P. S. Strelkov

Plasma relativistic microwave electronics

The principles of plasma relativistic microwave electronics based on the stimulated Cherenkov emission of electromagnetic waves during the interaction of a relativistic electron beam with a plasma are formulated. A theory of relativistic Cherenkov plasma microwave oscillators and amplifiers is developed, and model experimental devices are elaborated and investigated. The emission mechanisms are studied theoretically. The efficiencies and frequency spectra of relativistic Cherenkov plasma microwave oscillators and ampli-fiers are calculated. The theoretical predictions are confirmed by the experimental data: the power of the devices attains 500 MW, the microwave frequency can be continuously tuned over a wide band with an upper-to-lower boundary frequency ratio of 7 (from 4 to 28 GHz), and the emission frequency bandwidth can be varied from several percent to 100 percent. These microwave sources have no analogs in vacuum microwave electronics.

Experimental study and numerical simulations of a plasma relativistic microwave amplifier

The dependences of the radiation parameters of a plasma relativistic microwave amplifier on the external factors have been studied both experimentally and numerically. The calculated dependences are found to agree qualitatively with the measured ones. In contrast to experimental studies, numerical simulations make it possible to examine physical processes occurring inside the plasma waveguide. Good agreement between the measured and calculated dependences of the radiation parameters on the external factors shows that information provided by numerical simulations of the processes occurring inside the plasma waveguide can be considered quite reliable. The electromagnetic field structure and electron beam dynamics inside the plasma waveguide have been investigated.

Plasma Relativistic Microwave Amplifier with Smooth Frequency Tuning from 2.4 to 3.2 GHz

Earlier, it was shown that the plasma relativistic microwave amplifier can operate at two frequencies, 2 and 3.2 GHz. In the present work, it is shown that, by varying the plasma density from one microwave pulse to another, it is possible to amplify the input signals to a power of 50–80 MW at any frequency in the range 2.4–3.2 GHz.

Relativistic Cherenkov plasma maser of microsecond pulse duration

Experiments with a Cherenkov plasma maser (CPM) driven by a high-current relativistic electron beam of microsecond pulse duration are described. The results obtained show that the principle of operation of the CPM makes it possible to avoid the problem of microwave pulse shortening, which is inherent to vacuum devices of relativistic high-current microwave electronics. A 800-ns microwave pulse with an energy of 21 J was obtained at a peak power level of 40 MW (the efficiency being 4%) in a broad (/spl sim/100%) frequency band.

Dynamics of a high-current relativistic electron beam

The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as the electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations.

Output power variations in a plasma relativistic microwave amplifier during a 500-ns relativistic electron beam current pulse

A relativistic plasma microwave amplifier with a gain of about 30 dB and an output power of about 60–100 MW in the frequency range from 2.4 to 3.2 GHz is studied experimentally. The total duration of the output microwave pulse is equal to the duration of the current pulse of the driving relativistic electron beam (500 ns); however, the maximum output power is observed only within 200 ns. It is shown that variations in the output microwave power during the current pulse of the annular relativistic electron beam are caused by variations in the beam radius and thickness. Analysis of the experimental data and results of numerical simulations show that the thickness of the electron beam is determined by the density of the cathode emission current.

Repetitively rated plasma relativistic microwave oscillator with a controllable frequency in every pulse

A repetitively rated microwave oscillator whose frequency can be varied electronically from pulse to pulse in a predetermined manner is created for the first time. The microwave oscillator has a power on the order of 108 W and is based on the Cherenkov interaction of a high-current relativistic electron beam with a plasma preformed before each pulse. Electronic control over the plasma properties allows one to arbitrarily vary the microwave frequency from pulse to pulse at a pulse repetition rate of up to 50 Hz.

Emission spectra of a cherenkov plasma relativistic maser

The spectra of a plasma relativistic maser are measured. It is shown that the microwave frequency can be varied from 4 to 28 GHz by varying the plasma density from 4×1012 to 7×1013 cm−3 at a power of 30–50 MW. The relative width of the emission spectrum is within 50–80% for low plasma densities and 15–30% for high densities. Experimental results are compared with calculations.

A 50-MW broadband plasma microwave amplifier

A pure amplification regime (without accompanying generation) at two frequencies of 9.1 and 13 GHz is achieved in a plasma relativistic microwave amplifier. It is shown experimentally that an amplification regime with an output power of 40 MW can be achieved at both frequencies without changing the parameters of the system. This fact, along with the results of calculations, allows one to assert that the relative bandwidth of the amplifier is no less than 40%. It is shown experimentally that, by changing only one parameter, namely, the plasma density, the frequency corresponding to the maximum amplification can be varied from 9.1 to 13 GHz, which agrees with the results of calculations by a nonlinear model. At a frequency of 9.1 GHz, the maximum output power amounts to P=40 MW, the efficiency is η=4%, and the power gain is Kp=800 (29 dB). At a frequency of 13 GHz, these parameters are P=60 MW, η=6%, and Kp=1000 (30 dB). The measured plasma density range in which the amplification is observed agrees with calculations of the excitation of an E01 mode of a plasma waveguide.

Fine structure of the emission spectra of a relativistic Cherenkov plasma maser

The evolution of the emission spectrum of a relativistic Cherenkov plasma maser is studied both experimentally and numerically. The frequency range of emission is 1.5–6 GHz at a power level of 50 MW and pulse duration of up to 500 ns. It is shown that the relativistic Cherenkov plasma maser is capable of producing both broadband (with a spectrum width of ∼1 GHz) and narrowband (≈ 40 MHz) microwave pulses with a tunable mean frequency. Calculations by linear theory and numerical simulations provide a satisfactory explanation of the specific features and the time evolution of the spectra observed. It is suggested that the plasma nonlinearity is responsible for the experimentally observed shortening of the microwave pulses and the broadening of the emission spectrum.