On Kinetic Instabilities Driven By Ion Temperature Anisotropy and Differential Flow in the Solar Wind

2019 ◽  
Vol 884 (1) ◽  
pp. 44 ◽  
Author(s):  
Heyu Sun ◽  
Jinsong Zhao ◽  
Huasheng Xie ◽  
Dejin Wu
Keyword(s):  
Solar Wind ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Differential Flow ◽  
Kinetic Instabilities

scholarly journals LIMITS ON ALPHA PARTICLE TEMPERATURE ANISOTROPY AND DIFFERENTIAL FLOW FROM KINETIC INSTABILITIES: SOLAR WIND OBSERVATIONS

2013 ◽  
Vol 777 (1) ◽  
pp. L3 ◽  
Author(s):  
Sofiane Bourouaine ◽  
Daniel Verscharen ◽  
Benjamin D. G. Chandran ◽  
Bennett A. Maruca ◽  
Justin C. Kasper
Keyword(s):  
Solar Wind ◽  
Alpha Particle ◽  
Particle Temperature ◽  
Temperature Anisotropy ◽  
Differential Flow ◽  
Kinetic Instabilities

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 Solar wind temperature anisotropy constraints from streaming instabilities

2018 ◽  
Vol 613 ◽  
pp. A23 ◽  
Author(s):  
S. Vafin ◽  
M. Lazar ◽  
H. Fichtner ◽  
R. Schlickeiser ◽  
M. Drillisch
Keyword(s):  
Solar Wind ◽  
Large Deviations ◽  
The Other ◽  
Space Plasmas ◽  
Plasma Stability ◽  
Particle Collisions ◽  
Temperature Anisotropy ◽  
Large Interval ◽  
Low Rate ◽  
Kinetic Instabilities

Due to the relatively low rate of particle-particle collisions in the solar wind, kinetic instabilities (e.g., the mirror and firehose) play an important role in regulating large deviations from temperature isotropy. These instabilities operate in the high β∥ > 1 plasmas, and cannot explain the other limits of the temperature anisotropy reported by observations in the low beta β∥ < 1 regimes. However, the instability conditions are drastically modified in the presence of streaming (or counterstreaming) components, which are ubiquitous in space plasmas. These effects have been analyzed for the solar wind conditions in a large interval of heliospheric distances, 0.3–2.5 AU. It was found that proton counter-streams are much more crucial for plasma stability than electron ones. Moreover, new instability thresholds can potentially explain all observed bounds on the temperature anisotropy, and also the level of differential streaming in the solar wind.

scholarly journals Effects of Alpha–Proton Differential Flow on Proton Temperature Anisotropy Instabilities in the Solar Wind: Wind Observations

2019 ◽  
Vol 884 (1) ◽  
pp. 60 ◽  
Author(s):  
G. Q. Zhao ◽  
H. Li ◽  
H. Q. Feng ◽  
D. J. Wu ◽  
H. B. Li ◽  
...  
Keyword(s):  
Solar Wind ◽  
Temperature Anisotropy ◽  
Proton Temperature ◽  
Differential Flow

scholarly journals Hybrid models of solar wind plasma heating

2011 ◽  
Vol 29 (6) ◽  
pp. 1071-1079 ◽  
Author(s):  
L. Ofman ◽  
A.-F. Viñas ◽  
P. S. Moya
Keyword(s):  
Solar Wind ◽  
Heavy Ions ◽  
Plasma Heating ◽  
Wave Spectrum ◽  
Solar Wind Plasma ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Streaming Instability ◽  
Turbulent Spectrum

Abstract. Remote sensing and in-situ observations show that solar wind ions are often hotter than electrons, and the heavy ions flow faster than the protons by up to an Alfvén speed. Turbulent spectrum of Alfvénic fluctuations and shocks were detected in solar wind plasma. Cross-field inhomogeneities in the corona were observed to extend to several tens of solar radii from the Sun. The acceleration and heating of solar wind plasma is studied via 1-D and 2-D hybrid simulations. The models describe the kinetics of protons and heavy ions, and electrons are treated as neutralizing fluid.The expansion of the solar wind is considered in 1-D hybrid model. A spectrum of Alfvénic fluctuations is injected at the computational boundary, produced by differential streaming instability, or initial ion temperature anisotropy, and the parametric dependence of the perpendicular heating of H+-He++ solar wind plasma is studied. It is found that He++ ions are heated efficiently by the Alfvénic wave spectrum below the proton gyroperiod.

scholarly journals Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

2021 ◽  
Vol 9 ◽  
Author(s):  
Pablo S. Moya ◽  
Roberto E. Navarro
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Large Scale ◽  
Wave Spectrum ◽  
Collisionless Plasma ◽  
Space Plasmas ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Background Spectrum ◽  
Background Magnetic Field

Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by non-linear MHD wave-wave interactions following a −5/3 or −2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law k−α shape given by a spectral index α &gt; 5/3. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in an initially turbulent collisionless plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.

scholarly journals Apparent temperature anisotropies due to wave activity in the solar wind

2011 ◽  
Vol 29 (5) ◽  
pp. 909-917 ◽  
Author(s):  
D. Verscharen ◽  
E. Marsch
Keyword(s):  
Solar Wind ◽  
Distribution Function ◽  
Collisionless Plasma ◽  
Velocity Distribution Function ◽  
Wave Activity ◽  
Apparent Temperature ◽  
Time Averaging ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Underlying Distribution

Abstract. The fast solar wind is a collisionless plasma permeated by plasma waves on many different scales. A plasma wave represents the natural interplay between the periodic changes of the electromagnetic field and the associated coherent motions of the plasma particles. In this paper, a model velocity distribution function is derived for a plasma in a single, coherent, large-amplitude wave. This model allows one to study the kinetic effects of wave motions on particle distributions. They are by in-situ spacecraft measured by counting, over a certain sampling time, the particles coming from various directions and having different energies. We compare our results with the measurements by the Helios spacecraft, and thus find that by assuming high wave activity we are able to explain key observed features of the measured distributions within the framework of our model. We also address the recent discussions on nonresonant wave–particle interactions and apparent heating. The applied time-averaging procedure leads to an apparent ion temperature anisotropy which is connected but not identical to the intrinsic temperature of the underlying distribution function.

scholarly journals Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

2021 ◽  
Author(s):  
Pablo S Moya ◽  
Roberto E Navarro
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Large Scale ◽  
Wave Spectrum ◽  
Space Plasmas ◽  
Linear Wave ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Background Spectrum ◽  
Background Magnetic Field

&lt;p&gt;Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by MHD non-linear wave-wave interactions following a -5/3 or -3/2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law &lt;em&gt;k&lt;sup&gt;- &amp;#945;&lt;/sup&gt;&lt;/em&gt; shape given by a spectral index &lt;em&gt;&amp;#945; &lt;/em&gt;&gt; 5/3. The location of the break and the particular value of &lt;em&gt;&amp;#945;, &lt;/em&gt;depend on plasma conditions, and different space environments can exhibit different spectral indices. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in a solar wind-like plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.&lt;/p&gt;

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