Sergey V. Samsonov

Gyro-BWO experiments using a helical interaction waveguide

A helically corrugated waveguide was used for a gyrotron backward-wave oscillator (gyro-BWO) experiment. A thermionic cathode was used to produce an electron beam of 90-215 keV in energy, 2-3 A in current, and pitch alpha of up to 1.6. The oscillator achieved high-efficiency frequency-tunable operation. At a fixed beam voltage of 185 kV and a current of 2 A, the output frequency was tuned by adjusting the magnetic field in the interaction cavity. A maximum power of 62 kW and a 3-dB frequency-tuning band of 8.0-9.5 GHz (17% relative tuning range) with a maximum electronic efficiency of 16.5% were measured. In addition, the interaction frequency could be tuned by varying the electron beam energy. At a fixed cavity magnetic field of 0.195 T, the output frequency and power from the gyro-BWO were measured as a function of tuning electron beam energy while the beam current was maintained at 2.5 A. A 3-dB relative frequency tuning range of 8% was measured when the electron beam voltage was changed from 215 to 110 kV.

Ka-Band Gyrotron Traveling-Wave Tubes With the Highest Continuous-Wave and Average Power

The results of experimental investigation of two Ka-band gyrotron traveling-wave tube (gyro-TWT) amplifiers with helically corrugated waveguides are presented. The first tube produces pulsed output power of 130-160 kW within the frequency range of 33.1-35.5 GHz and is capable of operating with a 10% duty factor. Reliability of its major components in the high average power operation regime (about 10 kW) was proven in a continuous-wave (CW) experiment. The second gyro-TWT amplifier delivered CW power of up to 7.7 kW with -3-dB bandwidth of 2.6 GHz and -1-dB bandwidth of 2.1 GHz. Effective implementation of single-stage depressed collectors (to the best of our knowledge, for the first time for gyro-TWTs) enabled the electron efficiencies as high as 36% for the pulsed tube and 33% for the CW tube to be achieved at operation at the second cyclotron harmonic.

Microwave pulse compression using a helically corrugated waveguide

Cylindrical waveguide with a helical corrugation on the inner surface has proven an effective dispersive medium for the compression of smoothly frequency modulated microwave pulses. This paper presents the results of experiments where ~5.6kW, X-band (8.0GHz to 12.5GHz), microwave pulses of 80ns duration and 5% frequency modulation were compressed into 1.5ns pulses with 25 times higher peak power

Sources of Coherent Terahertz Radiation

New results in the field of high‐frequency gyrotrons, gyro‐multipliers and orotrons allow one to consider these electron devices as promising candidates for the realization of powerful and available sources in Terahertz range. Electron beams with a very high compression of up to a factor of 4,400 have been obtained and selective generation at the 1st–5th cyclotron harmonics have been demonstrated in Large Orbit Gyrotrons (LOGs) at millimeter and submillimeter wavelengths at operating voltages from 50 to 250 kV. When operating at the third cyclotron harmonic (TE3,8 and TE3,9 modes in the first oscillator; TE3,5 mode in the second oscillator) output power levels of 10–20 kW have been obtained in the frequency range of 0.37–0.41 THz. Gyro‐multipliers with self‐exciting low‐frequency sections are proposed and studied theoretically. Low‐voltage orotrons have been demonstrated in the frequency range of 0.1–0.4 THz with output powers of 1.0–0.1 W and typical electrical‐mechanical frequency tunability within an o...

Microwave System for Feeding and Extracting Power To and From a Gyrotron Traveling-Wave Tube Through One Window

A method, which enables feeding and extraction of microwave radiation to and from gyrotron traveling wave tubes (gyro-TWT) using a single highly oversized barrier window is proposed. The essential conditions for effective implementation of this method are as follows: 1) the operating mode of the amplifier should be a circularly polarized one and 2) the “cold” losses of its interaction circuit should be sufficiently low. A detailed explanation of the method and discussion of the major microwave components are presented.

Analysis of Dispersion and Losses in Helically Corrugated Metallic Waveguides by 2-D Vector Finite-Element Method

Hollow metallic circular waveguides with helical corrugation of the inner surface (helical waveguides) attract considerable interest for various applications such as interaction regions in gyrotron traveling-wave tubes and as a dispersive medium for passive microwave pulse compression. In this paper, we employ a vector finite-element method in 2-D formulation for computation of the dispersion, attenuation characteristics, and the distribution of electromagnetic fields of eigenwaves of helical waveguides. As shown by comparison with the results of previously performed 3-D calculations, the presented method provides sufficient accuracy of calculating the characteristics of helical waveguides for a number of practically important cases at much lesser consumption of computer resources.

Proof-of-Principle Experiment on High-Power Gyrotron Traveling-Wave Tube With a Microwave System for Driving and Extracting Power Through One Window

A previously proposed method, which enables feeding and extraction of microwave radiation to and from gyrotron traveling wave tubes (gyro-TWTs) using a single highly oversized barrier window has been experimentally proven. A Ka-band gyroTWT using a helically corrugated waveguide bounded by a reflector at the cathode side and a polarizer at the collector side and also having a polarization separator at the beginning of the output transmission line has produced 6 kW CW power with -3-dB bandwidth of 2.1 GHz in the zero-drive-drive stable regime and about 9 kW power in the frequency locking regime.

CW Ka-Band Kilowatt-Level Helical-Waveguide Gyro-TWT

Experimental results and design details are presented on an amplifier setup based on a helical-waveguide gyrotron traveling-wave tube delivering continuous-wave kilowatt-level output power with an instantaneous frequency bandwidth of about 3%.

Experimental Study of Microwave Pulse Compression Using a Five-Fold Helically Corrugated Waveguide

This paper presents the experimental study of microwave pulse compression using a five-fold helically corrugated waveguide. In the experiment, the maximum power compression ratio of 25.2 was achieved by compressing an input microwave pulse of 80-ns duration and 9.65-9.05-GHz frequency swept range into a 1.6-ns Gaussian-envelope pulse. For an average input power of 5.8 kW generated by a conventional traveling-wave tube, a peak pulse output power of 144.8 kW was measured corresponding to an energy efficiency of 66.3%.

A Helical-Waveguide Gyro-TWT at the Third Cyclotron Harmonic

In this paper, we present a design of a broadband powerful W-band gyroamplifier with an interaction circuit in the form of a helically corrugated waveguide operating at the third cyclotron harmonic. An analysis of stability of the gyrotron traveling wave tube (gyro-TWT) with respect to parasitic wave-beam interactions at the operating and nonoperating cyclotron harmonics has been performed, and the range of parameters at which the gyro-TWT is zero-drive stable is found. Moreover, a comparison with a traditional smooth-waveguide gyro-TWT revealed that the helical-waveguide gyro-TWT possess superior stability characteristics at higher cyclotron harmonics. For a set of parameters attractive for possible applications, the 3-D particle-in-cell simulations were performed, according to which the proposed gyro-TWT yielded a 6% amplification bandwidth with the maximum output power of 80 kW and gain of 25 dB for a 10-A, 70-kV electron beam.