Longitudinal multidomain structures formed in an optically bistable system under the action of a collimated annular beam

Several longitudinal domains may form under the action of a collimated annular beam propagating in an optically bistable cavity-free system. The computer simulation of this phenomenon indicates two possible pathways for the domain formation process.     

Electric conductivity of metal-dielectric-metal structures with dielectric layer formed by spherical metal oxide nanoparticles

The electrical properties of metal-dielectric-metal (MDM) structures with the dielectric layer representing a monolayer of spherical Al₂O₃ or ZrO₂ oxide nanoparticles have been studied. It is established that these heterogeneous structures exhibit electric conductivity according to the mechanism for which the differential resistance dU/dI is negative and reversibly approaches zero with increasing current I. The electric conductivity strongly depends on the polarity of the applied voltage U, provided that electrodes are made of basically different metals or the same metal with different surface conditions. The mechanism of the electric conductivity in the given MDM structure depends on the diameter of nanoparticles in the dielectric layer.     

On the possibility of a collective acceleration of ions in a magnetically insulated vircator in the regime of a traveling distributed virtual cathode boundary

A new scheme for the acceleration of ions by a traveling distributed virtual cathode boundary is proposed. Operation of the scheme is based on the phenomenon according to which an electron beam with a density exceeding a certain threshold exhibits a transition into the so-called compressed state. This state is characterized by a small velocity, a large electron density, and the developed turbulence of the opposite flows. The results of numerical calculations are presented.     

Enhanced emission during submillisecond low-energy electron beam generation in a diode with grid-stabilized plasma cathode and open anode plasma boundary

We have experimentally studied the phenomenon of emission enhancement in a gas-filled diode with grid-stabilized plasma cathode and open (mobile) anode plasma boundary at an accelerating voltage of up to 20 kV. As the working gas pressure is increased to p ≥ 10⁻² Pa and the longitudinal magnetic field is increased to B _z ≥ 20 mT, the current in the accelerating gap exhibits significant growth, sometimes by a factor of two or more. Experimental data show that the most probable mechanism responsible for this effect is ion-induced secondary electron emission from the emitting electrode surface bombarded by ions from plasma generated by the electron beam in the drift space. These ions are accelerated in the space charge layer between the emitting electrode surface and the mobile boundary of the beam-generated (anode) plasma.     

Plane-wave theory of a Michelson laser coupler with a dielectric slab beam splitter

The plane-wave theory for the transmittance and absorbtance of a perfectly aligned Michelson coupler with a dielectric slab beam splitter is presented. It is shown that the transmittance and absorbtance vary sinusoidally and in quadrature. As a result of this quadrature relationship, the maximum transmittance occurs at a setting of the translatable coupler mirror at which the absorbtance is not at an extremum, and so the curve of output power as a function of coupler setting is asymmetrical with respect to the setting yielding maximum transmittance. Experimental measurements of the output power of a far-infrared HCN laser as a function of the coupler setting confirm this asymmetry, which seems to have been overlooked or ignored in previous studies.     

Gasdynamic acceleration of microparticles and their interaction with a solid body

Based on the physicomathematical model developed before, verified by comparison results of calculations with experimental data, parameters of a gas-dispersed jet, interacting with a solid body, are numerically investigated. In a wide range of temperature and pressure values in a mixing chamber, material density, the size and mass fraction of particles, the nozzle geometry and the streamlined body form, ratio of specific heat capacities, and the Mach number of carrier gas, calculations are made, which allows one to determine the impact of specified factors on the boundary of a perfectly inelastic collision of particles with the body, accompanied by different physical processes (erosion, cold deposition, ultradeep penetration). Since temperature falls below the Debye value at high expansion of flow, the impact of a significant change of the heat capacity and thermal conductivity of particles are taken into account. Radial distributions of density and velocity of the dispersed mass are plotted, which characterize the “quality” of two-phase flow as a tool for the ground modelling of interaction of a flying vehicle with a dust-laden atmosphere (containing, for example, particles of volcanic outbursts or ice crystals) as well as in technologies of surface treatment.     

Electron source and acceleration regime of a picosecond electron beam in a gas-filled diode with inhomogeneous field

It is experimentally demonstrated that, upon the application of a subnanosecond high-voltage pulse to the gap of a diode filled with air at atmospheric pressure, a bunch of runaway electrons is formed in a sharply inhomogeneous electric field near the cathode. The bunch duration does not exceed 50 ps, which is shorter than the electron flight time through the interelectrode gap in the continuous acceleration regime. This duration remained unchanged when the gap width was varied between 6 and 26 mm. The electron energy in the picosecond electron beam, as determined from the time-of-flight measurements in the drift channel behind the anode foil of the diode, agree with the results of numerical calculations of the electron acceleration dynamics in the vacuum diode approximation.     

Autocompensation of an ion beam in an accelerator with an anode sheath

Experiments to study the autocompensation of an ion beam are described. It is shown that in accelerators with an anode sheath and isolated collector, autocompensation occurs as a result of the excitation of an auxiliary non-self-sustained gas discharge. Pis’ma Zh. Tekh. Fiz. 23, 69–73 (May 26, 1997)     

Axial force acting on a dielectric sphere in a focused laser beam

We present the detailed behavior of the axial force acting on a dielectric sphere exerted by the optical pressure of a focused Gaussian laser beam. Comparison is made between the numerical results and those calculated from the radiation pressure cross section. There is also a discussion as to whether the expressions for the axial force given in this paper are consistent with the previously reported experimental results. Moreover, a simple experimental method to measure the axial force on a polystyrene sphere suspended in water is demonstrated, and fairly good agreement between theoretical and experimental results was obtained.     

Nanoparticles formed by complexation of poly-gamma-glutamic acid with lead ions

The present investigation describes the preparation and characterization of novel biodegradable nanoparticles based on complexation of poly-gamma-glutamic acid (gamma-PGA) with bivalent lead ion. The prepared nano-systems were stable in aqueous media at low pH, neutral and mild alkaline conditions. The particle size and the size of the complexes were identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that the size of the complexes depended on the pH and concentrations of gamma-PGA and lead ions. Particle sizes measured by TEM revealed that at low concentrations, nanosized particles were formed, however, at high concentrations of gamma-PGA and lead ions, the formation of large aggregates with a broad size distribution was promoted. The size of individual particles was in the range of 40-100 nm measured by TEM. The results from the DLS measurements showed that the low and high pH values in mixtures with high concentrations of gamma-PGA and Pb2+ ions favored the growth of large complexes. The gamma-PGA nanoparticles, composed of a biodegradable biomaterial with high flocculating and heavy metal binding activity, may be useful for various water treatment applications.     

Virtual anode as a source of low-frequency oscillations of a high-current electron beam

We have studied the transport of a relativistic electron beam with supercritical current in a cylindrical drift chamber in the presence of an ion flux. A theoretical analysis of the electron-ion flux dynamics was based on the coarse particle PIC method (code SOM). Simultaneous injection of a supercritical electron beam and a weak-current low-energy ion beam may result in the formation of a virtual anode in addition to the electron virtual cathode in a drift chamber. The virtual anode exhibits periodic pulsations. Numerical results obtained for hydrogen and nitrogen ions show that the ratio of the frequencies of these pulsations is inversely proportional to the square root of the ion mass ratio. These oscillations of the virtual anode lead to temporal modulation, at the same frequency, of both electron and ion currents at the drift chamber output.     

Extinction and scattering of a guided beam in a hollow dielectric waveguide.

We present a theoretical approach to the problem of mode scattering by a spherical object that is placed inside a circular dielectric waveguide. This approach is based on the separation-of-variables method for each subsystem, namely, the spherical inclusion and the circular dielectric cylinder, and on the concept of the generalized recursive T-matrix algorithm for multilayered structures. We apply the technique to the backward and the forward scattering of a quasi-optical beam in the form of the fundamental HE11 mode by a sphere inside a circular hollow dielectric waveguide. The results calculated for the perfectly conducting spherical objects inside the circular hollow dielectric waveguide are compared with corresponding measured data of the backward-and the forward-scattering characteristics at the 4-mm wave band.     

Design and development of a thin film dielectric beam combiner

A multilayer thin film device called a beam combiner for a specific photodissociation experiment was designed and developed. The device when operated at 45° angle of incidence transmits auv laser beam and reflects a visible laser beam at the same time with minimum energy loss. The efficiency of the device was found to be better than 90%.     

Comparisons of discharge characteristics of a dielectric barrier discharge with different electrode structures

In order to analyze the homogeneous discharge of air dielectric barrier discharge (DBD) under ambient conditions, three different electrode structures are used in the paper. They are aluminum plane electrode, stainless mesh electrode and pure water electrode. The electrical characteristics are obtained and compared by using Lissajous figures, the waveforms of applied voltage and discharge current and the light emission images. The results show that the discharges of the different electrode structures are all filamentary discharges mode in ambient air and the discharge intensity of pure water electrode is much weaker than the other two electrodes.     

Demonstrating gain in a dielectric Cherenkov maser with a rod slow-wave system

We report the first results of experiments that demonstrate the amplification of megawatt nanosecond microwave pulses in a Cherenkov maser with a dielectric rod and moderately relativistic annular electric beam generated in a compact linear induction accelerator module. The input signal was generated by a resonant microwave compressor operating in a 3-cm wavelength range. A maximum gain of ∼12.5 dB and a maximum output power of ∼16 MW for a pulse duration of ∼4 ns at a frequency of 9.388 GHz were obtained with a quartz rod. The dependence of the gain on the compressor power was determined for various values of the accelerating voltage and beam current.     

Ablation plasma characteristics of flyer acceleration using a multi-pulsed ion beam irradiation

This paper presents the investigation of ablation plasma characteristics together with the flyer velocity for flyer acceleration when irradiating the 50-μm-Al target with a multi-pulsed ion beam. A one-dimensional hydrodynamic model is used in the calculations. The CIP method is used to describe the ablation plasma production and the acceleration mechanism by the repetition of ion beam irradiation. In the calculations, two shots of ion beam, which has a total energy density of 120 J/cm², are used. The time intervals between the first pulse and the second pulse of 0 ns, 20 ns, 50 ns and 100 ns were used for the investigation of flyer (target) velocity. Results indicate that irradiating the second pulse for 20 ns, 50 ns and 100 ns after the first pulse increases the flyer velocity by approximately 16%, 32% and 40%, respectively.     

Temperature field in a dielectric mirror during interaction with laser radiation

The general problem of the temperature distribution in a flat dielectric mirror during absorption of electromagnetic (EM) waves emitted by a laser in a broad spectrum range is solved.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 4, pp. 724–727, October, 1978.     

Reflection and refraction of an Airy beam at a dielectric interface

Reflection and refraction of a finite-power Airy beam at the interface between two dielectric media are investigated analytically and numerically. The formulation takes into account the paraxial nature of the optical beams to derive convenient field evolution equations in coordinate frames moving along Snell's refraction and reflection axes. Through numerical simulations, the self-accelerating dynamics of the Airy-like refracted and reflected beams are observed. Of special interest are the cases of critical incidence at Brewster and total-internal-reflection (TIR) angles. In the former case, we find that the reflected beam achieves self-healing, despite the severe suppression of a part of its spectrum, while, in the latter case, the beam remains nearly unaffected except for the Goos-H?nchen shift. The self-accelerating quality persists even if the beam is trapped by multiple TIRs inside a dielectric film. The grazing incidence of an Airy beam at the interface between two media with close refractive indices is also investigated, revealing that the interface can act as a filter depending on the beam scale and tilt. We finally consider reverse refraction and perfect imaging of an Airy beam into a left-handed medium.     

Cryogenic test of a superconducting half-wave resonator for the acceleration of heavy ions

We present the results of cryogenic tests on a superconducting half-wave resonator for the acceleration of heavy ions. The resonator was built out of OFHC copper and electroplated with 1.5 μm of Pb without chemical polish of the Pb surface. Measured properties include a low level Q of 4 × 10⁸ and a power dissipation of 6 W at 4 MV/m giving an energy gain of 1 MV per unit change to a particle of velocity 0.16 c.