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By means of reflecting the output radiation from a wideband Bragg reflector, a multifrequency radiation source was experimentally implemented based on a continuous wave (CW) helical gyroresonance traveling-wave tube (gyro-TWT) with an operating frequency of about 24 GHz. Oscillation regimes were obtained with distances between the spectral component at 93–122, 193–239, 311–376, 496, 624, and 736 MHz, corresponding to excitation of various combinations of longitudinal modes. Existence of regimes with the second spectral component in intensity at the same level as the intensity at the central frequency was demonstrated, which are of significant interest for multifrequency plasma heating applications.

Experimental details are discussed and millimeter wave measurements presented of a W-band gyrotron traveling-wave tube (gyro-TWT) that uses a helically corrugated interaction waveguide operating at the second electron cyclotron harmonic. A method for increasing the gain by using an interaction circuit with two sections separated by a long sub-cutoff drift section has been experimentally verified. A 10-mW driving source was sufficient to enable an amplified signal output power of 3 kWs. The continuous-wave (CW) operation with a single-stage depressed collector and deposited beam power of about 20 kW is believed to be the first demonstration of its kind for a W-band gyro-TWT.

A magneto-armored system for a new generation of technological complexes based on CW K-band gyrotrons (28–50 GHz), which operate on the main cyclotron resonance with an output power of 25–30 kW or higher, was developed and experimentally tested. The possibility of creating a homogeneous (better than 0.5%) sector of the magnetic field in the region of the electron–wave interaction with a length of several tens of millimeters has been demonstrated. Optimization of the configuration, shapes, and material that were used for the ferromagnetic screens for solenoids with copper windings and working-hole diameters of several tens of millimeters made it possible to obtain record values of constant magnetic fields with respect to the power consumption. For the operating mode with a uniform section of 65 mm and a magnetic-field induction of 1.03 T, the power consumption of the solenoid was 12.5 kW, which makes it possible to significantly (by ~1.5 times) increase the efficiency of the complex as a whole when using a gyrotron with a full radiation efficiency of nearly 50%, which is significantly superior to the existing analogues.

The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyrotron amplifiers, which produce pulsed or continuous-wave radiation in the millimeter-wavelength band at a power level that exceeds the powers produced by conventional TWTs with slow-wave structures and rectilinear beams by 1–2 orders of magnitude. Since 1996, researchers at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) have been developing the concept of the gyro-TWT based on the use of a waveguide with a helically corrugated surface, which changes the dispersion of one of the eigenmodes in a circular waveguide radically. In this paper, we discuss several problems that arise in implementation of such devices, which many years of experimental studies have revealed, present the parameters of gyro-TWTs developed with allowance for specific applications of their end users, and discuss lines of further perfection of such amplifiers.

An overview of the main principles of operation and design for major components of the gyrotron travelling-wave tube (gyro-TWT) based on a helically corrugated waveguide is presented.

Design, simulation results and first experimental results are presented for a W-band gyro-TWT using helically corrugated waveguides in its microwave circuit. The specific of this gyro-TWT is a sectioning (2 helical-waveguide sections separated by a sub-cutoff drift channel) which enables its operation at the second cyclotron harmonic with a high gain (45–50 dB) and high stability to the spurious oscillations. Using an available superconducting magnet with B-field of 1.9 T the tube was designed to be powered by a 40-kV 0.7-A electron beam with a pitch-factor of 1.3. The 3D PIC simulations predict the maximum output power of 3 kW at about 95 GHz and l-kW-level bandwidth of 7.2 GHz when driving by a 100-mW input signal.

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.

We consider in detail the method allowing one to input and output the microwave radiation produced by an elecrovacuum amplifier through the same barrier window, which was proposed earlier, in the context of its application in a traveling-wave tube based on a waveguide with a helically corrugated surface. Special attention is given to the splitter of differently polarized radiation, and the results of studying this splitter at wavelengths of about 6 and 1 mm theoretically and experimentally are presented.

We present experimental results on a high-power transmission line from the broadband pulsed Ka-band gyro-TWT to the phased antenna array. The transmission line is designed to operate in a pulse-periodic regime with a pulse width of up to 250 μs, a duty factor of 8, and an average output power of up to 15 kW. Amplitude–frequency and phase–frequency characteristics of the transmission line were measured at a low power level. It is shown that the nonlinearity of the phase–frequency characteristic does not exceed ±10° in the 34 ± 0.5 GHz frequency band.

A cascade of two gyrotron travelling-wave tubes (gyro-TWTs), one of those possesses a relatively high gain (46 dB) while the other provides high output power (350 kW) at the moderate (22 dB) gain, is under design and modeling. Both gyro-TWTs use helically corrugated waveguides and operate at the second cyclotron harmonic. A principal scheme of such an amplifier chain is discussed including issues of microwave input, output and transmission between the tubes. Computer modeling of the beam-wave interaction using CST Particle Studio PIC Solver shows feasibility of achieving of 350 kW pulse output power with 6-8 GHz bandwidth when driving by a 50-mW input source at W-band.

A brief review of research activity on gyrotron traveling-wave tube amplifiers (gyro-TWTs) with helically corrugated waveguides developing by the Institute of Applied Physics and GYCOM (Nizhny Novgorod, Russia) will be presented.

Research activity on development of gyrotron travelling-wave tubes (gyro-TWTs) at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) is presented. In the gyro-TWTs under discussion a helically corrugated waveguide is used as a principal part of their microwave circuits which ensures a number of advantages over other configurations of the gyro-TWTs.