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Dmitriyev B. S., Zharkov Yu. D., Klokotov D. V., Ryskin N.M.

Dept of Nonlinear Physics Saratov State University Saratov, Russia, 410012 phone +7 (8452) 516947 e-mail: dmitrievBS@info.sgu.ru

Abstract The results of experimentally investigating a delayed-feed back klystron oscillator in the single-frequency, selfmodulation and chaotic oscillations modes are presented.

I.  Introduction

A number of applications, such as charged particles accelerators, microwave plasma heating and modern communications systems, require powerful sources of noise-like microwave radiation with a relatively wide range attainable in the chaotic oscillations mode. Among such sources a delayed-feedback oscillator based on a multiple-cavity klystron amplifier appears to be one of the most promising due to its high power and efficiency.

II.  Main part

Experimental research has been carried out on an S-band five-cavity medium-power klystron with double-gap cavities operating in the 71 -mode. The input cavity was connected with the output one by a coaxial feedback line. To identify the oscillating regimes, oscillograms of the output signal envelope, its full spectrum, phase-plane portrait and averaged power were measured. The electron beam current and the feedback level were used for control parameters.

The oscillator under investigation has a discreet number of oscillation zones. In Figs. 1 and 2 these zones are represented along the following coordinates: power accelerating voltage and frequency accelerating voltage. When the level of the beam current is low, only two regularly-shaped zones are observed. With the growth of the current, these zones expand and overlap. A further increase of the current results in a periodic self-modulation with the frequency of about 3.5MHz, and then in the transition to chaos according to a scenario of sequentially doubling self-modulation periods.

Fig. 3 shows the phase diagram of oscillation modes over the parameter plane of beam current accelerating voltage. Regions of complex dynamics have a shape of discrete oscillation zones separated by wide areas of a single-frequency generation. Inside the regions of chaos small areas of regular oscillations are present, which is typical for such systems.

High levels of beam current initiate the transition to chaotic modes with a 32MHz bandwidth and a 40W output power.

III.  Conclusion

The results of the presented research show that it is possible to realize different oscillation modes (regular and chaotic) for a klystron self-oscillator by tuning the control parameters (the beam current and feedback level). Considerable power levels across wide frequency ranges are attainable in the chaotic mode.

Источник: Материалы Международной Крымской конференции «СВЧ-техника и телекоммуникационные технологии», 2003г.

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