The problem of signal amplification in a plasma microwave amplifier is considered in the linear approximation and with allowance for nonlinear effects leading to saturation of instability. The solutions of the exact dispersion equation and an approximate dispersion equation used in calculation of parameters of plasma microwave amplifiers are compared. It is shown that the solutions of these equations in the region of high frequencies are significantly different. Nonlinear dynamics of beam–plasma instability in plasma microwave amplifiers is described by a system of differential equations which is obtained by the slowly varying amplitude method and yields an approximate dispersion equation when it is linearized. A method for modifying parameters of a nonlinear system of differential equations to make it consistent with the exact dispersion equation is proposed and the calculation results are demonstrated.

The electrodynamic properties of the plasma of a radio-frequency capacitive discharge with a magnetic field along the capacitor plates are considered. The complex impedance of such a system is calculated. Based on the equivalent electrical circuit of a plasma capacitor, the resonant properties of the discharge are analyzed. The role of ions in the stability of an electron flow drifting in crossed electric and magnetic fields has been demonstrated.

A plasma relativistic microwave amplifier with a gain band of about 1.5 GHz and maximum gain at a frequency of about 3 GHz has been experimentally investigated. Previously the wide gain band of this amplifier made it possible to demonstrate the amplifier frequency tuning in the range from 2.4 to 3.1 GHz. Microwave radiation with a power of 100–150 MW and a pulse duration of 300 ns was obtained using a 2-kA electron beam having an electron energy of 500 keV. The high-current electron beam formed in the explosive emission cathode accelerator has a high noise level in the aforementioned frequency range. This leads to the transition from the mode of input signal amplification to the amplifier self-excitation in a wide frequency band. To suppress the latter process, one must suppress the feedback that is due to the wave reflection from the elements of the amplifier output part. The feedback in the amplifier is suppressed by incorporating a ceramic microwave absorber into its electrodynamic system. The role of the absorber in the suppression of amplifier noise at an input signal frequency of 2.716 GHz is investigated. The parameters of a microwave amplifier without a feedback (with an absorber) are compared with the parameters of a microwave amplifier having a feedback (without an absorber).

The role of the local absorber in suppressing self-excitation of a relativistic plasma surface-wave microwave amplifier is investigated. The thus obtained amplifier self-excitation conditions are analyzed for a wide range of parameters employed in plasma microwave electronics experiments. Requirements on an absorber for suppression of amplifier self-excitation are given.

In this paper, we consider the dynamics of plasma in a high-power plasma-microwave amplifier with a submicrosecond pulse duration. It is shown that, in the case of a linear mode (a short system length or a small input signal level), a discontinuity in the plasma density can form near the output boundary due to the escape of particles towards the amplifier input, which can lead to radiation breakdown. When the amplifier operates in the saturation mode, the plasma displacement has a multidirectional character, and a density discontinuity is not formed. At an increase in the initial plasma density, the effect of its pushing out weakens.

We analyze the possibility of increasing the operating frequency of available plasma Cherenkov microwave emitters operating on relativistic high-density electron beams. We consider high- and low-frequency surface waves of a high-density nonmagnetized tubular plasma in a waveguide and determine conditions for their pumping by electron beams. The coefficients of spatial amplification of surface waves in the regimes of one-particle and collective Cherenkov effects are calculated. Nonlinear equation of spatial enhancement of waves are derived, and the efficiencies of surface wave amplification are calculated. It is shown that an increase in the operating frequency of operating plasma emitters by an order of magnitude is quite feasible and can be attained by increasing only the density of the plasma.

We consider dynamics of radiation of a plasma microwave amplifier on a surface wave at the leading edge of the relativistic electron beam pulse. It has been shown that depending on the electron density of the plasma, different modes of operation of the amplifier are possible. At low plasma density, there is an early activation of the amplifier with large gain at the leading edge of the electron beam pulse and a significant decrease in the amplification of the signal when the electron energy reaches a plateau. With a higher plasma density, a later activation takes place with an almost constant output amplitude. The effect of ponderomotive force on plasmas was discussed.

A coaxial electrodynamic system for the amplification of microwaves with plasma filling, through which a relativistic electron beam moves, is studied theoretically. The dependences of the increments of the spatial amplification of the beam–plasma instability on the external signal frequency and the amplifier parameters are obtained. The nonlinear dynamics of the development of instability is simulated and the efficiency of the conversion of the energy of the electron beam into the energy of microwave oscillations is determined. The use of a coaxial electrodynamic system makes it possible to increase the electron beam current transported through the system, at which the instability increment and the efficiency of the conversion of the energy of directed motion of electrons also increase.

Surface waves in layered systems consisting of material media with different frequency dispersions are considered: dielectric–plasma–vacuum, vacuum–plasma–plasma, and dielectric–vacuum–plasma. It is shown that in such systems, one of the surface waves can be radiative into a medium that does not form an interface for the surface wave under consideration, in view of which the wave becomes decaying. In the dielectric–vacuum–plasma system, there is only one surface wave localized at the vacuum–plasma interface, which is radiative into the dielectric in a certain region of wavenumbers with a not too small thickness of the vacuum layer. For all cases, the possibilities of exciting surface waves of a layered structure by an electron beam are analyzed. It is indicated which surface waves will be excited most efficiently. The prospects of using such waves in plasma microwave electronics in the development of sub-terahertz and possibly terahertz frequency ranges are shown.

We consider the excitation and absorption of waves in a magnetoactive rf discharge plasma in the conditions when the generator frequency is lower than the electron cyclotron frequency. We consider the cases of unconfined and confined plasmas in the cylindrical geometry and different regimes of excitation of plasma waves with different dispersion relations and field polarizations. The power input to the plasma depends on the distribution of external-source currents initiating the discharge and on the density parameter characterizing the plasma density and transverse sizes of the system. In the case of a plasma cylinder with a free surface or a plasma cylinder in a large conducting casing, which is most interesting for applications, plasma contains only potential and nonpotential E -type oblique Langmuir waves as well as a strongly nonpotential surface wave. The latter wave is practically not excited by external currents flowing over the cylinder surface for real parameters of the system. For high values of the density parameter, the effective resistance of the plasma with inducting excitation of the discharge is predominant. For moderate and low values of this parameter, capacitive excitation of the wave by the current on the plasma cylinder surface is found to be most effective.

We have studied the excitation of surface plasma waves during the propagation of a cylindrical electromagnetic wave in a layered plasma–dielectric medium. The dielectric—vacuum—plasma and vacuum–plasma–plasma layers have been considered. It is shown that no surface waves are excited by the cylindrical electromagnetic wave at the plasma–dielectric boundary (like in the case of a plane wave). A surface wave in a layered medium is excited in a quite narrow range of frequencies and angles of propagation. We have calculated the structures of the electromagnetic field and the electromagnetic energy flux and determined the integral reflection and transmission coefficients using both numerical an analytic asymptotic methods. It is shown that the contribution of the field from the lateral wave is negligibly small in all cases.

Dependence of the shape of a microwave pulse in a plasma relativistic microwave amplifier (PRMA) on the initial plasma electron density in the system is detected experimentally. Depending on the plasma density, fast disruption of amplification, stable operation of the amplifier during the relativistic electron beam (REB) pulse, and its delayed actuation can take place. A reduction in the output signal frequency relative to the input frequency is observed experimentally. The change in the shape of the microwave signal and the reduction in its frequency are explained by a decrease in the plasma density in the system. The dynamics of the plasma density during the REB pulse is determined qualitatively from the experimental data by using the linear theory of a PRMA with a thin-wall hollow electron beam. The processes in a PRMA are analyzed by means of the KARAT particle-in-cell code. It is shown that REB injection is accompanied by an increase in the mean energy of plasma electrons and a significant decrease in their density.