Search

To cover the so-called terahertz gap in powerful sources of coherent electromagnetic waves, a second-harmonic gyrotron operating in a 10 T liquid helium-free superconducting magnet has been designed, manufactured, and tested. With an operating voltage of 15 kV and a beam current of 0.6 A, the gyrotron generated coherent continuous-wave radiation at a frequency of 0.526 Terahertz with an output power of 250 Watts and an efficiency of 2.7%.

Manufacturing of cylindrical cavities for short-wavelength gyrotrons is usually performed with micrometer-scale precision. In subterahertz (sub-THz) and terahertz (THz) gyrotrons, this often results in the fabrication of slightly up-tapered cavities instead of the cavities having the central parts of a constant radius. Correspondingly, the diffractive quality factors ( $Q_{\mathrm {D}}$ -factors) of such slightly conical cavities may differ from those calculated for the cavities with constant radius central parts. We show that the sensitivity of $Q_{\mathrm {D}}$ -factors to the cavity fabrication can be mitigated by introducing some local nonuniformities at the end of a slightly conical up-tapered section of the cavities. The proposed approach is illustrated with an example of a gyrotron designed for spectroscopic applications and having an output radiation power of tens of watts at the frequency of 0.527 THz. This article presents some numerical modeling results, which show how proposed local nonuniformities reduce the sensitivity of $Q_{\mathrm {D}}$ -factors to defects in fabrication.

The paper presents a series of model experiments devoted to the influence of a signal reflected from a non-resonant load on the gyrotron operation regime. The non-resonant reflector used in the experiments was in the form of an iris with remote control of its position in the waveguide. The possibility of frequency tuning in the band determined by the Q-factor of the gyrotron resonator and power modulation in a range of up to 20% was demonstrated in the experiment.

This paper presents the results of the first experiments demonstrating the possibility of wireless data transmission using a subterahertz band gyrotron signal as a carrier. The output power of the subterahertz gyrotron was modulated by a rapid change in the potential of the currentless anode. The resulting amplitude modulated (AM) signal with the medium power of about 50 W was received by the ultrafast THz detector. Successful transmission of an analog sound signal and transmission of a digital signal at a rate up to 1.5 Mbps over a distance of about 2 m was demonstrated. The investigated approach confirms its potential for data transmission using gyrotron in any frequency band without loss of generality.

An important problem in the gyrotron progress into the terahertz range is the increased requirements for the precision of fabrication of electrodynamic systems. It is shown that even minor inaccuracies in cavity manufacturing of a subterahertz gyrotron can significantly decrease the output power level. We propose a method for controlling the diffraction quality factor to reduce the influence of a weak taper of the cavity’s cylindrical part on the operation regime.

In this paper, theoretical and experimental results on the excitation of modes at higher cyclotron harmonics in gyrotrons using a reflector are considered. In particular, the excitation of the operating mode at the third cyclonic harmonic in a gyrotron with a frequency of 40.5 GHz and the design of the W-band gyrotron at the third cyclotron harmonic are discussed

The paper describes an experimental setup for obtaining nanopowders of metal oxides by the evaporation-condensation method when heating the initial material by electromagnetic radiation of THz band. A 0.26 THz/1 kW or 0.53 THz/240 W gyrotron were used as a radiation source. The setup is equipped with a quasi-optical transmission line that provides efficient transportation of radiation from the gyrotron window with subsequent focusing, providing a radiation intensity of several kW/cm2 on the surface of the evaporated material. The results of an experiment on the production of nanopowders using the described setup is also presented.

One of the most popular microwave bands now is the W-band. It is attractive by the atmospheric transparency window, which makes it promising for a number of scientific and technical applications including radiolocation, communication, detection of hidden objects and the creation of medical devices. The output power level in both continuous and pulsed regimes for the aforementioned applications should be in the order of several kilowatts and above. This makes the gyrotron one of the most high-potential sources of electromagnetic radiation in this range.The alternate design of an electrodynamic system based on the use of a diaphragm in a wave transition is proposed. This system has been theoretically and numerically analyzed for a W-band gyrotron at the third harmonic of the cyclotron frequency. The optimal parameters of the diaphragm and its position have been selected. With that parameters, the highest value of the starting current of the competing mode is reached while maintaining the starting current of the operating mode. It allows to increase the output radiation power by more than 7 times. An estimate of the accuracy of the manufacturing of the diaphragm has been made. It holds out a hope of scaling this selection method into higher frequency ranges. Further development of this system is primarily tied with a more complex optimization of the system particularly the variation of the length of the cylindrical part of the cavity, which will allow reducing the share of ohmic losses while maintaining high efficiency.The paper is based on the research results, which was conducted in the framework of projects of the Russian Science Foundation No. 17-79-10422. Keywords: Gyrotron, W-band, Mode selection

We consider the main features of a low-power frequency-tunable gyrotron with an oversized cavity, which is designed for the purposes of nuclear magnetic resonance spectroscopy and other applications and operates in the 0.20–0.27 frequency range producing an output power of 200 W. We study the possibilities of wideband output frequency tuning by exciting a sequence of modes with similar caustics using magnetic-field variations and smooth tuning due to the excitation of modes with a great number of longitudinal variations. Aiming at widening the frequency tuning range, we also analyzed the possibility of smooth frequency tuning determined by controlled variations of the cavity temperature. Specific features of the electron-optical system of such a gyrotron is discussed, along with the possibility of increasing its efficiency by means of single-stage recovery of the residual energy of the electron beam.

The excitation and effective selection of modes at high harmonics of the cyclotron frequency are experimentally demonstrated using a delayed feedback into the gyrotron. The operation at the third cyclotron harmonic at the frequency of 40.5 GHz with the output power of 3 kW and efficiency 8% is observed in a continuous wave gyrotron with an oil-cooled magnet with a field of 0.5 T in the interaction space.

A 527 GHz continuous-wave second harmonic gyrotron is in development at the IAP RAS jointly with GYCOM Ltd. as a microwave source for spectrometry and diagnostics of various media. We present first results of experimental measurements of this gyrotron including output power, power losses in the cavity, wave beam profile, frequency, and spectrum.

The paper presents recent results on the multi-beam gyrotrons operating at cyclotron harmonics in terahertz frequency range. The theoretical and experimental investigation of second harmonic 0.78 THz gyrotron includes comparison of generating and absorbing beam schemes, research on the effect of velocity spread and mode competition process, along with development of third harmonic 1.2 THz tube based on verified numerical codes and latest experimental results.

Previously, relativistic gyrotrons with thermionic magnetron-injection electron guns have been demonstrated successfully to produce radiation in the cm and long-mm wavebands with the pulse power exceeding 10 MW. This brief presents a new step toward generating higher-frequency microwaves with a relativistic gyrotron operated in the 3-mm wavelength band. The gyrotron employed with a 250 kV, 100 A, $1~\mu \text{s}$ helical electron beam. The operating wave was the rotating TE12,5,1 mode of a circular waveguide cavity. The mode was transformed into the Gaussian wave beam by a built-in mode converter. In the optimized single-mode regime, the gyrotron delivered 5.6 MW of the peak power in pulses with durations of about 0.5 $\mu \text{s}$ .

The paper presents the design of sub-THz gyrotron with field emitter and preliminary tests of its electron-optical system. In contrast with traditional tubes with thermionic cathodes, such a device can be switched on immediately, which looks promising for some applications. The theoretical investigation of mode excitation and results of trajectory analysis of the electron beam formed by the non-adiabatic electron-optical system are presented. The experimental tests of original field cathode confirm that it can stably operate at technical vacuum conditions inside the tube and provide beam current that exceeds starting current of operation mode. The output power of about 50 W at 0.5 THz has been predicted for obtained electron beam parameters.

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%.

In the last few years, gyrotron and other gyrodevises complexes based on “warm” magnets that do not require cooling to liquid-helium temperatures have been successfully created and investigated at many institutions [1]–[4]. A further step to improve the operation of such complexes is the development and design of gyrotrons operating on gyrofrequency harmonics. However, for such systems, the problem of selection of the working type of oscillations is exacerbated, especially when using oversized resonators whose ohmic losses are much lower than in the case of modes with relatively small indices. At present, a number of methods are proposed that provide high selection, both with the help of electron-optical systems and with the use of noncanonical electrodynamic systems. In this work, investigation the possibilities of using non-traditional electrodynamic systems with annular diaphragm to increase the selectivity of the working type of oscillations was done. Based on the results of the work, it is planned to develop the electrodynamic system for a W-band gyrotron operating on the third harmonic (in this case solenoid with water or oil cooling, which costs much less than a cryomagnet can be used).

Usually the gyrotron is associated with a very high power radiation source, for example, intended for heating plasma in thermonuclear projects. There are a number of promising applications of THz and sub-THz gyrotrons, such as nonlinear microwave spectroscopy, diagnostics of various media, remote detection of radioactive materials etc., for which extremely high power is not required, but the fast and flexible control of output parameters (frequency and power) is very important. The report provides an overview of the latest results obtained in IAP RAS related to control of gyrotrons output parameters.

We study experimentally the automated microwave complex for microwave spectroscopy and diagnostics of various media, which was developed at the Institute of Applied Physics of the Russian Academy of Sciences in cooperation with GYCOM Ltd. on the basis of a gyrotron with a frequency of 263 GHz and operated at the first gyrofrequency harmonic. In the process of the experiments, a controllable output power of 0.1–1 kW was achieved with an efficiency of up to 17% in the continuous-wave generation regime. The measured radiation spectrum with a relative width of about 10 −6 and the frequency values measured at various parameters of the device are presented. The results of measuring the parameters of the wave beam, which was formed by a built-in quasioptical converter, as well as the data obtained by measuring the heat loss in the cavity and the vacuum output window are analyzed.

We present the results of developing the main units of a gyrotron operated in the continuous-wave regime with a generation frequency of 0.26 THz. To improve selection of the operating mode in a oversized electrodynamic system, the gyrotron works at the fundamental cyclotron harmonic, which anticipates the use of a cryomagnet with a maximum magnetic field of 10 T, which does not require filling with liquid helium. The results of optimizing the electron-optical system, the cavity, and the quasi-optical converter of the output radiation are presented, and the control system, which is developed for the gyrotron setup, is described.

A double-beam scheme of a short-wavelength gyrotron operating at the second cyclotron harmonic is studied both within the framework of the averaged self-consistent approach and using 3-D particle in cell simulations. The analysis shows that the introduction of an additional generating electron beam allows drastically increasing the operating current of a second-harmonic gyrotron with the simultaneous suppression of self-excitation of spurious modes at the fundamental harmonic. As a result, the radiated power of a double-beam gyrotron exceeds the power of a single-beam gyrotron by a factor of four. The developed concept makes it possible to realize high-power (several hundred watts) single-mode gyrotrons in the 0.7–1.0-THz frequency range.

This paper presents the most essential steps of a design study of a novel second harmonic gyrotron operating in CW (continuous wave) regime at a frequency of 0.79 THz and an output power of 1–100 W. It is based on a novel idea for suppression of the parasitic modes using a double-beam electron-optical system (EOS). It includes a triode magnetron injection gun (MIG), which forms two high-quality helical electron beams (HEB). Different schemes, namely one with two generating beams and another with one generating and one absorbing beam, have been investigated and compared. It has been shown that the scheme with two generating beams is more advantageous since it allows an effective suppression of the parasitic modes and a stable single-mode operation at the second harmonic resonance. A MIG which is appropriate for the realization of the latter scheme has been optimized using numerical codes for computer-aided design (CAD). It forms beams with practically equal pitch factors and moderate velocity spread. The construction of the gun is not sensitive to small misalignments and shifts of the electrodes and the magnetic field. Among the most promising characteristics of the presented design are an improved mode selection and a stable single-mode generation at currents that are two to three times higher than the currents in the single-beam (i.e., conventional) gyrotrons.

Terahertz waves have the high potential for many applications. Terahertz radiation can be used for spectroscopy, especially for high-resolution DNP/NMR; for novel material processing, including production of nanopowders; for the creation and diagnostic of dense plasma (for example, such plasma looks promising for initiation of localized gas discharge as a source of multi-charge beams for nanolithography or remote detection of ionizing radiation); for security systems and so on [1]. At the same time, one of the most effective sources of such terahertz range are gyrotrons. Gyrotron is a device operating on the effect of cyclotron radiation of electrons rotating in a constant magnetic field [2]. In recent years, a series of THz band gyrotrons have been developed in the USA (CPI and MIT), Japan (FIR UF), Europe (EPFL) and Russia (IAP RAS) [3]. In the Institute of Applied Physics RAS (Nizhny Novgorod, Russia) several terahertz tubes were designed, manufactured and tested. In particular, at the fundamental cyclotron harmonic the 0.26 THz/CW gyrotron with output power about 1kW and 0.3 THz/CW gyrotron with power 2.5kW have been put into operation. Recently the gyrotron with operating frequency about 0.53 THz is under experimental test. Examples of numerical modeling and optimization of electron beam-microwave interaction are presented in this report.

Significant progress in the development of terahertz radiation sources, in particular gyrotrons, marked the last decade. A number of radiation sources have been developed at IAP RAS, including CW gyrotrons, providing an output power level up to 1kW in the frequency range 0.26–0.52 THz and the gyrotrons with pulsed magnetic systems with 100kW power level at 0.7 THz and 1kW at 1THz frequency. The report provides an overview of the latest results obtained in IAP RAS related to applications of THz band gyrotrons.

In this paper, we present the preliminary results of an ongoing experimental study of a novel double-beam gyrotron, which has been designed to operate in CW regime on the second harmonic of the cyclotron resonance with a frequency of 0.79 THz. A number of fundamental and second harmonic modes can be excited in the frequency range 0.3–0.8 THz. The observed output power levels of the order of several tens watt are available at the second harmonic of cyclotron resonance for application of this tube as a powerful radiation source for a high-field 1.2 GHz, proton DNP-NMR spectroscopy.

The relativistic gyrotron with thermionic magnetron-injection gun was developed and experimentally tested at 3-mm wavelength band. The gyrotron yielded stable generation of the rotating TE12,5,1 mode of a circular waveguide cavity with 250 kV/100A helical electron beam. The mode was transformed into the Gaussian wave beam by a built-in mode converter. Output power of the gyrotron was over 5 MW in pulses with durations of about 0.5 μs.

The state of the art for terahertz gyrotrons that are needed for various scientific research and practical applications is presented. Powers of 5 kW and 200 kW are obtained at frequencies of 1 and 0.7 THz using pulsed gyrotrons with pulse durations of tens of microseconds. A power of 100 W is demonstrated for cw gyrotrons at frequencies ranging from 0.2 to 0.5 THz.

This paper presents a comparison of simple self-consistent theory data and experimental results aimed to study the influence of the anode voltage on the frequency of the subterahertz gyrotron with the goal of frequency stabilization. Numerical simulations of the electron beam formation and beam-wave interaction in a 0.26 THz gyrotron are performed. The experimental dependence of the gyrotron frequency tuning on mod-anode voltage is in agreement with theoretical predictions.

The concept of a CW THz range gyrotrons operated at the second cyclotron harmonic is presented. To suppress the mode competition effects a double beams scheme is applied. The helical electron beams are formed in a double-beam triode magnetron-injection gun (MIG), where both emitters of the electron beams are located on a common cathode of the conventional MIG. Results of numerical simulation of electron beams formation and mode excitation have been presented. The concept makes possible output power about 200 W at the frequency 0.79 THz. The experimental tests of the tube are in progress.

We consider some effects connected with the axial misalignment of the electron beam and the cavity in gyrotrons. These effects are studied by the example of three gyrotrons with different parameters of the electron beam and output characteristics. The experimental data and the results of computer calculations are compared on the basis of a multi-mode nonstationary model of the electron-wave interaction in the gyrotron cavity.

We present the results of the experiments on a continuous-wave gyrotron with an output frequency of about 260 GHz, which has been developed for dynamic polarization of nuclei and is operated at the second cyclotron-frequency harmonic. For an accelerating voltage of 16 kV and a beam current of 0.3 A, a maximum continuous-wave radiation power of about 200 W has been obtained. Measurements of the thermal load on the resonator cavity allow evaluating its actual ohmic Q-factor. Gyrotron radiation is also observed at other frequencies and modes. Their generation zones and the structure of the output radiation have been studied. Long-term stability of gyrotron parameters has been determined.

We consider the features of a system for the formation of an electron beam in a continuouswave high-stability gyrotron at the second gyrofrequency harmonic with an operating frequency of 258 GHz. The problems related to the maintenance of the required beam parameters are analyzed. The procedure and results of numerical simulation of the electron gun and collector of the gyrotron are described. The influence of various physical factors on the characteristics of the electronoptical system of the gyrotron are studied. The design of the electron beam formation system is described along with the results of measuring its parameters.

We consider specific features of the development of a continuous-wave 258 GHz gyrotron operated at the second gyrofrequency harmonic, which are related to ensuring of high stability of its output parameters. The requirements to accuracy of manufacture of the cavity and adjustment of the electron beam are evaluated, as well as the necessary parameters of the power sources of the gyrotron complex, which should maintain the required level and stability of the generated power and frequency. The influence of the effect of spurious-mode reflection from the output window of the gyrotron is studied.

We present the results of numerical studies of the processes in the cavity of a continuous-wave gyrotron operated at the wavelength λ = 1.16 mm (operating frequency of 258 GHz) and having an output power of 100–200 W. Limitations for the choice of the working mode, which are posed by the system of electron beam formation, and the influence of parasitic modes synchronous with the electron beam at the first and second harmonics of the cyclotron frequency are considered. Optimization of the cavity profile is performed. The maximum efficiency and the radiation ower are determined for an accelerating voltage of up to 15 kV and an electron beam current of up to 0.5 A.

We compare the results of experimental studies and numerical simulation of continuous-wave gyrotrons with operating frequencies in the range 250–315 GHz. A self-consistent calculation model of the gyrotron with a nonfixed structure of the high-frequency field is used to study the influence of the ohmic loss in the cavity, the velocity spread and space charge of the electron beam, the mode interaction, and reflection of waves from the output vacuum window on the gyrotron output characteristics. The obtained results allow one to optimize the cavity profile from the viewpoint of excitation of high-efficiency single-mode oscillations at the second gyrofrequency harmonic and estimate electron beam parameters in actual gyrotrons.

The concept of a CW THz range gyrotrons operated at the second or third cyclotron harmonic is presented. To suppress the mode competition effects a double beams scheme is applied. The helical electron beams are formed in a double-beam triode magnetron-injection gun (MIG), where both emitters of the electron beams are located on a common cathode of the conventional MIG. Results of numerical simulation of electron beams formation and mode excitation have been presented. The concept makes possible high power (several hundred Watts) single-mode gyrotron operation at 0.7–1.0 THz frequency range at high harmonics.

We present the first experimental results of the study on a novel second harmonic THz-band double-beam gyrotron. The tube has demonstrated a stable single-mode operation with output parameters that are appropriate for the next-generation 1.2 GHz dynamic nuclear polarization-nuclear magnetic resonance spectroscopy. Besides the design mode (TE8,5), a series of other fundamental and second harmonic modes have been excited. This makes the new gyrotron a versatile radiation source, which can be used also in other applications of the high-power science and technologies.

The possibilities to obtain efficient operation of sub-THz gyrotrons at cyclotron harmonics are analyzed and the evolution of gyrotron optimal parameters is presented. 3D PIC simulations of THz band gyrotrons have been performed. The reasonable agreement with experimental results is demonstrated, that allows one to analyze some effects resulting from ellipticity of cavities, non-uniform emission and misalignment.

In low-power gyrotrons with weak electron-wave interaction, there is a problem of determining the optimal length of the operating cavity, which is found as a result of a tradeoff between the enhancement of the electron efficiency and the increase in the Ohmic loss share with increasing cavity length. In fact, this is the problem of an optimal ratio between the diffraction and Ohmic Q-factors of the operating gyrotron mode, which determines the share of the radiated rf power lost in the cavity wall. In this paper, this problem is studied on the basis of a universal set of equations, which are appropriate for a wide class of electron oscillators with low efficiencies of the electron-wave interaction.

Results of elaboration of continuous-wave 258.6 GHz gyrotron with output power about 100 W with high stability of output parameters is presented. This paper includes results of calculation, design, experiments and technical requirements for main subsystems of gyrotron and auxiliaries. The gyrotron setup is a main part of a complex experimental system for NDP spectroscopy.

The paper presents an overview of research activity for development of relatively low-power (10–100 W) submillimeter CW gyrotrons at the IAP RAS The design of CW IAP RAS gyrotrons on the second harmonic of gyrofrequency in the range 0.2–0.8 THz is discussed in this paper. The choosing of the operating mode was made basing on the one hand at the density of the parasitic mode spectrum, especially on the fundamental harmonic and on the other hand on possibility of formation of the electron beam in a magnetron injection gun. Optimization of the cavity profile for these gyrotrons was made and the maximum efficiency for reasonable accelerating voltage from 5 kV to 20 kV and current of the electron beam up to 1 A was determined. The main results of these calculations are presented in table 1. Also for these gyrotrons the influence of parasitic modes at the fundamental and second harmonics of the cyclotron frequency was investigated. One of these devices −0.26 THz gyrotron was developed, manufactured and tested at IAP RAS. The maximum CW output power of 200 W for accelerating voltage 16 kV and beam current 0.3 A was obtained at the experimental tests. During more than 8 hours CW operation tests at the customer's site (BRMZ of Frankfurt University) the frequency and power stability of 5⋆10−6 and 1 % respectively was demonstrated.