I. L. Bogdankevich

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.

Controlling the radiation frequency of a plasma relativistic microwave oscillator during a nanosecond pulse

It is shown experimentally and by numerical simulation that the radiation frequency of a 50-MW plasma relativistic microwave oscillator can be varied within 15% during a 60-ns-wide pulse by varying the plasma concentration. The plasma is generated by pre-ionization of a low-pressure gas. When the degree of ionization increases in a microwave field, the radiation frequency rises. Conversely, when plasma electrons are forced out by the electrostatic field of a high-current relativistic electron beam, the radiation frequency declines. By appropriately selecting the initial gas pressure and degree of gas ionization, one can control both trends and thereby the radiation frequency.

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.

Control over the radiation spectrum of a microwave plasma relativistic oscillator

General features of the operation of microwave oscillators based on the Cherenkov resonance interaction of a high-current relativistic electron beam with a preformed plasma are considered. Emphasis is placed on the presence of longitudinal modes of the plasma-beam resonator that make it possible to tune the radiation frequency. Methods by which the radiation frequency can be varied severalfold continuously or in discrete controlled steps and the width of the spectrum of simultaneously generated frequencies can be changed substantially are described. The results of numerical simulations are compared with available experimental data.

Surface wave and linear operating mode of a plasma antenna

The relation between the propagation conditions of a surface electromagnetic wave along a finiteradius plasma cylinder and the linear operating mode of a plasma antenna is investigated. The solution to the dispersion relation for a surface wave propagating along a finite-radius plasma cylinder is analyzed for weakly and strongly collisional plasmas. Computer simulations of an asymmetrical plasma dipole antenna are performed using the KARAT code, wherein the dielectric properties of plasma are described in terms of the Drude model. The plasma parameters corresponding to the linear operating mode of a plasma antenna are determined. It is demonstrated that the characteristics of the plasma antenna in this mode are close to those of an analogous metal antenna.

On the development of plasma relativistic microwave oscillator without strong magnetic field

A method for generating microwave pulses with a power of ∼1 GW and a frequency controlled in a band from 2 to 15 GHz during the interaction of relativistic electrons with plasma without strong magnetic field is proposed in the numerical model. The combination of a broadband plasma relativistic microwave oscillator and a monochromatic magnetically insulated transmission line oscillator (MILO) allows the development of a device combining advantages of both prototypes.

Mechanism of radiation pulse shortening in plasma relativistic microwave generator

The causes of emission quenching in the plasma relativistic microwave generator are studied by numerical calculations using the particle-in-cell method. The process mechanism in which the plasma boundary moves from the coaxial collector edge with a velocity above 107 cm/s is found. An electron flux with an energy of ∼105 eV and a current of ∼103 A is generated from the collector in the formed gap, which heats plasma and increases its potential. Microwave generation stops due to a multiple decrease in the wave reflectance from the collector. The use of the hollow collector is presumably a method for preventing microwave generation quenching.

Shortening of the radiation pulse from a plasma relativistic microwave generator in numerical calculations with plasma simulation by the particle-in-cell method

Spontaneous shortening of radiation pulses of Cherenkov microwave generators based on the interaction of a high-current relativistic electron beam with preliminarily generated plasma was studied in a numerical model. Microwave pulse shortening is caused by the appearance of a gradually expanding region near the collector, from which plasma is expelled by an electrostatic field of relativistic electrons. The absence of plasma results in a severalfold decrease in the plasma wave reflectance from the collector and violation of generator self-excitation conditions. The microwave emission duration increases with the plasma ion mass.

Normal Doppler effect in experiments on the interaction of relativistic electron beams with plasma: Plasma relativistic microwave amplifier

The Cherenkov interaction of a high-current relativistic electron beam with a spatially bounded plasma was studied experimentally. In the generation of electromagnetic radiation, an important role is played by the counterpropagating plasma wave produced due to the reflection from the end of the plasma column. It is shown that, at the resonant value of the magnetic field, the normal Doppler effect occurs and the amplitude of the counterpropagating wave decreases. This effect was used to design and create a plasma relativistic microwave amplifier in which 10% of the beam energy is converted into radiation. The radiation frequency is 9.1 GHz, and the radiation spectrum width (±0.17%) is determined by the microwave-pulse duration. The maximum radiation power is 100 MW, the gain factor being 32 dB.

Influence of the electrons reflected from the collector on the parameters of a high-current relativistic electron beam

In plasma microwave oscillators, electrons fall onto the surface of a graphite collector, which leads to the generation of secondary electrons. The influence of the electrons reflected from the collector on the parameters of a high-current relativistic electron beam propagating in a strong longitudinal magnetic field was studied experimentally and by numerical simulations. It is shown that the penetration of the reflected electrons into the drift space can lead to a substantial increase in the depth of the potential well in the drift space, a decrease in the velocity of the beam electrons, and a broadening of the electron energy distribution function.