Dmitry I. Sobolev

Bio: Dmitry I. Sobolev is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Gyrotron & Microwave. The author has an hindex of 8, co-authored 44 publications receiving 222 citations.

Method for synthesis of waveguide mode converters

Abstract: We propose an iterative method for synthesis of waveguide mode converters. An application of this method for bent circular waveguides is considered. Examples of synthesized converters calculated using this method are presented. The method offers fundamentally new solutions to the problems of mode converter development.

Principles of Synthesis of Multimode Waveguide Units

Abstract: We propose principles which represent a systematic approach to the synthesis of multimode waveguides converting a specific input field into a different output field. Using these principles, fast and efficient methods of synthesis with specified properties can be constructed for any field analysis method. Several new methods of synthesis for most important applications are offered, and synthesized waveguide components are presented to demonstrate their efficiency.

A high-speed quasi-optical wave phase switch based on the induced photoconductivity effect in silicon

Abstract: A new microwave switch is proposed, in which the active element represents a metal reflector with a semiconductor plate on a mirror surface. The wave beam phase switching is ensured by a conducting layer formed in the semiconductor by laser radiation with quantum energy approximately equal to the bandgap width. Using a disk of high-purity silicon irradiated by a pulsed Ti:sapphire laser, a 180° phase switching in a 30-GHz wave beam has been studied. At a low microwave power level, the wave phase was effectively switched during a time on the order of several nanoseconds.

Millimeter Wave Multi-mode Transmission Line Components

Abstract: The present paper reports on the recent development of several oversized millimeter wave transmission line components for different applications. The studies include a circular TE11-to-Gaussian beam mode converting horn, a TM01-to-rotating TE31 mode converter, a TE11-mode 90° bend, a series of different HE11-mode transmission line components, a notch filter and a fast laser controlled semiconductor microwave switch.

Nanosecond Microwave Semiconductor Switches for 258…266 GHz

Abstract: Optically controlled microwave switches open the way to commutate radiation frequencies up to terahertz. The switches are based on induced photoconductivity effect in semiconductors changing properties of resonant systems they are built in. The prospective applications—plasma heating, radars, particle accelerators, and spectroscopy—often require switching rapidness up to nanoseconds and coherence of output pulse packets between each other. Our waveguide semiconductor switches seem to be the most promising to satisfy these requirements. Several working switches have been built and tested for frequency range from 258 to 266 GHz at microwave power of 25 mW. The maximum possible microwave power to be switched is expected up to several watts or even higher with special heat dissipation means. The switches demonstrate nanosecond level of performance when controlled by a 10-ns green 527-nm laser with pulse energy of about 100 nJ.

State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

Abstract: This paper presents a review of the experimental achievements related to the development of high-power gyrotron oscillators for long-pulse or CW operation and pulsed gyrotrons for many applications. In addition, this work gives a short overview on the present development status of frequency step-tunable and multi-frequency gyrotrons, coaxial-cavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, relativistic gyrotrons, large orbit gyrotrons (LOGs), quasi-optical gyrotrons, fast- and slow-wave cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWOs, gyro-harmonic converters, gyro-peniotrons, magnicons, free electron masers (FEMs), and dielectric vacuum windows for such high-power mm-wave sources. Gyrotron oscillators (gyromonotrons) are mainly used as high-power millimeter wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control, and diagnostics of magnetically confined plasmas for clean generation of energy by controlled thermonuclear fusion. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons employing synthetic diamond output windows is 30 min (CPI and European KIT-SPC-THALES collaboration). The world record parameters of the European tube are as follows: 0.92 MW output power at 30-min pulse duration, 97.5% Gaussian mode purity, and 44% efficiency, employing a single-stage depressed collector (SDC) for energy recovery. A maximum output power of 1.5 MW in 4.0-s pulses at 45% efficiency was generated with the QST-TOSHIBA (now CANON) 110-GHz gyrotron. The Japan 170-GHz ITER gyrotron achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min) and the efficiency record of 57% for tubes with an output power of more than 0.5 MW. The Russian 170-GHz ITER gyrotron obtained 0.99 (1.2) MW with a pulse duration of 1000 (100) s and 53% efficiency. The prototype tube of the European 2-MW, 170-GHz coaxial-cavity gyrotron achieved in short pulses the record power of 2.2 MW at 48% efficiency and 96% Gaussian mode purity. Gyrotrons with pulsed magnet for various short-pulse applications deliver Pout = 210 kW with τ = 20 μs at frequencies up to 670 GHz (η ≅ 20%), Pout = 5.3 kW at 1 THz (η = 6.1%), and Pout = 0.5 kW at 1.3 THz (η = 0.6%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require tubes with the following parameters: f > 24 GHz, Pout = 4–50 kW, CW, η > 30%. The CW powers produced by gyroklystrons and FEMs are 10 kW (94 GHz) and 36 W (15 GHz), respectively. The IR FEL at the Thomas Jefferson National Accelerator Facility in the USA obtained a record average power of 14.2 kW at a wavelength of 1.6 μm. The THz FEL (NOVEL) at the Budker Institute of Nuclear Physics in Russia achieved a maximum average power of 0.5 kW at wavelengths 50–240 μm (6.00–1.25 THz).

Ultra-compact photonic crystal waveguide spatial mode converter and its connection to the optical diode effect.

Abstract: We design an extremely compact photonic crystal waveguide spatial mode converter which converts the fundamental even mode to the higher order odd mode with nearly 100% efficiency. We adapt a previously developed design and optimization process that allows these types of devices to be designed in a matter of minutes. We also present an extremely compact optical diode device and clarify its general properties and its relation to spatial mode converters. Finally, we connect the results here to a general theory on the complexity of optical designs.

THz Dynamic Nuclear Polarization NMR

Abstract: Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140- 600 GHz ). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

Development in Russia of high-power gyrotrons for fusion

Abstract: The paper presents the latest development achievements in Russian institutions IAP/GYCOM of MW power level gyrotrons for fusion installations.

Smart Surfaces: Large Area Electronics Systems for Internet of Things Enabled by Energy Harvesting

Abstract: Energy harvesting is well established as one of the prominent enabling technologies [along with radio-frequency identification (RFID), wireless power transfer, and green electronics] for the pervasive development of Internet of Things (IoT). This paper focuses on a particular, yet broad, class of systems that falls in the IoT category of large area electronics (LAE). This class is represented by “smart surfaces.” The paper, after an introductory overview about how smart surfaces are collocated in the IoT and LAE scenario, first deals with technologies and architectures involved, namely, materials, antennas, RFID systems, and chipless structures; then, some exemplifying solutions are illustrated to show the present development of these concurrent technologies in this area and to stimulate further solutions. Conclusions and future trends are then drawn.