N.I. Skripkin – Head of Laboratory, JSC «Pluton» (Moscow)
S.L. Morugin – Dr. Sc. (Eng.), Associate Professor, Head of Department, Nizhny Novgorod State Technical University n.a. R.E. Alekseev
For the last at least 15 years in domestic and foreign literature, published many articles and reports that discuss the issues of stabili-zation of the parameters of the magnetrons operating in the shortwave part of the millimeter wavelength range. One of the main problems faced by the developers of the magnetrons shortwave part of the millimeter wavelength range are enormous difficulties in developing constructive variants of the magnetrons to ensure micron tolerances on parts made necessary by the desire to achieve repeatability. To test ideas to optimize the dynamic characteristics of the device developed computational electrodynamics 3D model of a magnetron with an electron beam and further established and tested experimental samples.
The calculations and analysis of the field structure of the working harmonics, competing with her the second component of the doublet and the adjacent harmonics of the oscillations allowed us to determine the optimal number, size, location of control asymmetries in the resonator system of the magnetron, the location of the output energy to create a stable excitation of the magnetron at a maximum power in the load. The main objective was to control the spectral composition of spatial harmonics, with the aim of achieving the necessary degree of destruction of competing modes of oscillation while maintaining field symmetry of the working space harmonics due to the introduction of asymmetry of the resonator. Discussed options for asymmetric anode blocks in which competing spatial spectrum of harmonics the most «clogged» by other harmonics compared with symmetric anodic block with minimal distortion field of the working harmonics. By calculation, it was determined the optimal number of asymmetries (six) in a certain way located relative to the selected reference taken from any of the resonator anode block. Further, this asymmetric system has placed output energy in the resonators that have different amplitude of the field in the working space harmonics and 0.57; 0.7; of 0.82 relative units. In the proposed options was calculated spatial spectrum of fluctuations of the «cold» system without electron beam and also the excitation of a resonant system of the magnetron with an electron beam.
Analyzing the calculated oscillatory pattern, we define, that the broadest region of existence of stable oscillations in the magnetic field and less time of the transient process of excitation of the working harmonics is achieved in the system with the energy output located in the cavity, in which the relative field amplitude of the working harmonic is less (but not zero), i.e. weaker connected with the output of energy.
Based on the results of the calculation were collected and tested magnetrons with different options for the location of energy output relative to control asymmetries. Steadily worked magnetrons, in which the energy output was placed in the resonator with the relative amplitude of the field of 0.57, while the nearest rival was the amplitude of the field is 0.82, i.e., large.
Electrical parameters of the developed magnetrons: Wavelength – 3 mm;Power output – 11.5 kW (Copper system); – 8.5 kW (Copper-molybdenum system); The anode current pulse – 10 А; Anode voltage – 11.5 kV; Filament voltage – 6.3 V; Readiness time – 60 sec; Weight – 1.4 kg; The cooling - Air forced; The high frequency pulse duration 0.2 µs; The duty cycle – of 1000 or 2000/
The introduction of asymmetry in the resonant system of the magnetron leads to all kinds of fluctuations in the appearance of additional spectral component in the spatial distribution of the electromagnetic field; by fixing the spatial location of the field; shear resonance frequencies of competing modes of oscillations. The impact of well-chosen asymmetries in the properties of the work form of the average minimum, on its adjacent types is essential. To receive benefits under excitation operation view, it is desirable that connection level with load was less for working type oscillations than the closest competing species. The asymmetries of the resonator allows to achieve this condition.
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