V. D. Selemir

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. >

Generation of soft X-ray emission by Z-pinches powered from helical explosive magnetocumulative generators

Results are presented from experiments on the implosion of wire arrays powered from 100-and 200-mm-diameter helical explosive magnetocumulative generators with explosive opening switches. The experiments were performed at load currents of up to 4 MA, the current rise time being 0.3–0.4 μs. The maximum soft X-ray yield of ∼ 100 kJ was achieved at a pinch plasma temperature of 55 eV. A two-dimensional MHD code was developed to simulate the process of liner implosion and the generation of X-ray emission. The results of computer simulations agree satisfactorily with the experimental data.

Experimental Study of the Stability of the Interface between a Liquid Electrolyte and the Glow Discharge Plasma

The stability of the interface between a liquid electrolyte and the plasma of a contracted low-pressure dc glow discharge in air is investigated by means of digital photography. Water solutions of potassium permanganate and copper sulfate were used as electrolytes. It is found that, in the case of potassium permanganate, the instability of the interface leads to ejection of the electrolyte into the plasma and extinction of the discharge. Discharge modes with different types of quasi-steady interface are observed for copper sulfate at different values of the discharge current: a smooth interface, a solitary wave perturbation, regular ripples, and a churning foamed turbulent mixing zone.

Disk Magnetocumulative Generator of 480-mm Diameter for Explosive EMIR Facility

The first test of a disk magnetocumulative generator (DMCG) with high explosive charges of 480-mm diameter was carried out in the frameworks of a program on creation of an explosive EMIR facility, intended for high-power soft X-ray radiation pulses generation.The generator consists of five disk elements. The inductive load was equal to ~ 7 nH. The generator was twice larger than model DMCG240, successfully tested earlier. A comparison of calculation and experimental results is carried out.

Glow discharge based device for solving mazes

A glow discharge based device for solving mazes has been designed and tested. The device consists of a gas discharge chamber and maze-transformer of radial-azimuth type. It allows changing of the maze pattern in a short period of time (within several minutes). The device has been tested with low pressure air. Once switched on, a glow discharge has been shown to find the shortest way through the maze from the very first attempt, even if there is a section with potential barrier for electrons on the way. It has been found that ionization waves (striations) can be excited in the maze along the length of the plasma channel. The dependancy of discharge voltage on the length of the optimal path through the maze has been measured. A reduction in discharge voltage with one or two potential barriers present has been found and explained. The dependency of the magnitude of discharge ignition voltage on the length of the optimal path through the maze has been measured. The reduction of the ignition voltage with the presence of one or two potential barriers has been observed and explained.

Explosive complex for generation of pulsed fluxes of soft X-ray radiation

This paper describes the concept and realization principles of a project (EMIR complex) for generating pulsed fluxes of soft X-rays. EMIR is based on the development from VNIIEF technologies with high-power flux compression generators and systems on the basis of lines with distributed parameters and current opening switches. Vacuum lines with magnetic insulation or water coaxial lines are considered for energy pulse transmission to the load. Transformation of magnetic energy to kinetic energy, thermalization and X-ray production is performed in a Z-pinch with a double liner system.

High-power energy sources based on the FCG parallel and series connection

In the way of increasing currents and energies of flux compression generators (FCG) by enlarging their dimensions one can face technical and technologic difficulties. They are caused by the growth of electric voltages in the magnetic flux compression volume as well as by the growth of magnetic field force effects on the design elements. Moreover, enlarging the FCG dimensions results in the increase of characteristic time of current rise in the load, that is extremely undesirable for many applications. Parallel and series connection of several FCG, that are simultaneously operating modules, is one of the ways to obtain high currents and energies. This paper describes the possibilities of parallel and series connection of helical FCG and coaxial FCG with axial HE-charge initiation and also presents the project of high-current power unit Sprut based on using the multielement disk generators-modules connected in parallel with the common load.

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.

Calculation Method of Radiation Spectral Transfer in Frameworks of Two-Dimensional Magnetohydrodynamic Code FLUX-rz

A magnetohydrodynamic model of irradiating Z-pinch is the basis of a 2-D (in Euler cylindrical coordinates r-z) computer code FLUX-rz developed in VNIIEF (Russia). Earlier, the code considered the thermal radiation transfer in one-group (gray) diffusion approximation. This paper presents a modification of the FLUX-rz code in which we realized a multigroup diffusion model of the radiation transfer. Efficiency of an improved algorithm has been demonstrated by sample calculations of Shot 52 and Shot 567 on Z-machine at Sandia National Laboratories (U.S.).

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%.