This article reviews the state-of-the-art in high-power microwave source research. It begins with a discussion of the concepts involved in coherent microwave generation. The main varieties of microwave tubes are classified into three groups, according to the fundamental radiation mechanism involved: Cherenkov, transition, or bremsstrahlung radiation. This is followed by a brief discussion of some of the technical fundamentals of high-power microwave sources, including power supplies and electron guns. Finally, the history and recent developments of both high-peak power and high-average power sources are reviewed in the context of four main areas of application: (1) plasma resonance heating and current drive; (2) rf acceleration of charged particles; (3) radar and communications systems; and (4) high-peak power sources for weapons-effect simulation and exploratory development.

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Review of high-power microwave source research

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).

/pdf/state-of-the-art-of-high-power-gyro-devices-and-free-5avfirj4z9.pdf

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

This paper presents a comprehensive theory of the cyclotron resonance maser (CRM) interaction in a circular waveguide. The kinetic theory is used to derive the dispersion relationships for both TE and TM modes. The TE mode case has been investigated by several authors, but there has been comparatively little work on the TM mode case. However, the TM mode interaction competes effectively with the TE mode interaction at relativistic electron energies. The conditions for maximum temporal and spatial growth rates are shown. The TM mode growth rates are found to vanish when the RF wave group velocity equals the beam axial velocity (‘grazing incidence’). The single particle theory is used to derive a compact set of self-consistent non-linear equations for the TE and TM mode interactions. These equations are particularly appropriate for the cyclotron auto-resonance maser (CARM) regime but applicability extends to other regimes as well. The conditions for optimum efficiency are investigated for oscillator and amp...

Linear and nonlinear theory of the Doppler-shifted cyclotron resonance maser based on TE and TM waveguide modes

The history of gyrotron development, the principles of gyrotron operation, and possible ways to enhance the power level to increase the operating frequency of gyrotrons are outlined. The state of the art of gyrotrons, their present and possible applications, and perspectives on gyrotrons are considered. >

http://ieeexplore.ieee.org/iel1/5/247/00004454.pdf

Gyrotron oscillators

The gyrotron traveling-wave tube (gyro-TWT) is a millimeter-wave amplifier based on the electron cyclotron maser instability. It is a device of increasing importance because of its power and bandwidth capabilities. The current paper presents a brief overview of the gyro-TWT research over the past quarter of a century. Advances made by different groups employing various schemes are discussed and achieved performances are surveyed.

Overview of research on the gyrotron traveling-wave amplifier

A Ka‐ band gyrotron oscillator powered by a 600 kV pulse‐line accelerator has produced approximately 100 MW at 35 GHz in a circular TE62 mode. It has also demonstrated frequency tuning over the range 28 to 49 GHz by operating in a family of TEm2 modes, with the azimuthal index m ranging from 4 to 10, by variation of the guide magnetic field. Operation is in general agreement with the predictions of theory.

High peak power Ka‐band gyrotron oscillator experiment

A K/sub a/-band gyrotron oscillator powered by a compact pulseline accelerator has been operated using oscillator cavities with and without axial slots. The oscillator was operated at high voltage ( approximately 900 keV) and high current ( approximately 500 A) in the approximate frequency range of 20-50 GHz. The use of axial slots has been shown to suppress low-starting-current whispering-gallery modes, in particular, modes of the TE/sub m2/ type, allowing stable operation in a linearly polarized TE/sub 13/ mode. A peak power of 35 MW has been observed at 6% efficiency. >

High-peak power K/sub a/-band gyrotron oscillator experiments with slotted and unslotted cavities

An intense‐beam gyro‐traveling‐wave amplifier experiment has demonstrated an apparent growth rate of 2.2 dB/cm at 35 GHz, with total gain exceeding 30 dB, and an output power of ∼20 MW (±3 dB), corresponding to an efficiency of ∼11%.

High‐voltage millimeter‐wave gyro‐traveling‐wave amplifier

The design of a 10-20-MW 40-ns cyclotron autoresonance maser (CARM) is presented. The basic components of a CARM are a pulseline accelerator, magnetic-field coils, a novel 600-kV 200-A field-emission electron gun designed for p/sub perpendicular to //p/sub z/=0.6 and Delta p/sub z//p/sub z/ >

The design of a 100-GHz CARM oscillator experiment

The Cyclotron Auto-Resonance Maser (CARM) is under investigation at the US Naval Research Laboratory as an efficient source of high power millimeter-wave and submillimeter-wave radiation for applications such as plasma heating, advanced rf accelerators, and space-based radars. A short-pulse 100 GHz CARM oscillator experiment based on a 600 kV, 200 A, 50 ns electron beam is under way. The mode selective, high- Q waveguide cavity with rippled-wall Bragg reflectors is designed to operate in the TE 61 mode. A novel cold cathode diode is used to produce a high quality ( Δυ z / υ z ≤ 3%) annular beam with a momentum pitch ratio of 0.6. The cathode features nonemitting focussing electrodes and an annular velvet emitter. The main objective of the experiment is to demonstrate high efficiency (∼ 20%) at a power of approximately 20 MW. In addition, a long pulse, 250 GHz, CARM oscillator experiment based on a 500 kV, 100 A, 1 μs MIG-type thermionic cathode electron gun is planned. The design of these experiments and the optimization of CARM oscillator efficiency are discussed.

R. B. McCowan

Papers

High peak power Ka‐band gyrotron oscillator experiment

High-peak power K/sub a/-band gyrotron oscillator experiments with slotted and unslotted cavities

High‐voltage millimeter‐wave gyro‐traveling‐wave amplifier

The design of a 100-GHz CARM oscillator experiment

Development of high power CARM oscillators