E. V. Sokolov

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).

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%.

Recent results of development in Russia of 170 GHz gyrotron for ITER

The industrial production prototype of the ITER gyrotron was tested at the new test stand in Kurchatov institute with power 1.02 MW in 240 second pulses, and 0.8MW in 800 second pulses. Simultaneously at IAP a short pulse gyrotron with an increased size cavity was tested at power 1.5–2 MW.

New results in development of MW output power gyrotrons for fusion systems

Gyrotrons are widely used in electron-cyclotron-wave systems of fusion installations. Modern and future installations require microwave sources with power at least 1 MW. CVD diamond windows are implemented into the gyrotrons with frequencies 140 GHz and 170 GHz. The goal of these near-time tests is to demonstrate 0.8-1 MW power in microwave pulse of 10 seconds at least at two frequencies 105 GHz and 140 GHz, corresponding to pass bands of the single diamond disc.

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%.

Recent results in development in Russia of megawatt power gyrotrons for fusion

During last years several new gyrotrons were developed at IAP/GYCOM. Main efforts were spent for development 170GHz/1MW/50%/CW gyrotron for ITER and multi-frequency gyrotrons. The main ITER requirements to a gyrotron have been demonstrated: 1MW power, 1000 seconds pulse duration, 53% efficiency. The gyrotron operation regime of 1.2 MW was found for 100 second pulses. For a multi-frequency gyrotron a novel scheme for a tuneable window is discussed. Additionally some other new gyrotrons were shipped and installed at running plasma installations.

Theoretical and experimental investigation of ac space-charge effect on gain and bandwidth of two- and three-cavity gyroklystrons with TE011 operating mode

Both a small signal approach for ac space-charge effects on beam bunching in the gyroklystron drift tube and nonlinear self-consistent field slow-time scale ballistic theory are applied to investigate the wideband gyroklystron gain including the beam velocity spread effects. The analysis of ac space-charge effects on beam bunching, based on the parameters of existing electron guns, results in the possibility of the wideband amplification in the tremendously high gain gyroklystron using the drift tube of the approximately 20 (lambda) length or more. The test results of the IAP two-stage, 16kV, 3A, 20dB gyroklystron operating in TE011 mode are presented and discussed. Also, the test results of the Tory TE011 three-stage, 50kV, 14A gyroklystron are discussed. Having the first drift tube of the approximately 10 (lambda) length, this gyroklystron demonstrates the 40dB gain, the 1.3% bandwidth, and the 230kW output saturated power.

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

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.

Multi-frequency gyrotrons for plasma fusion installations

During last years several new gyrotrons were designed and tested at IAP/GYCOM. Main development efforts were spent for development 170GHz/1MW/50%/CW gyrotron for ITER and multi-frequency gyrotrons. The paper presents new results in development of gyrotrons capable to operate at several frequencies.

Experimental study of a two-cavity gyrotron with feedback between cavities

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.