Measurement of large parallel and perpendicular electric fields on electron spatial scales in the terrestrial bow shock

Large parallel (相似文献   

On nonlinear dynamics of a sheet electron beam

The nonstationary model is considered allowed to describe the sheet electron beam dynamics with nonuniform current density profile in collisionless approximation. The kinetic distribution function is used dependent on the particle motion integral, so the distribution function automatically satisfies to Vlasov equation. The results of numerical and analytical calculations are discussed.     

Self-consistent generation of superthermal electrons by beam-plasma interaction

It has been known since the early days of plasma physics research that superthermal electrons are generated during beam-plasma laboratory experiments. Superthermal electrons (the kappa distribution) are also ubiquitously observed in space. To explain such a feature, various particle acceleration mechanisms have been proposed. However, self-consistent acceleration of electrons in the context of plasma kinetic theory has not been demonstrated to date. This Letter reports such a demonstration. It is shown that the collisionality, defined via the "plasma parameter" g=1/n(lambda(D)(3), plays a pivotal role. It is found that a small but moderately finite value of is necessary for the superthermal tail to be generated, implying that purely collisionless (g=0) Vlasov theory cannot produce a superthermal population.     

Influence of the solar-wind magnetic field on the magnetosheath turbulence behind the bow shock

The experiment Sura–-WIND (1996–1997) on radio-raying of geodisturbed solar-wind region is interpreted in terms of modern knowledge of an interaction between the magnetized solar wind and the Earth's magnetosphere. Characteristics of the scattered signal at 9 MHz, determined by a plasma turbulence level with scales about 100 km, are statistically related to in situ measurements of solar wind parameters such as plasma density and the orientation and magnitude of the interplanetary magnetic field (IMF) onboard WIND spacecraft. The dependence of the scintillation index of the detected scattered signal, characterising the average turbulence level of the Earth's magnetosheath behind the bow shock, on the IMF orientation and magnitude is revealed. To verify the relation obtained, modern nonlinear correlation techniques based on the theory of artificial neural networks (ANN) are applied. The results obtained using a three-layer ANN with error backpropagation confirm an essential IMF influence on the plasma turbulence in the magnetosheath.     

Magnetosheath plasma turbulence and its spatiotemporal evolution as observed by the cluster spacecraft

We study the plasma turbulence, at scales larger than the ion inertial length scale, downstream of a quasiparallel bow shock using Cluster multispacecraft measurements. We show that turbulence is intermittent and well described by the extended structure function model, which takes into account the spatial inhomogeneity of the cascade rate. For the first time we use multispacecraft observations to characterize the evolution of magnetosheath turbulence, particularly its intermittency, as a function of the distance from the bow shock. The intermittency significantly changes over the distance of the order of 100 ion inertial lengths, being increasingly stronger and anisotropic away from the bow shock.     

A generalization of the van Kampen-Case treatment of the Vlasov equation

In the inhomogeneous collisionless system the collective modes are constructed in the physical representation using the method of subdynamics. They correspond to the explicit solutions of the non-linear Vlasov equation and they appear as the generalization of the van Kampen-Case treatment. The absence of entropy production is shown.     

Nonlinear Landau Damping in Spherically Symmetric Vlasov Poisson Systems

The Vlasov Poisson system is a partial differential equation widely used to describe collisionless plasma. It is formulated in a six-dimensional phase space, this prohibits a numerical solution on a complete phase space grid. In some applications, however, spherical symmetry is given, which introduces singularities into the Vlasov Poisson equation. We focus on such problems and propose a stable algorithm using accommodating boundaries. At first, the method is tested in the linear regime, where analytical solutions are available. Thereafter it is applied to large disturbances from equilibrium.     

Analysis of the evolution of perturbations in a magnetized collisionless plasma with an integral-equation technique

Summary A technique recently proposed to study the classical problem of the evolution of small perturbations in a collisionless unmagnetized plasma is extended to a magnetized plasma. A time-convolutive integral equation for the plasma density is obtained from the Vlasov equation for a homogeneous plasma in a uniform, stationary magnetic field. The equation can be solved by means of simple numerical algorithms and, in some cases, analytical solutions can be obtained. The procedure proves to be analytically simpler than the classical one and is more convenient from a numerical point of view. Techniques of solution are presented and analytical and numerical results for electrostatic perturbations are discussed.     

温度各向异性等离子体中的电磁波不稳定性产生的反常电阻率

本文考察了由于温度各向异性分布产生的电磁波不稳定性所联系的反常电阻率问题,讨论了这一现象与地球磁场磁尾区中“磁再联”现象的关系。     

Overturning of nonlinear Alfvén waves in a collisionless plasma

An analysis is made of the overturning of nonlinear Alfvén waves in a collisionless plasma. It is shown that overturning is followed by the appearance of a region which broadens with time and consists of two collisionless shock waves which can be joined at the point s²=1. If only one Riemann invariant changes in the region of the collisionless shock waves, the waves are simple. The structures of the collisionless shock waves are constructed for different initial conditions of the nonlinear wave. The Whitham averaging method is used for this purpose. Conditions are obtained which are similar to the Rankine-Hugoniot adiabats for passage through the collisionless shock waves. The effect of overturning one of the collisionless shock waves, involving the zeroing of the density at the soliton peak on its trailing edge, is treated as a bifurcation for which a discontinuity occurs in an analog of the hydrodynamic velocity and phase of the nonlinear Alfvén wave. The width of one of the collisionless shock waves decreases with an increase in the parametera which determines the magnitude of the field discontinuity when overturning occurs.L. N. Tolstoi State University, Checheno-Ingushk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–67, January, 1993.     

Contribution from the Earth's Bow Shock to Region 1 Current under Low Alfvén Mach Numbers

Using global MHD simulations of the solar wind-magnetosphere-ionosphere system, we investigate the dependence of the contribution from the Earth's bow shock (I_1bs) to ionospheric region 1 field aligned current (FAC) (I₁). It is found that I_1bs increases with increasing southward interplanetary magnetic field (IMF) strength B_s, if the Alfvén Mach number M_A of the solar wind exceeds 2, a similar result as obtained by previous authors. However, if M_A becomes close to or falls below 2, I_1bs will decrease with B_s in both magnitude and percentage (i.e., I_1bs}/I₁) because of the resultant reduction of the bow shock strength. Both the surface current density J_bs at the nose of the bow shock and the total bow shock current I_bs share nearly the same relationship with M_A, and vary non-monotonically with M_A or B_s. The maximum point is found to be located at M_A = 2.7. Three conclusions are then made as follows: (1) The surface current density at the nose, which is much easier to be evaluated, may be used to largely describe the behaviour of the bow shock instead of the total bow shock current. (2) The peak of the total bow shock current is reached at about M_A = 2.7 when only B_s is adjusted. (3) The non-monotonic variation of the bow shock current with M_A causes a similar variation of its contribution to region 1 FAC. The turning point for such contribution is found to be nearly M_A= 2. The implication of these conclusions to the saturation of the ionospheric transpolar potential is briefly discussed     

Quantum plasma description and Landau damping

The Schrödinger equation is shown to replace the Vlasov equation to simulate a classical collisionless plasma, provided we take a sophisticated initial condition. The Landau damping is then recovered within a high degree of accuracy.     

The perpendicular permittivity of magnetized toroidal plasmas with elliptic magnetic surfaces

The Vlasov equation for charged particles is analyzed in an axially symmetric toroidal plasma configuration with an elliptic cross section of magnetic surfaces. The asymptotic solution of the Vlasov equation is found. The analytical expressions for the perpendicular component of the dielectric permittivity tensor are obtained. These expressions are used for theoretical analyses of the trapped and untrapped ion influence on the collisionless cyclotron wave dissipation. The evaluated dielectric tensor components can be used for computer calculations of the radio frequency field structure and the collisionless dissipated power related to trapped and untrapped ions in tokamak plasmas. It is shown that ion cyclotron resonance dissipation in tokamaks depends on toroidicity and ellipticity parameters and does not depend on plasma temperature. This work was supported by the State University of Rio de Janeiro (UERJ), Rio de Janeiro Research Foundation (FAPERJ) and Brazilian National Council of Research (CNPq).     

A comparison between MEM and FFT for the spectral analysis of geophysical signals

Summary The results obtained by the maximum entropy method (MEM) for the spectral analysis of real signals (the magnetic-field observations performed by ISEE-2 during periods of solar-wind turbulence upstream of the Earth's bow shock) are compared with those obtained by the traditional fast Fourier transform (FFT) technique. The major relative importance of the dominant wave form suddenly emerges in the MEM analysis and the total frequency excursion of peaks is often smaller than the frequency resolution allowed by the FFT. The expected occurrence of spurious peaks might be less dramatic then in other cases; however, the definite choice of the best power spectrum remains often ambiguous. This research has been supported by the Ministero per la Pubblica Istruzione (40%) and by the Gruppo Italiano di Fisica Cosmica.     

Features of the generation of a collisionless electrostatic shock wave in a laser-ablation plasma

The appearance of a density bump is experimentally revealed in an electrostatic shock wave during the ablation of an aluminum foil by a femtosecond laser pulse. The numerical simulation shows that this phenomenon can be explained by the generation of a packet of ion acoustic waves under the action of high-energy electron flows in a collisionless plasma. It is found that, for the formation and maintenance of the dense plasma layer in the shock wave, the contributions of accelerated ions overtaking it and wave-captured ions of the background plasma formed by a nanosecond laser prepulse in the process of ablation are significant.     

K-P-Burgers equation in negative ion-rich relativistic dusty plasma including the effect of kinematic viscosity

The stationary solution is obtained for the K–P–Burgers equation that describes the nonlinear propagations of dust ion acoustic waves in a multi-component, collisionless, un-magnetized relativistic dusty plasma consisting of electrons, positive and negative ions in the presence of charged massive dust grains. Here, the Kadomtsev–Petviashvili(K–P) equation, threedimensional(3D) Burgers equation, and K–P–Burgers equations are derived by using the reductive perturbation method including the effects of viscosity of plasma fluid, thermal energy, ion density, and ion temperature on the structure of a dust ion acoustic shock wave(DIASW). The K–P equation predictes the existences of stationary small amplitude solitary wave,whereas the K–P–Burgers equation in the weakly relativistic regime describes the evolution of shock-like structures in such a multi-ion dusty plasma.     

Collisionless Plasma Expansion in the Presence of a Dipole Magnetic Field

The collisionless interaction of an expanding high–energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfvén–Mach numbers using the particle–in–cellmethod. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

热电子等离子体无碰撞漂移波的稳定性

本文采用Vlasov方程,分析了热电子等离子体中低频交换模和漂移波的性质,讨论了热电子成分的稳定作用。稳定交换模要求热电子成分约为10％,稳定漂移波要求热电子成分约为30%。文中还讨论了离子有限Larmor半径、等离子体密度梯度和温度、磁场曲率、扰动波长等参数对稳定性的影响。同MHD近似下强碰撞漂移波的结果相比较,热电子对无碰撞漂移波有更好的稳定作用。 关键词：     

Relativistic and nonrelativistic modulational instability of a laser radiation in an unmagnetized laser-produced plasma: Kinetic theory

Summary This paper presents a rigorous theoretical investigation of the relativistic and nonrelativistic modulational instability of a high-power laser radiation propagating in a collisionless and unmagnetized laser-produced plasma. The kinetic equationviz. the relativistic Vlasov equation has been employed to find the nonlinear response of electrons for this four-wave parametric process in the plasma. The actual motivation behind this theoretical investigation is to find the relativistic effect on this four-wave paremetric processviz. the modulational instability. Here, it can be noted that the modulational instability of the laser radiation under our situation has not a large but considerable relativistic effect and for the same set of plasma parameters the growth rate of the instability in ultrarelativistic consideration is approximately three times higher than that in the nonrelativistic consideration. The authors of this paper have agreed to not rective the proofs for correction.