Radiophysics and Quantum Electronics最新文献

We present a review of some fundamental results in the theory of dynamical systems, which have led to the discovery of dynamical chaos and its three forms, namely, two classical forms, such as conservative chaos and dissipative chaos, as well as the completely new third form, the so-called mixed dynamics in which the sets of attractors and repellers have non-empty intersection. The major part of the work is devoted to homoclinic Poincaré trajectories, i.e., doubly asymptotic trajectories to saddle periodic ones, as the main elements of dynamical chaos. Using simple examples, we show the appearance of such trajectories during periodic perturbations of two-dimensional conservative systems. As is known, the homoclinic trajectories were discovered by Poincaré. In this work, we discuss the problem (the planar circular restricted three-body problem) solving which this discovery was made. Some interesting facts concerning its history are given in the appendix.

We perform dispersion analysis of the Weibel-type electron instability in collisionless bi-Maxwellian plasma with an external magnetic field aligned with the anisotropy axis, which corresponds to the highest temperature. The range of the wave numbers of unstable modes, their growth rates, maximum growth rates, and the corresponding optimal wave number as a function of the density and anisotropy of the plasma and the external magnetic field are found for ordinary mode perturbations with the wave vector and the vector of the electric field being perpendicular and parallel to the external field, respectively. The external magnetic field, which suppresses the instability of these modes, and the r.m.s. generated magnetic field, which saturates it at the nonlinear stage, are also estimated.

We use the methods of supercontinuum generation and nonlinear parametric transformations to develop a laser system that forms femtosecond pulses with a duration of several field oscillations and a central wavelength of 910 nm, which are synchronized with the seed radiation of the pump laser. The duration of femtosecond pulses was 20 fs at a repetition rate of 1 kHz and a pulse energy higher than 5 μJ. For further amplification to an energy higher than 40 mJ, a pump laser has been developed, and the main parameters of the parametric amplifier have been calculated. The developed laser system will be used as the starting part of the PEARL petawatt parametric laser system.

We perform spectral studies of the vibrational phenomena which are caused by imperfection of the optical and mechanical units used in the technological process of applying an antireflection coating to the surfaces of large-scale optical elements. The ways of minimizing the negative effect of the revealed vibrational factors are indicated. In particular, it is shown that a decrease in the amplitudes of the low-frequency spectral components of the motion velocity of the treated elements due to the proposed modification of the optical and mechanical units allows one to create more uniform antireflection coatings. The spectrum of the laser-beam displacements spectrum in the near and far fields is also studied experimentally for various mechanical impacts on the optical and mechanical parts of a fiber laser system. It is established that the vibrations are nonlinear and, at certain impact frequencies, the laser beam in the far field oscillates at frequencies that are multiples of the impact frequency.

Being one of the most mysterious particles of the Standard Model, neutrinos have opened up new opportunities for astrophysical research. The high penetrating power of neutrinos provides insight into stellar interior and makes it possible to study the mechanisms of the origin of ultra-high energy cosmic rays. When a star explodes, a neutrino flare informs us about this event several hours earlier than electromagnetic radiation. Neutrino also plays a crucial role in cosmology, being the second most abundant known particle in the Universe. In the radiation-dominated epoch, neutrinos together with photons, determine the dynamics of the expansion of the Universe. Later, becoming nonrelativistic, the neutrinos increase the contribution Ω_m of nonrelativistic matter, which previously consisted of cold dark matter and baryonic matter. Since neutrinos affect the course of the evolution of the Universe, this fact should be taken into account when determining cosmological parameters. Recently, in addition to relic neutrinos from the Big Bang, antineutrinos of primordial nucleosynthesis have been theoretically predicted. Their detection could be additional evidence for baryon asymmetry of the Universe.

Current results from a number of independent experiments indicate the possibility of the existence of a light sterile neutrino (m_ν ~ 1–3 eV). The presence of such a neutrino is in poor agreement with the predictions of the Standard Cosmological Model, but these contradictions can be removed by its extension, for example, by the existence of a nonzero lepton asymmetry ξ_ν ~ 10⁻² of the Universe. Nowadays, there are little doubts about the existence of cosmological neutrinos, but unfortunately it is not yet possible to detect them directly due to the extremely small cross section of their interaction at low energies. However, if this can be done in the future, we will obtain direct information about the first seconds, minutes, and hours of the evolution of the Universe after the Big Bang. A review of key aspects related to the influence of cosmological neutrinos on the evolution of the Universe at different stages from the early Universe (primordial nucleosynthesis and primordial recombination) to present days is given.

We consider the current status of the binary neutron star stripping model to explain short gamma-ray bursts. After the historical joint detection of the gravitational wave event GW170817 and accompanying gamma-ray burst GRB170817A, the production of short gamma-ray bursts in the neutron star coalescence has been reliably confirmed. Many properties of GRB170817A that turned out to be peculiar compared to other short gamma-ray bursts are naturally explained in the stripping model proposed in our works in 1984. We emphasize the role of D. K. Nadyozhin (1937–2020), who quantitatively predicted the GRB and kilonova properties back in 1990. We also discuss problems that need to be solved in the context of this model, especially in simulations using the smoothed-particle hydrodynamics method.

We compare two methods of millimeter radio interferometry with and without frequency conversion using as an example experimental measurements of the transverse deformation magnitude of a metal rod under dynamic load. We reveal a good agreement between the results, demonstrating a possibility of measuring the surface deviations within times of about 1 μs with micron precision.

We study the absorption of microwave gyrotron radiation by aluminum microparticles taking into account the Al₂O₃ nano-oxide film. The heating process of metal microparticles (linear size from 1 to 400 μm) in Al/Al₂O₃ powder fillings for a metal mass concentration of 10% has been experimentally explored. The increase in the field strength of electromagnetic waves upon diffraction on a double-layer structure consisting of a quartz plate and a thin layer of Al₂O₃ is considered. The calculation of the absorbed and reflected power of microwave radiation from a gyrotron at a frequency of 75 GHz using the Mie solution for a sphere and the effective medium approximation to calculate the optical properties of aluminum particles in a dielectric shell is presented. It is shown that for a microwave pulse power of more than 400 kW, local heating of aluminum in the region of the maximum electric field strength (7.5 kV/cm) to the melting temperature is observed within times not exceeding the gyrotron pulse duration (less than 8 ms).

One of the possible applications of high-current relativistic electron beams (REBs) is to generate electromagnetic waves at plasma frequencies due to the propagation of a beam through a magnetized plasma column. Research work in this direction, aimed at creating terahertz radiation sources at the BINP, is underway using the GOL–PET facility. We study the relaxation of a REB beam with a current density of (1–2) kA/cm² in a magnetized plasma column with a density of 5 · 10¹⁴ cm^–3. The purpose of these studies is to create a pulse radiation source with a power of tens of megawatts in the frequency range 0.1–1 THz. To date, a radiation flux with a power level of 10 MW and a maximum power spectral density in the frequency range 150–200 GHz has been achieved in the experiments. Further progress in these studies was related to the experimental establishment of the dependence of the power and spectral composition of the radiation flux on the parameters of the injected beam, in particular, its current density. The current density of the injected beam was varied due to the different compression of the beam cross section by the magnetic field. The results of measuring the characteristics of the radiation flux are presented in correlation with the results of measurements of the beam current density and plasma density.

We consider the project of a sub-gigawatt free-electron laser (FEL) in the THz range based on a high-current electron beam proposed in 2020 by a scientific collaboration team from G. I.Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP SB RAS, Novosibirsk) and the Institute of Applied Physics of the Russian Academy of Sciences (Nizhny Novgorod). A new generation of linear induction accelerators (LIA) with a kiloampere current level and an energy of up to 10 MeV, which are capable of forming beams with a high current density and low normalized emittance, is developed at the BINP SB RAS and can be used as a source of an electron beam for such a FEL generator. The objective of our research is to develop and create a FEL generator producing pulses of coherent radiation in the THz range with a sub-GW power level and a record-breaking energy content in a pulse of about 10–100 J. Combination of a high current density of the beam and its long pulse duration (about 100 ns) together with a small spread in the longitudinal electron velocities of the beam opens up the possibility of implementing the FEL scheme in two different types of oversized electrodynamic systems. The first is based on a two-mirror Bragg resonator, in which waves are reflected due to the coupling of the traveling and quasi-critical waves on a corrugated surface. In the second type of the electrodynamic system, a quasi-optical resonator based on the Talbot effect is used. According to the theory, the simulation results, and the data of the cold experiments, both schemes make it possible to ensure a stable regime of narrow-band generation of THz radiation under the conditions of significant cavity oversize, i.e., the ratio of the cavity diameter and the radiation wavelength (ϕ/⋋ > 30–40). The main structural elements of the developed section of the FEL generator and their design parameters are discussed within the framework of this article. When developing the magnetic system of this section, we calculated the time dependence of the spatial configurations of pulsed magnetic field in a helix undulator with a period of d = 10 cm and a length of 2 m, as well as in the solenoid of a quasi-homogeneous magnetic field of the same length intended for compression of the beam cross section before its input in the vacuum channel of the FEL section and for consequent transport of the beam inside it. The presented results of modeling and testing of the manufactured elements for the FEL section will become the basis for the design of a high power FEL generator operated in the frequency range from 0.3 to 1.2 THz.