共查询到20条相似文献,搜索用时 31 毫秒
1.
E. G. Alexov 《等离子体物理论文集》1995,35(1):23-32
Backward waves in waveguides completely filled with magnetoactive plasma (gaseous or semiconductor plasma) have been investigated numerically. It is shown that two types of backward waves exist in such waveguides: cyclotron backward waves and waveguide HE-modes. While the cyclotron modes are backward waves at arbitrary system parameters (plasma density, magnetic field and waveguide radius), the waveguide backward waves appear only at certain values of there parameters. In addition the cyclotron backward waves can propagate at arbitrary wave-number kz and at arbitrary phase velocity. The backward waveguide modes exist only at limited values of kz and of phase velocities. 相似文献
2.
We present a new plasma-based method of guiding an electromagnetic pulse. The scheme consists of an inhomogeneous magnetic field and a uniform density plasma, in contrast to existing schemes that rely on transverse plasma density gradients but need not be magnetized. The refractive index of a magnetized plasma depends on the strength and direction of the magnetic field as well as the plasma density. A guiding channel is formed by using field inhomogeneity to generate the desired transverse profile of the index of refraction. The concept is analyzed with an envelope equation and, for the specific example of a wiggler magnetic field, with a two-dimension particle-in-cell simulation. A simplified model of this scheme as producing a magnetic wall in analogy to metallic waveguides is presented, for which corresponding approximate relations for the guided mode axial wavelength and radius are derived as functions of the plasma and magnetic field parameter. These are seen to be in good agreement with particle-in-cell simulation results. Since the desired inhomogeneity of the refractive index can be made easily when the electromagnetic wave frequency is close to the cyclotron frequency, this guiding scheme is most readily applied in the microwave regime. 相似文献
3.
4.
T. D. Kaladze A. B. Mikhailovskii L. V. Tsamalaschvili 《Czechoslovak Journal of Physics》1985,35(5):518-531
It is shown that the cyclotron excitation of fast magnetosonic waves by circulating α-particles in a tokamak reactor is possible. The general expression for the growth rate of such an excitation is obtained. The influence of the thermal motion of α-particles and background plasma damping on the growth rate is elucidated. Equations of the quasilinear relaxation of α-particles due to corresponding instability are obtained and analyzed. It is shown that, as a result of this relaxation, a spreading of the energetic spectrum of α-particles takes place, which is faster than that due to Coulomb collision. It is found that the quasilinear relaxation has a pulsating character and is accompanied by periodically repeating splashes of oscillations at harmonics of the cyclotron frequency of α-particles. 相似文献
5.
We study experimentally the effect of ionization self-channeling of waves at the whistler frequencies in a nonuniform magnetic field. It is shown that the formed plasma nonuniformity localizes the radiation from a short high-frequency source inside a discharge channel stretched along an external magnetic field. We found a possibility to control the parameters of the formed plasma-wave channel as well as the dispersion characteristics and structure of wave fields in wide limits by varying the magnetic field in a specified spatial region. We propose a method for the formation of a plasma resonator and test this method in the laboratory experiment. The spatial plasma and field distributions in this resonator are similar to those along a geomagnetic field tube of the magnetospheric resonator. We reveal the plasma instability in such a resonator in the vicinity of the frequency of electron bounce oscillations between magnetic mirrors. 相似文献
6.
A modulation of an electron beam density at frequencies lower than an ion cyclotron frequency enhanced the low frequency instability of broad band and heated plasma ions in a beam-plasma system. The heating of ions is explained by the stochastic process of a weakly turbulent plasma. 相似文献
7.
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
8.
Kan J.R. Akasofu S.-I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(2):83-108
The authors present a coherent picture of fundamental physical processes in three basic elements of the SW-I (solar wind-magnetosphere-ionosphere) coupling system: (i) the field-aligned potential structure which leads to the formation of auroral arcs; (ii) the magnetosphere coupling which leads to the onset of magnetospheric substorms; and (iii) the solar wind-magnetosphere dynamo which supplies the power for driving various magnetospheric processes. The field-aligned potential structure on auroral lines is forced into existence by the loss-cone constriction effect when the upward field-aligned current density exceeds the loss-cone thermal flux limit. The substorm onset occurs when the ionosphere responds fully to the enhanced magnetospheric convection driven by the solar wind. The energy is transferred from the solar wind to the magnetosphere by a dynamo process primarily on open field lines 相似文献
9.
A. G. Frank A. V. Artemyev L. M. Zelenyi 《Journal of Experimental and Theoretical Physics》2016,123(4):699-715
The main characteristics of current sheets (CSs) formed in laboratory experiments are compared with the results of satellite observations of CSs in the Earth’s magnetotail. We show that many significant features of the magnetic field structure and the distributions of plasma parameters in laboratory and magnetospheric CSs exhibit a qualitative similarity, despite the enormous differences of scales, absolute values of plasma parameters, magnetic fields, and currents. In addition to a qualitative comparison, we give a number of dimensionless parameters that demonstrate the possibility of laboratory modeling of the processes occurring in the magnetosphere. 相似文献
10.
《Waves in Random and Complex Media》2013,23(3):323-333
The characteristics of guided modes in circular waveguides of a uniaxial anisotropic chiral core and a cladding filled with anisotropic plasma are presented. The cladding region is assumed to be infinitely extended with an external applied magnetic field oriented along the direction of propagation in the waveguide. The characteristics equation for the modes in this waveguide are obtained. The variations of the propagation properties with the plasma parameters, chiral parameters, and the cyclotron frequency of plasma have been investigated. Particularly, the effects of the chirality and the cyclotron frequency of plasma on the magnitude and orientation of the energy flux of the guided modes for three kinds of uniaxial anisotropic chiral media have been numerically investigated. Comparisons of the computed results of the presented formulations with published results for some special cases confirm the accuracy of the presented analyses. 相似文献
11.
《Comptes Rendus de l''Academie des Sciences Series IV Physics》2000,1(7):975-980
In a previous report we had started a systematic study of the ballooning modes as the natural waves of the magnetospheric turbulence, substorm and reconnection. After many new results following from the very high mirror ratio of the magnetospheric plasma, summarized in this note, we explain the fundamental role of ion cyclotron instabilities generated by the closure of confinement currents, by field-aligned currents in a three-dimensional (3D) configurations resulting from the growth phase and (or) ballooning modes. These instabilities destroy the current system, dipolarize the magnetic field and are consequently the non linear missing piece of substorm phenomenology. An indirect proof of this theory (apart from observational evidence) is found in the fast heating of electrons, the so-called `dispersionless injection' and a smaller effect on the proton population (diffusion coefficients are in the minutes time scale for protons and seconds for electrons!). This magnetospheric mechanism is very likely operating in solar flares and is in fact an added stone to a 3D time-dependent reconnection and acceleration. 相似文献
12.
S. M. Grach 《Radiophysics and Quantum Electronics》1999,42(7):572-588
We consider effects related to acceleration of electrons by high-frequency plasma turbulence in the ionospheric F-region modified
by powerful radio waves. The threshold of avalanche growth of the number of accelerated particles due to additional ionization
is determined for pump-wave frequencies far from the multiple cyclotron resonance. The steady-state density of the accelerated
electrons is found for the above pump-frequency values taking into account both turbulent trapping in the accelerating layer
due to scattering of plasma waves and the return of electrons to this layer due to collisions. If the pump wave frequency
is close to the multiple cyclotron resonance, fast electron distribution with significant transverse anisotropy is formed.
Relaxation of this distribution due to collisions with charged particles outside the accelerating layer leads to the appearance
of a maximum over transverse velocities in the tail of the distribution function. We propose a generation mechanism for the
broad upshifted maximum feature in the spectrum of stimulated electromagnetic emission, which is related to the cyclotron
instability of the accelerated electrons. The instability occurs in the double-resonance region in which the pump frequency
is close to both the upper-hybrid and multiple-cyclotron frequency.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 42, No. 7, pp. 651–669, July 1999. 相似文献
13.
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
14.
The formation of the space-time structure of the intensity distribution for whistlers, as well as the content of the energetic electrons in the radiation belts of Jupiter, has been considered. Parametric nonlinear processes in a plasma magnetospheric maser have been analyzed. It has been shown that, owing to the azimuthal inhomogeneity of a magnetic trap in combination with the fast rotation of the planet, a component that is characterized by the periodic modulation and is independent of the azimuth coordinate is formed in the Q factor of the magnetospheric resonator. This modulation is manifested as an external force that ensures the synchronization of oscillations in the level of whistlers in individual magnetic field tubes under the global-resonance conditions. 相似文献
15.
Parks GK Lee E Lin N Mozer F Wilber M Dandouras I Rème H Lucek E Fazakerley A Goldstein M Gurgiolo C Canu P Cornilleau-Wehrlin N Décréau P 《Physical review letters》2007,98(26):265001
Solitary nonlinear (deltaB/B>1) electromagnetic pulses have been detected in Earth's geomagnetic tail accompanying plasmas flowing at super-Alfvénic speeds. The pulses in the current sheet had durations of approximately 5 s, were left-hand circularly polarized, and had phase speeds of approximately the Alfvén speed in the plasma frame. These pulses were associated with a field-aligned current J(parallel) and observed in low density (approximately 0.3 cm(-3)), high temperature (T(e) approximately T(i) approximately 3x10(7) K), and beta approximately 10 plasma that included electron and ion beams streaming along B. The wave activity was enhanced from below the ion cyclotron frequency to electron cyclotron and upper hybrid frequencies. The detailed properties suggest the pulses are nonlinearly steepened ion cyclotron or Alfvén waves. 相似文献
16.
In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly
interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the
normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron
density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is
small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods. 相似文献
17.
This paper establishes two artificial neural network models by using a multi layer perceptron algorithm and radial based function algorithm in order to predict the plasma density in a plasma system.In this model,the input layer is composed of five neurons:the radial position,the axial position,the gas pressure,the microwave power and the magnet coil current.The output layer is the target output neuron:the plasma density.The accuracy of prediction is tested with the experimental data obtained by the Langmuir probe.The effectiveness of two artificial neural network models are demonstrated,the results show good agreements with corresponding experimental data.The ability of the artificial neural network model to predict the plasma density accurately in an electron cyclotron resonance-plasma enhanced chemical vapour deposition system can be concluded,and the radial based function is more suitable than the multi layer perceptron in this work. 相似文献
18.
在给定的等离子体总电流和中心电流密度条件下,数值求解平衡方程,求出不同拉长比和三角形变因子的托卡马克等离子体温度、密度、磁场分布,然后通过求解波迹方程和Fokker-Planck方程,分别计算这些位形下的电子回旋波波迹和电流驱动.结果表明:电子回旋波X模从顶部发射时,随着拉长比的增大,波迹会向弱场侧偏移.电子回旋波X模从弱场侧发射时,电子回旋波在等离子体中传播沉积的功率份额随着拉长比的增大而增加,驱动电流位置随着三角形变因子的增大向等离子体中心移动.驱动电流位置随环向和极向发射角的减小向中心移动,对应的电流密度峰值也变大. 相似文献
19.
20.
Maliheh Khatibi Moghaddam Amir Reza Attari Mir Mojtaba Mirsalehi 《Photonics and Nanostructures》2010,8(1):47-53
We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure. 相似文献