Stability of a vortex sheet between collisionless plasmas

1973 ◽  
Vol 9 (2) ◽  
pp. 249-260 ◽  
Author(s):  
Ramaswamy Rajaram ◽  
G. L. Kalra ◽  
J. N. Tandon
Keyword(s):  
Solar Wind ◽  
Internal Structure ◽  
Collisionless Plasma ◽  
Vortex Sheet ◽  
Collisionless Plasmas ◽  
The Stability

The problem of stability of a vortex sheet between two collisionless plasma media described by Chew et al. (1956) equations is examined. The relevance of these investigations to the internal structure of the solar wind and to the stability of the magnetosphere–solar wind boundary is discussed.

scholarly journals Fluidization of collisionless plasma turbulence

2019 ◽  
Vol 116 (4) ◽  
pp. 1185-1194 ◽  
Author(s):  
Romain Meyrand ◽  
Anjor Kanekar ◽  
William Dorland ◽  
Alexander A. Schekochihin
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Magnetized Plasma ◽  
Landau Damping ◽  
Astrophysical Plasmas ◽  
Phase Mixing ◽  
Fluid Turbulence ◽  
Collisionless Plasmas

In a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of these fluctuations in a quiescent plasma—one of the most fundamental physical phenomena that makes plasma different from a conventional fluid. Nevertheless, broad power law spectra of compressive fluctuations are observed in turbulent astrophysical plasmas (most vividly, in the solar wind) under conditions conducive to strong Landau damping. Elsewhere in nature, such spectra are normally associated with fluid turbulence, where energy cannot be dissipated in the inertial-scale range and is, therefore, cascaded from large scales to small. By direct numerical simulations and theoretical arguments, it is shown here that turbulence of compressive fluctuations in collisionless plasmas strongly resembles one in a collisional fluid and does have broad power law spectra. This “fluidization” of collisionless plasmas occurs, because phase mixing is strongly suppressed on average by “stochastic echoes,” arising due to nonlinear advection of the particle distribution by turbulent motions. Other than resolving the long-standing puzzle of observed compressive fluctuations in the solar wind, our results suggest a conceptual shift for understanding kinetic plasma turbulence generally: rather than being a system where Landau damping plays the role of dissipation, a collisionless plasma is effectively dissipationless, except at very small scales. The universality of “fluid” turbulence physics is thus reaffirmed even for a kinetic, collisionless system.

scholarly journals On annihilation of the relativistic electron vortex pair in collisionless plasmas

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
K. V. Lezhnin ◽  
F. F. Kamenets ◽  
T. Zh. Esirkepov ◽  
S. V. Bulanov
Keyword(s):  
Magnetic Field ◽  
Collisionless Plasma ◽  
Vortex Formation ◽  
Vortex Pair ◽  
Skin Depth ◽  
Secondary Vortex ◽  
Vortex System ◽  
Collisionless Plasmas ◽  
Secondary Vortices ◽  
The Magnetic Field

In contrast to hydrodynamic vortices, vortices in a plasma contain an electric current circulating around the centre of the vortex, which generates a magnetic field localized inside. Using computer simulations, we demonstrate that the magnetic field associated with the vortex gives rise to a mechanism of dissipation of the vortex pair in a collisionless plasma, leading to fast annihilation of the magnetic field with its energy transforming into the energy of fast electrons, secondary vortices and plasma waves. Two major contributors to the energy damping of a double vortex system, namely, magnetic field annihilation and secondary vortex formation, are regulated by the size of the vortex with respect to the electron skin depth, which scales with the electron$\unicode[STIX]{x1D6FE}$factor,$\unicode[STIX]{x1D6FE}_{e}$, as$R/d_{e}\propto \unicode[STIX]{x1D6FE}_{e}^{1/2}$. Magnetic field annihilation appears to be dominant in mildly relativistic vortices, while for the ultrarelativistic case, secondary vortex formation is the main channel for damping of the initial double vortex system.

scholarly journals The construction and empirical verification of the Sense of Team Efficacy Questionnaire (Kwestionariusz Poczucia Druzynowej Skutecznosci)

2015 ◽  
Vol 7 (1) ◽  
pp. 14-28
Author(s):  
ZUZANNA WALACH-BISTA
Keyword(s):  
Construct Validity ◽  
Psychometric Properties ◽  
Internal Structure ◽  
Predictive Validity ◽  
Discriminant Validity ◽  
Internal Reliability ◽  
Team Efficacy ◽  
Convergent And Discriminant Validity ◽  
Group Environment ◽  
The Stability

Background: This article presents the procedure of the elaboration and verification of the first Polish Sense of Team Efficacy Questionnaire (Kwestionariusz Poczucia Druzynowej Skutecznosci – KPDS). Material/Methods: Two research stages involved a total of 373 professional athletes. Based on the collected data, the internal structure and psychometric properties of the instrument were established. Results: As a result of the conducted statistical analyses, a questionnaire was obtained. Analyses confirmed the stability of the internal structure of the questionnaire. The instrument also obtained satisfactory coefficients of reliability (using Cronbach’s alpha internal reliability coefficient) and construct validity. In order to establish the convergent and discriminant validity of the KPDS, the analysis of the multitrait-multimethod matrix was applied, using the Group Environment Questionnaire (GEQ). Predictive validity was established using the result obtained in a match played directly after the conducted study. Conclusions: The obtained results confirmed the relevance of creating the KPDS. The questionnaire was made up of 21 items representing 4 subscales: fitness, preparation, effort and endurance. Calculation of a general score for the KPDS also proved to be possible.

Power spectral density of magnetic field and ion velocity fluctuations from inertial to kinetic ranges

2021 ◽  
Author(s):  
Jana Šafránková ◽  
Zdeněk Němeček ◽  
František Němec ◽  
Luca Franci ◽  
Alexander Pitňa
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Large Scale ◽  
Collisionless Plasma ◽  
Power Spectra ◽  
Physical Parameters ◽  
Particle In Cell ◽  
High Reynolds ◽  
Experimental Findings ◽  
Turbulent Cascade

<p>The solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high Reynolds numbers. A turbulent cascade—the process that transfers the free energy contained within the large scale fluctuations into the smaller ones—is believed to be one of the most important mechanisms responsible for heating of the solar corona and solar wind. The paper analyzes power spectra of solar wind velocity, density and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. The study uses measurements of the Bright Monitor of the Solar Wind (BMSW) on board the Spektr-R spacecraft with a time resolution of 32 ms complemented with 10 Hz magnetic field observations from the Wind spacecraft propagated to the Spektr-R location. The statistics based on more than 42,000 individual spectra show that: (1) the spectra of both quantities can be fitted by two (three in the case of the density) power-law segments; (2) the median slopes of parallel and perpendicular fluctuation velocity and magnetic field components are different; (3) the break between MHD and kinetic scales as well as the slopes are mainly controlled by the ion beta parameter. These experimental results are compared with high-resolution 2D hybrid particle-in-cell simulations, where the electrons are considered to be a massless, charge-neutralizing fluid with a constant temperature, whereas the ions are described as macroparticles representing portions of their distribution function. In spite of several limitations (lack of the electron kinetics, lower dimensionality), the model results agree well with the experimental findings. Finally, we discuss differences between observations and simulations in relation to the role of important physical parameters in determining the properties of the turbulent cascade.</p>

Turbulent energy transfer in bidimensional numerical models of plasma

2021 ◽  
Author(s):  
Rocio Manobanda ◽  
Christian Vasconez ◽  
Denise Perrone ◽  
Raffaele Marino ◽  
Dimitri Laveder ◽  
...  
Keyword(s):  
Solar Wind ◽  
Energy Transfer ◽  
Numerical Models ◽  
Collisionless Plasma ◽  
Space Plasma ◽  
Turbulent Energy ◽  
Turbulent Medium ◽  
Scaling Properties ◽  
Magnetic Diffusivity ◽  
Out Of Plane

<p>Structured, highly variable and virtually collision-free. Space plasma is an unique laboratory for studying the transfer of energy in a highly turbulent environment. This turbulent medium plays an important role in various aspects of the Solar--Wind generation, particles acceleration and heating, and even in the propagation of cosmic rays. Moreover, the Solar Wind continuous expansion develops a strong turbulent character, which evolves towards a state that resembles the well-known hydrodynamic turbulence (Bruno and Carbone). This turbulence is then dissipated from magnetohydrodynamic (MHD) through kinetic scales by different -not yet well understood- mechanisms. In the MHD approach, Kolmogorov-like behaviour is supported by power-law spectra and intermittency measured in observations of magnetic and velocity fluctuations. In this regime, the intermittent cross-scale energy transfer has been extensively described by the Politano--Pouquet (global) law, which is based on conservation laws of the MHD invariants, and was recently expanded to take into account the physics at the bottom of the inertial (or Hall) range, e.g. (Ferrand et al., 2019). Following the 'Turbulence Dissipation Challenge', we study the properties of the turbulent energy transfer using three different bi-dimensional numerical models of space plasma. The models, Hall-MHD (HMHD), Landau Fluid (LF) and Hybrid Vlasov-Maxwell (HVM), were ran in collisionless-plasma conditions, with an out-of-plane ambient magnetic field, and with magnetic diffusivity carefully calibrated in the fluid models. As each model has its own range of validity, it allows us to explore a long-enough range of scales at a period of maximal turbulence activity. Here, we estimate the local and global scaling properties of different energy channels using a, recently introduced, proxy of the local turbulent energy transfer (LET) rate (Sorriso-Valvo et al., 2018). This study provides information on the structure of the energy fluxes that transfers (and dissipates) most of the energy at small scales throughout the turbulent cascade. </p>

The stability of an expanding circular vortex sheet

Mathematika ◽  
1974 ◽  
Vol 21 (1) ◽  
pp. 128-133 ◽  
Author(s):  
D. W. Moore ◽  
R. Griffith-Jones
Keyword(s):  
Vortex Sheet ◽  
The Stability ◽  
Circular Vortex Sheet

scholarly journals Mechanical behavior of a hydrated perfluorosulfonic acid membrane at meso and nano scales

RSC Advances ◽  
2019 ◽  
Vol 9 (17) ◽  
pp. 9594-9603 ◽  
Author(s):  
Cong Feng ◽  
Yan Li ◽  
Kunnan Qu ◽  
Zhiming Zhang ◽  
Pengfei He
Keyword(s):  
Mechanical Properties ◽  
Fuel Cells ◽  
Mechanical Behavior ◽  
Internal Structure ◽  
Proton Exchange Membrane ◽  
Proton Exchange ◽  
Membrane Material ◽  
Perfluorosulfonic Acid ◽  
The Stability ◽  
Exchange Membrane

Perfluorosulfonic acid (PFSA) is widely used as the membrane material for proton-exchange membrane fuel cells, and its mechanical properties directly affect the stability and the life of the internal structure of the proton exchange membrane.

Free energy sources in kinetic scale current sheets formed in collisionless plasma turbulence

2020 ◽  
Author(s):  
Neeraj Jain ◽  
Joerg Buechner
Keyword(s):  
Solar Wind ◽  
Free Energy ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Energy Sources ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Current Sheets ◽  
Adiabatic Cooling ◽  
Collisionless Dissipation

<p>Spacecraft observations show the radial dependence of the solar wind temperature to be slower than what is expected from the adiabatic cooling of the solar wind expanding radially outwards from the sun. The most viable process considered to explain the observed slower-than-adiabatic cooling is the heating of the solar wind plasma by dissipation of the turbulent fluctuations. In solar wind which is  a collisionless plasma in turbulent state, macroscopic energy is cascaded down to kinetic scales where kinetic plasma processes can finally dissipate the energy into heat. The kinetic scale plasma processes responsible  for the dissipation of energy are, however, not well understood. A number of observational and simulation studies have shown that the heating is concentrated in and around current sheets self-consistently formed at kinetic scales. The current sheets contain free energy sources for the growth of plasma instabilities which can serve as the mechanism of the collisionless dissipation. A detailed information on the free energy sources contained in these current sheets of plasma turbulence is lacking but essential to understand the role of  plasma instabilities in collisionless dissipation.</p><p>We carry out 2-D hybrid simulations of kinetic plasma turbulence to study in detail free energy sources available in the current sheets formed in the turbulence. We focus on three free energy sources, namely, plasma density gradient, velocity gradients for both ions and electrons and ion temperature anisotropy. Our simulations show formation of current sheets in which electric current parallel to the externally applied magnetic field flows in a thickness of the order of an ion inertial length. Inside a current sheet, electron flow velocity dominates ion flow velocity in the parallel direction resulting in a larger cross-gradient of the former. The perpendicular electron velocity inside a current sheet also has variations sharper than the corresponding ion velocity. Cross gradients in plasma density are weak (under 10 % variation inside current sheets). Ion temperature is anisotropic in current sheets. Thus the current in the sheets is primarily due to electron shear flow. A theoretical model to explain the difference between electron and ion velocities in current sheets is developed. Spacecraft observations of electron shear flow in space plasma turbulence will be pointed out.   </p><p>These results suggest that the current sheets formed in kinetic plasma turbulence are close to the force free equilibrium rather than the often assumed Harris equilibrium.  This demands investigations of the linear stability properties and nonlinear evolution of force free current sheets with temperature anisotropy. Such studies can provide effective dissipation coefficients to be included in macroscopic model of the solar wind evolution.   </p>

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