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Vol 60, No 2 (2017)
- Year: 2017
- Articles: 9
- URL: https://journals.rcsi.science/0033-8443/issue/view/15156
Article
Study of the Plasma Turbulence Dynamics by Measurements of Diagnostic Stimulated Electromagnetic Emission. Part II. Results of Numerical Simulation
Abstract
The data on measured dynamic characteristics of diagnostic stimulated electromagnetic emission (SEE) of the ionosphere are presented. Numerical simulations of the SEE evolution within the framework of a theoretical model of the broad-continuum SEE feature with the use of improved (3D) empirical model of the spatial spectrum of artificial irregularities of the HF pumped ionospheric plasma are performed and compared with the measurement data. Possible applications of such a comparison for determining the spectrum parameters and studying the evolution of the geomagnetic field-aligned artificial irregularities (striations) are discussed. It is concluded that changes in the intensity and spectrum shape of the striations, mainly for transverse scales l⊥ ~ 2–18 m, play the decisive role in the observed variations of the magnitude and temporal characteristics of the overshoot effect (formation of the intensity maximum followed by the suppression of the ionospheric SEE intensity).
89-102
Internal Gravity Waves in the Lower Thermosphere with Linear Temperature Profile: Theory and Experiment
Abstract
The problem of internal gravity waves in a medium with linear altitude profile of equilibrium temperature as applied to the experiments related to the creation of artificial periodic irregularities and diagnostics of the neutral atmosphere at the altitudes of the E region is considered. A solution to the initial linearized system of equations for weak disturbances of the thermospheric parameters, such as pressure, density, temperature, and velocity of the medium, is obtained. Among a large array of experimental data on the temperature profiles of the neutral component, the sessions in which the altitude dependence of the equilibrium temperature was well approximated by a linear function were selected. The characteristics of internal gravity waves obtained for such a temperature profile are compared with the results of measuring the atmospheric parameters. Satisfactory agreement between the theoretical and experimental values of the quantities being determined is established, which confirms the validity of the chosen model.
103-112
Realization of a Radiometric Channel as Part of the Microwave Sensing Complex in the Presence of Permanent Intrasystem Narrowband Interference
Abstract
We consider the problem of realization of a radiometric channel as part of the microwave sensing complex in the presence of permanent intrasystem narrowband interference. A method of radiometric-channel calibration and radiometric-signal processing is proposed. The results of the experiments on determining the dependences of the radiometric-channel calibration coefficients on the quasiharmonic-interference amplitude are presented.
113-118
Plasmon Resonances in an Elliptical Gold Cylinder
Abstract
We study plasmon resonances, which arise in the two-dimensional problem of diffraction of a plane wave on a gold cylinder with an elliptical shape of the transverse cross section. Numerical and asymptotical methods are used to find scattering and absorption spectra in the visible range. A simple analytical solution of the problem is found for a cylinder with an elongated shape of the transverse cross section. It is shown that in the case of normal incidence of a plane wave, a single quasistatic plasmon resonance is excited in such a cylinder.
119-127
Low-Frequency Instabilities of Electron Beams in Weakly Irregular Transportation Channels
Abstract
Evolution of low-frequency instabilities degrades electron beams in beam transportation channels and, not less importantly, deteriorates the coherence of the output radiation produced by microwave generators based on the use of such beams. These instabilities also determine the beam dynamics, including that associated with transitions of the beams from one stationary state to another. In this work, we use the method of coupled waves to study the stability of stationary states of the beams with high electron densities in weakly irregular vacuum beam transportation channels, specifically, in channels with shallow periodic wall corrugations. It is shown that in this case, the Bursian instability of the absolute type can evolve, which leads to a jump-wise transition of the beam to a state with a lower electron density.
128-135
Glow of the Plasma of a Pulse Discharge Produced in Nitrogen by High-Power Terahertz-Wave Radiation
Abstract
We studied the glow of the plasma of a pulse discharge ignited in nitrogen by high-power focused radiation of a terahertz-wave gyrotron (a radiation frequency of 0.67 GHz, a pulse duration of 20 μs, and a power of 40 kW). The pressure in the discharge chamber varied in the range 0.1–350 Torr. It was found that at high pressures (more than 50 Torr), long-term (about 1.0–1.5 ms), a non-monotonic afterglow exists after the end of the terahertz pulse, whose intensity can exceed the plasma glow intensity significantly (by several times) during the action of the terahertz radiation pulse on the plasma. At pressures below 50 Torr, the afterglow duration proves to be significantly shorter, specifically, about several tens of microseconds. The observed long-term afterglow is radiation in certain vibrational bands of the second positive system of N2 and is due, evidently, to the processes of associative excitation of electron levels in nitrogen molecules with the participation of long-living metastables \( {\mathrm{N}}_2\left({\mathrm{A}}^3{\varSigma}_{\mathrm{u}}^{+}\right) \).
136-142
Energy Limitations for Neodymium Glass Lasers with Beam Apertures of 45 and 60 mm
Abstract
We study the possibility of increasing the pulse energy and repetition rate of the 220-J neodymium glass laser for pumping high-power Ti:Sapphire chirped pulse amplifiers. Stable operation of neodymium glass rod amplifiers with an aperture of 45 mm for elastic stresses constituting 40% of the active-medium damage threshold has been demonstrated experimentally. This regime corresponds to the pulse repetition rate 1/30 Hz, which is a record one for pulsed laser amplifiers with stored energy exceeding 100 J. We have developed quantrons for neodymium glass rod active elements with an aperture of 60 mm, which permits a twofold increase in the output radiation energy with the same thermal load on the active elements as for rods 45 mm in diameter.
143-151
Measurement of the Radial Velocity of a Moving Object Under Nonlinear Variation in the Doppler Phase
Abstract
We solve the problem of measuring the radial velocity of a moving object under nonlinear variation in the Doppler phase with respect to time. The algorithm for measuring this velocity with high accuracy, which allows one to coherently accumulate the signal to improve the signal-to-noise ratio, is described. Compared with the existing analogs, the developed algorithm makes it possible to reduce the amount of calculations.
152-158
Quasilikelihood Estimate of the Number of Radio Signals with Unknown Amplitudes and Phases
Abstract
We perform synthesis and analysis of the quasilikelihood algorithm for estimating the number of signals. It is assumed that the signal parameters are known with accuracy up to a certain limited a priori interval. The estimation-algorithm efficiency is quantitatively characterized by the probability of signal-number estimation error. The analysis results are used to consider the possibility of employing the quasilikelihood algorithm for estimating the number of signals with partially unknown parameters.
159-170