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: ͑1͒ plasma resonance heating and current drive; ͑2͒ rf acceleration of charged particles; ͑3͒ radar and communications systems; and ͑4͒ high-peak power sources for weapons-effect simulation and exploratory development.

We report a new regime of single-surface multipactor that was observed during high-power testing of an 11.424-GHz alumina-based dielectric-loaded accelerating structure. Previous experimental observations of single-surface multipactor on a dielectric occurred in cases for which the rf electric field was tangential and the rf power flow was normal to the dielectric surface (such as on rf windows) and found that the fraction of power absorbed at saturation is approximately 1%, independent of the incident power. In this new regime, in which strong normal and tangential rf electric fields are present and the power flow is parallel to the surface, the fraction of power absorbed at saturation is an increasing function of the incident power, and more than half of the incident power can be absorbed. A simple model is presented to explain the experimental results.

Abstract. An overview is presented of the design of a 10 GeV laser plasma accelerator (LPA) that will be driven by a PW-class laser system and of the BELLA Project, which has as its primary goal to build and install the required Ti sapphire laser system for the acceleration experiments The basic design of the 10 GeV stage aims at operation in the quasi-linear regime, where the laser excited wakes are largely sinusoidal and offer the possibility of accelerating both electrons and positrons Simulations show that a 10 GeV electron beam can be generated in a meter scale plasma channel guided LPA operating at a density of about 10 17 cm 3 and powered by laser pulses containing 30-40 J of energy in a 50-200 fs duration pulse, focused to a spotsize of 50-100 micron The lay-out of the facility and laser system will be presented as well as the progress on building the facility

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We present the results of studies of the active compressor of 3-cm wavelength microwave pulses, which uses a high-Q storage Bragg resonator excited at the H 01 mode and new types of plasma switches. Phase variation during a compressed pulse and phase correlation of the input and compressed microwave pulses are studied both experimentally and theoretically. Using a singlechannel compressor excited at the megawatt power level by the magnicon radiation with frequency 11.4 GHz, a power amplification factor equal to 9 was reached for an output-pulse duration of 40-50 ns and a peak power of up to 25 MW.

Results obtained in several experiments on active rf pulse compression at X band using a magnicon as the high-power rf source are presented. In these experiments, microwave energy is stored in high-Q TE 01 and TE 02 modes of two parallel-fed resonators, and then discharged using switches activated with rapidly fired plasma discharge tubes. Designs and high-power tests of several versions of the compressor are described. In these experiments, coherent pulse superposition was demonstrated at a 5-9 MW level of incident power. The compressed pulses observed had powers of 50-70 MW and durations of 40-70 ns. Peak power gains were measured to be in the range of 7:1-11:1 with efficiency in the range of 50%-63%.