共查询到20条相似文献，搜索用时 31 毫秒
1.
Krzysztof Stasiewicz 《Planetary and Space Science》1984,32(3):379-389
On the basis of quasi-linear theory of ion-acoustic turbulence it is shown that the angular and energy distribution of the electron spectra observed in quasi-static inverted-V structures are natural products of electron heating and runaway processes occuring in a region of current-driven turbulence located at h ≈ 1 Re. The power law population J ∞ E?γ, with γ ≈ 1 observed in the energy range ~ 25–1000 eV, is interpreted as a quasi-stationary distribution of suprathermal electrons interacting resonantly with the ion sound waves. This spectrum is generated in the turbulent region and convectively transported earthward along the magnetic field lines. Field-aligned intense electron fluxes with collimation angle < 10° are explained as due to particles escaping from the turbulent region through the runaway cone—a characteristic feature of velocity-space in ion-acoustic turbulence. A complete, new interpretation of the observed electron spectra is given on the basis of the proposed physical acceleration mechanism along with many other implications of this theory. 相似文献
2.
《Chinese Astronomy and Astrophysics》1983,7(2):124-129
Starting with the quasi-linear equation of the distribution function of particles in a regular electric field, a combined diffusion coefficient in the momentum space conbining the effects of the regular field and a turbulent field is obtained and a combined mechanism of acceleration by the regular and turbulent fields in the neutral sheet of solar proton flares is proposed. It is shown by calculation that conditions in solar proton flares are such that the charged particles can be effectively accelerated to tens of MeV, even ~1 GeV. It is shown that the combined acceleration by a regular electric field and ion-acoustic turbulence pumps the protons and other heavy ions into ranges of energy where they can be accelerated by Langmuir turbulence. By considering the combined acceleration by Langmuir turbulence and the regular electric field, the observed spectrum of energetic protons and the power-law spectrum of energetic electrons can be reproduced. 相似文献
3.
The possibility is investigated that the plasma turbulence used in many recent models of the primary energy release and acceleration in solar flares should be detectable by radiation near the fundamental and second harmonic of the plasma frequency. Formulae are derived for fundamental emission due to the combination of ion-acoustic and Langmuir plasma turbulence and for second harmonic emission due to the combination of two Langmuir waves. These results are applied to recent primary energy release and acceleration models which shows that either such radiation should be detectable and possibly distinguishable with suitable microwave interferometers or that its absence places fairly stringent constraints on the possible level of Langmuir or Langmuir and ion-acoustic waves in these models.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
4.
Han Jiling 《Solar physics》1998,178(1):179-182
When ion-acoustic turbulence is fully developed, Coulomb collision damping and Landau collisionless damping can all be neglected. Since the electric field force is greater than the damping force, a coronal transient can be created by the acceleration caused by the electric field. Eruptive prominence and coronal mass ejection (CME) events can occur as a consequence of this mechanism. 相似文献
5.
The production mechanisms of backscattered electrons and trapped electrons along auroral field lines are examined. The backscattered electrons are produced not only by electron-neutral collisions, but also by electrostatic turbulence predominantly in the ion-cyclotron and ion-acoustic modes. The trapped electrons can only be produced by electron wave turbulence, most likely in the whistler and upper hybrid modes known as the auroral hiss. 相似文献
6.
Weak dust ion-acoustic (DIA) double- layers (DLs) in a dusty plasma with nonextensive electrons are addressed. A generalized Korteweg-de Vries equation with a cubic nonlinearity is derived. It is shown that under certain conditions, the effect of electron nonextensivity can be quite important. In particular, it may be noted that due to the net negative dust charge and electron nonextensivity, the present dusty plasma model may admit compressive as well as rarefactive weak DIA-DLS. Considering the wide relevance of nonlinear oscillations in space dusty plasmas, our investigation may be taken as a prerequisite for the understanding of the nonlinear structures observed in the ionosphere and the auroral acceleration regions. 相似文献
7.
Dean F. Smith 《Solar physics》1980,66(1):135-148
Requirements for the number of nonthermal electrons which must be accelerated in the impulsive phase of a flare are reviewed. These are uncertain by two orders of magnitude depending on whether hard X-rays above 25 keV are produced primarily by hot thermal electrons which contain a small fraction of the flare energy or by nonthermal streaming electrons which contain > 50% of the flare energy. Possible acceleration mechanisms are considered to see to what extent either X-ray production scenario can be considered viable. Direct electric field acceleration is shown to involve significant heating. In addition, candidate primary energy release mechanisms to convert stored magnetic energy into flare energy, steady reconnection and the tearing mode instability, transfer at least half of the stored energy into heat and most of the remaining energy to ions. Acceleration by electron plasma waves requires that the waves be driven to large amplitude by electrons with large streaming velocities or by anisotropic ion-acoustic waves which also require streaming electrons for their production. These in turn can only come from direct electric field acceleration since it is shown that ion-acoustic waves excited by the primary current cannot amplify electron plasma waves. Thus, wave acceleration is subject to the same limitations as direct electric field acceleration. It is concluded that at most 0.1% of the flare energy can be deposited into nonthermal streaming electrons with the energy conversion mechanisms as they have been proposed and known acceleration mechanisms. Thus, hard X-ray production above 10 keV primarily by hot thermal electrons is the only choice compatible with models for the primary energy release as they presently exist. 相似文献
8.
In high-speed solar wind, propagating Alfvén waves can be transferred into fast magnetosonic waves. When both the magnetic field strength and Alfvén wave velocity approach zero, fast magnetosonic waves will be transferred into ion-acoustic waves. As the phase velocity of ion-acoustic waves is slightly greater than the thermal velocity of protons, the turbulence energy of ion-acoustic waves can largely be absorbed by protons and can cause the mean temperature of protons to be greater than that of electrons by stochastic turbulence heating of ion-acoustic waves for protons. 相似文献
9.
The KdV equation is derived for weakly nonlinear ion-acoustic waves in an unmagnetized warm dusty plasma with electron inertia.
It has been shown that the inclusion of electron inertia and pressure variation of the species not only significantly modifies
the basic features (width and amplitude) of dust ion-acoustic solitions, but also introduces a new parametric regime for the
existence of positive and negative solitons. 相似文献
10.
Robert Selkowitz Eric G. Blackman 《Monthly notices of the Royal Astronomical Society》2007,382(3):1119-1123
We consider the dissipation by Fermi acceleration of magnetosonic turbulence in the Reynolds layer of the interstellar medium. The scale in the cascade at which electron acceleration via stochastic Fermi acceleration (STFA) becomes comparable to further cascade of the turbulence defines the inner scale. For any magnetic turbulent spectra equal to or shallower than Goldreich–Sridhar this turns out to be ≥1012 cm, which is much larger than the shortest length-scales observed in radio scintillation measurements. While STFA for such spectra then contradict models of scintillation which appeal directly to an extended, continuous turbulent cascade, such a separation of scales is consistent with the recent work of Boldyrev & Gwinn and Boldyrev & Konigl suggesting that interstellar scintillation may result from the passage of radio waves through the Galactic distribution of thin ionized boundary surfaces of H ii regions, rather than density variations from cascading turbulence. The presence of STFA dissipation also provides a mechanism for the non-ionizing heat source observed in the Reynolds layer of the interstellar medium. STFA accommodates the proper heating power, and the input energy is rapidly thermalized within the low-density Reynolds layer plasma. 相似文献
11.
A model for ion-acoustic waves in the solar atmosphere is presented. In the limit of strongly magnetized plasma this model leads to the Zakharov-Kuznetsov equation which possesses a flat solitary wave solution. An initial-value problem for this equation is solved numerically to show a transition of the flat solitary waves into spherical solitary waves. The paper suggests further developments of an ion-acoustic wave theory that may improve our knowledge of ion-acoustic waves and lead to the possibility of their being detected in the solar atmosphere. 相似文献
12.
V. Krishan 《Solar physics》1980,68(2):343-350
An energetic proton beam passing through a stationary ionized medium, excites ion-acoustic turbulence. The ion-acoustic instability saturates due to the non-linear indirect wave-particle scattering. The electric field associated with the ion-acoustic waves accelerates the plasma particles. Applicability of the results to cometary tails is discussed. 相似文献
13.
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
14.
The quasilinear theory of acceleration of relativistic particles by hydromagnetic turbulence is treated in the adiabatic limit of small gyration radius. The theory is based on the relativistic Vlasov equation; however, a given pitch-angle scattering rate by microturbulence is postulated and is added to this equation. The resulting acceleration is found to be given by a diffusion coefficient in total momentum, which is proportional to the spectrum of turbulence with a rate coefficient . is a frequency that represents the efficiency of each wave component of the turbulence in producing acceleration. It is given as an integral over the solution of a differential equation in pitch angle. is evaluated in various limiting cases and is shown to lead to familiar forms of acceleration, such as Fermi acceleration and magnetic pumping. Thus, a comprehensive theory of these forms of heating is achieved. 相似文献
15.
Weak ion-acoustic (IA) solitary wave propagation is investigated in the presence of electron trapping and background nonextensivity. A physically meaningful distribution is outlined and a Schamel-like equation is derived. The role a background electron nonextensivity may play on the energy carried by the IA soliton is then examined. It is found that nonextensivity may cause a soliton energy depletion. An increase of the amount of electron trapping leads to a net shift towards higher values of the soliton energy. 相似文献
16.
V. N. Tsytovich R. Bingham U. de Angelis D. A. Bryant C. M. C. Nairn 《Solar physics》1993,147(2):329-335
The possibility of accelerated protons in solar flares having a sharp change in their spectral index is discussed. The analysis is based on the Tsytovich (1982, 1984, 1987a, b, c) acceleration model by MHD turbulence, which is shown to have different resonant conditions for non-relativistic and relativistic particles. The different resonant condition is shown to result in a sharp change in the accelerated proton spectral index, even in the absence of any peculiarity in the spectra of the MHD turbulence. Time scales for accelerated protons to relativistic energies are also derived, and shown to be consistent with observations. We also show that the threshold energy for electron acceleration by low frequency MHD turbulence is much greater than for proton acceleration. The turbulence therefore preferentially accelerates protons. 相似文献
17.
A model of the cascading acceleration of quasi-thermal electrons by MHD turbulence in solar flares is considered. Analysis shows that fast magnetoacoustic wave modes with large wavenumbers (>3×10–8 cm–1) strongly damp due to ion viscosity for both preflare and flare conditions. The viscous damping of fast magnetoacoustic wave modes is 10–100 times more efficient than Fermi or transit-time electron acceleration. 相似文献
18.
M.J. Houghton 《Planetary and Space Science》1975,23(3):409-418
An astrophysical electron acceleration process is described which involves turbulent plasma effects: the acceleration mechanism will operate in ‘collision free’ magnetoactive astrophysical plasmas when ion-acoustic turbulence is generated by an electric field which acts parallel to the ambient magnetic lines of force. The role of ‘anomalous’ (ion-sound) resistivity is crucial in maintaining the parallel electric field. It is shown that, in spite of the turbulence, a small fraction of the electron population can accelerate freely, i.e. runaway, in the high parallel electric potential. The number density n(B) of the runaway electron component is of order , where n = background electron number density, cs = ion-sound speed and U∥? = relative drift velocity between the electron and ion populations. The runaway mechanism and the number density n(B) do not depend critically on the details of the non-linear saturation of the ion-sound instability. 相似文献
19.
The Ulysses Unified Radio and Plasma Wave Experiment (URAP) has observed Langmuir, ion-acoustic and associated solar type
III radio emissions in the interplanetary medium. Bursts of 50&#x2013;300 Hz (in the spacecraft frame) electric field
signals, corresponding to long-wavelength ion-acoustic waves are often observed coincident in time with the most intense Langmuir
wave spikes, providing evidence for the electrostatic decay instability. Langmuir waves often occur as envelope solitons,
suggesting that strong turbulence processes, such as modulational instability and soliton formation, often coexist with weak
turbulence processes, such as electrostatic decay, in a few type III burst source regions. 相似文献
20.
A. N. Kryshtal A. D. Voitsekhovska S. V. Gerasimenko M. V. Sidorenko 《Kinematics and Physics of Celestial Bodies》2014,30(5):234-243
The process of origination and development of instabilities of the longitudinal waves of two types, namely, low-frequency ion-acoustic and high-frequency (“electronic”) Langmuir waves, in the preflare atmosphere of an active solar region are studied. The area under study is located at the chromospheric part of the flare loop near its footpoint. A weak large-scale electric field of flaring loop is the main source of these instabilities. The velocity of an electronic flow in the preflare plasma is supposed to be much lower than thermal electron velocity. Instability development is considered against the background of small-scale Bernstein wave turbulence, which exists in the preflare plasma and has an extremely low threshold of excitation. The necessary conditions for the instability origination and development, as well as the boundary values of the main plasma and wave perturbation parameters, are calculated. 相似文献