Roman M. Rozental

This paper presents a theoretical study on the frequency locking of a high-power gyrotron by an external signal based on a time-dependent self-consistent model that accounts for electron energy fluctuations driven by voltage instabilities in the high-voltage power supply. To enable long-term interaction modeling, a highly efficient computational algorithm is proposed to accelerate the simulations. Analysis is performed for a megawatt-class, 170 GHz gyrotron, for which the experimental data are available both for free-running and frequency-locking regimes. The calculated free-running radiation spectrum linewidth, broadened by the given voltage fluctuations, is in close agreement with experimental results. The simulations with an external signal demonstrate that incorporating voltage fluctuations narrows the frequency-locking bandwidth by approximately 10% as compared to the case where this factor is neglected.

Radiation from a relativistic gyrotron is studied experimentally in the range of 25–29 GHz at a megawatt output power level. Radiation is recorded in the ranges of 126.3 and 146.2 GHz at the fifth cyclotron harmonic. Based on estimates of the signal from the detector, the power of radiation at the fifth harmonic of the gyrofrequency is determined indirectly and found to be –20 dB, relative to the level at the first harmonic.

A pulse-periodic oscillation regime was experimentally obtained in a gyro-resonant backward-wave oscillator (BWO) with a feedback circuit providing a high (approximately 0.9) transmission coefficient. The experiments were conducted by a 30 GHz gyro-BWO with a working space in the form of a three-pass corrugated waveguide. The pulse repetition frequency, with duration of ~1.5 ns, was approximately 220 MHz. The observed regime is interpreted as a mode-locking effect in a ring resonator formed by the interaction space of the gyro-BWO and the feedback circuit.

We theoretically study chaotic generation in helically waveguide gyro-TWTs with delayed feedback aimed at finding the possibility of improving the homogeneity of the output radiation spectrum. It is shown that with an increase in the length of the electron–wave interaction space, a region with a strong dependence of the phase shift on the amplitude of the input signal is formed on a gyro-TWT amplitude characteristic. For the parameters of the experimentally implemented 35-GHz gyro-TWT, we determine the acceptable interaction length at which the non-uniformity of the radiation spectrum decreases by more than 2 times with a simultaneous increase in the generation efficiency.

We report on the experimental investigations of radiation of a 25.27–25.41-GHz (K-band) relativistic gyrotron with a megawatt level of the output power. 126.4–127-GHz (D-band) radiation at the fifth cyclotron harmonic in the frequency multiplication regime is registered. Based on the estimations of the detector signal, we estimate indirectly the maximum radiation power level at the fifth harmonic of the gyrofrequency as −20 dB with respect to the first-harmonic radiation level.

We study a pulsed V-band relativistic gyrotron operating at the second cyclotron harmonic (CH) with megawatt power level. W-band radiation at the fourth CH is registered in the frequency multiplication regime. The power of this radiation is estimated about −35 to −40 dB with respect to the second-harmonic output power. Good agreement between the measured data and the results of simulations based on averaged equations is demonstrated. We also show that the radiation power level at the tenth CH in the 0.27 THz band can reach up to −25 dB with respect to the second-harmonic output power level.

The effect of passive mode locking is observed experimentally in a Ka-band helical-waveguide gyro-BWO equipped with a delayed feedback loop containing a saturable cyclotron-resonance absorber. Generation of periodic trains of 1.4-ns electromagnetic pulses with a repetition of 5.3 ns is obtained. The peak power of the pulses is three times higher than the average level of the radiation power.