共查询到20条相似文献，搜索用时 15 毫秒
1.
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. 相似文献
2.
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. 相似文献
3.
Mcllwain's electric and magnetic field distributions (E3H and M2) have been used to calculate the drift path of plasma density irregularities taking into account plasma interchange motion driven by the gravitational and inertial forces acting on the whole mass of the plasma elements.It has been shown that there is a region in the magnetosphere which is unstable with respect to the interchange motion of the cold plasma element. Any plasma hole in the background density drifts ultimately toward an asymptotic trajectory. Along this trajectory the inward gravitational force is balanced by the outward inertial force averaged over one revolution around the Earth. This asymptotic trajectory, along which all plasma holes ultimately accumulate, is identified with the equatorial plasmapause. The maximum velocity for the interchange motion is proportional to the excess (or defect) of density in the plasma element, and inversely proportional to the integrated Pedersen conductivity. Plasma detachment is shown to occur preferentially in the post-midnight sector. 相似文献
4.
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 , 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 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. 相似文献
5.
Inertial Alfvén waves are investigated using Maxwell-Boltzmann-Vlasov equation to evaluate the dispersion relation and growth/damping rate in inhomogeneous plasma. Expressions for the dispersion relation and growth/damping rate are evaluated in inhomogeneous plasma. The effects of density, temperature and velocity gradient are included in the analysis. The results are interpreted for the space plasma parameters appropriate to the plasma sheet boundary layer. It is found that the inhomogeneities of plasma contribute significantly to enhance the growth rate of inertial Alfvén wave. The applicability of this model is assumed for auroral acceleration region and plasma sheet boundary layer. 相似文献
6.
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. 相似文献
7.
Irakli S. Nanobashvili 《Astrophysics and Space Science》2004,294(3-4):125-134
Plasma mechanism for the generation of toroidal magnetic field in the magnetosphere of Crab pulsar is presented. The mechanism
is based on the development of parametric type instability in the relativistic electron-positron plasma of the pulsar magnetosphere.
As a result of plasma corotation with pulsar and its magnetic field, the effect of plasma radial braking takes place and the
time dependence of plasma particle radial velocity is harmonic. This triggers the development of parametric type instability
in the relativistic plasma of the pulsar magnetosphere. The energy for this process is drawn from the slowing down of pulsar
rotation. 相似文献
8.
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). 相似文献
9.
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。 相似文献
10.
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. 相似文献
11.
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 140RJ 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 110RJ 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. 相似文献
12.
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. 相似文献
13.
V. V. Zheleznyakov 《Astrophysics and Space Science》1983,97(2):229-259
The influence of radiation on the electron velocity distribution in a hot nonrelativistic plasma localized near the surface of magnetic white dwarfs is investigated. The part played by the plasma in the formation of cyclotron features in the optical spectrum of these stars is studied. The region of parameters where the transverse temperature of plasma is defined by the brightness temperature of extraordinary radiation at the gyrofrequency is found. When escaping from the plasma in a homogeneous magnetic field, this component forms a cyclotron line in absorption. The ordinary radiation at the gyrofrequency and both modes at higher cyclotron harmonics are in emission or absorption depending on the magnetic field strength and hot plasma density. Possible interpretation of the observed spectral features of magnetic white dwarfs in terms of the developed theory is discussed. 相似文献
14.
A method is described for the analytical evaluation of the force acting on a relativistic electron beam spreading in dense gas plasma by the ohmic plasma channel. This is useful for the solution of the general definitions for the force of the beam plasma interactions in the case of an arbitrary displacement of the symmetry axis of the plasma channel relative to the corresponding axis of the beam. The accuracy of these procedures is tested and their efficiency illustrated with practical applications, including the computation of the tracking force exerting on a relativistic electron beam by the ohmic plasma channel. 相似文献
15.
Nobuki Kawashima Susumu Sasaki Osamu Kaneko Akira Yamori Ryo Okamura Shoichi Okamura 《Planetary and Space Science》1978,26(4):367-373
A controlled active experiment was performed by a plasma gun on-board a rocket to study the plasma stream across the magnetic field in space. A mother and daughter system was employed. An 8 kV 0.8 μF (25 J) capacitor bank on the daughter rocket was discharged every 12 s and about 1016 ion and electron pairs were ejected. A plasma signal was detected on the electron temperature probe. The propagation speed of the plasma stream is estimated to be 106 cm/s, considerably lower than that obtained in the prelaunch test. The amplitude of the plasma signal decays as the inverse square of the mutual distance between the mother and daughter rockets and this decay is much slower than the free streaming. The importance of the geomagnetic field on the plasma propagation in space is discussed. 相似文献
16.
The charging of solid grains in a plasma environment is considered in this study. It is found that grains with zero initial potential gradually gain a negative potential and approach equilibrium. This potential depends most strongly on the plasma temperature. If secondary and photoemission of electrons from this grain is not considered, this equilibrium potential is about –2.7 times the plasma thermal energy. If secondary and photoemission is included, the grain can approach equilibrium at positive rather than negative potential. In this case the sign and the value of the equilibrium potential depends strongly on the material properties and to lesser extent on plasma temperature. This implies that grains of different composition can have different, possibly even opposite, equilibrium potentials in the same plasma environment. 相似文献
17.
该文讨论了太阳大气等离子体中电流的成因和对各种爆发活动的作用和影响,对目前的研究现状和存在的问题进行了分析讨论,指出虽然磁场是太阳物理观测和研究的关键要素,但是电流也是理解能量的传输与耗散、不稳定性的驱动和激发、等离子体的加热和粒子加速等太阳物理过程的重要概念.该文还提出了一个定性的改进电路模型,认为电流主要产生于太阳内部的发电机过程,同时电路在日冕部分的环形磁场位型也将产生部分新经典电流,通过磁通量管流入太阳大气,并在日冕区域通过磁场重联等过程释放能量.对该模型尚待解决的问题也进行了简单讨论. 相似文献
18.
Numerical analysis has been carried out on the one-dimensional quasi-linear relaxation of a group of fast electrons travelling through the plasma. It is demonstrated that the electron velocity distribution of fast electrons tends to be a plateau form exciting the electron plasma waves and that the plasma waves are almost completely reabsorbed later by electrons arriving later. Both the velocity range and time interval in which quasi-plateau distribution is formed increase with distance from the origin of the fast electrons. There is no net energy loss of the electron cloud during the travel through the plasma if we neglect both the collisional losses and the scattering of plasma waves. Although the present computation is preliminary and limited to rather low beam density, we can see that the characteristics of both the electron beam and the plasma waves tend, with distance, to those of the analytical solution given by Ryutov and Sagdeev; though a modification to set a low velocity cutoff on the plasma waves due to the thermal electrons is necessary. 相似文献
19.
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. 相似文献
20.
等离子体弧是日冕中的一种基本结构,其高温观测特性意味着它有较高的等离子体压力。本文在二维近似下,讨论了等离子体拱被两个强磁场区域所约束时的平衡。对于较大的等离子体标高,等离子体具有近似圆弧形的结构。通过求出强磁场区域中的磁场位形,可以得到孤立的等离子体拱的平衡状态。由于总压守恒的边界条件是高度非线性的,整个问题是一类非线性的自由边界问题。在近圆弧形近似下,其基态是一维的非线性问题,而相对于基态的偏离是二维的线性问题。这样,整个问题可以给出分析解。 相似文献