I. G. Gachev

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.

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%.

Cascade of Two

In order to realize a high-power (100 s of kilowatts at the W-band) wideband microwave amplifier, we suggest to use a cascade of two gyrotron traveling-wave tubes (gyro-TWTs), one of which possesses a relatively high gain (40–50 dB) while the other provides a high output power at a moderate (15–20 dB) gain. Both gyro-TWTs are assumed to use helically corrugated waveguides and operate at the second cyclotron harmonic. A principal scheme of such an amplifier chain is discussed, including issues on the microwave input, output, and transmission between the tubes. Computer modeling of the beam-wave interaction using CST Particle Studio PIC Solver shows the possibility of achieving of 200–370-kW output power with 8–10-GHz bandwidth when driving by a 50-mW input source at the W-band.

W

Recent results on low-relativistic second-harmonic gyro-devices using a microwave system in the form of a helically corrugated waveguide are presented. New Ka-band gyro-TWT is designed to operate with peak power of 100-120 kW, average power up to 10 kW and frequency bandwidth of about 10%. In the first experimental test a peak power of 130 kW, efficiency of 22-24% and bandwidth at least 2 GHz were achieved for 70-kV electron beam with pulse length up to 100 mus and repetition frequency up to 5 Hz. Frequency-tunable gyro-BWOs, attractive for some technological applications, enable CW output power of several kW at 24 GHz with smooth frequency tuning of 4-6%.

-Band Helical-Waveguide Gyro-TWTs With High Gain and Output Power: Concept and Modeling

New projects and experimental results on low-relativistic second-harmonic gyro-devices using a microwave system in the form of a helically corrugated waveguide will be presented. A CW 30 kV/0.7 A gyro-TWT with designed output power up to 4 kW and frequency bandwidth 29.8–31.3 GHz (5%) will be discussed in more detail.

Gyro-TWTs and Gyro-BWOs with helically corrugated waveguides

Methods for realization of two-wave gyro-oscillators with frequency multiplication provided in a single operating cavity are proposed. A possibility for realization of a moderately-relativistic (250 keV) THz gyro-multiplier operating at 5-6 cyclotron harmonic with the output power of about 1 kW, as well as of an analogous weakly-relativistic (80 keV) CW device with the output power of 1 W, is demonstrated.

Development of helical-waveguide gyro-TWT and gyro-BWO

An experimental study was carried out to test high-harmonic gyroklystron amplifier concept. A two-cavity 35-GHz second-harmonic gyroklystron with the TE021 cavity mode has been built and tested in pulse operation. Output power of 258 kW with efficiency 18% and 17-dB gain have been produced at 72 kV beam voltage and 20-A beam current. Bandwidth of about 0.3% have been observed. The restriction of the output power, efficiency and gain was caused by the spurious oscillations excited in the second cavity in the TE011 mode at the fundamental cyclotron frequency.

High-harmonic gyrodevices with frequency multiplication

One of the problems encountered in the design of high-power gyrotrons is the need to ensure stable single-mode generation. The conditions of spurious self-excitation in a gyrotron resonator have been studied fairly completely, and methods for its suppression have been developed (see Petelin [1] and Nusionvich [2], for example). At the same time, stable gyrotron operation can also be disrupted by the generation of spurious oscillations in the transition region between the electron gun and the resonator, where the electromagnetic field is nonuniform. A theoretical basis for this assumption is provided by results [1, 3, 4] indicating a fairly high efficiency of interaction of a high-frequency field with an electron current guided by a nonuniform magnetostatic field.

Experimental study of high-power Ka-band second-harmonic gyroklystron amplifier

A two-cavity gyrotron has some advantages in comparison with a traditional gyrotron. In particluar, the use of relatively short cavities with properly chosen length of the drift tube between them allows to enhance output power retaining the maximum efficiency, and to realize a tunable oscillator with high efficiency and power. The use of feedback between the cavities is proposed to solve the problem of mode competition in such an oscillator. The results of an experimental study of a Ka-band two-cavity gyrotron operating in the TE021 cavity mode are presented. The maximum power 300 kW was achieved with efficiency of 23%, the maximum efficiency was about 30%. Three zones of generation corresponding to different phase length of the feedback loop were observed. Experiments showed that the use of feedback in a two-cavity gyrotron subdues spurious oscillations.