Numerical computer simulation of cross-field propagation of a plasma stream in a magnetic field

A one-dimensional electrostatic particle simulation of plasma streaming perpendicular to a magnetic field with nonperiodic boundary condition has been carried out. When a bulk of plasma in injected across an ambient magnetic field, a stream of neutral plasma, consisting of equal numbers of ions and electrons, polarizes, and the resulting polarization electric field gives rise to the penetration of plasma across the magnetic field so that the integrity of plasma maintains. Computer simulation demonstrates the properties of cross-field propagation of plasma stream in a magnetic field with different plasma parameters.     

Solar wind energy transfer regions inside the dayside magnetopause: Accelerated heavy ions as tracers for MHD-processes in the dayside boundary layer

Plasma and magnetic field data from PROGNOZ-7 have revealed that solar wind (magnetosheath) plasma elements may penetrate the dayside magnetopause surface and form high density regions with enhanced cross-field flow in the boundary layer.The injected magnetosheath plasma is observed to have an excess drift velocity as compared to the local boundary layer plasma, comprising both “cold” plasma of terrestrial origin and a hot ring current component. A differential drift between two plasma components can be understood in terms of a momentum transfer process driven by an injected magnetosheath plasma population. The braking action of the injected plasma may be described as a dynamo process where particle kinetic energy is transferred into electromagnetic energy (electric field). The generated electric field will force the local plasma to $\text{ε×}\text{B}\text{-drift}$, and the dynamo region therefore also constitutes an accelerator region for the local plasma. Whenever energy is dissipated from the energy transfer process (a net current is flowing through a load), there will also be a difference between the induced electric field and the $\text{v}\text{×}\text{B}$ term of the generator plasma. Thus, the local plasma will drift more slowly than the injected generator plasma.We will present observations showing that a relation between the momentum transferred, the injected plasma and the momentum taken up by the local plasma exists. For instance, if the local plasma density is sufficiently high, the differential drift velocity of the injected and local plasma will be small. A large fraction of the excess momentum is then transferred to the local plasma. Conversely, a low local plasma density results in a high velocity difference and a low fraction of local momentum transfer.In our study cases the “cold” plasma component was frequently found to dominate the local magnetospheric plasma density in the boundary layer. Accordingly, this component may have the largest influence on the local momentum transfer process. We will demonstrate that this also seems to be the case. Moreover we show that the accelerated “cold” plasma component may be used as a tracer element reflecting both the momentum and energy transfer and the penetration process in the dayside boundary layer.The high He⁺ percentage of the accelerated “cold” plasma indicates a plasmaspheric origin. Considering the quite high densities of energetic He⁺ found in the boundary layer, the overall low abundance of He⁺ (as compared to e.g. O⁺) found in the plasma sheet and outer ring current evidently reduces the importance of the dayside boundary layer as a plasma source in the large scale magnetospheric circulation system.     

Highβ, energy flux conserving equilibria for alfvén wave

Magnetohydrodynamic waves in a high β, collisionless plasma with smooth variations in plasma parameters across the boundary is studied. The heating of collisionless plasma is analyzed in one dimension, including the effects of shear magnetic field and compressibility of plasma. Energy absorption rate and dispersion relation between central plasma, surrounded by tenuous plasma have also been derived.     

Collisionless Slowing Down of Nova and Supernova Shells in Magnetized Interstellar Medium

The collisionless interaction of an expanding plasma cloud with a magnetized background plasma is examined in the framework of a 3D kinetic-hydrodynamic model. The slowing down of a hydrogen cloud is studied for high Alfven-Mach numbers and magneto-laminar interaction parameters. A particle-in-cell method is used to study the dynamics of the magnetic field, plasma cloud, background plasma, and collisionless shock wave generated by the intense particle flux. A numerical simulation is consistent with the nonstationary interactions between the plasma shells formed during nova and supernova explosions and the interstellar plasma medium.     

Driven magnetic field reconnection

We consider the magnetic field reconnection in a plasma induced by perturbing the boundaries of a slab of incompressible plasma with a magnetic neutral surface inside. We assume that the boundaries of the plasma slab are perturbed at a rate which is fast compared with the hydromagnetic evolution rate; and investigate the ensuing adjustments in the plasma and the magnetic field threading through it.     

Stationary incompressible MHD perturbationsgenerated by a current source in a moving plasma

We consider the inductive interaction between a conducting body and a magnetizedincompressible plasma in relative uniform motion, which has application to the Io–Jupitersystem, for example. An incompressible plasma only supports one mode of propagation, namelythe Alfvén mode. In the case of free oscillations, this mode propagates the perturbations in themagnetic field and in the plasma velocity unattenuated along the direction of the backgroundfield, while the plasma pressure balances the magnetic pressure. The situation changes in thepresence of source currents and in a flowing plasma. In particular, the parallel plasma vorticityand parallel plasma current are propagated unattenuated along the familiar Alfvéncharacteristics, while the field and velocity perturbations suffer Laplacian decay in the near field.We study these perturbations in the frame of the body and compare them to the case of no sourceterms.     

Temporal Evolution of Whistler Instability Due to Cold Plasma Injection in the Presence of Perpendicular AC Electric Field in the Magnetosphere of Uranus

Temporal evolution of whistler instability has been studied due to cold plasma injectionin the presence of a perpendicular AC electric field in the magnetosphere of Uranus. Ageneralized distribution function with index j, which is a reducible to a bi-Maxwellianfor j = 0 and to a loss-cone for j = 1, for a plasma in the presence of a perpendicularAC electric field, has been derived from a hot/warm background plasma and atime-dependent plasma described by a simple Maxwellian distribution has been considered to represent the injected cold plasma. An expression for the growth rate of a system with added time-dependent cold plasma injection has been calculated using the method of characteristics and kinetic approach The results obtained for representative value of the parameters suited to the Uranian magnetosphere in both cases have been compared and discussed. It is inferred that the temperature anisotropy remains the major source of free energy whereas a loss-cone background acts as an additional source of free energy for the instability. It is not the magnitude but the frequency of the AC field which Influences the growth rate. In comparison to the Uranian magnetosphere this effect is more significant in Earth's magnetosphere. As the ionisation time of the time-dependent injected cold plasma increases, the growth rate goes on increasing, this effect being much greater in a loss-cone background in comparison to a bi-Maxwellian background plasma time-dependence of thecold plasma has been considered since it represents a more realistic situation in injection experiments.     

Jovian plasma sheet morphology: particle and field observations by the Galileo spacecraft

We present results from an investigation of the plasma sheet encounter signatures observed in the Jovian magnetosphere by the Energetic Particles Detector (EPD) and Magnetometer (MAG) onboard the Galileo spacecraft. Maxima in ion flux were used to identify over 500 spacecraft encounters with the plasma sheet between radial distances from Jupiter from 20 to 140R_J during the first 25 orbits (4 years of data). Typical signatures of plasma sheet encounters show a characteristic periodicity of either 5 or 10 hours that is attributed to an oscillation in the relative distance between the spacecraft and the plasma sheet that arises from the combination of planetary rotation and offset magnetic and rotational axes. However, the energetic particle and field data also display much variability, including instances of intense fluxes having little to no periodicity that persist for several Jovian rotation periods. Abrupt changes in the mean distance between the plasma sheet and the spacecraft are suggested to account for some of the transitions between typical flux periodicities associated with plasma sheet encounters. Additional changes in the plasma sheet thickness and/or amplitude of the plasma sheet displacement from the location of the spacecraft are required to explain the cases where the periodicity breaks down but fluxes remain high. These changes in plasma sheet characteristics do not display an obvious periodicity; however, the observations suggest that dawn/dusk asymmetries in both the structure of the plasma sheet and the frequency of anomalous plasma sheet encounters are present. Evidence of a thin, well-ordered plasma sheet is found out to 110R_J in the dawn and midnight local time sectors, while the dusk magnetosphere is characterized by a thicker, more disordered plasma sheet and has a potentially more pronounced response to an impulsive trigger. Temporal variations associated with changing solar wind conditions are suggested to account for the anomalous plasma sheet encounters there.     

A technique for calculating meteor plasma density and meteoroid mass from radar head echo scattering

Large-aperture radars detect the high-density plasma that forms in the vicinity of a meteoroid and moves approximately at its velocity; reflections from these plasmas are called head echoes. To determine the head plasma density and configuration, we model the interaction of a radar wave with the plasma without using assumptions about plasma density. This paper presents a scattering method that enables us to convert measurements of radar cross-section (RCS) from a head echo into plasma density by applying a spherical scattering model. We use three methods to validate our model. First, we compare the maximum plasma densities determined from the spherical solution using 30 head echoes detected simultaneously at VHF and UHF. Second, we use a head echo detected simultaneously at VHF, UHF and L-band to compare plasma densities at all frequencies. Finally, we apply our spherical solution to 723 VHF head echoes and calculate plasma density, line density and meteoroid mass in order to compare these values with those obtained from a meteoroid ablation and ionization model. In all three comparisons, our results show that the spherical solution produces consistent results across a wide frequency range and agrees well with the single-body ablation model.     

活动星系核中相对论电子束的物理效应

本文研究了Ｂｌａｚａｒ天体的辐射性质，提出一种新的喷流模型，即具有幂律分布的极端相对论电子团从中心核注入喷流等离子体中，它在一定的注入速度下，不仅能在喷流等离子体中激发等离子体湍动，产生电磁波的相干辐射，而且能产生强的同步辐射。利用等离子体的弱湍理论，我们研究了极端相对论电子团在喷流等离子体中的辐射过程，并详细研究了它在解释Ｂｌａｚａｒ天体辐射特性中的应用，本文认为，Ｂｌａｚａｒ天体的不稳定辐射与极端相对论电子团的无规注入、喷流等离子体的物理环境瞬息变化有关。Ｂｌａｚａｒ中快速变化的辐射偏振角摆动。产生于相对论电子团在湍动等离子体中的同步辐射过程。另外，Ｘ选和射电选的ＢＬＬａｃ天体之间的区别取决于喷流等离子体的运动状态和物理环境。     

A model for thinning of the plasma sheet

A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a₀. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a₀ is induced. The predictions of the model are in reasonable agreement with observations.     

Evolution of double layers in magnetised plasmas contaminated with dust charge fluctuations

Coherent structures entailing the existence of double layers have been studied in magnetised plasma contaminated with dust charging fluctuations. It has been shown that the dust charging in magnetic plasma leads to complexity in the derivation of the Sagdeev wave equation, but under way new procedure enable one to study the nature of double layers showing the effective role of the constituents of the plasma. A parametric analysis is a subject of interest in laboratory and space plasmas, and it has been explained with the input of various typical plasma numerics. The proposed mathematical mechanism has shown the success to yield plasma acoustic modes in a dusty plasma which, in turn, has been solved convincingly for double layers. Observations have been evaluated in an appropriate model with a view to agree with the observations in astrophysical problems dealing with present new findings.     

Thermal instability in slab geometry in the presence of anisotropical thermal conduction

Prominences and filaments are thought to arise as a consequence of a magnetized plasma undergoing thermal instability. Therefore, the thermal stability of a magnetized plasma is investigated under coronal conditions. The equilibrium structure of the plasma is approximated by a 1-D slab configuration. This is investigated in thermal instability taking into account optically thin plasma radiation and anisotropic thermal conduction. The thermal conduction perpendicular to the magnetic field is taken to be small but non-zero.The classic rigid wall boundary conditions which are often applied in the literature, either directly on the plasma or indirectly through some other medium, are replaced by a more physical situation in which the plasma column is placed in a low-density background stretching towards infinity. Results for a uniform equilibrium structure indicate the major effect of this change is on the eigenfunctions rather than on the growth rate. Essentially, perpendicular thermal conduction introduces field-aligned fine structure. It is also shown that in the presence of perpendicular thermal conduction, thermal instability in a slab model is only possible if the inner plasma has the shortest thermal instability time scale.Research Assistant of the National Fund for Scientific Research (Belgium).     

On Polarization of the Zebra Pattern in Solar Radio Emission

The problem of strong polarization of the zebra-type fine structure in solar radio emission is discussed. In the framework of the plasma mechanism of radiation at the levels of the double plasma resonance, the polarization of the observed radio emission may be due to a difference in rates of plasma wave conversion into ordinary and extraordinary waves or different conditions of escaping of these waves from the source. In a weakly anisotropic plasma which is a source of the zebra-pattern with rather large harmonic numbers, the degree of polarization of the radio emission at twice the plasma frequency originating from the coalescence of two plasma waves is proportional to the ratio of the electron gyrofrequency to the plasma frequency, which is a small number and is negligible. Noticeable polarization can therefore arise only if the observed radio emission is a result of plasma wave scattering by ions (including induced scattering) or their coalescence with low-frequency waves. In this case, the ordinary mode freely leaves the source, but the extraordinary mode gets into the decay zone and does not exit from the source. As a result, the outgoing radio emission can be strongly polarized as the ordinary mode. Possible reasons for the polarization of the zebra pattern in the microwave region are discussed.     

Dynamical behaviors of size graded dust grains levitated in robust sheath in inhomogeneous plasmas

Our interest is to study the sheath formation in an inhomogeneous plasma coexisting with an interaction of weak ionization. Pseudopotential analysis has been employed to derive the coherent structures of sheath in plasma. It has shown that the ionization affects the growth of sheath in plasma and nature depends fully on plasma constituents as well. After getting a robust sheath, dynamical behaviors of a levitated dust grain into the robust sheath has been studied which, in fact, leads to find the variation of dust potential, dust sizes along with the net force generated on grains. Results are obtained numerical for some typical plasma parameters. It has demonstrated that the plasma constituent effects the clustering of dust grains in different region within the sheath as a result of which dust agglomeration forms nebulons: patches of dust cloud-like structures with changing fleece.     

Whistler Mode Instability in a Lorentzian (κ) Magnetoplasma in the Presence of Perpendicular A.C. Electric Field and Cold Plasma Injection

The dielectric tensor, modified plasma dispersion function and dispersion relation for Whistler mode instability in an infinite magnetoplasma are obtained in the case of cold plasma injection to background hot anisotropic generalized bi-Lorentzian (κ) plasma in the presence of external perpendicular a.c. electric field. The method of characteristics solutions using perturbed and unperturbed particle trajectories have been used to determine the perturbed distribution function. Integrals and modified plasma dispersion function Z_κ ^*(ξ ) are reduced in power series expansion form. Numerical methods using computer technique have been used to obtained temporal growth rate for magnetospheric plasma at geostationary height. The bi-Lorentzian (κ) plasma is reducible to various forms of distribution function by changing the spectral index κ. The results of bi-Lorentzian (κ) plasma are compared with those of bi-Maxwellian plasma. It has been found that the addition of cold plasma injection gives different frequency spectra. The a.c. frequency of moderate amplitude increases the growth rate and instability in K space to lower range. Growth rate maximum is not affected by a.c. frequencies. However, it shifts the maximum to lower K space in both cases, rather than on the variation of the magnitude. Thus a physical situation like this may explain emission of various high frequency whistler emissions by cold plasma injection. The potential application of controlled plasma experiments in the laboratory and for planetary atmosphere are indicated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experiment on Collisionless Plasma Interaction with Applications to Supernova Remnant Physics

Results from a scaled, collision-free, laser-plasma experiment designed to address aspects of collisionless plasma interaction in a high-plasma β supernova remnant (SNR) are discussed. Ideal magneto-hydrodynamic scaling indicates that the experimental plasma matches the SNR plasma at 500 ps. Experimental data show that the magnetic field can alter the plasma density profile when two similar plasmas interact in a colliding geometry. These results are not explained by magnetic-field pressure; they do, however, suggest magnetic field penetration that localizes the plasma particles to the Larmor radius, which appears smaller than the size of the experiment and the particle mean-free paths and may thus increase the effective collisionality of the interacting plasma system.     

Almost-parallel electromagnetic wave propagation at frequencies near the electron plasma frequency

An approximate dispersion equation for almost-parallel electromagnetic wave propagation in a weakly relativistic plasma at frequencies near the electron plasma frequency is derived and investigated both analytically and numerically. It is pointed out that the cold plasma approximation cannot be applied to the analysis of these waves in any realistic (e.g., magnetospheric or astrophysical) plasma.     

Collective neutrino-plasma interactions

Nonlinear processes describing the interaction of neutrinos with collective plasma oscillations and the excitation of plasma turbulence by a large neutrino flux is discussed. The excitation considered is the inverse processes of neutrino emission by plasma waves first considered by Tsytovich (V.N. Tsytovich, Soviet Fiz. Dokl. 9 (1965) 1114). The process is similar to a beam plasma instability considered as inverse Landau damping in which the usual electromagnetic interactions are important. In the neutrino beam relaxation the weak interaction can play a similar role. We emphasize here the possibility of another process namely the interaction of an intense neutrino flux with a strongly turbulent plasma. The turbulence can also be assumed to be due to the shock produced at the early stages of a type II supernova (SN) explosion. The scattering of the neutrinos in the turbulent plasma is shown to be sufficient for transferring momentum and energy from the neutrino flux to the plasma causing the shock to continue moving outward and eventually creating the blow-off of the mantle of the star producing type II SN.