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

Microwave sources based on backward-wave oscillators (BWOs) with relativistic electron beams are capable of producing high-power coherent radiation in the centimeter- and millimeter-wavelength regimes. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical models which can be compared in detail with the experimental data. This work is devoted to filling this need. The linear and nonlinear theory if BWOs is developed taking into account reflection of the electromagnetic wave at the boundaries of the slow-wave structure. It is found that owing to end reflections the start oscillation current and the efficiency are sensitive functions of the operating parameters. Regions of stable single-frequency operation in these devices are determined numerically. The effects of finite duration and rise time of the electron beam pulse on device operation are discussed. >

Theory of relativistic backward-wave oscillators with end reflectors

A review of research on relativistic multiwave Cherenkov generators (MWCGs) is provided. Presented is the linear theory of these devices, allowing a detailed description of the multiwave interaction of a relativistic electron beam with an electromagnetic field in an electrodynamic superdimensional MWCG system. The results of theoretical research on the starting parameters of generation, power flows, and the structure of the radiated field in a MWCG of a 3-cm-wavelength band are reported. The experiments on obtaining and investigating high-power pulses of microwave radiation in a MWCG of 3-cm- and 8-mm-wavelength bands are described. In particular, the results of research on a MWCG with the power of 15 GW in a 3-cm-wavelength band and the power of 3 GW in a 8-mm-wavelength band are presented. The results of research on the spatial and temporal coherence of such generator radiation are reported. The possibility of conversion of the MWCG wavefield into a linearly polarized one is discussed. The investigation of the processes associated with the generation of high-power microwave radiation in a MWCG is described. >

Relativistic multiwave Cherenkov generators

Results of theoretical and experimental studies of a GW-class, large diameter microwave oscillator are presented The device consists of a large cross-section (overmoded), slow-wave structure with a unique profile of wall radius specifically designed to support surface waves and to provide a strong beam-wave coupling at moderate voltage (500 kV), an internal adjustable microwave reflector, a coaxial microwave extraction section, and a coaxial magnetically insulated field emission electron gun In preliminary experiments carried out at 83 GHz, the power level exceeding 05 GW and efficiency of 15% have been measured calorimetrically

Overmoded GW-class surface-wave microwave oscillator

We present the design and experimental results of a novel overmoded slow-wave high-power microwave (HPM) generator that is featured by its compactness, low-operation magnetic field, and potentially high power and high efficiency. The device includes two slow-wave structure (SWS) sections, a resonant cavity, and a tapered waveguide. The resonant cavity was well designed and was used to achieve the axial mode selection and to decrease the length of the SWS sections. The radial mode selection is achieved using the property of "surface wave" of the device to excite the TM/sub 01/ mode while making the higher TM/sub 0n/ modes unexcited. The physical mechanisms of axial and radial mode selections ensure that the microwave is produced with a single mode and a narrow band. The feasibility of low magnetic field operation is also investigated based on the characteristics of the overmoded slow-wave devices. Experiments were carried out at the Spark-2 accelerator. At diode voltage of 474 kV, beam current of 5.2 kA, and guiding magnetic field strength of 0.6 T, a microwave was generated with power of 510 MW, mode of TM/sub 01/, and frequency of 9.54 GHz. The relative half width of the frequency spectrum is /spl Delta/f/f= 0.6%, and the beam-to-microwave efficiency is about 21% in our experiment.

A novel overmoded slow-wave high-power microwave (HPM) Generator

A theoretical and experimental study has been made of the operation of a millimeter-wavelength-range sectional relativistic diffraction generator (RDG). Microwave power transported into the atmosphere with the peak parameters of 3.5 and 4.5 GW at the wavelengths of 6.5 to 6.8 mm and 9 to 11.3 mm, respectively, has been obtained. The power at the generator output, up to a horn antenna, has reached 7 and 9 GW for each of the regimes, respectively, the electronic efficiency being equal to approximately 30%. Plasma formed in a slow-wave structure of the RDG is shown to be of considerable importance for radiation pulse duration limitation. Experiments aimed at increasing the pulse duration up to 0.7 mu s have been performed. Theoretical investigation of the beam interaction with a slow-wave structure field has shown that the generation frequency may be determined by the resonance features due to the transverse motion of beam electrons. >

V. I. Koshelev

Papers

Investigation of a millimeter-wavelength-range relativistic diffraction generator

Relativistic multiwave Cerenkov generator

Relativistic diffraction oscillators in the millimeter-wave region

Atmospheric microwave discharge and study of the coherence of radiation from a multiwave Cerenkov oscillator