A Signal Input Selective Device for a High-Current Relativistic Cherenkov Amplifier
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al Input Selective Device for a High-Current Relativistic Cherenkov Amplifier Yu. Yu. Danilova*, E. B. Abubakirova, and A. P. Konyushkova a
Institute of Applied Physics, Federal Research Center, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received March 26, 2020; revised June 22, 2020; accepted June 23, 2020
Abstract—Selective unidirectional excitation of a cylindrical waveguide through the lateral wall is investigated as applied to the signal input into a millimeter high-current relativistic Cherenkov amplifier. The ratio of the parameters of the input device has been found providing the maximum transformation of the fundamental mode of a rectangular waveguide into the unidirectional lower axisymmetric mode of a cylindrical waveguide. In the absence of Ohmic losses, the conversion efficiency reaches 97.5%. An input device adapted to the design of a 35.5-GHz amplifier is implemented with an efficiency of 75%. Keywords: selective device, signal input, lowest axisymmetric mode, high-current amplifier, millimeter wave range. DOI: 10.1134/S1063785020090175
Recently, an increased interest in amplifiers of millimeter wavelength range with subgigawatt power for various applications has been observed (see, for example, [1]). In the long-wavelength millimeter range, the most effective devices are those based on induced Cherenkov radiation of rectilinear electron beams [2– 4]. They combine the simplicity of forming such beams with high values of the pulsed output power and gain factor. As a working wave in such devices, the most often used is the lowest axisymmetric mode E01 of a cylindrical waveguide. Its excitation requires a special approach, since the design of the input device must be compatible with a high-current relativistic electron beam. This circumstance makes the known exciters of mode E01 unacceptable [5, 6]. At the same time, the quasi-optical input of an external signal by means of a mirror, as used in [2], is cumbersome and ineffective. In this regard, the further development of such devices requires the creation of a compact and efficient signal input device. To create a selective unidirectional input device through the lateral wall, at least two exciting elements are required, in which the electric field is oriented parallel to the axis of the cylindrical waveguide. These two excitation elements are created by means of a 3-dB branching of the supply single-mode rectangular waveguide, which is matched to the source by the use of an inductive diaphragm. The unidirectionality of mode E01 is achieved by means of a stepped resonant expansion [7], which selectively reflects the power initially propagated in the cylindrical waveguide in the opposite direction.
Obviously, the optimal distance between the centers of elements exciting the waveguide should be ~nλw/4, where λw is the waveguide wavelength of E01 mode. The choice of a natural odd number n is due to a compromise made between the maximum possible dimensions of the input device determined by the amplifier
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