Instabilities in the solar wind

1980 ◽  
Vol 297 (1433) ◽  
pp. 555-563 ◽  
Keyword(s):  
Solar Wind ◽  
Plasma Physics ◽  
Linear Theory ◽  
Recent Progress ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Physical Processes ◽  
Nonlinear Plasma ◽  
Present Understanding

We review recent progress in the possible role of micro turbulence in the solar wind. The solar wind is expected to excite plasma microinstabilities owing to its transition from a collision-dominated to a collisionless plasma, with potentially drastic consequences for thermal transport and other physical processes. We discuss both the extensive linear theory of this subject and also our present understanding of nonlinear plasma turbulence. The solar wind is an excellent laboratory for studying many aspects of solar and plasma physics, and may soon provide some answers to several fundamental questions.

scholarly journals Modelling the solar wind interaction with Mercury by a quasi-neutral hybrid model

2003 ◽  
Vol 21 (11) ◽  
pp. 2133-2145 ◽  
Author(s):  
E. Kallio ◽  
P. Janhunen
Keyword(s):  
Solar Wind ◽  
Plasma Physics ◽  
Hybrid Model ◽  
Space Plasma ◽  
Physical Processes ◽  
Space Plasma Physics ◽  
Solar Wind Interaction ◽  
Plasma Parameters ◽  
Advantages And Disadvantages ◽  
Self Consistent

Abstract. Quasi-neutral hybrid model is a self-consistent modelling approach that includes positively charged particles and an electron fluid. The approach has received an increasing interest in space plasma physics research because it makes it possible to study several plasma physical processes that are difficult or impossible to model by self-consistent fluid models, such as the effects associated with the ions’ finite gyroradius, the velocity difference between different ion species, or the non-Maxwellian velocity distribution function. By now quasi-neutral hybrid models have been used to study the solar wind interaction with the non-magnetised Solar System bodies of Mars, Venus, Titan and comets. Localized, two-dimensional hybrid model runs have also been made to study terrestrial dayside magnetosheath. However, the Hermean plasma environment has not yet been analysed by a global quasi-neutral hybrid model. In this paper we present a new quasi-neutral hybrid model developed to study various processes associated with the Mercury-solar wind interaction. Emphasis is placed on addressing advantages and disadvantages of the approach to study different plasma physical processes near the planet. The basic assumptions of the approach and the algorithms used in the new model are thoroughly presented. Finally, some of the first three-dimensional hybrid model runs made for Mercury are presented. The resulting macroscopic plasma parameters and the morphology of the magnetic field demonstrate the applicability of the new approach to study the Mercury-solar wind interaction globally. In addition, the real advantage of the kinetic hybrid model approach is to study the property of individual ions, and the study clearly demonstrates the large potential of the approach to address these more detailed issues by a quasi-neutral hybrid model in the future.Key words. Magnetospheric physics (planetary magnetospheres; solar wind-magnetosphere interactions) – Space plasma physics (numerical simulation studies)

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>

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.

Fractal structures in nonlinear plasma physics

2011 ◽  
Vol 369 (1935) ◽  
pp. 371-395 ◽  
Author(s):  
R. L. Viana ◽  
E. C. Da Silva ◽  
T. Kroetz ◽  
I. L. Caldas ◽  
M. Roberto ◽  
...  
Keyword(s):  
Dynamical Systems ◽  
Plasma Physics ◽  
Discrete Dynamical Systems ◽  
Plasma Edge ◽  
Fractal Structures ◽  
Nonlinear Plasma ◽  
Dissipative Dynamical Systems ◽  
Area Preserving ◽  
The Magnetic Field

Fractal structures appear in many situations related to the dynamics of conservative as well as dissipative dynamical systems, being a manifestation of chaotic behaviour. In open area-preserving discrete dynamical systems we can find fractal structures in the form of fractal boundaries, associated to escape basins, and even possessing the more general property of Wada. Such systems appear in certain applications in plasma physics, like the magnetic field line behaviour in tokamaks with ergodic limiters. The main purpose of this paper is to show how such fractal structures have observable consequences in terms of the transport properties in the plasma edge of tokamaks, some of which have been experimentally verified. We emphasize the role of the fractal structures in the understanding of mesoscale phenomena in plasmas, such as electromagnetic turbulence.

scholarly journals The Role of Empirical Space-Weather Models (in a World of Physics-Based Numerical Simulations)

2017 ◽  
Vol 13 (S335) ◽  
pp. 254-257 ◽  
Author(s):  
Mathew J. Owens ◽  
Pete Riley ◽  
Tim Horbury
Keyword(s):  
Solar Wind ◽  
Numerical Model ◽  
Space Weather ◽  
Empirical Models ◽  
Physical Processes ◽  
Validation And Verification ◽  
Solar Observations ◽  
Magnetohydrodynamic Models

AbstractAdvanced forecasting of space weather requires prediction of near-Earth solar-wind conditions on the basis of remote solar observations. This is typically achieved using numerical magnetohydrodynamic models initiated by photospheric magnetic field observations. The accuracy of such forecasts is being continually improved through better numerics, better determination of the boundary conditions and better representation of the underlying physical processes. Thus it is not unreasonable to conclude that simple, empirical solar-wind forecasts have been rendered obsolete. However, empirical models arguably have more to contribute now than ever before. In addition to providing quick, cheap, independent forecasts, simple empirical models aid in numerical model validation and verification, and add value to numerical model forecasts through parameterization, uncertainty estimation and ‘downscaling’ of sub-grid processes.

Structure of current sheets formed in collisionless plasma turbulence

2021 ◽  
Author(s):  
Neeraj Jain ◽  
Joerg Buechner ◽  
Patricio Munoz ◽  
Lev M. Zelenyi
Keyword(s):  
Solar Wind ◽  
Free Energy ◽  
Collisionless Plasma ◽  
Solar Wind Plasma ◽  
Plasma Turbulence ◽  
Equilibrium Structure ◽  
Energy Sources ◽  
Spatial Gradient ◽  
Current Sheets ◽  
Hybrid Simulations

<p>Plasma turbulence is ubiquitous in space and astrophysical environments and believed to play important role in a variety of space and astrophysical phenomena ranging from the entry of  energetic particles in Earth's magnetic environment and non-adiabatic heating of the solar wind plasma to star formation in inter stellar medium. Space and astrophysical plasmas are usually magnetized and collisionless. An unsolved problem in turbulent collisionless plasmas, e.g., the solar wind, is the mechanism of dissipation of macroscopic energy into heat without collisional dissipation. A number of observational and simulation studies show that kinetic sale current sheets formed self-consistently in collisionless plasma turbulence are the sites of the dissipation. Mechanisms of dissipation in current sheets are, however,  not well understood. Free energy sources in and equilibrium structure of current sheets are important factors in the determination of the dissipation mechanism. Recent PIC hybrid simulations (with mass-less electrons) of collisionless plasma turbulence show that current sheets thin down to below ion inertial length with current carried mainly by electrons. This can lead  to embedded current sheet structure which was recently studied analytically.  We carry out 2-D PIC-hybrid simulations (with finite-mass electrons) using a recently developed code CHIEF to study the free energy sources and structure of current sheets formed in turbulence. In this paper, we focus on  the spatial gradient driven free energy sources and embedded structure of current sheets.  The results are compared to the results obtained from hybrid simulations with mass-less electrons. </p>

Identifying and Quantifying the Role of Magnetic Reconnection in Space Plasma Turbulence

2020 ◽  
Author(s):  
Jeffersson Andres Agudelo Rueda ◽  
Daniel Verscharen ◽  
Robert Wicks ◽  
Christopher Owen ◽  
Georgios Nicolaou ◽  
...  
Keyword(s):  
Solar Wind ◽  
Magnetic Reconnection ◽  
Space Plasma ◽  
Plasma Turbulence ◽  
Close Link ◽  
Particle In Cell ◽  
Open Questions ◽  
Strong Current ◽  
Characteristic Features

<p>One of the outstanding open questions in space plasma physics is the heating problem in the solar corona and the solar wind. In-situ measurements, as well as MHD and kinetic simulations, suggest a relation between the turbulent nature of plasma and the onset of magnetic reconnection as a channel of energy dissipation, particle acceleration and a heating mechanism. It has also been proven that non-linear interactions between counter propagating Alfvén waves drives plasma towards a turbulent state. On the other hand, the interactions between particles and waves becomes stronger at scales near the ion(electron) gyroradious ρi (ρe ), and so turbulence can enhance conditions for reconnection and increase the number of reconnection sites. Therefore, there is a close link between turbulence and reconnection. We use fully kinetic particle in cell (PIC) simulations, able to resolve the kinetic phenomena, to study the onset of reconnection in a 3D simulation box with parameters similar to the solar wind under Alfvénic turbulence. We identify in our simulations characteristic features of reconnection sites as steep gradients of the magnetic field strength alongside with the formation of strong current sheets and inflow-outflow patterns of plasma particles near the diffusion regions. These results will be used to quantify the role reconnection in plasma turbulence.</p>

scholarly journals Driving and Dissipation of Solar-Wind Turbulence: What is the Evidence?

2021 ◽  
Vol 7 ◽  
Author(s):  
Charles W. Smith ◽  
Bernard J. Vasquez
Keyword(s):  
Solar Wind ◽  
Plasma Physics ◽  
Thermal Plasma ◽  
Collisionless Plasma ◽  
Three Dimensional ◽  
Density Fluctuations ◽  
Plasma Dynamics ◽  
Solar Wind Turbulence ◽  
Close Proximity ◽  
Wind Turbulence

Fifty years of solar wind observations have provided extensive data that drives an evolving view of the fundamental nature and dynamics of the magnetic, velocity, and density fluctuations that are ubiquitous throughout the heliosphere. Despite the ongoing examination of ever improving data, fundamental questions remain unanswered because there are very few multi-point measurements from a sufficient number of spacecraft in close proximity to fully resolve the three-dimensional dynamics that are at the heart of the problem. Simulations provide new insights and new questions, but most simulations sacrifice one aspect of plasma physics in order to address another. Computers and computational methods remain insufficient to simulate fully compressive, fully nonlinear, collisionless plasma dynamics with sufficient spatial range and dimension to be considered a complete description of solar wind turbulence. For these reasons, there remain multiple divergent opinions as to the underlying dynamics of solar wind turbulence, dissipation, and the observed heating of the thermal plasma. We review observations of solar wind turbulence in so far as they contribute to an understanding of solar wind heating through the existence of energy reservoirs, the dynamics that move energy from the reservoirs to the dissipation scales, and the conversion into heat of energy associated with coherent fluctuations.

scholarly journals Recent progress in astrophysical plasma turbulence from solar wind observations

2016 ◽  
Vol 82 (6) ◽  
Author(s):  
C. H. K. Chen
Keyword(s):  
Solar Wind ◽  
Recent Progress ◽  
Three Dimensional ◽  
Turbulent Energy ◽  
Plasma Turbulence ◽  
Residual Energy ◽  
Dimensional Structure ◽  
Small Scale ◽  
Astrophysical Plasma ◽  
Cascade Models

This paper summarises some of the recent progress that has been made in understanding astrophysical plasma turbulence in the solar wind, fromin situspacecraft observations. At large scales, where the turbulence is predominantly Alfvénic, measurements of critical balance, residual energy and three-dimensional structure are discussed, along with comparison to recent models of strong Alfvénic turbulence. At these scales, a few per cent of the energy is also in compressive fluctuations, and their nature, anisotropy and relation to the Alfvénic component is described. In the small-scale kinetic range, below the ion gyroscale, the turbulence becomes predominantly kinetic Alfvén in nature, and measurements of the spectra, anisotropy and intermittency of this turbulence are discussed with respect to recent cascade models. One of the major remaining questions is how the turbulent energy is dissipated, and some recent work on this question, in addition to future space missions which will help to answer it, are briefly discussed.

scholarly journals Role of Magnetospheric Plasma Physics for Understanding Cosmic Phenomena

1990 ◽  
Vol 115 ◽  
pp. 90-93 ◽  
Author(s):  
Indra Mohan Lal Das
Keyword(s):  
Solar Wind ◽  
Plasma Physics ◽  
Laboratory Experiments ◽  
Magnetospheric Plasma ◽  
Proper Understanding ◽  
In Situ Observations

AbstractCosmic phenomena occur in the remote regions of space where in-situ observations are not possible. For proper understanding of these phenomena laboratory experiments are essential, but the in-situ observations of magnetospheric plasma provides even a better background to test various hypothesis of cosmic interest. This is because the ionospheric-magnetospheric plasma and the solar wind are the only cosmic plasmas accessible to extensive in-situ observations and experiments.

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