D. I. Sobolev

Method for Synthesis of Waveguide Mode Converters

We propose an iterative method for synthesis of waveguide mode converters. An application of this method for bent circular waveguides is considered. Examples of synthesized converters calculated using this method are presented. The method offers fundamentally new solutions to the problems of mode converter development.

Principles of Synthesis of Multimode Waveguide Units

We propose principles which represent a systematic approach to the synthesis of multimode waveguides converting a specific input field into a different output field. Using these principles, fast and efficient methods of synthesis with specified properties can be constructed for any field analysis method. Several new methods of synthesis for most important applications are offered, and synthesized waveguide components are presented to demonstrate their efficiency.

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.

Method for synthesis of wideband multimode waveguide units

We propose a modification of the iterative method for synthesis of waveguide mode converters, which allows obtaining various elements of microwave transmission lines with a wide operating frequency band. The efficiency of the synthesis is illustrated by the calculated waveguide components. This method makes it possible to synthesize converters with significantly improved characteristics, e.g., a converter of the TM0,1 mode to the rotating TE3,1 mode, a converter of the TM0,1 to the TE1,1 mode, a converter of the TE1,1 mode of a smooth waveguide to the HE1,1 mode of a corrugated waveguide, and a waveguide 90° bend for the TE1,1 mode.

Fast quasi-optical phase shifter based on induced photoconductivity in silicon

A 30 GHz commutator aimed to switch phase of 0.1-1 mks, 1-100 MW microwaves in pulse compression systems like SLED is suggested. The commutator in a form of circular (100 mm) Si-disk put on a surface of copper mirror is based on creation of thin photoconductive layer in high purity low-loss silicon. The photoconductivity is caused by means of Ti:Sa laser radiation (1-10 mJ, 0.1 ps) with wavelength 795 nm. Results of low power tests carried out with the 180 degrees phase shifter, which was operated with Gaussian wavebeam, have showed high efficient phase switching for time ~1 ns. High-power tests are scheduled in CERN on the end of 2007.

Oversized

A new millimeter-wave barrier window in an oversized metallic circular waveguide has been developed for high-power transmission. The novel design utilizes the traveling-wave regime in an oversized profiled guide and synthesized TE0n mode mixing to minimize field intensity at the alumina ceramics surface. Proper choice of ceramics thickness provides necessary broadening of the operation frequency band. Low-power measurements show a reflection level below -25 dB at the operating frequency band of 34.272 plusmn 0.06 GHz

Ka

Development of multi-mode waveguide transmission lines requires design of components ensuring that waveguide modes be preserved or converted from one into another when the transmission line is bent or its parameters (e.g., radius) are varied. The synthesis methods developed to date (see, e.g., [B. Plaum, et al., 2000]) were in some respects unsatisfactory, both in regard to converter parameters, such as the length and the conversion coefficient, and computer resources. The objective of this paper is to formulate and to illustrate a new efficient iterative algorithm for synthesis of waveguide mode converters.

-Band Traveling-Wave Window for a High-Power Transmission

This paper describes gyrotron-based setup developed by Gycom Ltd. jointly with IAP RAS and intended for use in superconducting ECR ion source FECRAL (a Fourth generation ECR ion source with Advanced design in Lanzhou, China) [1]. The setup is capable to provide output power up to 20 kW in both CW and pulse 15 - 200 ms duration with less than 10 μs fall time and up to 5 Hz repetition rate) modes with 45 GHz frequency. Gyrotron system uses a cryogen-free magnet JMTD-4T140 made by Jastec Inc. (Japan) that allows it to operate on fundamental harmonic (operation mode is TE63). Gyrotron tube is designed to operate with diode-type electron gun, and using of depressed collector for recuperation of the electron beam residual energy leads to considerable total efficiency increasing. Output gyrotron radiation is converted by two-mirror matching optics unit (MOU) to the TEM00 mode. Gaussian beam propagates from the MOU output through the air 1 to the distance of about 2 m) to the system of mirrors delivering the one to the mode converter (TEM00 to TE01) which is located on the high voltage (about 300 kV) platform and connected via waveguide with the FECRAL ion source. The gyrotron rack is under ground potential. The setup is fully equipped with the automated control, data acquisition and safety interlocks systems which guarantee convenient and safe operation. Currently the described system is under manufacturing. Commissioning tests are scheduled for the end of this year.

A method of waveguide mode converter synthesis

A new method for increasing the angular range of a waveguide antenna for remote steering of the wave-beam direction in thermonuclear-fusion experimental setups with plasma magnetic confinement is proposed. Characteristics for large beam inclination angles can be improved using the synthesized nonuniform waveguide profile. For small angles, the characteristics remain invariable, the waveguide profile differs only slightly from the regular shape, and can be fit to limited waveguide-channel sizes.

45 GHz/20 kW gyrotron-based system for ECR ION source

We propose principles which represent a systematic approach to the synthesis of multimode waveguides converting a specific input field into a different output field. Using these principles, fast and efficient methods of synthesis with specified properties can be constructed for any field analysis method. Synthesized waveguide components are presented to demonstrate their efficiency.