A. E. Dubinov

Theoretical and experimental studies of virtual cathode microwave devices

The results of theoretical and experimental studies of microwave devices with virtual cathodes (VCs) are reviewed. It is shown that the basic factors affecting operation efficiency of these devices are phase separation of electron flux, diode impedance matching with the high-voltage transmission line, and the availability of two characteristic features in the output spectrum. Using nonlinear theory, we have observed the evolution of the electron velocity distribution function in the vicinity of the VC, have found the VC effective temperature, and have studied the fractal indices for various functions in time. This report also describes a series of experiments where 2-D features of the electron dynamics in the vircator are rather important, and 11% generation efficiency with a pinch-vircator was achieved. The understanding of the physical processes occurring in VC microwave devices gained in this work supports the proposal of several new highly efficient concepts for such devices. >

Ion-Acoustic Super Solitary Waves in Dusty Multispecies Plasmas

The concept of a new form of solitary waves-super solitary waves-is proposed, specific for embracing one or several interior separatrices on their wave phase portraits. The super solitary waves of an ion-acoustic type exist, for example, in nonmagnetized plasma containing five species of charged particles. For such plasma, electrostatic potential for ion-acoustic super solitary waves is calculated. The super solitary waves can be easily identified among usual solitons, e.g., in differential circuits installed into the measuring channel.

Ion-acoustic supersolitons in plasma

A new class of solitary waves—supernonlinear solitons (supersolitons)—the phase trajectories of which envelop one or several inner separatrices on the wave phase portrait has been revealed. It is shown that supersolitons of the ion-acoustic type can exist in an unmagnetized plasma that contains no less than four kinds of charged particles. The conditions for the existence of supersolitons are specified. The profile of the electrostatic potential in an ion-acoustic supersoliton is determined. It is shown that a supersoliton can be easily recognized experimentally among conventional solitons by using a differentiating circuit in the measuring channel.

Interpretation of ion-acoustic solitons of unusual form in experiments in SF 6 -Ar plasma

The emergence in SF6-Ar plasma of ion-acoustic solitons with angular profiles or profiles with several maxima has been explained. It has been shown that the cause of these profiles is that the phase trajectories of the solitons of this type in the phase portrait cover one or more separatrices, which in turn can appear only in plasma with a complex chemical composition.

Nonlinear theory of ion-sound waves in a dusty electron-positron-ion plasma

A theory of ion-sound waves in a dusty electron-positron-ion plasma is developed. It is shown in the linear approximation that periodic waves exist in a bounded range of parameters. The expression for the sound velocity is derived and the dependence of the velocity on the space charge of dust particles is analyzed. In the nonlinear theory, the general exact solution is obtained, which is then analyzed using the Bernoulli pseudopotential method. Particular solutions are obtained in the form of nonlinear periodic waves, large-amplitude periodic waves (superlinear waves), and solitary compression and rarefaction waves (solitons).

Supernonlinear Waves in Plasma

A new class of nonlinear waves in plasma—supernonlinear waves (SNWs) characterized by the nontrivial topology of their phase portraits—has been revealed. The topological classification of such waves is given, and suitable notation for them is proposed. It is demonstrated using several examples that SNWs can exist in the form of plasma waves of different physical nature, e.g., electrostatic (ion-acoustic) and MHD (Alfvén) waves. It is shown that a necessary condition for the existence of SNWs is the presence of at least three different charged plasma components (electrons, positrons, ions, dust grains, etc.). As the number of plasma components increases, the topology of the SNW phase portrait becomes more complicated. Typical indications of SNWs are given, which make is possible to easily reveal such waves experimentally.

Generators of High-Power High-Frequency Pulses Based on Sealed-Off Discharge Chambers With Hollow Cathode

Repetitively pulsed generators of high-power high frequency pulses based on sealed-off discharge chambers with a hollow cathode are described in this paper. Pulses of length 100-800 ns and power up to 250 kW at a frequency of 120 MHz with a repetition rate of 100 Hz were obtained using the chamber equipped with a H2 source. Pulses of length 100-1300 ns and power up to 900 kW at a frequency of 120 MHz with a repetition rate of 100 Hz were obtained using the chamber of similar design and equipped with a N2 source. The chamber filled with H2 proved to be more efficient compared to the chamber filled with N2.

Study of high-power pulsed RF generators based on a hollow-cathode discharge

Results are presented from studies of physical principles underlying operation of high-power pulsed RF generators based on a hollow-cathode discharge (HCD). Various types of instabilities that may occur in an HCD and lead to 100% RF modulation of the electrode voltage in the megahertz frequency range are discussed. The design, electric characteristics, and operating modes of HCD-based RF generators are described. Results of experiments aimed at increasing the power and duration of RF pulses are presented. It is demonstrated that such devices are capable of generating 10- to 220-MHz pulses with a power of up to 8 MW, duration of up to 10 µs, and repetition rate of 1 kHz. The discharge chambers of such generators are very simple in design, they have very high stability, and their efficiency reaches 35%.

Hybrid Microwave Oscillators with a Virtual Cathode

A review is given of the developments and theoretical investigations of a fundamentally new class of microwave devices, namely, hybrid microwave oscillators with a virtual cathode, which combine the useful properties of virtual cathodes with the advantages of those traditional microwave oscillators that operate with subcritical-current beams and have a high efficiency in generating ultrarelativistic electron beams. Among such devices are the following: a hybrid diffractional microwave oscillator with a virtual cathode, a hybrid gyrodevice with a virtual cathode, a hybrid beam-plasma vircator, a hybrid gyrocon with a virtual cathode, a hybrid Cherenkov oscillator with a virtual cathode, a hybrid microwave oscillator of the “vircator + traveling-wave tube” type, an original two-beam tube with a virtual cathode, and a klystron-like vircator.

Beam discharge excited by distributed virtual cathode

A new type of beam discharge, i.e., beam discharge with a distributed virtual cathode (VC) is proposed and considered by numerical simulation. The discharge is established during counter motion of high-current electron beams in a gas-filled equipotential cavity and is characterized by a state of hot dense electron plasma of primary electrons. The discharge temporal dynamics is studied. It is shown that the VC lifetime depends linearly from this sum in a wide range of the sum of beam currents, from the boundary current of two-beam instability to the critical current of Pierce instability. Generation of nonlinear electrostatic structures shaped as phase bubbles in the discharge is detected, and their dynamics is studied. The parameters are determined, at which the multiple coexistence of phase bubbles and their coalescence during collisions is observed.