Change in the Generation Mode of the Plasma Relativistic Microwave Oscillator
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MA ELECTRONICS
Change in the Generation Mode of the Plasma Relativistic Microwave Oscillator S. E. Andreeva, b, *, I. L. Bogdankevicha, b, N. G. Gusein-zadea, b, and D. K. Ul’yanova a Prokhorov
General Physics Institute of the Russian Academy of Sciences, Moscow, 119991 Russia Russian National Research Medical University, Moscow, 117997 Russia *e-mail: [email protected]
b Pirogov
Received November 22, 2018; revised January 20, 2019; accepted February 7, 2019
Abstract—Time evolution of the parameters of output radiation of a plasma relativistic microwave oscillator (PRMO) based on the Sinus 550-80 accelerator during a single relativistic electron beam (REB) pulse was studied experimentally. Analysis of the experimental data was accompanied by numerical simulations under conditions close to the experimental ones. It is shown that qualitative changes in the parameters of the PRMO output radiation are associated with a change in the generation mode. The first half of the REB pulse is characterized by the maximum output radiation power and a broadband spectrum consisting of a great number of harmonics. The nonlinear beam–plasma interaction limits the growth of the field amplitude, decreases the number of plasma electrons, and leads to the emergence of longitudinal plasma inhomogeneity. The appearance of an ion background in the drift tube volume and the formation of a radially nonuniform plasma waveguide alter the conditions of beam–plasma interaction in the second half of the pulse. The second half of the REB pulse is characterized by a decrease in the output microwave power and the narrowing of the generation frequency band. Spectral analysis demonstrates preservation of a stable narrow spectral component throughout the microwave pulse. DOI: 10.1134/S1063780X1907002X
1. INTRODUCTION In recent years, much attention has been paid to the development and creation of high-power wideband microwave oscillators. One of the solutions to this problem is the use of plasma relativistic microwave sources. According to the theory and experimental studies [1–3], plasma relativistic microwave oscillator (PRMO) is able to generate wide and narrow emission spectra and its average generation frequency can be tuned in a wide range. The operating principle of this device is based on the Cherenkov mechanism of excitation of an electromagnetic wave by a high-current relativistic electron beam (REB) interacting with a slow eigenmode of a plasma waveguide in a magnetic field [1–6]. In plasma relativistic electronic devices, electromagnetic waves with phase velocities close to the speed of light are excited, which makes it possible to efficiently output these waves into free space in a wide frequency range. The average frequency of the PRMO output signal is adjusted by varying the plasma density. In particular, in [4, 5], a sevenfold tuning of the frequency (from 4 to 28 GHz) at an output power of about 50 MW and a microwave pulse duration of 30 ns was achieved by varying the plasma density. In an actual oscillator, in contrast to the co
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