The electron cyclotron maser (ECM) is based on a stimulated cyclotron emission process involving energetic electrons in gyrational motion. It constitutes a cornerstone of relativistic electronics, a discipline that has emerged from our understanding and utilization of relativistic effects for the generation of coherent radiation from free electrons. Over a span of four decades, the ECM has undergone a remarkably successful evolution from basic research to device implementation while continuously being enriched by new physical insights. By delivering unprecedented power levels, ECM-based devices have occupied a unique position in the millimeter and submillimeter regions of the electromagnetic spectrum, and find use in numerous applications such as fusion plasma heating, advanced radars, industrial processing, materials characterization, particle acceleration, and tracking of space objects. This article presents a comprehensive review of the fundamental principles of the ECM and their embodiment in practical devices.

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The electron cyclotron maser

Relativistic nonlinear effects in plasmas

This paper describes the genealogical tree of the gyrotron, stimulated emission of cyclotron radiation in microwave electronics from magnetron to gyrotron, and arrangement of the gyrotron. The structure of the alternating field in the gyrotron is also given, along with motion and bunching of electrons near cyclotron resonance, equations of the gyrotron, and varieties of the gyrotron. A review of experimental studies is discussed, with problems of utilization of stimulated emission cyclotron radiation.

http://ieeexplore.ieee.org/iel6/22/25041/01129149.pdf

The Gyrotron

This paper presents a review of the experimental achievements related to the development of high-power gyrotron oscillators for long-pulse or CW operation and pulsed gyrotrons for many applications. In addition, this work gives a short overview on the present development status of frequency step-tunable and multi-frequency gyrotrons, coaxial-cavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, relativistic gyrotrons, large orbit gyrotrons (LOGs), quasi-optical gyrotrons, fast- and slow-wave cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWOs, gyro-harmonic converters, gyro-peniotrons, magnicons, free electron masers (FEMs), and dielectric vacuum windows for such high-power mm-wave sources. Gyrotron oscillators (gyromonotrons) are mainly used as high-power millimeter wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control, and diagnostics of magnetically confined plasmas for clean generation of energy by controlled thermonuclear fusion. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons employing synthetic diamond output windows is 30 min (CPI and European KIT-SPC-THALES collaboration). The world record parameters of the European tube are as follows: 0.92 MW output power at 30-min pulse duration, 97.5% Gaussian mode purity, and 44% efficiency, employing a single-stage depressed collector (SDC) for energy recovery. A maximum output power of 1.5 MW in 4.0-s pulses at 45% efficiency was generated with the QST-TOSHIBA (now CANON) 110-GHz gyrotron. The Japan 170-GHz ITER gyrotron achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min) and the efficiency record of 57% for tubes with an output power of more than 0.5 MW. The Russian 170-GHz ITER gyrotron obtained 0.99 (1.2) MW with a pulse duration of 1000 (100) s and 53% efficiency. The prototype tube of the European 2-MW, 170-GHz coaxial-cavity gyrotron achieved in short pulses the record power of 2.2 MW at 48% efficiency and 96% Gaussian mode purity. Gyrotrons with pulsed magnet for various short-pulse applications deliver Pout = 210 kW with τ = 20 μs at frequencies up to 670 GHz (η ≅ 20%), Pout = 5.3 kW at 1 THz (η = 6.1%), and Pout = 0.5 kW at 1.3 THz (η = 0.6%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require tubes with the following parameters: f > 24 GHz, Pout = 4–50 kW, CW, η > 30%. The CW powers produced by gyroklystrons and FEMs are 10 kW (94 GHz) and 36 W (15 GHz), respectively. The IR FEL at the Thomas Jefferson National Accelerator Facility in the USA obtained a record average power of 14.2 kW at a wavelength of 1.6 μm. The THz FEL (NOVEL) at the Budker Institute of Nuclear Physics in Russia achieved a maximum average power of 0.5 kW at wavelengths 50–240 μm (6.00–1.25 THz).

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State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

FEL's based on the stimulated undulator radiation (ubitrons) are compared with those based on the stimulated cyclotron radiation [cyclotron autoresonance masers (CARM's)]. If the high-current accelerators are used as electron injectors, then from the viewpoint of simplicity of oscillatory electron energy pumping, criticality with respect to electron velocity dispersion, and efficiency, CARM's seem to be more effective than ubitrons at mm and sbmm waves. For such HF generators, resonators based on selective Bragg reflection of electromagnetic waves in corrugated metallic tubes are most atractive. CARM's of this type yield 6 MW at a 4 mm wavelength and 10 MW at a 2 mm wavelength in the single-mode regime.

FEL's with Bragg reflection resonators: Cyclotron autoresonance masers versus ubitrons

The induced radiation of excited classical oscillators and its use in high-frequency electronics

The gyrotron is a promising powerful source of millimetre and submillimetre waves. This paper is devoted to the State-of-thc-art of theoretical and experimental gyroton investigations. The theory of the gyrotron permits one to determine self-excitation conditions and optimum values of gyrotron parameters which provide high efficiency, taking into account electron velocity spread and an unfixed axial structure of the RF field in open cavities with low Q. The theory of intense helical electron beams formed by gyrotron electron guns of the magnetron type has been developed. The methods of analysis and synthesis of electron-optical systems permit one to form, taking into account the beam space charge, intense electron beams with a small velocity spread. The methods of clectrodynamic selection of modes consist in cavity profiling for axial mode selection, application of azimuthal slots for azimuthal mode selection and use of coaxial cavities for radial mode selection. Experiments on gyrotrons with coxial and t...

A. V. Gaponov

Papers

The Gyrotron

The induced radiation of excited classical oscillators and its use in high-frequency electronics

Invited paper. Powerful millimetre-wave gyrotrons

The gyrotron: High-power source of millimetre and submillimetre waves

Experimental investigation of centimeter-band gyrotrons