S. V. Kuzikov

RF Analysis of ITER Remote Steering Antenna for Electron-Cyclotron Plasma Heating

An application of remote RF beam steering concept, based on image multiplication phenomena in a corrugated square waveguide, to electron-cyclotron plasma heating and current drive for ITER has been considered. In the present paper high attention is paid to studies of reliability of the remote steering capability in realistic waveguide condition. Different factors, could limit efficiency (RF breakdown, random technological spread of parameters, and heating of system), are simulated. Polarization properties of the remote steering antenna, arising due to non-ideal corrugation, are investigated. It is suggested a new configuration of antenna to be not sensible to corrugation parameters. RF analysis of the system, supplemented by dog-legs and a vacuum window, is also presented. A new way to use beating wave transmission in the remote steering waveguide is suggested, in order to reduce losses caused by mitre bends.

Wavebeam Multiplication Phenomena to RF Power Distribution Systems of High-Energy Linear Accelerators

A new quasi-optical concept of electrically proof Delay Line Distribution System (DLDS) for high-energy electron/positron accelerators is proposed. In order to increase microwave power, used for particle acceleration, the concept assumes summing up of a few wavebeams in multimode rectangular waveguide. Operating by mutual phases of the wavebeams, to be produced by coherent sources, the system allows also a distribution of long multiplied RF pulses on a set of acceleration sections. Calculations of key components are fulfilled at 34 GHz frequency.

Demonstrating high-power 30-GHz free-electron maser operation on a resonant load

An effective narrow-band free-electron maser (FEM) with reversed axial guide magnetic field, based on a corrugated high-selectivity Bragg resonator with a jump in the ripple phase, has been constructed and tested. The FEM operates at 30 GHz with characteristics of the output radiation (power, pulse duration, spectrum width) and stability of the generation regime that allow the device to be used in testing electrodynamic components for future electron-positron supercolliders. Experiments have been performed with a high-Q resonator operating on a resonant load, which can be used to model the degradation of an accelerating structure of the CLIC collider (CERN) as a result of thermal fatigue caused by the multiply repeated (∼105 cycles) action of microwave pulses.

Mode content analysis from intensity measurements in a few cross sections of oversized waveguides

A method of mode content analysis in oversized waveguides basing on intensity measurements in a few cross sections is suggested. The method is based on iterative synthesis of phase fronts of the radiation measured in a few cross sections of an oversized waveguide. The phase reconstruction makes it possible to calculate field distribution as well as the mode content at any place of the waveguide. The method was tested in experiments with circular and rectangular waveguides with impedance corrugation of the walls [8].

A high-speed quasi-optical wave phase switch based on the induced photoconductivity effect in silicon

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.

Q-switching in the electron backward-wave oscillator

The use of Q-switching (periodical modulation of the feedback factor) is proposed for the electron backward-wave oscillator (BWO). This can be a way to realize regimes of a stable generation of periodical short high-power rf pulses with relatively high averaged efficiency. As compared to the conventional regime of the stable generation of a BWO with no feedback, in the Q-switched BWO the averaged electronic efficiency can be increased by an order of magnitude, whereas the peak power of output rf pulses is 40–50 times higher.

Observation of the high-Q modes inside the resonance zone of two-dimensional Bragg structures

Electrodynamical properties of two-dimensional Bragg resonators of planar geometry are studied in the frame of the geometrical-optical approach and in three-dimensional simulations. Results of the theoretical analysis are corroborated by data obtained in “cold” microwave measurements. Formation of the high-Q eigenmodes in the vicinity of the Bragg resonance frequency has been demonstrated.

Eigenmodes evolution due to changing the shape of the waveguide cross-section

The problem of eigenmodes in a hollow waveguide with an arbitrary shape of cross-section is considered. To calculate this problem rigorously, the formalism of Fredholm integral equations of the second kind is developed. Basing on it, phenomena of field mode structure evolution in a system of initially circular waveguides are analysed.

Paraxial approach to description of wave propagation in irregular oversized wavegues

Propagation of paraxial wavebeams in irregular oversized waveguides is considered using quasi-optical formalism. The description of wave propagation in quasi-cylindrical waveguides is developed basing on the computation of the integrals of the parabolic type. The method of the calculation and synthesis of millimeter waveguide components is proposed.

Simple millimeter wave notch filters based on rectangular waveguide extensions

A new efficient notch filter is proposed. Some details of notch filter operation at millimeter waves are discussed. A 110 GHz notch filter is numerically and experimentally tested.