M. V. Morozkin

Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media

A 263 GHz continuous-wave (CW) gyrotron was developed at the IAP RAS for future applications as a microwave power source in Dynamic Nuclear Polarization / Nuclear magnetic resonance (DNP/NMR) spectrometers. A new experimental facility with a computerized control was built to test this and subsequent gyrotrons. We obtained the maximum CW power up to 1 kW in the 15 kV/0.4 A operation regime. The power about 10 W, which is sufficient for many spectroscopic applications, was realized in the low current 14 kV/0.02 A regime. The possibility of frequency tuning by variation of the coolant temperature about 4 MHz/1 °C was demonstrated. The spectral width of the gyrotron radiation was about 10(-6).

Terahertz gyrotrons: State of the art and prospects

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.

The Ka-band 10-kW continuous wave gyrotron with wide-band fast frequency sweep

The dual-frequency gyrotron with fast 2% frequency sweep at about 28 GHz is designed to power an electron cyclotron resonance ion source (ECRIS). Operation with an output power of up to 10 kW in CW mode and efficiency of 20% was demonstrated at both frequencies. Frequency manipulation has a characteristic time of about 1 ms and is based on magnetic field variation with an additional low-power coil. Fast frequency sweep will supposedly increase the ion current and the average ion charge of ECRIS. The possibility of 100% power modulation is demonstrated using the same control method.

A pulse magnetic-field generator for terahertz gyrodevices

A pulse magnetic-field generator producing pulse amplitudes up to 50 T with base durations of unities of milliseconds is described. The pulse magnetic field is obtained during discharging a capacitive storage through a thyristor-diode switch into a nitrogen-cooled solenoid. The repetition of the pulse amplitude of the current in the solenoid is ensured with an accuracy up to tenth of shares of a percent by stabilizing the precharge voltage of the storage and thermally stabling the solenoid. Using this generator, experiments for obtaining terahertz kilowatt-power radiation from 0.9- to 1.3-THz frequencies were successfully performed.

Efficiency of gyrotrons working at the second harmonic of gyrofrequency with multistage systems for recuperation of residual electron energy

Comprehensive optimization of the output efficiency of the gyrotron with a multistage system for energy recuperation is performed for the first time with allowance for the electron-beam interaction with the high-frequency field in the resonator and the subsequent deceleration of the beam in the presence of the electric field of the collector immersion lenses. The energy approach makes it possible to estimate the upper-bound limit of the efficiency. The effect of the ohmic loss on the efficiency of the gyrotron with recuperation is taken into account. The efficiency of the gyrotron working at the harmonics of the gyrofrequency with the two-stage recuperation can be increased to the levels typical of the magnetron technological complexes with a simultaneous increase in the working frequency of the sample heating by at least an order of magnitude.

A Magnetron Injection Gun with a Reduced Filament Temperature and Elongated Cathode Lifetime

An optoelectronic gyrotron system that makes it possible to efficiently heat a cathode by electrons reflected from a magnetic mirror has been developed. The parameters of the primary electron beam are retained at a level that is acceptable for efficient microwave power generation. The results of a trajectory analysis of electrons and the cathode temperature conditions are reported. The corresponding decrease in power and temperature of the cathode filament suggests a significant (severalfold) increase in the filament lifetime, which is one of the main parameters determining the device lifetime.

First experimental tests of powerful 250 GHz gyrotron for future fusion research and collective Thomson scattering diagnostics

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%.

High-power sub-terahertz source with a record frequency stability at up to 1 Hz

Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10−4. Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 × 10−12 and 10−10, respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.

45 GHz/20 kW gyrotron-based system for ECR ION source

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 15 - 200 ms duration with less than 10 μs fall time and up to 5 Hz repetition rate) modes with 45 GHz frequency. Gyrotron system uses a cryogen-free magnet JMTD-4T140 made by Jastec Inc. (Japan) that allows it to operate on fundamental harmonic (operation mode is TE63). Gyrotron tube is designed to operate with diode-type electron gun, and using of depressed collector for recuperation of the electron beam residual energy leads to considerable total efficiency increasing. Output gyrotron radiation is converted by two-mirror matching optics unit (MOU) to the TEM00 mode. Gaussian beam propagates from the MOU output through the air 1 to the distance of about 2 m) to the system of mirrors delivering the one to the mode converter (TEM00 to TE01) which is located on the high voltage (about 300 kV) platform and connected via waveguide with the FECRAL ion source. The gyrotron rack is under ground potential. The setup is fully equipped with the automated control, data acquisition and safety interlocks systems which guarantee convenient and safe operation. Currently the described system is under manufacturing. Commissioning tests are scheduled for the end of this year.

Development and experimental investigations of high power THz gyrotrons

Terahertz waves are promising for diagnosis and spectroscopy of various media, including the development of high resolution electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy. Powerful terahertz radiation can be used to create dense plasma and control its parameters (controlled thermonuclear fusion, “point” plasma X-ray sources, remote detection of ionizing radiation). In the pioneering IAP RAS works in 1970-1980s was shown the principle possibility of a high-power CW and pulsed gyrotrons operation at frequencies from 0.33 to 0.65 THz. In recent years a number of new results at the development of THz band gyrotrons has been obtained at IAP (see, for detail, review [1-4]). This report will focused at two of them - the penetration of gyrotrons in the frequency range above 1 THz and generation of hundreds kW power at THz band. The experiments based on the original pulsed solenoid with a magnetic field up to 50 T yielded generation on the main cyclotron resonance with 5-0.5 kW power in single pulse duration of 50 microseconds at record frequencies 1-1.3 THz [5,6] and with pulsed power up to 200 kW at 0.7 THz band [7].