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Gyrotrons for plasma fusion installations operated at frequencies 40–170 GHz with an output power up to 1 MW are presented. Some novel ideas are proposed to enhance gyrotron output energy, efficiency, frequency spectrum. In the collaboration between the Institute of Applied Physics and industrial company GYCOM Ltd the series of gyrotrons for plasma installations has been realized. The brightest examples are 170 GHz gyrotrons for ITER, long-pulse 140 GHz gyrotrons developed for EAST and KSTAR installations, 82.6 GHz for T-15MD tokamak, 28 GHz and 45 GHz complex for modern electron cyclotron resonance ion sources (ECRIS) facilities. Some steps were done in development of 230–700 GHz gyrotrons for future plasma installations and for plasma diagnostics.

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.

Nearly 20 years ago demand had arisen in the world practice of plasma investigations with gyrotron usage - to have a source of long-pulse microwave radiation with step-tunable frequency at megawatt-power level. Transparency bands of typical modern 1.8-mm single disc diamond output windows are distant at step of ~35GHz. Attempts to build the reliable broad band output window unit capable to provide long-pulse gyrotron multi-frequency operation with much smaller steps has not succeeded yet. In the same time 10 dual-frequency 140/105GHz long-pulse gyrotrons using single disc diamond window successfully run now at megawatt-power level providing ECRH at ASDEX Upgrade and KSTAR facilities.

A brief summary of current developments in Russia of megawatt power gyrotrons is presented. The gyrotron developed are applied in experiments at several modern tokamaks. New demands to gyrotron parameters and possible ways to reach them are discussed.

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%.

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.

An experimental pressure field in operating clearance and flowrate parameters analysis for different eccentricities, inlet oil pressures, and journal rotating velocities are presented for a radial multilobe journal bearing. Lubricating film breakdown zones in bearing oil ducts caused by complicated construction and journal rotation are observed.

Design peculiarities and operational parameters of modern Russian gyrotrons developed for 105-170 GHz frequency range with pulse duration up to 3600 s and output power of 1-1.5MW at efficiency over 50 % (CPD collector) are presented.

A class of groups C is root in a sense of K. W. Gruenberg if it is closed under taking subgroups and satisfies the Gruenberg condition: for any group X and for any subnormal sequence Z \leqslant Y \leqslant X with factors in C, there exists a normal subgroup T of X such that T \leqslant Z and X/T \in C. We prove that a class of groups is root if, and only if, it is closed under subgroups and Cartesian wreath products. Using this result we prove also that, if C is a nontrivial root class of groups closed under taking quotient groups and G = is the generalized free product of two nilpotent C-groups A and B possessing \varphi-compartible central series, then G is residually a solvable C-group., Comment: This is an Author's Original Manuscript of an article submitted for consideration in the "Communications in Algebra" [copyright Taylor & Francis]; "Communications in Algebra" is available online at http://www.tandfonline.com

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.

Development of the gyrotron system for ITER is based on solution of many very difficult scientific and engineering problems. At present the main purpose of the system modification is an enhancement of the system reliability and implementation of all gyrotron systems into ITER machine and its control and safety system. Recently development of ITER gyrotron system in Russia came into completion phase.

The results of work accomplished in the field of computer-aided design at ZAO Ural Turbine Works (UTZ) are presented. A concept is described following which the tasks for a specialist’s workstations being developed at the UTZ are solved. Results from solution of problems with the use of modern numerical simulation computer programs for analyzing gas dynamic processes, casting, welding, and strength of complex structures are given. An example is given to show efficient use of a computer-aided design system for shifting an enterprise to a modern level of automation.

The paper presents development status of a gyrotron setup for ITER. Twenty four such setups are to be used for heating and current drive in ITER plasma. The setup includes a gyrotron in a superconducting magnet and several tens of other components. Recently the main required gyrotron parameters were demonstrated. In the last year tests confirmed 95% reliability of gyrotron operation. Now a prototype of complete gyrotron setup is assembled and it is under thorough testing.

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

Recent test results of newly designed 1.5-1.7 MW/170 GHz gyrotron which is considered as a possible RF source for the ITER program are presented.

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.

A new type of oscillator a two-cavity gyroklystron-oscillator, is proposed. In this device, auto-oscillations in the first cavity modulate the electron energy ; in the drift space the electrons are bunched, and the bunches excite powerful oscillations in the second cavity. A simple theory for such an oscillator has been developed. The design parameters of a two-cavity tube operating in the TE 011 cavity mode in the X-band have been calculated. As predicted by theory, the output power and efficiency are enhanced in comparison with those for a conventional gyrotron, and this is demonstrated experimentally.

In Russia gyrotrons are developed in cooperation of three institutions: Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Industrial company GYCOM Ltd, Nizhny Novgorod, and Kurchatov Institute, Moscow. During last year several new gyrotrons were designed and tested by Russian gyrotron team. Main efforts were spent for elaboration of 170GHz/1MW/50%/CW gyrotron for ITER project and multi-frequency gyrotrons. There are also several new other gyrotrons developed and delivered to tokamaks and stellarators.

Formulas for shifts of gyrotron autooscillation frequency due to change of electron beam parameters are presented. The frequency shifts can be commensurable with the frequency band of the beam-unloaded cavity. The autooscillation frequency is most sensitive to the change of the magnetic field, less to the change of the anode voltage and least to the the change of the beam voltage. Experiments presented are in satisfactory agreement with the theory.

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.

During last year several new gyrotrons were designed and tested by Russian gyrotron team. Main efforts were spent for elaboration of 170GHz/1MW/50%/CW gyrotron for ITER project and multi-frequency gyrotrons. The paper presents new results in development of gyrotrons 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 200 second pulses, and 0.6MW in 800 second pulses. Simultaneously a short pulse gyrotron mock-up with an increased size cavity was tested at power 1.5–2 MW aiming development of ITER gyrotron with the enhanced power.

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.

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).

A multi-frequency gyrotron equipped with a circular Brewster window made on the base of high-temperature-brazed ceramic disc was tested. Efficient gyrotron operation at 11 modes (frequencies) in the range of 105 GHz - 143 GHz was demonstrated. Gyrotron output power (0.8 MW/0.1 sec) was limited by the used power supply. The gyrotron scheme and the test results are used in the design of long-pulse gyrotron with a CVD diamond window.

A two-cavity gyrotron under study consists of two cavities separated by a drift area. The first cavity is excited at the fundamental cyclotron harmonic, the second one operates at the higher harmonic. The way is promising for production of high frequency (up to THz) microwaves by gyrotrons. In the work a "low-frequency" prototype of such a device is studied. The first cavity is excited at 95 GHz and the second cavity is optimized for radiation of the same electron beam at the third harmonic. With low power of the electron beam - 23 kV/0.3A - the CW radiation at 285 GHz frequency has power about 30W.

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.

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.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.