Radiophysics and Quantum Electronics最新文献

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.

We develop and study for the first time a high-current K_a-band gyrotron having an electron-optical system with magnetic compression, which ensures the formation of a helical electronc beam with an energy of 500 keV, a current of 2 kA, and a pitch factor of about 1.0. Generation of the radiation with a power of 35–40 MW and a pulse duration of about 5 ns is achieved at the TE_{−3, 2} and TE_{−4, 2} modes with frequencies of 30.6 and 35.7 GHz, respectively.

A biofilm as the main type of existence of bacterial associations, which has its spatial and metabolic structure, is formed on the mucosa in a human body. The study of the main pathobionts and their abilities for biofilm formation at chronic adenotonsillitis, with the identification of tissue metabolites and a comparative analysis confirming the effect of the pathogen, is carried out using the methods of high-resolution terahertz gas spectroscopy. The biofilms formed by Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumoniae, and Enterobacter coli are studied to reveal products of their thermal decomposition and identify the set which is characteristic of microorganisms. The sets of thermal-decomposition products of biofilms for different microorganisms demonstrate the composition difference, which can be used to create metabolic profiles of bacteria and the medical diagnostics methods.

We propose and test experimentally the design of a planar micro-undulator, which allows ensuring a simple profile of the undulator parameter with a value of about unity at a period of 1 mm, as well as the possibility to operate in a regime with a repetition frequency of tens of hertz. Along with small-size sources of high-density beams of accelerated electrons, such as the photo-injection accelerator or the plasma wakefield accelerator, this micro-undulator can be used to make small-size sources of the terahertz and X-ray radiation. It is shown that the Joule heating inhibits the further decrease in the period value. Analytical estimates of the undulator parameter agree well with both the results of numerical simulations and the results of experimental tests.

We describe the concept of a subterahertz gyrotron with frequency tuning, which is based on the regime of a resonance backward-wave oscillator with a combination of an irregular low-Q cavity and a narrow-band external reflector. The simulation performed for the gyrotron at the fundamental cyclotron resonance demonstrates the possibility of creating gyrotrons with high efficiency (10–30%) ensured in a wide frequency range (about 10%). For the gyrotron at the second cyclotron harmonic, the calculations predict that a gyrotron with frequency tuning in a band about 1% can be implemented with an efficiency of 5–10%. A possible solution of a problem of the narrow-band external frequency-tunable reflector is also discussed.

We study the possibility of using Bragg resonators that implement a three-dimensional distributed feedback mechanism ensuring synchronization of radiation and mode selection under conditions of substantial oversize in three spatial coordinates. To describe the electron–wave interaction in devices of this type, a three-dimensional spatiotemporal averaged model was developed within the framework of the coupled wave approach. On this basis, a planar free-electron maser (FEM) driven by a full-scale electron beam of a sheet configuration with a particle energy of 1 MeV, a current of up to 140 kA, and a cross section of about 1 × 140 cm, which is formed using a high-current accelerating complex U-2 (BINP RAS), was simulated. The possibility of achieving a stable narrow-band oscillation regime in FEMs with a multi-gigawatt power level in the W band with transverse sizes of the proposed resonators from tens to hundreds of radiation wavelengths is demonstrated.

We study the possibility to advance relativistic planar Čerenkov surface-wave oscillators, which are driven by intense sheet electron beams, to the subterahertz frequency range within the framework of the performed simulation. It is shown that the use of two-dimensional periodic slow-wave structures providing the two-dimensional distributed feedback allows one to ensure high coherence of radiation at the subgigawatt power level in oscillators of this kind for transverse sizes equal to hundreds of wavelengths. The design parameters and structural elements are discussed for implementing such high-power oscillators based on the ELMI accelerator complex within the framework of the joint BINP/IAP experiments.

We study theoretically the possibility of creating sources of terahertz radiation of high (up to several watts) power based on excitation of the fifth cyclotron harmonic in the frequency multiplication regime in high-power gyrotrons intended for plasma applications. It was previously shown that effective excitation of isolated (s = 4n + 1, n = 1, 2, 3, . . . ) cyclotron harmonics in gyrotrons is due to the specific property of the eigenmodes of cylindrical waveguides, according to which the conditions for simultaneous resonance of an electron beam with two TE modes having asymptotically multiple cutoff frequencies can be fulfilled. For the fifth cyclotron harmonic, this method was tested in experiments with a low-frequency kilowatt power level gyrotron. The use of gyrotrons for plasma applications will significantly increase the power and frequency of radiation based on the observed effect. To suppress spurious oscillation at the main cyclotron resonance, which occurs in the region of optimal magnetic fields for the multiplication effect, it is proposed to use frequency locking of the gyrotron by an external signal. Simulations performed in this work based on an averaged self-consistent gyrotron model shows the possibility of oscillation in the described radiation scheme with a power of several watts at a frequency of 1.25 THz with radiation at the fifth harmonic of the gyrofrequency in a recently developed sub-MW/0.25 THz gyrotron with TE_{19, 8} operating mode.