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Том 60, № 12 (2018)
- Год: 2018
- Статей: 6
- URL: https://journals.rcsi.science/0033-8443/issue/view/15166
Article
Nonlinear Effects in the Weibel Instability
Аннотация
Using the particle-in-cell code, we performed numerical simulations of the Weibel instability in plasmas with a two-temperature Maxwellian distribution function. We found harmonics in the power spectrum of the Weibel-generated turbulent magnetic field, which permitted us to measure directly the magnitude of the nonlinear effects. It is shown that by the time of the instability saturation the nonlinear effects are insignificant in the case of a large initial anisotropy and are vanishing in the case of a small initial anisotropy, so that the nonlinearity is not the reason why the magnetic field stops to increase. The asymptotic form of the power spectrum of the magnetic field in the region of small scales is determined. It is demonstrated that the nonlinearity is essential for the generation of a large-scale magnetic field and therefore plays a crucial role at the stage of the magnetic field decay. Astrophysical applications of the obtained results are discussed.
931-941
Resonance Interaction of Relativistic Electrons with Ion-Cyclotron Waves. I. Specific Features of the Nonlinear Interaction Regimes
Аннотация
We analyze the resonant interaction of relativistic electrons with ion-cyclotron waves in the Earth radiation belts. Finite-length wave packets with variable frequencies and different amplitude profiles are considered. Specific features of the nonlinear interaction regimes are analyzed on the basis of solving numerically a system of equations of the particle motion along with the efficiency of this interaction for a single pass of the particle through the wave packet. In the first part of this work, the peculiarities of the trajectories of individual particles are analyzed. The influence of the shape of the wave packet on the well-known regimes, such as particle trapping by the wave field and particle phase bunching, which leads to a non-zero average variation in the pitch angle in an inhomogeneous medium, are considered. It is shown that a long stay of a particle near the separatrix on the phase plane in the region far from the saddle leads to a strong decrease in the pitch angle of the particle in the absence of the trapping as well. This nonlinear regime (directed scattering) is possible for comparatively low initial pitch angles. In this case, the value of the pitch angle decrease depends on the initial phase of the particle. It is shown that the trajectories corresponding to the directed scattering can be regarded as a transitional type of trajectories, between the trajectories of the untrapped and trapped particles. Quantitative estimates of variations in the pitch angle are obtained, and it is confirmed that the directed scattering and trapping of particles by the wave field can lead to electron precipitation into the loss cone.
942-959
Single-Station Location of Radio Emission Sources in the Decameter Wavelength Range Using a Wide-Aperture Direction Finder and a Chirp Ionosonde–Radio Direction Finder
Аннотация
We present the results of single-station location of radio emission sources on the mid-latitude Vasil’sursk—Rostov-on-Don path using a wide-aperture direction finder and a chirp ionosonde–radio direction finder. Methods for determining the arrival angles under conditions of multipath reception of radio signals are described. It is shown that when single- and double-hop propagation modes are separated by different direction-finding techniques, deviations of the arrival angles reach 5° in the azimuthal plane and up to 10◦ in the elevation plane, which is due to the traveling ionospheric disturbances. It is established that under conditions of a sporadic Es layer, the chirptransmitter azimuth with averaging over frequency and sounding sessions can be determined to an accuracy of 0.1°. When regular 1F and 2F propagation modes are used to estimate the chirptransmitter azimuth, the average errors are 0.5° and 1°–2°, respectively. An algorithm for solving the inverse problem, by which the coordinates of the radio emission sources can be determined from the arrival angles using both the IRI-2012 ionospheric prediction model and correction of the data from the vertical sounding station at the reception point, have been developed. It is shown that the average error in determining the range to radio emission sources is 13%.
960-977
Structure of Integral Equations of Diffraction by a Strip and a Section of a Circular Cylinder
Аннотация
We study thoroughly the structure of integral equations of diffraction of electromagnetic waves by a strip and a section of a circular cylinder. The theorems of existence and uniqueness are proved, and an example of calculations is considered.
978-987
Sensitivity and Resolution of a Heterodyne Receiver Based on the NbN HEB Mixer with a Quantum-Cascade Laser as a Local Oscillator
Аннотация
We present the results of experimental studies of the basic characteristics and operation features of a terahertz heterodyne detector based on the superconducting NbN HEB mixer and a quantum cascade laser as a local oscillator operating at a frequency of 2.02 THz. The measured noise temperature of such a mixer amounted to 1500 K. The spectral resolution of the detector is determined by the width of the local-oscillator spectral line whose measured value does not exceed 1 MHz. The quantum-cascade laser could be linearly tuned with respect to frequency with the coefficient 7.2 MHz/mA within the limits of the current oscillation bandwidth.
988-992
Diversity Reception Based on the Correlation Processing of Signals
Аннотация
In this paper, we propose a method of adaptive diversity reception using the correlation processing of information signals. It allows one to develop the theory and propose the diversity-reception schemes which do not employ the test signals. For the proposed method, a gain in the output signal-to-noise ratio becomes close to a similar gain for the diversity method using the test signals if the signal-to-noise ratio in the master diversity branch exceeds unity. In the case of Rayleigh fading in the communication channel, it is recommended to choose the branch withthe maximum signal-to-noise ratio as the master one.
993-999