Investigation of non-isothermal electron effects on the dust acoustic waves in four components dusty plasma

The time fractional modified KdV, the so-called TFMKdV equation is solved to study the nonlinear propagation of the dust acoustic (DA) solitary waves in un-magnetized four components dusty plasma. This plasma consists of positively charged warm adiabatic dust, negatively charged cold dust, non-isothermal electrons and Maxwellian ions. The TFMKdV equation is derived by using semi-inverse and Agrawal’s method and solved by the Laplace Adomian decomposition method (LADM). The effects of the time fractional order (β), the ratio of dust to ion temperature (δ _d ), the time (τ), the mass and charge ratio (α), the non-isothermal parameter (γ) and wave velocity (v) on the DA solitary wave are studied. Our results show that the variations of the amplitude of DA solitary wave versus (γ) are in agreement with the results obtained previously. Moreover, the time fractional order plays a role of higher order perturbation in modulating the soliton shape. The achievements of this research for the DA solitary waves may be applicable in space plasma environments and laboratory plasmas.     

Arbitrary amplitude dust acoustic solitary waves in an electron-depleted dusty plasma with two high energy-tail ion distributions

Arbitrary amplitude dust acoustic waves (DAW’s) in two high energy-tail ion distributions are investigated. The electron number density has been assumed sufficiently depleted during the charging of the dust grains, on account of the attachment of the background plasma electrons on the surface of the dust grains. Our results reveal that under certain conditions, DA solitary waves with either negative or positive potential may be admitted. The high degree of suprathermalization of the relatively low temperature ion component favors the development of compressive localized structures. This behavior is preserved to a large extent in the small but finite amplitude regime. This means that the presence of additional relatively low temperature suprathermal ions does not only significantly modify the basic properties of DA structures, but also causes the existence of positive solitary potentials. This feature is completely new in a dusty plasma with two suprathermal ion components with widely disparate temperatures. Our results may be relevant to a number of space dusty plasma systems, particularly, the Saturn’s F-ring where electron depletion and suprathermality are thought to come into play.     

Dust acoustic shock waves in a suprathermal dusty plasma with dust charge fluctuation

The properties of small but finite amplitude dust acoustic (DA) shock waves are studied in a charge varying dusty plasma with ions and electrons having kappa velocity distribution. We obtain the global Debye length including the influence of suprathermality effects and dust charge fluctuations. It is shown that the effects of suprathermality of ions/electrons and dust charge fluctuation significantly modify the basic properties of DA shock wave. We observe that only negative DA shock waves will be excited in this model. The amplitude of DA shock wave increases with deviation of electrons or ions from Maxwellian distribution via decrease of spectral index, κ _j (j=i,e denotes, ions and electrons, respectively). Also, it is indicated that the amplitude and steepness of the shock front decreases with an increase in the ion temperature.     

Small Amplitude Nonlinear Dust Acoustic Wave Propagation in Saturn's F, G and E Rings

Nonlinear properties of small amplitude dust acoustic waves, incorporatingboth the ion inertial effect and dust drift effect have been studied.The effect of dust charge variation is also incorporated. It is seen thatdue to the dust charge variation, a Korteweg-de Vries (KdV) equationwith positive or negative damping term depending on the wave velocityand the ring parameters governes the nonlinear dust acoustic wave. It isseen that the damping or growth arises due to the assumption that dusthydrodynamical time scale is much smaller than that of the dust chargingscale. This assumption is valid only for planetary rings such as Saturn'sF, G and E rings. Numerical investigations reveal thatall the three rings in F, G and E, dust acoustic solitary wave admits both negative and positive potentials. Instability arises from the available freeenergy of drift motion of dust grains only for the wave with wave velocity 0, the drift velocity of the dust.     

Influence of suprathermality on the obliquely propagating dust-acoustic solitary waves in a magnetized dusty plasma

Dust-acoustic (DA) solitary waves are investigated in a magnetized dusty plasma comprising cold dust fluid and kappa-distributed ions and/or electrons. The influence of suprathermal particles, obliqueness, and ion temperature on the DA solitary waves is investigated. We find that only negative DA solitary waves will be excited in this model. Also it is shown that the amplitude of the DA solitary wave decreases with deviation of electrons or ions from Maxwellian distribution via decrease of κ _e or κ _i . The effect of the temperature of the ion decreases with the amplitude and steepness of the solitary wave front.     

Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Q_d is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Q_d as well as of the impact speed v_d. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Q_d between 1.3 and 5.4 fC. Knowledge of Q_d also allows us to estimate the grain mass m_d. Assuming a potential of φ_d≈+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Q_d were found to be in excess of 10⁻¹³ kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with m_d?10⁻¹³ kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine m_d and v_d, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Q_d is not affected by the subsequent impact of the grain with the detector. By relating m_d and v_d derived from Q_d of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system.     

Large amplitude dust ion-acoustic solitary waves in a plasma in the presence of positrons

Properties of propagation of large amplitude dust ion-acoustic solitary waves and double layers are investigated in electron-positron-ion plasma with highly charged negative dust. Sagdeev pseudopotential method has been used to derive the energy balance equation. The expression for the critical Mach number (lower/upper limit) for the existence of solitary structures has also been derived. The Sagdeev pseudopotential is a function of numbers of physical parameters such as ion temperature (σ), positron density (δ _p ), dust density (δ _d ) and electron to positron temperature ratio (β). These parameters significantly influence the properties of the solitary structures and double layers. Further it is found that both polarity (compressive and rarefactive) solitons and negative potential double layers are observed.     

Dust ion acoustic (DIA) solitary waves in plasmas with weak relativistic effects in electrons and ions

In the new investigation of dust-ion acoustic (DIA) waves with negative dust charges and weakly relativistic ions and electrons in the plasma, compressive and rarefactive DIA solitons of interesting characters are established through the Korteweg-de Vries (KdV) equation. Eventually, the amplitudes of the compressive DIA solitons are found to be constant at some critical temperature ratio α _c (electron to ion temperature ratio) identifying some critical dust charge Z _dc . It is predicted, that the reception of dust charges by the plasma particles at the variation of temperature starts functioning to the growth of compressive soliton’s constant stage of amplitude after the state of critical α _c . The identification of critical dust charge (Z _dc ) which is found to be very great for solitons of constant amplitudes becomes feasible for very small dust to ion density ratio (σ). But it can be achieved, we observe, due to the relativistic increase in ion-density as in mass, which is also a salient feature of this investigation.     

Nonplanar dust ion-acoustic solitary and shock excitations in electronegative plasmas with trapped electrons

It is shown that the three-dimensional cylindrical Kadomtsev-Petviashvili (CKP) and the extended cylindrical Kadomtsev-Petviashvili (ECKP) equations can describe the propagation of nonplanar dust ion-acoustic excitations in a dusty plasma composed of positive ions, negative ions, stationary dust particles, as well as trapped electrons or a small percentage of trapped electrons. It is found that the solution of the CKP equation supports only solitary pulses, while the ECKP equation describes the propagation of both solitary and shock excitations. The effects of physical parameters, namely negative ions density, dust grains density, positive-to-negative mass ratio, direction cosine of the wave propagation on the pulses profile are examined. Furthermore, the existence regions of either localized or shock pulses are investigated. The relevance of nonlinear structures in the Earth’s ionosphere and plasma experiment is discussed.     

Dust acoustic soliton energy in a mixed nonthermal high energy-tail electron distribution

Weak dust acoustic (DA) solitary waves are investigated in a mixed nonthermal high energy-tail electron distribution, focusing on the influence of an interplay between nonthermality and superthermality on the DA soliton energy. It is shown that in a pure superthermal plasma (α=0), electron thermalization (κ→∞) leads to an increase of the energy carried by the soliton. Addition of minute quantities of nonthermal electrons drastically modifies the κ-dependence of the soliton energy E _κ,α . The latter first decreases, then exhibits a local minimum before leveling at a constant value. The energy exchange between the non-Maxwellian electrons and the localized solitary structure depends drastically on the interplay between superthermality and nonthermality.     

Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions

The galactic and Extragalactic photodissociation regions are primarily heated by photoelectrons ejected from the surface of interstellar dust grains by Far-ultraviolet (FUV) photons. But there is no direct mechanism to measure the photoelectric heating efficiency. To understand the role of dust grains in processing the Interstellar Radiation Field (ISRF) and heating the gas, we compare the intensities I _CII, I _CO and I _FIR for (² P _3/2→² P _1/2) & (J = 1→ 0) line emission of CII & CO at 158 μm & 2.6 mm and integrated far-infrared from number of photodissociation regions, HII regions, planetary nebulae, reflection nebulae and high latitude translucent clouds (HLCs). It is found that I _CII is linearly correlated with I _FIR. In the cold medium where cloud is exposed to weak radiations temperature is low and most of the cooling is due to [CII] emissions. As a result the ratio of I _CII/I _FIR provide indirect method to evaluate the photoelectric heating efficiency. For the neutral cold medium it is evaluated to be ∼0.028. The FUV radiation field G ₀ are estimated through the model calculation of I _CII and I _CO for different galactic and photodissociation regions. The intensity of FIR radiation I _FIR are well represented as 1.23×10⁻⁴ G ₀(ergs cm⁻² s⁻¹ sr⁻¹) almost same as estimated for HLCs by Ingalls et al (2002). Hydrogen density for each source has also been estimated.     

Characteristic of ion acoustic shock waves in a dissipative quantum pair plasma with dust particulates

The behavior of quantum dust ion-acoustic (QDIA) shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions and stationary negative dust grains are studied, using a quantum hydrodynamic model (QHD). The effect of dissipation due to the viscosity of ions is taken into account. The propagation of small but finite amplitude QDIA shocks is governed by the Kortoweg-de Vries-Burgers (KdVB) equation. The existence regions of oscillatory and monotonic shocks will depend on the quantum diffraction parameter (H) and dust density (d) as well as dissipation parameter (η ₀). The effect of plasma parameters (d,H,η ₀), on these structures is investigated. Results indicate that the thickness and height of monotonic shocks; oscillation amplitude of the oscillatory shock wave and it’s wavelength effectively are affected by these parameters. Additionally, the possibility of propagation of both compressive and rarefactive shocks is investigated. It is found that depending on some critical value of dust density (d _c ), which is a function of H, compressive and rarefactive shock waves can’t propagate in model plasma. The present theory is applicable to analyze the formation of nonlinear structures at quantum scales in dense astrophysical objects.     

Electrostatic solitary structures in a four-component adiabatic dusty plasma

A theoretical investigation has been made of propagating electrostatic waves in a four-component adiabatic dusty plasma, whose constituents are adiabatic electrons, adiabatic ions, adiabatic positively and as well as negatively charged warm dust. The basic features of the solitary structures in such a four-component adiabatic dusty plasma are studied by the reductive perturbation method. It is found that the presence of the positive dust component does not only significantly modify the basic properties of the solitary waves, but also causes the existence of the positive solitary potential structures, which is an interesting feature shown in an adiabatic dusty plasma with the dust of opposite polarity. It is also observed that the basic properties (polarity, speed, amplitude and width) of the DA SWs are significantly modified by the effects of adiabaticity (γ>1) of electrons, ions, negatively as well as positively charged warm dust. The present investigation can be of relevance to the electrostatic solitary structures observed in various dusty space plasma environments (viz. cometary tails, upper mesosphere, Jupiter’s magnetosphere, etc.).     

Bifurcations of dust acoustic solitary waves and periodic waves in an unmagnetized plasma with nonextensive ions

Bifurcations of dust acoustic solitary waves and periodic waves in an unmagnetized plasma with q-nonextensive velocity distributed ions are studied through non-perturbative approach. Basic equations are reduced to an ordinary differential equation involving electrostatic potential. After that by applying the bifurcation theory of planar dynamical systems to this equation, we have proved the existence of solitary wave solutions and periodic wave solutions. Two exact solutions of the above waves are derived depending on the parameters. From the solitary wave solution and periodic wave solution, the effect of the parameter (q) is studied on characteristics of dust acoustic solitary waves and periodic waves. The parameter (q) significantly influence the characteristics of dust acoustic solitary and periodic structures.     

Detection of ionospheric perturbation due to a soft gamma ray repeater SGR J1550-5418 by very low frequency radio waves

The properties of cylindrical and spherical dust acoustic (DA) solitary and shock waves in an unmagnetized electron depleted dusty plasma consisting of inertial dust fluid and ions featuring Tsallis statistics are investigated by employing the reductive perturbation technique. A Korteweg-de Vries Burgers (KdVB) equation is derived and its numerical solution is obtained. The effects of ion nonextensivity and dust kinematic viscosity on the basic features of DA solitary and shock waves are discussed in nonplanar geometry. It is found that nonextensive nonplanar DA waves behave quite differently from their one-dimensional planar counterpart.     

DuneXpress

The DuneXpress observatory will characterize interstellar and interplanetary dust in-situ, in order to provide crucial information not achievable with remote sensing astronomical methods. Galactic interstellar dust constitutes the solid phase of matter from which stars and planetary systems form. Interplanetary dust, from comets and asteroids, represents remnant material from bodies at different stages of early solar system evolution. Thus, studies of interstellar and interplanetary dust with DuneXpress in Earth orbit will provide a comparison between the composition of the interstellar medium and primitive planetary objects. Hence DuneXpress will provide insights into the physical conditions during planetary system formation. This comparison of interstellar and interplanetary dust addresses directly themes of highest priority in astrophysics and solar system science, which are described in ESA’s Cosmic Vision. The discoveries of interstellar dust in the outer and inner solar system during the last decade suggest an innovative approach to the characterization of cosmic dust. DuneXpress establishes the next logical step beyond NASA’s Stardust mission, with four major advancements in cosmic dust research: (1) analysis of the elemental and isotopic composition of individual interstellar grains passing through the solar system, (2) determination of the size distribution of interstellar dust at 1 AU from 10^− 14 to 10^− 9 g, (3) characterization of the interstellar dust flow through the planetary system, (4) establish the interrelation of interplanetary dust with comets and asteroids. Additionally, in supporting the dust science objectives, DuneXpress will characterize dust charging in the solar wind and in the Earth’s magnetotail. The science payload consists of two dust telescopes of a total of 0.1 m² sensitive area, three dust cameras totaling 0.4 m² sensitive area, and a nano-dust detector. The dust telescopes measure high-resolution mass spectra of both positive and negative ions released upon impact of dust particles. The dust cameras employ different detection methods and are optimized for (1) large area impact detection and trajectory analysis of submicron sized and larger dust grains, (2) the determination of physical properties, such as flux, mass, speed, and electrical charge. A nano-dust detector searches for nanometer-sized dust particles in interplanetary space. A plasma monitor supports the dust charge measurements, thereby, providing additional information on the dust particles. About 1,000 grains are expected to be recorded by this payload every year, with 20% of these grains providing elemental composition. During the mission submicron to micron-sized interstellar grains are expected to be recorded in statistically significant numbers. DuneXpress will open a new window to dusty universe that will provide unprecedented information on cosmic dust and on the objects from which it is derived.     

Korteweg-de Vries equation for ion acoustic soliton with negative ions in the presence of nonextensive electrons

Korteweg-de Vries (KdV) equation for electrostatic ion acoustic wave in a three component plasma containing positive and negative ions along with the nonextensive electrons is derived. Fast and slow ion acoustic modes which propagate with different velocities are excited. The effects of variation of quantities like q (nonextensive parameter), Q (mass ratio of positive to negative ion), μ (electron to positive ion number density ratio), θ _i (positive ion to electron temperature ratio) and θ _n (negative ion to electron temperature ratio) have been presented for fast and slow ion acoustic modes. Both compressive and rarefactive solitons are observed. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as on nonextensive electron parameter.     

Scalar field as dark energy accelerating expansion of the Universe

The features of a homogeneous scalar field ϕ with classical Lagrangian L = ϕ_;i ϕ^;i /2 − V(ϕ) and tachyon field Lagrangian L = −V(ϕ)√1 − ϕ_;i ϕ^;i causing the observable accelerated expansion of the Universe are analyzed. The models with constant equation-of-state parameter w _de = p _de/ρ_de < −1/3 are studied. For both cases the fields ϕ(a) and potentials V(a) are reconstructed for the parameters of cosmological model of the Universe derived from the observations. The effect of rolling down of the potential V(ϕ) to minimum is shown. Published in Ukrainian in Kinematika i Fizika Nebesnykh Tel, 2008, Vol. 24, No. 5, pp. 345–359. The article was translated by the authors.     

Compressive and rarefactive dust-acoustic Gardner solitons beyond the K-dV limit with two-temperature ions dusty plasma

The Gardner equation is derived and numerically solved. This equation shows the existence of compressive and rarefactive dust-acoustic (DA) solitons with two-temperature ions beyond the K-dV (Korteweg–de Vries) limit. These may be referred to as DA Gardner solitons (DA-GSs). Here we deal with a dusty plasma, composed of negatively charged cold mobile dust fluids, inertialess Boltzmann electrons and ions with two distinctive temperatures. The basic features of the compressive and rarefactive DA solitons are identified. These solitons are found to exist beyond the K-dV limit, i.e. they exist for μ _i1～μ _c. Here μ _i1=n _i10/Z _d n _d0, Z _d is the number of electrons residing upon the dust grain surface, and n _i0 (n _d0) is the lower temperature ion (dust) number density at equilibrium. These DA-GSs are completely different from the K-dV solitons, because μ _c (the critical value) corresponds to vanishing of the nonlinear coefficient of the K-dV equation, and μ _i1～μ _c corresponds to K-dV solitons, with extremely large amplitude, for which the validity of the reductive perturbation method breaks down. It has been found that, depending on whether the parameter μ _i1 is less than or greater than the critical value, the DA-GSs exhibit compression for μ _i1>μ _c and rarefaction for μ _i1<μ _c. The basic features of double layers with arbitrary amplitude are also briefly discussed, employing the pseudo-potential approach. The present investigation might be relevant to the electrostatic solitary structures observed in various cosmic dust-laden plasmas, such as supernova shells, Saturn’s F-ring, the ionopause of Halley’s comet, etc.     

Influence of arbitrarily charged dust and trapped electrons on propagation of localized dust ion-acoustic waves

A theoretical investigation is developed to study the existence, formation and basic properties of arbitrary amplitude dust ion-acoustic solitary potentials in a dusty plasma consisting of warm ions, trapped electrons and immobile negative (positive) dust particles. It is found a definite interval for the Mach number for which solitary waves exist and depend sensitively on the ion temperature and negative (positive) dust concentration. In addition, the effects of ion temperature, two oppositely charged dust species and resonant electrons on the shape of the solitary waves are also investigated extensively. For both cases of negative and positive dust grains, the effect of ion temperature is found to be destructive for the formation of localized structures. Further, the amplitude of the solitary structures decreases (increases) with the increase in the negative (positive) dust concentration.