共查询到20条相似文献,搜索用时 15 毫秒
1.
Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L = 4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1 MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms. 相似文献
2.
The first observation of hiss-triggered discrete chorus riser emissions recorded during daytime at our newly setup low latitude
ground station Srinagar (geomag. lat., 24° 10′ N; L = 1.28), India on March 30, 2009 are reported. From the spectral analysis
of these emissions, it is found that the chorus is hiss-triggered and each chorus element has the tendency to originate from
the hiss band. A possible generation mechanism of these hiss-triggered chorus riser emissions is proposed. 相似文献
3.
A new type of discrete VLF emissions recorded at the low-latitude ground station Varanasi (geomag. lat. 14°55′ N, geomag.
long. 154°E;L = 1.07) during the strong magnetic activity on 29–30 April 1990 have been reported. A generation mechanism for various temporal
and spectral features of discrete VLF emissions recorded at Varanasi is presented on the basis of cyclotron resonance interaction
between whistler mode wave and energetic electrons ejected by substorm electric fields. An attempt is also made to determine
parallel energy and wave growth relevant to the generation process of discrete VLF emissions. Finally, our results are discussed
with other published works 相似文献
4.
Excitation of chorus-like waves by temperature anisotropy in dipole research experiment (DREX): A numerical study
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Due to their significant roles in the radiation belts dynamics, chorus waves are widely investigated in observations,experiments, and simulations. In this paper, numerical studies for the generation of chorus-like waves in a launching device,dipole research experiment(DREX), are carried out by a hybrid code. The DREX plasma is generated by electron cyclotron resonance(ECR), which leads to an intrinsic temperature anisotropy of energetic electrons. Thus the whistler instability can be excited in the device. We then investigate the effects of three parameters, i.e., the cold plasma density nc, the hot plasma density nh, and the parallel thermal velocity of energetic electrons, on the generation of chorus-like waves under the DREX design parameters. It is obtained that a larger temperature anisotropy is needed to excite chorus-like waves with a high nc with other parameters fixed. Then we fix the plasma density and parallel thermal velocity, while varying the hot plasma density. It is found that with the increase of nh, the spectrum of the generated waves changes from no chorus elements, to that with several chorus elements, and then further to broad-band hiss-like waves. Besides, different structures of choruslike waves, such as rising-tone and/or falling-tone structures, can be generated at different parallel thermal velocities in the DREX parameter range. 相似文献
5.
We present the results of laboratory experiments in which the mechanisms of interaction of electron beams with whistler waves
in a magnetoplasma are studied. Different mechanisms of whistler generation during the injection of a modulated electron beam
in the plasma are studied, and the mechanism of conversion of the beam kinetic energy to radiation is demonstrated. The processes
of whistler wave generation by the modulated beam at the ˇ Cerenkov and Doppler resonances are analyzed in detail. The excitation
of whistler waves by means of a nonresonant mechanism of the transition radiation is studied. 相似文献
6.
A gyrating ion beam, with a ring-shaped distribution in velocity, supports negative energy beam modes near the harmonics of
beam gyro-frequency. An investigation of the non-linear interaction of high-frequency whistler waves with the negative energy
beam cyclotron mode is made. A non-linear dispersion relation is derived for the coupled modes. It is shown that a gyrating
ion-beam frequency upconverts the whistler waves separated by harmonics of beam gyro-frequency. The expression for the growth
rate of whistler mode waves has been derived. In Case 1, a high-amplitude whistler wave decays into two lower frequency waves,
called a low-frequency mode and a side band of frequency lower than that of pump wave. In Case 2 a high-amplitude whistler
wave decays into two lower frequency daughter waves, called the low-frequency mode and whistler waves. Generation mechanism
of these waves has application in space and laboratory plasmas. 相似文献
7.
N. C. Mondal S. K. Sarkar A. B. Bhattacharya P. Mali 《International Journal of Infrared and Millimeter Waves》2001,22(3):495-504
There is a dearth of results on rain height over Indian tropical stations.The results on rain height in relation to 0°C isotherm height over four stations having different latitudes are presented in this paper. Four stations have been chosen in such a way that all have different latitudes and are located in different geographical regions having different local weather conditions. The seaonal variation of rain height in relation to 0°C isotherm height has been found to be appreciable over the station located in Indian east coast and Gujarat region, while seasonal variation is not significant at lower and intermediate probability levels over the stations located in Indian south-east coast and island. The prevailing local weather conditions over different stations also have been discussed. Based on observed rain heights and rain rates, the attenuation of radio wave at different frequencies lying in the range from 10 GHz to 150 GHz for different probability levels over Indian south-east coastal station have been deduced and presented in this paper. 相似文献
8.
We study the influence of the magnetic-field inhomogeneity on the nonlinear dynamics of the absolute instability of whistler-mode
waves in the Earth’s magnetosphere in the presence of a step-like deformation in the distribution function of energetic electrons.
Development of this instability, implying the transition of the magnetospheric cyclotron maser to the regime of a backward-wave
oscillator (BWO), was proposed earlier as a generation mechanism of magnetospheric chorus emissions. We analyze the results
of numerical simulations of the simplified nonlinear equations describing the magnetospheric-BWO dynamics in the case of low
efficiency of wave-particle interactions. We found that the case of an inhomogeneous magnetic field where the system length
is much greater than the length characterizing the linear stage of the BWO regime has important specific features compared
with the case of a homogeneous medium. The main feature of the nonlinear wave dynamics in the magnetospheric BWO in an inhomogeneous
magnetic field consists in the fact that for a sufficiently large excess over the generation threshold, a sequence of separate
wave packets, i.e., discrete elements, is formed. The frequency within each packet varies in time, and these discrete elements
are close in their properties to the chorus elements observed in the magnetosphere. The results of calculations confirm the
quantitative estimates of parameters of chorus emissions, which were performed earlier on the basis of the BWO model.
†Deceased
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 977–987, November 2008. 相似文献
9.
We consider the nonlinear dynamics of absolute instability of whistler-mode waves in the Earth's magnetosphere in the presence
of a step-like deformation in the distribution function of energetic electrons. Development of this instability, implying
the transition of the magnetospheric cyclotron maser to the regime of a backward-wave oscillator (BWO), was proposed earlier
as a generation mechanism of magnetospheric chorus emissions. We derive simplified nonlinear equations describing the dynamics
of the magnetospheric BWO in the case of low efficiency of wave-particle interactions. Numerical simulations of these equations
confirm qualitative similarity of the laboratory and magnetospheric BWOs and justify quantitative estimates of parameters
of chorus emissions.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 719–729, September 2005. 相似文献
10.
A. G. Demekhov V. Yu. Trakhtengerts Y. Hobara M. Hayakawa 《Radiophysics and Quantum Electronics》1999,42(8):625-638
Recent analytical and numerical results concerning the role of the second-order cyclotron resonance effects in formation of
discrete emissions in the magnetosphere are reviewed. Peculiarities of whistler cyclotron interactions with energetic particles
having sharp (step-like or beam-like) distribution functions evolving in space and time are studied. Formation of such distributions
is considered, and an analytical self-consistent theory of the second-order cyclotron resonance effects is developed. In particular,
characteristics of electron beams produced by the interaction of a VLF wave packet from a ground-based transmitter are studied.
It is shown that spatial and temporal gradients of the parallel velocity of the beams formed can be opposite to the case of
a pure adiabatic motion of a single particle. Such a behavior can be significant for the generation of secondary emissions.
It is proven that the optimal conditions for the instability occur for a nonstationary quasi-monochromatic wavelets whose
frequency changes in time. The theory developed permits one to estimate the wave amplification and spatio-temporal characteristics
of these wavelets. Numerical results on beam formation and generation of secondary emissions are presented.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 713–727, August 1999. 相似文献
11.
The nonlinear generation of shear field and flow in whistler waves is considered. It is shown that a coherent parametric process leads to modulational instability of four waves whistler interaction. Growth rates for the flow/field are compared with published simulation results. 相似文献
12.
It is shown that there exists a new series of resonances due to the interaction between a whistler propagating along an ambient magnetic field and the particles which are trapped in a large amplitude electrostatic wave. These resonances seem to produce sideband growths of the whistler. 相似文献
13.
This paper contains the plasma maser interaction between high frequency nonresonant whistler R-mode and low frequency resonant
ion acoustic mode in a relativistic plasma. It shows that the whistler R-mode grows through the plasma maser interaction between
the relativistic electrons and the ion acoustic fluctuation.
相似文献
14.
Angana Goswami 《光谱学快报》2013,46(5):253-260
Bioluminescence emissions from fireflies have been well-studied for over a century. From the apparent features of the emitted light, conclusions have been drawn and hypotheses put forward on the characteristics of the highly efficient light emitting system. The basic emitter oxyluciferin, being chemically unstable, is difficult to study in isolation and, therefore, its analogs have been prepared and analyzed. In this letter, the lifetimes of the excited-state emitter oxyluciferin are measured, and an inference is drawn on the chemiluminescence reaction in vivo. The light from the Indian species of firefly Luciola praeusta contains three color-sectors: green, yellow, and red, and hence three optical filters are used to study time-resolved emissions from these sectors at different temperatures. All the three color-sectors are observed to be temperature sensitive in the time domain. An exponential variation of lifetime with temperature is observed for the emissions in these three regions. 相似文献
15.
In this paper we consider the plasma maser theory of whistler waves in the presence of ion cyclotron waves in a magnetized plasma. In a plasma with low frequency ion cyclotron turbulence and a high frequency test whistler wave, growth of the whistler wave takes place because of the turbulent bremsstrahlung interaction between the resonant electrons and the modulated electric fields. The growth rate of the whistler wave is calculated and the results discussed. 相似文献
16.
It is shown that the drift of plasma across a homogeneous magnetic field causes the generation of a wave electric field which, for waves propagating along the magnetic field in the whistler mode, is in the direction of the magnetic field. This leads to Landau damping of the wave field by the background electron distribution, simultaneously with amplification via the electromagnetic cyclotron instability. The drift velocity of the plasma for zero net growth of a whistler mode signal is calculated. It is suggested that such a process occurs in the equatorial region of the magnetosphere during a geomagnetic storm and accounts for the missing band of emissions at half the equatorial gyrofrequency. 相似文献
17.
《Physics letters. A》1988,127(2):99-101
Simplified equations for the nonlinear interaction between whistlers and magnetosonic waves are formulated. These equations describe all the different branches for modulational instabilities of whistler waves, and lead to dispersion relations which are the same as those found from the full set of equations. Our new equations are much more convenient than previously used equations in describing nonlinear whistler wave phenomena. 相似文献
18.
The radiation, resulting from the nonlinear interaction of whistler solitons, which act as localized antennae, with the upperhybrid
waves in the coronal loop, is shown to give rise to fine structures in solar radio bursts. All the observed features of microwave
spikes in radio flares,e.g. their frequency, polarization and short duration can be explained by the presence of about 106 solitons occupying a volume of ∼ 108 m3, provided this interaction takes place at low altitudes. However, if this interaction takes place close to the top of the
coronal loop, it gives rise to the isolated tadpole ‘eyes’ features in the dynamic spectra. About 109 solitons are needed to account for the observed flux of these ‘eyes’. 相似文献
19.
We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth's radiation belt L = 4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5 - 1 MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm. 相似文献
20.
The characteristic features of VLF hiss emissions during quiet and disturbed conditions observed at ground stations and on-board
satellites are summarized. The increased intensity of the hiss emissions during magnetic storm period is explained by considering
the enhanced flux of energetic electrons during magnetic storm period. The generation and propagation mechanism of VLF hiss
are also briefly discussed. 相似文献