing wave train exists only for (M sub F)2 is smaller than 2. Oblique fast shocks have a leading ion inertia wave train if M sub A is smaller than root of M(+)/M(-) cos theta/2 and a trailing electron inertia train if M sub A is greater than root of M(+)/M(-) cos theta/2. If the downstream sound speed exceeds the flow speed, linear wave theory predicts a trailing ion acoustic structure which probably resides within the magnetic shock. For a turbulent shock model in which an effective electron-ion collision frequency exceeds the lower hybrid frequency, ions decouple from the magnetic field; the shock wave train now trails with electron inertia and electron gyroradius lengths. Comparisons of this turbulent model and observations on the earth's bow shock are made.
Collisionless shock experiments with lasers and observation of Weibel instabilities
Park, H.-S. Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V.; Drake, R. P.; Kuranz, C. C.; Froula, D. H.; Rosenberg, M.; Gregori, G.; Meinecke, J.; Koenig, M.; Kugland, N. L.; Lamb, D. Q.; Tzeferacos, P.; and others
2015-05-15
Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.
Symbiotic two-species contact process.
de Oliveira, Marcelo Martins; Dos Santos, Renato Vieira; Dickman, Ronald
2012-07-01
We study a contact process (CP) with two species that interact in a symbiotic manner. In our model, each site of a lattice may be vacant or host individuals of species A and/or B; multiple occupancy by the same species is prohibited. Symbiosis is represented by a reduced death rate μ<1 for individuals at sites with both species present. Otherwise, the dynamics is that of the basic CP, with creation (at vacant neighbor sites) at rate λ and death of (isolated) individuals at a rate of unity. Mean-field theory and Monte Carlo simulation show that the critical creation rate λ(c)(μ) is a decreasing function of μ, even though a single-species population must go extinct for λ<λ(c) (1), the critical point of the basic CP. Extensive simulations yield results for critical behavior that are compatible with the directed percolation (DP) universality class, but with unusually strong corrections to scaling. A field-theoretic argument supports the conclusion of DP critical behavior. We obtain similar results for a CP with creation at second-neighbor sites and enhanced survival at first neighbors in the form of an annihilation rate that decreases with the number of occupied first neighbors. PMID:23005382
Symbiotic two-species contact process
NASA Astrophysics Data System (ADS)
de Oliveira, Marcelo Martins; Dos Santos, Renato Vieira; Dickman, Ronald
2012-07-01
We study a contact process (CP) with two species that interact in a symbiotic manner. In our model, each site of a lattice may be vacant or host individuals of species A and/or B; multiple occupancy by the same species is prohibited. Symbiosis is represented by a reduced death rate μ<1 for individuals at sites with both species present. Otherwise, the dynamics is that of the basic CP, with creation (at vacant neighbor sites) at rate λ and death of (isolated) individuals at a rate of unity. Mean-field theory and Monte Carlo simulation show that the critical creation rate λc(μ) is a decreasing function of μ, even though a single-species population must go extinct for λ<λc(1), the critical point of the basic CP. Extensive simulations yield results for critical behavior that are compatible with the directed percolation (DP) universality class, but with unusually strong corrections to scaling. A field-theoretic argument supports the conclusion of DP critical behavior. We obtain similar results for a CP with creation at second-neighbor sites and enhanced survival at first neighbors in the form of an annihilation rate that decreases with the number of occupied first neighbors.
Substratum preference of two species of Xanthoparmelia.
Deduke, Chris; Piercey-Normore, Michele D
2015-09-01
The distribution of established saxicolous lichens has been previously studied but substratum preference and elemental composition has been relatively unexplored. The objectives of this study were to compare ascospore germination and growth for two species of Xanthoparmelia using media supplemented with pulverized rock and to explore photobiont selectivity relative to ecological guilds. Mature apothecia from X. cumberlandia and X. viriduloumbrina were subjected to five treatments, which include water agar supplemented with crushed granodiorite, basalt, mica schist, dolostone, and malt yeast agar as the control. The algal actin gene was sequenced and the closest algal matches were retrieved from GenBank and analysed to produce a haplotype network. X. cumberlandia exhibited substratum preference for the mica schist treatment, while X. viriduloumbrina grew better on granodiorite and malt yeast agar relative to dolostone. Ascospore germination for both species failed to progress beyond the initial swelling and protrusion stage on the dolostone treatment. The actin gene sequences for the algae were most similar to those of Trebouxia jamesii. The rock substrates did not correspond with the photobiont haplotypes, which does not support the ecological guild hypothesis. This study provided insights into substratum preference and the suitability of the substratum for algal selection. PMID:26321730
Substratum preference of two species of Xanthoparmelia.
Deduke, Chris; Piercey-Normore, Michele D
2015-09-01
The distribution of established saxicolous lichens has been previously studied but substratum preference and elemental composition has been relatively unexplored. The objectives of this study were to compare ascospore germination and growth for two species of Xanthoparmelia using media supplemented with pulverized rock and to explore photobiont selectivity relative to ecological guilds. Mature apothecia from X. cumberlandia and X. viriduloumbrina were subjected to five treatments, which include water agar supplemented with crushed granodiorite, basalt, mica schist, dolostone, and malt yeast agar as the control. The algal actin gene was sequenced and the closest algal matches were retrieved from GenBank and analysed to produce a haplotype network. X. cumberlandia exhibited substratum preference for the mica schist treatment, while X. viriduloumbrina grew better on granodiorite and malt yeast agar relative to dolostone. Ascospore germination for both species failed to progress beyond the initial swelling and protrusion stage on the dolostone treatment. The actin gene sequences for the algae were most similar to those of Trebouxia jamesii. The rock substrates did not correspond with the photobiont haplotypes, which does not support the ecological guild hypothesis. This study provided insights into substratum preference and the suitability of the substratum for algal selection.
Collisionless Reconnection with Weak Slow Shocks Under Anisotropic MHD Approximation
NASA Astrophysics Data System (ADS)
Hirabayashi, K.; Hoshino, M.
2014-12-01
Magnetic reconnection accompanied by a pair of slow-mode shock waves, known as Petschek's theory, has been widely studied as an efficient mechanism to convert magnetically stored energy to thermal and/or kinetic energy in plasmas. Satellite observations in the Earth's magnetotail, on the other hand, report that the detection of slow shocks is rare compared with the theory. As an important step to bridge the gap between the observational fact and the Petschek-type reconnection, we performed one- and two- dimensional collisionless magnetohydrodynamic (MHD) simulations of magnetic reconnection paying special attention to the effect of temperature anisotropy. In high-beta plasmas such as a plasma sheet in the magnetotail, it is expected that even weak temperature anisotropy can greatly modify the dynamics. We demonstrate that the slow shocks do exist in the reconnection layer even under the anisotropic temperature. The resultant shocks, however, are weaker than those in isotropic MHD in terms of plasma compression. In addition, the amount of magnetic energy released across the shock is extremely small, that is, the shock is no longer switch-off type. In spite of the weakness of the shocks, the reconnection rates measured by the inflow velocities are kept at the same level as the isotropic cases. Once the slow shock forms, the downstream plasma is heated in highly anisotropic manner, and the firehose-sense anisotropy affects the wave structure in the system. In particular, it is remarkable that the sequential order of propagation of slow shocks and rotational discontinuities reverses depending upon the magnitude of a superposed guide field. Our result is consistent with the rareness of the slow shock detection in the magnetotail, and implies that shocks do not necessarily play an important role. Furthermore, a variety of wave structure of a reconnection layer shown here will help interpretation of observational data in collisionless reconnection.
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.
NASA Astrophysics Data System (ADS)
Treumann, R. A.; Baumjohann, W.
2015-10-01
The present review concerns the relevance of collisionless reconnection in the astrophysical context. Emphasis is put on recent developments in theory obtained from collisionless numerical simulations in two and three dimensions. It is stressed that magnetic reconnection is a universal process of particular importance under collisionless conditions, when both collisional and anomalous dissipation are irrelevant. While collisional (resistive) reconnection is a slow, diffusive process, collisionless reconnection is spontaneous. On any astrophysical time scale, it is explosive. It sets on when electric current widths become comparable to the leptonic inertial length in the so-called lepton (electron/positron) "diffusion region", where leptons de-magnetise. Here, the magnetic field contacts its oppositely directed partner and annihilates. Spontaneous reconnection breaks the original magnetic symmetry, violently releases the stored free energy of the electric current, and causes plasma heating and particle acceleration. Ultimately, the released energy is provided by mechanical motion of either the two colliding magnetised plasmas that generate the current sheet or the internal turbulence cascading down to lepton-scale current filaments. Spontaneous reconnection in such extended current sheets that separate two colliding plasmas results in the generation of many reconnection sites (tearing modes) distributed over the current surface, each consisting of lepton exhausts and jets which are separated by plasmoids. Volume-filling factors of reconnection sites are estimated to be as large as {<}10^{-5} per current sheet. Lepton currents inside exhausts may be strong enough to excite Buneman and, for large thermal pressure anisotropy, also Weibel instabilities. They bifurcate and break off into many small-scale current filaments and magnetic flux ropes exhibiting turbulent magnetic power spectra of very flat power-law shape W_b∝ k^{-α } in wavenumber k with power becoming as
Self-Regulation of Solar Coronal Heating Process via the Collisionless Reconnection Condition
Uzdensky, Dmitri A.
2007-12-31
I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nanoflares), evaporation episodes, and long periods of slow magnetic stress buildup and radiative cooling of the coronal plasma.
Self-regulation of solar coronal heating process via the collisionless reconnection condition.
Uzdensky, Dmitri A
2007-12-31
I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nanoflares), evaporation episodes, and long periods of slow magnetic stress buildup and radiative cooling of the coronal plasma. PMID:18233563
Collisionless “thermalization” in the sheath of an argon discharge
Coulette, David Manfredi, Giovanni
2015-04-15
We performed kinetic Vlasov simulations of the plasma-wall transition for a low-pressure argon discharge without external magnetic fields, using the same plasma parameters as in the experiments of Claire et al. [Phys. Plasmas 13, 062103 (2006)]. Experimentally, it was found that the ion velocity distribution function is highly asymmetric in the presheath, but, surprisingly, becomes again close to Maxwellian inside the sheath. Here, we show that this “thermalization” can be explained by purely collisionless effects that are akin to the velocity bunching phenomenon observed in charged particles beams. Such collisionless thermalization is also observed in the presheath region close to the sheath entrance, although it is much weaker there and in practice probably swamped by collisional processes (standard or enhanced by instabilities)
Physics of collisionless shocks: theory and simulation
NASA Astrophysics Data System (ADS)
Stockem Novo, A.; Bret, A.; Fonseca, R. A.; Silva, L. O.
2016-01-01
Collisionless shocks occur in various fields of physics. In the context of space and astrophysics they have been investigated for many decades. However, a thorough understanding of shock formation and particle acceleration is still missing. Collisionless shocks can be distinguished into electromagnetic and electrostatic shocks. Electromagnetic shocks are of importance mainly in astrophysical environments and they are mediated by the Weibel or filamentation instability. In such shocks, charged particles gain energy by diffusive shock acceleration. Electrostatic shocks are characterized by a strong electrostatic field, which leads to electron trapping. Ions are accelerated by reflection from the electrostatic potential. Shock formation and particle acceleration will be discussed in theory and simulations.
A new fast reconnection model in a collisionless regime
Tsiklauri, David
2008-11-15
Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm's law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnetic reconnection in a collisionless regime is formulated. The model is general, resembling its collisional Sweet-Parker analog in that it is not specific to any initial configuration, e.g., Harris-type tearing unstable current sheet, X-point collapse or otherwise. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate [M{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/(r{sub L,e}L)] than Sweet-Parker's classical one (M{sub sp}=S{sup -1/2}). The width of the diffusion region (current sheet) in the collisionless regime is found to be {delta}{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/r{sub L,e}, which is independent of the global reconnection scale L and is only prescribed by microphysics (electron inertial length, c/{omega}{sub pe}, and electron Larmor radius, r{sub L,e}). Amongst other issues, the fastness of the reconnection rate alleviates, e.g., the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be a few minutes, as opposed to Sweet-Parker's equivalent value of less than a day. The new theoretical reconnection rate is compared to the Magnetic Reconnection Experiment device experimental data by Yamada et al. [Phys. Plasmas 13, 052119 (2006)] and Ji et al. [Geophys. Res. Lett. 35, 13106 (2008)], and a good agreement is obtained.
Model and particle-in-cell simulation of ion energy distribution in collisionless sheath
Zhou, Zhuwen; Kong, Bo; Luo, Yuee; Chen, Deliang; Wang, Yuansheng
2015-06-15
In this paper, we propose a self-consistent theoretical model, which is described by the ion energy distributions (IEDs) in collisionless sheaths, and the analytical results for different combined dc/radio frequency (rf) capacitive coupled plasma discharge cases, including sheath voltage errors analysis, are compared with the results of numerical simulations using a one-dimensional plane-parallel particle-in-cell (PIC) simulation. The IEDs in collisionless sheaths are performed on combination of dc/rf voltage sources electrodes discharge using argon as the process gas. The incident ions on the grounded electrode are separated, according to their different radio frequencies, and dc voltages on a separated electrode, the IEDs, and widths of energy in sheath and the plasma sheath thickness are discussed. The IEDs, the IED widths, and sheath voltages by the theoretical model are investigated and show good agreement with PIC simulations.
Hewett, D.W.; Francis, G.E.; Max, C.E.
1990-06-29
Evidence from magnetospheric and solar flare research supports the belief that collisionless magnetic reconnection can proceed on the Alfven-wave crossing timescale. Reconnection behavior that occurs this rapidly in collisionless plasmas is not well understood because underlying mechanisms depend on the details of the ion and electron distributions in the vicinity of the emerging X-points. We use the direct implicit Particle-In-Cell (PIC) code AVANTI to study the details of these distributions as they evolve in the self-consistent E and B fields of magnetic reconnection. We first consider a simple neutral sheet model. We observe rapid movement of the current-carrying electrons away from the emerging X-point. Later in time an oscillation of the trapped magnetic flux is found, superimposed upon continued linear growth due to plasma inflow at the ion sound speed. The addition of a current-aligned and a normal B field widen the scope of our studies.
Two-fluid regimes of the resistive and collisionless tearing instability
Hosseinpour, M.; Vekstein, G.; Bian, N.
2009-01-15
The two-fluid (electrons and ions) plasma description is used to investigate spontaneous magnetic reconnection (tearing instability) in a sheared force-free magnetic configuration. The study includes both collisional (resistive) and collisionless (electron inertia) reconnection mechanisms. Together with the Hall effect, this yields various instability regimes, which can be identified by the magnitude of the four nondimensional parameters: Lundquist number S>>1, electron/ion mass ratio {mu}{identical_to}m{sub e}/m{sub i}<<1, plasma {beta}, and the scaled ion inertial skin-depth d{sub i}=c/({omega}{sub pi}l), with l being the shear length of the magnetic field. The role of the electron gyroviscosity in the collisionless case is also clarified.
Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons
Swamy, Aditya K.; Ganesh, R.; Brunner, S.; Vaclavik, J.; Villard, L.
2015-07-15
Collisionless microtearing modes have recently been found linearly unstable in sharp temperature gradient regions of large aspect ratio tokamaks. The magnetic drift resonance of passing electrons has been found to be sufficient to destabilise these modes above a threshold plasma β. A global gyrokinetic study, including both passing electrons as well as trapped electrons, shows that the non-adiabatic contribution of the trapped electrons provides a resonant destabilization, especially at large toroidal mode numbers, for a given aspect ratio. The global 2D mode structures show important changes to the destabilising electrostatic potential. The β threshold for the onset of the instability is found to be generally downshifted by the inclusion of trapped electrons. A scan in the aspect ratio of the tokamak configuration, from medium to large but finite values, clearly indicates a significant destabilizing contribution from trapped electrons at small aspect ratio, with a diminishing role at larger aspect ratios.
Effects of electron inertia in collisionless magnetic reconnection
Andrés, Nahuel Gómez, Daniel; Martin, Luis; Dmitruk, Pablo
2014-07-15
We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.
NASA Astrophysics Data System (ADS)
Olson, J.; Egedal, J.; Greess, S.; Myers, R.; Clark, M.; Endrizzi, D.; Flanagan, K.; Milhone, J.; Peterson, E.; Wallace, J.; Weisberg, D.; Forest, C. B.
2016-06-01
The spontaneous formation of magnetic islands is observed in driven, antiparallel magnetic reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that the plasmoid instability is active at the electron scale inside the ion diffusion region in a low collisional regime. The experiments show the island formation occurs at a smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding of magnetic islands emphasizes their importance to reconnection in naturally occurring 3D plasmas.
Two species of myxomycetes causing slime mold of sweet potato.
Kim, Wan Gyu; Lee, Sang Yeob; Cho, Weon Dae
2007-06-01
Specimens collected from sweet potato plants with slime mold symptoms in fields in Daejeon, Korea were examined. Two species of Myxomycetes, Fuligo septica and Stemonitis herbatica were identified based on their morphological characteristics. This is the first report that the two species of Myxomycetes cause slime mold of sweet potato in Korea.
Expansion techniques for collisionless stellar dynamical simulations
NASA Astrophysics Data System (ADS)
Meiron, Yohai
2016-02-01
We present ETICS, a collisionless N-body code based on two kinds of series expansions of the Poisson equation, implemented for graphics processing units (GPUs). The code is publicly available and can be used as a standalone program or as a library (an AMUSE plugin is included). One of the two expansion methods available is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a ``pure'' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms.
Ion acoustic waves in a multi-ion plasma.
NASA Technical Reports Server (NTRS)
Fried, B. D.; White, R. B.; Samec, T. K.
1971-01-01
An exact treatment of the multispecies ion acoustic dispersion relation is given for an argon/helium plasma. Phase velocity and damping are obtained as a function of ion-electron temperature ratio and relative densities of the two species. There are two important modes in the plasma, with quite different phase velocities, which are referred to as principal heavy ion mode and principal light ion mode. Which of these is dominant depends on the relative densities of the two components, but, in general, the light ion mode becomes important for surprisingly small light ion contamination. Approximate analytic expressions are derived from damping rates and phase velocities and their domains of validity are investigated. Relevance of the results for the investigation of collisionless shocks is discussed.
Igor D. Kaganovich; Oleg V. Polomarov; Constantine E. Theodosiou
2004-01-30
In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for the nonuniform plasma density profile for computing the current density profile and the EEDF is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the potential well and the external radio-frequency electric field is investigated. It is shown that a nonlinear and self-consistent treatment is necessary for the correct description of collisionless heating.
Collisionless spectral-kinetic Simulation of the Multipole Resonance Probe
NASA Astrophysics Data System (ADS)
Dobrygin, Wladislaw; Szeremley, Daniel; Schilling, Christian; Oberrath, Jens; Eremin, Denis; Mussenbrock, Thomas; Brinkmann, Ralf Peter
2012-10-01
Plasma resonance spectroscopy is a well established plasma diagnostic method realized in several designs. One of these designs is the multipole resonance probe (MRP). In its idealized - geometrically simplified - version it consists of two dielectrically shielded, hemispherical electrodes to which an RF signal is applied. A numerical tool is under development, which is capable of simulating the dynamics of the plasma surrounding the MRP in electrostatic approximation. In the simulation the potential is separeted in an inner and a vacuum potential. The inner potential is influenced by the charged partilces and is calculated by a specialized Poisson solver. The vacuum potential fulfills Laplace's equetion and consists of the applied voltage of the probe as boundary condition. Both potentials are expanded in spherical harmonics. For a practical particle pusher implementation, the expansion must be appropriately truncated. Compared to a PIC simulation a grid is unnecessary to calculate the force on the particles. This work purpose is a collisionless kinetic simulation, which can be used to investigate kinetic effects on the resonance behavior of the MRP.[4pt] [1] M. Lapke et al., Appl. Phys. Lett. 93, 2008, 051502.
Landau, Case, van Kampen and Collisionless Fluid Closures
NASA Astrophysics Data System (ADS)
Joseph, Ilon
2015-11-01
Landau damping represents a fundamental paradox within plasma physics. The equations of motion of classical particles and fields are symmetric under time-reversal; yet, the open system formed by integration over velocity space is not invariant and damping results from phase-mixing. Here, it is shown that the Case-van Kampen theorem can be extended to magnetized plasmas: the linear eigenfunctions provide a complete representation of the particle distribution function and exponentially damped and growing eigenmodes must appear in pairs. The numerical Case-van Kampen transformation can performed efficiently in Fourier velocity space and allows fast timescales in the evolution of the system to be treated using exponential integration. On the other hand, fluid moments require integration over velocity space, and, thus, representation of Landau damping requires explicit introduction of the arrow of time through a collisionless damping operator. This operator captures linear phenomena at the cost of damping nonlinear phenomena such as the plasma echo. Numerical comparisons of these two rather different representations will be presented. LLNL-ABS-674917 prepared by LLNL under Contract DE-AC52-07NA27344.
Hamiltonian derivation of a gyrofluid model for collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Tassi, E.
2014-11-01
We consider a simple electromagnetic gyrokinetic model for collisionless plasmas and show that it possesses a Hamiltonian structure. Subsequently, from this model we derive a two-moment gyrofluid model by means of a procedure which guarantees that the resulting gyrofluid model is also Hamiltonian. The first step in the derivation consists of imposing a generic fluid closure in the Poisson bracket of the gyrokinetic model, after expressing such bracket in terms of the gyrofluid moments. The constraint of the Jacobi identity, which every Poisson bracket has to satisfy, selects then what closures can lead to a Hamiltonian gyrofluid system. For the case at hand, it turns out that the only closures (not involving integro/differential operators or an explicit dependence on the spatial coordinates) that lead to a valid Poisson bracket are those for which the second order parallel moment, independently for each species, is proportional to the zero order moment. In particular, if one chooses an isothermal closure based on the equilibrium temperatures and derives accordingly the Hamiltonian of the system from the Hamiltonian of the parent gyrokinetic model, one recovers a known Hamiltonian gyrofluid model for collisionless reconnection. The proposed procedure, in addition to yield a gyrofluid model which automatically conserves the total energy, provides also, through the resulting Poisson bracket, a way to derive further conservation laws of the gyrofluid model, associated with the so called Casimir invariants. We show that a relation exists between Casimir invariants of the gyrofluid model and those of the gyrokinetic parent model. The application of such Hamiltonian derivation procedure to this two-moment gyrofluid model is a first step toward its application to more realistic, higher-order fluid or gyrofluid models for tokamaks. It also extends to the electromagnetic gyrokinetic case, recent applications of the same procedure to Vlasov and drift- kinetic systems.
Generation and amplification of magnetic fields in laser-driven collisionless shocks
NASA Astrophysics Data System (ADS)
Fiuza, Frederico; Ryutov, Dmitri; Sptikovsky, Anatoly; Huntington, Channing; Ross, Steven; Silva, Luis; Mori, Warren; Remington, Bruce; Park, Hye-Sook
2014-10-01
Collisionless shocks are ubiquitous in astrophysical plasmas and are believed to play an important role in magnetic field amplification; however, the magnetic field dynamics in shocks is still poorly understood as in situ measurements are not available. Recent developments in high-power lasers are bringing the study of collisionless shocks into the realm of laboratory experiments. We have performed detailed 2D and 3D particle-in-cell simulations to explore the generation of collisionless shocks for laboratory conditions associated with counter-streaming high-velocity plasma flows. We capture all the relevant physics, which range from the generation of Biermann battery fields at the laser-foil region, to the micro-instabilities associated with the counter-streaming flows, and to the generation of turbulence at the shock. We show the generation of strong (>1% of equipartition) magnetic fields mediated by the Weibel instability and the conversion from well-defined filaments to magnetic turbulence as the shock is formed. We identify the conditions required to observe this magnetic field dynamics in shocks for the first time in the upcoming experiments at the National Ignition Facility.
The Fast Collisionless Reconnection Condition and the Self-Organization of Solar Coronal Heating
Uzdensky, D. A.
2007-12-20
I propose that solar coronal heating is a self-regulating process that keeps the coronal plasma roughly marginally collisionless. The proposed self-regulating mechanism is based on the interplay of two effects. First, plasma density controls coronal energy release via the transition between the slow collisional Sweet-Parker regime and the fast collisionless reconnection regime. This transition takes place when the Sweet-Parker layer becomes thinner than the characteristic collisionless reconnection scale. I present a simple criterion for this transition in terms of the upstream plasma density (n_{e}), the reconnecting (B_{0}) and guide (B_{z}) magnetic field components, and the global length (L) of the reconnection layer: L ≲ 6 × 10^{9} cm (n_{e}/1010 cm^{-3})^{-3}(B_{0}/30G)^{4}(B_{0}/B_{z})^{2}. Next, coronal energy release by reconnection raises the ambient plasma density via chromospheric evaporation, and this in turn temporarily inhibits subsequent reconnection involving the newly reconnected loops. Over time, however, radiative cooling gradually lowers the density again below the critical value and fast reconnection again becomes possible. As a result, the density is highly inhomogeneous and intermittent but, statistically, does not deviate strongly from the critical value, which is comparable with the observed coronal density. Thus, in the long run the coronal heating process can be represented by repeating cycles that consist of fast reconnection events (i.e., nanoflares), followed by rapid evaporation episodes, followed by relatively long periods ( 1 hr) during which magnetic stresses build up and the plasma simultaneously cools down and precipitates.
Collisionless shocks in the heliosphere: A tutorial review
NASA Technical Reports Server (NTRS)
Stone, Robert G. (Editor); Tsurutani, Bruce T. (Editor)
1985-01-01
An update is presented on current knowledge of collisionless shocks in the heliosphere. The individual papers address: a quarter century of collisionless shock research, some macroscopic properties of shock waves in the heliosphere, microinstabilities and anomalous transport, and acceleration of energetic particles.
New Expression for Collisionless Magnetic Reconnection Rate
NASA Technical Reports Server (NTRS)
Klimas, Alexander J.
2014-01-01
For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, a new expression for the reconnection rate in the electron diffusion region is introduced. It is shown that this expression can be derived in just a few simple steps from a physically intuitive starting point; the derivation is given in its entirety and the validity of each step is confirmed. The predictions of this expression are compared to the results of several long-duration, open-boundary PIC reconnection simulations to demonstrate excellent agreement.
Evidence for collisionless magnetic reconnection at Mars
NASA Astrophysics Data System (ADS)
Eastwood, J. P.; Brain, D. A.; Halekas, J. S.; Drake, J. F.; Phan, T. D.; Øieroset, M.; Mitchell, D. L.; Lin, R. P.; Acuña, M.
2008-01-01
Using data from Mars Global Surveyor (MGS) in combination with Particle-In-Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion - the Hall magnetic field - that uniquely indicate the reconnection process. These are the first such in-situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars' recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.
Cascaded proton acceleration by collisionless electrostatic shock
NASA Astrophysics Data System (ADS)
Xu, T. J.; Shen, B. F.; Zhang, X. M.; Yi, L. Q.; Wang, W. P.; Zhang, L. G.; Xu, J. C.; Zhao, X. Y.; Shi, Y.; Liu, C.; Pei, Z. K.
2015-07-01
A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.
Cascaded proton acceleration by collisionless electrostatic shock
Xu, T. J.; Shen, B. F. E-mail: zhxm@siom.ac.cn; Zhang, X. M. E-mail: zhxm@siom.ac.cn; Yi, L. Q.; Wang, W. P.; Zhang, L. G.; Xu, J. C.; Zhao, X. Y.; Shi, Y.; Liu, C.; Pei, Z. K.
2015-07-15
A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.
New expression for collisionless magnetic reconnection rate
Klimas, Alex
2015-04-15
For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, new expressions for the reconnection rate in the electron diffusion region are introduced. It is shown that these expressions can be derived in just a few simple steps from a physically intuitive starting point; the derivations are given in their entirety, and the validity of each step is confirmed. The predictions of these expressions are compared to the results of several long-duration, open-boundary particle-in-cell reconnection simulations to demonstrate excellent agreement.
Improved Boundary Model for Particle Simulation of Collisionless Driven Reconnection
NASA Astrophysics Data System (ADS)
Ohtani, H.; Horiuchi, R.
2006-10-01
To clarify the relationship between particle kinetic effects and anomalous resistivity due to plasma instabilities in collisionless driven reconnection, we develop a three-dimensional Particle Simulation code for Magnetic reconnection in an Open system (PASMO). Recently, we have improved a model of upstream boundary to satisfy sufficiently the frozen-in condition both for ions and electrons. From the condition, plasma inflow is driven by ExB drift due to a driving electric field. In the previous model, particles are supplied into the system each time step, based on the particle flux through upstream boundary. The number density changes in proportion to magnetic field. In the improved model, particles in a cell near upstream boundary are newly loaded so as to satisfy shifted Maxwellian rigorously every time step. Using this model, the frozen-in condition is satisfied near the boundary both for electrons and ions. We will discuss the relationship between excitation of instability and mechanism of magnetic reconnection in the meeting.
Collisionless inter-species energy transfer and turbulent heating in drift wave turbulence
Zhao, L.; Diamond, P. H.
2012-08-15
We reconsider the classic problems of calculating 'turbulent heating' and collisionless inter-species transfer of energy in drift wave turbulence. These issues are of interest for low collisionality, electron heated plasmas, such as ITER, where collisionless energy transfer from electrons to ions is likely to be significant. From the wave Poynting theorem at steady state, a volume integral over an annulus r{sub 1}
Multiscale dynamics based on kinetic simulation of collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Fujimoto, Keizo; Takamoto, Makoto
2016-07-01
Magnetic reconnection is a natural energy converter which allows explosive energy release of the magnetic field energy into plasma kinetic energy. The reconnection processes inherently involve multi-scale process. The breaking of the field lines takes place predominantly in a small region called the diffusion region formed near the x-line, while the fast plasma jets resulting from reconnection extend to a distance far beyond the ion kinetic scales from the x-line. There has been a significant gap in understanding of macro-scale and micro-scale processes. The macro-scale model of reconnection has been developed using the magnetohydrodynamics (MHD) equations, while the micro-scale processes around the x-line have been based on kinetic equations including the ion and electron inertia. The problem is that these two kinds of model have significant discrepancies. It has been believed without any guarantee that the microscopic model near the x-line would connect to the macroscopic model far downstream of the x-line. In order to bridge the gap between the macro and micro-scale processes, we have performed large-scale particle-in-cell simulations with the adaptive mesh refinement. The simulation results suggest that the microscopic processes around the x-line do not connect to the previous MHD model even in the region far downstream of the x-line. The slow mode shocks and the associated plasma acceleration do not appear at the exhaust boundary of kinetic reconnection. Instead, the ions are accelerated due to the Speiser motion in the current layer extending to a distance beyond the kinetic scales. The different acceleration mechanisms between the ions and electrons lead to the Hall current system in broad area of the exhaust. Therefore, the previous MHD model could be inappropriate for collisionless magnetic reconnection. Ref. K. Fujimoto & M. Takamoto, Phys. Plasmas, 23, 012903 (2016).
The collisionless magnetoviscous-thermal instability
Islam, Tanim
2014-05-20
It is likely that nearly all central galactic massive and supermassive black holes are nonradiative: their accretion luminosities are orders of magnitude below what can be explained by efficient black hole accretion within their ambient environments. These objects, of which Sagittarius A* is the best-known example, are also dilute (mildly collisional to highly collisionless) and optically thin. In order for accretion to occur, magnetohydrodynamic (MHD) instabilities must develop that not only transport angular momentum, but also gravitational energy generated through matter infall, outward. A class of new magnetohydrodynamical fluid instabilities—the magnetoviscous-thermal instability (MVTI)—was found to transport angular momentum and energy along magnetic field lines through large (fluid) viscosities and thermal conductivities. This paper describes the analog to the MVTI, the collisionless MVTI (CMVTI), that similarly transports energy and angular momentum outward, expected to be important in describing the flow properties of hot, dilute, and radiatively inefficient accretion flows around black holes. We construct a local equilibrium for MHD stability analysis in this differentially rotating disk. We then find and characterize specific instabilities expected to be important in describing their flow properties, and show their qualitative similarities to instabilities derived using the fluid formalism. We conclude with further work needed in modeling this class of accretion flow.
Measure synchronization in a two-species bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Tian, Jing; Qiu, Haibo; Wang, Guanfang; Chen, Yong; Fu, Li-bin
2013-09-01
Measure synchronization (MS) in a two-species bosonic Josephson junction (BJJ) is studied based on semiclassical theory. Six different scenarios for MS, including two in the Josephson oscillation regime (the zero-phase mode) and four in the self-trapping regime (the π-phase mode), are clearly shown. Systematic investigations of the common features behind these different scenarios are performed. We show that the average energies of the two species merge at the MS transition point. The scaling of the power law near the MS transition is verified and the critical exponent is 1/2 for all of the different scenarios for MS. We also illustrate MS in a three-dimensional phase space; from this illustration, more detailed information on the dynamical process can be obtained. In particular, by analyzing the Poincaré sections with changing interspecies interactions, we find that the two-species BJJ exhibits separatrix crossing behavior at the MS transition point and such behavior depicts the general mechanism behind the different scenarios for the MS transitions. The new critical behavior found in a two-species BJJ is expected to be found in real systems of atomic Bose gases.
Measure synchronization in a two-species bosonic Josephson junction.
Tian, Jing; Qiu, Haibo; Wang, Guanfang; Chen, Yong; Fu, Li-Bin
2013-09-01
Measure synchronization (MS) in a two-species bosonic Josephson junction (BJJ) is studied based on semiclassical theory. Six different scenarios for MS, including two in the Josephson oscillation regime (the zero-phase mode) and four in the self-trapping regime (the π-phase mode), are clearly shown. Systematic investigations of the common features behind these different scenarios are performed. We show that the average energies of the two species merge at the MS transition point. The scaling of the power law near the MS transition is verified and the critical exponent is 1/2 for all of the different scenarios for MS. We also illustrate MS in a three-dimensional phase space; from this illustration, more detailed information on the dynamical process can be obtained. In particular, by analyzing the Poincaré sections with changing interspecies interactions, we find that the two-species BJJ exhibits separatrix crossing behavior at the MS transition point and such behavior depicts the general mechanism behind the different scenarios for the MS transitions. The new critical behavior found in a two-species BJJ is expected to be found in real systems of atomic Bose gases.
Phorid Flies in Alabama: A tale of two species
Technology Transfer Automated Retrieval System (TEKTRAN)
Two species of phorid fly have been released at 11 sites in Alabama and have been recovered from 9 sites. Pseudacteon tricuspis Borgmeier (Diptera: Phoridae) was released in South Alabama in populations of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), and Pseudacteon...
NASA Astrophysics Data System (ADS)
Dubin, D. H. E.
This chapter explores several aspects of the linear electrostatic normal modes of oscillation for a single-species non-neutral plasma in a Penning trap. Linearized fluid equations of motion are developed, assuming the plasma is cold but collisionless, which allow derivation of the cold plasma dielectric tensor and the electrostatic wave equation. Upper hybrid and magnetized plasma waves in an infinite uniform plasma are described. The effect of the plasma surface in a bounded plasma system is considered, and the properties of surface plasma waves are characterized. The normal modes of a cylindrical plasma column are discussed, and finally, modes of spheroidal plasmas, and finite temperature effects on the modes, are briefly described.
Riquelme, Mario A.; Quataert, Eliot; Sharma, Prateek; Spitkovsky, Anatoly E-mail: eliot@astro.berkeley.edu E-mail: anatoly@astro.princeton.edu
2012-08-10
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the disk is essentially collisionless. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell plasma simulations. We focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field, B, until the Alfven velocity, v{sub A} , is comparable to the speed of light, c (independent of the initial value of v{sub A} /c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the pressure perpendicular to B being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume-averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emission-from the radio to the gamma-rays-of systems such as Sgr A*.
Theory of a cylindrical probe in a collisionless magnetoplasma
NASA Technical Reports Server (NTRS)
Laframboise, J. G.; Rubinstein, J.
1976-01-01
A theory is presented for a cylindrical electrostatic probe in a collisionless plasma in the case where the probe axis is inclined at an angle to a uniform magnetic field. The theory is applicable to electron collection, and under more restrictive conditions, to ion collection. For a probe at space potential, the theory is exact in the limit where probe radius is much less than Debye length. At attracting probe potentials, the theory yields an upper bound and an adiabatic limit for current collection. At repelling probe potentials, it provides a lower bound. The theory is valid if the ratios of probe radius to Debye length and probe radius to mean gyroradius are not simultaneously large enough to produce extrema in the probe sheath potential. The numerical current calculations are based on the approximation that particle orbits are helices near the probe, together with the use of kinetic theory to relate velocity distributions near the probe to those far from it. Probe characteristics are presented for inclination angles from 0 to 90 deg and for probe-radius mean-gyroradius ratios from 0.1 to infinity. For an angle of 0 deg, the end-effect current is calculated separately.
Electron nongyrotropy in the context of collisionless magnetic reconnection
Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria
2013-09-15
Collisionless magnetized plasmas have the tendency to isotropize their velocity distribution function around the local magnetic field direction, i.e., to be gyrotropic, unless some spatial and/or temporal fluctuations develop at the particle gyroscales. Electron gyroscale inhomogeneities are well known to develop during the magnetic reconnection process. Nongyrotropic electron velocity distribution functions have been observed to play a key role in the dissipative process breaking the field line connectivity. In this paper, we present a new method to quantify the deviation of a particle population from gyrotropy. The method accounts for the full 3D shape of the distribution and its analytical formulation allows fast numerical computation. Regions associated with a significant degree of nongyrotropy are shown, as well as the kinetic origin of the nongyrotropy and the fluid signature it is associated with. Using the result of 2.5D Particle-In-Cell simulations of magnetic reconnection in symmetric and asymmetric configurations, it is found that neither the reconnection site nor the topological boundaries are generally associated with a maximized degree of nongyrotropy. Nongyrotropic regions do not correspond to a specific fluid behavior as equivalent nongyrotropy is found to extend over the electron dissipation region as well as in non-dissipative diamagnetic drift layers. The localization of highly nongyrotropic regions in numerical models and their correlation with other observable quantities can, however, improve the characterization of spatial structures explored by spacecraft missions.
COSMIC-RAY-INDUCED FILAMENTATION INSTABILITY IN COLLISIONLESS SHOCKS
Caprioli, D.; Spitkovsky, A.
2013-03-01
We used unprecedentedly large two-dimensional and three-dimensional hybrid (kinetic ions-fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.
Collisionless shock structures of Earth and other planets
NASA Technical Reports Server (NTRS)
Greenstadt, Eugene W.; Moses, Stewart L.
1993-01-01
This report summarizes the closing segment of our multi-spacecraft, multi-instrument study of collisionless shock structure. In this last year of our study, we have necessarily concentrated on subjects that limited time and remaining resources could be expected to bring to reasonable stopping points, if not full conclusions. Our attention has been focused therefore on matters that were either well underway when the year began or that could be expected to yield rapidly completed reports publishable quickly in abbreviated versions. Contemporary publication delays prevent any new initiatives from reaching the literature within the year in the best of circumstances. The topics that fell into these categories were detailed plasma wave (pw) phenomenology in slow shocks in the Earth's distant geomagnetic tail, instantaneous orientations of theta(sub Bn) in quasiparallel (Q(sub parallel)) shock structure, and a comprehensive overview of the relationship between structural ULF waves in the Qll shock environment and waves in the magnetosphere, i.e. geomagnetic ULF pulsations. The remainder of this report describes our freshly completed results, discusses two related investigations of pw waves in the foreshock and magnetosheath, and appends the abstracts of published papers and the texts of papers in press.
Kinetic Study of the Collisionless Expansion of Spherical Nanoplasmas
NASA Astrophysics Data System (ADS)
Peano, Fabio; Peinetti, Federico; Coppa, Gianni; Silva, Luis
2006-10-01
The collisionless expansion of spherical plasmas composed of cold ions and hot electrons is analyzed using a novel Lagrangian model [1], which allows a highly accurate, kinetic description of the radial motion of the ions and of the three-dimensional motion of nonrelativistic electrons (the validity of the model is checked both with 3D particle-in-cell simulations, performed with the OSIRIS framework [2], and using a new, ad-hoc developed particle method). The paradigmatic case of initially-Maxwellian electrons is investigated in detail for a wide range of initial conditions: simple relationships are deduced for the key expansion features [1], and a threshold in the electron energy is identified, beyond which the energy spectrum becomes monotonic and the Coulomb explosion regime is approached. Non-Maxwellian initial distributions of the electrons are also considered. [1] F. Peano et al., Phys. Rev. Lett. 96, 175002 (2006). [2] R.A. Fonseca et al., Lect. Notes Comp. Sci. 2331, 342 (Springer-Verlag, Heidelberg, 2002).
Collisionless Dynamics and the Cosmic Web
NASA Astrophysics Data System (ADS)
Hahn, Oliver
2016-10-01
I review the nature of three-dimensional collapse in the Zeldovich approximation, how it relates to the underlying nature of the three-dimensional Lagrangian manifold and naturally gives rise to a hierarchical structure formation scenario that progresses through collapse from voids to pancakes, filaments and then halos. I then discuss how variations of the Zeldovich approximation (based on the gravitational or the velocity potential) have been used to define classifications of the cosmic large-scale structure into dynamically distinct parts. Finally, I turn to recent efforts to devise new approaches relying on tessellations of the Lagrangian manifold to follow the fine-grained dynamics of the dark matter fluid into the highly non-linear regime and both extract the maximum amount of information from existing simulations as well as devise new simulation techniques for cold collisionless dynamics.
Charging-delay induced dust acoustic collisionless shock wave: Roles of negative ions
Ghosh, Samiran; Bharuthram, R.; Khan, Manoranjan; Gupta, M. R.
2006-11-15
The effects of charging-delay and negative ions on nonlinear dust acoustic waves are investigated. It has been found that the charging-delay induced anomalous dissipation causes generation of dust acoustic collisionless shock waves in an electronegative dusty plasma. The small but finite amplitude wave is governed by a Korteweg-de Vries Burger equation in which the Burger term arises due to the charging-delay. Numerical investigations reveal that the charging-delay induced dissipation and shock strength decreases (increases) with the increase of negative ion concentration (temperature)
NASA Technical Reports Server (NTRS)
Collins, William
1989-01-01
The dispersion equation of Barnes (1966) is used to study the dissipation of asymptotic wave packets generated by localized periodic sources. The solutions of the equation are linear waves, damped by Landau and transit-time processes, in a collisionless warm plasma. For the case of an ideal MHD system, most of the waves emitted from a source are shown to cancel asympotically through destructive interference. The modes transporting significant flux to asymptotic distances are found to be Alfven waves and fast waves with theta (the angle between the magnetic field and the characteristics of the far-field waves) of about 0 and about pi/2.
NASA Astrophysics Data System (ADS)
Moritaka, Toseo; Sakawa, Youichi; Kuramitsu, Yasuhiro; Morita, Taichi; Yamaura, Yuta; Ishikawa, Taishi; Takabe, Hideaki
2016-03-01
Collisionless shocks mediated by Weibel instability are attracting attention for their relevance to experimental demonstrations of astrophysical shocks in high-intensity laser facilities. The three dimensional structure of Weibel-mediated shocks is investigated through a fully kinetic particle-in-cell simulation. The structures obtained are characterized by the following features: (i) helical magnetic field lines elongated in the direction upstream of the shock region, (ii) high and low density filaments inside the helical field lines. These structures originate from the interaction between counter-streaming plasma flow and magnetic vortexes caused by Weibel instability, and potentially affect the shock formation mechanism.
Effects of Noise in Symmetric Two-Species Competition
NASA Astrophysics Data System (ADS)
Vilar, José M. G.; Solé, Ricard V.
1998-05-01
We have analyzed the interplay between noise and periodic modulations in a classical Lotka-Volterra model of two-species competition. We have found that the consideration of noise changes drastically the behavior of the system and leads to new situations which have no counterpart in the deterministic case. Among others, noise is responsible for temporal oscillations, spatial patterns, and the enhancement of the response of the system via stochastic resonance.
The Saturnian Environment as a Unique Laboratory for Collisionless Shock Waves
NASA Astrophysics Data System (ADS)
Sulaiman, Ali; Masters, Adam; Dougherty, Michele; Burgess, David; Fujimoto, Masaki; Hospodarsky, George
2016-04-01
Collisionless shock waves are ubiquitous in the universe and fundamental to understanding the nature of collisionless plasmas. The interplay between particles (ions and electrons) and fields (electromagnetic) introduces a variety of both physical and geometrical parameters such as Mach numbers (e.g. MA, Mf), β, and θBn. These vary drastically from terrestrial to astrophysical regimes resulting in radically different characteristics of shocks. This poses two complexities. Firstly, separating the influences of these parameters on physical mechanisms such as energy dissipation. Secondly, correlating observations of shock waves over a wide range of each parameter, enough to span across different regimes. Investigating the latter has been restricted since the majority of studies on shocks at exotic regimes (such as supernova remnants) have been achieved either remotely or via simulations, but rarely by means of in-situ observations. It is not clear what happens in the higher MA regime. Here we show the parameter space of MA for all bow shock crossings from 2004-2012 as measured by the Cassini spacecraft. We found that the Saturnian bow shock exhibits characteristics akin to both terrestrial and astrophysical regimes (MA of order 100), which is principally controlled by the upstream magnetic field strength. Moreover, we estimated the θbn of each crossing and were able to further constrain the sample into categories of similar features. Our results demonstrate how MA plays a central role in controlling the onset of physical mechanisms in collisionless shocks, particularly reformation. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. We show conclusive evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted timescale of ˜0.3 τc, where τc is the ion gyroperiod. In addition, we experimentally underpin the relationship between
Gravitational Instability in Collisionless Cosmological Pancakes
NASA Astrophysics Data System (ADS)
Valinia, Azita; Shapiro, Paul R.; Martel, Hugo; Vishniac, Ethan T.
1997-04-01
The gravitational instability of cosmological pancakes composed of collisionless dark matter in an Einstein-de Sitter universe is investigated numerically to demonstrate that pancakes are unstable with respect to fragmentation and the formation of filaments. A ``pancake'' is defined here as the nonlinear outcome of the growth of a one-dimensional, sinusoidal, plane-wave, adiabatic density perturbation. We have used high-resolution, two-dimensional, N-body simulations by the particle mesh (PM) method to study the response of pancakes to perturbation by either symmetric (density) or antisymmetric (bending or rippling) modes, with corresponding wavevectors ks and ka transverse to the wavevector kp of the unperturbed pancake plane wave. We consider dark matter that is initially ``cold'' (i.e., with no random thermal velocity in the initial conditions). We also investigate the effect of a finite, random, isotropic, initial velocity dispersion (i.e., initial thermal velocity) on the fate of pancake collapse and instability. Our results include the following: (1) For ``cold'' initial conditions, pancakes are gravitationally unstable with respect to all perturbations of wavenumber k >~ 1 (where k = λp/λ, and λp and λ are the wavelengths of the unperturbed pancake and of the perturbation, respectively). This is contrary to the expectations of an approximate, thin-sheet energy argument applied to the results of one-dimensional pancake simulations. The latter predicts that unstable wavenumbers are restricted to the range kmin < k < kmax, where perturbations with k < kmin ~ 1 are stabilized by Hubble expansion, while those with k > kmax > 1 are stabilized by the one-dimensional velocity dispersion of the collisionless particles along the direction of pancake collapse, within the region of shell crossing. (2) Shortly after the pancake first reaches a nonlinear state of collapse, the dimensionless growth rate of the perturbation of pancake surface density by unstable
Expansion techniques for collisionless stellar dynamical simulations
Meiron, Yohai; Li, Baile; Holley-Bockelmann, Kelly; Spurzem, Rainer
2014-09-10
We present graphics processing unit (GPU) implementations of two fast force calculation methods based on series expansions of the Poisson equation. One method is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other method is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a 'pure' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms. We show that despite the expansion bias, these methods are more accurate than direct techniques for the same number of particles. The performance of our GPU code, which we call ETICS, is profiled and compared to a CPU implementation. On the tested GPU hardware, a full force calculation for one million particles took ∼0.1 s (depending on expansion cutoff), making simulations with as many as 10{sup 8} particles fast for a comparatively small number of nodes.
Collisionless shock formation and the prompt acceleration of solar flare ions
NASA Technical Reports Server (NTRS)
Cargill, P. J.; Goodrich, C. C.; Vlahos, L.
1988-01-01
The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.
Steady-State Electrostatic Layers From Weibel Instability in Relativistic Collisionless Shocks
Milosavljevic, Milos; Nakar, Ehud; Spitkovsky, Anatoly; /KIPAC, Menlo Park
2005-08-04
It is generally accepted that magnetic fields generated in the nonlinear development of the transverse Weibel instability provide effective collisionality in unmagnetized collisionless shocks. Recently, extensive two and three dimensional simulations improved our understanding of the growth and saturation of the instability in colliding plasma shells. However, the steady-state structure of the shock wave transition layers remains poorly understood. We use basic physical considerations and order-of-magnitude arguments to study the steady state structure in relativistic unmagnetized collisionless shocks in pair plasmas. The shock contains an electrostatic layer resulting from the formation of stationary, magnetically-focused current filaments. The filaments form where the cold upstream plasma and the counterstreaming thermal plasma interpenetrate. The filaments are not entirely neutral and strong electrostatic fields are present. Most of the downstream particles cannot cross this layer into the upstream because they are trapped by the electrostatic field. We identify the critical location in the shock transition layer where the electromagnetic field ceases to be static. At this location, the degree of charge separation in the filaments reaches a maximum value, the current inside the filaments comes close to the Alfven limit, and the phase space distribution function starts to isotropize. We argue that the radius of the current filaments upstream of the critical location is about twice the upstream plasma skin depth. Finally, we show that some downstream particles cross the electrostatic layer and run ahead of the shock into the preshock medium without causing instability. These particles may play an important role in particle acceleration.
General Allee effect in two-species population biology.
Livadiotis, G; Elaydi, S
2012-01-01
The main objective of this work is to present a general framework for the notion of the strong Allee effect in population models, including competition, mutualistic, and predator-prey models. The study is restricted to the strong Allee effect caused by an inter-specific interaction. The main feature of the strong Allee effect is that the extinction equilibrium is an attractor. We show how a 'phase space core' of three or four equilibria is sufficient to describe the essential dynamics of the interaction between two species that are prone to the Allee effect. We will introduce the notion of semistability in planar systems. Finally, we show how the presence of semistable equilibria increases the number of possible Allee effect cores.
Richards-like two species population dynamics model.
Ribeiro, Fabiano; Cabella, Brenno Caetano Troca; Martinez, Alexandre Souto
2014-12-01
The two-species population dynamics model is the simplest paradigm of inter- and intra-species interaction. Here, we present a generalized Lotka-Volterra model with intraspecific competition, which retrieves as particular cases, some well-known models. The generalization parameter is related to the species habitat dimensionality and their interaction range. Contrary to standard models, the species coupling parameters are general, not restricted to non-negative values. Therefore, they may represent different ecological regimes, which are derived from the asymptotic solution stability analysis and are represented in a phase diagram. In this diagram, we have identified a forbidden region in the mutualism regime, and a survival/extinction transition with dependence on initial conditions for the competition regime. Also, we shed light on two types of predation and competition: weak, if there are species coexistence, or strong, if at least one species is extinguished.
Richards-like two species population dynamics model.
Ribeiro, Fabiano; Cabella, Brenno Caetano Troca; Martinez, Alexandre Souto
2014-12-01
The two-species population dynamics model is the simplest paradigm of inter- and intra-species interaction. Here, we present a generalized Lotka-Volterra model with intraspecific competition, which retrieves as particular cases, some well-known models. The generalization parameter is related to the species habitat dimensionality and their interaction range. Contrary to standard models, the species coupling parameters are general, not restricted to non-negative values. Therefore, they may represent different ecological regimes, which are derived from the asymptotic solution stability analysis and are represented in a phase diagram. In this diagram, we have identified a forbidden region in the mutualism regime, and a survival/extinction transition with dependence on initial conditions for the competition regime. Also, we shed light on two types of predation and competition: weak, if there are species coexistence, or strong, if at least one species is extinguished. PMID:25112794
Particle simulation of collisionless reconnection using TRISTAN
NASA Astrophysics Data System (ADS)
Kotzé, P. B.; Nishikawa, K.-I.; Büchner, J.
Magnetic reconnection is an important mechanism in the dynamics of the magnetosphere in facilitating the change in magnetospheric topology in response to the orientation of the interplanetary magnetic field (IMF). In the magnetosphere the classical collision rate is small, while the inertia of the electrons allows the frozen-in flux constraint to be broken. At small values of resistivity, this dissipation region then controls the rate of reconnection by forming an elongated Sweet-Parker layer, with an inflow velocity νi into the x-line that scales like: νi = δ ∆ νA νA (1) where δ and ∆ are the width (controlled by resistivity) and length (macroscopic) of the dissipation region respectively and νA is the Alfvén velocity. The scale length around the x-line where the electrons become demagnetised is of the order of the electron skin depth c/ωpe. This region is however much smaller than the ion inertial length c/ωpi, below which the Hall terms in the kinetic Ohm's law become important. Within this distance from the x-line the ions decouple from the electrons and are accelerated away at Alfv´enic velocities (Burkhart et al., 1990) The dynamics of the system at the scale length of the electron dissipation layer is therefore linked to Hall physics, making it a critical ingredient in determining collisionless reconnection rates. Particle simulation techniques have been used to investigate magnetic reconnection in 2-D for a Harris sheet equilibrium. A set of parameters are chosen as well as the dimensions of the computational domain, the boundary conditions and the initial amplitude and form of a seed magnetic island to start the reconnection process. Some preliminary results will be given in this paper.
A Semianalytical Ion Current Model for Radio Frequency Driven Collisionless Sheaths
NASA Technical Reports Server (NTRS)
Bose, Deepak; Govindan, T. R.; Meyyappan, M.; Arnold, Jim (Technical Monitor)
2001-01-01
We propose a semianalytical ion dynamics model for a collisionless radio frequency biased sheath. The model uses bulk plasma conditions and electrode boundary condition to predict ion impact energy distribution and electrical properties of the sheath. The proposed model accounts for ion inertia and ion current modulation at bias frequencies that are of the same order of magnitude as the ion plasma frequency. A relaxation equation for ion current oscillations is derived which is coupled with a damped potential equation in order to model ion inertia effects. We find that inclusion of ion current modulation in the sheath model shows marked improvements in the predictions of sheath electrical properties and ion energy distribution function.
Studies of collisionless shockwaves using high-power laser pulses in laboratories
NASA Astrophysics Data System (ADS)
Yuan, Da-Wei; Li, Yu-Tong
2015-01-01
The remarkable experimental progress in the studies of collisionless shockwave (CS) in laboratories employing high-power lasers is briefly reviewed. The results show that CS can be generated in laser-produced plasmas due to the micro-turbulence associated with instabilities. CS is one of the most important astronomical phenomena. It has been found in supernova remnants (SNRs), Sun-Earth space, etc. This paper focuses on CS in ways relevant to SNRs. Laboratory astrophysics (LA), a new interdisciplinary frontier of astrophysics, plasma and laser physics, has developed rapidly in recent years. As an accessory to the astronomical observation, LA experimenters can closely study some astronomical events scaled-down to controllable phenomena. Project supported by the National Basic Research Program of China (Grant No. 2013CBA01501) and the National Natural Science Foundation of China (Grant No. 11135012).
Kinetic turbulence in 3D collisionless magnetic reconnection with a guide magnetic field
NASA Astrophysics Data System (ADS)
Alejandro Munoz Sepulveda, Patricio; Kilian, Patrick; Jain, Neeraj; Büchner, Jörg
2016-04-01
The features of kinetic plasma turbulence developed during non-relativistic 3D collisionless magnetic reconnection are still not fully understood. This is specially true under the influence of a strong magnetic guide field, a scenario common in space plasmas such as in the solar corona and also in laboratory experiments such as MRX or VINETA II. Therefore, we study the mechanisms and micro-instabilities leading to the development of turbulence during 3D magnetic reconnection with a fully kinetic PIC code, emphasizing the role of the guide field with an initial setup suitable for the aforementioned environments. We also clarify the relations between these processes and the generation of non-thermal populations and particle acceleration.
The model of a collisionless current sheet in a homogeneous gravity field
NASA Astrophysics Data System (ADS)
Veselovsky, Igor S.; Kislov, Roman A.; Malova, Helmi V.; Khabarova, Olga V.
2016-10-01
The self-consistent 1D kinetic Harris-like model of a collisionless current sheet is developed for the case of the current sheet experiencing the impact of an external uniform gravity field. The ambipolar Pannekoek-Rosseland electric field appears in the system as a result of the additional drift motion of ions and electrons. This produces separation of charges, which is responsible for corresponding changes of the current sheet form. The presence of gravitation leads to formation of asymmetric distributions of the magnetic field as well as the plasma and the current density changes. Our estimations show that gravity-forced disruptions of the current sheet profile may occur in the Mercurial magnetosphere and, most probable, in the Io plasma torus near the Jupiter. Also, the model can be applied to magnetospheres of exoplanets.
Collisionless shocks driven by 800 nm laser pulses generate high-energy carbon ions
Zhang, H.; Shen, B. F. Wang, W. P.; Xu, Y.; Liu, Y. Q.; Liang, X. Y.; Leng, Y. X.; Li, R. X. Xu, Z. Z.; Yan, X. Q.; Chen, J. E.
2015-01-15
We present experimental studies on ion acceleration from diamond-like carbon (DLC) foils irradiated by 800 nm, linearly polarized laser pulses with peak intensity of 1.7 × 10{sup 19 }W/cm{sup 2} to 3.5 × 10{sup 19 }W/cm{sup 2} at oblique incidence. Diamond-like carbon foils are heated by the prepulse of a high-contrast laser pulse and expand to form plasmas of near-critical density caused by thermal effect before the arrival of the main pulse. It is demonstrated that carbon ions are accelerated by a collisionless shock wave in slightly overdense plasma excited by forward-moving hot electrons generated by the main pulse.
Low Frequency Waves at and Upstream of Collisionless Shocks
NASA Astrophysics Data System (ADS)
Wilson, L. B.
2016-02-01
This chapter focuses on the range of low frequency electromagnetic modes observed at and upstream of collisionless shocks in the heliosphere. It discusses a specific class of whistler mode wave observed immediately upstream of collisionless shock ramps, called a whistler precursor. Though these modes have been (and are often) observed upstream of quasi-parallel shocks, the authors limit their discussion to those observed upstream of quasi-perpendicular shocks. The chapter discusses the various ion velocity distributions observed at and upstream of collisionless shocks. It also introduces some terminology and relevant instabilities for ion foreshock waves. The chapter discusses the most common ultra-low frequency (ULF) wave types, their properties, and their free energy sources. It discusses modes that are mostly Alfvénic (i.e., mostly transverse but can be compressive) in nature.
Some Considerations on the Pulsed Electromagnetic Acceleration of Plasma
NASA Technical Reports Server (NTRS)
Thio, Y. C. F.; Markusic, T. E.; Cassibry, J. T.; Sommers, J. C.; Turchi, P. J.; Rodgers, Stephen L. (Technical Monitor)
2002-01-01
In applying pulsed electromagnetic acceleration of plasma to space propulsion (known as pulsed plasma thrusters in the community), the mode of acceleration used has been mostly in the collisionless or near-collisionless regime. The preparation of the initial plasma is given scant attention. Collisional regime of accelerating the plasma, however, have been encountered in a variety of plasma accelerating devices. Both of these modes of acceleration are reviewed in a companion paper. In this paper, we discuss the considerations governing the controlled introduction and preparation of the initial plasma, so that the collisional mode of accelerating the plasma may be suitably enhanced.
Laboratory plasma probe studies
NASA Technical Reports Server (NTRS)
Heikkila, W. J.
1975-01-01
Diagnostic experiments performed in a collisionless plasma using CO2 as the working gas are described. In particular, simultaneous measurements that have been performed by means of Langmuir- and RF-probes are presented. A resonance occurring above the parallel resonance in the frequency characteristic of a two electrode system is interpreted as being due to the resonant excitation of electroacoustic waves.
NASA Astrophysics Data System (ADS)
Garasev, Mikhail; Derishev, Evgeny
2016-09-01
We present numerical simulations of the magnetic field turbulence in a collisionless electron-positron plasma with continuous injection of new pairs, which maintains the anisotropy in the particle distribution over a long time. With these simulations, we follow the evolution of a small (and, therefore, uniform) region in the fluid comoving frame to model the generation and decay of the magnetic field in shocks. The upstream is modified by two-photon pair production due to self-absorption of the shock's high-energy radiation. We find that the overall picture of the magnetic field build-up is consistent with the development of Weibel instability. However, the long-term injection of anisotropic pairs in the upstream leads to the formation of large-scale structures in the magnetic field, while small-scale structures are almost absent. We find that being amplified at the shock front, this magnetic field mostly preserves its large spatial scale and then slowly decays in the downstream on a time-scale approximately equal to the duration of the injection phase. The observed decay of the magnetic field is in exceptionally good agreement with predictions of the so-called phase mixing model. The generation of a long-lived magnetic field in relativistic collisionless shocks with an injection-modified upstream explains how they can efficiently produce the synchrotron radiation in gamma-ray bursts.
Heat flux and viscosity of ions in the collisionless solar wind
NASA Technical Reports Server (NTRS)
Williams, L. L.
1995-01-01
Between 1 and 2 solar radii, the Coulomb-collision mean free path for thermal ions exceeds the scale height of the solar atmosphere. The expanding solar plasma becomes collisionless and the kinetics of the solar wind are no longer dominated by thermalizing collisions. The usual Braginskii-type expressions for solar wind ion heat flux and viscosity are no longer valid. However, another microscale still exists in the solar wind, dictated by the gyro-radius of ions in the turbulent embedded solar wind magnetic field. Wave-particle interactions will act to isotropize (but not thermalize) particle distributions, and the relevant microscale for this process is the ion gyro-radius. The ion distribution can be modelled as undergoing isotropizing 'collisions,' with the relevant mean free path scaling with gyro-radius. Here, the author presents the heat flux and viscosity expected for solar wind protons which are relaxing to isotropy on a microscale that scales with gyro-radius. The collisionless viscosity and heat flux have a functional dependence different than their collisional analogs. The collisional expressions for ion viscosity and heat flux drastically overestimate the efficiency of diffusive energy and momentum transport actually operative in the solar wind.
Laboratory studies of magnetized collisionless flows and shocks using accelerated plasmoids
NASA Astrophysics Data System (ADS)
Weber, T. E.; Smith, R. J.; Hsu, S. C.
2015-11-01
Magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those found in both space and astrophysical shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to high velocities (100s of km/s); resulting in β ~ 1, collisionless plasma flows with sonic and Alfvén Mach numbers of ~10. The FRC subsequently impacts a static target such as a strong parallel or anti-parallel (reconnection-wise) magnetic mirror, a solid obstacle, or neutral gas cloud to create shocks with characteristic length and time scales that are both large enough to observe yet small enough to fit within the experiment. This enables study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental capabilities of MSX will be presented, including diagnostics, selected recent results, and future directions. Supported by the DOE Office of Fusion Energy Sciences under contract DE-AC52-06NA25369.
Landau damping of Gardner solitons in a dusty bi-ion plasma
NASA Astrophysics Data System (ADS)
Misra, A. P.; Barman, Arnab
2015-07-01
The effects of linear Landau damping on the nonlinear propagation of dust-acoustic solitary waves (DASWs) are studied in a collisionless unmagnetized dusty plasma with two species of positive ions. The extremely massive, micron-seized, cold, and negatively charged dust particles are described by fluid equations, whereas the two species of positive ions, namely, the cold (heavy) and hot (light) ions are described by the kinetic Vlasov equations. Following Ott and Sudan [Phys. Fluids 12, 2388 (1969)], and by considering lower and higher-order perturbations, the evolution of DASWs with Landau damping is shown to be governed by Korteweg-de Vries (KdV), modified KdV (mKdV), or Gardner (KdV-mKdV)-like equations. The properties of the phase velocity and the Landau damping rate of DASWs are studied for different values of the ratios of the temperatures (σ) and the number densities (μ) of hot and cold ions as well as the cold to hot ion mass ratio m. The distinctive features of the decay rates of the amplitudes of the KdV, mKdV, and Gardner solitons with a small effect of Landau damping are also studied in different parameter regimes. It is found that the Gardner soliton points to lower wave amplitudes than the KdV and mKdV solitons. The results may be useful for understanding the localization of solitary pulses and associated wave damping (collisionless) in laboratory and space plasmas (e.g., the F-ring of Saturn), in which the number density of free electrons is much smaller than that of ions and the heavy, micron seized dust grains are highly charged.
Carbon Metabolism in Two Species of Pereskia (Cactaceae) 1
Rayder, Lisa; Ting, Irwin P.
1981-01-01
The Pereskia are morphologically primitive, leafed members of the Cactaceae. Gas exchange characteristics using a dual isotope porometer to monitor 14CO2 and tritiated water uptake, diurnal malic acid fluctuations, phosphoenolpyruvate carboxylase, and malate dehydrogenase activities were examined in two species of the genus Pereskia, Pereskia grandifolia and Pereskia aculeata. Investigations were done on well watered (control) and water-stressed plants. Nonstressed plants showed a CO2 uptake pattern indicating C3 carbon metabolism. However, diurnal fluctuations in titratable acidity were observed similar to Crassulacean acid metabolism. Plants exposed to 10 days of water stress exhibited stomatal opening only during an early morning period. Titratable acidity, phosphoenolpyruvate carboxylase activity, and malate dehydrogenase activity fluctuations were magnified in the stressed plants, but showed the same diurnal pattern as controls. Water stress causes these cacti to shift to an internal CO2 recycling (“idling”) that has all attributes of Crassulacean acid metabolism except nocturnal stomata opening and CO2 uptake. The consequences of this shift, which has been observed in other succulents, are unknown, and some possibilities are suggested. PMID:16661857
Male-killing Wolbachia in two species of insect
Hurst, G. D. D.; Jiggins, F. M.; Schulenburg, J. H. G. von der; Bertrand, D.; West, S. A.; Goriacheva, I. I.; Zakharov, I. A.; Werren, J. H.; Stouthamer, R.; Majerus, M. E. N.
1999-01-01
The inherited bacterium Wolbachia spreads through the manipulation of host reproduction, and has been suggested to be an important factor in arthropod evolution, from host speciation to the evolution of sex-determination systems. Past work has shown that members of this group may produce cytoplasmic incompatibility, feminize genetically male hosts, and induce host parthenogenesis. Here, we report an expansion of the range of reproductive manipulations produced by members of this clade, recording Wolbachia strains that kill male hosts during embryogenesis in two host species, the ladybird Adalia bipunctata, and the butterfly Acraea encedon. Both male-killing bacteria belong to the B group of Wolbachia. However, phylogenetic analyses were unable to resolve whether the bacteria in the two species are monophyletic, or represent independent origins of male-killing among the B-group Wolbachia. We also found significant divergence within the wsp gene of Wolbachia strains found in different A. bipunctata individuals, suggesting this host species contains two Wolbachia strains, diverged in wsp sequence but monophyletic. Our observations reinforce the notion that Wolbachia may be an important agent driving arthropod evolution, and corroborates previous suggestions that male-killing behaviour is easily evolved by invertebrate symbionts.
Dynamic screening in a two-species asymmetric exclusion process.
Kim, Kyung Hyuk; den Nijs, Marcel
2007-08-01
The dynamic scaling properties of the one-dimensional Burgers equation are expected to change with the inclusion of additional conserved degrees of freedom. We study this by means of one-dimensional (1D) driven lattice gas models that conserve both mass and momentum. The most elementary version of this is the Arndt-Heinzel-Rittenberg (AHR) process, which is usually presented as a two-species diffusion process, with particles of opposite charge hopping in opposite directions and with a variable passing probability. From the hydrodynamics perspective this can be viewed as two coupled Burgers equations, with the number of positive and negative momentum quanta individually conserved. We determine the dynamic scaling dimension of the AHR process from the time evolution of the two-point correlation functions, and find numerically that the dynamic critical exponent is consistent with simple Kardar-Parisi-Zhang- (KPZ) type scaling. We establish that this is the result of perfect screening of fluctuations in the stationary state. The two-point correlations decay exponentially in our simulations and in such a manner that in terms of quasiparticles, fluctuations fully screen each other at coarse grained length scales. We prove this screening rigorously using the analytic matrix product structure of the stationary state. The proof suggests the existence of a topological invariant. The process remains in the KPZ universality class but only in the sense of a factorization, as (KPZ)2. The two Burgers equations decouple at large length scales due to the perfect screening.
Phase diagram of the symbiotic two-species contact process
NASA Astrophysics Data System (ADS)
de Oliveira, Marcelo Martins; Dickman, Ronald
2014-09-01
We study the two-species symbiotic contact process, recently proposed by de Oliveira, Santos, and Dickman [Phys. Rev. E 86, 011121 (2012), 10.1103/PhysRevE.86.011121]. In this model, each site of a lattice may be vacant or host single individuals of species A and/or B. Individuals at sites with both species present interact in a symbiotic manner, having a reduced death rate μ <1. Otherwise, the dynamics follows the rules of the basic contact process, with individuals reproducing to vacant neighbor sites at rate λ and dying at a rate of unity. We determine the full phase diagram in the λ-μ plane in one and two dimensions by means of exact numerical quasistationary distributions, cluster approximations, and Monte Carlo simulations. We also study the effects of asymmetric creation rates and diffusion of individuals. In two dimensions, for sufficiently strong symbiosis (i.e., small μ), the absorbing-state phase transition becomes discontinuous for diffusion rates D within a certain range. We report preliminary results on the critical surface and tricritical line in the λ-μ-D space. Our results raise the possibility that strongly symbiotic associations of mobile species may be vulnerable to sudden extinction under increasingly adverse conditions.
A cooperative system of two species with bidirectional interactions.
Wang, Yuanshi; Wu, Hong
2014-06-01
Cooperation between species is often regarded to mean that the increase of each species promotes the growth of the other. The well-known cooperative model is the Lotka-Volterra equations (LVEs). In the LVEs, population densities of species increase infinitely as the cooperation is strong, which is called the divergence problem. Moreover, LVEs never exhibit an Allee effect in the case of obligate cooperation. In order to avoid these problems, several models have been established although most of them are rather complex. In this paper, we consider a cooperative system of two species with bidirectional interactions, in which each species also has negative feedback on the other. Population densities of the species will not increase infinitely because of the limited resource and negative feedback. Then, we focus on an extended lattice model of cooperation, which is deduced from reactions on lattice and has the same form as that of LVEs. In the case of obligate cooperation, the model predicts an Allee effect. Global dynamics of the system exhibit essential features of cooperation and basic mechanisms by which the cooperation can lead to coexistence/extinction of species. Intermediate cooperation is shown to be beneficial in cooperation under certain conditions, while extremely strong cooperation is demonstrated to lead to extinction of one/both species. Numerical simulations confirm and extend our results. PMID:24816998
Carbon metabolism in two species of pereskia (cactaceae).
Rayder, L; Ting, I P
1981-07-01
The Pereskia are morphologically primitive, leafed members of the Cactaceae. Gas exchange characteristics using a dual isotope porometer to monitor (14)CO(2) and tritiated water uptake, diurnal malic acid fluctuations, phosphoenolpyruvate carboxylase, and malate dehydrogenase activities were examined in two species of the genus Pereskia, Pereskia grandifolia and Pereskia aculeata. Investigations were done on well watered (control) and water-stressed plants. Nonstressed plants showed a CO(2) uptake pattern indicating C(3) carbon metabolism. However, diurnal fluctuations in titratable acidity were observed similar to Crassulacean acid metabolism. Plants exposed to 10 days of water stress exhibited stomatal opening only during an early morning period. Titratable acidity, phosphoenolpyruvate carboxylase activity, and malate dehydrogenase activity fluctuations were magnified in the stressed plants, but showed the same diurnal pattern as controls. Water stress causes these cacti to shift to an internal CO(2) recycling ("idling") that has all attributes of Crassulacean acid metabolism except nocturnal stomata opening and CO(2) uptake. The consequences of this shift, which has been observed in other succulents, are unknown, and some possibilities are suggested.
Dynamic screening in a two-species asymmetric exclusion process
NASA Astrophysics Data System (ADS)
Kim, Kyung Hyuk; den Nijs, Marcel
2007-08-01
The dynamic scaling properties of the one-dimensional Burgers equation are expected to change with the inclusion of additional conserved degrees of freedom. We study this by means of one-dimensional (1D) driven lattice gas models that conserve both mass and momentum. The most elementary version of this is the Arndt-Heinzel-Rittenberg (AHR) process, which is usually presented as a two-species diffusion process, with particles of opposite charge hopping in opposite directions and with a variable passing probability. From the hydrodynamics perspective this can be viewed as two coupled Burgers equations, with the number of positive and negative momentum quanta individually conserved. We determine the dynamic scaling dimension of the AHR process from the time evolution of the two-point correlation functions, and find numerically that the dynamic critical exponent is consistent with simple Kardar-Parisi-Zhang- (KPZ) type scaling. We establish that this is the result of perfect screening of fluctuations in the stationary state. The two-point correlations decay exponentially in our simulations and in such a manner that in terms of quasiparticles, fluctuations fully screen each other at coarse grained length scales. We prove this screening rigorously using the analytic matrix product structure of the stationary state. The proof suggests the existence of a topological invariant. The process remains in the KPZ universality class but only in the sense of a factorization, as (KPZ)2 . The two Burgers equations decouple at large length scales due to the perfect screening.
Electron precipitation in solar flares - Collisionless effects
NASA Technical Reports Server (NTRS)
Vlahos, L.; Rowland, H. L.
1984-01-01
A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with a set of rate equations that follows, in time, the nonlinearly coupled system of plasma waves-ion fluctuations. As an outcome of the fast transfer of wave energy from the beam to the ambient plasma, nonthermal electron tails are formed which can stabilize the anomalous Doppler resonance instability responsible for the pitch angle scattering of the beam electrons. The non-collisional losses of the precipitating electrons are estimated, and the observational implication of these results are discussed.
Santos-Lima, R.; De Gouveia Dal Pino, E. M.; Kowal, G.; Falceta-Gonçalves, D.; Lazarian, A.; Nakwacki, M. S.
2014-02-01
The amplification of magnetic fields (MFs) in the intracluster medium (ICM) is attributed to turbulent dynamo (TD) action, which is generally derived in the collisional-MHD framework. However, this assumption is poorly justified a priori, since in the ICM the ion mean free path between collisions is of the order of the dynamical scales, thus requiring a collisionless MHD description. The present study uses an anisotropic plasma pressure that brings the plasma within a parametric space where collisionless instabilities take place. In this model, a relaxation term of the pressure anisotropy simulates the feedback of the mirror and firehose instabilities, in consistency with empirical studies. Our three-dimensional numerical simulations of forced transonic turbulence, aiming the modeling of the turbulent ICM, were performed for different initial values of the MF intensity and different relaxation rates of the pressure anisotropy. We found that in the high-β plasma regime corresponding to the ICM conditions, a fast anisotropy relaxation rate gives results that are similar to the collisional-MHD model, as far as the statistical properties of the turbulence are concerned. Also, the TD amplification of seed MFs was found to be similar to the collisional-MHD model. The simulations that do not employ the anisotropy relaxation deviate significantly from the collisional-MHD results and show more power at the small-scale fluctuations of both density and velocity as a result of the action of the instabilities. For these simulations, the large-scale fluctuations in the MF are mostly suppressed and the TD fails in amplifying seed MFs.
NASA Astrophysics Data System (ADS)
Tsiklauri, D.; Haruki, T.
2008-09-01
Dungey's (1953) work on X-point collapse is the earliest analysis done on magnetic reconnection and predates the tearing mode, Sweet-Parker and Petcheck reconnection models. X-point collapse soon fell out of favour because in the collisional (MHD) regime, for the plausible space plasma parameters, it was found to be inefficient. We however show [Tsiklauri D. and T. Haruki, Phys. of Plasmas, 14, 112905, (2007)] that in the collisionless regime, which is indeed more applicable to space plasmas, the reconnection is efficient. We study magnetic reconnection during collisionless, stressed, X-point collapse using kinetic, 2.5D, fully electromagnetic, relativistic Particle-in-Cell numerical code. Two cases of weakly and strongly stressed X-point collapse were considered. Here descriptors weakly and strongly refer to 20% and 124% unidirectional spatial compression of the X-point, respectively. We found that within about one Alfven time, 2% and 20% of the initial magnetic energy is converted into heat and accelerated particle energy in the case of weak and strong stress, respectively. In the both cases, during the peak of the reconnection, the quadruple out-of-plane magnetic field is generated. These results strongly suggest the importance of the collisionless, stressed X-point collapse as an efficient mechanism of converting magnetic energy into heat and super-thermal particle energy. In the weakly stressed case, the reconnection rate, defined as the out-of-plane electric field in the X-point normalized by the product of external magnetic field and Alfven speeds, peaks at 0.11, with its average over 1.25 Alfven times being 0.04. Electron energy distribution in the current sheet, at the high-energy end of the spectrum, shows a power-law distribution with the index varying in time, attaining a maximal value of -4.1 at the final simulation time step (1.25 Alfven times). In the strongly stressed case, magnetic reconnection peak occurs 3.4 times faster and is more efficient
Magnetoacoustic solitons in quantum plasma
Hussain, S.; Mahmood, S.
2011-08-15
Nonlinear magnetoacoustic waves in collisionless homogenous, magnetized quantum plasma is studied. Two fluid quantum magneto-hydrodynamic model (QMHD) is employed and reductive perturbation method is used to derive Korteweg de Vries (KdV) equation for magnetoacoustic waves. The effects of plasma density and magnetic field intensity are investigated on magnetoacoustic solitary structures in quantum plasma. The numerical results are also presented, which are applicable to explain some aspects of the propagation of nonlinear magnetoacosutic wave in dense astrophysical plasma situations.
Lerche, I.; Schlickeiser, R.; Tautz, R. C.
2008-02-15
This Comment discusses the representations of infinite sums of Bessel functions that occur in plasma problems involving collisionless plasmas treated from a plasma kinetic viewpoint. In addition, the influence of such summation techniques on dispersion relations for plasma waves involving a background magnetic field is discussed.
Nocera, L.; Palumbo, L. J.
2013-01-15
We present new elementary, exact weak singular solutions of the steady state, two species, electrostatic, one dimensional Vlasov-Poisson equations. The distribution of the hot, finite mass, mobile ions is assumed to be log singular at the position of the electric potential's minimum. We show that the electron energy distributions on opposite sides of this minimum are not equal. This leads to a jump discontinuity of the electron distribution across its separatrix. A simple relation exists between the difference of these two electron distributions and that of the ions. The velocity Fourier transform of the electron singular distribution is smooth and appears as a simple Neumann series. Elementary, finite amplitude profiles of the electric potential result from Poisson equation, which are smoothly, but nonmonotonically and asymmetrically distributed in space. Two such profiles are given explicitly as appropriate for a nonmonotonic double layer and for a plasma bounded by a surface. The distributions of both electrons and ions supporting such potential meet smooth and kinetically stable boundary conditions at one plasma boundary. For sufficiently small potential to electron temperature ratios, the nonthermal, discontinuous electron distribution resulting at the other plasma boundary is also stable against Landau damped perturbations of the electron distribution.
Hydrodynamics of Collisionless Boltzmann Equation for a Highly Flattened Galaxy
NASA Astrophysics Data System (ADS)
Aoki, S.
The collisionless Boltzmann equation is studied in order to be connected with hydrodynamic equations. Each of the later equations can be obtained by taking a moment of the former equation. The difficulty against the system of moment equations, called closure problem, can be overtaken by a trick of neglecting the terms of higher order moments under small-pressure assumption.
NASA Astrophysics Data System (ADS)
Schaeffer, D. B.; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Winske, D.; Gekelman, W.; Niemann, C.
2015-11-01
Recent experiments at the University of California, Los Angeles have successfully generated subcritical magnetized collisionless shocks, allowing new laboratory studies of shock formation relevant to space shocks. The characteristics of these shocks are compared with new data in which no shock or a pre-shock formed. The results are consistent with theory and 2D hybrid simulations and indicate that the observed shock or shock-like structures can be organized into distinct regimes by coupling strength. With additional experiments on the early time parameters of the laser plasma utilizing Thomson scattering, spectroscopy, and fast-gate filtered imaging, these regimes are found to be in good agreement with theoretical shock formation criteria.
Nonlinear plasma wave in magnetized plasmas
NASA Astrophysics Data System (ADS)
Bulanov, Sergei V.; Zh. Esirkepov, Timur; Kando, Masaki; Koga, James K.; Hosokai, Tomonao; Zhidkov, Alexei G.; Kodama, Ryosuke
2013-08-01
Nonlinear axisymmetric cylindrical plasma oscillations in magnetized collisionless plasmas are a model for the electron fluid collapse on the axis behind an ultrashort relativisically intense laser pulse exciting a plasma wake wave. We present an analytical description of the strongly nonlinear oscillations showing that the magnetic field prevents closing of the cavity formed behind the laser pulse. This effect is demonstrated with 3D PIC simulations of the laser-plasma interaction. An analysis of the betatron oscillations of fast electrons in the presence of the magnetic field reveals a characteristic "Four-Ray Star" pattern.
NASA Technical Reports Server (NTRS)
Ellison, Donald C.; Jones, Frank C.
1988-01-01
The electron heating required if protons scatter elastically in a parallel, collisionless shock is calculated. Near-elastic proton scattering off large amplitude background magnetic field fluctuations might be expected if the waves responsible for the shock dissipation are generated by the fire hose instability. The effects of an electrostatic potential jump in the shock layer are included by assuming that the energy lost by protons in traversing the potential jump is converted into electron thermal pressure. It is found that the electron temperature increase is a strong function of the potential jump. Comparison is made to the parallel shock plasma simulation of Quest (1987).
Evolution of velocity dispersion along cold collisionless flows
NASA Astrophysics Data System (ADS)
Banik, Nilanjan; Sikivie, Pierre
2016-05-01
The infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behavior of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the big flow from the sharpness of its nearby caustic and a prediction for the dispersions in its velocity components.
Evolution of velocity dispersion along cold collisionless flows
Banik, Nilanjan; Sikivie, Pierre
2016-05-01
We found that the infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We also discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results aremore » used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components.« less
NASA Technical Reports Server (NTRS)
Yamaguchi, Hiroya; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Petre, Robert; Slane, Patrick O.; Smith, Randall K.
2013-01-01
Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K beta (3p yields 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe K alpha (2p yields 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe K alpha morphology from the Chandra observations. Since strong Fe K beta fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.
NASA Astrophysics Data System (ADS)
Yamaguchi, Hiroya; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Petre, Robert; Slane, Patrick O.; Smith, Randall K.
2014-01-01
Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect Kβ (3p → 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe Kα (2p → 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe Kα morphology from the Chandra observations. Since strong Fe Kβ fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.
Yamaguchi, Hiroya; Petre, Robert; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Slane, Patrick O.; Smith, Randall K.
2014-01-10
Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect Kβ (3p → 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe Kα (2p → 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe Kα morphology from the Chandra observations. Since strong Fe Kβ fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.
Effect of background plasma nonlinearities on dissipation processes in plasmas
NASA Astrophysics Data System (ADS)
Nekrasov, F. M.; Elfimov, A. G.; de Azevedo, C. A.; de Assis, A. S.
1999-01-01
The Coulomb collision effect on the bounce-resonance dissipation is considered for toroidal magnetized plasmas. The solution of the Vlasov equation with a simplified Fokker-Planck collision operator is presented. The parallel components of the dielectric tensor are obtained. A collisionless limit of wave dissipation is found.
Connections between comets and plasmas in space
NASA Technical Reports Server (NTRS)
Scarf, F. L.
1979-01-01
The dynamical processes in the cometary system represent unusual examples of very important, widespread natural phenomena. Topics covered include: (1) the comet as an obstacle in the solar wind; (2) the nature of the plasma flow; (3) collisionless shocks; and (4) plasma processes in the comet tail.
Whistler waves observed upstream from collisionless shocks
NASA Technical Reports Server (NTRS)
Fairfield, D. H.
1973-01-01
Waves in the frequency range 0.5 - 4 Hz were studied in the region upstream of the earth's bow shock using data from the fluxgate magnetic field experiment on IMP-6. Analysis of 150 examples of these waves during a three month interval indicates that amplitudes are generally less than 1 or 2 gammas and propagation directions generally make angles of between 20 and 40 degrees with the field direction. The waves as measured in the spacecraft frame of reference are either left or right hand polarized with respect to the average field direction. It is concluded that the observed waves are right handed waves in the plasma frame of reference with wavelengths of approximately 100 km propagating upstream in the whistler mode. Doppler shifting reduces the observed frequencies in the spacecraft frame and reverses the observed polarization for those waves propagating more directly upstream. Similar waves are seen ahead of most interplanetary shocks.
Lu, San; Lu, Quanming; Huang, Can; Wang, Shui
2013-06-15
By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.
Linear theory for fast collisionless magnetic reconnection in the lower-hybrid frequency range
NASA Astrophysics Data System (ADS)
Jovanović, D.; Shukla, P. K.
2005-05-01
A linear theory is presented for the interplay between the fast collisionless magnetic reconnection and the lower-hybrid waves that has been observed in recent computer simulations [J. F. Drake, M. Swisdak, C. Cattell et al., Science 299, 873 (2003)]. In plasma configurations with a strong guide field and anisotropic electron temperature, the electron dynamics is described within the framework of standard electron magnetohydrodynamic equations, accounting also for the effects of the electron polarization and ion motions in the presence of perpendicular electric fields. In the linear phase, we find two types of instabilities of a thin current sheet with steep edges, corresponding to its filamentation (or tearing) and bending. Using a surface-wave formalism for the perturbations whose wavelength is larger than the thickness of the current sheet, the corresponding growth rates are calculated as the contributions of singularities in the plasma dispersion function. These are governed by the electron inertia and the linear coupling of the reconnecting magnetic field with local plasma modes propagating in the perpendicular direction that are subject to the Buneman instability. The linear surface wave instability may be particularly important as a secondary instability, dissipating the thin current sheets that develop in the course of the fast reconnection in the shear-Alfvén and kinetic-Alfvén regimes, and providing the anomalous resistivity for the growth of magnetic islands beyond the shear-Alfvén and kinetic-Alfvén scales.
Geometry of thermal plasma oscillations
Burton, Da; Noble, A.
2009-01-22
We develop a method for investigating the relationship between the shape of a 1-particle distribution and non-linear electrostatic oscillations in a collisionless plasma, incorporating transverse thermal motion. A general expression is found for the maximum sustainable electric field, and is evaluated for a particular highly anisotropic distribution.
Electron heating in capacitively coupled plasmas revisited
NASA Astrophysics Data System (ADS)
Lafleur, T.; Chabert, P.; Booth, J. P.
2014-06-01
We revisit the problem of electron heating in capacitively coupled plasmas (CCPs), and propose a method for quantifying the level of collisionless and collisional heating in plasma simulations. The proposed procedure, based on the electron mechanical energy conservation equation, is demonstrated with particle-in-cell simulations of a number of single and multi-frequency CCPs operated in regimes of research and industrial interest. In almost all cases tested, the total electron heating is comprised of collisional (ohmic) and pressure heating parts. This latter collisionless component is in qualitative agreement with the mechanism of electron heating predicted from the recent re-evaluation of theoretical models. Finally, in very electrically asymmetric plasmas produced in multi-frequency discharges, we observe an additional collisionless heating mechanism associated with electron inertia.
Electromagnetic drift waves dispersion for arbitrarily collisional plasmas
Lee, Wonjae Krasheninnikov, Sergei I.; Angus, J. R.
2015-07-15
The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvén wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionless and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvén wave instability with synergistic effects of high beta stabilization and Landau resonance.
Disruption of pubertal onset by exogenous testosterone and estrogen in two species of rodents.
Pak, Toni R; Lynch, G Robert; Ziegler, D Matthew; Lunden, Jason B; Tsai, Pei-San
2003-01-01
The administration of adult physiological levels of testosterone (T) and 17beta-estradiol (E(2)) to male Siberian hamsters was previously shown to delay the onset of puberty. To examine whether this is a response common to other rodents, we investigated whether exogenous steroids also alter the onset of puberty in Syrian hamsters and mice. Juvenile male Syrian hamsters and mice were implanted with Silastic capsules containing T, E(2), or cholesterol control. After 15 days, plasma, pituitaries, and testes were processed for histological analysis or measurements of gonadotropins and circulating steroid hormones. T and E(2) implants reduced testis mass and gonadotropin stores in both species and arrested spermatogenesis in Syrian hamsters. In contrast, spermatogenesis in mice was unaffected by T and only modestly affected by E(2). Although E(2) inhibited circulating follicle-stimulating hormone (FSH) in both species, T inhibited circulating FSH in mice only. Overall, our results demonstrate that the hypothalamic-pituitary-gonadal axis of each rodent species responds uniquely to T and E(2) during the pubertal transition. Despite the highly varied effects of T and E(2) in these two species, the ability of steroid hormones to disrupt the onset of puberty appears to be a feature common to many rodents.
Evolution Of Nonlinear Waves in Compressing Plasma
P.F. Schmit, I.Y. Dodin, and N.J. Fisch
2011-05-27
Through particle-in-cell simulations, the evolution of nonlinear plasma waves is examined in one-dimensional collisionless plasma undergoing mechanical compression. Unlike linear waves, whose wavelength decreases proportionally to the system length L(t), nonlinear waves, such as solitary electron holes, conserve their characteristic size {Delta} during slow compression. This leads to a substantially stronger adiabatic amplification as well as rapid collisionless damping when L approaches {Delta}. On the other hand, cessation of compression halts the wave evolution, yielding a stable mode.
Entropy production rate as a constraint for collisionless fluid closures
Fleurence, E.; Sarazin, Y.; Garbet, X.; Dif-Pradalier, G.; Ghendrih, Ph.; Grandgirard, V.; Ottaviani, M.
2006-11-30
A novel method is proposed to construct collisionless fluid closures accounting for some kinetic properties. The first dropped fluid moment is assumed to be a linear function of the lower order ones. Optimizing the agreement between the fluid and kinetic entropy production rates is used to constrain the coefficients of the linear development. This procedure is applied to a reduced version of the interchange instability. The closure, involving the absolute value of the wave vector, is non-local in real space. In this case, the linear instability thresholds are the same, and the linear growth rates exhibit similar characteristics. Such a method is applicable to other models and classes of instabilities.
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
Dodin, I. Y.; Fisch, N. J.
2010-11-15
The modification of the Vlasov equation, in its standard form describing a charged particle distribution in the six-dimensional phase space, is derived explicitly within a formal Hamiltonian approach for arbitrarily curved spacetime. The equation accounts simultaneously for the Lorentz force and the effects of general relativity, with the latter appearing as the gravity force and an additional force due to the extrinsic curvature of spatial hypersurfaces. For an arbitrary spatial metric, the equations of collisionless hydrodynamics are also obtained in the usual three-vector form.
Analytical collisionless damping rate of geodesic acoustic mode
NASA Astrophysics Data System (ADS)
Ren, H.; Xu, X. Q.
2016-10-01
Collisionless damping of geodesic acoustic mode (GAM) is analytically investigated by considering the finite-orbit-width (FOW) resonance effect to the 3rd order in the gyro-kinetic equations. A concise and transparent expression for the damping rate is presented for the first time. Good agreement is found between the analytical damping rate and the previous TEMPEST simulation result (Xu 2008 et al Phys. Rev. Lett. 100 215001) for systematic q scans. Our result also shows that it is of sufficient accuracy and has to take into account the FOW effect to the 3rd order.
Collisionless drift-tearing modes in the magnetopause
NASA Technical Reports Server (NTRS)
Gladd, N. T.
1990-01-01
The linear stability properties of collisionless drift-tearing modes are analyzed in a modified Harris equilibrium model of the magnetopause. Particular attention is paid to the relevance of the parametric behavior of growth rates to the 'magnetic percolation' theory of flux transfer event formation (Galeev et al., 1986). Numerical methods are used to solve the drift-tearing eigenmode equations and the results are compared with those previously obtained by analytical methods. The analytical results are found to correctly model important parametric dependencies but to typically overestimate the rate of growth. The eigenmode equations are numerically difficult, and an integration scheme utilizing Ricatti transforms is developed to affect their solution.
Collisionless Magnetic Reconnection and Dynamo Processes in a Spatially Rotating Magnetic Field
NASA Astrophysics Data System (ADS)
Choe, Gwangson; Lee, Junggi
2016-04-01
Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. It is found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.
Critical pitch angle for electron acceleration in a collisionless shock layer
NASA Astrophysics Data System (ADS)
Narita, Y.; Comişel, H.; Motschmann, U.
2016-07-01
Collisionless shock waves in space and astrophysical plasmas can accelerate electrons along the shock layer by an electrostatic potential, and scatter or reflect electrons back to the upstream region by the amplified magnetic field or turbulent fluctuations. The notion of the critical pitch angle is introduced for non-adiabatic electron acceleration by balancing the two timescales under a quasi-perpendicular shock wave geometry in which the upstream magnetic field is nearly perpendicular to the shock layer normal direction. An analytic expression of the critical pitch angle is obtained as a function of the electron velocity parallel to the magnetic field, the ratio of the electron gyro- to plasma frequency, the cross-shock potential, the width of the shock transition layer, and the shock angle (which is the angle between the upstream magnetic field and the shock normal direction). For typical non-relativistic solar system applications, the critical pitch angle is predicted to be about 10°. An efficient acceleration is expected below the critical pitch angle.
Conditions for Debris-Background Ion Interactions and Collisionless Shock Wave Generation
Winske, Dan; Cowee, Misa
2012-07-10
We use hybrid simulations and simple theoretical arguments to determine when debris ions streaming relative to background ions in a collisionless, magnetized plasma couple strongly enough to generate a magnetosonic shock wave. We consider three types of configurations: one-dimensional, the two-dimensional extension of the 1-D case, and a more complex 2-D geometry that contains some effects that would be found in a laser-produced, laboratory plasma. We show that the simulation results as well as previous Russian and LLNL results reduce to a simple condition (R{sub m}/{rho}{sub d} = equal mass radius/debris ion gyroradius {ge} 0.7) for the generation of a shock wave. Strong debris interaction with the background is characterized by the formation of a magnetic pulse that steepens and speeds up as it encounters the debris ions deflected by the magnetic field. The pulse further evolves into a shock. As the earlier work has indicated, the process also involves the generation of a transverse electric field perpendicular to the flow and the magnetic field that accelerates the background ions radially outward, which in turn causes the speedup of the pulse. With electric and magnetic field probes, the UCLA laser experiments should be able to detect these signatures of coupling as well as the generation of the shock wave.
The ion polytropic coefficient in a collisionless sheath containing hot ions
NASA Astrophysics Data System (ADS)
Lin, Binbin; Xiang, Nong; Ou, Jing
2016-08-01
The fluid approach has been widely used to study plasma sheath dynamics. For a sheath containing hot ions whose temperature is greater than the electron's, how to truncate the fluid hierarchy chain equations while retaining to the fullest extent of the kinetic effects is always a difficult problem. In this paper, a one-dimensional, collisionless sheath containing hot ions is studied via particle-in-cell simulations. By analyzing the ion energy equation and taking the kinetic effects into account, we have shown that the ion polytropic coefficient in the vicinity of the sheath edge is approximately constant so that the state equation with the modified polytropic coefficient can be used to close the hierarchy chain of the ion fluid equations. The value of the polytropic coefficient strongly depends on the hot ion temperature and its concentration in the plasma. The semi-analytical model is given to interpret the simulation results. As an application, the kinetic effects on the ion saturation current density in the probe theory are discussed.
Nonlinear studies of m = 1 modes in high-temperature plasmas
Aydemir, A.Y.
1992-07-01
Nonlinear evolution of the m = 1 mode is examined in high-temperature plasmas where the mode is in the semi-collisional or collisionless regime. Unlike the resistive m = 1 mode, both the semi-collisional mode, with a very weak resistivity dependence, and the collisionless mode, driven by finite electron inertia, can be robustly unstable in today's large tokamaks. And unlike the finite-{Delta}{prime}(m {ge} 2) tearing modes, the nonlinear evolution of which is collisional, both the semi-collisional and collisionless m = 1 modes exhibit nonlinearly enhanced growth rates that far exceed their linear values, thus making their nonlinear evolution collisionless; this accelerated growth of a collisionless m = 1 mode may explain the fast sawtooth-crashes observed in large tokamaks.
Nonlinear studies of m = 1 modes in high-temperature plasmas
Aydemir, A.Y.
1992-07-01
Nonlinear evolution of the m = 1 mode is examined in high-temperature plasmas where the mode is in the semi-collisional or collisionless regime. Unlike the resistive m = 1 mode, both the semi-collisional mode, with a very weak resistivity dependence, and the collisionless mode, driven by finite electron inertia, can be robustly unstable in today`s large tokamaks. And unlike the finite-{Delta}{prime}(m {ge} 2) tearing modes, the nonlinear evolution of which is collisional, both the semi-collisional and collisionless m = 1 modes exhibit nonlinearly enhanced growth rates that far exceed their linear values, thus making their nonlinear evolution collisionless; this accelerated growth of a collisionless m = 1 mode may explain the fast sawtooth-crashes observed in large tokamaks.
Two Species of Bryoria (Lichenized Ascomycota, Parmeliaceae) from the Sino-Himalayas
Wang, Li-song; Harada, Hiroshi; Koh, Young Jin
2005-01-01
We performed a taxonomic study on two species of the genus Bryoria from the Sino-Himalayas, SW-China. B. nadvornikiana is new to China and B. furcellata is new to Yunnan and Sichuan provinces in the Sino-Himalayas. Morphology, habitat, distributions and chemistry of the two species are discussed. PMID:24049496
Plasma in the Jovian magnetosphere
NASA Technical Reports Server (NTRS)
Goertz, C. K.
1975-01-01
It is shown that the plasma in Jupiter's ionosphere is collisionless above a certain level. In the outer magnetosphere, where the rotational force dominates the gravitational force, the collisionless plasma has a beam-like distribution and gives rise to a two-stream instability. This leads to trapping of plasma in the centrifugally dominated region of the magnetosphere. Plasma is lost by recombination. Equilibrium-trapped particle densities are calculated by requiring a balance between trapping by wave-particle interaction and loss by recombination. The results are compared with recent observations from Pioneer 10. It is suggested that the observations require an unexplained ion-heating mechanism. Some consequences of the model are discussed.
Modulational interactions in quantum plasmas
NASA Astrophysics Data System (ADS)
Sayed, F.; Vladimirov, S. V.; Tyshetskiy, Yu.; Ishihara, O.
2013-07-01
A formalism for treating modulational interactions of electrostatic fields in collisionless quantum plasmas is developed, based on the kinetic Wigner-Poisson model of quantum plasma. This formalism can be used in a range of problems of nonlinear interaction between electrostatic fields in a quantum plasma, such as development of turbulence, self-organization, as well as transition from the weak turbulent state to strong turbulence. In particular, using this formalism, we obtain the kinetic quantum Zakharov equations that describe nonlinear coupling of high frequency Langmuir waves to low frequency plasma density variations, for cases of non-degenerate and degenerate plasma electrons.
Modulational interactions in quantum plasmas
Sayed, F.; Tyshetskiy, Yu.; Vladimirov, S. V.; Ishihara, O.
2013-07-15
A formalism for treating modulational interactions of electrostatic fields in collisionless quantum plasmas is developed, based on the kinetic Wigner-Poisson model of quantum plasma. This formalism can be used in a range of problems of nonlinear interaction between electrostatic fields in a quantum plasma, such as development of turbulence, self-organization, as well as transition from the weak turbulent state to strong turbulence. In particular, using this formalism, we obtain the kinetic quantum Zakharov equations that describe nonlinear coupling of high frequency Langmuir waves to low frequency plasma density variations, for cases of non-degenerate and degenerate plasma electrons.
NASA Astrophysics Data System (ADS)
Wang, Liang; Hakim, Ammar H.; Bhattacharjee, A.; Germaschewski, K.
2015-01-01
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.
Wang, Liang Germaschewski, K.; Hakim, Ammar H.; Bhattacharjee, A.
2015-01-15
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.
Liseykina, T.; Mulser, P.; Murakami, M.
2015-03-15
Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague term “vacuum heating.” The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at Iλ{sup 2}≅(0.3−1.2)×10{sup 21} Wcm{sup −2}μm{sup 2} in the plasma target with the electron density of n{sub e}λ{sup 2}∼10{sup 23}cm{sup −3}μm{sup 2}, the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain Iλ{sup 2}≅(10{sup 18}−10{sup 20}) Wcm{sup −2}μm{sup 2}, a scaling in vague accordance with current published estimates in the range Iλ{sup 2}≅(0.14−3.5)×10{sup 21} Wcm{sup −2}
Warm wavebreaking of nonlinear plasma waves with arbitrary phasevelocities
Schroeder, C.B.; Esarey, E.; Shadwick, B.A.
2004-11-12
A warm, relativistic fluid theory of a nonequilibrium, collisionless plasma is developed to analyze nonlinear plasma waves excited by intense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave phase velocities. The maximum amplitude is shown to increase in the presence of a laser field. These results set a limit to the achievable gradient in plasma-based accelerators.
NASA Astrophysics Data System (ADS)
Muñoz, P. A.; Büchner, J.
2016-10-01
Non-Maxwellian electron velocity space distribution functions (EVDFs) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, EVDFs were obtained mainly for antiparallel reconnection and under the influence of weak guide-fields in the direction perpendicular to the reconnection plane. EVDFs are, however, not well known, yet, for oblique (or component-) reconnection in case and in dependence on stronger guide-magnetic fields and for the exhaust (outflow) region of reconnection away from the diffusion region. In view of the multi-spacecraft Magnetospheric Multiscale Mission (MMS), we derived the non-Maxwellian EVDFs of collisionless magnetic reconnection in dependence on the guide-field strength bg from small ( b g ≈ 0 ) to very strong (bg = 8) guide-fields, taking into account the feedback of the self-generated turbulence. For this sake, we carried out 2.5D fully kinetic Particle-in-Cell simulations using the ACRONYM code. We obtained anisotropic EVDFs and electron beams propagating along the separatrices as well as in the exhaust region of reconnection. The beams are anisotropic with a higher temperature in the direction perpendicular rather than parallel to the local magnetic field. The beams propagate in the direction opposite to the background electrons and cause instabilities. We also obtained the guide-field dependence of the relative electron-beam drift speed, threshold, and properties of the resulting streaming instabilities including the strongly non-linear saturation of the self-generated plasma turbulence. This turbulence and its non-linear feedback cause non-adiabatic parallel electron acceleration. We further obtained the resulting EVDFs due to the non-linear feedback of the saturated self-generated turbulence near the separatrices and in the exhaust region of reconnection in dependence on the guide field strength. We found that the influence of the self-generated plasma turbulence
Nonlinear Plasma Effects in Natural and Artificial Aurora
Mishin, E. V.
2011-01-04
This report describes common features of natural ('Enhanced') aurora and 'artificial aurora'(AA) created by electron beams injected from sounding rockets. These features cannot be explained solely by col-lisional degradation of energetic electrons, thereby pointing to collisionless plasma effects. The fundamental role in electron beam-ionosphere interactions belongs to Langmuir turbulence. Its development in the (weakly-ionized) ionosphere is significantly affected by electron-neutral collisions, so that the heating and acceleration of plasma electrons proceed more efficiently than in collisionless plasmas. As a result, a narrow layer of enhanced auroral glow/ionization is formed above the standard collisional peak.
On the electron-ion temperature ratio established by collisionless shocks
NASA Astrophysics Data System (ADS)
Vink, Jacco; Broersen, Sjors; Bykov, Andrei; Gabici, Stefano
2015-07-01
Astrophysical shocks are often collisionless shocks, in which the changes in plasma flow and temperatures across the shock are established not through Coulomb interactions, but through electric and magnetic fields. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature (non-equilibration of temperatures), or whether they quickly equilibrate in the shock region. Here we provide a simple, thermodynamic, relation for the minimum electron-ion temperature ratios that should be expected as a function of Mach number. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all particle species should undergo the same density jump across the shock, in order for the plasma to remain charge neutral. The only form of additional electron heating that we allow for is adiabatic heating, caused by the compression of the electron gas. These assumptions result in an analytic treatment of expected electron-ion temperature ratio that agrees with observations of collisionless shocks: at low sonic Mach numbers, Ms ≲ 2, the electron-ion temperature ratio is close to unity, whereas for Mach numbers above Ms ≈ 60 the electron-ion temperature ratio asymptotically approaches a temperature ratio of Te/Ti = me/ ⟨ mi ⟩. In the intermediate Mach number range the electron-ion temperature ratio scales as Te/Ti ∝ Ms-2. In addition, we calculate the electron-ion temperature ratios under the assumption of adiabatic heating of the electrons only, which results in a higher electron-ion temperature ratio, but preserves the Te/Ti ∝ Ms-2 scaling. We also show that for magnetised shocks the electron-ion temperature ratio approaches the asymptotic value Te/Ti = me/ ⟨ mi ⟩ for lower magnetosonic Mach numbers (Mms), mainly because for a strongly magnetised shock the sonic Mach number is larger than the magnetosonic Mach number (Mms ≤ Ms). The predicted scaling of the electron
Bai, Xiao-Dong; Zhang, Mei; Xiong, Jun; Yang, Guo-Jian; Deng, Fu-Guo
2015-01-01
We investigate the formation of discrete breathers (DBs) and the dynamics of the mixture of two-species Bose-Einstein condensates (BECs) in open boundary optical lattices using the discrete nonlinear Schrödinger equations. The results show that the coupling of intra- and interspecies interaction can lead to the existence of pure single-species DBs and symbiotic DBs (i.e., two-species DBs). Furthermore, we find that there is a selective distillation phenomenon in the dynamics of the mixture of two-species BECs. One can selectively distil one species from the mixture of two-species BECs and can even control dominant species fraction by adjusting the intra- and interspecies interaction in optical lattices. Our selective distillation mechanism may find potential application in quantum information storage and quantum information processing based on multi-species atoms. PMID:26597592
Technology Transfer Automated Retrieval System (TEKTRAN)
Two species of Gelechioidea (Lepidoptera), Metharmostis multilineata Adamski, n. sp. (Cosmopterigidae), and Idiophantis soreuta Meyrick, 1906 (Gelechiidae), were collected in southeastern Asia for evaluation as potential biocontrol agents against downy rose myrtle, Rhodomyrtus tomentosa (Aiton) Hass...
Effects of time delay on symmetric two-species competition subject to noise
NASA Astrophysics Data System (ADS)
Nie, Linru; Mei, Dongcheng
2008-03-01
Noise and time delay act simultaneously on real ecological systems. The Lotka-Volterra model of symmetric two-species competition with noise and time delay was investigated in this paper. By means of stochastic simulation, we find that (i) the time delay induces the densities of the two species to periodically oscillate synchronously; (ii) the stationary probability distribution function of the two-species densities exhibits a transition from multiple to single stability as the delay time increases; (iii) the characteristic correlation time for the sum of the two-species densities squared exhibits a nonmonotonic behavior as a function of delay time. Our results have the implication that the combination of noise and time delay could provide an efficient tool for understanding real ecological systems.
MHD description of plasma: handbook of plasma physics
Kulsrud, R.M.
1980-10-01
The basic sets of MHD equations for the description of a plasma in various limits are derived and their usefulness and limits of validity are discussed. These limits are: the one fluid collisional plasma, the two fluid collisional plasma, the Chew-Goldberger Low formulation of the guiding center limit of a collisionless plasma and the double-adiabatic limit. Conservation relations are derived from these sets and the mathematics of the concept of flux freezing is given. An example is given illustrating the differences between guiding center theory and double adiabatic theory.
NASA Astrophysics Data System (ADS)
Guo, F.; Giacalone, J.
2009-12-01
We investigate electron acceleration at collisionless shocks propagating into an upstream plasma containing large-scale magnetic fluctuations in the direction normal to the mean field. We treat electrons as test particles, and integrate their trajectories numerically, in a time dependent electromagnetic field which is determined from a two-dimensional hybrid (kinetic ions, fluid electron) simulation. We find the large-scale magnetic fluctuations effect the electrons in a number of ways leading to efficient and rapid energization at the shock front. Since the electrons move freely along the magnetic field lines, the large scale field line meandering allows the fast-moving electrons to cross the shock front multiple times, leading to efficient acceleration. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring electrons back and forth between them. The downstream spectrum is broadened, with a power-law like tail at high energies up to 200-300 times of the original energy. It is also shown that the spatial distribution of energetic electrons appears to be similar to in-situ observations (e.g. Bale 1999; Simnett 2005). The study may be important in understanding observations of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures in type II solar radio bursts.
Jain, Neeraj; Büchner, Jörg
2014-06-15
In collisionless magnetic reconnection, electron current sheets (ECS) with thickness of the order of an electron inertial length form embedded inside ion current sheets with thickness of the order of an ion inertial length. These ECS's are susceptible to a variety of instabilities which have the potential to affect the reconnection rate and/or the structure of reconnection. We carry out a three dimensional linear eigen mode stability analysis of electron shear flow driven instabilities of an electron scale current sheet using an electron-magnetohydrodynamic plasma model. The linear growth rate of the fastest unstable mode was found to drop with the thickness of the ECS. We show how the nature of the instability depends on the thickness of the ECS. As long as the half-thickness of the ECS is close to the electron inertial length, the fastest instability is that of a translational symmetric two-dimensional (no variations along flow direction) tearing mode. For an ECS half thickness sufficiently larger or smaller than the electron inertial length, the fastest mode is not a tearing mode any more and may have finite variations along the flow direction. Therefore, the generation of plasmoids in a nonlinear evolution of ECS is likely only when the half-thickness is close to an electron inertial length.
Micro-instabilities and anomalous transport effects in collisionless guide field reconnection
NASA Astrophysics Data System (ADS)
Munoz Sepulveda, Patricio Alejandro; Büchner, Jörg; Kilian, Patrick
2016-07-01
It is often the case that magnetic reconnection takes place in collisionless plasmas with a current aligned guide magnetic field, such as in the Solar corona. The general characteristics of this process have been exhaustively analyzed with theory and numerical simulations, under different approximations, since some time ago. However, some consequences and properties of the secondary instabilities arising spontaneously -other than tearing instability-, and their dependence on the guide field strength, have not been completely understood yet. For this sake, we use the results of fully kinetic 2D PIC numerical simulations of guide field reconnection. By using a mean field approach for the Generalized Ohm's law that explains the balance of the reconnected electric field, we find that some of the cross-streaming and gradient driven instabilities -in the guide field case- produce an additional anomalous transport term. The latter can be interpreted as a result of the enhanced correlated electromagnetic fluctuations, leading to a slow down of the current carriers and kinetic scale turbulence. We characterize these processes on dependence on the guide field strength, and explore the causal relation with the source of free energy driving the mentioned instabilities. Finally, we show the main consequences that a fully 3D approach have on all those phenomena in contrast to the reduced 2D description.
Yang, Zhongwei; Lu, Quanming; Gao, Xinliang; Huang, Can; Yang, Huigen; Hu, Hongqiao; Han, Desheng; Liu, Ying
2013-09-15
Supercritical perpendicular collisionless shocks are known to exhibit foot, ramp, and overshoot structures. The shock ramp structure is in a smaller scale in contrast to other microstructures (foot and overshoot) within the shock front. One-dimensional full particle simulations of strictly perpendicular shocks over wide ranges of ion beta β{sub i}, Alfvén Mach number M{sub A}, and ion-to-electron mass ratio m{sub i}/m{sub e} are presented to investigate the impact of plasma parameters on the shock ramp scale. Main results are (1) the ramp scale can be as small as several electron inertial length. (2) The simulations suggest that in a regime below the critical ion beta value, the shock front undergoes a periodic self-reformation and the shock ramp scale is time-varying. At higher ion beta values, the shock front self-reformation is smeared. At still higher ion beta value, the motion of reflected ions is quite diffuse so that they can lead to a quasi-steady shock ramp. Throughout the above three conditions, the shock ramp thickness increases with β{sub i}. (3) The increase (decrease) in Mach number and the decrease (increase) in the beta value have almost equivalent impact on the state (i.e., stationary or nonstationary) of the shock ramp. Both of front and ramp thicknesses are increased with M{sub A}.
ENTROPY PRODUCTION IN COLLISIONLESS SYSTEMS. III. RESULTS FROM SIMULATIONS
Barnes, Eric I.; Egerer, Colin P. E-mail: egerer.coli@uwlax.edu
2015-05-20
The equilibria formed by the self-gravitating, collisionless collapse of simple initial conditions have been investigated for decades. We present the results of our attempts to describe the equilibria formed in N-body simulations using thermodynamically motivated models. Previous work has suggested that it is possible to define distribution functions for such systems that describe maximum entropy states. These distribution functions are used to create radial density and velocity distributions for comparison to those from simulations. A wide variety of N-body code conditions are used to reduce the chance that results are biased by numerical issues. We find that a subset of initial conditions studied lead to equilibria that can be accurately described by these models, and that direct calculation of the entropy shows maximum values being achieved.
Nonlinear Particle Pinch in Collisionless Trapped Electron Mode Turbulence
NASA Astrophysics Data System (ADS)
Terry, P. W.; Gatto, R.
2005-10-01
Collisionless trapped electron mode turbulence is shown to have an anomalous particle pinch fundamentally unlike pinches identified previously. It arises from a nonlinear fluctuation eigenmode, placing it outside the purview of quasilinear theory. The nonlinear eigenmode develops because the nonlinearity excites a damped linear eigenmode, changing the density- potential correlation. The flux is solved from spectrum balance equations in a complete basis spanning the fluctuation space under a joint expansion in collision frequency and instability threshold parameter. The solution accounts for saturation by anisotropic energy transfer to zonal wavenumbers of the damped eigenmode. To lowest order the pinch is a convective-like flux driven by temperature gradient. It arises from the damped eigenmode energy and the real part of the correlation between damped and growing eigenmodes. The pinch is slightly smaller than the outwardly directed flux associated with the growing eigenmode, making the flux a small fraction of the quasilinear value. Work supported by US DOE.
Electron Force Balance in Steady Collisionless-Driven Reconnection
Li Bin; Horiuchi, Ritoku
2008-11-21
Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfven velocity averaged over the electron dissipation region.
Plasma separation from magnetic field lines in a magnetic nozzle
NASA Technical Reports Server (NTRS)
Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.
1993-01-01
This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.
Umeda, Takayuki Kidani, Yoshitaka; Matsukiyo, Shuichi; Yamazaki, Ryo
2014-02-15
Large-scale two-dimensional (2D) full particle-in-cell (PIC) simulations are carried out for studying the relationship between the dynamics of a perpendicular shock and microinstabilities generated at the shock foot. The structure and dynamics of collisionless shocks are generally determined by Alfven Mach number and plasma beta, while microinstabilities at the shock foot are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the ratio of the plasma-to-cyclotron frequency. With a fixed Alfven Mach number and plasma beta, the ratio of the upstream bulk velocity to the electron thermal velocity is given as a function of the ion-to-electron mass ratio. The present 2D full PIC simulations with a relatively low Alfven Mach number (M{sub A} ∼ 6) show that the modified two-stream instability is dominant with higher ion-to-electron mass ratios. It is also confirmed that waves propagating downstream are more enhanced at the shock foot near the shock ramp as the mass ratio becomes higher. The result suggests that these waves play a role in the modification of the dynamics of collisionless shocks through the interaction with shock front ripples.
Wakefields generated by collisional neutrinos in neutral-electron-positron plasma
Tinakiche, Nouara
2013-02-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.
Mode-conversion induced tearing effects in a plasma neutral sheet
Kaw, P.K.; Sudan, R.N.
1981-01-01
A new collisionless dissipation mechanism which can drive tearing modes in a plasma neutral sheet is described. The new mechanism relies on the presence of a background cold plasma which leads to mode conversion into a continuous spectrum of cold plasma waves.
Time-dependence in relativistic collisionless shocks: theory of the variable
Spitkovsky, A
2004-02-05
We describe results from time-dependent numerical modeling of the collisionless reverse shock terminating the pulsar wind in the Crab Nebula. We treat the upstream relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. The relativistic cyclotron instability of the ion gyrational orbit downstream of the leading shock in the electron-positron pairs launches outward propagating magnetosonic waves. Because of the fresh supply of ions crossing the shock, this time-dependent process achieves a limit-cycle, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in the magnetic field and pair density associated with these waves, as well as their propagation speed, semi-quantitatively reproduce the behavior of the wisp and ring features described in recent observations obtained using the Hubble Space Telescope and the Chandra X-Ray Observatory. By selecting the parameters of the ion orbits to fit the spatial separation of the wisps, we predict the period of time variability of the wisps that is consistent with the data. When coupled with a mechanism for non-thermal acceleration of the pairs, the compressions in the magnetic field and plasma density associated with the optical wisp structure naturally account for the location of X-ray features in the Crab. We also discuss the origin of the high energy ions and their acceleration in the equatorial current sheet of the pulsar wind.
Weak turbulence theory of collisionless trapped electron driven drift instability in tokamaks
Hahm, T.S.; Tang, W.M.
1990-10-01
The toroidal collisionless trapped electron modes are analyzed in the weak turbulence regime treating both ions and trapped electrons nonlinearly in the presence of ion and electron temperature gradients. The spectral intensity of the density fluctuations in the nonlinearly saturated state is analytically obtained from the steady state solution of the wave-kinetic equation. Distant nonlinear interactions between low-k{sub {theta}} and high-k{sub {theta}} modes of similar frequencies via trapped electron scattering (the resonance between the beat wave and the trapped electron precession drift frequencies) suppress the low-k{sub {theta}} (k{sub {theta}}{rho}{sub s} {much lt} (L{sub n}/R){sup 1/2}) modes while close interactions via ion Compton scattering (nonlinear ion Landau damping) produce a monotonically decreasing spectrum from k{sub {theta}}{rho}{sub s} {congruent} (L{sub n}/R){sup 1/2} to k{sub {theta}}{rho}{sub s} {congruent} 1 according to an approximate power law k{sub {theta}}{sup {minus}3}. Various fluctuation amplitudes at saturation and the fluctuation-induced anomalous particle and heat fluxes are found to be smaller than the mixing length estimates. The plasma confinement is predicted to improve with higher T{sub i}/T{sub e}, more peaked density profile, larger aspect ratio, and higher plasma current. Also, a significant dependence of transport on the electron temperature gradient is found which could contribute to the rigidity of the electron temperature profile often experimentally observed.
Multiflow approach to plasma kinetics
Ignatov, A. M.
2015-10-15
Instead of the commonly used Vlasov equation, one is able to treat kinetic phenomena in collisionless plasma with the help of the infinite set of hydrodynamic equations. The present paper deals with the linear approximation of multiflow hydrodynamics. It is shown that single-particle and collective excitations analogous to Van Kampen waves are explicitly separated. Expressions for the energy of all eigenmodes are obtained.
NASA Astrophysics Data System (ADS)
Bamford, R. A.; Alves, E. P.; Cruz, F.; Kellett, B. J.; Fonseca, R. A.; Silva, L. O.; Trines, R. M. G. M.; Halekas, J. S.; Kramer, G.; Harnett, E.; Cairns, R. A.; Bingham, R.
2016-10-01
Investigation of the lunar crustal magnetic anomalies offers a comprehensive long-term data set of observations of small-scale magnetic fields and their interaction with the solar wind. In this paper a review of the observations of lunar mini-magnetospheres is compared quantifiably with theoretical kinetic-scale plasma physics and 3D particle-in-cell simulations. The aim of this paper is to provide a complete picture of all the aspects of the phenomena and to show how the observations from all the different and international missions interrelate. The analysis shows that the simulations are consistent with the formation of miniature (smaller than the ion Larmor orbit) collisionless shocks and miniature magnetospheric cavities, which has not been demonstrated previously. The simulations reproduce the finesse and form of the differential proton patterns that are believed to be responsible for the creation of both the “lunar swirls” and “dark lanes.” Using a mature plasma physics code like OSIRIS allows us, for the first time, to make a side-by-side comparison between model and space observations. This is shown for all of the key plasma parameters observed to date by spacecraft, including the spectral imaging data of the lunar swirls. The analysis of miniature magnetic structures offers insight into multi-scale mechanisms and kinetic-scale aspects of planetary magnetospheres.
Quantum Entanglement and Spin Squeezing of Two Species Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Li, Song-Song
2016-09-01
We investigate quantum entanglement and spin squeezing of two species Bose-Einstein condensates. By the rotating-wave approximation, we obtain the effective Hamiltonian and the wave function of the system. It's shown that more entanglement and squeezing may be achieved by increasing the population difference of particles.
Permanence for two-species Lotka-Volterra cooperative systems with delays.
Lu, Guichen; Lu, Zhengyi
2008-07-01
In this paper, a two-species Lotka-Volterra cooperative delay system is considered, and the relationships between the delays and the permanence are obtained. Some sufficient conditions for the permanence under the assumption of smallness of the delays are obtained. Two examples are given to illustrate the theorems.
Modeling the Lyα Forest in Collisionless Simulations
NASA Astrophysics Data System (ADS)
Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.
2016-08-01
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.
THE FINAL-PARSEC PROBLEM IN THE COLLISIONLESS LIMIT
Vasiliev, Eugene; Antonini, Fabio; Merritt, David E-mail: fabio.antonini@northwestern.edu
2015-09-01
A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. We find that the binary hardening rate is always substantially lower than the maximum possible, “full-loss-cone” rate, and that it decreases with time, but that stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale ≲1 Gyr in any triaxial galaxy.
Modeling the Lyα Forest in Collisionless Simulations
NASA Astrophysics Data System (ADS)
Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.
2016-08-01
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%-80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.
STATISTICAL MECHANICS OF COLLISIONLESS ORBITS. II. STRUCTURE OF HALOS
Williams, Liliya L. R.; Hjorth, Jens E-mail: jens@dark-cosmology.d
2010-10-10
In this paper, we present the density, {rho}, velocity dispersion, {sigma}, and {rho}/{sigma}{sup 3} profiles of isotropic systems which have the energy distribution, N({epsilon}) {proportional_to} [exp({phi}{sub 0} - {epsilon}) - 1], derived in Paper I. This distribution, dubbed {sup D}ARKexp{sup ,} is the most probable final state of a collisionless self-gravitating system, which is relaxed in terms of particle energies, but not necessarily in terms of angular momentum. We compare the DARKexp predictions with the results obtained using the extended secondary infall model (ESIM). The ESIM numerical scheme is optimally suited for this purpose because (1) it relaxes only through energy redistribution, leaving shell/particle angular momenta unaltered and (2) being a shell code with radially increasing shell thickness, it has very good mass resolution in the inner halo, where the various theoretical treatments give different predictions. The ESIM halo properties, and especially their energy distributions, are very well fit by DARKexp, implying that the techniques of statistical mechanics can be used to explain the structure of relaxed self-gravitating systems.
The Final-parsec Problem in the Collisionless Limit
NASA Astrophysics Data System (ADS)
Vasiliev, Eugene; Antonini, Fabio; Merritt, David
2015-09-01
A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. We find that the binary hardening rate is always substantially lower than the maximum possible, “full-loss-cone” rate, and that it decreases with time, but that stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale ≲1 Gyr in any triaxial galaxy.
NASA Astrophysics Data System (ADS)
Bhattacharjee, A.; Germaschewski, K.; Wang, X.; Linde, T.; Rosner, R.; Siegel, A.
2002-12-01
There has been considerable interest in recent years in collisionless reconnection dynamics governed by the generalized Ohm's law in which electron inertia provides the mechanism for breaking field lines. It has been suggested in several theoretical studies that the nonlinear reconnection dynamics, to leading order, is independent of the mechanism that breaks field lines (that is, electron inertia). We test this suggestion carefully using the new Magnetic Reconnection Code (MRC) developed at the Center for Magnetic Reconnection Studies. The MRC is a new massively parallel code with Adaptive Mesh Refinement (AMR) that integrates the equations of Hall MHD. The use of AMR enables unprecedented levels of resolution of the current and vorticity layers and uncovers interesting secondary dynamics not seen in previous studies. We apply the MRC to the study of two problems, one involving free reconnection caused by a spontaneous and fast collisionless instability, the other involving forced reconnection induced by boundary perturbations on a stable plasma. In the case of free reconnection, over the range of parameters covered by our simulations, it is shown that the nonlinear reconnection rate is near-explosive, and furthermore, that the nonlinear magnetic island width is an invariant function of a dimensionless variable which is the product of the linear growth rate and time. Now, since the linear growth rate is a function of the ion sound radius as well as the electron skin depth, we conclude that the nonlinear reconnection rate is not independent of electron inertia. In the case of forced reconnection, after a slow growth phase, the dynamics exhibits an impulsive growth in the amplitude of the thin current sheet, and a subsequent current disruption mediated by secondary instabilities. These results, in which electron inertia provides the mechanism for breaking field lines, are contrasted with resistive Hall MHD simulations in which resistivity provides the mechanism for
ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HAeRM TO THE COLLISIONLESS LIMIT
Bale, S. D.; Quataert, E.; Pulupa, M.; Salem, C.; Chen, C. H. K.
2013-06-01
We use a statistically significant set of measurements to show that the field-aligned electron heat flux q{sub Parallel-To} in the solar wind at 1 AU is consistent with the Spitzer-Haerm collisional heat flux q{sub sh} for temperature gradient scales larger than a few mean free paths L{sub T} {approx}> 3.5{lambda}{sub fp}. This represents about 65% of the measured data and corresponds primarily to high {beta}, weakly collisional plasma ({sup s}low solar wind{sup )}. In the more collisionless regime {lambda}{sub fp}/L{sub T} {approx}> 0.28, the electron heat flux is limited to q{sub Parallel-To }/q{sub 0} {approx} 0.3, independent of mean free path, where q{sub 0} is the ''free-streaming'' value; the measured q{sub Parallel-To} does not achieve the full q{sub 0}. This constraint q{sub Parallel-To }/q{sub 0} {approx} 0.3 might be attributed to wave-particle interactions, effects of an interplanetary electric potential, or inherent flux limitation. We also show a {beta}{sub e} dependence to these results that is consistent with a local radial electron temperature profile T{sub e} {approx} r {sup -{alpha}} that is a function of the thermal electron beta {alpha} = {alpha}({beta}{sub e}) and that the {beta} dependence of the collisionless regulation constraint is not obviously consistent with a whistler heat flux instability. It may be that the observed saturation of the measured heat flux is a simply a feature of collisional transport. We discuss the results in a broader astrophysical context.
Plasma Astrophysics: Kinetic Processes in Solar and Stellar Coronae, Second Edition
NASA Astrophysics Data System (ADS)
Gary, S. Peter
A collision-less plasma is an ionized fluid that is so hot and tenuous that interactions between individual particles are unimportant. In such a plasma, electric and magnetic fields mediate interactions among particles, and fundamental physics is addressed by kinetic theories that describe not only the spatial and temporal variations of the medium, but also its velocity-space properties. The outer corona of our Sun and the outer coronae of many stars are collision-less plasmas. Thus, the preface begins, ``This textbook is intended as an introduction to the physics of solar and stellar coronae, emphasizing kinetic plasma processes.'' But the content of Plasma Astrophysics extends well beyond the stated purview. In fact, many plasmas of the universe are collisionless, including many space plasmas-those that are subject to in situ measurements by spacecraft-and a wide variety of astrophysical plasmas. Thus, although the parameters and phenomena that characterize the collision-less plasmas of space, the solar corona, and astrophysics are often very different, the physics in each case derives from the same fundamental kinetic plasma theory.
PARTICLE ACCELERATION BY COLLISIONLESS SHOCKS CONTAINING LARGE-SCALE MAGNETIC-FIELD VARIATIONS
Guo, F.; Jokipii, J. R.; Kota, J. E-mail: jokipii@lpl.arizona.ed
2010-12-10
Diffusive shock acceleration at collisionless shocks is thought to be the source of many of the energetic particles observed in space. Large-scale spatial variations of the magnetic field have been shown to be important in understanding observations. The effects are complex, so here we consider a simple, illustrative model. Here we solve numerically the Parker transport equation for a shock in the presence of large-scale sinusoidal magnetic-field variations. We demonstrate that the familiar planar-shock results can be significantly altered as a consequence of large-scale, meandering magnetic lines of force. Because the perpendicular diffusion coefficient {kappa}{sub perpendicular} is generally much smaller than the parallel diffusion coefficient {kappa}{sub ||}, the energetic charged particles are trapped and preferentially accelerated along the shock front in the regions where the connection points of magnetic field lines intersecting the shock surface converge, and thus create the 'hot spots' of the accelerated particles. For the regions where the connection points separate from each other, the acceleration to high energies will be suppressed. Further, the particles diffuse away from the 'hot spot' regions and modify the spectra of downstream particle distribution. These features are qualitatively similar to the recent Voyager observations in the Heliosheath. These results are potentially important for particle acceleration at shocks propagating in turbulent magnetized plasmas as well as those which contain large-scale nonplanar structures. Examples include anomalous cosmic rays accelerated by the solar wind termination shock, energetic particles observed in propagating heliospheric shocks, galactic cosmic rays accelerated by supernova blast waves, etc.
Constraining the magnetic field in GRB relativistic collisionless shocks using radio data
NASA Astrophysics Data System (ADS)
Barniol Duran, R.
2014-08-01
Using gamma-ray burst (GRB) radio afterglow observations, we calculate the fraction of shocked plasma energy in the magnetic field in relativistic collisionless shocks (ɛB). We obtained ɛB for 38 bursts by assuming that the radio afterglow light curve originates in the external forward shock, and that its peak at a few to tens of days is due to the passage of the minimum (injection) frequency through the radio band. This allows for the determination of the peak synchrotron flux of the external forward shock, fp, which is f_p ∝ ɛ _B^{1/2}. The obtained value of ɛB is conservatively a minimum if the time of the `jet break' is unknown, since after the `jet break' fp is expected to decay with time faster than before it. Claims of `jet breaks' have been made for a subsample of 23 bursts, for which we can estimate a measurement of ɛB. Our results depend on the blast wave total energy, E, and the density of the circumstellar medium (CSM), n, as ɛB ∝ E-2n-1. However, by assuming a CSM magnetic field (˜10 μG), we can express the lower limits/measurements on ɛB as a density-independent ratio, B/Bsc, of the magnetic field behind the shock to the CSM shock-compressed magnetic field. We find that the distribution on both the lower limit on and the measurement of B/Bsc spans ˜3.5 orders of magnitude and both have a median of B/Bsc ˜ 30. This suggests that some amplification, beyond simple shock compression, is necessary to explain these radio afterglow observations.
NASA Astrophysics Data System (ADS)
Kucharek, H.; Pogorelov, N. V.; Gamayunov, K. V.
2015-12-01
Collisionless shocks are an important feature in astrophysical, heliospheric and magnetospheric settings. At these structures plasma is heated, the properties of flows are changed, and particles are accelerated to high energies. Particles are accelerated throughout the heliosphere. There are no times or conditions where suprathermal ions forming tails are not present on the solar wind ion distribution, and given the low speeds of these particles they must be accelerated locally in the heliosphere. Coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs) accelerate particles up to 10s of MeV/nucleon. The termination shock of the solar and the heliosheath produce energetic particles including the Anomalous Cosmic Rays (ACRs), with energies in excess of 100 MeV. In the last few years' very interesting observations at low energies showing power laws that cannot be explained with commonly accepted acceleration mechanisms and thus increased the need for alternative acceleration processes. Fully consistent kinetic particle simulations such as hybrid simulations appear to be a powerful tool to investigated ion acceleration. Nowadays these simulations can be performed in 3D and relative large simulation domains covering up to hundreds of ion inertial length in size and thus representing the MHD scale. These 3D hybrid simulations show filamentary magnetic and density structures, which could be interpreted as small-scale flux ropes. The growth of these small-scale structures is also associated with ion acceleration. In this talk we will discuss properties of these filamentary structures, their spatial and temporal evolution and the particle dynamics during the acceleration process. The results of this study may be of particular importance for future high resolution magnetospheric and heliospheric mission such as THOR.
Daughton, W.; Roytershteyn, V.; Yin, L.; Albright, B. J.; Gary, S. P.; Karimabadi, H.; Bowers, Kevin J.
2011-01-04
The evolution of magnetic reconnection in large-scale systems often gives rise to extended current layers that are unstable to the formation of secondary magnetic islands. The role of these islands in the reconnection process and the conditions under which they form remains a subject of debate. In this work, we benchmark two different kinetic particle-in-cell codes to address the formation of secondary islands for several types of global boundary conditions. The influence on reconnection is examined for a range of conditions and collisionality limits. Although secondary islands are observed in all cases, their influence on reconnection may be different depending on the regime. In the collisional limit, the secondary islands play a key role in breaking away from the slow Sweet-Parker scaling and pushing the evolution towards small scales where kinetic effects can dominate. In the collisionless limit, fast reconnection can proceed in small systems (30x ion inertial scale) without producing any secondary islands. However, in large-scale systems the diffusion region forms extended current layers that are unstable to the formation of secondary islands, giving rise to a time-dependent reconnection process. These instabilities provide one possible mechanism for controlling the average length of the diffusion region in large systems. New results from Fokker-Planck kinetic simulations are used to examine the role of secondary islands in electron-positron plasmas for both collisional and kinetic parameter regimes. Simple physics arguments suggest the transition should occur when the resistive layers approach the inertial scale. These expectations are confirmed by simulations, which demonstrate the average rate remains fast in large systems and is accompanied by the continuous formation of secondary islands.
Multifactorial Competition and Resistance in a Two-Species Bacterial System
Khare, Anupama; Tavazoie, Saeed
2015-01-01
Microorganisms exist almost exclusively in interactive multispecies communities, but genetic determinants of the fitness of interacting bacteria, and accessible adaptive pathways, remain uncharacterized. Here, using a two-species system, we studied the antagonism of Pseudomonas aeruginosa against Escherichia coli. Our unbiased genome-scale approach enabled us to identify multiple factors that explained the entire antagonism observed. We discovered both forms of ecological competition–sequestration of iron led to exploitative competition, while phenazine exposure engendered interference competition. We used laboratory evolution to discover adaptive evolutionary trajectories in our system. In the presence of P. aeruginosa toxins, E. coli populations showed parallel molecular evolution and adaptive convergence at the gene-level. The multiple resistance pathways discovered provide novel insights into mechanisms of toxin entry and activity. Our study reveals the molecular complexity of a simple two-species interaction, an important first-step in the application of systems biology to detailed molecular dissection of interactions within native microbiomes. PMID:26647077
Collisionless encounters and the origin of the lunar inclination.
Pahlevan, Kaveh; Morbidelli, Alessandro
2015-11-26
The Moon is generally thought to have formed from the debris ejected by the impact of a planet-sized object with the proto-Earth towards the end of planetary accretion. Models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the Moon in a near-equatorial orbit. Forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value--a long-standing discrepancy known as the lunar inclination problem. Here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with Earth-crossing planetesimals that were not yet accreted at the time of the Moon-forming event. The currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass (corresponding to 0.0075-0.015 Earth masses eventually accreted to the Earth) carried by a few bodies, consistent with the constraints and models of late accretion. Although the encounter process has a stochastic element, the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters. The excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the Earth-Moon system with strong dissipation of tidal energy on the early Earth. This mechanism obviates the need for previously proposed (but idealized) excitation mechanisms, places the Moon-forming event in the context of the formation of Earth, and constrains the pristineness of the dynamical state of the Earth-Moon system. PMID:26607544
Statistical mechanics of collisionless orbits. IV. Distribution of angular momentum
Williams, Liliya L. R.; Hjorth, Jens; Wojtak, Radosław E-mail: jens@dark-cosmology.dk
2014-03-01
It has been shown in previous work that DARKexp, which is a theoretically derived, maximum entropy, one shape parameter model for isotropic collisionless systems, provides very good fits to simulated and observed dark matter halos. Specifically, it fits the energy distribution, N(E), and the density profiles, including the central cusp. Here, we extend DARKexp N(E) to include the distribution in angular momentum, L {sup 2}, for spherically symmetric systems. First, we argue, based on theoretical, semi-analytical, and simulation results, that while dark matter halos are relaxed in energy, they are not nearly as relaxed in angular momentum, which precludes using maximum entropy to uniquely derive N(E, L {sup 2}). Instead, we require that when integrating N(E, L {sup 2}) over squared angular momenta one retrieves the DARKexp N(E). Starting with a general expression for N(E, L {sup 2}) we show how the distribution of particles in L {sup 2} is related to the shape of the velocity distribution function, VDF, and velocity anisotropy profile, β(r). We then demonstrate that astrophysically realistic halos, as judged by the VDF shape and β(r), must have linear or convex distributions in L {sup 2}, for each separate energy bin. The distribution in energy of the most bound particles must be nearly flat, and become more tilted in favor of radial orbits for less bound particles. These results are consistent with numerical simulations and represent an important step toward deriving the full distribution function for spherically symmetric dark matter halos.
Collisionless encounters and the origin of the lunar inclination.
Pahlevan, Kaveh; Morbidelli, Alessandro
2015-11-26
The Moon is generally thought to have formed from the debris ejected by the impact of a planet-sized object with the proto-Earth towards the end of planetary accretion. Models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the Moon in a near-equatorial orbit. Forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value--a long-standing discrepancy known as the lunar inclination problem. Here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with Earth-crossing planetesimals that were not yet accreted at the time of the Moon-forming event. The currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass (corresponding to 0.0075-0.015 Earth masses eventually accreted to the Earth) carried by a few bodies, consistent with the constraints and models of late accretion. Although the encounter process has a stochastic element, the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters. The excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the Earth-Moon system with strong dissipation of tidal energy on the early Earth. This mechanism obviates the need for previously proposed (but idealized) excitation mechanisms, places the Moon-forming event in the context of the formation of Earth, and constrains the pristineness of the dynamical state of the Earth-Moon system.
Asymmetric evolution of magnetic reconnection in collisionless accretion disk
Shirakawa, Keisuke Hoshino, Masahiro
2014-05-15
An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J{sub 0}×Ω{sub 0}, where J{sub 0} is the initial current density in the neutral sheet and Ω{sub 0} is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.
Igor D. Kaganovich; Oleg Polomarov
2003-05-19
In low-pressure discharges, when the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially non-local. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the non-local conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, non-uniform, nearly collisionless plasmas of low-pressure discharges is derived. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. The importance of accounting for the non-uniform plasma density profile on both the current density profile and the EEDF is demonstrated.
Effects of cross diffusion on Turing bifurcations in two-species reaction-transport systems
NASA Astrophysics Data System (ADS)
Kumar, Niraj; Horsthemke, Werner
2011-03-01
We study the Turing bifurcation in general two-species reaction-transport systems, where particle dispersal is governed by diffusion, including cross diffusion. By performing a linear stability analysis, we find conditions for the Turing instability and compare the results with the standard Turing conditions. We apply our results to two model systems, the Lengyel-Epstein model and the Brusselator, and find strong effects of cross diffusion on the Turing bifurcation.
Effects of cross diffusion on Turing bifurcations in two-species reaction-transport systems.
Kumar, Niraj; Horsthemke, Werner
2011-03-01
We study the Turing bifurcation in general two-species reaction-transport systems, where particle dispersal is governed by diffusion, including cross diffusion. By performing a linear stability analysis, we find conditions for the Turing instability and compare the results with the standard Turing conditions. We apply our results to two model systems, the Lengyel-Epstein model and the Brusselator, and find strong effects of cross diffusion on the Turing bifurcation. PMID:21517556
Sculpted-multilayer optical effects in two species of Papilio butterfly.
Vukusic, P; Sambles, R; Lawrence, C; Wakely, G
2001-03-01
The wing-scale microstructures associated with two species of Papilio butterfly are described and characterized. Despite close similarities in their structures, they do not exhibit analogous optical effects. With Papilio palinurus, deep modulations in its multilayering create bicolor reflectivity with strong polarization effects, and this leads to additive color mixing in certain visual systems. In contrast to this, Papilio ulysses features shallow multilayer modulation that produces monocolor reflectivity without significant polarization effects. PMID:18357096
Zacharias, O.; Kleiber, R.; Borchardt, M.; Comisso, L.; Grasso, D.; Hatzky, R.
2014-06-15
The first detailed comparison between gyrokinetic and gyrofluid simulations of collisionless magnetic reconnection has been carried out. Both the linear and nonlinear evolution of the collisionless tearing mode have been analyzed. In the linear regime, we have found a good agreement between the two approaches over the whole spectrum of linearly unstable wave numbers, both in the drift kinetic limit and for finite ion temperature. Nonlinearly, focusing on the small-Δ′ regime, with Δ′ indicating the standard tearing stability parameter, we have compared relevant observables such as the evolution and saturation of the island width, as well as the island oscillation frequency in the saturated phase. The results are basically the same, with small discrepancies only in the value of the saturated island width for moderately high values of Δ′. Therefore, in the regimes investigated here, the gyrofluid approach can describe the collisionless reconnection process as well as the more complete gyrokinetic model.
Sayed, F.; Tyshetskiy, Yu.; Vladimirov, S. V.; Ishihara, O.
2015-05-15
The modulational and filamentational instabilities of a monochromatic Langmuir pump wave are investigated for the case of collisionless quantum plasmas, using renormalized quantum linear and nonlinear plasma polarization responses. We obtain the quantum-corrected dispersion equation for the modulational and filamentational instabilities growth rates. It is demonstrated that the quantum effect suppresses the growth rates of the modulational and filamentational instabilities.
Time-resolved characterization of the formation of a collisionless shock.
Ahmed, H; Dieckmann, M E; Romagnani, L; Doria, D; Sarri, G; Cerchez, M; Ianni, E; Kourakis, I; Giesecke, A L; Notley, M; Prasad, R; Quinn, K; Willi, O; Borghesi, M
2013-05-17
We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching particle-in-cell simulation and theoretical considerations, we suggest that this process is analogous to ion reflection at supercritical collisionless shocks in supernova remnants. PMID:25167421
Chromodynamic fluctuations in quark-gluon plasma
Mrowczynski, Stanislaw
2008-05-15
Fluctuations of chromodynamic fields in the collisionless quark-gluon plasma are found as a solution of the initial value linearized problem. The plasma initial state is on average colorless, stationary, and homogeneous. When the state is stable, the initial fluctuations decay exponentially and in the long-time limit a stationary spectrum of fluctuations is established. For the equilibrium plasma it reproduces the spectrum which is provided by the fluctuation-dissipation relation. Fluctuations in the unstable plasma, where the memory of initial fluctuations is not lost, are also discussed.
Metastability of collisionless current sheets. Hannes Alfven Lecture on behalf of Albert Galeev
NASA Astrophysics Data System (ADS)
Zelenyi, L.; Galeev, A.
2009-04-01
Complicated magnetic configurations containing numerous magnetic field reversals are widespread in nature. Each of such reversals is supported by corresponding current sheet (CS) which could often have very small thickness comparable to ion skin depth. Since the beginning of Space Age "in situ" investigations of current sheets in the Earth's magnetosphere (magnetopause and magnetotail) acquired one of the highest priorities in national space programs and became one of the cornerstones of various international activities, like ISTP, IACG, and ILWS, which appeared to be very effective. Intense theoretical efforts were undertaken by theorists all over the world to develop both equilibrium models of current sheets and analyze its stability and further nonlinear evolution. Lack of collisions and smallness of many characteristic scales in comparison with ion Larmor radius made an application of straightforward MHD approach dramatically questionable. Professor Alfven was one of the first who suggested in 1968 simple but very physical self-consistent particle model of CS. One of the most intriguing features of current sheets in collisionless plasma is their ability to accumulate tremendous amounts of magnetic energy (1015 J for magnetospheric substorms , 1024 J for solar flare associated sheets) and then suddenly sometimes almost explosively release them. We will demonstrate in this talk that such METASTABILITY is a principal intrinsic feature of current sheets in hot plasma. Very intense theoretical debates of 80-ies and late 90-ies resulted in some consensus that current sheets with the small component of magnetic field normal to their plane become overstable for spontaneous reconnection (i.e. versus the development of ion tearing mode). Analysis of INTERBALL and especially 4- point CLUSTER data have shown that real current sheets observed in the Earth's magnetotail very rarely resemble simplistic HARRIS current sheets which have been used for an early stability
PARTICLE ACCELERATION IN RELATIVISTIC MAGNETIZED COLLISIONLESS ELECTRON-ION SHOCKS
Sironi, Lorenzo; Spitkovsky, Anatoly E-mail: anatoly@astro.princeton.edu
2011-01-10
We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5-dimensional particle-in-cell simulations with ion-to-electron mass ratios (m{sub i} /m{sub e} ) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In 'subluminal' shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via the first-order Fermi process. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains {approx}5% of ions and {approx}30% of ion energy. Its slope is -2.1 {+-} 0.1. The scattering is provided by short-wavelength non-resonant modes produced by Bell's instability, whose growth is seeded by the current of shock-accelerated ions that propagate ahead of the shock. Upstream electrons enter the shock with lower energy than ions (albeit by only a factor of {approx}5 << m{sub i} /m{sub e} ), so they are more strongly tied to the field. As a result, only {approx}1% of the incoming electrons are accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5 {+-} 0.1). For 'superluminal' shocks, where relativistic particles cannot outrun the shock along the field, the self-generated turbulence is not strong enough to permit efficient Fermi acceleration, and the ion and electron downstream spectra are consistent with thermal distributions. The incoming electrons are heated up to equipartition with ions, due to strong electromagnetic waves emitted by the shock into the upstream. Thus, efficient electron heating ({approx}>15% of the upstream ion energy) is the universal property of relativistic electron-ion shocks, but significant nonthermal acceleration of electrons ({approx}>2% by number, {approx}>10% by energy, with slope flatter than -2.5) is hard to achieve in
Comparison of sterols and fatty acids in two species of Ganoderma
2012-01-01
Background Two species of Ganoderma, G. sinense and G. lucidum, are used as Lingzhi in China. Howerver, the content of triterpenoids and polysaccharides, main actives compounds, are significant different, though the extracts of both G. lucidum and G. sinense have antitumoral proliferation effect. It is suspected that other compounds contribute to their antitumoral activity. Sterols and fatty acids have obvious bioactivity. Therefore, determination and comparison of sterols and fatty acids is helpful to elucidate the active components of Lingzhi. Results Ergosterol, a specific component of fungal cell membrane, was rich in G. lucidum and G. sinense. But its content in G. lucidum (median content 705.0 μg·g-1, range 189.1-1453.3 μg·g-1, n = 19) was much higher than that in G. sinense (median content 80.1 μg·g-1, range 16.0-409.8 μg·g-1, n = 13). Hierarchical clustering analysis based on the content of ergosterol showed that 32 tested samples of Ganoderma were grouped into two main clusters, G. lucidum and G. sinense. Hierarchical clustering analysis based on the contents of ten fatty acids showed that two species of Ganoderma had no significant difference though two groups were also obtained. The similarity of two species of Ganoderma in fatty acids may be related to their antitumoral proliferation effect. Conclusions The content of ergosterol is much higher in G. lucidum than in G. sinense. Palmitic acid, linoleic acid, oleic acid, stearic acid are main fatty acids in Ganoderma and their content had no significant difference between G. lucidum and G. sinense, which may contribute to their antitumoral proliferation effect. PMID:22293530
On the evolution of linear waves in cosmological plasmas
Dodin, I. Y.; Fisch, N. J.
2010-08-15
The scalings for basic plasma modes in the Friedmann-Robertson-Walker model of the expanding Universe are revised. Contrary to the existing literature, the wave collisionless evolution must comply with the action conservation theorem. The proper steps to deduce the action conservation from ab initio analytical calculations are presented, and discrepancies in the earlier papers are identified. In general, the cosmological wave evolution is more easily derived from the action conservation in the collisionless limit, whereas when collisions are essential, the statistical description must suffice, thereby ruling out the need for using dynamic equations in either case.
Sikes, Derek S.; Allen, Robert T.
2016-01-01
Abstract Species in the class Diplura are recorded from Alaska for the first time. Two species, Tricampa rileyi Silvestri from Dall and Prince of Wales Islands in the Alexander Archipelago of Southeast Alaska and Metriocampa allocerca Conde & Geeraert from near Quartz Lake, southeast of Fairbanks, both in the family Campodeidae, are documented based on recently collected specimens deposited in the University of Alaska Museum Insect Collection. A brief review of the history of the documentation of the Alaskan soil microarthropod fauna is provided, as well as discussion of possible glacial refugia. PMID:27047242
Nedorezov, L V
2015-01-01
Analysis of deviations between trajectories of Lotka-Volterra model of competition between two species and G.F. Gause experimental time series on combined cultivation of Paramecium aurelia and Paramecium caudatum shows that with rather big probability there is no correspondence between model and experimental datasets. Testing of sets of deviations was provided on symmetry with. respect to origin (Kolmogorov-Smirnov, Lehmann-Rosenblatt, Wald-Wolfowitz, and Munn-Whitney criterions) and on existence/absence of serial correlation in sequences of residuals (Swed-Eisenhart and "jumps up-jumps down" tests).
Reovirus infection in two species of Psittaciformes recently imported into Italy.
Conzo, G; Magnino, S; Sironi, G; Lavazza, A; Vigo, P G; Fioretti, A; Kaleta, E F
2001-02-01
An outbreak of reovirus infection with high mortality in two groups of recently imported psittacine birds is reported. The disease in the two species involved, African grey parrots (Psittacus erithacus erithacus) and Australian king parrots (Alisterus scapularis), had differences in clinical presentation and gross lesions. Reovirus particles were observed by electron microscopy and ultrastructural examination of tissues, and two viruses were isolated in cell culture, one from each bird species. Both isolates were studied by cross-neutralization with antisera against reference avian reoviruses isolated from chickens and parrots, and were found to have the greatest similarity to viruses isolated from a budgerigar and a southern screamer. PMID:19184872
Nedorezov, L V
2015-01-01
Analysis of deviations between trajectories of Lotka-Volterra model of competition between two species and G.F. Gause experimental time series on combined cultivation of Paramecium aurelia and Paramecium caudatum shows that with rather big probability there is no correspondence between model and experimental datasets. Testing of sets of deviations was provided on symmetry with. respect to origin (Kolmogorov-Smirnov, Lehmann-Rosenblatt, Wald-Wolfowitz, and Munn-Whitney criterions) and on existence/absence of serial correlation in sequences of residuals (Swed-Eisenhart and "jumps up-jumps down" tests). PMID:26591617
Protaeolidiella atra Baba, 1955 versus Pleurolidia juliae Burn, 1966: One or two species?
NASA Astrophysics Data System (ADS)
Carmona, Leila; Pola, Marta; Gosliner, Terrence M.; Cervera, Juan Lucas
2015-06-01
Protaeolidiella atra Baba, 1955 and Pleurolidia juliae Burn, 1966 are two species traditionally regarded as the members of Aeolidiidae but recently attributed to Facelinidae. Because of their apparent similarities, Rudman (J Molluscan Stud 56:505-514, 1990) rendered P. juliae as a junior synonym of P. atra. In this paper, we conducted a review of both species and completed their descriptions with new data regarding the anatomy of the reproductive system . P. atra and P. juliae have differences in their colouration, number of cerata and characteristics of their reproductive system. Based on these differences, we conclude that these species are not conspecific and should be regarded as distinct taxa.
NASA Astrophysics Data System (ADS)
Hsu, S. C.; Moser, A. L.; Merritt, E. C.; Adams, C. S.
2015-11-01
Over the past 4 years on the Plasma Liner Experiment (PLX) at LANL, we have studied obliquely and head-on-merging supersonic plasma jets of an argon/impurity or hydrogen/impurity mixture. The jets are formed/launched by pulsed-power-driven railguns. In successive experimental campaigns, we characterized the (a) evolution of plasma parameters of a single plasma jet as it propagated up to ~ 1 m away from the railgun nozzle, (b) density profiles and 2D morphology of the stagnation layer and oblique shocks that formed between obliquely merging jets, and (c) collisionless interpenetration transitioning to collisional stagnation between head-on-merging jets. Key plasma diagnostics included a fast-framing CCD camera, an 8-chord visible interferometer, a survey spectrometer, and a photodiode array. This talk summarizes the primary results mentioned above, and highlights analyses of inferred post-shock temperatures based on observations of density gradients that we attribute to shock-layer thickness. We also briefly describe more recent PLX experiments on Rayleigh-Taylor-instability evolution with magnetic and viscous effects, and potential future collisionless shock experiments enabled by low-impurity, higher-velocity plasma jets formed by contoured-gap coaxial guns. Supported by DOE Fusion Energy Sciences and LANL LDRD.
Collisionless relaxation of downstream ion distributions in low-Mach number shocks
Gedalin, M.; Friedman, Y.; Balikhin, M.
2015-07-15
Collisionlessly formed downstream distributions of ions in low-Mach number shocks are studied. General expressions for the asymptotic value of the ion density and pressure are derived for the directly transmitted ions. An analytical approximation for the overshoot strength is suggested for the low-β case. Spatial damping scale of the downstream magnetic oscillations is estimated.
Cardoso, Adauto Lima; Sales, Karline Alves Holanda; Nagamachi, Cleusa Yoshiko; Pieczarka, Julio Cesar; Noronha, Renata Coelho Rodrigues
2013-01-01
Abstract The family Loricariidae encompasses approximately 800 species distributed in six subfamilies. The subfamily Hypostominae consists of five tribes; of them, the tribe Ancistrini is relatively diverse, but it is not well known from the cytogenetic point of view. Genus Scobinancistrus Isbrücker et Nijssen, 1989, which is part of the tribe Ancistrini, has two species that occur in sympatry in the Xingu River, Brazil. In this work, we performed the first karyotypic characterizations of these two species and sought to identify the processes involved in their karyotypic evolution. Chromosomal preparations were subjected to Giemsa staining, silver nitrate impregnation, C-banding, CMA3 staining, DAPI staining, and FISH (fluorescence in situ hybridization) with 18S rDNA and telomeric probes. We found that Scobinancistrus aureatus Burgess, 1994 and Scobinancistrus pariolispos Isbrücker et Nijssen, 1989 shared the diploid number, 2n=52, but differed in their karyotypic formulae (KFs), distribution of constitutive heterochromatin (CH), and the localizations of their nucleolus organizer regions (NORs), which were found on the interstitial and distal regions of the long arm of chromosome pair 3 in Scobinancistrus aureatus and Scobinancistrus pariolispos respectively. We suggest that these interspecific variations may have arisen via paracentric inversion or transposition of the NOR. The karyotypic differences found between these two Scobinancistrus species can be used to identify them taxonomically, and may have functioned as a mechanism of post-zygotic reproductive isolation during the speciation process. PMID:24260689
Lisney, Thomas J; Stecyk, Karyn; Kolominsky, Jeffrey; Graves, Gary R; Wylie, Douglas R; Iwaniuk, Andrew N
2013-12-01
Vultures are highly reliant on their sensory systems for the rapid detection and localization of carrion before other scavengers can exploit the resource. In this study, we compared eye morphology and retinal topography in two species of New World vultures (Cathartidae), turkey vultures (Cathartes aura), with a highly developed olfactory sense, and black vultures (Coragyps atratus), with a less developed sense of olfaction. We found that eye size relative to body mass was the same in both species, but that black vultures have larger corneas relative to eye size than turkey vultures. However, the overall retinal topography, the total number of cells in the retinal ganglion cell layer, peak and average cell densities, cell soma area frequency distributions, and the theoretical peak anatomical spatial resolving power were the same in both species. This suggests that the visual systems of these two species are similar and that vision plays an equally important role in the biology of both species, despite the apparently greater reliance on olfaction for finding carrion in turkey vultures. PMID:24249399
Lisney, Thomas J; Stecyk, Karyn; Kolominsky, Jeffrey; Graves, Gary R; Wylie, Douglas R; Iwaniuk, Andrew N
2013-12-01
Vultures are highly reliant on their sensory systems for the rapid detection and localization of carrion before other scavengers can exploit the resource. In this study, we compared eye morphology and retinal topography in two species of New World vultures (Cathartidae), turkey vultures (Cathartes aura), with a highly developed olfactory sense, and black vultures (Coragyps atratus), with a less developed sense of olfaction. We found that eye size relative to body mass was the same in both species, but that black vultures have larger corneas relative to eye size than turkey vultures. However, the overall retinal topography, the total number of cells in the retinal ganglion cell layer, peak and average cell densities, cell soma area frequency distributions, and the theoretical peak anatomical spatial resolving power were the same in both species. This suggests that the visual systems of these two species are similar and that vision plays an equally important role in the biology of both species, despite the apparently greater reliance on olfaction for finding carrion in turkey vultures.
Appearance and possible homing of two species of sculpins in Maine tidepools
Muring, J.R.
2001-01-01
Two species of sculpins (Cottidae), the grubby, Myoxocephalus aenaeus, and the shorthorn sculpin, M. scorpius, were studied in rocky tidepools along the coast of Maine. Fishes were captured and measured during 116 sampling trips between 1979 and 1996. Both of these species of sculpins are from the northwestern Atlantic Ocean and are present in tidepools nearly every month of the year and are the only fish species found in Maine tidepools during winter. Both sculpin species are important components of tidepool ecosystems and dominate the rocky tidepool fish communities from late autumn to early spring, a time when other fish species decline in abundance or are absent. There was no apparent relationship between sculpin abundance and salinity, but the two species of Myoxocephalus were encountered in water temperatures of 1.5 to 18.9??C, with 55.0% of the shorthorn sculpins and 57.3% of the grubbies encountered in tidepools where water temperatures ranged from 12 to 15??C. Between 1988 and 1996, 102 individuals from both species were marked. Of these, 21.3% were recaptured, some repeatedly in the same tidepools and even at specific locations within tidepools over successive tidal cycles - an indication of homing behavior.
Cardoso, Adauto Lima; Sales, Karline Alves Holanda; Nagamachi, Cleusa Yoshiko; Pieczarka, Julio Cesar; Noronha, Renata Coelho Rodrigues
2013-01-01
The family Loricariidae encompasses approximately 800 species distributed in six subfamilies. The subfamily Hypostominae consists of five tribes; of them, the tribe Ancistrini is relatively diverse, but it is not well known from the cytogenetic point of view. Genus Scobinancistrus Isbrücker et Nijssen, 1989, which is part of the tribe Ancistrini, has two species that occur in sympatry in the Xingu River, Brazil. In this work, we performed the first karyotypic characterizations of these two species and sought to identify the processes involved in their karyotypic evolution. Chromosomal preparations were subjected to Giemsa staining, silver nitrate impregnation, C-banding, CMA3 staining, DAPI staining, and FISH (fluorescence in situ hybridization) with 18S rDNA and telomeric probes. We found that Scobinancistrus aureatus Burgess, 1994 and Scobinancistrus pariolispos Isbrücker et Nijssen, 1989 shared the diploid number, 2n=52, but differed in their karyotypic formulae (KFs), distribution of constitutive heterochromatin (CH), and the localizations of their nucleolus organizer regions (NORs), which were found on the interstitial and distal regions of the long arm of chromosome pair 3 in Scobinancistrus aureatus and Scobinancistrus pariolispos respectively. We suggest that these interspecific variations may have arisen via paracentric inversion or transposition of the NOR. The karyotypic differences found between these two Scobinancistrus species can be used to identify them taxonomically, and may have functioned as a mechanism of post-zygotic reproductive isolation during the speciation process. PMID:24260689
Wu, X Y; Chilton, N B; Zhu, X Q; Xie, M Q; Li, A X
2005-06-01
Sequences of the first internal transcribed spacer (ITS-1) and the D1-D3 domains of the large subunit (LSU) of the ribosomal DNA (rDNA) were determined for multiple specimens of 4 operational taxonomic units (OTUs) of the monogenean, Pseudorhabdosynochus lantauensis. OTUs were defined based on their collecting localities, host and/or morphological characteristics. All P. lantauensis specimens of one group (OTUs 1 and 3) differed in their sequences of the ITS-1 and partial LSU rDNA when compared with specimens of a second group (OTUs 2 and 4) by 12% and 2%, respectively. Results of the phylogenetic analyses of the LSU rDNA sequence data showed total (100%) bootstrap support for the separation of P. lantauensis into 2 distinct clades. At least 11 of the 18 nucleotide differences in the LSU sequence between the two P. lantauensis clades were derived (i.e. autapomorphic) characters when the morphologically distinct species, P. epinepheli and P. coioidesis, were used as outgroups. Furthermore, there were several autapomorphic character states for each P. lantauensis clade. This provides sufficient evidence to reject the null hypothesis that P. lantauensis represents a single species. Morphological and morphometric differences between these two clades provided additional strong support for the separation of P. lantauensis into two species. These two parasite species were found to co-exist on one of the two species of serranid fish (i.e. Epinephelus coioides) examined in the South China Sea (Guangdong Province, China).
Gebhardt, K; Böhme, M; von der Emde, G
2012-12-01
This study compares electrocommunication behaviour in groups of freely swimming weakly electric fishes of two species, Marcusenius altisambesi and Mormyrus rume. Animals emitted variable temporal sequences of stereotyped electric organ discharges (EOD) that served as communication signals. While the waveform of individual signals remained constant, the inter-discharge interval (IDI) patterns conveyed situation-specific information. Both species showed different types of group behaviour, e.g. they engaged in collective (group) foraging. The results show that in each species, during different behavioural conditions (resting, foraging and agonistic encounters), certain situation-specific IDI patterns occurred. In both species, neighbouring fishes swimming closely together interacted electrically by going in and out of synchronization episodes, i.e. periods of temporally correlated EOD production. These often resulted in echo responses between neighbours. During group foraging, fishes often signalled in a repetitive fixed order (fixed-order signalling). During foraging, EOD emission rates of M. altisambesi were higher and more regular than those of M. rume. The two species also differed in the quantity of group behaviours with M. altisambesi being more social than M. rume, which was reflected in the lack of specific agonistic IDI patterns, more fixed-order signalling and more communal resting behaviour in M. altisambesi.
Measurements of plasma potential in high-pressure microwave plasmas
Tarasova, A. V.; Podder, N. K.; Clothiaux, E. J.
2009-04-15
Plasma potential of a high-pressure ({approx}1 Torr) microwave-generated argon plasma is measured using a Langmuir probe and a cold emissive probe. The operation of a hot emissive probe in a high-pressure plasma has been very difficult due to frequent burn-outs and significantly reduced lifetime of the probe filament, which, in turn, limits the possibility of collecting a wide range of data. The I-V characteristics from both Langmuir and emissive probes are interpreted using the collisionless probe theory since the collision correction factor is not very significant. The plasma potential determined from both Langmuir and cold emissive probe characteristics agrees well with one another and is observed to be dependent on the operating gas pressure but relatively unchanged as a function of the microwave power. An average plasma potential determined over the operating range of microwave powers varies nonlinearly with the gas pressure.
Measurements of plasma potential in high-pressure microwave plasmas.
Tarasova, A V; Podder, N K; Clothiaux, E J
2009-04-01
Plasma potential of a high-pressure ( approximately 1 Torr) microwave-generated argon plasma is measured using a Langmuir probe and a cold emissive probe. The operation of a hot emissive probe in a high-pressure plasma has been very difficult due to frequent burn-outs and significantly reduced lifetime of the probe filament, which, in turn, limits the possibility of collecting a wide range of data. The I-V characteristics from both Langmuir and emissive probes are interpreted using the collisionless probe theory since the collision correction factor is not very significant. The plasma potential determined from both Langmuir and cold emissive probe characteristics agrees well with one another and is observed to be dependent on the operating gas pressure but relatively unchanged as a function of the microwave power. An average plasma potential determined over the operating range of microwave powers varies nonlinearly with the gas pressure.
Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria
2013-04-15
Numerical studies implementing different versions of the collisionless Ohm's law have shown a reconnection rate insensitive to the nature of the non-ideal mechanism occurring at the X line, as soon as the Hall effect is operating. Consequently, the dissipation mechanism occurring in the vicinity of the reconnection site in collisionless systems is usually thought not to have a dynamical role beyond the violation of the frozen-in condition. The interpretation of recent studies has, however, led to the opposite conclusion that the electron scale dissipative processes play an important dynamical role in preventing an elongation of the electron layer from throttling the reconnection rate. This work re-visits this topic with a new approach. Instead of focusing on the extensively studied symmetric configuration, we aim to investigate whether the macroscopic properties of collisionless reconnection are affected by the dissipation physics in asymmetric configurations, for which the effect of the Hall physics is substantially modified. Because it includes all the physical scales a priori important for collisionless reconnection (Hall and ion kinetic physics) and also because it allows one to change the nature of the non-ideal electron scale physics, we use a (two dimensional) hybrid model. The effects of numerical, resistive, and hyper-resistive dissipation are studied. In a first part, we perform simulations of symmetric reconnection with different non-ideal electron physics. We show that the model captures the already known properties of collisionless reconnection. In a second part, we focus on an asymmetric configuration where the magnetic field strength and the density are both asymmetric. Our results show that contrary to symmetric reconnection, the asymmetric model evolution strongly depends on the nature of the mechanism which breaks the field line connectivity. The dissipation occurring at the X line plays an important role in preventing the electron current layer
Physics of collisionless reconnection in a stressed X-point collapse
Tsiklauri, D.; Haruki, T.
2008-10-15
Recently, magnetic reconnection during collisionless, stressed, X-point collapse was studied using kinetic, 2.5-dimensional, fully electromagnetic, relativistic particle-in-cell numerical code [D. Tsiklauri and T. Haruki, Phys. Plasmas 14, 112905 (2007)]. Here we finalize the investigation of this topic by addressing key outstanding physical questions: (i) Which term in the generalized Ohm's law is responsible for the generation of the reconnection electric field? (ii) How does the time evolution of the reconnected flux vary with the ion-electron mass ratio? (iii) What is the exact energy budget of the reconnection process; i.e., in which proportion initial (mostly magnetic) energy is converted into other forms of energy? (iv) Are there any anisotropies in the velocity distribution of the accelerated particles? The following points have been established. (i) A reconnection electric field is generated by the electron pressure tensor off-diagonal terms, resembling to the case of tearing unstable Harris current sheet studied by the GEM reconnection challenge. (ii) For m{sub i}/m{sub e}>>1, the time evolution of the reconnected flux is independent of ion-electron mass ratio. In addition, in the case of m{sub i}/m{sub e}=1, we show that reconnection proceeds slowly as the Hall term is zero; when m{sub i}/m{sub e}>>1 (i.e., the Hall term is nonzero) reconnection is fast and we conjecture that this is due to magnetic field being frozen into electron fluid, which moves significantly faster than ion fluid. (iii) Within one Alfven time, somewhat less than half ({approx}40%) of the initial total (roughly magnetic) energy is converted into the kinetic energy of electrons, and somewhat more than half ({approx}60%) into kinetic energy of ions (similar to solar flare observations). (iv) In the strongly stressed X-point case, in about one Alfven time, a full isotropy in all three spatial directions of the velocity distribution is seen for superthermal electrons (also commensurate
NASA Astrophysics Data System (ADS)
Doxas, Isidoros
1988-12-01
One-wave vec E times vec B motion in a slab geometry is described by a hamiltonian with a phase space composed of an infinite square lattice of counterrotating rolls. When a small amount of a second wave is added, the hamiltonian becomes time dependent, the energy of a single particle is no longer conserved, and all energy values are accessible to the particle. Most of the contribution to the change in the energy of a particle that moves close to the separatrix from the vicinity of one X-point to the next, is shown to be imparted to the particle during a short interaction time around the midpoint of the particle's trajectory. The magnitude of the change in energy is calculated, and particle motion near the separatrix is reduced to the standard map. Collisionless magnetic reconnection is studied in the context of a reversed field with a small normal component b, modelling the geomagnetic tail. The magnetic moment is adiabatically conserved far from the reversal layer, but it changes in small increments Deltamu as the particle crosses the layer. The magnitude of Deltamu is calculated and the analytic expression is found to agree well with numerical calculations for epsilon < 1, where epsilon is the small parameter in the adiabatic expansion. A test particle code is used to study the time evolution of ensembles of particles placed in the model magnetic field. The code gives ion temperatures of a few keV and earthward drift velocities of 400 -900 km/s in the Plasma Sheet Boundary Layer, in good quantitative agreement with observed values. The numerical value of the height-integrated in-phase current < jcdot E> seems to be in qualitative agreement with theoretical values based on a decorrelation time equal to half a gyroperiod around the normal field, while a decorrelation time equal to 1/kv, where k is the wavenumber of the tearing mode, seems to give the wrong scaling. Finally the system seems to always tend to the same (qualitatively) state around the time the
On the relationship between quadrupolar magnetic field and collisionless reconnection
Smets, R. Belmont, G.; Aunai, N.; Boniface, C.
2014-06-15
Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed.
NASA Astrophysics Data System (ADS)
Liu, Yi-Hsin; Drake, J. F.; Swisdak, M.
2011-09-01
Simulations of collisionless oblique propagating slow shocks have revealed the existence of a transition associated with a critical temperature anisotropy ɛ = 1 - μ0(P|| - P⊥)/B2 = 0.25 (Y.-H. Liu, J. F. Drake, and M. Swisdak, Phys. Plasmas 18, 062110 (2011)). An explanation for this phenomenon is proposed here based on anisotropic fluid theory, in particular, the anisotropic derivative nonlinear-Schrödinger-Burgers equation, with an intuitive model of the energy closure for the downstream counter-streaming ions. The anisotropy value of 0.25 is significant because it is closely related to the degeneracy point of the slow and intermediate modes and corresponds to the lower bound of the coplanar to non-coplanar transition that occurs inside a compound slow shock (SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of compound SS/RD waves that bound the outflows in magnetic reconnection, instead of a pair of switch-off slow shocks as in Petschek's model. This fact might explain the rareness of in-situ observations of Petschek-reconnection-associated switch-off slow shocks.
Liu, Yi-Hsin; Drake, J. F.; Swisdak, M.
2011-09-15
Simulations of collisionless oblique propagating slow shocks have revealed the existence of a transition associated with a critical temperature anisotropy {epsilon} = 1 - {mu}{sub 0}(P{sub ||} - P{sub perpendicular})/B{sup 2} = 0.25 (Y.-H. Liu, J. F. Drake, and M. Swisdak, Phys. Plasmas 18, 062110 (2011)). An explanation for this phenomenon is proposed here based on anisotropic fluid theory, in particular, the anisotropic derivative nonlinear-Schroedinger-Burgers equation, with an intuitive model of the energy closure for the downstream counter-streaming ions. The anisotropy value of 0.25 is significant because it is closely related to the degeneracy point of the slow and intermediate modes and corresponds to the lower bound of the coplanar to non-coplanar transition that occurs inside a compound slow shock (SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of compound SS/RD waves that bound the outflows in magnetic reconnection, instead of a pair of switch-off slow shocks as in Petschek's model. This fact might explain the rareness of in-situ observations of Petschek-reconnection-associated switch-off slow shocks.
Sperm ultrastructure in two species of Panorpa and one Bittacus (Mecoptera).
Xie, Sha; Hua, Baozhen
2010-08-01
The sperm ultrastructure of the scorpionflies Panorpa liui and P. longihypovalva in Panorpidae and the hangingfly Bittacus planus in Bittacidae were investigated using transmission electron microscopy. The common features of the spermatozoa shared by all the mecopterans examined include a bilayered acrosome with a central perforatorium, an elongated homogeneously condensed nucleus, and a long flagellum with a 9+2 axoneme pattern and two mitochondrial derivatives. The two species of Panorpa possess a fossa at the posterior end of the nucleus, and differ from B. planus by lacking both the globular units running laterally from the head to the flagellum and the Golgi complex-derived membrane present in the flagellum. P. liui has pear-shaped mitochondrial derivatives and two small accessory bodies, while P. longihypovalva has elliptical mitochondrial derivatives and only one accessory body. The marked differences of the sperm structure among the Panorpa examined further confirm the paraphyly of this genus.
Heart rates increase after hatching in two species of natricine snakes
Aubret, Fabien
2013-01-01
Experimental studies have shown heart rates to decrease from embryo to hatchling stage in turtles, remain steady in skinks, and increase in birds. However, no snake species has been studied in this regard. I recorded heart rate evolution trajectories from embryo to juvenile stage in 78 eggs from two species of European Natricine snakes. Unexpectedly, snakes behaved more like birds than turtles or lizards: heart rates increased after hatching in both N. maura and N. natrix, respectively by 43.92 ± 22.84% and 35.92 ± 24.52%. Heart rate shift was not related to an abrupt elevation of metabolism per se (snakes that increased their heart rates the most sharply grew the least after birth), but rather due to a number of smaller eggs that experienced lower than normal heart rates throughout the incubation and recovered a normal heart rate post-birth. This finding is discussed in the light of hatching synchrony benefits. PMID:24287712
Kemppainen, P; Panova, M; Hollander, J; Johannesson, K
2009-10-01
Some mitochondrial introgression is common between closely related species, but distinct species rarely show substantial introgression in their entire distribution range. In this study, however, we report a complete lack of mitochondrial divergence between two sympatric species of flat periwinkles (Littorina fabalis and Littorina obtusata) which, based on previous allozyme studies, diverged approximately 1 Ma. We re-examined their species status using both morphology (morphometric analysis) and neutral genetic markers (microsatellites) and our results confirmed that these species are well separated. Despite this, the two species shared all common cytochrome-b haplotypes throughout their NE Atlantic distribution and no deep split between typical L. fabalis and L. obtusata haplotypes could be found. We suggest that incomplete lineage sorting explains most of the lack of mitochondrial divergence between these species. However, coalescent-based analyses and the sympatric sharing of unique haplotypes suggest that introgressive hybridization also has occurred. PMID:19678865
Two-species-coagulation approach to consensus by group level interactions
Escudero, Carlos; Macia, Fabricio
2010-07-15
We explore the self-organization dynamics of a set of entities by considering the interactions that affect the different subgroups conforming the whole. To this end, we employ the widespread example of coagulation kinetics, and characterize which interaction types lead to consensus formation and which do not, as well as the corresponding different macroscopic patterns. The crucial technical point is extending the usual one species coagulation dynamics to the two species one. This is achieved by means of introducing explicitly solvable kernels which have a clear physical meaning. The corresponding solutions are calculated in the long time limit, in which consensus may or may not be reached. The lack of consensus is characterized by means of scaling limits of the solutions. The possible applications of our results to some topics in which consensus reaching is fundamental, such as collective animal motion and opinion spreading dynamics, are also outlined.
NASA Astrophysics Data System (ADS)
Rocha, M. L. F.; Dias, J. F.; Boufleur, L. A.; Santos, C. E. I.; Dias, J. F.
2014-01-01
The aim of this study was to investigate metals in muscles of two species of flatfish, using Particle Induced X-ray Emission (PIXE). Specimens were caught monthly throughout the year 2005. Sampling was done at six points in the Santos Bay under different anthropogenic influences. Analysis of 56 samples of muscle showed detectable amounts of Al, As, Pb, Cu, Cr, Fe, Sr, Mn, Hg, Ni, Se and Zn. Except Cu, there were no correlations with the levels of sediment contamination by metals and those found in muscles. Moreover, there were significant differences between juveniles and adults concerning the concentration of Al, Mn and As. According to Brazilian Health Surveillance Agency, some elements detected in the samples of muscle were above of permitted by law for consumption: Hg and Pb (in samples from the internal area), As (from the west side) and Se and Cr (from east side of the bay).
Two-species mixing in a nested Penning trap for antihydrogen trapping
Ordonez, C. A.; Weathers, D. L.
2008-08-15
There exists an international quest to trap neutral antimatter in the form of antihydrogen for scientific study. One method that is being developed for trapping antihydrogen employs a nested Penning trap. Such a trap serves to mix positrons and antiprotons so as to produce low energy antihydrogen atoms. Mixing is achieved when the confinement volumes of the two species overlap one another. In the work presented here, a theoretical understanding of the mixing process is developed by analyzing a mixing scheme that was recently reported [G. Gabrielse et al., Phys. Rev. Lett. 100, 113001 (2008)]. The results indicate that positron space charge or collisions among antiprotons may substantially reduce the fraction of antiprotons that have an energy suitable for antihydrogen trapping.
Heart rates increase after hatching in two species of Natricine snakes.
Aubret, Fabien
2013-11-29
Experimental studies have shown heart rates to decrease from embryo to hatchling stage in turtles, remain steady in skinks, and increase in birds. However, no snake species has been studied in this regard. I recorded heart rate evolution trajectories from embryo to juvenile stage in 78 eggs from two species of European Natricine snakes. Unexpectedly, snakes behaved more like birds than turtles or lizards: heart rates increased after hatching in both N. maura and N. natrix, respectively by 43.92 ± 22.84% and 35.92 ± 24.52%. Heart rate shift was not related to an abrupt elevation of metabolism per se (snakes that increased their heart rates the most sharply grew the least after birth), but rather due to a number of smaller eggs that experienced lower than normal heart rates throughout the incubation and recovered a normal heart rate post-birth. This finding is discussed in the light of hatching synchrony benefits.
Schmidt, Olga
2015-01-01
Based on the study of morphological characters and DNA barcode (CO1) data, the present review revealed the existence of at least three species of Visiana Swinhoe (Lepidoptera: Geometridae: Larentiinae) in Australia. Visiana brujata (Guenée) is redescribed, and two species V. incertata (Walker), stat. rev. and V. repentinata (Walker), stat. rev. are resurrected from synonymy with V. brujata. Visiana breviaria (Walker), syn. rev., previously cited as a synonym of V. brujata, is now considered a synonym of V. incertata. Visiana brujata and V. incertata show close affinities with the sordidata group of species, whereas V. repentinata belongs to the vinosa species group. Images of adults and genitalia of all types are illustrated and the presence of the gnathos in the genus Visiana is discussed.
Uni-directional trail sharing by two species of ants a Monte Carlo study
NASA Astrophysics Data System (ADS)
Kunduraci, T.; Kayacan, O.
2015-06-01
We study insect traffic, specifically ant traffic on a uni-directional trail which is shared by two species of ants, one of which is ‘good’ at smelling and the other ‘poor’. The two distinct species of ants are placed mixed on the same trail and individuals of both are permitted to make a U-turn when they encounter another ant in front of them. The theoretical scheme for the ant traffic is based on an asymmetric simple exclusion model. The ant traffic on the uni-directional trail is studied as a function of the number of ‘good-smelling’ ants and the evaporation probability of pheromones by keeping the number of ‘poor-smelling ants’ constant during Monte Carlo simulations.
Schmidt, Olga
2015-01-01
Based on the study of morphological characters and DNA barcode (CO1) data, the present review revealed the existence of at least three species of Visiana Swinhoe (Lepidoptera: Geometridae: Larentiinae) in Australia. Visiana brujata (Guenée) is redescribed, and two species V. incertata (Walker), stat. rev. and V. repentinata (Walker), stat. rev. are resurrected from synonymy with V. brujata. Visiana breviaria (Walker), syn. rev., previously cited as a synonym of V. brujata, is now considered a synonym of V. incertata. Visiana brujata and V. incertata show close affinities with the sordidata group of species, whereas V. repentinata belongs to the vinosa species group. Images of adults and genitalia of all types are illustrated and the presence of the gnathos in the genus Visiana is discussed. PMID:26624149
NASA Astrophysics Data System (ADS)
Pattinson, R. W.; Billam, T. P.; Gardiner, S. A.; McCarron, D. J.; Cho, H. W.; Cornish, S. L.; Parker, N. G.; Proukakis, N. P.
2013-01-01
We investigate the mean-field equilibrium solutions for a two-species immiscible Bose-Einstein condensate confined by a harmonic confinement with additional linear perturbations. We observe a range of equilibrium density structures, including ball and shell formations and axially or radially separated states, with a marked sensitivity to the potential perturbations and the relative atom number in each species. Incorporation of linear trap perturbations, albeit weak, are found to be essential to match the range of equilibrium density profiles observed in a recent 87Rb-133Cs Bose-Einstein condensate experiment [McCarron , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.011603 84, 011603(R) (2011)]. Our analysis of this experiment demonstrates that sensitivity to linear trap perturbations is likely to be an important factor in interpreting the results of similar experiments in the future.
Structure formation in immiscible two-species Bose-Einstein condensates in perturbed harmonic traps
NASA Astrophysics Data System (ADS)
Pattinson, Robert; Parker, Nick; Proukakis, Nick; Liu, I.-Kang; Gou, Shih-Chuan; Gardiner, Simon; McCarron, Daniel; Cho, Hung-Wen; Cornish, Simon; Billam, Tom
2013-05-01
We investigate the mean-field equilibrium solutions for a trapped two-species 87Rb-133Cs immiscible Bose-Einstein condensate, and show that the density profiles observed in a recent Bose-Einstein experiment (D. J. McCarron et al. Phys. Rev. A 84, 011603 (2011)), which include ball and shell formations and axially/radially separated states, can be reproduced when accounting for weak linear perturbations. We also demonstrate the importance of the coupled growth of the two condensates by a simple finite temperature model which reveals such structures to be generally metastable in the presence of dissipation, with our findings confirmed by the more accurate Stochastic Projected Gross-Pitaevskii equation.
Morphological and hormonal parameters in two species of macaques: impact of seasonal breeding.
Muehlenbein, Michael P; Campbell, Benjamin C; Murchison, Mark A; Phillippi, Kathrine M
2002-03-01
To compare physiological and developmental differences between two cogeneric species that differ by seasonal vs. aseasonal breeding, values for morphological measurements, testicular volume, serum testosterone, estradiol, and dehydroepiandrosterone-sulfate levels were obtained from 53 rhesus during the early breeding season, as well as 41 pig-tailed macaque males maintained at the Tulane Primate Center. The two species exhibited similar body size, testosterone, and estradiol levels, but differed substantially in testicular volume (3.00 +/- 1.7 vs. 1.72 +/- 1.3 cc), abdominal skinfold measures (15.7 +/- 9.2 vs. 9.0 +/- 7.7 mm), and DHEA-S levels (18.0 +/- 11.7 vs. 7.6 +/- 5.4 microg/dl). Significant interaction effects for species by age group were found for weight, tricep circumference, length, and estradiol level. In addition, length was more closely related to testicular volume among rhesus compared to pig-tailed macaques, suggesting different developmental patterns between the species. Predictors of hormonal levels differed between the two species. In the rhesus, estradiol levels were related to testicular volume and testosterone levels while there were no anthropometric predictors of testosterone or DHEA-S. For the pig-tailed macaques, testicular volume was related to tricep circumference, testosterone to triceps skinfold and testicular volume, and estradiol to weight. It is argued that rhesus have larger testes for body size and more abdominal fat deposits during the early breeding season relative to pig-tailed macaques reflecting the increased demands of sperm competition in a seasonally breeding species. Hormonal differences associated with the difference in breeding system appear to be primarily related to adrenal rather than testicular activity.
Haptoral neuromusculature in two species of Dactylogyrus Diesing, 1850 (Monogenea: Dactylogyridae).
Petrov, Anatoly; Gerasev, Pavel; Popyuk, Maryana; Dmitrieva, Evgenija
2016-05-01
The taxonomy of Dactylogyrus Diesing, 1850 (Monogenea: Dactylogyridae), like that of most monopisthocotyleans, relies heavily on the morphology of sclerites of the posterior attachment organ (haptor). However, the associated neuromusculature is essentially unknown and, therefore, the aim of this study was to use confocal microscopy to examine the haptoral neuromusculature in two species of Dactylogyrus: D. amphibothrium Wagener, 1857 and D. crucifer Wagener, 1857. The monogeneans were stained with phalloidin for muscle and with antibodies for FMRFamide and 5HT and confocal reflectance microscopy was used to visualise the sclerites (i.e. anchors, marginal hooks and bars). Both species had a similar architecture of the anchoral musculature, with a pair of extrinsic muscles, two interconnecting muscles and muscles attached to the haptoral wall, anchoral openings and a connecting bar. The musculature of most marginal hooks consisted of retractors and protractors inserted on the proximal ends of the hooks. The two species differed significantly in the musculature of the accessory ventral bar: D. crucifer had a four-rayed bar with an elaborate musculature associated with the marginal hooks and D. amphibothrium had a rod-shaped bar with simple musculature. Patterns of neurotransmitter immunoreactivity (IR) in the haptor were similar in both species: RFamide-IR cells were clustered in a pair of pre-anchoral ganglia interconnected by a neurite bundle, 5HT-IR cells formed a ventral loop projecting neurites to the marginal hooks. The functional roles of haptoral muscles and patterns of neurotransmitters are discussed. In D. crucifer, the confocal reflectance microscopy revealed an additional sclerite (accessory dorsal bar) that had never been described previously in this or any other species of Dactylogyrus, suggesting that the reflected-light technique might be useful in identifying sclerites undetectable by conventional methods. PMID:27095663
The wave speed of intergradation zone in two-species lattice Müllerian mimicry model.
Kawaguchi, Isao; Sasaki, Akira
2006-12-21
A spatially explicit model is studied to analyse the movement of coupled clines in two-species Müllerian mimicry system as exemplified by the comimicking helicoiine butterflies in Central-South America Heliconius erato and Heliconius melpomene. In this system, a pair of comimicking wing patterns of two species (mimicry ring) is found in a geographical region but another pair of wing patterns is found in a different geographical region. The distribution of mimicry rings thus forms a spatial mosaic in a large geographical scale, and the mechanism responsible for their stable maintenance has been a long-standing question in evolutionary biology. We here examine the speed of the movement of boundaries that divide the regions inhabited by different mimetic morphs in each comimicking species, by assuming coupled two-state stochastic cellular automatons where the flipping rate of the site occupied by a mimetic morph depends on the local density of the same morph and of the comimicking morph in the other species. The speed of cline movement shows a complex dependence on the coupling parameter between mimetic species--greater coupling of comimicking morphs between species slows down the cline movement only when the reduction in predation rate exhibits diminishing return to the increase of local mimetic morph density. The analytical predictions are confirmed by the results of Monte Carlo simulations. The speed of advance is quite different from that predicted from the conventional reaction-diffusion model, indicating that demographic stochasticity plays a critical role in determining the speed of cline movement. We also examine if the spatial heterogeneity in migration rate can stably maintain clines.
Landau Fluid Models for Magnetized Plasmas
Sulem, P. L.; Passot, T.; Marradi, L.
2008-10-15
A Landau fluid model for a magnetized plasma, that retains a linear description of low-frequency kinetic effects involving transverse scales significantly smaller than the ion Larmor radius, is discussed and validated in the context of nonlinear wave dynamics. Preliminary simulations of the turbulent regime are presented in one space dimension, as a first step towards more realistic three-dimensional computations, aimed to analyze the combined effect of dispersion and collisionless dissipation on the energy cascade.
Southworth, Lizabeth O.; Holick, Michael F.; Chen, Tai C.; Kunz, Thomas H.
2013-01-01
It has long been accepted that most vertebrate animals meet their vitamin D requirements from exposure of skin to UV-B (UV-B) radiation. Many factors affect this endogenous synthesis of vitamin D, including season, latitude, time of day, age, presence of hair, and degree of skin pigmentation. Most bats roost in dark places by day and forage at night, and thus have little or no potential for sunlight exposure. Notwithstanding, some tropical species are diurnal and are known to roost in the canopy of trees where they may be exposed to sunlight for up to 12 h each day. In this study, two species of captive tropical bats (both species are active at night but one, Rousettus aegyptiacus, roosts in caves, tombs, and buildings, whereas the other, Pteropus hypomelanus, roosts in trees) were evaluated for their ability to endogenously synthesize vitamin D. Following timed periods of sunlight exposure, blood plasma was analyzed using a competitive protein binding assay (CPBA) to determine concentrations of 25-hydroxyvitamin D [25(OH)D], the major circulating vitamin D metabolite. The ability to photoconvert provitamin D (7-dehydrocholesterol, 7-DHC) in the sub-tropical winter was determined using sunlight exposed borosilicate samples of 7-DHC in hourly increments. Finally, both species were evaluated in their preference for a roost site by the release of individuals into sunlight or shade in timed trials. Our results support the hypotheses: (1) when exposed to natural sunlight, both species exhibited an ability to endogenously synthesize vitamin D, although significant differences were found between the two, (2) photoconversion of 7-DHC to previtamin D3 is possible during the mid-day hours of a sub-tropical winter day and (3) captive, cave roosting R. aegyptiacus will choose shaded roost sites while captive P. hypomelanus will show no preference for either shade or sun. PMID:24494054
Effects of nonthermal electrons on plasma expansion into vacuum
Bennaceur-Doumaz, D. Bara, D.; Benkhelifa, E.; Djebli, M.
2015-01-28
The expansion of semi-infinite plasma into vacuum is analyzed with a hydrodynamic model for cold ions assuming electrons modelled by a kappa-type distribution. Similarly to Mora study of a plasma expansion into vacuum [P. Mora, Phys. Rev. Lett. 90, 185002 (2003)], we formulated empirical expressions for the electric field strength, velocity, and position of the ion front in one-dimensional nonrelativistic, collisionless isothermally expanding plasma. Analytic expressions for the maximum ion energy and the spectrum of the accelerated ions in the plasma were derived and discussed to highlight the electron nonthermal effects on enhancing the ion acceleration in plasma expansion into vacuum.
Laminar shocks in high power laser plasma interactions
Cairns, R. A.; Bingham, R.; Norreys, P.; Trines, R.
2014-02-15
We propose a theory to describe laminar ion sound structures in a collisionless plasma. Reflection of a small fraction of the upstream ions converts the well known ion acoustic soliton into a structure with a steep potential gradient upstream and with downstream oscillations. The theory provides a simple interpretation of results dating back more than forty years but, more importantly, is shown to provide an explanation for recent observations on laser produced plasmas relevant to inertial fusion and to ion acceleration.
Scime, Earl E.
2000-12-11
This is the final report for the Office of Fusion Energy sponsored project entitled, "Experimental Investigation of Collisionless Electron-Electron Microinstabilities." The report summarizes the scientific and human resource development accomplishments supported through this project.
Collisionless stellar hydrodynamics as an efficient alternative to N-body methods
NASA Astrophysics Data System (ADS)
Mitchell, Nigel L.; Vorobyov, Eduard I.; Hensler, Gerhard
2013-01-01
The dominant constituents of the Universe's matter are believed to be collisionless in nature and thus their modelling in any self-consistent simulation is extremely important. For simulations that deal only with dark matter or stellar systems, the conventional N-body technique is fast, memory efficient and relatively simple to implement. However when extending simulations to include the effects of gas physics, mesh codes are at a distinct disadvantage compared to Smooth Particle Hydrodynamics (SPH) codes. Whereas implementing the N-body approach into SPH codes is fairly trivial, the particle-mesh technique used in mesh codes to couple collisionless stars and dark matter to the gas on the mesh has a series of significant scientific and technical limitations. These include spurious entropy generation resulting from discreteness effects, poor load balancing and increased communication overhead which spoil the excellent scaling in massively parallel grid codes. In this paper we propose the use of the collisionless Boltzmann moment equations as a means to model the collisionless material as a fluid on the mesh, implementing it into the massively parallel FLASH Adaptive Mesh Refinement (AMR) code. This approach which we term `collisionless stellar hydrodynamics' enables us to do away with the particle-mesh approach and since the parallelization scheme is identical to that used for the hydrodynamics, it preserves the excellent scaling of the FLASH code already demonstrated on peta-flop machines. We find that the classic hydrodynamic equations and the Boltzmann moment equations can be reconciled under specific conditions, allowing us to generate analytic solutions for collisionless systems using conventional test problems. We confirm the validity of our approach using a suite of demanding test problems, including the use of a modified Sod shock test. By deriving the relevant eigenvalues and eigenvectors of the Boltzmann moment equations, we are able to use high order
Technology Transfer Automated Retrieval System (TEKTRAN)
Thalassinid shrimp are recognized as important ecosystem engineers due to their ability to influence the benthic communities they inhabit We describe the isolation and characterization of several microsatellite loci from two species, Neotrypaea californiensis Upogebia pugettensis which inhabit es...
Sundkvist, David; Krasnoselskikh, V; Bale, S D; Schwartz, S J; Soucek, J; Mozer, F
2012-01-13
Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.
Stability and instability of equilibria in collisionless plasmas and ideal plane flows
NASA Astrophysics Data System (ADS)
Lin, Zhiwu
In this dissertation, I study instability and stability of steady solutions to the one-dimensional Vlasov-Poisson system (VP) and two-dimensional Euler equation of incompressible inviscid fluids (E). Some new methods are developed to find exponentially growing solutions (growing modes) to the linearized equation around the equilibrium. In order to obtain growing modes, I use several different methods, including the concept of neutral modes and of infinite determinant as well as continuation arguments. These methods are used to analyze a corresponding dispersion operator or the neutral mode equations (such as Rayleigh's classical equation). The new results obtained include: the proof of linear instability of any BGK waves of (VP) under multipy-periodic perturbations, new sufficient conditions for instability of plane shear flows and rotating flows for (E) and a criterion of finding purely growing modes for general steady ideal plane flows (E). These methods are flexible and might be applicable to study instability problems of other conservative systems in continuum physics. I also get some stability criteria for quite general ideal plane flows and compare the different types of stability in this case.
FULL PARTICLE ELECTROMAGNETIC SIMULATIONS OF ENTROPY GENERATION ACROSS A COLLISIONLESS SHOCK
Yang, Zhongwei; Liu, Ying D.; Wang, Rui; Hu, Huidong; Parks, George K.; Wu, Pin; Huang, Can; Shi, Run
2014-09-20
Experimental data from Cluster have shown that entropy density can be generated across Earth's bow shock. These new observations are a starting point for a more sophisticated analysis that includes computer modeling of a collisionless shock using observed shock parameters as input. In this Letter, we present the first comparison between observations and particle-in-cell simulations of such entropy generation across a collisionless shock. The ion heating at the shock is dominated by the phase mixing of reflected and directly transmitted ions, which are separated from the incident ions. The electron heating is a nearly thermal process due to the conservation of their angular momentum. For both species, we calculate the entropy density across the shock, and obtain good consistency between observations and simulations on entropy generation across the shock. We also find that the entropy generation rate is reduced as the shock Mach number decreases.
Xie, Lianghai Li, Lei; Wang, Jingdong; Zhang, Yiteng
2014-04-15
We present a three-dimensional, two-species (Ba{sup +} and H{sup +}) MHD model to study the early time behaviors of a barium release at about 1 R{sub E} like Combined Release and Radiation Effects Satellite G2, with emphasis placed on the three-dimensional evolution of the barium cloud and its effects on the ambient plasma environment. We find that the perturbations caused by the cloud are the combined results of the initial injection, the radial expansion, and the diamagnetic effect and propagate as fast MHD waves in the magnetosphere. In return, the transverse expansion and the cross-B motion of barium ions are constrained by the magnetic force, which lead to a field-aligned striation of ions and the decoupling of these ions from the neutrals. Our simulation shows the formation and collapse of the diamagnetic cavity in the barium cloud. The estimated time scale for the cavity evolution might be much shorter if photoionization time scale and field aligned expansion of barium ions are considered. In addition, our two species MHD simulation also finds the snowplow effect resulting from the momentum coupling between barium ions and background H{sup +}, which creates density hole and bumps in the background H{sup +} when barium ions expanding along the magnetic field lines.
Geographical variation in the clouded leopard, Neofelis nebulosa, reveals two species.
Kitchener, Andrew C; Beaumont, Mark A; Richardson, Douglas
2006-12-01
The clouded leopard, Neofelis nebulosa, is an endangered semiarboreal felid with a wide distribution in tropical forests of southern and southeast Asia, including the islands of Sumatra and Borneo in the Indonesian archipelago. In common with many larger animal species, it displays morphological variation within its wide geographical range and is currently regarded as comprising of up to four subspecies. It is widely recognized that taxonomic designation has a major impact on conservation planning and action. Given that the last taxonomic revision was made over 50 years ago, a more detailed examination of geographical variation is needed. We describe here the results of a morphometric analysis of the pelages of 57 clouded leopards sampled throughout the species' range. We conclude that there are two distinct morphological groups, which differ primarily in the size of their cloud markings. These results are supported by a recent genetic analysis. On that basis, we give diagnoses for the distinction of two species, one in mainland Asia (N. nebulosa) and the other in Indonesia (N. diardi). The implications for conservation that arise from this new taxonomic arrangement are discussed. PMID:17141621
Condition dependence of iridescent wing flash-marks in two species of dabbling ducks.
Legagneux, Pierre; Théry, Marc; Guillemain, Matthieu; Gomez, Doris; Bretagnolle, Vincent
2010-03-01
Growing empirical evidence supports the hypothesis of male mate choice for female ornaments which are thought to reflect individual quality and future breeding ability. While structural colors are clearly used in mate choice and pairing, the condition dependence of such traits is less obvious, particularly in females. We present spectral measurements of wing flash-marks in two species of dabbling ducks during the pairing period and evaluate color and brightness contrasts as seen through the mallard's (Anas platyrhynchos) visual system. We tested for possible relationships between body size (and condition) and feather measurements both on captive and wild individuals. By analyzing reflectance spectra of semi-captive mallards soon after the molting period, we found that brightness was condition related. Color contrast was positively related to body size, but only in females. In wild ducks, color contrast was positively related to body size in the common teal A. crecca only for females. These results suggest that female color traits are likely to be used by males for mate choice, and support the hypothesis that the structural color is condition-dependent. Finally, brightness contrast decreased over time in both duck species. Natural abrasion or the effect of keratinolytic bacteria could explain such pattern.
Three peroxisome proliferator-activated receptor isotypes from each of two species of marine fish.
Leaver, Michael J; Boukouvala, Evridiki; Antonopoulou, Efthimia; Diez, Amalia; Favre-Krey, Laurence; Ezaz, M Tariq; Bautista, José M; Tocher, Douglas R; Krey, Grigorios
2005-07-01
The cloning and characterization of cDNAs and genes encoding three peroxisome proliferator-activated receptor (PPAR) isotypes from two species of marine fish, the plaice (Pleuronectes platessa) and the gilthead sea bream (Sparus aurata), are reported for the first time. Although differences in the genomic organization of the fish PPAR genes compared with their mammalian counterparts are evident, sequence alignments and phylogenetic comparisons show the fish genes to be homologs of mammalian PPARalpha, PPARbeta/delta, and PPARgamma. Like their mammalian homologs, fish PPARs bind to a variety of natural PPAR response elements (PPREs) present in the promoters of mammalian or piscine genes. In contrast, the mRNA expression pattern of PPARs in the two fish species differs from that observed in other vertebrates. Thus, PPARgamma is expressed more widely in fish tissues than in mammals, whereas PPARalpha and beta are expressed similarly in profile to mammals. Furthermore, nutritional status strongly influences the expression of all three PPAR isotypes in liver, whereas it has no effect on PPAR expression in intestinal and adipose tissues. Fish PPARalpha and beta exhibit an activation profile similar to that of the mammalian PPAR in response to a variety of activators/ligands, whereas PPARgamma is not activated by mammalian PPARgamma-specific ligands. Amino acid residues shown to be critical for ligand binding in mammalian PPARs are not conserved in fish PPARgamma and therefore, together with the distinct tissue expression profile of this receptor, suggest potential differences in the function of PPARgamma in fish compared with mammals.
Evidence for nest-odour recognition in two species of diving petrel.
Bonadonna, Francesco; Cunningham, Gregory B; Jouventin, Pierre; Hesters, Florence; Nevitt, Gabrielle A
2003-10-01
In nearly every procellariiform species, the sense of smell appears to be highly adapted for foraging at sea, but the sense of smell among the diving petrels is enigmatic. These birds forage at considerable depth and are not attracted to odour cues at sea. However, several procellariiform species have recently been shown to relocate their nesting burrows by scent, suggesting that these birds use an olfactory signature to identify the home burrow. We wanted to know whether diving petrels use smell in this way. We tested the common diving petrel Pelecanoides urinatrix and the South-Georgian diving petrel Pelecanoides georgicus to determine whether diving petrels were able to recognise their burrow by scent alone. To verify the efficacy of the method, we also tested a bird that is known to use olfaction for foraging and nest recognition, the thin-billed prion Pachyptila belcheri. In two-choice T-maze trials, we found that, for all species, individuals significantly preferred the odour of their own nest material to that of a conspecific. Our findings strongly suggest that an individual-specific odour provides an olfactory signature that allows burrowing petrels to recognize their own burrow. Since this ability seems to be well developed in diving petrels, our data further implicate a novel adaptation for olfaction in these two species that have been presumed to lack a well-developed sense of smell. PMID:12966063
A two-species occupancy model accommodating simultaneous spatial and interspecific dependence.
Rota, Christopher T; Wikle, Christopher K; Kays, Roland W; Forrester, Tavis D; McShea, William J; Parsons, Arielle W; Millspaugh, Joshua J
2016-01-01
Occupancy models are popular for estimating the probability a site is occupied by a species of interest when detection is imperfect. Occupancy models have been extended to account for interacting species and spatial dependence but cannot presently allow both factors to act simultaneously. We propose a two-species occupancy model that accommodates both interspecific and spatial dependence. We use a point-referenced multivariate hierarchical spatial model to account for both spatial and interspecific dependence. We model spatial random effects with predictive process models and use probit regression to improve efficiency of posterior sampling. We model occupancy probabilities of red fox (Vulpes vulpes) and coyote (Canis latrans) with camera trap data collected from six mid-Atlantic states in the eastern United States. We fit four models comprising a fully factorial combination of spatial and interspecific dependence to two-thirds of camera trapping sites and validated models with the remaining data. Red fox and coyotes each exhibited spatial dependence at distances > 0.8 and 0.4 km, respectively, and exhibited geographic variation in interspecific dependence. Consequently, predictions from the model assuming simultaneous spatial and interspecific dependence best matched test data observations. This application highlights the utility of simultaneously accounting for spatial and interspecific dependence.
Hoch, Jeffrey Matthew; Levinton, Jeffrey S
2012-05-01
Sex allocation theory for simultaneous hermaphrodites predicts increases in relative allocation to male-specific function as competition for fertilizations increases. Theoretical models developed specifically for competing acorn barnacles predict that the proportional allocation to male function increases toward an asymptote of 50% as the number of competitors for fertilizations increases. Experimental manipulations were used to investigate how mate competition affected both relative and absolute allocation to the sex functions for two species of acorn barnacle: Semibalanus balanoides and Balanus glandula. The ratio of male to female allocation did not increase with the number of competitors for either species. However, both species showed increased allocation to male function (estimated as total mass of sex-specific tissues) with increased crowding. Allocation to female function seemed to be limited by other factors and did not vary with mating group size as predicted. Allocation to male and female function were both positively related to body size, but a trade-off between male and female function, a key assumption of prior models, was not observed.
Martinez, Pablo Ariel; Jacobina, Uedson Pereira; Molina, Wagner Franco
2011-09-01
Some groups of fish, such as those belonging to the Order Tetraodontiformes, may differ significantly in the amount and location of heterochromatin in the chromosomes. There is a marked variation in DNA content of more than seven-fold among the families of this Order. However, the karyoevolutionary mechanisms responsible for this variation are essentially unknown. The largest genomic contents are present in species of the family Ostraciidae (2.20-2.60pg). The present study cytogenetically characterized two species of the family Ostraciidae, Acanthostracion polygonius and A. quadricornis, using conventional staining, C-bandings, Ag-NOR, CMA(3)/DAPI, AluI, PstI, EcoRI, TaqI and HinfI restriction enzymes (REs) and double FISH with 18S and 5S rDNA probes. The karyotypes of both species showed 2n=52 acrocentric chromosomes (FN=52; chromosome arms) and pronounced conserved structural characteristics. A significant heterochromatic content was observed equilocally distributed in pericentromeric position in all the chromosome pairs. This condition is unusual in relation to the karyotypes of other families of Tetraodontiformes and probability is the cause of the higher DNA content in Ostraciidae. Given the role played by repetitive sequences in the genomic reorganization of this Order, it is suggested that the conspicuous heterochromatic blocks, present in the same chromosomal position and with apparently similar composition, may have arisen or undergo evolutionary changes in concert providing clues about the chromosomal mechanisms which led to extensive variation in genomic content of different Tetraodontiformes families.
Primary structure of profilins from two species of Echinoidea and Physarum polycephalum.
Takagi, T; Mabuchi, I; Hosoya, H; Furuhashi, K; Hatano, S
1990-09-24
Profilin is a small G-actin-binding protein, the amino acid sequence of which was previously reported for calf, human, Acanthamoeba and yeast. Here the amino acid sequences of three profilins obtained from eggs of two species of Echinoidea, Clypeaster japonicus (order, Clypeasteroida) and Anthocidaris crassispina (order, Echinoida), and plasmodium of Physarum polycephalum were determined. Two echinoid profilins were composed of 139 amino acid residues, N-termini were acylated and the molecular mass was calculated to be 14.6 kDa, slightly larger than that of 13 kDa estimated by SDS/PAGE [Mabuchi, I. & Hosoya, H. (1982) Biomed. Res. 3, 465-476]. On the other hand, Physarum profilin was composed of 124 amino acid residues, the N-terminus was acylated, and the calculated molecular mass was 13132 Da. The sequences of C. japonicus and A. crassispina profilins were homologous (84% identical). However, the similarity of these profilins with those form other organisms was low. The sequence of Physarum profilin was homologous with Acanthamoeba profilin isoforms (51% identical) and with yeast profilin (42% identical), but not with other profilins. The relatively conservative sequence of profilins from yeast, Physarum, Acanthamoeba, echinoid eggs and mammalian cells was found in the N-terminal region, which was suggested to be a common actin-binding region. The C-terminal region was also conserved, although to a lesser extent than the N-terminal region. PMID:2209623
Liu, Xuan; Wang, Wen-Xiong
2016-02-15
The Jiulong Estuary in Southern China suffers from serious metal pollution, leading to the appearance of 'colored' oysters in this estuary. In this study, two species of oysters Crassostrea hongkongensis and Crassostrea angulata were transplanted to three sites in the Jiulong Estuary over a two-month period. The time-series changes of various biomarkers were measured, coupled with simultaneous quantification of metal bioaccumulation (Ag, Cd, Cr, Cu, Ni and Zn). Cu and Zn accumulation increased linearly and reached up to 2% and 1.5% dry tissue weight by the end of exposure. Negative correlations between the tissue Cu or Zn accumulation and catalase or superoxide dismutase activities strongly indicated that Cu and Zn in 'colored' oysters induced the adjustments of oyster antioxidant systems. Metallothionein (MT) detoxification was insufficient for sequestering all the absorbed metals and its concentrations in the oysters were suppressed following an initial increase, primarily due to the high metal accumulation in the tissues. Interestingly, gradual recoveries of lysosomal membrane stability after the initial strong inhibitions were observed in both oysters. We also documented an increasing 'watering' of oyster tissues presumably as a result of rupturing of tissue cells under metal stress. This study demonstrated the complexity of biomarker responses under field condition, therefore the time changes of biomarker responses to metals need to be considered in evaluating the biological impacts of metal pollution on estuarine organisms.
The relevance of morphology for habitat use and locomotion in two species of wall lizards
NASA Astrophysics Data System (ADS)
Gomes, Verónica; Carretero, Miguel A.; Kaliontzopoulou, Antigoni
2016-01-01
Understanding if morphological differences between organisms that occupy different environments are associated to differences in functional performance can suggest a functional link between environmental and morphological variation. In this study we examined three components of the ecomorphological paradigm - morphology, locomotor performance and habitat use - using two syntopic wall lizards endemic to the Iberian Peninsula as a case study to establish whether morphological variation is associated with habitat use and determine the potential relevance of locomotor performance for such an association. Differences in habitat use between both lizards matched patterns of morphological variation. Indeed, individuals of Podarcis guadarramae lusitanicus, which are more flattened, used more rocky environments, whereas Podarcis bocagei, which have higher heads, used more vegetation than rocks. These patterns translated into a significant association between morphology and habitat use. Nevertheless, the two species were only differentiated in some of the functional traits quantified, and locomotor performance did not exhibit an association with morphological traits. Our results suggest that the link between morphology and habitat use is mediated by refuge use, rather than locomotor performance, in this system, and advise caution when extrapolating morphology-performance-environment associations across organisms.
A population analysis of two species of streamside salamanders, genus Desmognathus
Hall, R.J.
1977-01-01
Desmognathus fuscus and Desmognathus ochrophaeus mere studied over a 6-wk period by mark-recapture and removal methods. Density is ~. 0.8/m2 in D. fuscus and 0.6 - l.l/m2 in D. ochrophaeus; respective biomass densities are 1.5 and 1.0 g/m2. Adjusted estimates indicate a greater proportion of adults in D. ochrophaeus. The observed sex ratio is unbalanced in favor of males but may be close to 1:1 in each species. Adult male age structures based on testis lobes indicate greater adult survivorship in D. ochrophaeus than D. fuscus. Local populations of D. ochrophaeus may differ from others studied in having a shortened larval period. Indirect evidence may indicate greater predation on D. fuscus than on D. ochrophaeus. Fecundity is positively correlated with the size of females in both species and the slopes of the regression lines are similar. Mean egg complements are 21.2 for D. fuscus and 15.6 for D. ochrophaeus. Most observations support the hypothesis that demographic differences are related to differences in degree of terrestrialism between the two species.
da Silva, Maelin; Ribeiro, Emanuell D; Matoso, Daniele A; Sousa, Leandro M; Hrbek, Tomas; Py-Daniel, Lucia Rapp; Feldberg, Eliana
2014-04-01
Structural chromosome changes are widely described in different vertebrate groups and generate genetic, phenotypic and behavioral diversity. During the evolution of loricariids, several rearrangements (fissions, fusions, inversions) seem to have occurred. Hypancistrus, tribe Ancistrini, are highly demanded for fishkeeping around the world. In this tribe, the diploid chromosome number 2n = 52 is considered a synapomorphy, and paracentric-type inversions appear to be involved in the chromosomal evolution of the tribe. The present study investigated the karyotypes of H. zebra and H. cf. debilittera using cytogenetic, classical and molecular tools, as well as DNA barcoding. Data reveal that, although diploid number in both species corroborates the proposed synapomorphy for the tribe, there is a complex karyotype dynamics, reflected in the intense chromosomal polymorphism, resulting from rearrangements involving ribosomal regions (5S and 18S rDNA), which are suggested to be paracentric inversions. Besides, DNA barcode confirms reciprocal monophyletism between the species, validating the existence of two species, only. This scenario, coupled with genomic instability caused by exogenous sequences such as Rex-3 retrotransposons and the species' sedentary lifestyle, which helps the fast polymorphism fixation, may reflect different phenotypic color patterns in natural populations, as observed in H. cf. debilittera.
Lui, Roberto Laridondo; Blanco, Daniel Rodrigues; Margarido, Vladimir Pavan; Troy, Waldo Pinheiro; Filho, Orlando Moreira
2013-01-01
Abstract Auchenipteridae is divided in two subfamilies, Centromochlinae and Auchenipterinae. Centromochlinae has 31 valid species, from which 13 are included in the genus Tatia Miranda Ribeiro, 1911. Among these, Tatia jaracatia Pavanelli & Bifi, 2009 and Tatia neivai (Ihering, 1930) are the only two representative species from the Paraná-Paraguay basins. This study aimed to analyze cytogenetically these two species and thus provide the first chromosomal data for the genus. Although Tatia jaracatia and Tatia neivai presented 2n=58 chromosomes, some differences were observed in the karyotypic formula. The heterochromatin was dispersed in the centromeric and terminal regions of most chromosomes of Tatia jaracatia, and only in the terminal region of most chromosomes of Tatia neivai. The AgNORs were detected in the subtelocentric pair 28 for both species, which was confirmed by FISH with 18S rDNA probe. The 5S rDNA sites were detected in four chromosome pairs in Tatia jaracatia and three chromosome pairs in Tatia neivai. Both species of Tatia presented great chromosomal similarities among themselves; however, when compared to other species of Auchenipteridae, it was possible to identify some differences in the karyotype macrostructure, in the heterochromatin distribution pattern and in the number and position of 5S rDNA sites, which until now seems to be intrinsic to the genus Tatia. PMID:24260691
A two-species occupancy model accommodating simultaneous spatial and interspecific dependence.
Rota, Christopher T; Wikle, Christopher K; Kays, Roland W; Forrester, Tavis D; McShea, William J; Parsons, Arielle W; Millspaugh, Joshua J
2016-01-01
Occupancy models are popular for estimating the probability a site is occupied by a species of interest when detection is imperfect. Occupancy models have been extended to account for interacting species and spatial dependence but cannot presently allow both factors to act simultaneously. We propose a two-species occupancy model that accommodates both interspecific and spatial dependence. We use a point-referenced multivariate hierarchical spatial model to account for both spatial and interspecific dependence. We model spatial random effects with predictive process models and use probit regression to improve efficiency of posterior sampling. We model occupancy probabilities of red fox (Vulpes vulpes) and coyote (Canis latrans) with camera trap data collected from six mid-Atlantic states in the eastern United States. We fit four models comprising a fully factorial combination of spatial and interspecific dependence to two-thirds of camera trapping sites and validated models with the remaining data. Red fox and coyotes each exhibited spatial dependence at distances > 0.8 and 0.4 km, respectively, and exhibited geographic variation in interspecific dependence. Consequently, predictions from the model assuming simultaneous spatial and interspecific dependence best matched test data observations. This application highlights the utility of simultaneously accounting for spatial and interspecific dependence. PMID:27008774
Collisionless Heating in Capacitive Discharges Enhanced by Dual-Frequency Excitation
Turner, M.M.; Chabert, P.
2006-05-26
We discuss collisionless electron heating in capacitive discharges excited by a combination of two disparate frequencies. By developing an analytical model, we find, contrary to expectation, that the net heating in this case is much larger than the sum of the effects occurring when the two frequencies act separately. This prediction is substantiated by kinetic simulations, which are also in excellent general quantitative agreement with the model for discharge parameters that are typical of recent experiments.
NASA Technical Reports Server (NTRS)
Lin, C. H.; Heritage, J. P.; Gustafson, T. K.; Chiao, R. Y.; Mctague, J. P.
1974-01-01
The refractive index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. For the limit of an extremely short-duration excitation, a multilevel coherent effect resulted in delayed refractive index bursts. Both stationary and transient responses of this birefringence to an optical field were considered for symmetric top molecules, with particular emphasis on the special case of linear molecules.
NASA Technical Reports Server (NTRS)
Lin, C. H.; Heritage, J. P.; Gustafson, T. K.; Chiao, R. Y.; Mctague, J. P.
1976-01-01
The refractive-index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. In the limit of an extremely-short-duration excitation, a multilevel coherent effect results in delayed refractive-index bursts. Both stationary and transient responses of this birefringence to an optical field are considered for symmetric-top molecules, with particular emphasis on the special case of linear molecules.
Wakefields generated by collisional neutrinos in neutral-electron-positron-ion plasma
Tinakiche, Nouara
2015-12-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron-ion plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in presence of a fraction of ions in a neutral-electron-positron plasma. The results obtained in the present work are interpreted and compared with previous studies.
Dynamical properties of a family of collisionless models of elliptical galaxies
NASA Astrophysics Data System (ADS)
Bertin, G.; Trenti, M.
2004-04-01
N-body simulations of collisionless collapse have offered important clues to the construction of realistic stellar dynamical models of elliptical galaxies. Such simulations confirm and quantify the qualitative expectation that rapid collapse of a self-gravitating collisionless system, initially cool and significantly far from equilibrium, leads to incomplete relaxation, that is to a quasi-equilibrium configuration characterized by isotropic, quasi-Maxwellian distribution of stellar orbits in the inner regions and by radially biased anisotropic pressure in the outer parts. In earlier studies, as illustrated in a number of papers several years ago, the attention was largely focused on the successful comparison between the models (constructed under the qualitative clues offered by the N-body simulations mentioned above) and the observations. In this paper we revisit the problem of incomplete violent relaxation, by making a direct comparison between the detailed properties of a family of distribution functions and those of the products of collisionless collapse found in N-body simulations.
Intermittent Dissipation at Kinetic Scales in Plasma Turbulence (Invited)
NASA Astrophysics Data System (ADS)
Wan, M.; Matthaeus, W. H.; Karimabadi, H.; Roytershteyn, V.; Shay, M. A.; Wu, P.; Daughton, W. S.; Loring, B.; Chapman, S. C.
2013-12-01
The nature of collisionless dissipation has been hotly debated in recent years, with alternative ideas posed in terms of various wave modes, such as kinetic Alfven waves, whistlers, linear Vlasov instabilities, cyclotron resonance, and Landau damping. Here we use high resolution kinetic simulations of collisionless plasma driven by shear which show the development of turbulence characterized by dynamic coherent sheetlike current density structures spanning a range of scales down to electron scales. We present evidence that these structures are sites for heating and dissipation, and that stronger current structures signify higher dissipation rates. Evidently, kinetic scale plasma, like magnetohydrodynamics, becomes intermittent due to current sheet formation, leading to the expectation that heating and dissipation in astrophysical and space plasmas may be highly nonuniform and patchy. Comparison with high frequency solar wind observational data, as well as latest results from three-dimensional PIC simulations will also be discussed.
Two-species MHD study of the comet tail disconnection event
NASA Astrophysics Data System (ADS)
Jia, Yingdong; Russell, C. T.; Jian, Lan; Combi, Michael; Manchester, Ward, IV; Gombosi, Tamas
When a comet enters the inner heliosphere, its surface is heated and ejects water group gas molecules. These neutrals are ionized by the solar ultra-violet radiation into water group ions. The magnetized solar wind proton flow picks up these heavier ions to form a straight tail close to the comet-sun line. Changes in plasma conditions across discontinuities in the solar wind may affect the plasma tail, and lead to a disconnection event. Our previous single-species MHD study addressed the importance of magnetic discontinuities in triggering such events, but the single fluid model did not distinguish protons and water group ions. In this work, we track the protons and water group ions separately, to allow us to display the cometary ions that lead to the visual emissions. Such an improvement allows us to better compare simulations with observations.
Energetic Electron Transport In An Inhomogeneous Plasma Medium
Das, Amita
2010-11-23
A review of the work carried out at IPR on energetic electron transport through an inhomogeneous plasma medium is presented in this article. A Generalized Electron Magnetohydrodynamic (G-EMHD) fluid model has been developed and employed for such studies. Novel observations such as (i) the trapping of electron current pulse structure in a high density plasma region, (ii) the formation of sharp magnetic field shock structures at the inhomogeneous plasma density layer (iii) and intense energy dissipation at the shock layer even in the collisionless limit are reported. The intense energy dissipation of the electron current pulse at the shock layer provides a mechanism whereby highly energetic electrons which are essentially collision-less can also successfully deposit their energy in a local region of the plasma. This is specially attractive as it opens up the possibility of heating a localized region of an overdense plasma (where lasers cannot penetrate) by highly energetic collision-less electrons. A direct application of this mechanism to Fast Ignition (FT) experiments is discussed.
Integrating species distribution models (SDMs) and phylogeography for two species of Alpine Primula.
Schorr, G; Holstein, N; Pearman, P B; Guisan, A; Kadereit, J W
2012-06-01
The major intention of the present study was to investigate whether an approach combining the use of niche-based palaeodistribution modeling and phylo-geography would support or modify hypotheses about the Quaternary distributional history derived from phylogeographic methods alone. Our study system comprised two closely related species of Alpine Primula. We used species distribution models based on the extant distribution of the species and last glacial maximum (LGM) climate models to predict the distribution of the two species during the LGM. Phylogeographic data were generated using amplified fragment length polymorphisms (AFLPs). In Primula hirsuta, models of past distribution and phylogeographic data are partly congruent and support the hypothesis of widespread nunatak survival in the Central Alps. Species distribution models (SDMs) allowed us to differentiate between alpine regions that harbor potential nunatak areas and regions that have been colonized from other areas. SDMs revealed that diversity is a good indicator for nunataks, while rarity is a good indicator for peripheral relict populations that were not source for the recolonization of the inner Alps. In P. daonensis, palaeo-distribution models and phylogeographic data are incongruent. Besides the uncertainty inherent to this type of modeling approach (e.g., relatively coarse 1-km grain size), disagreement of models and data may partly be caused by shifts of ecological niche in both species. Nevertheless, we demonstrate that the combination of palaeo-distribution modeling with phylogeographical approaches provides a more differentiated picture of the distributional history of species and partly supports (P. hirsuta) and partly modifies (P. daonensis and P. hirsuta) hypotheses of Quaternary distributional history. Some of the refugial area indicated by palaeodistribution models could not have been identified with phylogeographic data. PMID:22833799
Polychlorinated biphenyls in two species of Arctic seabirds from the Svalbard Area
Daelemans, F.F.; Schepens, P.J.C.; Mehlum, F.
1992-06-01
Anthropogenic long-range pollution of the Arctic could lead to rapid environmental changes at a large geographical scale. Arctic ecosystems are regarded as very vulnerable since the energy flow is channeled through only one or a few essential links. The apparent stability and its survival over longer periods is probably due to the large spatial scale involved which provides the mending of regions of disturbance by repopulation from undisturbed areas. The large geographical scale of man-made pollution from the industrialized countries may interfere with this basic factor of stability in the Arctic ecosystem. Organochlorine compounds is one important group of pollutants transported through the atmosphere and ocean currents from the industrial areas to the Arctic. The ability of organochlorine compounds to enter the food chain in significant quantities, as a result of their relative high stability, lipid solubility and tendency for bioaccumulation, poses a possible hazard for the Arctic fauna. In this respect polychlorinated hydrocarbons and more in particular polychlorinated biphenyls (PCBs) seem to be one of the most dangerous pollutants of the Arctic environment. The archipelago of Svalbard in the European Arctic is an area with only minor local industrial activities, and the anthropogenic pollution recorded in the area is assumed to be mainly of foreign origin. In this paper we present data on PCB levels in two species of Arctic seabirds from the Svalbard area. One is the Glaucous Gull and the other the Black Guillemot. Concentrations of total PCB as well as those of 10 different congeners are given. Special attention is given to three of the most toxic non-orthochlorobiphenyls. 15 refs., 2 figs., 3 tabs.
Living close, doing differently: small-scale asynchrony in demography of two species of seabirds.
Tavecchia, Giacomo; Minguez, Eduardo; De León, Ana; Louzao, Maite; Oro, Daniel
2008-01-01
Studies on spatiotemporal pattern of population abundance predict that close populations should exhibit a high level of synchrony, reflected in a parallel time variation of at least one demographic parameter. We tested this prediction for two threatened species of Procellariiformes sharing similar life history traits: the European Storm Petrel (Hydrobates pelagicus) and the Balearic Shearwater (Puffinus mauretanicus). Within each species, we compared adult survival, proportion of transients (breeders that do not settle), and average productivity at two neighboring colonies. Physical and environmental features (e.g., food availability) of the breeding sites were similar. However, while Balearic Shearwater colonies were free of predators, aerial predators occurred especially in one colony of the European Storm Petrel. Despite this difference, we found similar results for the two species. A high proportion of transient birds was detected in only one colony of each species, ranging between 0.00-0.38 and 0.10-0.63 for the petrels and shearwaters, respectively. This seems to be an emergent feature of spatially structured populations of seabirds, unrelated to colony size or predator pressure, that can have important demographic consequences for local population dynamics and their synchrony. Local survival of resident birds was different at each colony, an unexpected result, especially for predator-free colonies of Balearic Shearwater. Productivity varied between the two colonies of European Storm Petrels, but not between the two colonies of Balearic Shearwaters. We demonstrated that within each species, several demographic parameters were colony specific and sufficiently different to generate short-term asynchronous dynamics. Our findings suggest that, in spatially structured populations, local factors, such as predation or small-scale habitat features, or population factors, such as individual quality or age structure, can generate unexpected asynchrony between
Modeling of bovine spongiform encephalopathy in a two-species feedback loop.
Barnes, Richard; Lehman, Clarence
2013-06-01
Bovine spongiform encephalopathy, otherwise known as mad cow disease, can spread when an individual cow consumes feed containing the infected tissues of another individual, forming a one-species feedback loop. Such feedback is the primary means of transmission for BSE during epidemic conditions. Following outbreaks in the European Union and elsewhere, many governments enacted legislation designed to limit the spread of such diseases via elimination or reduction of one-species feedback loops in agricultural systems. However, two-species feedback loops-those in which infectious material from one-species is consumed by a secondary species whose tissue is then consumed by the first species-were not universally prohibited and have not been studied before. Here we present a basic ecological disease model which examines the rôle feedback loops may play in the spread of BSE and related diseases. Our model shows that there are critical thresholds between the infection's expansion and decrease related to the lifespan of the hosts, the growth rate of the prions, and the amount of prions circulating between hosts. The ecological disease dynamics can be intrinsically oscillatory, having outbreaks as well as refractory periods which can make it appear that the disease is under control while it is still increasing. We show that non-susceptible species that have been intentionally inserted into a feedback loop to stop the spread of disease do not, strictly by themselves, guarantee its control, though they may give that appearance by increasing the refractory period of an epidemic's oscillations. We suggest ways in which age-related dynamics and cross-species coupling should be considered in continuing evaluations aimed at maintaining a safe food supply. PMID:23746801
Metabolism during flight in two species of bats, Phyllostomus hastatus and Pteropus gouldii.
Thomas, S P
1975-08-01
The energetic cost of flight in a wind-tunnel was measured at various combinations of speed and flight angle from two species of bats whose body masses differ by almost an order of magnitude. The highest mean metabolic rate per unit body mass measured from P. hastatus (mean body mass, 0.093 kg) was 130.4 Wkg-1, and that for P. gouldii (mean body mass, 0.78 kg) was 69.6 Wkg-1. These highest metabolic rates, recorded from flying bats, are essentially the same as those predicted for flying birds of the same body masses, but are from 2.5 to 3.0 times greater than the highest metabolic rates of which similar-size exercising terrestrial mammals appear capable. The lowest mean rate of energy utilization per unit body mass P. hastatus required to sustain level flight was 94.2 Wkg-1 and that for P. gouldii was 53.4 Wkg-1. These data from flying bats together with comparable data for flying birds all fall along a straight line when plotted on double logarithmic coordinates as a function of body mass. Such data show that even the lowest metabolic requirements of bats and birds during level flight are about twice the highest metabolic capabilities of similar-size terrestrial mammals. Flying bats share with flying birds the ability to move substantially greater distance per unit energy consumed than walking or running mammals. Calculations show that P. hastatus requires only one-sixth the energy to cover a given distance as does the same-size terrestrial mammal, while P. gouldii requires one-fourth the energy of the same-size terrestrial mammal. An empirically derived equation is presented which enables one to make estimates of the metabolic rates of bats and birds during level flight in nature from body mass data alone. Metabolic data obtained in this study are compared with predictions calculated from an avian flight theory.
Integrating species distribution models (SDMs) and phylogeography for two species of Alpine Primula.
Schorr, G; Holstein, N; Pearman, P B; Guisan, A; Kadereit, J W
2012-06-01
The major intention of the present study was to investigate whether an approach combining the use of niche-based palaeodistribution modeling and phylo-geography would support or modify hypotheses about the Quaternary distributional history derived from phylogeographic methods alone. Our study system comprised two closely related species of Alpine Primula. We used species distribution models based on the extant distribution of the species and last glacial maximum (LGM) climate models to predict the distribution of the two species during the LGM. Phylogeographic data were generated using amplified fragment length polymorphisms (AFLPs). In Primula hirsuta, models of past distribution and phylogeographic data are partly congruent and support the hypothesis of widespread nunatak survival in the Central Alps. Species distribution models (SDMs) allowed us to differentiate between alpine regions that harbor potential nunatak areas and regions that have been colonized from other areas. SDMs revealed that diversity is a good indicator for nunataks, while rarity is a good indicator for peripheral relict populations that were not source for the recolonization of the inner Alps. In P. daonensis, palaeo-distribution models and phylogeographic data are incongruent. Besides the uncertainty inherent to this type of modeling approach (e.g., relatively coarse 1-km grain size), disagreement of models and data may partly be caused by shifts of ecological niche in both species. Nevertheless, we demonstrate that the combination of palaeo-distribution modeling with phylogeographical approaches provides a more differentiated picture of the distributional history of species and partly supports (P. hirsuta) and partly modifies (P. daonensis and P. hirsuta) hypotheses of Quaternary distributional history. Some of the refugial area indicated by palaeodistribution models could not have been identified with phylogeographic data.
Integrating species distribution models (SDMs) and phylogeography for two species of Alpine Primula
Schorr, G; Holstein, N; Pearman, P B; Guisan, A; Kadereit, J W
2012-01-01
The major intention of the present study was to investigate whether an approach combining the use of niche-based palaeodistribution modeling and phylo-geography would support or modify hypotheses about the Quaternary distributional history derived from phylogeographic methods alone. Our study system comprised two closely related species of Alpine Primula. We used species distribution models based on the extant distribution of the species and last glacial maximum (LGM) climate models to predict the distribution of the two species during the LGM. Phylogeographic data were generated using amplified fragment length polymorphisms (AFLPs). In Primula hirsuta, models of past distribution and phylogeographic data are partly congruent and support the hypothesis of widespread nunatak survival in the Central Alps. Species distribution models (SDMs) allowed us to differentiate between alpine regions that harbor potential nunatak areas and regions that have been colonized from other areas. SDMs revealed that diversity is a good indicator for nunataks, while rarity is a good indicator for peripheral relict populations that were not source for the recolonization of the inner Alps. In P. daonensis, palaeo-distribution models and phylogeographic data are incongruent. Besides the uncertainty inherent to this type of modeling approach (e.g., relatively coarse 1-km grain size), disagreement of models and data may partly be caused by shifts of ecological niche in both species. Nevertheless, we demonstrate that the combination of palaeo-distribution modeling with phylogeographical approaches provides a more differentiated picture of the distributional history of species and partly supports (P. hirsuta) and partly modifies (P. daonensis and P. hirsuta) hypotheses of Quaternary distributional history. Some of the refugial area indicated by palaeodistribution models could not have been identified with phylogeographic data. PMID:22833799
Discrimination of closed shapes by two species of bee, Apis mellifera and Megachile rotundata.
Campan, Raymond; Lehrer, Miriam
2002-02-01
In the present study, the performance of two bee species, the honeybee Apis mellifera and the leaf-cutter bee Megachile rotundata, in discriminating among various closed (convex) shapes was examined systematically for the first time. Bees were trained to each of five different shapes, a disc, a square, a diamond and two different triangles, all of the same area, using fresh bees in each experiment. In subsequent tests, the trained bees were given a choice between the learned shape and each of the other four shapes. Two sets of experiments were conducted with both species. In the first, solid black shapes were presented against a white background, thus providing a high luminance contrast. In the second, the shapes carried a random black-and-white pattern and were presented 5 cm in front of a similar pattern, thus producing motion contrast, rather than luminance contrast, against the background. The results obtained with the solid shapes reveal that both bee species accomplish the discrimination, although the performance of the honeybee is significantly better than that of the leaf-cutter bee. Furthermore, the effectiveness of the various shapes differs between the two species. However, in neither species is the discrimination performance correlated with the amount of overlap of the black areas contained in the various pairs of shapes, suggesting that, in our experiments, shape discrimination is not based on a template-matching process. We propose that it is based on the use of local parameters situated at the outline of the shape, such as the position of angles or acute points and, in particular, the position and orientation of edges. This conclusion is supported by the finding that bees of both species accomplish the discrimination even with the patterned shapes. These shapes are visible only because of the discontinuity of the speed of image motion perceived at the edge between the shape and the background. PMID:11893770
Causes of habitat divergence in two species of agamid lizards in arid central Australia.
Daly, Benjamin G; Dickman, Chris R; Crowther, Mathew S
2008-01-01
The deserts of central Australia contain richer communities of lizards than any other arid regions, with the highest diversity occurring in sand dune habitats dominated by hummock-forming spinifex grasses. To investigate the mechanisms that permit coexistence, we studied two species of coexisting agamid lizards that exhibit striking divergence in their use of habitat in the Simpson Desert of central Australia. Here, the military dragon Ctenophorus isolepis is restricted primarily to sites providing > 30% cover of hard spinifex Triodia basedowii, whereas the central netted dragon C. nuchalis occurs in areas with much sparser (< 10%) cover. We constructed four mechanistic models to explain this pattern and then derived hypotheses to test them. One hypothesis, that competition restricts each species to its preferred habitat, was rejected after dyad encounters in field enclosures failed to elicit any habitat shift or any overt interactions between the species. Our next hypotheses were that each species exhibits preferences for different thermal environments or different prey types and that each selects the habitats that maximize access to them. Both were supported. C. isolepis preferred lower temperatures when active and specialized in eating ants < 5 mm long and selected spinifex-dominated areas where these requirements were met. In contrast, C. nuchalis preferred higher temperatures and a diversity of prey, both of which were available mostly in open areas. Finally, we used plasticine models to test the hypothesis that each species faced lower risk of predation in its selected habitat. This was partly supported, as models of both species were attacked more often in the open than under spinifex cover. The results show that habitat divergence occurs along several, probably covarying, niche axes. We suggest that different levels of spinifex cover provide the template for a broad range of ecological interactions, allowing lizard species to partition biotic and abiotic
Alkaline single-cell gel (comet) assay and genotoxicity monitoring using two species of tadpoles.
Ralph, S; Petras, M; Pandrangi, R; Vrzoc, M
1996-01-01
Small bodies of water (e.g., creeks, ponds, and drainage ditches) have received very little attention in genotoxicity studies, yet these areas are important because they are often the first to be affected by industrial effluents, sewage contaminants, accidental spills, internal combustion engine emissions, landfill runoffs, and pesticide uses. To address this deficiency, we examined erythrocytes in two species of tadpoles, Rana clamitans and Bufo americanus, using the alkaline single-cell gel (SCG) ("comet") assay. This approach involves detection, under alkaline conditions, of cell DNA fragments, which on electrophoresis migrate from the nuclear core, resulting in a "comet-with-tail" formation. Exposure of R. clamitans todpoles to a range of concentrations of methyl methanesulfonate (MMS) produced a linear increase in DNA length to DNA core width ratios. This is consistent with findings in a number of other species. Time-dose experiments using MMS suggest that the peak level of DNA damage in R. clamitans todpoles occurred 42 hr after exposure. B. americanus tadpoles exposed to 6.25 mg/l of MMS for 12 hours had a significant increase in DNA damage over that seen in the controls. Freshly caught R. clamitans tadpoles from Highgate and B. americanus tadpoles from Duart, both on the north shore of Lake Erie, gave ratios of 2.78 and 2.07, respectively. This region of Ontario is a prime agricultural area and pesticide use is extensive. Tadpoles from Highgate and Duart, maintained in the laboratory for 4 months and 6 weeks, respectively, gave ratios of 1.29 and 1.44. The results of the SCG procedure in tadpoles indicate that this assay is extremely sensitive and suitable for detecting genotoxicity in the environment.
Champoux, Louise; Rodrigue, Jean; Desgranges, Jean-Luc; Trudeau, Suzanne; Hontela, Alice; Boily, Monique; Spear, Philip
2002-10-01
This study was undertaken to validate potential biomarkers of exposure and effects due to chemical contaminants in breeding colonies of the Great Blue Heron and the Black-crowned Night-Heron on the St. Lawrence River. Eggs and fledglings from both species were collected from many colonies along the River. The fledglings from colonies in freshwater and brackish water were more contaminated by mercury and PCBs than those from estuarine and gulf colonies. With respect to fledglings of the two heron species, some morphometric and blood biochemical measurements, including plasma thyroid hormones and retinol, were significantly different among colonies. Significant differences were also observed in liver retinoids, EROD and porphyrins among colonies. The results of this study suggest that plasma retinoids and thyroid hormones are good biomarkers of exposure and effects, and are sufficiently sensitive to reflect local and regional variations in contamination. Along with the measure of contaminants in egg and plasma, they constitute non-invasive biomarkers which represent an important criteria for long term monitoring of wildlife species. It is concluded that the Great Blue Heron is an appropriate sentinel species in the surveillance network for the St. Lawrence River.
Application of cylindrical Langmuir probes to streaming plasma diagnostics.
NASA Technical Reports Server (NTRS)
Segall, S. B.; Koopman, D. W.
1973-01-01
The current-voltage characteristics of cylindrical probes in a high velocity collisionless plasma flow have been investigated experimentally and theoretically. The plasma was generated by a focused laser pulse incident on a metallic target in vacuum. An analysis, developed from a stationary plasma analog to the flowing case, demonstrated a failure of plasma shielding of probe potential in the electron attracting region. Modifications of relatively simple previous treatments were found to be valid for computing electron current to a probe. The electron characteristics derived from the present analysis agree well with experimental results. The ion and electron portions of the characteristics are consistent with each other and with independent diagnostic measurements.
Differential turbulent heating of different ions in electron cyclotron resonance ion source plasma
Elizarov, L.I.; Ivanov, A.A.; Serebrennikov, K.S.; Vostrikova, E.A.
2006-03-15
The article considers the collisionless ion sound turbulent heating of different ions in an electron cyclotron resonance ion source (ECRIS). The ion sound arises due to parametric instability of pumping wave propagating along the magnetic field with the frequency close to that of electron cyclotron. Within the framework of turbulent heating model the different ions temperatures are calculated in gas-mixing ECRIS plasma.
NASA Astrophysics Data System (ADS)
Latyshev, A. V.; Yushkanov, A. A.
2016-09-01
From the Vlasov-Boltzmann kinetic equation for a collisional degenerate plasma, the electron distribution function is constructed in the quadratic approximation in the electric field strength. A formula for calculating the electric current is derived. It is shown that nonlinearity leads to the rise of a longitudinal electric current directed along the wave vector. The longitudinal current is orthogonal to the known transverse classical current obtained in the linear analysis. When the collision frequency tends to zero, all results obtained for a collisional plasma pass into the corresponding results for a collisionless plasma. The case of small wavenumbers is considered. It is shown that, when the collision frequency tends to zero, the expression for the current passes into the corresponding expression for the current in a collisionless plasma. Graphic analysis of the real and imaginary parts of the current density is performed. The dependence of the electromagnetic field oscillation frequency and electron-plasma-particle collision frequency on the wavenumber is studied.
Germaine, Stephen S.; Ignizio, Drew; Keinath, Doug; Copeland, Holly
2014-01-01
Species distribution models are an important component of natural-resource conservation planning efforts. Independent, external evaluation of their accuracy is important before they are used in management contexts. We evaluated the classification accuracy of two species distribution models designed to predict the distribution of pygmy rabbit Brachylagus idahoensis habitat in southwestern Wyoming, USA. The Nature Conservancy model was deductive and based on published information and expert opinion, whereas the Wyoming Natural Diversity Database model was statistically derived using historical observation data. We randomly selected 187 evaluation survey points throughout southwestern Wyoming in areas predicted to be habitat and areas predicted to be nonhabitat for each model. The Nature Conservancy model correctly classified 39 of 77 (50.6%) unoccupied evaluation plots and 65 of 88 (73.9%) occupied plots for an overall classification success of 63.3%. The Wyoming Natural Diversity Database model correctly classified 53 of 95 (55.8%) unoccupied plots and 59 of 88 (67.0%) occupied plots for an overall classification success of 61.2%. Based on 95% asymptotic confidence intervals, classification success of the two models did not differ. The models jointly classified 10.8% of the area as habitat and 47.4% of the area as nonhabitat, but were discordant in classifying the remaining 41.9% of the area. To evaluate how anthropogenic development affected model predictive success, we surveyed 120 additional plots among three density levels of gas-field road networks. Classification success declined sharply for both models as road-density level increased beyond 5 km of roads per km-squared area. Both models were more effective at predicting habitat than nonhabitat in relatively undeveloped areas, and neither was effective at accounting for the effects of gas-energy-development road networks. Resource managers who wish to know the amount of pygmy rabbit habitat present in an
2013-01-01
Background Amorphophallus is a genus of perennial plants widely distributed in the tropics or subtropics of West Africa and South Asia. Its corms contain a high level of water-soluble glucomannan; therefore, it has long been used as a medicinal herb and food source. Genetic studies of Amorphophallus have been hindered by a lack of genetic markers. A large number of molecular markers are required for genetic diversity study and improving disease resistance in Amorphophallus. Here, we report large scale of transcriptome sequencing of two species: Amorphophallus konjac and Amorphophallus bulbifer using deep sequencing technology, and microsatellite (SSR) markers were identified based on these transcriptome sequences. Results cDNAs of A. konjac and A. bulbifer were sequenced using Illumina HiSeq™ 2000 sequencing technology. A total of 135,822 non-redundant unigenes were assembled from about 9.66 gigabases, and 19,596 SSRs were identified in 16,027 non-redundant unigenes. Di-nucleotide SSRs were the most abundant motif (61.6%), followed by tri- (30.3%), tetra- (5.6%), penta- (1.5%), and hexa-nucleotides (1%) repeats. The top di- and tri-nucleotide repeat motifs included AG/CT (45.2%) and AGG/CCT (7.1%), respectively. A total of 10,754 primer pairs were designed for marker development. Of these, 320 primers were synthesized and used for validation of amplification and assessment of polymorphisms in 25 individual plants. The total of 275 primer pairs yielded PCR amplification products, of which 205 were polymorphic. The number of alleles ranged from 2 to 14 and the polymorphism information content valued ranged from 0.10 to 0.90. Genetic diversity analysis was done using 177 highly polymorphic SSR markers. A phenogram based on Jaccard’s similarity coefficients was constructed, which showed a distinct cluster of 25 Amorphophallus individuals. Conclusion A total of 10,754 SSR markers have been identified in Amorphophallus using transcriptome sequencing. One hundred and
Full Two-Fluid Collisionless Magnetic Reconnection Simulations
NASA Astrophysics Data System (ADS)
Gomez, D. O.; Andres, N.; Dmitruk, P.
2015-12-01
Magnetic reconnection is an important energy conversion process in space environments such as the solar corona or planetary magnetospheres. At the theoretical level of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which are expected to increase the reconnection rates. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This level of description brings two new spatial scales into play, namely, the ion and electron inertial scales. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed 2.5D two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. In a stationary regime, the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.
Ion Dynamics Model for Collisionless Radio Frequency Sheaths
NASA Technical Reports Server (NTRS)
Bose, Deepak; Govindan, T.R.; Meyyappan, M.
2000-01-01
Full scale reactor model based on fluid equations is widely used to analyze high density plasma reactors. It is well known that the submillimeter scale sheath in front of a biased electrode supporting the wafer is difficult to resolve in numerical simulations, and the common practice is to use results for electric field from some form of analytical sheath model as boundary conditions for full scale reactor simulation. There are several sheath models in the literature ranging from Child's law to a recent unified sheath model [P. A. Miller and M. E. Riley, J. Appl. Phys. 82, 3689 (1997)l. In the present work, the cold ion fluid equations in the radio frequency sheath are solved numerically to show that the spatiotemporal variation of ion flux inside the sheath, commonly ignored in analytical models, is important in determining the electric field and ion energy at the electrode. Consequently, a semianalytical model that includes the spatiotemporal variation of ion flux is developed for use as boundary condition in reactor simulations. This semianalytical model is shown to yield results for sheath properties in close agreement with numerical solutions.
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.
Effect Of The Anisotropy On The Transport In Plasmas Created By Ultra-Short Laser Pulse
Hasnaoui, A.; Bendib, A.
2008-09-23
The formation of a high anisotropic photoelectron distribution, as a result of the interaction of a powerful ultra-short laser pulse with a nonequilibrium and a collisionless plasma, in some aspects fundamentally changes the laser-material interaction mechanisms compared with a long pulse. In this work, using the initial conditions, the analytic solution of the Vlasov equation linearised with respect to the bi-Maxwellian distribution function is presented. To unsure the conservative properties, we have added formally the Krook collision term in the limit of a vanishing collision frequency. We have deduced the generalized transport coefficients, witch constitute very reliable closure relations for the collisionless anisotropic fluid equations.
Blasi, P.; Morlino, G.; Bandiera, R.; Amato, E.; Caprioli, D.
2012-08-20
A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high-velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, which we refer to as the neutral return flux, is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge-exchange interaction lengths of fast neutrals moving toward upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities <3000 km s{sup -1}. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test particles accelerated at the shock. We find that, for shocks slower than {approx}3000 km s{sup -1}, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely, {proportional_to}E{sup -2}.
Lagrangian description of warm plasmas
NASA Technical Reports Server (NTRS)
Kim, H.
1970-01-01
Efforts are described to extend the averaged Lagrangian method of describing small signal wave propagation and nonlinear wave interaction, developed by earlier workers for cold plasmas, to the more general conditions of warm collisionless plasmas, and to demonstrate particularly the effectiveness of the method in analyzing wave-wave interactions. The theory is developed for both the microscopic description and the hydrodynamic approximation to plasma behavior. First, a microscopic Lagrangian is formulated rigorously, and expanded in terms of perturbations about equilibrium. Two methods are then described for deriving a hydrodynamic Lagrangian. In the first of these, the Lagrangian is obtained by velocity integration of the exact microscopic Lagrangian. In the second, the expanded hydrodynamic Lagrangian is obtained directly from the expanded microscopic Lagrangian. As applications of the microscopic Lagrangian, the small-signal dispersion relations and the coupled mode equations are derived for all possible waves in a warm infinite, weakly inhomogeneous magnetoplasma, and their interactions are examined.
Instabilities in counterstreaming plasmas
NASA Astrophysics Data System (ADS)
Park, Hye-Sook
2013-10-01
We are performing high power laser experiments showing large, stable, reproducible electromagnetic field structures that arise in counter-streaming interpenetrating supersonic plasma flows in the laboratory. Self organization, whereby energy progressively transfers from smaller to larger scales in an inverse cascade, is widely observed in fluid flows, such as in the nonlinear evolution of multimode Rayleigh-Taylor and Kelvin-Helmholtz instabilities. There are many scenarios in astrophysics where self organization involving magnetic or electric fields in collisionless settings is observed. These surprising structures, predominantly oriented transverse to the primary flow direction, extend for much larger distances than the intrinsic plasma spatial scales, and persist for much longer than the plasma kinetic timescales. Their origin may be magnetic field advection from the recompression of the Biermann battery fields in the midplane. Understanding interactions of high velocity plasma flows is interests to the ICF and astrophysics. This paper will present experimental results and interpretation of these counterstreaming plasma experiments. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Sironi, Lorenzo; Narayan, Ramesh
2015-02-01
In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the electron-to-proton temperature ratio is T 0e /T 0i >~ 0.2, whereas for T 0e /T 0i <~ 0.2 the ion cyclotron instability triggers the growth of strong Alfvén-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold electrons (β0e <~ 2 me /mi , where β0e is the ratio of electron thermal pressure to magnetic pressure), the electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the initial electron temperature, so it provides a solid energy floor even for electrons starting with extremely low temperatures. On the other hand, the electron energy gain for β0e >~ 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of
Sironi, Lorenzo; Narayan, Ramesh E-mail: rnarayan@cfa.harvard.edu
2015-02-20
In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P > P {sub ∥} because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β{sub 0i} ∼ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β{sub 0i} is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the electron-to-proton temperature ratio is T {sub 0e}/T {sub 0i} ≳ 0.2, whereas for T {sub 0e}/T {sub 0i} ≲ 0.2 the ion cyclotron instability triggers the growth of strong Alfvén-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold electrons (β{sub 0e} ≲ 2 m{sub e} /m{sub i} , where β{sub 0e} is the ratio of electron thermal pressure to magnetic pressure), the electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the initial electron temperature, so it provides a solid energy floor even for electrons starting with extremely low temperatures. On the other hand, the electron energy gain for β{sub 0e} ≳ 2 m{sub e} /m{sub i}
Ebrahimi, V.; Esfandyari-Kalejahi, A.
2014-09-15
In this paper, first we represent the differences between spatial and temporal dispersions and their dependence on the measurement techniques for electrostatic waves in unmagnetized collisionless plasma. Then, three different experimental data are compared to the solutions of exact nonextensive dispersion relations for electron-ion and pair plasma. The results confirm the existence of new acoustic plasma waves. Furthermore, these comparisons yield a Maxwellian and a nonextensive plasma with nonextensive parameter q larger than one, and a Maxwellian plasma with some abnormal dispersion properties.
Pulsed Electromagnetic Acceleration of Plasmas
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Cassibry, Jason T.; Markusic, Tom E.; Rodgers, Stephen L. (Technical Monitor)
2002-01-01
A major shift in paradigm in driving pulsed plasma thruster is necessary if the original goal of accelerating a plasma sheet efficiently to high velocities as a plasma "slug" is to be realized. Firstly, the plasma interior needs to be highly collisional so that it can be dammed by the plasma edge layer not (upstream) adjacent to the driving 'vacuum' magnetic field. Secondly, the plasma edge layer needs to be strongly magnetized so that its Hall parameter is of the order of unity in this region to ensure excellent coupling of the Lorentz force to the plasma. Thirdly, to prevent and/or suppress the occurrence of secondary arcs or restrike behind the plasma, the region behind the plasma needs to be collisionless and extremely magnetized with sufficiently large Hall parameter. This places a vacuum requirement on the bore conditions prior to the shot. These requirements are quantified in the paper and lead to the introduction of three new design parameters corresponding to these three plasma requirements. The first parameter, labeled in the paper as gamma (sub 1), pertains to the permissible ratio of the diffusive excursion of the plasma during the course of the acceleration to the plasma longitudinal dimension. The second parameter is the required Hall parameter of the edge plasma region, and the third parameter the required Hall parameter of the region behind the plasma. Experimental research is required to quantify the values of these design parameters. Based upon fundamental theory of the transport processes in plasma, some theoretical guidance on the choice of these parameters are provided to help designing the necessary experiments to acquire these data.
Nemov, V. V.; Kasilov, S. V.; Kernbichler, W.
2014-06-15
An approach for the direct computation of collisionless losses of high energy charged particles is developed for stellarator magnetic fields given in real space coordinates. With this approach, the corresponding computations can be performed for magnetic fields with three-dimensional inhomogeneities in the presence of stochastic regions as well as magnetic islands. A code, which is based on this approach, is applied to various stellarator configurations. It is found that the life time of fast particles obtained in real-space coordinates can be smaller than that obtained in magnetic coordinates.
Pulsed Electromagnetic Acceleration of Plasma: A Review
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Turchi, Peter J.; Markusic, Thomas E.; Cassibry, Jason T.; Sommer, James; Rodgers, Stephen L. (Technical Monitor)
2002-01-01
Much have been learned in the acceleration mechanisms involved in accelerating a plasma electromagnetically in the laboratory over the last 40 years since the early review by Winston Bostik of 1963, but the accumulated understanding is very much scattered throughout the literature. This literature extends back at least to the early sixties and includes Rosenbluth's snowplow model, discussions by Ralph Lovberg, Colgate's boundary-layer model of a current sheet, many papers from the activity at Columbia by Robert Gross and his colleagues, and the relevant, 1-D unsteady descriptions developed from the U. of Maryland theta-pinch studies. Recent progress on the understanding of the pulsed penetration of magnetic fields into collisionless or nearly collisionless plasmas are also be reviewed. Somewhat more recently, we have the two-dimensional, unsteady results in the collisional regime associated with so-called wall-instability in large radius pinch discharges and also in coaxial plasma guns (e.g., Plasma Flow Switch). Among other things, for example, we have the phenomenon of a high- density plasma discharge propagating in a cooaxial gun as an apparently straight sheet (vs paraboloid) because mass re-distribution (on a microsecond timescale) compensates for the 1/r- squared variation of magnetic pressure. We will attempt to collate some of this vast material and bring some coherence tc the development of the subject.
Covariant constitutive relations and relativistic inhomogeneous plasmas
Gratus, J.; Tucker, R. W.
2011-04-15
The notion of a 2-point susceptibility kernel used to describe linear electromagnetic responses of dispersive continuous media in nonrelativistic phenomena is generalized to accommodate the constraints required of a causal formulation in spacetimes with background gravitational fields. In particular the concepts of spatial material inhomogeneity and temporal nonstationarity are formulated within a fully covariant spacetime framework. This framework is illustrated by recasting the Maxwell-Vlasov equations for a collisionless plasma in a form that exposes a 2-point electromagnetic susceptibility kernel in spacetime. This permits the establishment of a perturbative scheme for nonstationary inhomogeneous plasma configurations. Explicit formulae for the perturbed kernel are derived in both the presence and absence of gravitation using the general solution to the relativistic equations of motion of the plasma constituents. In the absence of gravitation this permits an analysis of collisionless damping in terms of a system of integral equations that reduce to standard Landau damping of Langmuir modes when the perturbation refers to a homogeneous stationary plasma configuration. It is concluded that constitutive modeling in terms of a 2-point susceptibility kernel in a covariant spacetime framework offers a natural extension of standard nonrelativistic descriptions of simple media and that its use for describing linear responses of more general dispersive media has wide applicability in relativistic plasma modeling.
NASA Technical Reports Server (NTRS)
1973-01-01
Three aspects of barium ion cloud dynamics are discussed. First, the effect of the ratio of ion cloud conductivity to background ionospheric conductivity on the motion of barium ion clouds is investigated and compared with observations of barium ion clouds. This study led to the suggestion that the conjugate ionosphere participates in the dynamics of barium ion clouds. Second, analytic work on the deformation of ion clouds is presented. Third, a linearized stability theory was extended to include the effect of the finite extent of an ion cloud, as well as the effect of the ratio of ion cloud to ionospheric conductivities. The stability properties of a plasma with contra-streaming ion beams parallel to a magnetic field are investigated. The results are interpreted in terms of parameters appropriate for collisionless shock waves. It is found that this particular instability can be operative only if the up-stream Alfven Mach number exceeds 5.5.
Seasonal reproductive biology of two species of freshwater catfish from the Venezuelan floodplains.
Marcano, Dayssi; Cardillo, Elizabeth; Rodriguez, Christian; Poleo, Germán; Gago, Nathalie; Guerrero, Hilda Y
2007-01-01
Oxydoras sifontesi and Pimelodus blochii are seasonal breeder fish. Spawn occurs once a year over a short interval of time, at the beginning of the rainy season. The gonadosomatic index (GSI), and plasma levels of steroid hormones of P. blochii and O. sifontesi were studied from fish samples, collected from the Portuguesa River (Portuguesa State, Venezuela) in 1998 and 2004-2005, respectively. Gonadal tissue samples were obtained and processed for histology. A macroscopic classification of the degree of gonadal maturation was performed using a six-stage maturity scale. Data was analyzed and compared as a function of the gonadal maturation stage. The GSI of both O. sifontesi and P. blochii increases from stages II to V (preparatory and prespawning periods) and decreases in the stage VI (postspawning). In males, the GSI was usually lower than in females. In both species, the higher plasmatic concentration of 17beta-estradiol (17beta-E) and testosterone (T) were obtained from specimens in stages IV or V. A significant decrease in both hormones was observed in stage VI, except for the males of P. blochii where T concentration did not change between gonadal stages IV-VI. The relevance of these results is discussed in relation to the seasonality and the particular hydrological conditions of the region.
Solitary and shock waves in magnetized electron-positron plasma
Lu, Ding; Li, Zi-Liang; Abdukerim, Nuriman; Xie, Bai-Song
2014-02-15
An Ohm's law for electron-positron (EP) plasma is obtained. In the framework of EP magnetohydrodynamics, we investigate nonrelativistic nonlinear waves' solutions in a magnetized EP plasma. In the collisionless limit, quasistationary propagating solitary wave structures for the magnetic field and the plasma density are obtained. It is found that the wave amplitude increases with the Mach number and the Alfvén speed. However, the dependence on the plasma temperature is just the opposite. Moreover, for a cold EP plasma, the existence range of the solitary waves depends only on the Alfvén speed. For a hot EP plasma, the existence range depends on the Alfvén speed as well as the plasma temperature. In the presence of collision, the electromagnetic fields and the plasma density can appear as oscillatory shock structures because of the dissipation caused by the collisions. As the collision frequency increases, the oscillatory shock structure becomes more and more monotonic.
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.
A nonlinear kinetic energy principle for two-dimensional collision-free plasmas
NASA Astrophysics Data System (ADS)
Schindler, K.; Goldstein, H.
1983-08-01
The existence of a nonlinear kinetic-energy principle for the 2D collisionless plasmas described by the Vlasov theory is demonstrated analytically, accounting for the relevant dynamical constraints. A method similar to that of Gardner (1963) is applied to spatially inhomogeneous plasmas, restricting the theory to cases with translational invariance. Despite this limitation, the principle is considered applicable in analyses such as that of the stability of the geomagnetic tail.
Filamentation due to the Weibel Instability in two counterstreaming laser ablated plasmas
NASA Astrophysics Data System (ADS)
Dong, Quan-Li; Yuan, Dawei; Gao, Lan; Liu, Xun; Chen, Yangao; Jia, Qing; Hua, Neng; Qiao, Zhanfeng; Chen, Ming; Zhu, Baoqiang; Zhu, Jianqiang; Zhao, Gang; Ji, Hantao; Sheng, Zheng-Ming; Zhang, Jie
2016-05-01
Weibel-type filamentation instability was observed in the interaction of two counter streaming laser ablated plasma flows, which were supersonic, collisionless, and closely relevant to astrophysical conditions. The plasma flows were created by irradiating a pair of oppositely standing plastic (CH) foils with 1ns-pulsed laser beams of total energy of 1.7 kJ in two laser spots. With characteristics diagnosed in experiments, the calculated features of Weibel-type filaments are in good agreement with measurements.
Collisionless microinstabilities in stellarators. I. Analytical theory of trapped-particle modes
Helander, P.; Proll, J. H. E.; Plunk, G. G.
2013-12-15
This is the first in a series of papers about collisionless, electrostatic micro-instabilities in stellarators, with an emphasis on trapped-particle modes. It is found that, in so-called maximum-J configurations, trapped-particle instabilities are absent in large regions of parameter space. Quasi-isodynamic stellarators have this property (approximately), and the theory predicts that trapped electrons are stabilizing to all eigenmodes with frequencies below the electron bounce frequency. The physical reason is that the bounce-averaged curvature is favorable for all orbits, and that trapped electrons precess in the direction opposite to that in which drift waves propagate, thus precluding wave-particle resonance. These considerations only depend on the electrostatic energy balance and are independent of all geometric properties of the magnetic field other than the maximum-J condition. However, if the aspect ratio is large and the instability phase velocity differs greatly from the electron and ion thermal speeds, it is possible to derive a variational form for the frequency showing that stability prevails in a yet larger part of parameter space than what follows from the energy argument. Collisionless trapped-electron modes should therefore be more stable in quasi-isodynamic stellarators than in tokamaks.
Stellar dynamics around a massive black hole - I. Secular collisionless theory
NASA Astrophysics Data System (ADS)
Sridhar, S.; Touma, Jihad R.
2016-06-01
We present a theory in three parts, of the secular dynamics of a (Keplerian) stellar system of mass M orbiting a black hole of mass M• ≫ M. Here we describe the collisionless dynamics; Papers II and III are on the (collisional) theory of resonant relaxation. The mass ratio, ε = M/M• ≪ 1, is a natural small parameter implying a separation of time-scales between the short Kepler orbital periods and the longer orbital precessional periods. The collisionless Boltzmann equation (CBE) for the stellar distribution function (DF) is averaged over the fast Kepler orbital phase using the method of multiple scales. The orbit-averaged system is described by a secular DF, F, in a reduced phase space. F obeys a secular CBE that includes stellar self-gravity, general relativistic corrections up to 1.5 post-Newtonian order, and external sources varying over secular times. Secular dynamics, even with general time dependence, conserves the semimajor axis of every star. This additional integral of motion promotes extra regularity of the stellar orbits, and enables the construction of equilibria, F0, through a secular Jeans theorem. A linearized secular CBE determines the response and stability of F0. Spherical, non-rotating equilibria may support long-lived, warp-like distortions. We also prove that an axisymmetric, zero-thickness, flat disc is secularly stable to all in-plane perturbations, when its DF, F0, is a monotonic function of the angular momentum at fixed energy.
Evidence of Magnetic Field Switch-off in Collisionless Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Innocenti, M. E.; Goldman, M.; Newman, D.; Markidis, S.; Lapenta, G.
2015-09-01
The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine-Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.
EVIDENCE OF MAGNETIC FIELD SWITCH-OFF IN COLLISIONLESS MAGNETIC RECONNECTION
Innocenti, M. E.; Lapenta, G.; Goldman, M.; Newman, D.; Markidis, S. E-mail: giovanni.lapenta@wis.kuleuven.be E-mail: david.newman@colorado.edu
2015-09-10
The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine–Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.
Collisionless loss-cone refilling: there is no final parsec problem
NASA Astrophysics Data System (ADS)
Gualandris, Alessia; Read, Justin I.; Dehnen, Walter; Bortolas, Elisa
2016-10-01
Coalescing massive black hole binaries, formed during galaxy mergers, are expected to be a primary source of low frequency gravitational waves. Yet in isolated gas-free spherical stellar systems, the hardening of the binary stalls at parsec-scale separations owing to the inefficiency of relaxation-driven loss-cone refilling. Repopulation via collisionless orbit diffusion in triaxial systems is more efficient, but published simulation results are contradictory. While sustained hardening has been reported in simulations of galaxy mergers with N ˜ 106 stars and in early simulations of rotating models, in isolated non-rotating triaxial models the hardening rate continues to fall with increasing N, a signature of spurious two-body relaxation. We present a novel approach for studying loss cone repopulation in galactic nuclei. Since loss cone repopulation in triaxial systems owes to orbit diffusion, it is a purely collisionless phenomenon and can be studied with an approximated force calculation technique, provided the force errors are well behaved and sufficiently small. We achieve this using an accurate fast multipole method and define a proxy for the hardening rate that depends only on stellar angular momenta. We find that the loss cone is efficiently replenished even in very mildly triaxial models (with axis ratios 1 : 0.9 : 0.8). Such triaxiality is unavoidable following galactic mergers and can drive binaries into the gravitational wave regime. We conclude that there is no `final parsec problem'.
NASA Astrophysics Data System (ADS)
You, Jhih-Shih; Liu, I.-Kang; Wang, Daw-Wei; Gou, Shih-Chuan; Wu, Congjun
We investigate the unconventional Bose-Einstein condensations of two-species mixture with p-wave symmetry in the second band of a bipartite optical lattice. Different from the single-species case, the two-species boson mixture exhibits two non-equivalent complex BECs in the intraspecies-interaction-dominating regime, with one breaking time-reversal symmetry while the other not. When the interspecies interaction is tuned across the SU(2) invariant point, the system undergoes a quantum phase transition toward a real-valued checkerboard state characterized by a staggered spin density structure. An experimental scheme for phase measurement is presented. Finally, we will show strong coupling analysis on anti-Hund'srule, Mott-insulating states and the superfluid.
Beckmann, Björn C; Purse, Bethan V; Roy, David B; Roy, Helen E; Sutton, Peter G; Thomas, Chris D
2015-01-01
There are large variations in the responses of species to the environmental changes of recent decades, heightening interest in whether their traits may explain inter-specific differences in range expansions and contractions. Using a long-term distributional dataset, we calculated range changes of grasshoppers and crickets in Britain between the 1980s and the 2000s and assessed whether their traits (resource use, life history, dispersal ability, geographic location) explain relative performance of different species. Our analysis showed large changes in the distributions of some species, and we found a positive relationship between three traits and range change: ranges tended to increase for habitat generalists, species that oviposit in the vegetation above ground, and for those with a southerly distribution. These findings accord well with the nature of environmental changes over this period (climatic warming; reductions in the diversity and increases in the height of vegetation). However, the trait effects applied mainly to just two species, Conocephalus discolor and Metrioptera roeselii, which had shown the greatest range increases. Once they were omitted from the analysis, trait effects were no longer statistically significant. Previous studies on these two species emphasised wing-length dimorphism as the key to their success, resulting in a high phenotypic plasticity of dispersal and evolutionary-ecological feedback at their expanding range margins. This, combined with our results, suggests that an unusual combination of traits have enabled these two species to undertake extremely rapid responses to recent environmental changes. The fact that our results are dominated by two species only became apparent through cautious testing of the results' robustness, not through standard statistical checks. We conclude that trait-based analyses may contribute to the assessment of species responses to environmental change and provide insights into underlying mechanisms, but
Beckmann, Björn C; Purse, Bethan V; Roy, David B; Roy, Helen E; Sutton, Peter G; Thomas, Chris D
2015-01-01
There are large variations in the responses of species to the environmental changes of recent decades, heightening interest in whether their traits may explain inter-specific differences in range expansions and contractions. Using a long-term distributional dataset, we calculated range changes of grasshoppers and crickets in Britain between the 1980s and the 2000s and assessed whether their traits (resource use, life history, dispersal ability, geographic location) explain relative performance of different species. Our analysis showed large changes in the distributions of some species, and we found a positive relationship between three traits and range change: ranges tended to increase for habitat generalists, species that oviposit in the vegetation above ground, and for those with a southerly distribution. These findings accord well with the nature of environmental changes over this period (climatic warming; reductions in the diversity and increases in the height of vegetation). However, the trait effects applied mainly to just two species, Conocephalus discolor and Metrioptera roeselii, which had shown the greatest range increases. Once they were omitted from the analysis, trait effects were no longer statistically significant. Previous studies on these two species emphasised wing-length dimorphism as the key to their success, resulting in a high phenotypic plasticity of dispersal and evolutionary-ecological feedback at their expanding range margins. This, combined with our results, suggests that an unusual combination of traits have enabled these two species to undertake extremely rapid responses to recent environmental changes. The fact that our results are dominated by two species only became apparent through cautious testing of the results' robustness, not through standard statistical checks. We conclude that trait-based analyses may contribute to the assessment of species responses to environmental change and provide insights into underlying mechanisms, but
Beckmann, Björn C.; Purse, Bethan V.; Roy, David B.; Roy, Helen E.; Sutton, Peter G.; Thomas, Chris D.
2015-01-01
There are large variations in the responses of species to the environmental changes of recent decades, heightening interest in whether their traits may explain inter-specific differences in range expansions and contractions. Using a long-term distributional dataset, we calculated range changes of grasshoppers and crickets in Britain between the 1980s and the 2000s and assessed whether their traits (resource use, life history, dispersal ability, geographic location) explain relative performance of different species. Our analysis showed large changes in the distributions of some species, and we found a positive relationship between three traits and range change: ranges tended to increase for habitat generalists, species that oviposit in the vegetation above ground, and for those with a southerly distribution. These findings accord well with the nature of environmental changes over this period (climatic warming; reductions in the diversity and increases in the height of vegetation). However, the trait effects applied mainly to just two species, Conocephalus discolor and Metrioptera roeselii, which had shown the greatest range increases. Once they were omitted from the analysis, trait effects were no longer statistically significant. Previous studies on these two species emphasised wing-length dimorphism as the key to their success, resulting in a high phenotypic plasticity of dispersal and evolutionary-ecological feedback at their expanding range margins. This, combined with our results, suggests that an unusual combination of traits have enabled these two species to undertake extremely rapid responses to recent environmental changes. The fact that our results are dominated by two species only became apparent through cautious testing of the results’ robustness, not through standard statistical checks. We conclude that trait-based analyses may contribute to the assessment of species responses to environmental change and provide insights into underlying mechanisms
Bondarenko, A. S. Schaeffer, D. B.; Everson, E. T.; Clark, S. E.; Constantin, C. G.; Niemann, C.
2014-12-15
The collision-less transfer of momentum and energy from explosive debris plasma to magnetized background plasma is a salient feature of various astrophysical and space environments. While much theoretical and computational work has investigated collision-less coupling mechanisms and relevant parameters, an experimental validation of the results demands the measurement of the complex, collective electric fields associated with debris-background plasma interaction. Emission spectroscopy offers a non-interfering diagnostic of electric fields via the Stark effect. A unique experiment at the University of California, Los Angeles, that combines the Large Plasma Device (LAPD) and the Phoenix laser facility has investigated the marginally super-Alfvénic, quasi-perpendicular expansion of a laser-produced carbon (C) debris plasma through a preformed, magnetized helium (He) background plasma via emission spectroscopy. Spectral profiles of the He II 468.6 nm line measured at the maximum extent of the diamagnetic cavity are observed to intensify, broaden, and develop equally spaced modulations in response to the explosive C debris, indicative of an energetic electron population and strong oscillatory electric fields. The profiles are analyzed via time-dependent Stark effect models corresponding to single-mode and multi-mode monochromatic (single frequency) electric fields, yielding temporally resolved magnitudes and frequencies. The proximity of the measured frequencies to the expected electron plasma frequency suggests the development of the electron beam-plasma instability, and a simple saturation model demonstrates that the measured magnitudes are feasible provided that a sufficiently fast electron population is generated during C debris–He background interaction. Potential sources of the fast electrons, which likely correspond to collision-less coupling mechanisms, are briefly considered.
Parker, D J; Vesala, L; Ritchie, M G; Laiho, A; Hoikkala, A; Kankare, M
2015-01-01
For many organisms the ability to cold acclimate with the onset of seasonal cold has major implications for their fitness. In insects, where this ability is widespread, the physiological changes associated with increased cold tolerance have been well studied. Despite this, little work has been done to trace changes in gene expression during cold acclimation that lead to an increase in cold tolerance. We used an RNA-Seq approach to investigate this in two species of the Drosophila virilis group. We found that the majority of genes that are differentially expressed during cold acclimation differ between the two species. Despite this, the biological processes associated with the differentially expressed genes were broadly similar in the two species. These included: metabolism, cell membrane composition, and circadian rhythms, which are largely consistent with previous work on cold acclimation/cold tolerance. In addition, we also found evidence of the involvement of the rhodopsin pathway in cold acclimation, a pathway that has been recently linked to thermotaxis. Interestingly, we found no evidence of differential expression of stress genes implying that long-term cold acclimation and short-term stress response may have a different physiological basis. PMID:25669607
Turbulence in solar wind and laboratory plasmas
Carbone, V.
2010-06-16
Recent studies of plasma turbulence based on measurements within solar wind and laboratory plasmas has been discussed. Evidences for the presence of a turbulent energy cascade, using the Yaglom's law for MHD turbulence, has been provided through data from the Ulysses spacecraft. This allows, for the first time, a direct estimate of the turbulent energy transfer rate, which can contribute to the in situ heating of the solar wind. The energy cascade has been evidenced also for ExB electrostatic turbulence in laboratory magnetized plasmas using measurements of intermittent transport (bursty turbulence) at the edge of the RFX-mod reversed field pinch plasma device. Finally the problem of the dispersive region of turbulence in solar wind above the ion-cyclotron frequency, where a spectral break is usually observed, and the problem of dissipation in a collisionless fluid as the solar wind, are briefly discussed.
Zank, G. P.; Hunana, P.; Mostafavi, P.; Goldstein, M. L.
2014-12-20
Pickup ions (PUIs) in the outer heliosphere and the local interstellar medium are created by charge exchange between protons and hydrogen (H) atoms, forming a thermodynamically dominant component. In the supersonic solar wind beyond >10 AU, in the inner heliosheath (IHS), and in the very local interstellar medium (VLISM), PUIs do not equilibrate collisionally with the background plasma. Using a collisionless form of Chapman-Enskog expansion, we derive a closed system of multi-fluid equations for a plasma comprised of thermal protons and electrons, and suprathermal PUIs. The PUIs contribute an isotropic scalar pressure to leading order, a collisionless heat flux at the next order, and a collisionless stress tensor at the second-order. The collisionless heat conduction and viscosity in the multi-fluid description results from a non-isotropic PUI distribution. A simpler one-fluid MHD-like system of equations with distinct equations of state for both the background plasma and the PUIs is derived. We investigate linear wave properties in a PUI-mediated three-fluid plasma model for parameters appropriate to the VLISM, the IHS, and the solar wind in the outer heliosphere. Five distinct wave modes are possible: Alfvén waves, thermal fast and slow magnetoacoustic waves, PUI fast and slow magnetoacoustic waves, and an entropy mode. The thermal and PUI acoustic modes propagate at approximately the combined thermal magnetoacoustic speed and the PUI sound speed respectively. All wave modes experience damping by the PUIs through the collisionless PUI heat flux. The PUI-mediated plasma model yields wave properties, including Alfvén waves, distinctly different from those of the standard two-fluid model.
Low-frequency fluctuations in plasma magnetic fields
Cable, S.; Tajima, T.
1992-02-01
It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.
NASA Astrophysics Data System (ADS)
Voloshin, Dmitry; Kovalev, Alexander; Mankelevich, Yuri; Proshina, Olga; Rakhimova, Tatyana; Vasilieva, Anna
2015-01-01
Experimental measurements of current-voltage relationship in RF CCP discharge in argon at 81 MHz have been performed by cylindrical Langmuir probes technique. Two different probe radii have been used: 50 and 250 μm. The high plasma density 1010-1011 cm-3 has been estimated at specific input power under study. The experimental data on nonmonotonic behavior of probe current with pressure were observed firstly for conditions of RF discharge plasmas. To analyze the probe measurements the fast numerical model for ion current collected by a cylindrical probe has been developed. This model is based on the particle-in-cell with Monte-Carlo collision method for ions motion and Boltzmann relation for electrons. The features of probe data at studied conditions were discussed. The comparative analysis of different collisionless approaches for plasma density calculation from ion probe current is done. It is shown that in general collisionless theories underestimate the plasma density value. For correct evaluation of plasma density experimental I- V probe measurement should be supplied by the numerical simulation. It was demonstrated that the collisionless analytical theory of orbital motion can formally give correct results on plasma density at some plasma conditions even when ion collisions take place. The physical reasons of this accidental validity are explained.
THREE-DIMENSIONAL MODELING OF RELATIVISTIC COLLISIONLESS ION-ELECTRON SHOCKS
Haugboelle, Troels
2011-10-01
Two-dimensional (2D) modeling of collisionless shocks has been of tremendous importance in understanding the physics of nonlinear evolution, momentum transfer, and particle acceleration, but current computer capacities have now reached a point where three-dimensional (3D) modeling is becoming feasible. We present the first 3D model of a fully developed and relaxed relativistic ion-electron shock, and analyze and compare it to similar 2D models. Quantitative and qualitative differences are found with respect to the 2D models. The shock jump conditions are naturally different, because of the extra degree of freedom, but in addition it is found that strong parallel electric fields develop at the shock interface, the level of magnetic field energy is lower, and the non-thermal particle distribution is shallower with a power-law index of {approx}2.2.
NASA Technical Reports Server (NTRS)
Bernhardt, P. A.
1979-01-01
The paper is motivated by a need for describing high-altitude gas releases from rockets or the Space Shuttle. In the tenuous upper atmosphere, the injected gases expand from a collisionless to a collision-dominated state. The analysis presented extends the efforts of Baum (1973-1974) to include the effects of a nonuniform background atmosphere and a velocity-dependent collision frequency. The unsteady expansion of gas releases is analyzed using gas kinetic theory. The Boltzmann equation with the Krook collision integral is solved numerically. At late times (after many collisions with the background atmosphere) the solution is identical to the one given by diffusion in a nonuniform atmosphere (Bernhardt, 1979). The theoretical model predicts elongation and heating of the vapor trails due to collisions.
Optical conductivity of disordered Weyl semimetals in collisionless regime at zero temperature
NASA Astrophysics Data System (ADS)
Juricic, Vladimir; Roy, Bitan
Weyl semimetals have recently attracted considerable attention as prime examples of topologically nontrivial gapless states of quantum matter. They have been experimentally found and the chiral anomaly, which represents their hallmark feature, has been measured. In this work, we study transport in the disordered Weyl semimetals using the Kubo formalism. We consider point-like impurity potentials, which are irrelevant in the renormalization-group sense, and compute the corresponding leading correction to the collisionless conductivity at zero temperature. As a result, we find that all eight possible types of the point-like disorder potentials give rise to a correction to the real part of the optical conductivity in the clean limit, which is universal up to a sign. Consequently, the dielectric constant of a Weyl material receives a disorder correction which is linear in frequency. Finally, we discuss some experimental consequences of our findings.
Numerical Tests of the Cosmic Censorship Conjecture with Collisionless Matter Collapse
NASA Astrophysics Data System (ADS)
Okounkova, Maria; Hemberger, Daniel; Scheel, Mark
2016-03-01
We present our results of numerical tests of the weak cosmic censorship conjecture (CCC), which states that generically, singularities of gravitational collapse are hidden within black holes, and the hoop conjecture, which states that black holes form when and only when a mass M gets compacted into a region whose circumference in every direction is C <= 4 πM . We built a smooth particle methods module in SpEC, the Spectral Einstein Code, to simultaneously evolve spacetime and collisionless matter configurations. We monitor RabcdRabcd for singularity formation, and probe for the existence of apparent horizons. We include in our simulations the prolate spheroid configurations considered in Shapiro and Teukolsky's 1991 numerical study of the CCC. This research was partially supported by the Dominic Orr Fellowship at Caltech.
Li, Yongfeng; Cui, Jingan; Song, Xinyu
2009-01-01
In this paper, the nonautonomous competing two-species Lotka-Volterra models with impulsive effect are considered, where all the parameters are time-dependent and asymptotically approach the corresponding periodic functions. Under some conditions, it is shown that the semi-trivial positive solutions of the models asymptotically approach the semi-trivial positive periodic solutions of the corresponding periodic system. It is also shown that the positive solution of the models asymptotically approach the positive periodic solution of the corresponding periodic system.
Khan, R A
2010-08-01
Two species of marketable-size flatfish, winter flounder (Pleuronectes americanus) and American plaice (Hippoglossoides platessoides) from a fjord, were examined as sentinels for the effects of effluent discharged by a pulp and paper mill in Newfoundland, Canada. Reference samples for comparison were obtained from a pristine fjord. Condition factor, lymphocyte levels and the abundance of two intestinal parasites were significantly greater in flounder and plaice sampled at the reference site while macroscopic and microscopic lesions, and hepatic somatic indices were greater in flatfish taken from the contaminated site. These results suggest that both species of commercial flatfish are useful as sentinels for studying environmental pollution.
Kashmiri, S V; Mehdi, R; Ferrer, J F
1983-01-01
Cocultivation of uninfected and bovine leukemia virus-producing bat cells yielded, in addition to the unintegrated linear DNA duplex, DNA molecules that migrated as 4.4- and 4.8-kilobase-pair DNA fragments in gel electrophoresis. These DNA molecules were purified by acid-phenol extraction and cleaved with restriction endonucleases EcoRI, and HindIII, which have one recognition site each on the bovine leukemia virus proviral DNA. Such cleavage generated DNA molecules of approximately 10.0 and 9.4 kilobase pairs, thus indicating the existence of two species of covalently closed circular molecules of bovine leukemia virus proviral DNA. Images PMID:6300454
Shielding of a Moving Charged Dust Particle in the Nonequilibrium Plasma
Filippov, A. V.; Pal, A. F.; Starostin, A. N.; Momot, A. I.; Zagorodny, A. G.
2008-09-07
Study of shielding of a moving charged dust particle in the nonequilibrium plasma was performed. It is known that in the collisionless so-called Vlasov plasma the electric field of a slowly moving charged particle at high distances corresponds to quadrupole [1, 2, 3]. It was found that in the collisional plasma the electric field of a moving dust particle had the dipole component and the long distance behavior of the electric fields was defined by this component. Therefore the interaction of dust particles in plasma flow became dependent on the relative orientation of the interpaticle radius-vector and the flow velocity vector.
Cahill, Abigail E; Levinton, Jeffrey S
2016-01-01
Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping-by-sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, Crepidula convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high-dispersing species, Crepidula fornicata, are distinct from more central populations, although this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genomewide markers was slight, and it is not yet known whether there are functional consequences for the marginal populations. PMID:26615052
Cahill, Abigail E; Levinton, Jeffrey S
2016-01-01
Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping-by-sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, Crepidula convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high-dispersing species, Crepidula fornicata, are distinct from more central populations, although this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genomewide markers was slight, and it is not yet known whether there are functional consequences for the marginal populations.
Lone, Shahnaz Rahman; Ilangovan, Vinodh; Murugan, Madhuvika; Sharma, Vijay Kumar
2011-03-01
We assessed the effect of different day/night lengths on the pre-adult developmental time of two species of Camponotus ants that normally develop in dark underground nests. We assayed larval (egg-to-pupal formation), pupal (pupal formation-to-adult emergence), and pre-adult (egg-to-adult emergence) durations in these ants under three different light/dark (LD) cycles of 12:12 h, 10:14 h, and 14:10 h. We observed that the pre-adult development time of ants under these day lengths was significantly different. Although both species developed fastest under 12:12 h LD, when asymmetric LD cycles were compared, night-active species (Camponotus compressus) developed faster under short days (10:14 h) and day-active species (C. paria) developed faster under long days (14:10 h). This day/night-length-mediated difference in pre-adult developmental duration was mostly due to modulation of larval duration; however, in day-active species it was also via altered pupal duration. These results thus indicate that the two species of Camponotus ants respond differently to short and long days, suggesting that seasonal timers regulate pre-adult development time in tropical ant species living in dark underground nests.
Analysis of stability of a homogeneous state of anisotropic plasma
Zakharov, V. Yu. Chernova, T. G. Stepanov, S. E.
2015-04-15
Small-amplitude waves in collisionless magnetized plasma are considered in the framework of one-fluid anisotropic magnetohydrodynamics with allowance for the anisotropy of the pressure and thermal flux. Stability of a homogeneous plasma state is analyzed using an eighth-order dispersion relation. Restrictions on the parameters of the homogeneous state at which the dispersion relation has no complex roots at any value of the angle between the wave vector and the unperturbed magnetic field are obtained. The applied method also makes it possible to determine the types of unstable waves.
On Variational Methods in the Physics of Plasma Waves
I.Y. Dodin
2013-03-08
A fi rst-principle variational approach to adiabatic collisionless plasma waves is described. The focus is made on one-dimensional electrostatic oscillations, including phase-mixed electron plasma waves (EPW) with trapped particles, such as Bernstein-Greene-Kruskal modes. The well known Whitham's theory is extended by an explicit calculation of the EPW Lagrangian, which is related to the oscillation-center energies of individual particles in a periodic fi eld, and those are found by a quadrature. Some paradigmatic physics of EPW is discussed for illustration purposes. __________________________________________________
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.