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

A high-efficiency, high-power magnicon at 34.272 GHz has been designed and built as a microwave source to develop radio frequency (RF) technology for future multi-TeV electron-positron linear colliders. To develop this technology, this new RF source is being perfected for necessary tests of accelerating structures, RF pulse compressors, RF components, and to determine limits of breakdown and metal fatigue. The design of this high-power amplifier tube, as well as the first experimental results are presented.

Commissioning of the 34-GHz, 45-MW pulsed magnicon

Recent commissioning of a 45-MW peak power 34.3 GHz magnicon amplifier makes possible, for the first time, high-power tests of components and structures for a possible future high-gradient millimeter-wave linear accelerator. A brief survey is presented of the status of this Ka-band magnicon and component development efforts now underway.

http://ieeexplore.ieee.org/iel5/9723/30686/01422197.pdf

Technology developments for a future millimeter-wave high-gradient linear accelerator

Proper design of e-cient microwave energy compressors requires precise understanding of the physics pertinent to energy accumulation and exhaust processes in resonant waveguide cavities. In this paper, practically for the flrst time these highly non-monotonic transient processes are studied in detail using a rigorous time-domain approach. Additionally, in∞uence of the geometrical design and excitation parameters on the compressor's performance is quantifled in detail.

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Compression and Radiation of High-Power Short RF Pulses. I. Energy Accumulation in Direct-Flow Waveguide Compressors

The self-induced transparency effects that emerge when short (on the relaxation time scale) light pulses propagate in a two-level noninverted medium are well known in optics. The interaction of microwave pulses with an initially rectilinear electron beam under cyclotron resonance conditions can serve as a classical analog of the described effects. In this case, at a certain intensity of the input signal, the cyclotron absorption is replaced by self-induced transparency when the input pulse propagates almost without any change of its profile, forming a soliton whose amplitude and duration are rigidly related to its velocity. In a certain domain of parameters, this process is accompanied by significant two- or threefold compression of the initial pulse, which is of practical interest for the generation of multigigawatt picosecond microwave pulses. Since the soliton velocity lies between the unperturbed group velocity of the radiation and the translational velocity of the particles, another nontrivial effect in the case of interaction with a counterpropagating electron beam is the possibility of a significant deceleration or full stopping of the electromagnetic pulse.

Self-induced transparency, compression, and stopping of electromagnetic pulses interacting with beams of unexcited classical oscillators

Principles and preliminary design considerations for microwave pulse compressors using electrically-switched Bragg reflectors were presented by Petelin, Vikharev and Hirshfield at AAC’96 (1). This paper presents results of experiments to study performance of several proto-type designs of such compressors. In moderate-power tests using a plasma-switched TE011 cavity as the active element, a 25 nsec, 1.8 MW output pulse was realized, corresponding to a peak power gain of 20:1, with an energy efficiency of 30%. A high-power prototype of a 60% energy efficient compressor is under construction that is designed to yield a 100 nsec. 100 MW output pulse with a peak power gain of 17:1. Details of this design are described.

Active microwave pulse compressors employing oversized resonators and distributed plasma switches

A novel active microwave pulse compressor in the form of an axisymmetric cavity is implemented and investigated. The cavity is formed by: a) a Bragg reflector, b) a cylindrical section, and c) an output resonance reflector in the form of an electrically controlled gas-filled spark gap. The compressor is excited by the TE01 mode of a circular waveguide at a frequency of 9.4 GHz. Working at atmospheric pressure, the compressor produces output pulses with a power of 1.8 MW and duration 25 ns at a compression coefficient of around 20.

Active microwave pulse compressor utilizing an axisymmetric mode of a circular waveguide

A novel switched energy storage (SES) pulse compressor is described with the apparent capability for high efficiency compression of high power 11.4 GHz pulses in the pulse energy range of interest for future electron-positron collider applications.

Pulse compressor based on electrically switched Bragg reflectors

A two-channel active pulse compressor has been developed that is able to provide output-pulses of at least 100 MW peak power with pulse duration of 100 nsec at X-band, with a power gain of 12–15 and with an energy efficiency of 60%. This paper describes the design of the compressor and the driving generator-compressor microwave circuit. Each channel of the compressor is connected to the driving generator and the load via a novel 3-dB quasi-optical coupler. Variations in phase of compressed output pulses from this active pulse compressor were measured. The moderate-power tests of a prototype design of such a compressor using 100 kW-level microwaves demonstrated coherent addition of the compressed pulses from each of the compressor channels. The paper also describes design of a modified output reflector, with which the two-channel active pulse compressor can produce output pulses with a peak power of at least 500 MW and a power gain 12–15.

Two-channel active high-power X-band pulse compressor

Efforts are underway within the accelerator community to develop high-gradient RF accelerators using microwave sources at relatively high frequencies (in particular, at 34.272 GHz). Yet no corresponding high-power components providing pulse compression, transmission and input coupling to the accelerating structure are currently available. Results of investigations of many components including resonator passive pulse compressor, controllable launcher for a DLDS system, low-loss miter bends, and mode converters, are presented.

M. I. Petelin

Papers

Active microwave pulse compressors employing oversized resonators and distributed plasma switches

Active microwave pulse compressor utilizing an axisymmetric mode of a circular waveguide

Pulse compressor based on electrically switched Bragg reflectors

Two-channel active high-power X-band pulse compressor

Study of Ka-band components for a future high-gradient linear accelerator