The authors propose the concept of a two-beam gyrotron with an original electrodynamic system, which consists of coaxially nested cavities. From an applied point of view, such a system can be used, e.g., for simultaneous generation of microwave radiation at two frequencies with significant powers. Dual-frequency plasma heating is of interest for ECR ion sources with improved characteristics. An example of the design of such a cavity is given, which provides simultaneous generation of 28 GHz and 14 GHz with powers of several kilowatts. At the same time the proposed scheme allows to switch between two arbitrary frequencies with appropriate tuning of the magnetic field.

Bacteria are numerous and diverse organisms that have a significant impact on the functioning of aquatic ecosystems. On the vast territory of the West Siberian Lowland (Russia) there are many rivers, lakes and bogs, the microbial communities of which are almost unexplored. Here, we report the study results on the distribution, diversity, community structure and functions of bacterioplankton in the pelagic and littoral zones of one of the lakes, located in this region (Lake Kuchak) obtained using microscopic techniques and 16S rRNA gene metabarcoding. The high total bacterial abundance and biomass, the diversity indices, and the high number of Actinobacteria amplicon sequence variants (ASVs), along with the relatively low number of Betaproteobacteria ASVs, indicate the eutrophication of the lake, especially in its overgrown littoral zone. Similar bacterial communities developed in the pelagic and littoral zones due to similar environmental conditions in these habitats of this small and shallow lake. Nevertheless, there were some differences between the pelagic and littoral zones, causing differences in the bacterial communities of these zones more in size and morphological structure than in taxonomic composition. Comparative analysis of the bacterial metabolic ways showed the higher functional potential in the pelagic zone compared to the littoral one. Signs of methylotrophic and methanotrophic activities, as well as pollutant biodegradation potential of the bacterioplankton were identified. The bacterial distribution and community composition indicates the input of organic substances into the lake from the watershed, but also shows the community resistance to allochthonous microorganisms. Alpha diversity indices, distribution of taxonomic groups and some other results indicate deterioration of water quality in the overgrown littoral zone.

We give a brief review of the results of using gyrotrons to study molecular spectra by means of a radioacoustic absorption detection (RAD) spectrometer. Examples of recording molecular spectral lines of sulfur dioxide (SO2), carbon sulfide (OCS), and methane (CH4) are presented. The achievement of a record-breaking sensitivity for the sub-terahertz frequency range in terms of the absorption coefficient is demonstrated when observing weak methane lines. The possibility of spectroscopy at harmonics of the gyrotron radiation with a frequency of up to 1 THz is shown. Spectroscopic estimates of the radiation power at the second and third harmonics with respect to the power at the fundamental frequency are given. The possibilities of using the methods of nonlinear spectroscopy, namely, two-photon spectroscopy, which extend the range of potential spectroscopic studies using intense gyrotron radiation, are demonstrated. The results of observations with a RAD spectrometer and a direct absorption spectrometer for the lines of two-photon rotational transitions of OCS and SO2 molecules, which have well-studied spectra and a large dipole moment, are presented. Promising opportunities for using gyrotrons to solve fundamental and practical problems are discussed.

Fish in the Volga-Kama River System (the largest river system in Europe) are important as a crucial food source for local populations; fish have the highest trophic level among hydrobionts. The purpose of this research is to describe the diversity of non-indigenous and native fish in the Volga and Kama Rivers, in the European part of Russia. This dataset encompasses data from June 2001 to September 2021 and comprises 1888 records (36,376 individual observations) for littoral and pelagic habitats from 143 sampling sites, representing 52 species from 42 genera in 22 families. The dataset has a Darwin Core standard format and has been fully released in the Global Biodiversity Information Facility (GBIF) under CC-BY 4.0 International license. The data are validated with several international databases such as FishBase, Eschmeyer’s Catalog of Fishes, the Barcode of Life Data System, and the SAS.Planet geoinformations system. Newly established populations have been found for several species belonging to the following Actinopteri families: Alosidae, Anguillidae, Cichlidae, Ehiravidae, Gobiidae, Odontobutidae, Syngnathidae, and Xenocyprididae. Therefore, this dataset can be used in the particular taxon species distribution analysis, which are especially important for non-indigenous species.

This paper presents a new concept of a complex electron-optical system for advanced gyrodevices. The system forms two helical electron beams moving towards each other in the interaction space and makes it possible to independently control the parameters of each beam.

The Mekong River is the 10th largest river in the world. It is recognised as the most productive river in Southeast Asia and economically essential to the region, with an estimated 60-65 million people living in the lower Mekong Basin. The Mekong Delta within Vietnam is considered a highly vulnerable ecosystem under threat from increasing anthropogenic pressure, such as dam construction and, as a consequence, the Delta is sinking and altering the natural hydrological cycle. Dams also lead to eutrophication and pollution of downstream water from regulated water flux and water stagnation. Another threat is climate change coupled with the lower rainfall, which could lead to an increased risk of drought in the Mekong Delta Basin. Thus, these project data represent an important baseline reference. The ecological health of the Mekong Delta’s environment, as indicated by the quality and availability of its water and biological resources, largely determines the economic and social development of the region, which produces about half of the agriculture and aquaculture products of Vietnam.This paper reports quantitative data on the biodiversity of six groups of aquatic organisms: bottom and pelagic fish, macrozoobenthos, microorganisms, phyto- and zooplankton in the Mekong Delta within Vietnam, as well as data on the physicochemical parameters of water and bottom sediments. The data were collected during 2018-2022 as part of the Ecolan E-3.4 programme within the framework of the research plan of the Joint Russian-Vietnamese Tropical Research and Technological Center. All presented datasets are published for the first time.

The paper describes the experimental setup and some results of experiments on the production of highly dispersed metal oxides powders using the example of tungsten trioxide WO 3 by the evaporation-condensation method when the initial material is heated by focused radiation of 0.53 THz / 240 W gyrotron. By focusing the gyrotron radiation, it was possible to achieve an intensity of several kW/cm 2 on the surface of the evaporated initial sample. The use of a system with a rotating crucible made it possible to increase the evaporation rate of the substance by 3–4 times, which is very important in conditions of a lack of power.

Xenophthalmus pinnotheroides is a tiny subtidal marine crab from the West Pacific and Northern Indian Oceans. Its native range is poorly documented, with few records from the wild. Although it is not exploited by humans, degradation of suitable habitats by anthropogenic activities can significantly threaten this species. Here we bring the first record of the species in Vietnamese waters and prediction of its native range based on climate matching analysis. The areas of its potential occurrence are highlighted and future confirmation through field survey is recommended. The present findings indicate the range extension of X. pinnotheroides in Asia.

We discovered a specific property of the eigenmodes of a cylindrical waveguide, due to which efficient mode excitation at ultrahigh (s = 4n + 1, n is integer) multiples of the gyrofrequency can be provided by a polyhelical weakly relativistic electron beam, standardly used for gyrotron operation. In the proof-of-principle experiment with a V-band gyrotron driven by a 25-keV, 2-A beam, about 100 mW radiation power at the fifth cyclotron harmonic (0.22 THz) has been detected in the cw regime. Based on the gyrotron theory, we demonstrate in simulations that, using parameters of existing gyrotrons, this method can be applied for producing cw radiation at a power level of up to several watts in the terahertz gap.

The results of the development and experimental implementation of a device for controlling the parameters of high-power microwave radiation, the principle of operation of which is based on the controlled rotation of the polarizing plate in a plane perpendicular to the linearly polarized microwave beam propagation axis are presented. Stabilization of the power of a subterahertz gyrotron at a level of several percent in a wide range of tuning of control parameters is experimentally demonstrated. The developed device can be successfully used to solve a number of problems aimed at studying the interaction of high-power microwave radiation with matter.

A semiquantitative technique for imaging of high-power millimeter wave (MMW) beam using visible light from the plasma of an MMW-induced gas breakdown, which was initiated by a metal-dielectric (MD) screen, is discussed. The design of the gas breakdown sensor for imaging of the wave beam is presented. A plane MD screen was placed in a shallow airtight chamber with a transparent window of a thin mylar film. The chamber was filled with gas at a near atmospheric pressure. An MMW-induced breakdown in air, nitrogen, helium, and krypton, initiated by an MD screen, has been experimentally studied. In the experiments, a high-power 250-GHz pulsed gyrotron served as the source of MMWs. In a chamber filled with noble gases, bulk plasma was formed at an MMW intensity above the gas breakdown threshold. A single-pulse wave beam was imaged using a profile of the flux density of light from the breakdown plasma in helium and krypton. It was shown that using the presented technique, one can determine the position of the intensity maxima and the beam profile of an MMW beam in the range from one to two threshold intensities of an MMW-induced gas breakdown initiated by an MD screen.

This paper presents concept of the active Moon radar based on 0.26 THz frequency-stabilized gyrotron. The aim of the project is to demonstrate the possibility of using a gyrotron for millimeter wavelength detection of space objects, which may make it possible in the future to implement radars of the specified range with a high spatial resolution using advantages of coherent radar systems.

The results of theoretical and experimental studies aimed at ensuring long-term stability of the power of a subterahertz gyrotron when tuning the generation frequency are presented. Power stabilization is performed via the coordinated change in the technical parameters of the generation mode. Two pairs of such parameters are considered: the accelerating voltage and the temperature of the resonator coolant or the magnetic field and the temperature of the resonator coolant. As a result of experiments performed with a subterahertz gyrotron of a kilowatt power level, power stability was demonstrated at a level of several percent with a frequency tuning range of more than 100 MHz, which confirms the correctness of the proposed approaches.

In this paper, the temperature dependence of the absorption index of Al 2 O 3 , ZnO, and TiO 2 powders at a frequency of 527 GHz was studied. A continuous-wave gyrotron with an output power up to 240 W was used as a microwave power source for heating the samples. The power absorbed by the samples was measured in the temperature range from 300 to 1000°C. A significant increase (by four to six times) in the absorption index was observed as compared with the experiments at a frequency of 263 GHz.

A method of obtaining highly dispersed tin (II) oxide (SnO) powder by the evaporation-condensation method was investigated when the initial material was heated by focused radiation of a subterahertz gyrotron with a frequency of 0.26 THz and a power of 1 kW. The process was carried out with a purge with nitrogen inert with respect to SnO. A powder with a SnO weight content of 92% was obtained. The specific surface was 7.20 m2/g, which corresponds to an average particle size of 130 nm. The characteristics of the obtained powder are analyzed. The applicability of the experimental setup for the production of nanopowders from compounds requiring special gas conditions during the evaporation-condensation process has been demonstrated.

We present two sets of experiments on the multiplication of gyrotron radiation frequency. The first one utilizes the second-order susceptibility of the crystal lattice in InP semiconductor with maximum conversion efficiency estimated at 1%. The second experiment is focused on the effect of simultaneous excitation of modes of the cylindrical resonator, resonant with the first, second, and third cyclotron harmonics with the conversion efficiency of up to 10 −4 .

The temperature dependences of the absorption coefficient of Al2O3, ZnO, TiO2 powders at a frequency of 527 GHz are investigated. A gyrotron with an output power of up to 240 W in CW mode was used as a radiation source for heating the samples. The power absorbed in the samples was measured in the temperature range from 300 to 1000 ° C (for some samples). Compared with experiments at a frequency of 263 GHz, a significant increase (by a factor of 4 - 6) in the absorption coefficient is observed. The results may be of interest to researchers involved in microwave heating of materials.

To cover the so-called terahertz gap in powerful sources of coherent electromagnetic waves, a second-harmonic gyrotron operating in a 10 T liquid helium-free superconducting magnet has been designed, manufactured, and tested. With an operating voltage of 15 kV and a beam current of 0.6 A, the gyrotron generated coherent continuous-wave radiation at a frequency of 0.526 Terahertz with an output power of 250 Watts and an efficiency of 2.7%.

The free space radar equation has been analyzed for the field of parameters of a mighty source of sub-terahertz electromagnetic waves used for radar applications and long-range space telecommunication in surface and ground-to-space channels. Some new potential tasks of such coherent radars have been found feasible including active search for space debris and new radar astronomy tasks.

The changes in depth, temperature, water conductivity, and dissolved oxygen concentration in six floodplain lakes are described in regard to the dynamics of spring flooding and overgrowth by macrophytes. The influence of these factors on the composition and structure of macrozoobenthos communities is analyzed. The observed number of species refers to 60% of the theoretically predicted, which allows us to assume that the fauna has been identified sufficiently enough to analyze the interannual changes. Six families of invertebrates, which form together 55% of the fauna, are the richest in species number. The distribution of species by families also confirms enough data on the fauna representing in the obtained and analyzed samples. Abundance of only two species depend significantly on environmental characteristics; the taxonomic and trophic groups exhibit more links to the environment. Totally, 45 mutually associated species (43.7% of the total list) have been identified; they form 8 groups that are characterized by connectivity of the species composition ranging as 0.28–1.0 link/species, the average connectivity strength of 0.67–0.80, and the strength of species connectivity of 0.38–0.84 (the last index is proposed for the first time). Groups of mutually associated species may be defined as “faunistic cores of communities” confined to certain lakes and/or years of study. According to the redundancy analysis with multidimensional scaling ordination, the environmental factors affect the quantitative characteristics and overall taxonomic richness of communities. The indices, describing the structure of communities, do not depend on the analyzed factors, which is also confirmed by correlation analysis.