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1.
In the present study existence domains of large amplitude dust–ion acoustic (DIA) solitary structures are analyzed in an unmagnetized and collisionless, electronegative plasma containing inertial positive and negative ions, inertialess superthermal electrons with two different temperatures and negatively charged stationary dust. Using the Sagdeev pseudopotential technique, the energy-balance equation has been derived and the critical values (lower and upper limits) of the Mach number are also determined. The effect of different physical parameters has been analyzed for the formation of these nonlinear structures. Also the critical values of different physical parameters have been determined to establish parametric regimes for the existence of positive/negative potential DIA solitary structures.  相似文献   

2.
It is shown that stationary turbulence consisting of an ensemble of small amplitude whistler wave packets becomes unstable against adiabatic perturbations. The rate of increase of the purely growing instability is presented. A stationary non-linear BGK solution for the whistler electric fields is obtained.  相似文献   

3.
The large amplitude Ion-acoustic solitons in collisionless plasma consisting of warm adiabatic ions, isothermal positrons and two-temperature distribution of electrons are investigated. Using pseudo-potential approach, an energy integral equation for the system has been derived which encompasses complete nonlinearity for the plasma system. The existence region of the solitons is analyzed numerically. It is found that for selected set of plasma parameters, both rarefactive and compressive solitons exist in the electron-positron-ion (EPI) plasma. It is also found that due to finite positron concentration both subsonic and supersonic rarefactive soliton exist in EPI plasma. An increase in finite ion temperature ratio decreases the amplitude of the rarefactive solitons. In the case of small amplitude, it is found that there exist supersonic compressive as well as rarefactive solitons simultaneously. The amplitude of the solitons decreases with increase in ion temperature ratio (σ), however an increase in positron concentration (α) and temperature ratio of positron to electrons (γ) increases the amplitude of the solitons. Effect of various plasma parameters on the characteristics of the solitons are discussed in detail. The results of the investigation may be helpful to understand the nonlinear structures in auroral plasma, pulsars and magnetospheric astrophysical environment as well as laboratory plasmas.  相似文献   

4.
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.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
Small amplitude dust-acoustic solitary waves in an unmagnetized dusty plasma consisting of electrons and two temperature ions obeying the q-nonextensive distribution are investigated. Employing reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived. From the solitonic solutions of KdV equation, the influence of nonextensivity of electrons as well as ions and dust concentration on the amplitude and width of dust-acoustic solitary waves has been studied. It is observed that both positive and negative potential dust acoustic solitary waves occur in this case. The modified KdV (mKdV) equation is derived in order to examine the solitonic solutions for the critical plasma parameters for which KdV theory fails. The parametric regimes for the existence of mKdV solitons and double layers (DLs) have also been determined. Positive potential double layers are found to occur in the present study.  相似文献   

8.
Taking into account of ion temperature effect, existence conditions of arbitrary amplitude solitary Kinetic Alfvén Waves (KAWs) in a plasma with q-nonextensive electrons are investigated by the conventional Sagdeev pseudo potential method. It is found that only solitons with density hump can exist, the amplitude of which depends sensitively on the parameter q, ion temperature ( \(\sigma= \frac{T_{i}}{T_{e}}\) ) and plasma β. There is an upper limit of solitary wave amplitude which decreases with increase of q, σ and β. The amplitude of solitary KAWs is found to increase with increase in ion temperature. The results obtained in the framework of Maxwellian distribution are reproduced when q→1.  相似文献   

9.
The stationary ion-acoustic double layer is investigated in a plasma with an electron beam. The condition of the existence sensitively depends on the parameters such as the electron beam temperature, the ion temperature, the beam density and the effect of the trapped electrons. The properties of the double layer are also depicted. It turns out that the electron beam velocity is relatively small. This investigation predicts new findings of the ion-acoustic double layers in a plasma with an electron beam.  相似文献   

10.
An attempt is made to account for the decimetre portion of the Type-IV solar radio bursts by plasma emission. Non-thermal electrons (E ～ 500 keV) trapped in a magnetic mirror (IVdm, burst source) having loss-cone gap distribution excite plasma waves which are transformed into transverse waves through non-linear scattering by ions. A good agreement was reached between the calculated spectrum and the observed fluxes for the event of 1972 August 2. A distribution of the number of non-thermal electrons with height, and a total number of 1032, were obtained. Also it was found that the Langmuir waves can accelerate some background thermal electrons to the MeV range.  相似文献   

11.
Investigation of nonlinear wave modulation of electron-acoustic solitary wave packets in planar as well as nonplanar geometry is carried out for an unmagnetized two temperature plasma composed of cold and hot (featuring q-nonextensive distribution) electrons with stationary ions. It is shown that in such plasma, propagation of EA wave packets is governed by a modified NLSE which accounts for the geometrical effect and the nonextensivity of the hot electron species. It is found that the nature of the modulational instabilities would be significantly modified due to the geometrical effects, density ratio α of the hot-to-cold electrons species as well as their temperature ratio θ. Also, there exists a modulation instability period for the cylindrical and spherical envelope excitations, which does not exist in the one-dimensional case. Furthermore, spherical EA solitary wave packets are more structurally stable to perturbations than the cylindrical ones. The relevance of the current study to EA wave modulation in auroral zone plasma is highlighted.  相似文献   

12.
In the gravity field of an asteroid with the second order and degree harmonics C 20 and C 22, the attitude stability of a spacecraft with two flexible solar arrays on a stationary orbit subjected to the fourth-order gravity gradient torque is investigated in this paper. The sufficient conditions of attitude stability of the spacecraft are obtained, the effect of the direction of the flexible solar arrays and some special cases are discussed. Taking the asteroids 4769 Castalia, 25143 Itokawa and the imaginary asteroids as examples, the attitude stability domains, determined by the sufficient conditions, of the spacecrafts moving on stationary orbits around them are presented. It is found that the attitude stability domains of the spacecraft with two flexible solar arrays are evidently different when the solar arrays are installed in different directions; the effect of the harmonics C 20 and C 22 of the asteroids has the significant influence on the attitude stability domains of the spacecrafts with flexible appendages moving on stationary orbits; in the certain case, the effect of the harmonics C 20 and C 22 of the asteroids has no influence on the attitude stability domains of the rigid spacecrafts moving on stationary orbits, but in the other cases, the effect of the harmonics C 20 and C 22 of the asteroids has also the significant influence on the attitude stability domains of the rigid spacecrafts moving on stationary orbits; whether the harmonics C 20 and C 22 of the asteroids are considered or not, the effect of flexible appendages decreases the attitude stability domains.  相似文献   

13.
The occurrence of superluminal motion in extragalactic radio sources is believed to be quite common. Among others, the geometrical scattering of radio radiation can also cause superluminal expansion and or motion and halo formation, In this paper, the effectiveness of the stimulated Raman scattering in producing these features is investigated. The scattering medium is a plasma whose position, density and temperature decide the rate and angle of scattering. When the radiation from a stationary and constant source gets scattered from a stationary plasma, a halo is formed around the source. However, the scattering of a rotating radiation beam does produce superluminal motion of the virtual source. It is found that the plasma should have the characteristics of the emission-line regions and the intercloud medium in order to Raman scatter the radiation. Since the scattering is polarization dependent, it is possible to estimate the rotation of the electric vector along the direction of the apparent motion of a radio source.  相似文献   

14.
C. E. Parnell 《Solar physics》2007,242(1-2):21-41
The magnetic fields within the solar atmosphere have a complex topology owing to the fragmentary nature with which they thread the solar surface. The topologies of the potential magnetic fields containing only a few (up to four) point photospheric sources have been classified. For small numbers of sources determining the connectivity of source pairs is equivalent to counting the number of flux domains. As the numbers of sources increase this, however, is no longer the case. Instead, a pair of connected sources can have more than one distinct flux domain linking them. We call these multiply connected source pairs. Pairs of nulls connected by more than one separator are called multiply connected null pairs. Multiply connected source and null pairs go hand-in-hand such that two separators connecting the same pair of nulls immediately implies multiple flux domains linking the same source pair and vice versa. It is found that multiply connected source pairs are common not only in fairly complex potential magnetic fields but more interestingly in the resistive-MHD evolution of both simple and complex magnetic fields. Magnetic energy release is often significant around separators. Thus fields with multiply connected source pairs, which naturally have more separators, (i) have more sites for intense energy release and (ii) are likely to release energy more quickly than other magnetic fields. Moreover, the combination of multiply connected source and null pairs can give rise to a situation where flux is reconnected repeatedly between two flux domains.  相似文献   

15.
High-resolution ultraviolet spectrophotometry of the complex close binary systemβ Lyrae was performed with the Princeton Telescope Spectrometer onCopernicus. Observations were made at phases 0.0, 0.25, 0.5, and 0.75 with the resolution of 0.2 Å (far-ultraviolet) and 0.4 Å (mid-ultraviolet). The far-ultraviolet spectrum is completely dominated by emission lines indicating existence of high temperature plasma in this binary. The spectrum ofthis object is unlike any other object observed fromCopernicus. It is believed that this high temperature plasma results from dynamic mass transfer taking place in this binary. The current results are compared with the OAO-2 Wisconsin Experiment Package observations and other observational results. The possibility that the secondary component is a collapsed object is also discussed; theCopernicus observations are consistent with the hypothesis that the spectroscopically invisible secondary component is a black hole.  相似文献   

16.
The electrostatic shocks and solitons are studied in weakly relativistic and collisional electron-positron-ion plasmas occurring in polar regions of pulsar. The plasma system is composed of relativistically streaming electrons, positrons while ions are taken to be stationary. Dissipative effects in the system are due to collision phenomena among the constituents of relativistic plasma. Nonlinear dynamics of the dissipation and dispersion dominated relativistic plasma systems are governed by Korteweg-de Vries Burger (KdVB) and Korteweg-de Vries (KdV) equations respectively. Numerical results, exploring the effects of plasma parameters on the profile of nonlinear waves are expedited graphically for illustration. Positron to electron temperature ratio plays the role of a decisive parameter. It is noticed that compressive shocks and solitons evolve in the system if the positron to electron temperature ratio is less than a critical value. However, there exists a threshold value of positron to electron temperature ratio beyond which the system supports the rarefactive shocks and solitons. The results may have importance in the relativistic plasmas of pulsar magnetosphere.  相似文献   

17.
Seeking to establish whether active-region upflow material contributes to the slow solar wind, we examine in detail the plasma upflows from Active Region (AR) 10978, which crossed the Sun’s disc in the interval 8 to 16 December 2007 during Carrington rotation (CR) 2064. In previous work, using data from the Hinode/EUV Imaging Spectrometer, upflow velocity evolution was extensively studied as the region crossed the disc, while a linear force-free-field magnetic extrapolation was used to confirm aspects of the velocity evolution and to establish the presence of quasi-separatrix layers at the upflow source areas. The plasma properties, temperature, density, and first ionisation potential bias [FIP-bias] were measured with the spectrometer during the disc passage of the active region. Global potential-field source-surface (PFSS) models showed that AR 10978 was completely covered by the closed field of a helmet streamer that is part of the streamer belt. Therefore it is not clear how any of the upflowing AR-associated plasma could reach the source surface at 2.5 R⊙ and contribute to the slow solar wind. However, a detailed examination of solar-wind in-situ data obtained by the Advanced Composition Explorer (ACE) spacecraft at the L1 point shows that increases in O7+/O6+, C6+/C5+, and Fe/O – a FIP-bias proxy – are present before the heliospheric current-sheet crossing. These increases, along with an accompanying reduction in proton velocity and an increase in density are characteristic of both AR and slow-solar-wind plasma. Finally, we describe a two-step reconnection process by which some of the upflowing plasma from the AR might reach the heliosphere.  相似文献   

18.
The problems of large amplitude double layers are discussed using Sagdeev’s pseudo-potential technique for a dusty plasma comprising two temperature isothermal ions and nonextensive nonthermal velocity distributed electron. For different sets of plasma parameter values, the Sagdeev potential V(?) has been plotted. It is found that nonextensive q parameter plays a significant role in determining the shape and size of large amplitude double layers. Also, it is observed that the existence of large amplitude double layers depends on different plasma parameters.  相似文献   

19.
The procedure developed in Smith (1974) to model the radiation source for type III bursts is modified to include scattering of radiation in the source itself. Since the inhomogeneities in the source must have the same statistical properties as the inhomogeneities used in tracing radiation from the source to the observer, these two parts of the type III problem are no longer uncoupled. Thus we use inhomogeneities consistent with the scattering inhomogeneities of Steinberg et al. (1971) and Riddle (1974) and apply the procedure to an archetype ‘fundamental-harmonic’ pair observed at Culgoora on 28 September, 1973 at 0319 UT. We find that it is impossible to model this burst with a source which is homogeneous in the sense that every part of the source has the same energy density in plasma waves. The density inhomogeneities in the source severely hamper amplification of the supposed fundamental. Possible ways out of this dilemma are discussed, including second harmonic pairs and a source with an inhomogeneous distribution of plasma waves. It is concluded that none of the possibilities are completely satisfactory to explain present observations and suggested that critical observations are missing.  相似文献   

20.
In our article (Zhuravlev, 1979) a formal method of constructing conditionally periodic solutions of canonical systems of differential equations with a quick-rotating phase in the case of sharp commensurability was presented. The existence of stationary (or periodic) solutions of an averaged system of differential equations corresponding to the initial system of differential equations is necessary for an effective application of the method for different problems.Evidently, the stationary solutions do not always exist but in numerous papers on stationary solutions (oscillations or motions), the conditions of existence of such solutions are very often not considered at all. Usually a simple assumption is used that the stationary solutions do exist.Otherwise it is well known that Poincaré's theory of periodic solutions (Poincaré, 1892) let one set up conditions of existence of periodic solutions in different systems of differential equations. Particularly, in papers,Mah (1949, 1956), see alsoexmah (1971), the necessary and sufficient conditions of the existence of periodic solutions of (non-canonical) systems of differential equations which are close to arbitrary non-linear systems are given. For canonical autonomous systems of differential equations the conditions of existence of periodic solutions and a method of calculation are presented in the paperMepmah (1952).In our paper another approach is given and the conditions of existence of stationary solutions of canonical systems of differential equations with a quick-rotating phase are proved. For this purpose Delaunay-Zeipel's transformation and Poincaré's small parameter method are used.  相似文献   

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