Observation of chaotic dynamics in a powerful backward-wave oscillator

Self-modulation regimes of generation in a powerful 10-micros X-band backward-wave oscillator were studied theoretically and experimentally. The sequence of the self-modulation patterns and corresponding bifurcation values observed as the current was increased were in good agreement with the results of simulations. It was found that at a current of 120 A chaotic self-modulation set in at a power of 2 MW and a relative spectral width of 4%.     

Nonlinear dynamics of a backward-wave tube under the condition of competition of two modes

We study the nonlinear dynamics of backward-wave tubes in the regime of interaction of an electron flux with two transverse modes. In the region where the threshold values of parameters are slightly exceeded, one can observe a stationary single-mode oscillation when the other mode is suppressed, which is in good agreement with experimental observations of the competition of two modes in the relativistic backward-wave tube. It is shown that nonlinear competition can lead to the establishment of a single-mode stochastic regime of oscillation in the wide range of parameters in which the conditions of stochastic self-modulation are fulfilled for each mode individually. This work was presented at the Summer Workshop “Dynamic Days” (Nizhny Novgorod, June 30–July 2, 1998). Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 12, pp. 1565–1571, December, 1998.     

Pulsed high-order volume mode gyroklystron

We present the results of studies of a gyroklystron with the TE₅₃ output mode. A 30-dB gain is obtained at a frequency of 30 GHz for an output power of 5 MW, efficiency 25%, pulse duration 0.4 ms, and amplification bandwidth 40 MHz.     

Experimental study of a powerful magnetron-injection gun for relativistic gyrodevices

We show that it is possible to increase significantly (up to one-half of the Langmuir value) the current of the electron beam in a magnetron-injection gun operated in the nonadiabatic regime of formation of a relativistic helical electron beam if the velocity spread is small. The obtained beam has a current of 200 A, a velocity spread of about 10%, a pitch factor of about 1, and an electron energy of 340 keV. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radio.zika, Vol. 49, No. 8, pp. 680–685, August 2006.     

Controllable spectrum of an axial-mode gyrotron with external reflections

The feasibility of controlling the spectrum of multifrequency oscillations in a gyrotron by means of external reflections is studied. It is shown that, in self-modulation oscillation modes of operation, the radiation spectrum lines may come close to the resonance frequencies of a combined electromagnetic system including the reflector-limited part of the output waveguide. Under these conditions, the frequency separation of modes and, accordingly, the self-modulation period can be controlled by varying the position of the reflector. Theoretical results are corroborated by experiments with a 30-GHz relativistic gyrotron with an external reflector.     

Nonlinear optical detection of terahertz-frequency radiation in crystals with periodic domain structure

The temporal and spectral characteristics of the terahertz response are measured for crystals of doped lithium niobate with an as-grown domain structure. It is shown that the crystals can be used for narrow-band generation and detection of terahertz waves in the processes of nonlinear-optical conversion of the laser radiation frequency. Frequency tuning in the range from 0.5 to 2.5 THz can be performed, due to both variations in the domain structure period and changes in the nonlinear-optical interaction geometry.