The paper presents the summary of the experiments on the frequency locked operation of the 1MW gyrotron with operating frequency 170GHz. We describe the design and performance of the locking signal source and different gyrotron subsystems used in the experiment. The 20kW "driver" gyrotron, equipped with frequency stabilization by means of PLL-control of modulating anode voltage in short pulses was used as the source of the stabilized locking signal. The input of the radiation into the MW gyrotron was performed by the specially designed transmission line and the quasi-optical mode converter for co- and counter-rotating modes of the cylindrical waveguide. In the experiment the frequency-locked operation of the 1MW gyrotron was demonstrated in different regimes of operation. The maximum output power was increased to 1.2MW while the spectrum width of the radiation of the powerful gyrotron was reduced to 30kHz, limited by the pulse duration. The operating zone of the TE 28,12 mode on the magnetic field was increased twofold by suppression of excitation of parasitic modes. Demonstrated results open up the new prospects for the expansion of the gyrotrons to higher frequencies and output powers for the next generation of fusion plants.

Using the technology of photopolymer three-dimensional printing with subsequent metallization, a prototype of a slow-wave system for a Q-band traveling wave lamp was manufactured. The deviations in the size of one period of the slow-wave system detected on the measuring microscope did not exceed 5 μm. The results of “cold” electrodynamic measurements of the manufactured system demonstrated good agreement with the calculated data.

The work demonstrates the division of wave beams into 2 and 4 channels using the Talbot effect in a rectangular quasi-optical waveguide, one pair of walls of which is corrugated. The calculated mode purity in each channel is 98%. In the low power experiment, the separated wave beams have a mode purity of 95% ± 2%. In addition, successful experiments on beam division were carried out at a power of 600kW and a frequency of 140GHz in pulsed mode.

We present theoretical and experimental results on mechanically machined multilayer antireflective coating of a dielectric plate. The microwave ouptut window made of fluoroplast with the refractive index n = 1.41, was studied experimentally. Holes of two different diameters were drilled in a honeycomb pattern on the surface of the dielectric to different depths in such a way that two thin quarter-wave layers were formed. The effective dielectric permittivity of the obtained layers with cylindrical inhomogeneities was calculated by the Maxwell–Garnett method. The parameters of the layers were chosen according to the Chebyshev method. This allowed us to achieve a reflection coefficient of −30 dB in the frequency range 65–100 GHz. The experimental results were compared with the theoretical calculation and the numerical analysis performed via the multiple-reflection method.

A 20 kW gyrotron-driver has been used to control the RF generation of a 170 GHz/1 MW ITER prototype gyrotron. The frequency-locked operation regime has been obtained, accompanied by an increase in power and efficiency as well as stabilization of the frequency of the slave MW-level tube.

We discovered a specific property of the eigenmodes of a cylindrical waveguide, due to which efficient mode excitation at ultrahigh (s = 4n + 1, n is integer) multiples of the gyrofrequency can be provided by a polyhelical weakly relativistic electron beam, standardly used for gyrotron operation. In the proof-of-principle experiment with a V-band gyrotron driven by a 25-keV, 2-A beam, about 100 mW radiation power at the fifth cyclotron harmonic (0.22 THz) has been detected in the cw regime. Based on the gyrotron theory, we demonstrate in simulations that, using parameters of existing gyrotrons, this method can be applied for producing cw radiation at a power level of up to several watts in the terahertz gap.

Main parameters of the possible system of electron cyclotron resonance heating of the plasma for the compact tokamak with strong magnetic field (TRT) are presented. Preliminary estimates show that, to deposit radiation with calculated power of 10 MW into the plasma at pulse duration of 100 s, 12 1-MW gyrotron complexes will be required that operate at a frequency of 230 GHz. Preliminary calculations of the main components of the system are presented.

To create electrodynamic elements of microwave and millimeter-wave devices, the possibility of using the technology of photopolymer 3D printing with the subsequent surface metallization has been investigated. The applicability of the technology is considered by the example of prototypes of a profiled helical waveguide for a microwave undulator of a Compton free-electron laser and a periodic slow-wave structure of a backward-wave tube with a ribbon electron beam. The results of low-power measurements of the parameters of the indicated electrodynamic systems are in good agreement with the simulation results.

We study a technique for diagnostics of the loss tangent inhomogeneity in semi-insulating gallium arsenide within a frequency band of 0.3THz and higher. The low-oversize-factor resonator of the recently developed optical switch formed by an intersection of a single-mode waveguide and a cutoff waveguide in the presence of a semiconductor is used to analyze small fragments of a movable test wafer. The obtained spatial resolution (0.1mm(2)) is much higher than that of the known methods. The results of using the finite difference time domain theory for synthesis of the optimal resonator are compared with the experimental data and with the data of the reference experiment performed by the known alternative method. The intrinsic precision of the loss tangent measured by our method is about 3%. The most significant difference from the known methods is that the test wafer does not overlap the traveling mode waveguide, nor perturb an existing resonator, but creates a resonator by itself. Opportunities of increasing the precision and frequency are discussed.

The paper presents the tests of a medium-powered 170 GHz gyrotron, which was developed as a master oscillator for frequency locking of megawatt-level sources. In the experiment, the output power of more than 25 kW with about 30% efficiency was obtained in CW mode. With the use of a PLL system, we stabilized this gyrotron frequency and demonstrated the spectrum width of less than 2 Hz, which corresponds to the relative value of about 10 −11 .

The paper presents gyrotron-based system (developed by IAP RAS jointly with GYCOM Ltd.) for ECR plasma heating in the new T-15MD tokamak which is under construction in National Research Center "Kurchatov Institute". The first of a series (8 units) of microwave setups of a megawatt power level was developed and successfully tested. The setup includes a gyrotron, set of power supplies, a microwave radiation transmission line, and a fast protection system. 1 MW/82.6 GHz generation regime during 30 second pulse with an efficiency of 57% was experimentally demonstrated.

We study the possibility of using the technology of 3D photopolymer printing with subsequent metallization of working surfaces for developing electrodynamic components of microwave devices. The technology applicability is considered by examples of mockups of a profiled helical waveguide for a microwave undulator of a Compton free-electron laser and a periodic slow-wave system of a backward-wave oscillator with a ribbon electron beam. The results of “cold” measurements of the parameters of these electrodynamic systems are presented and good agreement with the simulation results is obtained, which confirms the prospects of using additive technologies for developing components of the vacuum microwave electronic devices.

As part of the creation of a unique T-15MD tokamak with a magnetic field of 2 T and an aspect ratio of 2.2, the first one of a series (8 pieces) of microwave setups of a megawatt power level for electron–cyclotron plasma heating and current drive was developed and successfully tested. The setup includes a gyrotron, power supplies, a microwave radiation transmission line, and a fast (response time is no more than 10 μs) gyrotron emergency protection system. The generation regime was experimentally demonstrated with the parameters 1 MW/30 s/82.6 GHz for an efficiency of 57%.

A new type of electron cyclotron resonance (ECR) ion sources a gasdynamic ECR ion source was invented recently at the Institute of Applied Physics (IAP RAS, Nizlmiy Novgorod, Russia). The main advantages of such devices are extremely high ion beam current with a current density up to 600 700 mA/cm(2) in combination with low emittance i.e. normalized RMS emittance below 0.1 nun. mrad. The main part of previous experiments were carried out in a pulsed operation mode. Preliminary studies of plasma parameters were performed using a continuous wave (CW) source with 24 GHz/5 kW gyrotron heating. Obtained experimental results have demonstrated that all gasdynamic source advantages could be realized in CW operation. To continue development of a CW gasdynamic ion source a new experimental facility named GISMO (Gasdynamie Ion Source for Multipurpose Operation) is under construction at the IAP RAS. Future source will utilize 28 Gflz/10 kW gyrotron radiation for plasma heating. A fully permanent magnet system with magnetic field configuration close to simple mirror trap will be used for plasma confinement. Microwave radiation will be delivered from the gyrotron to a plasma chamber through a quasioptical line equipped with 100 kV DC-break. Up to 100 kV extraction will be used for intense beams formation.

A 45-GHz gyrotron-based microwave oscillator setup has been purposefully developed for powering of a superconducting electron cyclotron resonance (ECR) ion source. The setup provides a smoothly regulated output power in the 0.1–20-kW range (up to 26 kW in manual mode) with an efficiency of up to 50% and collector depression in both continuous wave (CW) and pulse modes. Pulse mode specifications: duration 5–200 ms, leading edge less than ${2}~\mu \text{s}$ , trailing edge less than ${1}~\mu \text{s}$ , repetition rate 1–10 Hz, and triggered operation using an external reference oscillator. The set of high-voltage power supplies (HVPSs) is equipped with a fast electronic protective system to ensure trouble-free operation of the gyrotron. The functional structure of the setup corresponds to the general design method for feedback-controlled microwave sources. The feedback loop consists of a power meter (or a detector unit, to the user’s choice), a control system, and an anode HVPS, the regulated voltage of which controls the output power of the gyrotron. The feedback characteristic time is less than 1 s. Feedback control is provided for both CW and pulse modes. The setup includes a unique quasi-optical line that transmits the microwave beam through a 2-m air gap, as well as a synthesized mode converter from the Gaussian beam to the TE01 or TE11 mode (to the user’s choice) installed on a 300-kV platform. During the tests, the developed setup proved to be a reliable and user-friendly tool applicable for long-term powering of the fourth-generation ECR ion sources.

This paper describes gyrotron-based microwave generator setup developed by IAP RAS jointly with GYCOM Ltd. and intended for use in superconducting ECR ion source FECRAL (a Fourth generation ECR ion source with Advanced design in Lanzhou, China) [1, 2]. The setup is capable to provide output power up to 20 kW in both CW and pulse (5-200 ms duration with less than 1 μs fall time and up to 10 Hz repetition rate) operation modes with 45 GHz frequency. The system includes quasioptical transmission line and mode converter from the Gaussian beam to TE01 or HE11 mode (at the user's option).

The paper discusses several approaches which allow development of microwave components with unique parameters. Results of two recent experiments illustrate practical value of the methods applied.

This paper describes gyrotron-based setup developed by Gycom Ltd. jointly with IAP RAS and intended for use in superconducting ECR ion source FECRAL (a Fourth generation ECR ion source with Advanced design in Lanzhou, China) [1]. The setup is capable to provide output power up to 20 kW in both CW and pulse (5–200 ms duration with less than 10 μs fall time and up to 5 Hz repetition rate) modes with 45 GHz frequency.

The paper presents the calculation of the power combiner of coherent microwave signals. The combiner is based on the Talbot effect in an oversized rectangular waveguide. Parameters of the combiner fed by one source were simulated and experimentally confirmed.