Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave (mmw) to terahertz (THz) regime electromagnetic radiation, from 0.1 to 10THz. While vacuum electronic sources are a natural choice for high power, the challenges have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, high resolution radar, next generation acceleration drivers, and analysis of fluids and condensed matter. The compact size requirements for many of these high frequency sources require miniscule, microfabricated slow wave circuits. This necessitates electron beams with tiny transverse dimensions and potentially very high current densities for adequate gain. Thus, an emerging family of microfabricated, vacuum electronic devices share many of the same plasma physics challenges that are currently confronting “classic” high power microwave (HPM) generators including long-life bright electron beam sources, intense beam transport, parasitic mode excitation, energetic electron interaction with surfaces, and rf air breakdown at output windows. The contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of HPM generation, and future research challenges and opportunities are discussed.

Plasma physics and related challenges of millimeter-wave-to-terahertz and high power microwave generationa)

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

Dynamic nuclear polarization for sensitivity enhancement in modern solid-state NMR.

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

We present the newly developed Maryland Gyrotron (MAGY) code for modeling of slow and fast microwave sources. The code includes a time-dependent description of the electromagnetic fields and a self-consistent analysis of the electrons. The calculations of the electromagnetic fields are based on the waveguide modal representation, which allows the solution of a relatively small number of coupled one-dimensional partial differential equations for the amplitudes of the modes, instead of the full solution of Maxwell's equations. Moreover, the basic time scale for updating the electromagnetic fields is the cavity fill time and not the high frequency of the fields. The equations of motion of the electrons are formulated within the framework of the guiding-center approximation and solved with the electromagnetic fields as the driving forces. Therefore, at each time step, a set of trajectories are calculated and used as current sources for the fields. We present two examples for the operation of the code, namely the two-cavity gyroklystron and the backward-wave oscillator (BWO). These examples demonstrate the possible usage of the code for a wide variety of electron-beam systems.

MAGY: a time-dependent code for simulation of slow and fast microwave sources

Contents Introduction Origins of High Power Microwaves High Power Microwave Operating Regimes Future Directions in HPM Further Reading References Designing High Power Microwave Systems The Systems Approach to HPM Looking at Systems Linking Components into a System Systems Issues Scoping an Advanced System Conclusion Problems References High Power Microwave Applications Introduction High Power Microwave Weapons High Power Radar Power Beaming Space Propulsion Plasma Heating Particle Accelerators Problems References Microwave Fundamentals Introduction Basic Concepts in Electromagnetics Waveguides Periodic Slow-Wave Structures Cavities Intense Relativistic Electron Beams Magnetically Insulated Electron Layers Microwave-Generating Interactions Amplifiers and Oscillators, High- and Low-Current Operating Regimes Phase and Frequency Control Summary Problems References Enabling Technologies Introduction Pulsed Power Electron Beams and Layers Microwave Pulse Compression Antennas and Propagation Diagnostics HPM Facilities Problems Further Reading References Ultrawideband Systems UWB Defined UWB Switching Technologies UWB Antenna Technologies UWB Systems Conclusion Problems References Relativistic Magnetrons and MILOS Introduction History Design Principles Operational Features Research and Development Issues Fundamental Limitations MILOs Crossed-Field Amplifiers Summary Problems References BWOs, MWCGs, and O-Type Cerenkov Devices Introduction History Design Principles Operational Features Research and Development Issues Fundamental Limitations Summary Problems References Klystrons and Reltrons Introduction History Design Principles Operational Features Research and Development Issues Fundamental Limitations Summary Problems References Vircators, Gyrotrons and Electron Cyclotron Masers, and Free-Electron Lasers Introduction Vircators Gyrotrons and Electron Cyclotron Masers Free-Electron Lasers Summary Problems References Appendix: High Power Microwave Formulary A.1 Electromagnetism A.2 Waveguides and Cavities A.3 Pulsed Power and Beams Diodes and Beams A.4 Microwave Sources A.5 Propagation and Antennas A.6 Applications Power Beaming Plasma Heating Index

High power microwaves

High Power Microwaves, Second Edition

There is a strong symbiotic relationship between a developing technology and its applications. New technologies can generate applications previously either unrealizable or impractical. Conversely, applications can demand the development of new technological capability. Examples of both types of development can be found in the evolution of HPM. The high power and energy output made possible by HPM have created a technology driven interest in directed energy weapons and short pulse radar. On the other hand, the requirements for heating of fusion plasmas have resulted in an application driven program to develop high average power microwave devices. In this paper we address these and other applications such as RF electron linacs, laser pumping, and beaming of power. Emerging applications, such as ionispheric modification and environmental cleanup, are also touched upon. The approach in this paper will be to review each application separately and then compare the requirements of the applications in terms of the power, frequency and other key requirements necessary for HPM to usefully address the application.

Applications of high-power microwaves

Relativistic Magnetrons and MILOs

The field of high-power microwaves (HPM) has matured considerably in the 25 years since the initial development of relativistic backward wave oscillators (BWOs) by researchers from the Institute of Applied Physics and the Lebedev Institute in Russia and from Cornell University in the US. In this paper, we review some of the signs of the maturity of the field, including changes such as an observed narrowing in the number of source types under development, an increase in commercial suppliers, and a growing internationalization of the research field. In addition, within the context of historical developments in the field, we discuss the development of high peak power systems and the apparent abandonment of the pursuit of ever-higher power in favor of the development of gigawatt-level systems with manageable weight and volume, repetitive operation, and tunability.

http://ieeexplore.ieee.org/iel5/6634/17763/00822405.pdf

John A. Swegle

Papers

High power microwaves

High Power Microwaves, Second Edition

Applications of high-power microwaves

Relativistic Magnetrons and MILOs

High-power microwaves at 25 years: the current state of development