Investigation of Plasma Parameters in a Magnetoplasma Compressor

The article presents the results of experimental investigations that were carried out at the Center for Science and Technology Development in Belgrade (Yugoslavia) and pertained to the plasma streams generated by a gasdischarge magnetoplasma compressor (MPC). The integral characteristics of the discharge, the dynamic parameters of a compression flux, and the concentration of the plasma electrons in the magnetoplasma compressor have been determined. The distinguishing features of the discharge afterglow from the volume of a vacuum chamber for a long time after the termination of the discharge current have been investigated.     

Dynamics of erosion plasma formation and formation of a plasma flame with a condensed disperse phase when quasi-continuous laser radiation acts on bismuth

The dynamics of near-surface plasma formation and the formation of an erosion plasma flame was investigated for quasi-continuous laser radiation (λ=1.06 μm, q=0.1–10 MW/cm², τ∼1.5 msec) acting on bismuth targets in air. The absence of low-threshold plasma formation at q<2 MW/cm² was established and explained. Instabilities in the plasma formation were revealed and the range of laser radiation power densities (2≤q≤4 MW/cm²) at which these instabilities take place was determined. At q≥5.4 MW/cm², brightening of the flame was noted. The dependence of the luminescence temperature of the flame on the laser radiation power density q was determined. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 126–133, January–February, 1998.     

Compression of erosion plasma fluxes of given composition in air at atmospheric pressure (letters to the editor)

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 6, pp. 903–905, December, 1991.     

高密度等离子体融断开关融蚀现象的粒子模拟研究

 利用自行研制的2.5维全电磁柱坐标粒子模拟程序对高密度等离子体融断开关融断区域中的融蚀现象进行了模拟研究,详细地介绍了计算模型的建立以及复杂边界的算法处理。模拟结果表明在融断开关导通电流的最后阶段,由于磁压力、磁场渗透作用和非中性静电融蚀作用,在融断区域的阴极附近会形成一定宽度的真空鞘层。由于等离子体密度的下降以及初始真空鞘层的存在,使得即使只有较小的离子电流,融蚀机制也完全可以导致PEOS最终断开。     

Frequency shift and pulse compression of an ultrashort pulse in a large-amplitude plasma wave

By calculating the momenta of a coupled set of nonlinear equations of laserpulse-plasma wave interaction in the weak relativistic approximation,the conditions for fre-quency up-shift have been found.That the energy change of the pulse due to frequency shiftis compensated by the change of plasma wave energy results in photon number conservation.Some factors that affect the frequency up-shift are studied.It is also found that the laser pulsecan be compressed when it is located near the valley of plasma density perturbation and ifsome threshold value of the plasma wave field is exceeded.     

激光冲击波压缩稠密铝辐射不透明度实验研究

基于稠密物质辐射不透明度的理论计算目前有相当大的难度, 而稠密物质高精度不透明度数据又对聚变研究中的理论设计和模拟以及状态诊断等方面非常有用. 在"神光II"激光装置上建立一发次中能同时测量背光谱、 样品自发谱和吸收谱的大谱窗高分辨椭圆弯晶测谱系统, 并利用一维辐射流体力学程序MULTI仿真冲击波碰撞压缩样品的过程.在测量中, 用点投影背光法、激光烧蚀冲击波碰撞压缩产生稠密铝(Al)样品, 激光镱等离子体3d–4f 跃迁辐射为短脉冲背光提供样品吸收谱时空分辨诊断, 在一发次打靶中得到了背光谱、样品自发谱和X射线吸收精细结构谱, 以及稠密Al辐射吸收谱向长波偏移.实验结果给出了诊断能谱区稠密Al相对透射率分布和吸收谱偏移量. 这些工作都有益于丰富不透明度这一基础研究领域和进一步开拓许多重要应用. 关键词： 冲击波压缩等离子体 X射线吸收谱 线移 精细结构     

Head-on collision of quantum ion-acoustic solitary waves in a dense electron-positron-ion plasma

The characteristics of the head-on collision between two-quantum ion-acoustic solitary waves (QIASWs) in a dense electron-positron-ion plasma are investigated. Using the extended Poincaré-Lighthill-Kuo (PLK) method, the Korteweg-de Vries (KdV) equations and the analytical phase shifts, after two QIASWs collision occurs, are derived. This study is a first attempt to illustrate the effects of both of the quantum diffraction corrections and the Fermi temperature ratio of positrons to electrons on the phase shifts. It is found that the electron-positron-ion plasma parameters modify significantly the phase shifts of the two colliding solitary waves.     

Determination of electron temperature based on a semicoronal model in Hall accelerator plasma flows

We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which relates the intensity ratios for two successive ionization steps for the same element. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 93–96, January–February, 2007.     

Acceleration and radiation of externally injected electrons in laser plasma wakefield driven by a Laguerre-Gaussian pulse

By using three-dimensional particle-in-cell simulations, externally injected electron beam acceleration and radiation in donut-like wake fields driven by a Laguerre-Gaussian pulse are investigated. Studies show that in the acceleration process the total charge and azimuthal momenta of electrons can be stably maintained at a distance of a few hundreds of micrometers. Electrons experience low-frequency spiral rotation and high-frequency betatron oscillation, which leads to a synchrotron-like radiation. The radiation spectrum is mainly determined by the betatron motion of electrons. The far field distribution of radiation intensity shows axial symmetry due to the uniform transverse injection and spiral rotation of electrons. Our studies suggest a new way to simultaneously generate hollow electron beam and radiation source from a compact laser plasma accelerator.     

Formation of chemical compounds in a laser plasma

Using the methods of laser-induced fluorescence and emissive spectroscopy, we carried out investigations of the formation of TiO molecules in a laser plasma produced by focusing the radiation of an AYG:Nd³⁺ laser on the surface of a titanium target in air. The radiation flux density varied within the range 10⁸–10¹⁰ W/cm². We investigated the distribution of molecules over internal states and the space-time distributions of Ti atoms in the ground, metastable, and excited states, as well as of TiO molecules in the ground and excited states. We found that gas-phase reactions with participation of Ti atoms in the ground state provide the most probable channel for the formation of TiO molecules; the role of reagents in ionized, excited, and metastable states is of secondary importance. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 109–115, January–February, 1999.     

The role of vibrational temperature variations in a pulsed dielectric barrier discharge plasma device

The use of dielectric barrier discharge (DBD) plasmas has become a practical way to carry out surface treatment where precise control of the plasma parameters, such as rotational and vibrational temperatures (T_rot and T_vib), is required. As the T_vib of an atmospheric pressure plasma jet appears to be the most important parameter related to the improvement of surface treatments, in this work, we analysed two methods to increase the values of T_vib in a DBD plasma jet device. One of the methods is to reduce the exit size (ø) of the DBD reactor, which results in an increase in the measured T_vib values, due to an increase in the pressure inside the reactor. The other method is to change the gas flow rate (GFR) used to produce the plasma jets. This leads to a T_vib reduction when the GFR is increased in the case of using helium or nitrogen as the working gas, but the opposite happens (an increase in the T_vib values) when argon is used, with different phenomena causing the variation of T_vib in each situation.     

Formation of excited states of atoms and ions in laser plasma from CuInS2

Emission spectra and the energy distribution of the excited-state population density of atoms and ions in erosion laser plasma from CuInS₂ with various crystal-structure orderings are analyzed. It is shown that increased ordering of the target crystal structure causes the excited-state energies of indium atoms generated in the laser erosion plume to increase and that sulfur atoms always emit only in transitions from highly excited states. The ratio of relative ion concentrations in the laser plasma plume is Cu⁺/In⁺/S⁺ = 0.3/0.08/2, which corresponds neither to the atomic ratio of Cu/In/S (1/1/2) in the target nor to the ratio of ionization energies. The results are explained by recombination processes for ions and by the atomization specifics of the CuInS₂ target exposed to long-wavelength radiation. The atomization consists essentially of dissociative processes expressed by CuInS₂ → CuInS + S and CuInS₂ → Cu + InS + S. The electron temperature of polycrystal (single-crystal) plasma at a distance of 1 mm from the target is 0.3 eV (0.4 eV) for atoms and 1.3 eV (2.7 eV) for ions and varies negligibly for plasma up to a distance of 7 mm from the target. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 217–223, March–April, 2008.     

Kinetic theory of time correlation functions for a dense one-component plasma in a magnetic field

The time-dependent correlations of a one-component plasma in a uniform magnetic field are studied with the help of kinetic theory. The time correlation functions of the particle density, the momentum density, and the kinetic energy density are evaluated for large time intervals. In the collision-dominated regime the results agree with those found from linearized magnetohydrodynamics.     

On the excitation temperature of pulsed plasma produced from washer plasma gun in a compact plasma system

The washer plasma gun is widely used to produce pulsed plasma and has various applications in plasma physics. A washer plasma gun and a Guillemin-E type pulse forming network are designed and fabricated in the laboratory to produce pulsed argon plasma in the Compact Plasma System. The spectroscopic signals of pulsed plasma are taken through toughened float glass at a distance of about 0.3 m from the plasma gun by a USB4000 digital spectrometer. Assuming the gun plasma is in Local Thermodynamic Equilibrium, Boltzmann plot method and the line ratio method are used to measure the excitation/electron temperature of pulsed plasma with different base pressure varying from 0.2 mbar to 1 mbar. The excitation/electron temperature of the plasma increases slightly with increasing base pressure within the range of 0.2 mbar to 0.8 mbar and then decreases slightly at a pressure of 1 mbar. Both methods produce almost similar results in temperature measurement, but the Boltzmann Plot method is most accurate than line ratio method and widely used method to obtain the excitation/electron temperature of plasma in Local Thermodynamic equilibrium condition.     

Formation of a symmetric vortex configuration in a pure electron plasma trapped with a penning trap

In the formation of vortical crystal structures of electrons, the distribution of background electrons works as a “cooler” of randomly moving, intense vortices. We examine the supporting effect of background electrons to forming crystal structures from the perspective of a reduction of the vortices’ random motion.     

Effects of the System Temperature on Dust Cluster Formation in Plasma

Effects of the system temperature on dust aggregation in plasmas are investigated using two‐dimensional molecular dynamics simulations. It is shown that as the system temperature increases, the boundary of the clusters becomes gradually irregular (i.e., deviating from sphere‐like), and the cluster system gradually changes from solid to liquid and finally to gas state. The mean square displacement, mean nearest‐neighbor distance in the clusters, cluster size and coupling parameter of the system are obtained and the properties of the system structure and dynamics are investigated. The time τ needed for reaching equilibrium for different temperatures is obtained. It is shown that τ firstly decreases and then increases with the temperature, indicating that there is an optimum temperature allowing a dust aggregation to reach an equilibrium state most rapidly. The simulation results agree qualitatively with the experimental observations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of the high pressure graphite and BC8 phases in a cold compression experiment by Raman scattering

We use Raman scattering to study phase transition in the graphitic g‐BC₈ phase and graphite at high pressure up to 84 GPa. The E_2g Raman active mode of graphite (G peak) can be detected up to 84 GPa. We demonstrate that there is (1) a phase transition in g‐BC₈ and in graphite at 35 GPa and (2) that above 35 GPa, the g‐BC₈ and graphite transform under high pressure to possibly fully sp³‐bonded, disordered hp‐BC₈, and hp‐C phases. Below the phase transition, a polynomial fit to the G peak position versus pressure data yielded a quadratic relation; above the phase transition, it demonstrates linear behavior. The phase transition at high pressure in BC₈ system and graphite is reversible. Quenched hp‐BC₈ and hp‐C phases have the Raman spectrum typical to that of the graphitic phases. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetic theory of monochromatic waves bunching in a low-voltage beam discharge in rare gases

The kinetic theory of phase focusing, that is bunching in a low-voltage beam discharge in rare gases (LVBD) during the propagation of longitudinal electrostatic oscillations at the Knudsen numbers of the order of unity have developed. The anomalous relaxation of the almost monoenergetic electron beam in momentum and energy is described for the case when this process cannot be explained by electron–atom collisions. The paper has shown the important role of electrons that have the beam energy and isotropic directional distribution, which is formed as a result of elastic collisions between the beam electrons and atoms. The dependence of the anomalous relaxation length on parameters of the LVBD in rare gases is studied.The developed theory makes it possible to quantitatively interpret experimental data on the LVBD under conditions when the electron mean free path is of the order of the interelectrode gap. According to these data, regardless of the density of the charged particles in the LVBD plasma in rare gases, five Langmuir plasma wavelengths fit along the length of the anomalous relaxation of the electron beam. The study of the electron beam dynamics laws in a plasma is important for the development of plasma-electrical devices, where the beam discharge is applied, namely: widely used all-movable stabilizers, sources of intense electromagnetic radiation, controlled elements of electronic circuits, plasma chemical reactors, etc.