Showing papers in "Radiophysics and Quantum Electronics in 2019"
TL;DR: In this paper, the authors describe a series of gyrotron facilities developed at the Institute of Applied Physics of the Russian Academy of Sciences for studying physical processes during interaction of millimeter-wave electromagnetic radiation and matter.
Abstract: We describe a series of gyrotron facilities developed at the Institute of Applied Physics of the Russian Academy of Sciences for studying physical processes during interaction of millimeter-wave electromagnetic radiation and matter. This paper presents the universal principle of designing such systems on the basis of a facility having an output radiation power of 5 kW at a frequency of 24 GHz. The main components of the facility and their technical parameters are described. Design of high-efficiency radiation sources and radiation transmission lines for various research applications is a sophisticated radiophysical problem, and the need for long-term stable operation with automatic adjustment of the parameters of the generation regime requires unique engineering solutions. Application of multimode electrodynamic devices in the radiation transmission line allows one to treat materials with significantly different dielectric properties, in particular, heat them up to temperatures of about (and exceeding) 2000°C. The vacuum-tight working chamber of the facility is a high-Q untuned cavity resonator having a volume of about 0.1 m3, in which microwave heating of items with characteristic dimensions of more than 10 cm can be performed. The automatic control system of the facility ensures its reliable and long-term failure-free operation.
29 citations
TL;DR: A new algorithm for determining the basic significant points of various electrocardiographic-signal waves taking into account information from all available leads and ensuring a similar or higher accuracy compared with that of other up-to-date technologies is proposed.
Abstract: We propose a new algorithm for determining the basic significant points of various electrocardiographic-signal waves taking into account information from all available leads and ensuring a similar or higher accuracy compared with that of other up-to-date technologies. The test results of the algorithm efficiency for the QT data base [1] show a sensitivity above 97% when detecting the electrocardiographic-signal peaks, and 96% for their onsets and offsets, as well as the positive predictive value exceeding 97% for the peaks of the complexes, which is the best result compared with those of the previously known algorithms. As distinct from them, the proposed approach also allows one to determine the wave morphology. For the proposed algorithm, the delineation errors of all significant points are below the tolerances specified by the Committee of General Standards for Electrocardiography.
25 citations
TL;DR: In this paper, the authors proposed a scenario of appearance of mixed dynamics in reversible two-dimensional diffeomorphisms, where a jump-like increase in the sizes of the strange attractor and strange repeller, which is due to the heteroclinic intersections of the invariant manifolds of the saddle points belonging to the attractors and the repellers, is the key point of the scenario.
Abstract: In this work, we propose a scenario of appearance of mixed dynamics in reversible two-dimensional diffeomorphisms. A jump-like increase in the sizes of the strange attractor and strange repeller, which is due to the heteroclinic intersections of the invariant manifolds of the saddle points belonging to the attractor and the repeller, is the key point of the scenario. Such heteroclinic intersections appear immediately after the collisions of the strange attractor and the strange repeller with the boundaries of their attraction and repulsion basins, respectively, after which the attractor and the repeller intersect. Then the dissipative chaotic dynamics related to the existence of the mutually separable strange attractor and strange repeller immediately becomes mixed when the attractor and the repeller are essentially inseparable. The possibility of realizing the proposed scenario is demonstrated using a well-known problem of the rigid-body dynamics, namely, the nonholonomic model of the Suslov top.
19 citations
TL;DR: In this paper, a method for deriving systems of closed equations for the dynamics of order parameters in the ensembles of phase oscillators is developed, which corresponds to two-bunch states of the ensemble.
Abstract: We have developed a method for deriving systems of closed equations for the dynamics of order parameters in the ensembles of phase oscillators. The Ott–Antonsen equation for the complex order parameter is a particular case of such equations. The simplest nontrivial extension of the Ott–Antonsen equation corresponds to two-bunch states of the ensemble. Based on the equations obtained, we study the dynamics of multi-bunch chimera states in coupled Kuramoto–Sakaguchi ensembles. We show an increase in the dimensionality of the system dynamics for two-bunch chimeras in the case of identical phase elements and a transition to one-bunch “Abrams chimeras” for imperfect identity (in the latter case, the one-bunch chimeras become attractive).
17 citations
TL;DR: In this article, the evolution of radiation harmonics in a single-pass free-electron laser using a phenomenological model, in which the main losses are taken into account separately for each of the harmonics, is compared with the corresponding FEL experiments and the simulations, which are performed using the PERSEO code.
Abstract: We model the evolution of radiation harmonics in a single-pass free-electron laser using a phenomenological model, in which the main losses are taken into account separately for each of the harmonics. The modeling results are compared with the corresponding FEL experiments and the simulations, which we performed using the PERSEO code. A wide wavelength range (0.15–500 nm) is considered. The phenomenological description based on the use of several basic FEL parameters, such as the electron beam current, average energy, energy spread, and emittance of electrons, yields the results that correspond well to the LEUTL, SPARC, and LCLS experiments in various conditions. The evolution of the radiation power, bunching, and electron energy spread in the Spring 8 FEL at the follow-up stage is also considered. The necessity to improve electron beam parameters for generation of harmonics in this FEL is shown. The phenomenological model allows assessing the operation of the available and future FELs fast. Using it, one can model FELs with nearly any undulator with allowance for higher harmonics of their magnetic fields. Moreover, this model makes it possible to describe easily various effects in designed FELs, e.g., those with dephasing of electrons and photons, filtering of harmonics, and other features.
16 citations
TL;DR: In this article, a 3D resonator with an active element made of a semiconductor, whose conductivity is controlled by a laser, is proposed to obtain very long durations (up to tens of seconds) along with nanosecond pulses in one and the same device prototype.
Abstract: We consider nanosecond subterahertz waveguide switches based on a 3D resonator with an active element made of a semiconductor, whose conductivity is controlled by a laser. Recently discovered possibilities to use these switches to obtain pulses with very long durations (up to tens of seconds) along with nanosecond pulses in one and the same device prototype are discussed. Switching with no distortion of the coherent radiation of promising subterahertz gyrotrons, which have powers of about several watts and pulse durations of up to ten seconds are demonstrated experimentally. The theoretical estimate of limiting powers of the switched subterahertz waves, which was proposed earlier, is confirmed and generalized. For this purpose, we perform a measurement of the powers by reducing it to a trivial measurement of the power of radiation of an industrial IR laser. Improvement of the resonance characteristics of the developed switch after switching several sequential long subterahertz pulses has been revealed. Most probably, it is due to “burning-off” of microscopic manufacturing defects and the approach of the actual frequency-amplitude characteristic to the calculated one. It has been predicted theoretically and partially confirmed experimentally that it is not possible to disable the switch being in the fundamental equilibrium state upon switching arbitrarily high powers of subteraheratz waves near the resonance band.
13 citations
TL;DR: The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyroron amplifiers, which produces pulsed or continuous-wave radiation in the millimeter-wavelength band at a power level that exceeds the powers produced by conventional TWTs with slow-wave structures and rectilinear beams by 1-2 orders of magnitude.
Abstract: The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyrotron amplifiers, which produce pulsed or continuous-wave radiation in the millimeter-wavelength band at a power level that exceeds the powers produced by conventional TWTs with slow-wave structures and rectilinear beams by 1–2 orders of magnitude. Since 1996, researchers at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) have been developing the concept of the gyro-TWT based on the use of a waveguide with a helically corrugated surface, which changes the dispersion of one of the eigenmodes in a circular waveguide radically. In this paper, we discuss several problems that arise in implementation of such devices, which many years of experimental studies have revealed, present the parameters of gyro-TWTs developed with allowance for specific applications of their end users, and discuss lines of further perfection of such amplifiers.
12 citations
TL;DR: In this paper, an external signal from a magnetron is applied to the operation space of the gyrotron at a frequency of 35 GHz via a synthesized two-mirror quasi-optical converter developed at the Institute of Applied Physics of the Russian Academy of Sciences.
Abstract: The radiation-frequency locking by an external signal is experimentally studied for a megawatt gyrotron. An external signal from a magnetron is applied to the operation space of the gyrotron at a frequency of 35 GHz via a synthesized two-mirror quasioptical converter developed at the Institute of Applied Physics of the Russian Academy of Sciences. The radiation spectra are measured for both the frequency locking regime and the frequency beats. The locking region is constructed on the plane of two parameters, namely, the external-signal power and frequency. The experimental and theoretical results are compared to show a good agreement.
11 citations
TL;DR: In this paper, the authors consider two-parameter families of nonholonomic models of a Celtic stone moving along a plane and show that the chaotic dynamics of such models can be rather diverse.
Abstract: We study dynamic properties of a Celtic stone moving along a plane. We consider two-parameter families of the corresponding nonholonomic models in which bifurcations leading to changing the types of stable motions of the stone, as well as the chaotic-dynamics onset are analyzed. It shown that the multistability phenomena are observed in such models when stable regimes various types (regular and chaotic) can coexist in the phase space of the system. We also show that chaotic dynamics of the nonholonomic model of a Celtic stone can be rather diverse. In this model, in the corresponding parameter regions, one can observe both spiral strange attractors various types, including the so-called discrete Shilnikov attractors, and mixed dynamics, when an attractor and a repeller intersect and almost coincide. A new scenario of instantaneous transition to the mixed dynamics as a result of the reversible bifurcation of merging of the stable and unstable limit cycles is found.
10 citations
TL;DR: In this article, the authors show experimentally the possibility to expand significantly the band of smooth tuning of the generation frequency in gyrotrons using cavities that have shorter lengths.
Abstract: We show experimentally the possibility to expand significantly the band of smooth tuning of the generation frequency in gyrotrons using cavities that have shorter lengths. Due to a decrease in the sensitivity of the electron-wave interaction process to the spread in the electron beam velocities, one can increase the power of generation at higher longitudinal modes up to a level comparable with the radiation power in the case of excitation of a mode with one longitudinal variation. In this case, overlapping of generation bands at the neighboring longitudinal modes is achieved by increasing the current of the electron beam. In the experiment performed in a gyrotron having an operating frequency of about 12 GHz, we demonstrated a frequency tuning band which exceeded 4% at the kilowatt level of the output radiation power in its greater part. The obtained results open up the possibility of developing tunable high-frequency moderate-power gyrotrons.
8 citations
TL;DR: In this article, the influence of solar and magnetic activity in September 2017 on the HF signal characteristics on subauroral and midlatitude paths was studied. And the formation of a strong sporadic Es layer in the auroral ionosphere during a magnetic storm makes it possible to use the propagation mode with reflection from Es in the interests of HF communication to neutralize the effects of the negative phase of the storm and absorption growth.
Abstract: We present the results of studying the influence of solar and magnetic activity in September 2017 on the HF signal characteristics on subauroral and midlatitude paths. A connection between the ionospheric effects caused by the magnetic storm and the magnetic disturbance intensity is established. It is shown that the formation of a strong sporadic Es layer in the auroral ionosphere during a magnetic storm makes it possible to use the propagation mode with reflection from Es in the interests of HF communication to neutralize the effects of the negative phase of the storm and absorption growth when unfavorable conditions for the F-mode propagation with reflection from the upper ionosphere occur.
TL;DR: In this article, the authors consider the problem of existence of discrete Lorenz attractors in the nonholonomic model of a Celtic stone and study the main local and global bifurcations leading to the appearance and destruction of attractors.
Abstract: In this work, we consider the problem of existence of discrete Lorenz attractors in the nonholonomic model of a Celtic stone. To this end, the main local and global bifurcations leading to the appearance and destruction of the attractors are studied in two-parameter families of such models of certain types. The corresponding bifurcation diagram, in which the region of existence of a discrete Lorenz attractor is shown and its boundaries are described, is obtained on the plane of the governing parameters (the angle of dynamic asymmetry of the stone–the total-energy value). The similarities and differences in the scenarios of the appearance of a discrete Lorenz attractor in the nonholonomic model of a Celtic stone and attractor in the classical Lorenz model are found.
TL;DR: In this article, a set of correlation effects due to the inherent dynamics of the spectral density of polarization of an active medium with strong inhomogeneous broadening of the working transition line was found.
Abstract: We have found a set of correlation effects, which are due to the inherent dynamics of the spectral density of polarization of an active medium with strong inhomogeneous broadening of the working transition line and occur if the rate of incoherent relaxation of optical dipole oscillations of the active centers is lower than the rate of optical-field attenuation in the laser cavity. Our analysis is based on the numerical studies of the stationary superradiant laser generation during continuous pumping with self-locking of some of the quasistationary modes. For the purposes of studying the detected effects, the methods of comparative analysis of the dynamic spectra of polarization and the field have been developed. In these methods, the time-frequency and space-time empirical modes of the spectra are used, which are determined by orthogonal eigenfunctions of special correlation matrices. The interconnection of the superradiance phenomena and mode self-locking in the considered class of lasers with low-Q cavities is discussed.
TL;DR: In this paper, the behavior of the maximum observed frequencies (MOF) of the F2 and Es layers during a magnetic storm of September 7-8, 2017 is considered. The storm has a specific, not classical form and can be divided into two parts, namely, the first and the second storms.
Abstract: Ionograms of the oblique ionospheric sounding radio paths Cyprus—Lovozero and Lovozero—Gor’kovskaya (near St. Petersburg) are analyzed using magnetometers and riometers. The behavior of the maximum observed frequencies (MOF) of the F2 and Es layers during a magnetic storm of September 7–8, 2017 is considered. The storm has a specific, not classical form and can be divided into two parts, namely, the first and the second storms. The main results are as follows. 1) The manifestation of the first storm is accompanied by a significant increase in absorption and frequent absence of signals on the paths. The second storm is characterized by increased values of MOF-Es and the presence of signals. 2) The signals on the midlatitude Cyprus—Lovozero path propagate both as 1F2, 2F2, and 3F2 modes and as 2Es and 3Es modes. 3) On the subpolar Lovozero—Gor’kovskaya path, during the disturbance, the signals mainly propagate via reflection from the sporadic Es layer of very high intensity. 4) Modeling of the propagation of HF radio waves using the IRI-2016 model adapted to the vertical sounding data made it possible to match the model ionograms with the real oblique sounding ionograms, including the cases of presence of the M and N modes, as well as triplets, in both quiet and disturbed conditions, which is a new result.
TL;DR: In this article, the authors present experimental results concerning the features and origin of the outshifted plasma lines in the high-latitude ionospheric F region, which are excited by high-power HF O-mode radio waves radiated by the EISCAT/Heating facility at pump-wave frequencies near the fourth and fifth gyroharmonics.
Abstract: We present experimental results concerning the features and origin of the outshifted plasma lines in the high-latitude ionospheric F region, which are excited by high-power HF O-mode radio waves radiated by the EISCAT/Heating facility at pump-wave frequencies near the fourth and fifth gyroharmonics. HF pump waves were transmitted towards the magnetic zenith during long-lasting (2–20 min) heater-on cycles. The studies were carried out using the measurement data obtained by the EISCAT incoherent scatter radar in Tromso (the radar operating frequency 930 MHz). The analysis of the radar data has demonstrated the simultaneous excitation of several plasma lines at frequencies close to the pump frequency and at frequencies upshifted by 0.15–0.45 MHz on long-lasting (longer than 30 s) time intervals. The spectral width of the outshifted plasma lines was 0.10–0.15 MHz. The features of their occurrence were analyzed as functions of the relation between the pump-wave frequency and gyroharmonics and the proximity of the pump-wave frequency to the cutoff frequency of the ionospheric F2 layer. Plausible excitation mechanisms of the outshifted plasma lines are discussed. Comparison between the experimental data and calculation results concerning the features of the outshifted plasma lines for different pump-wave frequencies was made.
TL;DR: In this paper, the damping rate of a clamped liquid drop in an alternating electric field was studied as a function of the Hocking parameter, and it was shown that the amplitude of oscillations of the side surface is always finite.
Abstract: We consider oscillations of a clamped liquid drop in an alternating electric field. The frequencies and damping rates of the drop eigenmodes are studied as functions of the problem parameters. The fundamental frequency of free oscillations can vanish in a certain interval of values of the Hocking parameter. The length of this interval depends on the ratio of the drop dimensions. Frequencies of other drop eigenmodes decrease monotonically with increasing Hocking parameter. Well-pronounced resonance effects are observed when studying forced oscillations. For any unequal values of the Hocking parameter, the amplitude of oscillations of the side surface is always finite. However, for identical Hocking parameters, the amplitude increases indefinitely in the case of low dissipation. It is shown that traveling capillary waves propagate on the side surface of the drop.
TL;DR: In this article, the statistical moments of the soliton gas (mean field, variance, skewness, and kurtosis) were studied in the framework of the Gardner equation with negative cubic nonlinearity.
Abstract: We study the statistical moments of the soliton gas (mean field, variance, skewness, and kurtosis), which is described within the framework of the Gardner equation with negative cubic nonlinearity. The influence of the limiting (thick or table-like) soliton on the statistical moments of the soliton gas is considered. It is shown to be substantial if the thick-soliton intensity is comparable with that of the moderate-amplitude solitons.
TL;DR: In this article, a spatially extended narrow-band Cerenkov surface-wave oscillators (SWO) was developed in the specified frequency range driven by Sinus-6, a high current accelerator, with a particle energy of 0.5 MeV, a current of 5 kA, and a pulse duration of 25 ns.
Abstract: The concept of Compton-type free-electron lasers (FELs) operating in short wavelength ranges with a high efficiency and power level is currently underway at the IAP RAS (Nizhny Novgorod). This concept is aimed at reducing the energy of a driving relativistic electron beam and thereby increasing the efficiency of the electron–wave interaction in FELs, as well as making the oscillator relatively compact. The basis of this concept is microwave undulators of a new type—the so-called “flying” undulators. This paper is devoted to the results of the current studies of these undulators, their simulation, and “cold” electrodynamic tests in the Ka band. For powering microwave undulators, a spatially extended narrow-band ˇ Cerenkov surface-wave oscillators (SWOs) are developed in the specified frequency range driven by Sinus-6, a high-current accelerator, with a particle energy of 0.5 MeV, a current of 5 kA, and a pulse duration of 25 ns. The required sub-gigawatt power level of output radiation combined with a high stability of the narrow-band oscillation regime is achieved under conditions of a strongly oversized oscillator by using two-dimensional distributed feedback provided in a 2D doubly-periodic slow-wave structure. The design parameters of a 32 GHz/0.5 GW SWO intended for powering microwave undulators are presented and the results of its simulation and reported.
TL;DR: In this article, a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in optical coherence tomography is proposed and experimentally tested.
Abstract: We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in optical coherence tomography. The method is based on the analysis of phase shifts of the neighboring scans, which are due to microscale displacements, and further compensation for these displacements by using phasefrequency correction in the spectral domain. Unlike the known correlation methods, the proposed method does not distort the represented shape of the object surface. Its operability is demonstrated in model experiments in the cases of harmonic and random types of the motion of the scattering object, as well as in vivo imaging of the structures of the human middle ear.
TL;DR: In this paper, the authors describe the results of the first (undedicated) experiments on studying large-scale (about 1000 km) aperiodic and quasi-periodic disturbances in the lower and middle ionosphere.
Abstract: We briefly describe the results of the first (undedicated) experiments on studying large-scale (about 1000 km) aperiodic and quasi-periodic disturbances in the lower and middle ionosphere. The main results of modern experiments are listed. Multi-instrument radiophysical observations of large-scale (about 1000 km) aperiodic disturbances in the lower ionosphere and quasi-periodic disturbances in the middle ionosphere, which accompanied the Sura heater action with high-power (effective power 40–95 MW) nonstationary radio emission, were performed in 2017–2018 using partial-reflection and vertical/oblique multipath multifrequency sounding techniques. The observations were performed in the observatories of the V. N. Karazin National University of Kharkov during four heating campaigns in 2017–2018. The aperiodic disturbances in the lower ionosphere had a delay time of 15–18 min and a duration of 5–10 min. The disturbances followed the heater switch-on and off. The nature of these disturbances is discussed. The main effects in the middle ionosphere include the following. When the effective radiated power is no less than 40–60 MW, the Doppler spectra become considerably broader and multipathing appears on radio paths that are 1000 km distant from the heater in 40–60 min after the Sura switch-on. Periodic heating of the ionosphere resulted in periodic variations in the Doppler frequency shift (with a maximum deviation of 0.1–0.2 Hz) and in the signal amplitude. The time delay of the ionospheric response lies in the range 40–60 min, while the relative disturbance in the electron density varies from 3% to 12%. Quasi-periodic variations in the Doppler frequency shift and in amplitude are caused by the generation and propagation of waves with 0.2–1.6 km/s speeds and 15–30 min periods. The 0.2–0.4 km/s speeds, as opposed to the 1.6 km/s speed, are regularly observed. The main directions of the future studies of how large-scale aperiodic and quasi-periodic disturbances manifest themselves in the ionosphere and the studies of how these disturbances affect the parameters of radio waves on remote radio paths are also discussed.
TL;DR: In this article, the causes of artifact appearance in the images obtained by the method of spectral domain optical coherence tomography with parallel reception of the optical-spectrum components, which are manifested in repetition and overlay of the structural elements of the images of the studied medium with a shift in depth.
Abstract: We study the causes of artifact appearance in the images obtained by the method of spectral domain optical coherence tomography with parallel reception of the optical-spectrum components, which are manifested in repetition and overlay of the structural elements of the images of the studied medium with a shift in depth. It is shown that nonidentity of the transfer characteristics of the channels of the multichannel photoreceiving elements is one of the sources of such artifacts. A numerical method for eliminating such artifacts is proposed and experimentally verified. This method is based on using the models whose parameters are estimated by the recorded signal and does not require a priori information on the transfer characteristics of the channels. The method efficiency is demonstrated during the experiments on the in vivo visualization of the human middle-ear elements.
TL;DR: In order to separate global and local effects of atmospheric electricity, measurements of the fair-weather electric field were performed in Nizhny Novgorod in 2013-2018 as mentioned in this paper.
Abstract: In order to separate global and local effects of atmospheric electricity, measurements of the fair-weather electric field were performed in Nizhny Novgorod in 2013-2018. As a result of processing 139 diurnal records from four observation points spaced 6–8 km apart, diurnal variations in the fair-weather atmospheric electric field for different seasons and weekdays (working days and weekends) were studied. The curve of the local diurnal variation is shown to always have two maxima. The evening maximum of the diurnal variation (19:00–20:00 UT) coincides in time with the maximum of the Carnegie curve, which is a characteristic of the global electrical circuit. The highest values of the field amplitude are reached in the winter period. The field-intensity maximum in the first half of the day (09:00–11:00 LT) is characteristic of the urban environment and shows that local effects associated with the presence of aerosol particles in the air significantly contribute to the formation of diurnal variation, especially in summer. According to the 2013–2018 measurements, the seasonal variation in the monthly-average values of the atmospheric electric field is revealed and analyzed compared with the results of measurements of seasonal variation in other regions of the globe. The obtained results allow one to reveal the role of local effects in the formation of diurnal variation in the mid-latitude areas with temperate continental climate and provide a basis for developing a theory which can explain the physical mechanisms of local effects and suggest appropriate parametrization for finding the surface electric field in the weather and climate models.
TL;DR: In this article, the results of the experiment on the polar ionosphere heating by a high-power modulated HF wave conducted by the AARI at the EISCAT/heating facility in October 2016 are considered.
Abstract: We consider the results of the experiment on the polar ionosphere heating by a high-power modulated HF wave conducted by the AARI at the EISCAT/heating facility in October 2016. The data on joint processing of the values of the equivalent polar electrojet current above the heated ionosphere region retrieved by the IMAGE network of ground-based stations and the amplitudes of a signal of the horizontal component of the magnetic field from an ionospheric source at the modulation frequency recorded in the PGI network of high-latitude stations are presented. The events with a strong positive correlation between the magnetic field amplitude variations and the polar electrojet current variations are considered. It is shown that if the direction of the current changes from eastward to northward, correlation between the current variations and magnetic field variations almost disappears at a modulation frequency of 3017 Hz. Temporal and spatial variations of the coefficient of linear regression of the amplitude of the horizontal magnetic-field component with respect to the electrojet current are analyzed. In the transition from day to night, which is accompanied by the electrojet current decrease, the regression slope increases, and it decreases with increasing distance between the heater and the observation point.
TL;DR: In this paper, a maximum likelihood algorithm for detecting an ultra-wideband quasi radio signal with an arbitrary shape and unknown amplitude, initial phase, and duration, which is observed against the background of additive Gaussian white noise, is presented.
Abstract: We develop the maximum likelihood algorithm for detecting an ultra-wideband quasi radio signal with an arbitrary shape and unknown amplitude, initial phase, and duration, which is observed against the background of additive Gaussian white noise. The structure and statistical characteristics of this algorithm are found. The influence of a priori ignorance of the duration of a quasi radio signal on its detection efficiency is studied. The operation efficiencies of the maximum-likelihood and quasioptimal detectors of the ultra-wideband quasi radio signal are compared. Using computer simulation, the efficiency of the synthesized algorithm is examined and the applicability ranges of the obtained asymptotic expressions for its characteristics are determined.
TL;DR: In this paper, the authors studied the dynamics of the spectra of multiband sporadic magnetic pulsations in the Pc1 range (0.2-5.0 Hz) during the event of 5-6 March 2011 by using ground-based magnetic measurements at stations largely spaced from each other in latitude and longitude.
Abstract: We study the dynamics of the spectra of multiband sporadic magnetic pulsations in the Pc1 range (0.2–5.0 Hz) during the event of 5–6 March 2011 by using ground-based magnetic measurements at stations largely spaced from each other in latitude and longitude. The event is characterized by a long duration (about 16 h), the presence of several bands with varying frequencies, splitting of these bands into narrower subbands, significant variations in the amplitude and polarization of the signals on the ground, and their observation in a wide range of latitudes and longitudes. On the basis of a joint analysis of the Pc1 pulsation properties and the data of low-orbiting spacecraft detecting localized precipitations of energetic protons into the ionosphere, we infer the possible generation regions of these waves in the magnetosphere and conclude that they are multiple. The results of analysis allowed us to determine the mechanisms of broadening and splitting of Pc1 frequency bands even in the absence of direct wave observations in the magnetosphere. We also propose an explanation of the atypical (for ground-based detection) character of two-band Pc1 spectra when the signal at frequencies above the helium ion gyrofrequency has a higher amplitude than at lower frequencies. We also explain the inhomogeneous frequency profile of polarization in different frequency bands. Possible variations in the magnetospheric plasma parameters that resulted in the observed dynamics of amplitude and polarization spectra of Pc1 pulsations are revealed by using calculations of the wave cyclotron amplification by energetic protons in the magnetosphere.
TL;DR: In this article, the influence of an external quasi-monochromatic signal on a multimode gyrotron in the case where the signal frequency is close to the frequency of the operating mode was studied.
Abstract: We consider the influence of an external quasi-monochromatic signal on a multimode gyrotron in the case where the signal frequency is close to the frequency of the operating mode of the gyrotron. The influence of the mode competition on the generation regime at a harmonic frequency modulation is studied. The calculations were performed for a high-power 170 GHz gyrotron developed at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS). Depending on the parameters of the gyrotron and the external signal, various generation regimes were determined, including locking of the operating-mode frequency when the radiation frequency is close to the frequency of the external signal, beats of the frequency and amplitude of the operating mode, and excitation of spurious modes.
TL;DR: In this paper, the authors presented the results of prediction and extrapolation of the maximum usable frequency (MUF) on the subauroral and midlatitude paths of the Euro-Asian region by adapting the reference ionosphere model IRI-2007 based on the oblique chirp sounding of the ionosphere on the reference and working radio links.
Abstract: We present the results of prediction and extrapolation of the maximum usable frequency (MUF) on the subauroral and midlatitude paths of the Euro-Asian region by adapting the reference ionosphere model IRI-2007 based on the results of the oblique chirp sounding of the ionosphere on the reference and working radio links. It is shown that under conditions of a quiet ionosphere where the adapted ionospheric model is used, the errors of the MUF prediction on the reference path and the error of the MUF extrapolation to the neighboring paths not equipped with diagnostic tools are 2–8%, which is significantly less than the long-term prediction data which amount to 9–20% [1–3].
TL;DR: In this article, specific features of the radio occultation method and the possibility of using it to study the altitude profiles of electron density and the characteristics of sporadic formations in the daytime polar ionosphere of the Arctic at latitudes above 67° in the period from June 19 to July 1, 2015.
Abstract: We analyze specific features of the radio occultation method and the possibility of using it to study the altitude profiles of electron density and the characteristics of sporadic formations in the daytime polar ionosphere of the Arctic at latitudes above 67° in the period from June 19 to July 1, 2015. Electron density at altitudes of 90 to 650 km is determined by ionospheric occultation sounding on GPS–FormoSat satellite-to-satellite paths, and its dependence on solar illumination at an altitude of 100 km is demonstrated. Data on sporadic Es formations at altitudes of 80 to 120 km are presented. Two types of Es structures attributed to the wind shear and precipitation of energetic particles from the magnetosphere are discussed.
TL;DR: In this paper, a universal sub-terahertz source for magnetic resonance spectroscopy is studied using a facility that generates long-pulse and continuous electron beams with particle energies of up to 30 KeV.
Abstract: The Institute of Applied Physics of the Russian Academy of Sciences has for many years been developing sub-terahertz and terahertz large-orbit gyrotrons that permit selective oscillation at higher cyclotron harmonics than is possible in the conventional gyrotrons. Currently, experimental studies are conducted at two specialized facilities. A prototype universal sub-terahertz source for magnetic resonance spectroscopy is studied using a facility that generates long-pulse and continuous electron beams with particle energies of up to 30 KeV. Continuous selective oscillation at the second and third cyclotron harmonics with frequencies of 0.267 and 0.394 THz was obtained for a radiation power of 900 and 370 W, respectively. New resonators with periodic phase correctors have been developed to increase the efficiency of third-harmonic oscillation and obtain fourth-harmonic oscillation with frequencies of up to 0.65 THz. Using a facility with an electron energy of up to 80 KeV, we study the possibilities of increasing the pulse generation power at the third harmonic at frequencies close to 1 THz to employ in experiments on obtaining a gas discharge in a focused terahertz wave beam and generating high-power extreme ultraviolet radiation.
TL;DR: In this article, the principles of the developed method of ultrafast sintering of oxide ceramics with rates exceeding those typical of the conventional methods by two or three orders of magnitude are described.
Abstract: Gyrotron systems operated at frequencies of 24 to 30 GHz with an output power of 3 to 15 kW have been used at the Institute of Applied Physics of the Russian Academy of Sciences for more than 20 years for the studies of high-temperature processes in polycrystalline dielectric materials under intense electromagnetic irradiation. The research has mostly been focused on the study of the physically specific features of diffusive mass transfer in solids and on the possible use of these features for applications. A distinguishing feature of the studied processes is a significant enhancement of their rates compared to similar processes performed with the use of conventional heating methods. Examples of enhanced sintering of a broad range of ceramic materials, including optical and laser ceramics and composition-graded metal–ceramic products are considered. The principles of the developed method of ultrafast sintering of oxide ceramics with rates exceeding those typical of the conventional methods by two or three orders of magnitude are described. The development of this method has resulted from a purposeful use of the functional capabilities of the gyrotron systems and the engineering solutions implemented therein.