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Splitting of the fundamental mode in an oversized Bragg resonator with a step of the corrugation phase, which operates over the feedback loop involving the waveguide waves of different transverse structures, was found to be the result of mutual influence of the neighboring zones of the Bragg scattering. Theoretical description of this effect was developed within the framework of the advanced (four-wave) coupled-wave approach. It is shown that mode splitting reduces the selective properties, restricts the output power, and decreases the stability of the narrow-band operating regime in the free-electron maser (FEM) oscillators based on such resonators. The results of the theoretical analysis were confirmed by 3D simulations and "cold" microwave tests. Experimental data on Bragg resonators with different parameters in a 30-GHz FEM are presented. The possibility of reducing the mode splitting by profiling the corrugation parameters is shown. The use of the mode splitting effect for the output power enhancement by passive compression of the double-frequency pulse generated in the FEM with such a resonator is discussed. [ABSTRACT FROM AUTHOR]

We describe a facility for testing the properties of different objects affected by a sequence of highpower pulses of the microwave electromagnetic field. The facility performance is implemented due to the power level and stability of the single-mode generation of a free electron maser with an output frequency of 30 GHz, which have been achieved at the Joint Institute for Nuclear Research and the Institute of Applied Physics of the Russian Academy of Sciences. This paper describes the experiments on studying of the thermal fatigue of the copper surface in a test cavity, which models the thermal regime of the accelerating structure of the CLIC project (CERN), as well as the experiments on irradiation of biological tissues, metal films, and nanoclusters. [ABSTRACT FROM AUTHOR]

We propose a new accelerating structure for teraelectronvolt linear electron–positron colliders [1–4]. The structure is based on acceleration of a sequence of particle bunches (accelerated beam) by means of a periodic system of quasioptical cavities. Each cavity is operated at several eigenmodes with equidistant frequencies which are excited by a drive beam bunched with the same spatial period as the accelerated beam. The accelerating field represents a time-periodic sequence of narrow peaks separated by wide intervals of a field close to zero. This makes it possible to significantly decrease the effective time of exposure of the structure surface by ultrahigh microwave fields compared with the single-frequency structure. To maximize filling of the structure by accelerating-field regions and minimize ohmic losses, we suggest using a set of modes with a nonzero number of longitudinal variations strictly proportional to the frequencies of these modes. Such modes are able to provide long effective interaction of the total microwave field with a bunch of particles passing across the cavity. In this way, the acceleration gradient averaged over the structure length can be increased. A variant of the accelerating structure which is based on two-mirror cavities with small curvature of the mirrors is proposed. Such cavities can provide approximate frequency equidistance of a large number of modes with nonzero longitudinal variations. [ABSTRACT FROM AUTHOR]

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 H01 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 single-channel 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. [ABSTRACT FROM AUTHOR]

We study, both numerically and experimentally, a microwave commutator (phase shifter), whose active element comprises a metal plane mirror with a semiconductor plate on it. Phase shifting of the reflected microwave beam is attained by creating a conducting layer in the semiconductor by a laser with quantum energy approximately equal to the forbidden band width. Using a disk of high-purity silicon and a titatnium-sapphire pulsed laser, we study experimentally a 180° phase shifter operated with a Gaussian wave beam at a frequency of 30 GHz. Efficient phase shifting of the wave beam over a time of several nanoseconds is shown at a low power level. [ABSTRACT FROM AUTHOR]

The operation of a pulsed free-electron maser with a Bragg resonator and resonant termination is simulated in terms of nonstationary equations. It is shown that the termination partially loses its reflection properties and accumulates microwave energy when the eigenfrequency of the terminating resonator coincides with the frequency of the maser transition radiation. The difference between these frequencies produces considerable reflections and in the long run quenches masing. The masing stability depends on the lag of the reflected signal and channel losses. [ABSTRACT FROM AUTHOR]

We present the results of a study of single-channel and two-channel compressors of microwave pulses, operated at a frequency of 11.4 GHz, in which a high-Q factor storing resonator and a novel plasma switch are used. In the single-channel compressor excited by magnicon radiation at a frequency of 11.4 GHz, 24-MW pulses have been obtained for a compression ratio equal to 8. In the two-channel compressor, coherent composition of pulses with the use of a 3-dB directional coupler has been demonstrated. Compressed pulses with powers of 9 to 11 MW and durations of 50 to 60 ns have been obtained at the incident-power level 1-1.5 MW, which corresponded to the compression ratio k = 8-9.3. [ABSTRACT FROM AUTHOR]

A new type of a plasma switch is proposed, which provides Q-switching of the energy storage cavity of a high-power microwave compressor and ensures high electric strength in all stages of compressor operation. In a compressor with this switch, the energy is accumulated on the TE02 mode and extracted on the TE01 round-waveguide mode. The principle of operation of the proposed switch is based on a sharp increase in the TE02 → TE01 mode conversion coefficient during plasma generation in an electrically controlled gas-filled discharge tube arranged in the switch. The high electric strength of the switch is ensured by placing the discharge tube surface at the node of a standing wave field formed in the switch. [ABSTRACT FROM AUTHOR]

A new microwave switch is proposed, in which the active element represents a metal reflector with a semiconductor plate on a mirror surface. The wave beam phase switching is ensured by a conducting layer formed in the semiconductor by laser radiation with quantum energy approximately equal to the bandgap width. Using a disk of high-purity silicon irradiated by a pulsed Ti:sapphire laser, a 180° phase switching in a 30-GHz wave beam has been studied. At a low microwave power level, the wave phase was effectively switched during a time on the order of several nanoseconds. [ABSTRACT FROM AUTHOR]

The radiation damping ratio and the transmission coefficient were calculated for a passive compressor of microwave pulses that is built around a length of an oversized waveguide with a helical-corrugated internal surface. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

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 TE[sub 01] 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. [ABSTRACT FROM AUTHOR]

This paper outlines the preliminary radiofrequency analysis of the prominent microwave components of the LHCD system for ITER. The general overview and inclusive analysis of the system is given in Ph. Bibet et al. (Overview of the ITER-Feat LH System; this Conference), a companion paper in this Conference. The results of the analysis and optimisation of the most relevant components is reported as computed by the ‘high frequency structure simulator’ (HFSS), a computer code developed by ANSOFT and based on the finite elements method. [Copyright &y& Elsevier]