V. D. Kuznetsov, A. I. Osin
The research is aimed at the study of the properties of solutions for parallel MHD shock waves in collisionless plasma with heat fluxes, using 8-moment MHD approximation. Restrictions have been established on the upstream shock parameters preserving physical meaning of the downstream plasma parameters.
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Evolutionarity of MHD shock waves in collisionless plasma with heat fluxes
本文在 8 矩近似下研究带热通量无碰撞等离子体中 MHD 激波的演化性，利用平行激波解在无量纲参数平面上确定快、慢激波的演化区域。
The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell (PIC) simulation over MHD time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.
Effective resistivity for magnetohydrodynamic simulation of collisionless magnetic reconnection
本文将含带电粒子动力学的有效电阻率模型应用于无引导场无碰撞磁重联的2.5维MHD与Hall MHD模拟，显著提升重联率并使结构与PIC及混合模拟吻合。
Collisionless tearing instability in relativistic non-thermal pair plasma and its application to MHD turbulence
本文研究相对论性非热正负电子等离子体中幂律分布下的无碰撞撕裂不稳定性，揭示粒子谱硬化和无力极限对增长率的影响，并将其应用于MHD湍流，推导出不稳定涡旋尺寸及临界磁化参数。
When applied to compute the density jump of a shock, the standard magnetohydrodynamic (MHD) formalism assumes, 1) that all the upstream material passes downstream, together with the momentum and energy it carries, and 2) that pressures are isotropic. In a collisionless shock, shock accelerated particles going back and forth around the front can invalid the first assumption. In addition, an external magnetic field can sustain stable pressure anisotropies, invaliding the second assumption. It is therefore unclear whether the density jump of a collisionless shock fulfils the MHD jump or not. Here…
The amplification and maintenance of the observed magnetic fields in the ICM are usually attributed to the turbulent dynamo action. This is generally derived employing a collisional MHD model. However, in the ICM the ion mean free path between collisions is of the order of the dynamical scales, thus requiring a collisionless MHD description. Unlike collisional MHD simulations, our study uses an anisotropic plasma pressure with respect to the direction of the local magnetic field, which brings the plasma within a parameter space where collisionless instabilities should take place. Within the ad…
Density jump as a function of the field for parallel relativistic collisionless shocks
本文将强平行磁场下非相对论无碰撞激波模型扩展至相对论 regime，发现密度跃变显著偏离MHD预测并与PIC模拟吻合。
Density jump for oblique collisionless shocks in pair plasmas: physical solutions
针对成对等离子体斜向无碰撞激波模型的多下游解问题，本文利用磁场倾斜角接近准则和演化性准则筛选物理解，并经PIC模拟验证，实现唯一或无解的下游配置。
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 Re…
Shocks waves are a ubiquitous feature of many astrophysical plasma systems, and an important process for energy dissipation and transfer. The physics of these shock waves are frequently treated/modeled as a collisional, fluid MHD discontinuity, despite the fact that many shocks occur in the collisionless regime. In light of this, using fully kinetic, 3D simulations of non-relativistic, parallel propagating collisionless shocks comprised of electron-positron plasma, we detail the deviation of collisionless shocks form MHD predictions for varying magnetization/Alfvénic Mach numbers, with particu…
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 me…
The properties of collisionless shocks, like the density jump, are usually derived from magnetohydrodynamics (MHD), where isotropic pressures are assumed. Yet, in a collisionless plasma, an external magnetic field can sustain a stable anisotropy. In \cite{BretJPP2018}, we devised a model for the kinetic history of the plasma through the shock front, allowing to self-consistently compute the downstream anisotropy, hence the density jump, in terms of the upstream parameters. This model dealt with the case of a parallel shock, where the magnetic field is normal to the front both in the upstream a…
Comparison of MHD and gyrokinetic simulations of linear instabilities at the q = 1 surface
本文比较了回旋动理学和 MHD 代码对托卡马克核心内部扭曲模和无碰撞撕裂模的模拟，发现通过合理设置参数两者在描述内部扭曲模时可达成一致，但无碰撞撕裂模需超越 MHD 的高级处理。
Shockwaves in plasma are usually dealt with using Magnetohydrodynamics (MHD). Yet, MHD entails the assumption of a short mean free path, which is not fulfilled in a collisionless plasma. Recently, for pair plasmas, we devised a model allowing to account for kinetic effects within an MHD-like formalism. Its relies on an estimate of the anisotropy generated when crossing the front, with a subsequent assessment of the stability of this anisotropy in the downstream. We solved our model for parallel, perpendicular and switch-on shocks. Here we bridge between all these cases by treating the problem …
This paper presents Sweet-Parker type scaling arguments in the context of hyper-resistive Hall magnetohyrdodynamics (MHD). The predicted steady state scalings are consistent with those found by Chacón et al. [PRL 99, 235001 (2007)], though as with that study, no prediction of electron dissipation region \emph{length} is made. Numerical experiments confirm that both cusp-like and modestly more extended geometries are realizable. However, importantly, the length of the electron dissipation region, which is taken as a parameter by several recent studies, is found to depend explicitly on the level…
The scale locality of energy fluxes for magnetohydrodynamics (MHD) is investigated numerically for stationary states of turbulence. Two types of forces are used to drive turbulence, a kinetic force that acts only on the velocity field and a kinetic-inductive forcing mechanism, which acts on the velocity and magnetic fields alike. The analysis is performed in spectral space, which is decomposed into a series of shells following a power law for the boundaries. The triadic transfers occurring among these shells are computed and the fluxes and locality functions are recovered by partial summation …
Statistical analysis of Faraday Rotation Measure (RM) maps of the intracluster medium (ICM) of galaxy clusters provides a unique tool to evaluate some spatial features of the magnetic fields there. Its combination with numerical simulations of magnetohydrodynamic (MHD) turbulence allows the diagnosis of the ICM turbulence. Being the ICM plasma weakly collisional, the thermal velocity distribution of the particles naturally develops anisotropies as a consequence of the large scale motions and the conservation of the magnetic moment of the charged particles. A previous study (Paper I) analyzed t…
The ideal invariants present in the formalism of magnetohydrodynamics (MHD), i.e. global quantities that are conserved in the absence of sources and dissipative effects, play an important role in various theoretical and numerical studies of MHD turbulence. The fluxes of these ideal invariants represent separate channels that transfer the information across different scales in a turbulent system. Once a statistically stationary state of turbulence is reached, the amount of any ideal invariant quantity introduced in the system by a forcing mechanism equals the amount of the same quantity removed…
Within the context of Magnetohydrodynamics (MHD), the properties of a parallel shock do not depend on the field strength, as the field and the fluid are disconnected for such a geometry. However, in the collisionless case, the field can sustain a stable anisotropy in the downstream, triggering a departure from the expected MHD behavior. In a recent work [A. Bret and R. Narayan, J. Plasma Phys. \textbf{84}, 905840604 (2018)], a theoretical model was presented allowing to derive the density ratio of a non-relativistic parallel collisionless shock in an electron/positron plasma, as a function of …
It has recently been proposed (Loureiro & Boldyrev 2017; Mallet et al. 2017) that the inertial interval in magnetohydrodynamic (MHD) turbulence is terminated at small scales not by a Kolmogorov-like dissipation region, but rather by a new sub-inertial interval mediated by tearing instability. However, many astrophysical plasmas are nearly collisionless so that the MHD approximation is not applicable to turbulence at small scales. In this Letter, we propose the extension of the theory of reconnection-mediated turbulence to plasmas which are so weakly collisional that the reconnection occurring …
The first complete estimation of the compressible energy cascade rate $|\varepsilon_\text{C}|$ at magnetohydrodynamic (MHD) and sub-ion scales is obtained in the Earth's magnetosheath using Magnetospheric MultiScale (MMS) spacecraft data and an exact law derived recently for {\it compressible} Hall MHD turbulence. A multi-spacecraft technique is used to compute the velocity and magnetic gradients, and then all the correlation functions involved in the exact relation. It is shown that when the density fluctuations are relatively small, $|\varepsilon_\text{C}|$ identifies well with its incompres…
The properties of collisionless shocks are frequently assessed in the magnetohydrodynamics (MHD) model. Yet, in a collisionless plasma, an ambient magnetic field can sustain a stable anisotropy in the upstream or the downstream, resulting in a departure from the MHD predicted behavior. We present a model allowing to derive the downstream anisotropy, hence the shock density jump, in terms of the upstream quantities. For simplicity, the case of a parallel shock in pair plasma is considered. Contrary to previous works where the upstream was assumed isotropic, here the upstream anisotropy $A=T_\pe…
We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We 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. Our results showed that once magnetic reconnection takes place, a firehose-sense pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with t…
Turbulence Mode Decomposition and Anisotropy in Magnetically Dominated Collisionless Plasmas
研究相对论性湍流在磁主导非碰撞等离子体中的湍流模和各向异性，扩展Cho和Lazarian(2002)方法分解非相对论磁流体动力学湍流为阿尔芬、快和慢模，发现阿尔芬和慢模符合Goldreich和Sridhar(1995)标度，快模则各向同性。
Compressible Turbulence as a Source of Particle Beams and Ion Bernstein Waves in Collisionless Plasmas
通过高分辨率粒子云模拟，研究可压缩湍流如何通过渡越时间阻尼产生超热电子和质子束，并在亚离子尺度激发离子伯恩斯坦波，揭示其在无碰撞等离子体湍流中驱动跨尺度能量传输和动能耗散的核心作用。
The kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations. In the magnetohydrodynamic regime this vortex leads rapidly to broadband turbulence. Significant differences from MHD arise at small scales, where the fluid scale energy dissipates into heat almost exclusively through the magnetic field because the protons are decoupled from the magnetic field. Although cyclotron resonance is absent, the protons heat preferentially in the plane perpendicular to the mean field, as in the corona and solar wind. Effective transport coefficients are calculated.
Estimation of Effective Viscosity to Quantify Collisional Behavior in Collisionless Plasma
本研究针对近无碰撞等离子体耗散形式不明的问题，通过2.5D动力学PIC湍流模拟结合尺度滤波法估算各尺度有效黏度，验证了设定该黏度的MHD和双流体模拟与PIC模拟整体行为高度相似，并探究了有效黏度的尺度依赖性。
In the absence of frequent binary collisions to isotropize the plasma, the fulfillment of the magnetohydrodynamic (MHD) Rankine-Hugoniot jump conditions by collisionless shocks is not trivial. In particular, the presence of an external magnetic field can allow for stable anisotropies, implying some departures from the isotropic MHD jumps. The functional dependence of such anisotropies in terms of the field is yet to be determined. By hypothesizing a kinetic history of the plasma through the shock front, we recently devised a theory of the downstream anisotropy, hence of the density jump, in te…
The linear MHD Kelvin-Helmholtz instability (KHI) in an anisotropic plasma concerning the direction of an external magnetic field is examined in detail. For this purpose, the MHD equations are used to describe the motion of plasma as a fluid, which is derived from 16 moments of Boltzmann-Vlasov kinetic equations for collisionless plasma. In addition, the heat flux along the magnetic field is taken into account. The growing rates of KHI are calculated as functions of the anisotropic plasma properties for a shear flow along the magnetic field at supersonic velocities. On the other hand, the quas…
A conserved thermo-mechanic invariant in extended fluid description of collisionless plasmas
该研究通过扩展16矩流体描述，发现无碰撞各向异性等离子体中存在与热通量耦合的新型守恒热-力学不变量，揭示了其稳态分支的独特性质。
In this paper we describe the mode-to-mode energy transfers and energy fluxes of MHD turbulence. These energy transfers are very useful for understanding the turbulence dynamics, as well as for applications such as dynamo. We illustrate how the energy fluxes provide valuable insights into the mechanism of growth of the large-scale magnetic energy in dynamo.
This work presents an analysis of the ion outflow from magnetic reconnection throughout fully kinetic simulations with typical laboratory plasmas values. A symmetric initial configuration for the density and magnetic field is considered across the current sheet. After analyzing the behavior of a set of nine simulations with a reduced mass ratio and with a permuted value of three initial electron temperature and magnetic field intensity, the best ion acceleration scenario is further studied with a realistic mass ratio in terms of the ion dynamics and energy budget. Interestingly, a series of sh…
Density jump as a function of magnetic field strength for perpendicular collisionless shocks with anisotropic upstream pressure
本文通过假设垂直流动方向温度在激波波阵面守恒来封闭 MHD 方程组，研究了上游压力各向异性垂直无碰撞激波的密度跳跃随磁场强度的变化，揭示了 MHD 无法描述的丰富行为，并与平行激波情形进行了比较。
The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser p…
Biermann-battery driven magnetized collisionless shock precursors in laser produced plasmas
本研究在OMEGA装置上通过激光产生磁化等离子体与未磁化氢等离子体碰撞，首次完整观测到Biermann电池驱动的磁化无碰撞激波前驱，结合多类模拟验证了相关过程与电子加速结果。
On hydromagnetic wave interactions in collisionless, high-$β$ plasmas
该研究结合解析理论与CGL-MHD数值模拟，揭示高β无碰撞等离子体中Alfvén波与声波、其他Alfvén波的相互作用规律，修正了相关天体物理湍流理论的适用前提。
Self-organization in collisionless, high-$β$ turbulence
本文研究了无碰撞、高$β$湍流中由压力各向异性和Larmor尺度不稳定性引发的“磁不可变性”自组织效应，发现该效应能抑制磁场涨落与耗散，使Alfvénic级联在粘性尺度下形成近守恒的类MHD惯性区，并通过Landau-fluid模拟证实了微不稳定性仅占据极小体积。
We investigate the locality or nonlocality of the energy transfer and of the spectral interactions involved in the cascade for decaying magnetohydrodynamic (MHD) flows in the presence of a uniform magnetic field $\bf B$ at various intensities. The results are based on a detailed analysis of three-dimensional numerical flows at moderate Reynold numbers. The energy transfer functions, as well as the global and partial fluxes, are examined by means of different geometrical wavenumber shells. On the one hand, the transfer functions of the two conserved Elsässer energies $E^+$ and $E^-$ are found l…
We present a linear stability analysis of the perturbation modes in anisotropic MHD flows with velocity shear and strong magnetic field. Collisionless or weakly collisional plasma is described within the 16-momentum MHD fluid closure model, that takes into account not only the effect of pressure anisotropy, but also the effect of anisotropic heat fluxes. In this model the low frequency acoustic wave is revealed into a standard acoustic mode and higher frequency fast thermo-acoustic and lower frequency slow thermo-acoustic waves. It is shown that thermo-acoustic waves become unstable and grow e…
We study the role of the Hall current and electron inertia in collisionless magnetic reconnection within the framework of full two-fluid MHD. At spatial scales smaller than the electron inertial length, a topological change of magnetic field lines exclusively due to electron inertia becomes possible. Assuming stationary conditions, we derive a theoretical scaling for the reconnection rate, which is simply proportional to the Hall parameter. Using a pseudo-spectral code with no dissipative effects, our numerical results confirm this theoretical scaling. In particular, for a sequence of differen…
Small-amplitude Compressible Magnetohydrodynamic Turbulence Modulated by Collisionless Damping in Earth's Magnetosheath: Observation Matches Theory
本研究利用Cluster卫星数据首次观测证实无碰撞阻尼调制地球磁鞘中小振幅可压缩MHD湍流，分解三种模式并揭示其对各向异性的影响，观测与理论相符。
In weakly collisional astrophysical plasmas, such as the intracluster medium of galaxy clusters, the amplification of cosmic magnetic fields by chaotic fluid motions is hampered by the adiabatic production of magnetic-field-aligned pressure anisotropy. This anisotropy drives a viscous stress parallel to the field that inhibits the plasma's ability to stretch magnetic-field lines. I demonstrate through the use of kinetic simulations that in high-$β$ plasmas, kinetic ion-Larmor scale instabilities sever the adiabatic link between the thermal and magnetic pressures, reducing this viscous stress a…
Planar Collisionless Shock Simulations with Semi-Implicit Particle-in-Cell Model FLEKS
本研究验证了半隐式PIC代码FLEKS用于日球层激波模拟的可行性，明确二维空间模拟的必要性及参数影响，为相关大规模等离子体模拟提供指导。
Identification and characterization of current sheets in collisionless plasma turbulence
本研究扩展了Zhdankin等人（2013）的电流片分析算法，用于识别离子动力学尺度湍流无碰撞等离子体中的电流片，推导了其核心特性，并发现无电子惯性时电流片会变薄至数值耗散限制的尺度。
Magnetic reconnection in strongly magnetized (low-beta), weakly collisional plasmas is investigated using a novel fluid-kinetic model [Zocco & Schekochihin, Phys. Plasmas 18, 102309 (2011)] which retains non-isothermal electron kinetics. It is shown that electron heating via Landau damping (linear phase mixing) is the dominant dissipation mechanism. In time, electron heating occurs after the peak of the reconnection rate; in space, it is concentrated along the separatrices of the magnetic island. For sufficiently large systems, the peak reconnection rate is $cE_{max}\approx 0.2v_AB_{y,0}$, whe…
Previous studies of phase mixing of ion cyclotron (IC), Alfvénic, 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 2.5D, relativistic, fully electromagnetic PIC (Particle-In-Cell) code and an analytic MHD (Magnetohydrodynamic) formulation, to establish the following points: (i) Using the generalised Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a …
Magnetized turbulence is ubiquitous in many astrophysical and terrestrial systems but no complete, uncontested theory even in the simplest form, magnetohydrodynamics (MHD), exists. Many theories and phenomenologies focus on the joint (kinetic and magnetic) energy fluxes and spectra. We highlight the importance of treating kinetic and magnetic energies separately to shed light on MHD turbulence dynamics. We conduct an implicit large eddy simulation of subsonic, super-Alfvénic MHD turbulence and analyze the scale-wise energy transfer over time. Our key finding is that the kinetic energy spectrum…
We develop a general theory of buoyancy instabilities in the electron-ion plasma with the electron heat flux based not upon MHD equations, but using a multicomponent plasma approach in which the momentum equation is solved for each species. We investigate the geometry in which the background magnetic field is perpendicular to the gravity and stratification. General expressions for the perturbed velocities are given without any simplifications. Collisions between electrons and ions are taken into account in the momentum equations in a general form, permitting us to consider both weakly and stro…
In collisional fluids, a number of key processes rely on the frequency of binary collisions. Collisions seem necessary to generate a shock wave when two fluids collide fast enough, to fulfill the Rankine-Hugoniot relations, to establish an equation of state or a Maxwellian distribution. Yet, these seemingly collisional features are routinely either observed or assumed, in relation with collision\emph{less} astrophysical plasmas. This article will review our current answers to the following questions: How do colliding collisionless plasmas end-up generating a shock as if they were fluids? To wh…
Results from a numerical study of fluctuation dynamo in a collisionless, weakly magnetized plasma are presented. The key difference between this dynamo and its magnetohydrodynamic (MHD) counterpart is the adiabatic production of magnetic-field-aligned pressure anisotropy by the amplification of a weak seed field. This in turn drives kinetic instabilities on the ion-Larmor scale---namely, firehose and mirror---which sever the adiabatic link between the thermal and magnetic pressures, thereby allowing the dynamo to proceed. After an initial phase of rapid growth driven by these instabilities, th…
Three-dimensional numerical simulations of decaying turbulence in a magnetized plasma are performed using a so-called FLR-Landau fluid model which incorporates linear Landau damping and finite Larmor radius (FLR) corrections. It is shown that compared to simulations of compressible Hall-MHD, linear Landau damping is responsible for significant damping of magnetosonic waves, which is consistent with the linear kinetic theory. Compressibility of the fluid and parallel energy cascade along the ambient magnetic field are also significantly inhibited when the beta parameter is not too small. In con…
We derive the conductivity tensor for axisymmetric perturbations of a hot, collisionless, and charge-neutral plasma in the shearing sheet approximation. Our results generalize the well-known linear Vlasov theory for uniform plasmas to differentially rotating plasmas and can be used for wide range of kinetic stability calculations. We apply these results to the linear theory of the magneto-rotational instability (MRI) in collisionless plasmas. We show analytically and numerically how the general kinetic theory results derived here reduce in appropriate limits to previous results in the literatu…
Critical magnetic Reynolds number of the turbulent dynamo in collisionless plasmas
本文利用三维混合动力学粒子模拟研究无碰撞等离子体中的湍流发电机机制，确定了未磁化与磁化两种区域下的临界磁雷诺数分别约为107和124，并揭示了磁能增长率不依赖种子磁场强度。
A simplified model of particle transport at a quasiparallel one-dimensional collisionless shock is suggested. In this model the MHD-turbulence behind the shock is dominated by a circularly polarized, large amplitude Alfvén wave originated upstream from the turbulence excited by particles leaking from the downstream medium. It is argued that such a wave having significantly increased its magnetic field during the transmission through the shock interface can effectively trap thermal ions, regulating their leakage upstream. Together with a background turbulence this wave also plays a fundamental …
In the previous works harmonic, phase-mixed, Alfven wave dynamics was considered both in the kinetic and magnetohydrodynamic regimes. Up today only magnetohydrodynamic, phase-mixed, Gaussian Alfven pulses were investigated. In the present work we extend this into kinetic regime. Here phase-mixed, Gaussian Alfven pulses are studied, which are more appropriate for solar flares, than harmonic waves, as the flares are impulsive in nature. Collisionless, phase-mixed, dispersive, Gaussian Alfven pulse in transversely inhomogeneous plasma is investigated by particle-in-cell (PIC) simulations and by a…
Microphysically modified magnetosonic modes in collisionless, high-$β$ plasmas
本文通过混合动力学模拟和解析理论，研究了高$β$无碰撞等离子体中NP模式和快磁声波的非线性行为，发现它们会激发镜像和火管等微观不稳定性，进而通过粒子散射影响波衰减和激波形成，为低碰撞等离子体湍流理论奠定基础。
A prediction of the steady-state reconnection electric field in asymmetric reconnection is obtained by maximizing the reconnection rate as a function of the opening angle made by the upstream magnetic field on the weak magnetic field (magnetosheath) side. The prediction is within a factor of two of the widely examined asymmetric reconnection model [Cassak and Shay, Phys. Plasmas 14, 102114, 2007] in the collisionless limit, and they scale the same over a wide parameter regime. The previous model had the effective aspect ratio of the diffusion region as a free parameter, which simulations and o…
Wave properties and instabilities in a magnetized, anisotropic, collisionless, rarefied hot plasma in fluid approximation are studied, using the 16-moments set of the transport equations obtained from the Vlasov equations. These equations differ from the CGL-MHD fluid model (single fluid equations by Chew, Goldberger, and Low, 1956) by including two anisotropic heat flux evolution equations, where the fluxes invalidate the double polytropic CGL laws. We derived the general dispersion relation for linear compressible wave modes. Besides the classic incompressible fire hose modes there appear fo…
According to magnetohydrodynamics (MHD), the encounter of two collisional magnetized plasmas at high velocity gives rise to shock waves. Investigations conducted so far have found that the same conclusion still holds in the case of collisionless plasmas. For the case of a flow-aligned field, MHD stipulates that the field and the fluid are disconnected, so that the shock produced is independent of the field. We present a violation of this MHD prediction when considering the encounter of two cold pair plasmas along a flow-aligned magnetic field. As the guiding magnetic field grows, isotropizatio…
In the past years we have experienced an increasing interest in understanding of the physical properties of collisionless plasmas, mostly because of the large number of astrophysical environments, e.g. the intracluster medium (ICM), containing magnetic fields which are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions a new class of kinetic instabilities arises, such as firehose and mirror ones, which were extensively studied in the literatur…
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