共查询到20条相似文献，搜索用时 15 毫秒
1.
Presented is a new method for retrieving the topside electron density distribution from space-based observations of the total electron content. By assuming an adequate topside density distribution, the profile reconstruction technique utilizes ionosonde and oxygen-hydrogen ion transition level measurements for uniquely determining the unknown ion scale heights and the corresponding ion and electron density profiles. The method is tested on actual measurements from the CHAMP satellite. Important applications are envisaged, such as developing and evaluating empirical and theoretical ionosphere-plasmasphere models. 相似文献
2.
K. G. McClements 《Solar physics》1987,109(2):355-363
The conditions required for the stability of a steady-state electron beam propagating in the solar corona are determined using the quasi-linear theory. The growth rate for electron plasma waves in a magnetized plasma is evaluated, with the electron distribution function being given by an analytic solution of the linearized Fokker-Planck equation. It is shown that, when the gyrofrequency is less than the plasma frequency, the instability has a narrow angular range, with the maximum growth rate occuring along the magnetic field. A stability boundary in parameter space is determined, indicating that electron beams must be highly collimated at injection to be Langmuir unstable at any point in space. The implications of the results for alternative models of hard X-ray bursts are discussed and it is argued that Langmuir instability will not occur on either the trap model or the thermal model. Such models would, therefore, be refuted by the detection of a large flux of plasma microwave radiation associated with hard X-ray emission. 相似文献
3.
Thomas J. Zega Larry R. Nittler Henner Busemann Peter Hoppe Rhonda M. Stroud 《Meteoritics & planetary science》2007,42(7-8):1373-1386
Abstract— We describe a focused ion beam scanning electron microscope (FIB‐SEM) technique that enables coordinated isotopic and mineralogic analysis of planetary materials. We show that site‐specific electron‐transparent sections can be created and extracted in situ using a microtweezer and demonstrate that they are amenable to analysis by secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These methods greatly advance the ability to address several fundamental questions in meteoritics, such as accretion and alteration histories of chondrules and the origin and history of preserved nebular and presolar materials. 相似文献
4.
Yasunori Nejoh 《Astrophysics and Space Science》1996,235(2):245-253
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
5.
The propagation of dense electron beams and the interaction with the ambient plasmas are studied by using two-dimensional electrostatic simulations. When the width of the beam is of the order of electron gyro-radius, the beam electrons move across the magnetic field lines and the beam-plasma interaction becomes prominent with the reduced beam density. When the width of the beam is of the order of ion gyro-radius, the propagation of beam electrons is possible only with the formation of the ion channel. However, since the time scale of the ionic motion is much longer than that of the electronic motion, most of the beam electrons return back to the original beam injection region 相似文献
6.
The interaction between an artificially produced narrow beam of electrons and the upper atmosphere has been studied by the POLAR 5 electron accelerator “mother”-“daughter” rocket. It is shown how the beam develops a “halo” of scattered electrons and how the low energy electron population in this “halo” is produced partly during the ionization process (at low altitudes), partly by a “wave-plasma” interaction which accelerates the ionospheric background electrons. 相似文献
7.
Takashi Yamamoto 《Planetary and Space Science》1976,24(11):1073-1080
Models of acceleration of auroral electrons by electrostatic shock waves are considered based on the model electron beam, calculated by Evans (1974), to account for the observed precipitating electron fluxes. Electron populations in our models include a primary accelerated beam, originating from the plasma sheet, the secondary electrons and the energy-degraded and backscattered primary electrons produced by precipitating electrons of that beam. We find a feasible electrostatic shock model with appropriate ion populations from considerations on the conditions for the existence of shock solutions. 相似文献
8.
D. L. Ziegler J. H. Newman L. N. Goeller K. A. Smith R. F. Stebbings 《Planetary and Space Science》1982,30(12):1269-1274
In 1979 significant concentrations of singly and multiply charged sulfur ions were observed in the Io torus. Attempts to model these observations revealed a need for new fundamental cross section data. In response, laboratory measurements of the cross-sections for single, double, triple and quadruple ionization of sulfur atoms by electron impact are presented for collision energies from threshold to 500 eV. 相似文献
9.
T. Takakura 《Solar physics》1979,62(2):383-391
Numerical simulation for the type III solar radio bursts in meter wavelengths was made with the electron beam of a high number density enough to emit fundamental radio waves comparable in intensity with the second harmonic.This requirement is fulfilled if the optical thickness
1 for the negative absorption (amplification) becomes -23 to -25. Since
1 is roughly proportional to the time-integral of the electron flux of the beam, the intensity of the fundamental waves depends strongly on the parameters which determine the electron flux. Therefore, it is most unlikely that the harmonic pairs of type III bursts of the first and the second harmonics occur frequently with comparable intensities in a wide frequency range, say 200 MHz to 20 MHz, if we take the working hypothesis that the fundamental waves are caused by the scattering of electron plasma waves by thermal ions and amplified during the propagation along the beam.However, we cannot rule out the possibility that single type III bursts with short durations or group of such bursts are the fundamental waves emitted by the above mechanism, but only if the observed large size of the radio source can be attributed to the radio scattering alone. 相似文献
10.
Low frequency turbulence in the solar corona and fundamental radiation of type III solar radio burst
T. Takakura 《Solar physics》1979,62(2):375-382
On the basis of the previous numerical simulations, a new mechanism for the emission of the fundamental radio waves of solar radio type III bursts is presented. This hypothesis is to attribute the fundamental radio emission to the coalescence of the plasma waves with the low frequency turbulence, whistler or ion acoustic waves, pre-existing on the way of the electron beam which excite the plasma waves.It is estimated that ion acoustic waves could be occasionally unstable in the solar corona due to that drifting bi-Maxwellian distribution of electrons as observed in the solar wind, which is probably caused by collision-less heat conduction.It is also suggested that the reduced damping of the ion acoustic waves in such a distorted electron distribution in the corona may decrease the threshold electric current to cause the anomalous resistivity to be the onset of the solar flares. 相似文献
11.
12.
For the laboratory astrophysics community,those spectroscopic modeling codes extensively used in astronomy,e.g.Chianti,AtomDB,Cloudy and Xstar,cannot be directly applied to analyzing laboratory measurements due to their discrepancies from astrophysical cases.For example,plasma from an electron beam ion trap has an electron energy distribution that follows a Gaussian profile,instead of a Maxwellian one.The laboratory miniature for a compact object produced by a laser-driven implosion shows a departure from equilibrium,that often occurs in celestial objects,so we setup a spectral analysis system for astrophysical and laboratory(sasal) plasmas to act as a bridge between them,which benefits the laboratory astrophysical community. 相似文献
13.
H. Khalilpour 《Astrophysics and Space Science》2014,353(1):37-45
Dynamics of fundamental and second harmonic electromagnetic emissions are simulated in the solar wind plasma in the presence of non-thermal electron distribution function in which primary Langmuir waves are driven by an electron beam. The electron velocity distribution function is separated into two distributions representing the distribution of the ambient electrons (Maxwellian) and the suprathermal electrons (non-thermal electrons). The effects of the non-thermal electrons on the generation of primary Langmuir waves, emission rates of the fundamental (F) and harmonic waves (H) and their distributions are investigated. The both of the F and H emissions are sensitive to the characterizes of the non-thermal electrons. It is found that in the presence of non-thermal electrons the production of the Langmuir waves decreases and consequently the levels of fundamental and second harmonic waves are reduced. The emission rate of the fundamental transverse waves decreases and its peak moves slightly toward smaller wave-numbers. 相似文献
14.
Experimental and theoretical work on the transverse dimensions of meteoric plasma trains have not converged to provide generally
accepted values especially uncertain is the dependence of the train radii on meteor speeds. The roles of the meteoroid structure, fragmentation
and plasma processes such as ion–electron instabilities need establishing. Knowledge of the quantitative spatial distribution
of plasma in meteor trains is essential for a correct interpretation of fluxes and orbital characteristics. A current project
is described which employs the AMOR 26 MHz radar facility in conjunction with a frequency managed radar operating at longer
wavelengths designed to measure the ionization train radii, heights, atmospheric speeds and orbits of individual meteors. 相似文献
15.
Measurements of electron density, plasma potential, and mean ion mass from the Explorer 31 satellite and measurements of ion current, plasma potential, and ion composition from the Atmosphere Explorer C (AE-C) satellite were used in a comparative study with theory regarding the charged particle distribution in the near wake of an ionospheric satellite. The theoretical wake model of Parker (1976) has been used in the study. It is shown that theory and experiment agree fairly well in the angle-of-attack range between 90 and 135°. In that angular range even the neutral approximation (which treats ions as if they were neutral particles thus ignoring the influence of the electric field) gives fair agreement with the measurements. In the maximum rarefaction zone (145 < θ < 180°), however, the theoretical model overestimates the measured ion depletion (AE-C measurements) by several orders of magnitude. A similar conclusion is drawn from the comparison between theory and the Explorer 31 electron measurements where the theory also significantly overestimates the electron depletion. The study indicates that the discrepancies are mainly due to the use of a steady-state theory and of a single ion equation (using a mean ion mass). It is recommended that improved agreement between theory and experiment be obtained by the use of the timedependent Vlasov-Poisson equations with separate equations for the various ion species. 相似文献
16.
《Planetary and Space Science》1987,35(7):867-870
An attempt to give theoretical foundation for understanding the origin of electrostatic waves at electron gyrofrequency in the magnetosphere is presented. The electrostatic dispersion equation describ- ing wave propagation at electron gyrofrequency is investigated in different limiting cases. It is pointed out that this equation can describe weakly damped waves when the electron plasma frequency is above electron gyrofrequency. 相似文献
17.
Kinetic Alfven waves are examined in the presence of electron and ion beam and an inhomogeneous magnetic field with bi-Maxwellian distribution function. The theory of particle aspect analysis is used to evaluate the trajectories of the charged particles. The expressions for the field-aligned currents, perpendicular currents (with respect to B 0), dispersion relation and growth/damping rate with marginal instability criteria are derived. The effect of electron and ion beam and inhomogeneity of magnetic field are discussed. The results are interpreted for the space plasma parameter appropriate to the auroral acceleration region of the earth’s magnetoplasma. 相似文献
18.
V. V. Zharkova 《Solar physics》2008,251(1-2):641-663
In this paper the mechanisms responsible for observational features associated with sunquakes induced by different classes of solar flares are compared. The role of high-energy particle beams via Coulomb and Ohmic heating of the ambient plasma and nonthermal excitation and ionization is explored for different beam parameters at various atmospheric depths. On the one hand, only hard electron beams with high-energy fluxes are found producing extensive nonthermal hydrogen ionization, four orders of magnitude higher than in the quiet atmosphere. This excess ionization leads to the white-light flares associated with the seismic emission appearing simultaneously with hard X-ray emission and, consequently, to a strong increase of Ni-line emission observed as the seismic emission measured with the holographic technique. On the other hand, the ambient plasma hydrodynamic response to heating by such beam electrons forms hydrodynamic shocks just below the transition region, in the upper chromosphere, and they travel with supersonic velocity for up to five minutes before reaching the photosphere. These hydrodynamic responses caused by the beam electrons are maximized in the lower chromosphere for moderate electron beams because of their smaller Ohmic losses in the upper atmosphere compared to those for higher-energy electron beams whose bulk energy is deposited in the transition region. These shocks caused by electron beams can explain the observations of seismic emission by time?–?distance (TD) diagrams and the holographic method in M- and C-class flares, whereas to account for the quakes in X-class flares, high-energy quasi-thermal protons or power-law proton beams either by themselves or blended with electron beams are the most likely agents. Nonthermal ionization and excitation of lower atmospheric levels during the beam injection followed by thermo-conductive heating after the beam is stopped can contribute to the seismic signatures observed with the holographic technique caused by strong nonthermal ionization and back-warming heating occurring in the shock while it loses its energy by optically-thick radiation in the photospheric lines and continua. 相似文献
19.
The problem of producing the hard X-ray burst at the onset of solar flares may be thought of in terms of the problem of producing the non-thermal electrons which emit the X-rays via bremsstrahlung. Electron acceleration to relativistic energies without similar ion acceleration is difficult to achieve, even in an ad hoc theoretical model. Yet from global energetic considerations, it is not feasible to accelerate the electrons as a minor constituent of the total energetic particle population. Therefore, it is necessary to invoke a more sophisticated process for the electron acceleration. In this paper we describe a mechanism for achieving this via an initial acceleration of a neutralized ion beam. When such a beam impacts the chromosphere, the electrons start to scatter while the ions continue downwards, rapidly setting up an electric field which is either cancelled by the inflow of background chromospheric electrons or results in the runaway acceleration of beam electrons. In the former case the result is simply heating, whereas in the latter case much of the ion kinetic energy is transferred into electron kinetic energy. The final electron energy may be similar to the typical energy of the ions. The electrons that are accelerated are those in the neutral beam that experience an electric field greater than the critical Dreicer field. Thus there will be a low-energy cut-off to the electron spectrum which overcomes the well-known energetics problem at low energies with certain other spectral forms. 相似文献
20.
A previous study of electromagnetic radiation from a finite train of electron pulses is extended to an infinite train of such pulses. The electrons are assumed to follow an idealized helical path through a space plasma in such a manner as to retain their respective position within the beam. This leads to radiation by coherent spontaneous emission. The waves of interest in this region are the whistler slow (compressional) and fast (torsional) Alfvén waves. Although a general theory is developed, analysis is then restricted to two approximations, the short and long electron beam. Formulas for the radiation per unit solid angle from the short beam are presented as a function of both propagation and ray angles, electron beam pulse width and separation and beam current, voltage, and pitch angle. Similar formulas for the total power radiated from the long beam are derived as a function of frequency, propagation angle, and ray angle. Predictions of the power radiated are presented for representative examples as determined by the long beam theory. 相似文献