A. I. Tsvetkov

An immunoelectron study of karyosphere and nuclear bodies in oocytes of mealworm beetle, Tenebrio molitor (Coleoptera: polyphaga).

Abstract. The karyosphere and nuclear bodies (NBs) were studied in Tenebrio molitor oocytes using immunoelectron cytochemistry. During early diplotene (previtellogenic stage), oocyte chromosomes begin to unite in a small nuclear volume forming the karyosphere. In vitellogenic oocyte nuclei, the chromatin undergoes condensation, and the karyosphere acquires a ring-shaped structure. The karyosphere is the only structure containing DNA in the oocyte nucleus. Pre-mRNA splicing factors [small nuclear ribonucleoproteins (snRNPs) and SC35] are not found in the karyosphere itself. In previtellogenic oocyte nuclei, these factors are present in NBs and in a fibrogranular substance surrounding the chromosomes in the early stages of karyosphere formation. At this stage, larger fibrillar NBs contain the non-snRNP splicing factor SC35. Smaller roundish NBs were shown to contain snRNPs. Some NBs with the same morphology contain neither snRNPs nor SC35. In the vitellogenic oocyte, there are fibrogranular NBs containing both snRNPs and SC35 splicing factors, fibrillar NBs containing snRNPs only, and complex NBs containing both. Complex NBs are often connected with the ring-shaped karyosphere. Based on the obtained immunoelectron data, we suggest that T. molitor oocyte NBs containing both snRNPs and the non-snRNP splicing factor SC35 are homologs of the well-characterized B-snurposomes in amphibian germinal vesicles and clusters of interchromatin granules in mammalian oocyte nuclei. Other NBs containing only snRNPs are suggested to represent a special class of insect oocyte snurposomes. The nuclear organelles mentioned seem to play a role as storage domains for pre-mRNA splicing factors during T. molitor oogenesis.

Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media

A 263 GHz continuous-wave (CW) gyrotron was developed at the IAP RAS for future applications as a microwave power source in Dynamic Nuclear Polarization / Nuclear magnetic resonance (DNP/NMR) spectrometers. A new experimental facility with a computerized control was built to test this and subsequent gyrotrons. We obtained the maximum CW power up to 1 kW in the 15 kV/0.4 A operation regime. The power about 10 W, which is sufficient for many spectroscopic applications, was realized in the low current 14 kV/0.02 A regime. The possibility of frequency tuning by variation of the coolant temperature about 4 MHz/1 °C was demonstrated. The spectral width of the gyrotron radiation was about 10(-6).

Time-resolved imaging of millimeter waves using visible continuum from the positive column of a Cs-Xe dc discharge

We present a high-sensitivity technique for time-resolved imaging of millimeter waves (MMWs) using the visible continuum (VC) from the positive column (PC) of a medium-pressure Cs–Xe dc discharge. For the MMW imaging application, a uniform plasma slab of the PC of a Cs–Xe discharge with 10×8 cm2 aperture and 2 cm in thickness was generated for 45 Torr xenon. The imaging technique is based on the fact that the intensity of the e-Xe bremsstrahlung continuum from the PC increases in the visible region when the electrons in the plasma are heated by MMWs. It is shown that in the MMW intensity range from zero to the threshold of the microwave-induced plasma breakdown, the intensity of the VC from the PC of a Cs–Xe discharge increases approximately as a second-order polynomial function of the MMW intensity. The obtained experimental data agree well with our calculations of the dependence of the VC intensity on electron temperature. The Ka-band MMW field patterns at the output of conical horn antennas and in the ...

First experimental tests of powerful 250 GHz gyrotron for future fusion research and collective Thomson scattering diagnostics

A 250 GHz continuous-wave (CW) gyrotron has been developed at the IAP RAS jointly with GYCOM Ltd., as a prototype of the microwave source for the envisaged prospective nuclear fusion power plants (DEMO). The main applications of such a tube are electron cyclotron resonance heating and electron cyclotron resonance current drive of magnetically confined plasma as well as its diagnostics based on collective Thomson scattering in various reactors for controlled thermonuclear fusion (e.g., tokamaks and stellarators). The results of the preliminary experimental tests in a pulsed mode of operation are presented. The microwave power of up to 330 kW with an efficiency of 30% without collector depression was obtained. At an accelerating voltage of 55 kV and an electron beam current of 12.5 A (which corresponds to the design parameters for CW operation), the measured output power was about 200 kW. The TEM00 mode content evaluated at the tube output is not less than 98.6%.

High-power sub-terahertz source with a record frequency stability at up to 1 Hz

Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10−4. Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 × 10−12 and 10−10, respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.

Imaging of spatial distributions of the millimeter wave intensity by using the Visible Continuum Radiation from a discharge in a Cs–Xe mixture. Part II: Demonstration of application capabilities of the technique

The paper presents the second part of the review on a high-sensitive technique for time-resolved imaging and measurements of the 2D intensity profiles of millimeter-wave radiation by means of Visible Continuum Radiation emitted by the positive column of a medium-pressure Cs-Xe DC Discharge (VCRD method). The first part of the review was focused on the operating principles and fundamentals of this new technique [Plasma Phys. Rep. 43, 253 (2017)]. The second part of the review focuses on experiments demonstrating application of this imaging technique to measure the parameters of radiation at the output of moderate-power millimeter-wave sources. In particular, the output waveguide mode of a moderate-power W-band gyrotron with a pulsed magnetic field was identified and the relative powers of some spurious modes at the outputs of this gyrotron and a pulsed D-band orotron were evaluated. The paper also reviews applications of the VCRD technique for real-time imaging and nondestructive testing with a frame rate of higher than 10 fps by using millimeter waves. Shadow projection images of objects opaque and transparent for millimeter waves have been obtained using pulsed watt-scale millimeter waves for object illumination. Near video frame rate millimeter-wave shadowgraphy has been demonstrated. It is shown that this technique can be used for single-shot screening (including detection of concealed objects) and time-resolved imaging of time-dependent processes.

45 GHz/20 kW gyrotron-based system for ECR ION source

This paper describes gyrotron-based setup developed by Gycom Ltd. jointly with IAP RAS and intended for use in superconducting ECR ion source FECRAL (a Fourth generation ECR ion source with Advanced design in Lanzhou, China) [1]. The setup is capable to provide output power up to 20 kW in both CW and pulse 15 - 200 ms duration with less than 10 μs fall time and up to 5 Hz repetition rate) modes with 45 GHz frequency. Gyrotron system uses a cryogen-free magnet JMTD-4T140 made by Jastec Inc. (Japan) that allows it to operate on fundamental harmonic (operation mode is TE63). Gyrotron tube is designed to operate with diode-type electron gun, and using of depressed collector for recuperation of the electron beam residual energy leads to considerable total efficiency increasing. Output gyrotron radiation is converted by two-mirror matching optics unit (MOU) to the TEM00 mode. Gaussian beam propagates from the MOU output through the air 1 to the distance of about 2 m) to the system of mirrors delivering the one to the mode converter (TEM00 to TE01) which is located on the high voltage (about 300 kV) platform and connected via waveguide with the FECRAL ion source. The gyrotron rack is under ground potential. The setup is fully equipped with the automated control, data acquisition and safety interlocks systems which guarantee convenient and safe operation. Currently the described system is under manufacturing. Commissioning tests are scheduled for the end of this year.

Multiparametric gyrotron power control during microwave processing of materials

Optimization of the control of gyrotron generation regime through consistent variation of the cathode voltage and solenoid magnetic field makes possible a significant (up to threefold) decrease in power consumption during microwave processing of materials. It is experimentally established that, for this purpose, it is possible to use fast (with a characteristic time on the order of a fraction of millisecond) modulation of microwave power through variation of the working magnetic field by the current of an auxiliary coil arranged near the cavity.

Electrokinetic and Biochemical Changes in Erythrocytes under the Action of Terahertz Range Electromagnetic Waves

The effects of electromagnetic radiation of a gyrotron with an operating frequency of 263 GHz on rat erythrocyte electrophoretic mobility, malonic dialdehyde, ATP, and 2,3-diphosphoglycerate concentration have been studied in vitro. The blood was irradiated under continuous and pulsed gyrotron emission modes with the estimated incident energy flux on an object from 0.1 to 20 mW/cm2. It has been established that the studied erythrocyte characteristics changed in different directions depending on the mode and the incident energy flux: the erythrocyte electrophoretic mobility rate and ATP concentration decreased, while the malonic dialdehyde and 2,3-diphosphoglycerate concentration increased at a low incident energy flux and continuous exposure mode; all studied parameters increased under the pulsed exposure mode. An incident energy flux increase caused a reduction of these effects.

Experimental investigations of 263 GHz/1 kW gyrotron based system for diagnostic of various media

The last decade has contributed to the rapid development of THz gyrotrons. The series of pulsed and CW tubes has been developed by FIR FU (Japan), MIT, CCR and CPI (USA), EPFL (EU), and IAP RAS (Russia) [1]. Some novel applications have been developed, but the most actual is high resolution spectrometry. The DNP/NMR spectrometers based on gyrotrons with relatively high microwave power (several tens Watts) give a possibility increase spectrometer signal to nose ration about two orders. First commercially available gyrotron based spectrometer has been developed by Bruker Biospin based on CPI gyrotron. Gyrotron with operation frequency 258 GHz developed developed by IAP RAS jointly with GYCOM Ltd. (Nizhny Novgorod, Russia), successfully used for DNP/NMR experiments and result signal enhancements up to 80 times [2].