Ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field of laser radiation

Simple analytical expressions are obtained for the energy and angular distributions of outgoing electrons in ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field as well as for the ionization probabilities per unit time. The cases of linear and circular polarization of the laser radiation are studied. It is shown that in contrast to the case of the ionization of atoms oscillations appear in the energy spectra of the photoelectrons as a function of their kinetic energy. The well-known limits for the tunneling ionization probabilities for the hydrogen atom by a strong low-frequency alternating field are obtained in the case of large internuclear separations. Zh. é ksp. Teor. Fiz. 113, 583–592 (February 1998)     

A Basic Predator‐Prey Type Model for Low Frequency Discharge Oscilations in Hall Thrusters

The mechanism of low frequency oscillations in Hall thrusters is usually explained using the predator‐prey type model, but the reasonable boundary conditions for the model have not been given. Analyses on thrusters' model equations show that besides the processes of neutral replenishment and ionization avalanche, the effects of dynamic electric field are also necessary for low frequency oscillations. The dynamic electric field reflects the interaction of ionization zone with acceleration zone, and is embodied in boundary conditions of the predator‐prey type model. Furthermore, a basic predator‐prey type model with reasonable boundary conditions and complete physical mechanism is proposed. And the effects of electric field on low frequency oscillations are verified by experiment (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Excitation of low-frequency oscillations via interaction of a high-current relativistic electron beam with a radial ion flux

The nonlinear excitation of low-frequency oscillations in the case when an ion flux is radially injected into the drift chamber where a tubular relativistic electron beam propagates is studied. A mechanism behind low-frequency ion oscillations is discussed.     

Dynamic processes in helical electron beams in gyrotrons

The results of theoretical and experimental studies of collective processes in helical electron beams in gyrotron-type devices are generalized. Main attention is paid to low-frequency oscillations associated with the development of instability in the space charge trapped between the cathode and the magnetic mirror. The mechanism of evolution of instability is substantiated and the effect of oscillations on the main parameters of the electron flow determining its quality is analyzed. Data on the suppression of low-frequency oscillations and resulting enhancement of the gyrotron efficiency are considered.     

Study of low‐frequency oscillations in a double‐stage Hall thruster

The characteristics of low‐frequency oscillations of double‐stage Hall thrusters are quite different from those of conventional single‐stage Hall thrusters. In this paper, the effects of double‐stage discharge on the low‐frequency oscillations are experimentally investigated. The results indicate that the amplitude significantly decreases with increasing magnetic field strength and voltage during the ionization stage. Meanwhile, data analysis reveals that ionization occurs in both stages and that the transport ion current between the two stages is the key factor that affects the amplitude and main frequency of the oscillations. Two new processes, namely the ion transport and ion recombination caused by double‐stage discharge, are found to be relevant to the change in the current oscillations. To summarize, the ionization stage relieves the oscillations in the acceleration stage, leading to a reduction in the amplitude of the discharge current.     

Nonlinear dynamics of breathing current filaments inn-GaAs andp-Ge

A novel model is presented for spatio-temporal pattern formation in semiconductors. It leads to self-generated nonlinear current oscillations due to “breathing” current filaments in the regime of impurity impact ionization. The four qualitatively different regimes which have been observed in Ge with increasing current are consistently explained as: a stationary nonconducting state; bulkdominated oscillations; breathing filaments; stable filaments. The physical origin of the breathing oscillations is impact ionization coupled with transverse diffusion and longitudinal dielectric relaxation. A method is developed to derive simple nonlinear dynamic equations for the filament radius and the position of the peak transverse electric field by a nonlinear mode expansion.     

利用静电场中光电离效率谱精确确定1,3-二乙氧基苯分子的电离能

电离能是原子和分子的重要的特性参数,在光物理和光化学过程中起着重要作用,精确电离能对相关研究具有重要意义.电离能是调试零动能光谱信号的重要参考数据,在判断异构物数量和分子构型方面也起着关键作用.1,3-二乙氧基苯是一种重要的苯的衍生物,实验证实在超声分子束中包含两种旋转异构物Ⅰ(downup)和Ⅲ(down-down).它们的精确电离能还未见文献报道.本文采用直线式飞行时间质谱仪测量了静电场中1,3-二乙氧基苯光电离效率曲线,通过不同电场强度下测量的电离能(Stark效应)对场强的平方根线性拟合给出了两种异构物Ⅰ和Ⅲ精确的电离能分别为(62419±2)cm^–1和(63378±2)cm^–1.相对于通常的脉冲电场加速机制和零动能光谱测量的电离能,精确度大约分别由(±10)cm^–1和(±5)cm^–1提高到(±2)cm^–1.分析和讨论了不同方法测量的物理机制和优缺点.     

Low-Frequency Parasitic Space-Charge Oscillations in the Helical Electron Beam of a Gyrotron

We developed a medium-power pulsed gyrotron equipped with diagnostic systems for studying low-frequency parasitic space-charge oscillations in the helical electron beam and the energy spectrum of electrons in the collector region. Methods for suppressing parasitic oscillations are proposed and tested. An explanation of the mechanism of suppression of these oscillations is given.     

Collective processes in a microsecond relativistic electron beam: Basic rules and mechanisms

Collective processes taking place in the space charge of a microsecond relativistic electron beam with magnetic insulation are considered. The space-time characteristics of the low-frequency and high-frequency oscillations are found, and the effect of the magnetic compression of the beam near the cathode on these oscillations is studied. It is shown that the basic source of the low-frequency oscillations is the collective motion of the space charge, which takes place in crossed electric and magnetic fields near the cathode, while the primary reason for the high-frequency oscillations is two-stream instability in the beam. The possibility of suppressing both types of oscillations by compressing relativistic electron beams near the cathode is demonstrated. The effect of nonuniform magnetic fields, including their effect on the cathode plasma motion, is elucidated.     

Anomalies in the electrophysical, thermal, and elastic properties of layered ferroelectric semiconductor TlGaSe2: Instability in the electronic subsystem

The temperature dependences of the permittivity, dark current, and current-voltage characteristics of the layered ferroelectric semiconductor TlGaSe₂ were measured over the range 77–300 K. The ε(T) curve measured perpendicular to the layers at low frequencies is discovered for the first time to exhibit an anomalous dip with clearly defined boundaries at ～150 and ～200 K. Electrical instability in the form of low-frequency oscillations of current in current-voltage characteristics of a sample in the same temperature range are also observed experimentally for the first time. It is shown that this instability occurs only if an electric field is applied to a sample using potential-controlling contactless electrodes in the form of thin mica spacer layers. The nature of the instability and its influence on various physical properties of the layered TlGaSe₂ crystal are discussed.     

Laser Raman spectroscopy of the effect of solvent on the low-frequency oscillations of organic molecules

The effect of solvent on low-frequency oscillations is studied using an example of the 1,1,2,2-tetrachloroethane (TCE) and 1,1,2,2-tetrabromoethane (TBE) molecules, which exhibit torsional oscillations in the terahertz range. Dimethylsulfoxide (DMSO) and carbon tetrachloride (CTC) are used as solvents. It is demonstrated that a decrease in the concentration of the substance under study in the TBE/CTC, TCE/DMSO, and TCE/CTC mixtures leads to a frequency shift of the low-frequency oscillation. The shift is not observed in the TBE/DMSO mixture but a decrease in the TBE concentration causes significant broadening of the low-frequency line.     

Mechanism of delayed double ionization in a strong laser field

When intense laser pulses release electrons nonsequentially, the time delay between the last recollision and the subsequent ionization may last longer than what is expected from a direct impact scenario [recollision excitation with subsequent ionization (RESI)]. We show that the resulting delayed ionization stems from the inner electron being promoted to a sticky region. We identify the mechanism that traps and releases the electron from this region. As a signature of this mechanism, we predict oscillations in the ratio of RESI to double ionization yields versus laser intensity.     

On the minimum drag of a supersonic high-speed air vehicle with a conical stabilizer

The parameters of a conical stabilizer and its effect on the aerodynamic characteristics of the high-speed air vehicle, in general, are examined. The flow characteristics of an high-speed air vehicle with a conical stabilizing device are analyzed. Simulation results are compared with experimental data. Qualitative features of the supersonic flow associated with the characteristics of the drag of an aerodynamic configuration with a stabilizing device in the form of a truncated cone are considered. Particular attention is paid to the physical aspects of the flow around the considered configurations and to elucidating the mechanisms responsible for a minimum in the drag coefficient of a wingless high-speed air vehicle. A general mechanism of occurrence of the minimum in the drag coefficient for aerodynamic configurations with a conical tail stabilizer is studied.     

Low-frequency dielectric-barrier discharge in the Townsend mode

An analytic model is proposed of a dielectric-barrier discharge in the Townsend mode, in which the space charge is small compared to the charge accumulated on the dielectric surface. The discharge mode depends substantially on the ratio between the frequency of the external voltage and the ion drift time through the gap. A low-frequency case is investigated, in which the space charge can be ignored. The analytic expressions obtained agree well with experiments and numerical simulations. The physical mechanism for the onset of relaxation oscillations in the Townsend mode is revealed. The time behavior of a dielectric-barrier discharge is qualitatively described, and its basic scaling parameters are determined.     

纯电动汽车车身泄压阀引起的低频涡声耦合问题识别分析

由于纯电动汽车底部平整,高速行驶时可能容易诱发气流与车身泄压阀耦合,从而引起车内低频噪声问题,严重降低乘坐舒适性。以某纯电动汽车高速行驶低频涡声耦合问题的测试排查分析过程为例,系统地介绍了低频涡声耦合问题的发生机理,设计了一种用于验证低频噪声问题的静置试验方法,识别出影响低频噪声的关键要素,并设计了泄压阀罩工程化方案,实车验证了方案的有效性,这对于解决纯电动汽车低频涡声耦合问题和前期开发问题识别具有借鉴和参考价值。     

Local electron mean energy profile of positive primary streamer discharge with pin-plate electrodes in oxygen nitrogen mixtures

Local electron mean energy (LEME) has a direct effect on the rates of collisional ionization of molecules and atoms by electrons. Electron-impact ionization plays an important role and is the main process for the production of charged particles in a primary streamer discharge. Detailed research on the LEME profile in a primary streamer discharge is extremely important for a comprehensive understanding of the local physical mechanism of a streamer. In this study, the LEME profile of the primary streamer discharge in oxygen-nitrogen mixtures with a pin-plate gap of 0.5 cm under an impulse voltage is investigated using a fluid model. The fluid model includes the electron mean energy density equation, as well as continuity equations for electrons and ions and Poisson’s electric field equation. The study finds that, except in the initial stage of the primary streamer, the LEME in the primary streamer tip tends to increase as the oxygen-nitrogen mole ratio increases and the pressure decreases. When the primary streamer bridges the gap, the LEME in the primary streamer channel is smaller than the first ionization energies of oxygen and nitrogen. The LEME in the primary streamer channel then decreases as the oxygen-nitrogen mole ratio increases and the pressure increases. The LEME in the primary streamer tip is primarily dependent on the reduced electric field with mole ratios of oxygen-nitrogen given in the oxygen-nitrogen mixtures.     

Influence of positive ions on oscillatory processes in an electron beam with virtual cathode

We numerically simulate the influence of positive ions on characteristics of the microwave oscillations in a nonrelativistic electron beam with the virtual cathode formed in a decelerating field (low-voltage vircator). A numerical scheme allowing for ionization of a residual gas by an electron flow is proposed. It is shown that the residual-gas ionization in the operating chamber of a low-voltage vircator leads to a forcing of the virtual cathode out of the transit gap and to a cutoff of microwave oscillations. The obtained numerical data are confirmed by an experimental study using a low-voltage vircator model. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 853–863, October 2006.     

经由脉冲式爆炸连接的复合式张弛振荡

张弛振荡现象普遍存在于自然科学以及工程技术的各个领域,探索张弛振荡的可能路径是张弛振荡研究的重要问题之一.最近,一种名为"脉冲式爆炸"(pulse-shaped explosion,PSE)的可以诱发张弛振荡的新机制被相继报道.PSE意味着平衡点和极限环表现出了与参数变化相关的脉冲式急剧量变,这导致系统出现急剧转迁现象,进而诱发张弛振荡.本文以多频激励Mathieu-van der Pol-Duffing系统为例,探讨了复合式的张弛振荡现象.当参数激励和外部激励存在相位差时,快子系统包含了两个不同的向量场部分,由此得到了系统的双稳定特性.特别地,在狭小的参数范围内,分岔会随着PSE的产生而产生,这使得PSE更具复杂性.基于此,揭示了两种复合式的张弛振荡,其特征是每一周期的演化过程包含了由PSE连接的两个张弛振荡簇.我们的研究深化了对PSE及张弛振荡复杂动力学行为的理解.     

Laboratory studies of spectral features of stimulated electromagnetic emission during the ionospheric heating experiments

We present the results of laboratory studies of the formation of a number of spectral components of stimulated electromagnetic emission, which are related to the excitation of small-scale irregularities in the heated ionosphere. In the laboratory experiment, the small-scale irregularity was formed as a result of thermal self-channeling of short-wavelength quasielectrostatic oscillations in a magnetoplasma. Using the method of probing waves, it is experimentally shown that the trapping and waveguide propagation in a small-scale plasma irregularity are exclusively due to Langmuir waves, whereas the upper-hybrid waves with anomalous dispersion are not trapped into the irregularity. It is found that satellites shifted by about 1–2 MHz from the carrier frequency (700 MHz under the experimental conditions) are formed in the Langmuir wave spectrum during the thermal self-channeling. Two mechanisms of generation of spectral satellites have been detected. The first (dynamic) mechanism is observed during the formation of a small-scale irregularity with rapidly increasing longitudinal size. In this case, one low-frequency satellite is excited in the trapped-wave spectrum. The mechanism of the formation of this satellite is apparently related to the Doppler shift of the frequency of the Langmuir waves trapped inside the irregularity. The second (stationary) mechanism is observed in the case of a developed irregularity where its shape is close to cylindrical. In this regime, the trapped-wave spectrum has two symmetric spectral satellites, namely, high- and low-frequency ones. It may be hypothesized that the generation of these satellites is due to scattering of trapped Langmuir waves from drift oscillations of the irregularity.