Влияние внешнего электрического поля на оптический разряд в скоростном потоке

The influence of an electric field on the plasma of an optical discharge in subsonic and supersonic air flows has been studied experimentally. The presence of a weak electric field practically does not affect the size of the plasma formation, but, regardless of the configuration of the field lines and the polarity of the applied voltage, it leads to a decrease in the probability of optical breakdown. The experiment has shown that the plasma created by focused laser radiation is very sensitive to the presence of an electric field. When a voltage exceeding 22 kV was applied to the ring electrodes, powerful quasi-stationary streamers were formed in the flow. The presence of an optical discharge plasma made it possible to create an electric discharge in fields with an intensity below the breakdown threshold of the medium. The effect of quenching and the processes of development of an optical discharge were studied depending on the speed and characteristics of the electric field. Quenching of the optical discharge was observed when a voltage of 22 kV and higher was applied. Despite the preservation of the geometric dimensions of the optical discharge, the high-temperature region in the flow can be increased by using electric streamers. This leads to an increase in the energy supplied to the flow, and thus allows combustion to be initiated and flame stabilized at higher flow rates. Key words: experimental modeling, laser radiation, optical breakdown, electric field, electric discharge, sub- and supersonic air flow.

Investigating the Threshold Conditions of Air Breakdown with Mode-Locked Q-Switched Laser Pulses, and the Temporal Dynamics of Induced Plasma with Self-Scattering Phenomenon

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations.

Design and simulation of a compact Ku-band RTTO with power divider extraction structure

The radial transit time oscillator (RTTO) has attracted much attention because of its high power capacity and pure mode of output microwave. To make the high power microwave (HPM) source devices more compact and to enable it to measure the output microwave mode quantitatively, this paper proposed a compact Ku-band RTTO with the power divider extraction structure (PDES). The radial decreasing magnetic field is applied to decreasing the mass of excitation system. Compared the conventional uniform solenoids, it can reduce the mass by about 30%. In the coaxial output waveguide, the PDES is used instead of the traditional support rods connecting the inner and outer conductors so as to convert TEM mode into TE10 mode efficiently. This structure can not only help shorten the axial dimension of the device, but also make it possible to measure the output microwave mode more accurately online. In particle-in-cell (PIC) simulation, the proposed Ku-band RTTO can output HPMs with the power of 3.05 GW and the frequency of 14.36 GHz, and the working efficiency is 40.3%. The maximum radial electric field intensity in the extraction cavity is 0.92 MV/cm, and the maximum electric field intensity in the PDES is 0.52 MV/cm, both of which are lower than the radio frequency (RF) breakdown threshold of metal materials.

STOCHASTIC MODEL FOR TIME TO RECRUITMENT IN A SINGLE GRADE MANPOWER SYSTEM WITH TWO TYPES OF INTERDECISION TIMES WHEN THE BREAKDOWN THRESHOLD HAS THREE COMPONENTS

In this paper, the problem of time to recruitment is analyzed for a single grade manpower system in which attrition takes place due to two types of policy decisions where this classification is done according to intensity of attrition, it form an ordinary renewal process. Assuming (i) policy decisions and exits occur at different epochs (ii) wastage of manpower due to exits and wastage due to frequent breaks taken by the personnel working in the manpower system separately form a sequence of independent and identically distributed exponential random variables with different means and (iii) breakdown threshold for the cumulative wastage of manpower in the system has three components which are independent exponential random variables. A stochastic model is constructed and the variance of the time to recruitment is obtained using an univariate CUM policy of recruitment. Employing a different probabilistic analysis, analytical results in closed form for system characteristics are derived.

DETERMINATION OF VARIANCE OF TIME TO RECRUITMENT WITH INTER-DECISION TIME AS GEOMETRIC PROCESS WHEN THE THRESHOLD HAS THREE COMPONENTS

In this paper, the problem of time to recruitment is analyzed for a single grade manpower system using an univariate CUM policy of recruitment. Assuming policy decisions and exits occur at different epochs, wastage of manpower due to exits form a sequence of independent and identically distributed exponential random variables, the inter-decision times form a geometric process and inter-exist time form an independent and identically distributed random variable. The breakdown threshold for the cumulative wastage of manpower in the system has three components which are independent exponential random variables. Employing a different probabilistic analysis, analytical results in closed form for system characteristics are derived

Electrification of Dielectric Satellites under the Influence of Electron Flows of the Earth’s Radiation Belts

The effect of electron fluxes from the Earth’s radiation belts on satellites made of dielectric materials is studied theoretically. Spherical shaped nanosatellites of the BLITS and BLITS-M types are considered as a model. An analytical solution is obtained for the dependence of the electric field on the distance to the center of the satellite. Empirical formulas are used for the electron flux density and the track length in matter depending on the electron energy. The energy losses of incident electrons in the Debye shielding layer that surrounds the satellite, as well as the appearance of radiation conductivity in the surface layer of the dielectric, are taken into account. The reasons for the nonmonotonic dependence of the electric field on the satellite radius are established. Despite the fact that the electric field inside the satellite is smaller than the electrical breakdown threshold of the solid dielectric, it can be assumed that the dielectric micro-breakdown can occur in the surface layer of the dielectric and near inhomogeneities.

A computational analysis of nanoparticle-mediated optical breakdown

A theoretical model of the optical breakdown phenomena during picosecond and femtosecond laser pulse exposure with gold nanoparticles in water was developed. The model provides new and valuable insight into the dependence of the optical breakdown on the wavelength, morphology and environment in the vicinity of the nanoparticles. The developed model was successfully validated against experimental data, which also revealed some insights to the criterion for optical breakdown. Three studies were performed using the model. In the first study, the effects of the dielectric environment on the optical extinction spectra of individual bare and silica-coated gold nanorods were examined. The experimental extinction spectra of an individual gold nanorod was compared to a calculation from a numerical model that included environmental features present in the measurements and the morphology of the corresponding nanorod measured by transmission electron microscopy. The combination of these experimental and theoretical tools permitted a detailed interpretation of the optical properties of an individual gold nanorod. In the second study, a strongly coupled finite element model of nanoparticle-mediated optical breakdown phenomena was developed. This model was used to theoretically study a 6 ps laser pulse interaction with uncoupled and plasmon coupled gold nanoparticles. The study showed how the one-dimensional assembly of nanoparticles affects the optical breakdown threshold of its surroundings. The optical breakdown threshold had a stronger dependence on the optical near-field enhancement than on the volume of the nanostructure or its absorption cross-section. Finally, a model was developed to study the wavelength dependence of the threshold of gold nanorod-mediated optical breakdown during picosecond and femtosecond near infrared optical pulses. This study showed that the wavelength dependence in the picosecond regime is governed solely by the changes of the nanorod’s optical properties. On the other hand, the optical breakdown during femtosecond pulse exposures was found to depend on the multiphoton ionization and its wavelength dependence when, Eratio, the ratio of the maximum electric field from the outside to the inside of the nanorod was greater than 7. The developed model and conducted research deepens the understanding of the nanoparticlemediated optical breakdown in water and updates the theoretical formulation of the process with the latest findings, which leads to advancing this technology further.