Some Physical Processes in Dusty Plasmas

Ionized gases containing fine (μm to sub-μm sized) charged dust grains, referred to as dusty plasmas, occur in diverse cosmic and laboratory environments. Dust occurs in many space and astrophysical environments, including planetary rings, comets, the Earth's ionosphere, and interstellar molecular clouds. Dust also occurs in laboratory plasmas, including processing plasmas, and crystallized dusty plasmas. Charged dust can lead to various effects in a plasma. In this review, some physical processes in dusty plasmas are discussed, with an emphasis on applications to dusty plasmas in space. This includes theoretical work on several wave instabilities, the role of dust as an electron source, and Coulomb crystals of positively charged dust. This revised version was published online in July 2006 with corrections to the Cover Date.     

Waves and Instabilities in Magnetized Dusty Plasmas

The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential which can be responsible for the charged dust grain attraction. The relevance of our investigation to laboratory and space plasmas has been pointed out. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Instability for Convection in Astrophysical Plasmas

The plasma thermal stability condition under convection is discutided. Using Cattaneo law and mixing length theory before relaxation lets show a new thermal stability condition for plasmas in astrophysics. Application in neutron stars and low mass x-ray binaries stars is mentioned.     

Alfvén-Jeans and Magnetosonic Modes in Multispecies Self-Gravitating Dusty Plasmas

Perpendicularly propagating electromagnetic waves in magnetized, multispecies, self-gravitating dusty plasmas are investigated in terms of their wave dispersion properties as well as with respect to their susceptibility to gravitational collapse. In particular, waves on the ordinary as well as extraordinary mode branches are considered. Within the one-dimensional propagation model employed, all modes except the ordinary mode produce density perturbations that can be unstable to gravitational collapse. The wavelengths that are unstable are comparable to the well-known Jeans length for a neutral gas/dust, but there are interesting modifications due to the presence of a magnetic field and charged particles. Furthermore, the effects of the gravitational coupling of a multicomponent plasma to a neutral dust are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Limits for the Firehose Instability in Space Plasmas

Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence of temperature anisotropies T _∥ /T _⊥ >1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined. The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold, so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized by an excess of parallel kinetic energy.     

On the Thermochemical Instability of Optically Thin Plasmas

The effects of the thermal conduction on the linear stability analysis of an optically thin plasma with metallicity Z = 1 and including chemical relaxation time effects, is carried out. Generally, a further stabilizing effect on the unstable modes and an increasing of the damping of stable modes appear for disturbances with values of wave number large enough. However, the oscillating mode appearing at low temperature remain unaffected by the thermal conduction.     

Jeans Instability of a Protoplanetary Gas Cloud with Radiation in Nonextensive Tsallis Kinetics

Solar System Research - In the framework of Tsallis statistics, we study the effect of medium nonextensivity on the Jeans gravitational instability criterion for a self-gravitating protoplanetary...     

Rotation of Weakly Collisional Plasmas in Tokamaks, Operated with Alfvén Waves

In this paper we consider rotation induced by kinetic Alfvén waves in weakly collisional plasma of slightly rippled tokamaks in plateau and banana regimes. Rippled magnetic field of tokamaks retards the plasma rotation in toroidal direction. Here, we are going to find the quasistationary poloidal and toroidal plasma velocities and the radial electric field taking into account the complete form of ponderomotive forces.     

Jeans Instability of a Protoplanetary Circular Disk Taking into Account the Magnetic Field and Radiation in Nonextensive Tsallis Kinetics

Solar System Research - Within the framework of Tsallis nonextensive statistics, the criteria for the Jeans gravitational instability are derived for a self-gravitating protoplanetary disk, whose...     

对金斯定则的几点认识

用物理学基本定律可导出金斯经验定则,它似应称为金斯定则,该定则的速度、高度或能量等表述完全等效,可随意选用,用能量观点更容易解释此定则,满足金斯定则只是给定的粒子成为具有稠密大气的行星或卫星的主要大气成分的必要条件,该定则的适应范围可用方程或其图像表示,也能用诺模图确定,它适用于太阳系内的行星,卫星,小行星,流星体和像柯伊伯带天体与半人马族星这样的外太阳系天体,此定则现在仍有普遍的现实意义。     

Dusty KING Spheres

In order to determine the quantitative influence of small amounts of dust on the luminosity profile of spherical galaxies, we represent an elliptical galaxy by a KING sphere filled with dust. The density of dust particles is assumed to be related to the density of stars according to a simple power law. Assuming that the observed central reddenings in NGC 4874 and NGC 4889 are really caused by dust, we estimate the optical depths in the centres of both galaxies to be about 0.75.     

Collisional records in LL-chondrites

Abstract One-third of all the LL-chondrites have exposure ages of ～15 Ma and were exposed to cosmic rays following a collisional break-up. The probability that the 15-Ma peak represents a random signal is calculated to be less than 2%. Considerably lower probabilities are obtained if only LL5s or subgroups of high ⁴⁰Ar retention are used. Furthermore, we show that the peak shape agrees with statistical constraints obtained from multiple analyses of samples from the St. Severin LL6-chondrite. The frequency in and out of the 15-Ma peak varies significantly for different petrographic LL-types. The radiogenic ⁴⁰Ar retention systematics (most LL-chondrites retained ⁴⁰Ar_rad) shows that no substantial heat pulse resulted in the 15-Ma collisional event. Interestingly, smaller exposure age clusters at ～28 Ma and ～40 Ma match up well with clusters in the histogram of L-chondrites. The distribution of LL-exposure ages is not consistent with that expected for a quasi-continuous injection of LL material into a resonance zone of the asteroid belt. The near absence of exposure ages shorter than 8 Ma either indicates a lack of recent collisional events or considerably longer transfer times than inferred from dynamical considerations.     

Jeans instability of collisionless systems

Linear dispersion relations are solved numerically for collisionless self-gravitating systems. The results are compared to those of hydrodynamic approach. Both theories yield similar dispersion relations, with predictions of instability when the system is cold enough. In a collisionless system, however, the perturbation is found to die away without oscillations when the system is stable. A mixed system of hot-component particles and cold-component particles is also studied. The stability of such system is dominated by the temperature of the cold particles. Again, the oscillatory behaviour is not found in this case, regardless of the stability of the system.     

The Jeans instability in smoothed particle hydrodynamics

We derive analytically the Jeans criterion for a gas simulated using an SPH code in which the number of neighbours N _neighb is held constant (approximately) and the gravity-softening length, ε, equals the smoothing length, h (approximately). We show that the Jeans criterion is reproduced accurately for resolved structures, i.e. those represented by >  N _neighb particles. Unresolved structures are stabilized, as long as (i) the smoothing kernel W ( u ) is sufficiently centrally peaked, and (ii) the Jeans mass is resolved. Provided that these conditions are satisfied, then, in simulations of the formation of stars and galaxies, any fragmentation that occurs should be both physical and resolved. In particular there should be no creation of sub-Jeans condensations owing to numerical instability.     

Collisional processes in stellar systems

The theory of collisional relaxation in stellar systems is discussed in terms of an expansion in powers of 1/N, the inverse of the total number of stars. The results are expressed in terms of the concept of gravitational polarization.     

Collisional growth of planetesimals

Safronov's (1972) demonstration that relative velocities of planetesimals would be comparable to the dominant size bodies' escape velocities, combined with a plausible size distribution that has most mass in the largest bodies, yielded his evolution model with limited growth of the largest planetesimal with respect to its next largest neighbors. A numerical simulation of planetesimal accretion (Greenberget al., 1978) suggests that at least over one stage of collisional accretion, velocities were much lower than the escape velocity of the largest bodies, because the bulk of the mass still resided in km-scale bodies. The low velocities at this early stage may conceivably have permitted early runaway growth, which, in turn, would have kept the velocities low and permitted continued runaway growth of the largest bodies.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.