共查询到20条相似文献，搜索用时 15 毫秒
1.
T. Takakura 《Solar physics》1977,52(2):429-461
Numerical analysis of quasi-linear relaxation has been made for four models of electron beam with a finite length travelling through the plasma. In Model 4, a model atmosphere of the corona is adopted and also an increase in the cross-section of the electron beam is taken into account. The electron velocity distribution generally becomes a quasi-plateau form in limited velocity and time ranges. If, however, collisional decay of the fast electrons is too strong and the initial beam density is not high enough, the plateau does not appear. Collisional damping of plasma waves cannot be neglected, since the growth rate of the waves is strongly suppressed by the appearance of the quasi-plateau.An approximate formula for the velocity distribution of the solar electrons passing through the corona has been derived analytically taking into account not only the interaction with plasma waves, but also the collisional damping of the plasma waves and collisions with thermal particles. By the use of this formula, we can easily compute the time profile of the plasma waves caused by these solar electrons at any given place in the interplanetary space. The validity of this semi-analytical approach is checked by the numerical analysis of Model 4, showing a satisfactory fit between the numerical and semi-analytical results.The direct application of this method to the problems of type III radio bursts is left to a later paper. 相似文献
2.
Using a kappa velocity distribution function for the electrons of the background plasma, the dynamics of a beam of hot electrons
streaming through the plasma and the generation of Langmuir waves are investigated in the frame work of quasilinear theory.
It is shown that the Langmuir waves are strongly damped by high energy tail of the Kappa distribution function. The spatial
expansion of the beam is reduced and the spectral density of Langmuir waves becomes narrower. The height of the plateau in
the beam distribution function increases at small velocities and the average velocity of beam is larger than that of a Maxwellian
distribution. The influence of Kappa velocity distribution function on the gasdynamical parameters is investigated. It is
found that, the height of plateau in the beam distribution function, and its lower velocity boundary are enhanced while, the
local beam width in velocity space decreases. 相似文献
3.
T. Takakura 《Solar physics》1982,75(1-2):277-292
It is demonstrated by a numerical simulation that both the whistler waves and plasma waves are excited by a common solar electron beam. The excitation of the whistler waves is ascribed to the loss-cone distribution which arises at a later phase of the passage of the beam at a given height due to a velocity dispersion in the electron beam with a finite length. It is highly probable that the fundamental of type III bursts are caused by the coalescence of the whistler waves and the plasma waves excited by a common electron beam, although the plasma waves must suffer induce scatterings by thermal ions to have small wave numbers before the coalescence to occur. 相似文献
4.
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
5.
T. Takakura 《Solar physics》1979,61(1):161-186
A simulation of normal type III radio bursts has been made in a whole frequency range of about 200 MHz to 30 kHz by the usage of the semi-analytical method as developed in previous papers for the plasma waves excited by a cloud of fast electrons. Three-dimensional plasma waves are computed, though the velocities of fast electrons are assumed to be one-dimensional. Many basic problems about type III radio bursts and associated solar electrons have been solved showing the following striking or unexpected results.Induced scattering of plasma waves, by thermal ions, into the plasma waves with opposite wave vectors is efficient even for a solar electron cloud of rather low number density. Therefore, the second harmonic radio emission as attributed to the coalescence of two plasma waves predominates in a whole range from meter waves to km waves. Fundamental radio emission as ascribed to the scattering of plasma waves by thermal ions is negligibly small almost in the whole range. On the other hand, third harmonic radio emission can be strong enough to be observed in a limited frequency range.If, however, the time integral of electron flux is, for example, 2 × 1013 cm–2 (>5 keV) or more at the height of 4.3 × 1010 cm (
p = 40 MHz) above the photosphere, the fundamental may be comparable with or greater than the second harmonic, but an effective area of cross-section of the electron beam is required to be very small, 1017 cm2 or less, and hence much larger sizes of the observed radio sources must be attributed to the scattering alone of radio waves.The radio flux density expected at the Earth for the second harmonic can increase with decreasing frequencies giving high flux densities at low frequencies as observed, if x-dependence of the cross-sectional area of the electron beam is x
1.5 or less instead of x
2, at least at x 2 × 1012 cm.The second harmonic radio waves are emitted predominantly into forward direction at first, but the direction of emission may reverse a few times in a course of a single burst showing a greater backward emission at the low frequencies.In a standard low frequency model, a total number of solar electrons above 18 keV arriving at the Earth orbit reduces to 12% of the initial value due mainly to the collisional decay of plasma waves before the waves are reabsorbed by the beam electrons arriving later. However, no deceleration of the apparent velocity of exciter appears. A change in the apparent velocity, if any, results from a change in growth rate of the plasma waves instead of the deceleration of individual electrons.Near the Earth, the peak of second harmonic radio flux as emitted from the local plasma appears well after the passage of a whole solar electron cloud through this layer. This is ascribed to the secondary and the third plasma waves as caused in non-resonant regions by the induced scattering of primary plasma waves in a resonant region. 相似文献
6.
L. Muschietti 《Solar physics》1990,130(1-2):201-228
The dynamics of fast electrons streaming from the Sun through the interplanetary plasma is reviewed from the kinetic viewpoint. How can a bump appear on the tail of the electron distribution function? How can the beam survive the beam-plasma instability and propagate up to 1 AU as observed? These two questions are discussed in light of the recent data acquired in situ on electron distributions, Langmuir waves, ion acoustic waves, and background density fluctuations. 相似文献
7.
The dynamics of an electron beam is considered when the initial electron distribution is localized in a space region. Analysis is conducted for the parameters of the beam and plasma that give radio emission. We demonstrate both numerically and analytically that beam electrons propagate as a beam-plasma structure at large distances. The speed of the beam-plasma structure is equal to half of the maximum velocity of the electrons involved in this structure. The structure conserves the shape of the initial spatial distribution of electrons. A plateau with a constant maximum velocity is formed at the electron distribution function in each spatial point. 相似文献
8.
C. C. Harvey 《Solar physics》1975,40(1):193-216
In an earlier paper (Harvey and Aubier, 1973) the large scale radial electron density gradient in the corona and solar wind was shown to cause the phase velocity of plasma waves to decrease as they propagate away from the Sun, thus leading to appreciable Landau damping of the plasma waves. It is proposed here that this same phase velocity decrease creates conditions which facilitate the stabilisation of a beam of exciter electrons of finite duration, provided that three conditions are fulfilled. Two of these conditions concern the velocity-time distribution of the exciter electrons at their point of ejection from the Sun, while the third is simply that, above a certain altitude, the coronal electron density decreases with altitude r faster than r ?2. The plasma wave source is then associated with the leading edge of the electron stream. The spatial density of the power converted into plasma waves is calculated as a function of position and time, and is shown to be independent of the nature of the stabilisation mechanism. The maximum of this power density is found to move outwards from the Sun at a uniform speed when a simple electron injection model with a Maxwellian velocity distribution is introduced. 相似文献
9.
On the hypothesis that the time profile of a type III burst corresponds directly to the flux of electron beam, the similarity of time profile is shown to be maintained even if the electron velocity decreases with distance provided that the time is normalized to unity at the time of maximum flux. The observed time profiles of type III bursts with simple shape seem to follow the similarity law in almost all frequency range. This evidence may indicate that the time profile, both the rising and decaying phases, of a type III burst should be attributed to a common origin, e.g., the time variation of exciter determined by the initial velocity distribution in the electron beam, instead of attributing the rising time to the beam length and the decay time to the damping of plasma waves after the passage of the electron beam. 相似文献
10.
V. G. Ledenev 《Solar physics》1994,149(2):279-288
The problem of energetic electron flux propagation in the solar coronal plasma is solved with due regard for the influence of the oppositely directed neutralizing cold electron flux and the kinematic escape effect of the electrons with different velocities. It is shown that the flux electrons are accelerated in the process of propagation, thus forming a beam, whose velocity is constant on rather long time scales. Three regimes can be realized in this case. In the first regime, plasma waves do not have time to be excited because they escape rapidly from resonance with the beam. In the second regime, waves are excited, but the beam does not have time to relax. The third regime is quasi-linear relaxation.The generation of solar type III radio bursts in the second regime of electron flux propagation is considered. 相似文献
11.
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
12.
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
13.
A specific combination of spectral fine structures in meter – decimeter dynamic spectra of solar radio burst emission is
reported in observations carried out at the Astrophysical Institute Potsdam. We describe and interpret the occurrence of zebra
patterns in fast drifting (type III burst-like) envelopes of absorbed continuum emission. A possible mechanism of the origin
of such an involved spectral pattern is put forward, leading to a necessarily multinonequlibrium component coronal plasma.
The suggested mechanism is based on the fact that during the passage of a fast electron beam through the corona the loss cone
instability (which is caused by electrons captured in a magnetic trap generating the continuum) is quenched. As result, a
fast drift burst appears in absorption, and the zebra pattern becomes visible on the low background emission. This zebra pattern
is generated by a group of electrons with a nonequilibrium distribution over transverse velocities. In the absence of the
beam the pattern is invisible against the background of the stronger continuum. It is shown that the mechanism is sensitive
to the distribution parameters of the different electron ensembles. Therefore the effect in dynamic radio spectra is comparatively
rare but its proper existence underlines that the simultaneous presence of different ensembles of electrons in the flaring
corona can be quite a frequent situation. This can explain some problems in deconvolving X-ray photon spectra to electron
energy spectra. 相似文献
14.
电子是太阳风粒子中最为重要的组分之一,它可以通过多种机制对太阳风产生影响.太阳风中的电子通常具有温度各向异性和束流两种非热平衡分布特征,这些偏离热平衡分布的特征可以通过波粒相互作用激发电子不稳定性和等离子体波动,激发的等离子体波动又可以通过波粒相互作用调制太阳风粒子的分布,从而加热太阳风中的背景粒子.因此电子动力学不稳定性在太阳风的演化过程中扮演了极为重要的角色.详细介绍了太阳风中常见的电子动力学不稳定性,并基于等离子体动力论,详细介绍太阳风传播过程中所出现的各种不稳定性,尤其是在近日球层和太阳大气区域所出现的电子声热流不稳定性以及低混杂热流不稳定性,并分析其波粒相互作用机制,以便更加深入地研究太阳风传播过程中的电子分布函数演化. 相似文献
15.
T. Takakura 《Solar physics》1982,78(1):141-156
Numerical simulation of type III bursts is made by the use of fully numerical scheme showing a general rule for obtaining a numerically stable difference scheme. Although the electron distribution function is one-dimensional in velocity space, the plasma waves is cylindrically symmetric two-dimensional in K-space.It is confirmed that the previous simulation made by the use of semi-analytical method assuming the plateau distribution of electron distribution is qualitatively correct, but the number density of electron beam to have a typical type III burst was overestimated by a factor of about 3.It is demonstrated that a tentative neglection of a term for the induced scattering of plasma waves into nonresonant K-range gives no remarkable effect on the energy loss of the electron beam, though the scattering is strong. The reason is that the scattering reduces the saturation level of plasma waves resulting in a reduction of the energy loss, while a part of the energy of electron beam is indirectly lost by the scattering. 相似文献
16.
IMP-6 spacecraft observations of low frequency radio emission, fast electrons, and solar wind plasma are used to examine the dynamics of the fast electron streams which generate solar type-III radio bursts. Of twenty solar electron events observed between April, 1971 and August, 1972, four were found to be amenable to detailed analysis. Observations of the direction of arrival of the radio emission at different frequencies were combined with the solar wind density and velocity measurements at 1 AU to define an Archimedean spiral trajectory for the radio burst exciter. The propagation characteristics of the exciter and of the fast electrons observed at 1 AU were then conpared. We find that: (1) the fast electrons excite the radio emission at the second harmonic; (2) the total distance travelled by the electrons was between 30 and 70% longer than the length of the smooth spiral defined by the radio observations; (3) this additional distance travelled is the result of scattering of the electrons in the interplanetary medium; (4) the observations are consistent with negligible true energy loss by the fast electrons. 相似文献
17.
It was found recently that fast electrons travel through the plasma of the solar corona in the form of beam-plasma structure
(BPS), which consists of electrons and Langmuir waves. In this paper the influence of scattering BPS Langmuir waves off plasma
ions (l+i=l+i) on BPS velocity is studied. We show that the maximum BPS velocity equals 0.35c, which is close to the velocity of Type III bursts sources. 相似文献
18.
H. Alinejad 《Astrophysics and Space Science》2010,325(2):209-215
For an unmagnetized collisionless electron–positron–ion plasma, the effects of trapped and non-thermal electron distributions
are incorporated in the study of arbitrary amplitude ion-acoustic solitary structures. Both highly and weakly analyses are
examined by deriving an energy integral equation involving the Sagdeev potential for the large amplitude limit, and obtaining
the non-linear partial-differential equations for the small but finite amplitude limit. It is shown that there exist ion-acoustic
solitary waves with qualitatively different structures in a way that depend on the population of trapped and non-thermal electrons.
In the presence of trapped electrons, fully non-linear analyses show that plasma can support only arbitrary amplitude compressive
solitary waves. On the other hand, a consideration of the fast or non-thermal electron distribution provides the possibility
of the coexistence of large amplitude compressive and rarefactive solitary waves, whereas both of them are decoupled in the
small amplitude limit. It is found that the effects of such electron distributions and positron concentration change the maximum
values of the Mach number and the amplitude for which solitary waves can exist. Furthermore, the non-thermally distributed
electrons provide a KdV equation in the small amplitude limit, whereas the trapped electrons give rise to a modified KdV equation
which exhibits a stronger non-linearity. 相似文献
19.
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
20.
T. Takakura 《Solar physics》1990,127(1):95-107
The Fokker-Planck equation is numerically solved to study the electron velocity distribution under steady heat conduction with an applied axial electric current in a model coronal loop.If the loop temperature is so high that the electron mean-free path is longer than the local temperature scale height along the loop, a velocity hump appears at about the local thermal electron velocity. The hump is attributed to cooler electrons moving up the temperature gradient to compensate for the runaway electrons moving down the gradient. If the ratio between the mean free path and temperature scale height is greater than about 2, negative absorption for the plasma waves can appear (waves grow). This effect is enhanced by the presence of axial electric current in the half of the coronal loop in which the electrons carrying the current are drifting up the temperature gradient. Thus, the plasma instability may occur in the coronal elementary magnetic flux tubes. Although the present paper is limited to show the critical condition and linear growth rate of the instability, the following scenarios may be inferred.If the flux tubes change from marginally stable to unstable against the plasma instability, due to an increase in the loop temperature, anomalous resistivity may suddenly appear because of the growth of plasma waves. Then a high axial electric field is induced that may accelerate particles. This could be the onset of impulsive loop flares.For a low electric current, if the loop temperature is sufficiently high to give the negative absorption for the plasma waves in a large part of the coronal loop, steady plasma turbulence may originate. This could be a source for the type I radio noise storm. 相似文献