Diffraction of optical radiation on spatially ordered structures of macroparticles in a strongly nonideal thermal plasma

The first observation of the diffraction of optical radiation on ordered structures of macroparticles in a low-temperature thermal plasma was reported. The experiments were conducted in an air thermal plasma at atmospheric pressure with CeO₂ particles at temperatures 1800–2200 K. The parameters of the plasma medium were determined using probe and optical diagnostics methods. The binary correlation function of the system of macroparticles was reconstructed from measurements of the structure factor. Simulation of nonideal plasma with the parameters corresponding to experiment was performed by the molecular dynamic method. The computed and experimental correlation functions were compared, and it was noted that they are in good agreement with one another.     

Magnetic properties of a two-dimensional spatially ordered array of nickel nanowires

The structural and magnetic characteristics of two-dimensional spatially ordered arrays of magnetic nickel nanowires embedded in the anodized alumina template have been investigated. It has been shown using small-angle polarized-neutron diffraction that, there exists the samples under investigation, in a highly ordered hexagonal structure of pores and magnetic nanowires separated by a characteristic distance d = 106 ± 2 nm. An analysis has been made of different contributions to neutron scattering, such as the nonmagnetic (nuclear) contribution, the magnetic contribution dependent on the magnetic field, and the interference contribution indicating a correlation between the magnetic and nuclear structures. The performed analysis of the results obtained has demonstrated that, when the magnetic field is applied perpendicular to the longitudinal axis of the nanowire in a completely magnetized sample, there arise demagnetizing fields around each nanowire that form a regular hexagonal lattice.     

On the structure of the two-dimensional spatially periodic inner transition layers in a gas-discharge plasma

We investigate the structure of the spatially periodic inner boundary layers in the plasma of a positive glow-discharge column produced in a long cylindrical tube with an electropositive gas inside. Asymptotic methods, namely, the method of boundary functions, are used to analyze the initial mathematical model. We consider the formation of contrast burst-type structures. We have found all principal terms of the boundary-layer asymptotics of the solution. The results obtained are compared with the available probe measurements of basic physical parameters of ionization waves (strata) in neon at low pressures.     

Observation of an ordered surface structure on the edge surface of graphite by LEED

We report the first observation of an ordered LEED pattern from the edge or prism surface of graphite. The surface structure was developed after in-situ gasification and is not equivalent to that resulting from any termination of the low index crystal planes of graphite. The pattern is indexed c(2 × $\text{2}\text{3}$) relative to termination parallel to {101̄0} and its occurrence can be rationalized.     

Enhanced infrared absorption of spatially ordered quantum dot arrays

We have investigated the intersubband absorption for spatially ordered and non-ordered quantum dots (QDs). It is found that the intersubband absorption of spatially ordered QDs is much stronger than that of non-ordered QDs. The enhanced absorption is attributed to the improved size uniformity concurrent with the spatial ordering for the growth condition employed. For the FTIR measurement under normal incidence geometry, using a undoped sample as reference can remove the interference effect due to multiple reflections.     

HL-1M装置边缘等离子体结构研究

描述HL-1M装置上几种典型放电中的边缘等离子体物理实验结果.利用马赫/朗缪尔6探针组、静电4探针组、20组三探针阵列研究了低杂波电流驱动、超声分子束注入、多发弹丸注入和中性束注入放电中的粒子约束性能、等离子体旋转和边缘静电雷诺胁强的变化对改善约束的影响.给出了雷诺胁强和极向相速度的关系.结果表明，雷诺胁强的径向变化可以自发产生托卡马克等离子体的剪切极向流.LHCD能使低密度放电的粒子约束增加1至2倍.弹丸注入后，粒子约束时间和极向旋转至少可增加1倍，而SMBI可使粒子约束时间增加约一个数量级并取得高性能等离子体. 关键词： 粒子约束 雷诺胁强 极向流剪切 马赫/朗缪尔6探针组     

Formation of ordered micro-porous membranes

Regular micro-porous polymeric membranes have recently been discovered by rapidly evaporating a solution of CS₂ containing poly(p-phenylene)-block-polystyrene [#!ref1!#]. 1,2-dichloroethane (a chlorated solvent in which polystyrene gel phase has never been observed) is also found to produce ordered structures, which definitively excludes eventual effect of the gelation process during the membrane formation. The observation of the solution surface during the solvent evaporation reveals the growing of micron-sized water droplets trapped at the surface and forming compact aggregates. The study of the solution/water interface shows that the water droplets profile is in agreement with the pore shape observed in the membranes. Moreover, the copolymer was found to precipitate at the interface, forming a layer encapsulating the droplets and preventing their coalescence. In that way, the final structure results from the droplets stacking under the action of large surface currents. Finally, we argue that the decisive element in the formation of ordered structures is the ability of the polymer to precipitate at the solution/water interface, which seems to be related the star-polymer microstructure. Received: 18 August 1998     

Formation of ordered structures of charged macroparticles in a photoemission trap

The possibility of confining positively charged macroscopic dust particles in a unique photoemission trap was studied. The spatial distributions of the potentials for a cylindrical geometry of a phototrap were obtained (by the particles in a cell method) and the dynamics of the formation of ordered structures of dust particles in the potential field of the trap was studied (by the molecular-dynamics method). The dependence of the number of dust particles confined by a phototrap on the particle energies and sizes and the buffer-gas pressure were obtained.     

Two-dimensional spatially ordered system of nickel nanowires probed by polarized SANS

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic nickel nanowires embedded into Al₂O₃ matrix have been studied using polarized small-angle neutron scattering. The small-angle diffraction pattern exhibits many diffraction peaks, which corresponds to the scattering from highly correlated hexagonal structure of pores and magnetic nanowires. Magnetic contribution to the scattering has complex behavior and cannot be explained without taking into account stray fields located between magnetized nanowires.     

Formation of defect structure by the effect of a gas-discharge plasma on metals

A layer-by-layer electron-microscope analysis has been made of the defect structure at different depths from an irradiation surface to establish the effect of a gas-discharge plasma on the metals Fe, Cu, and Mo and the alloy Ni₃Fe. A long-range effect has been established, namely, an increase in the scalar density of dislocations to depths of about 10 mm. The dislocation density increases with irradiation time, with approach to the irradiated surface, and with decrease of the yield point of the irradiated material. This effect depends nonmonotonically on the discharge voltage and the conditions of shielding of the samples. The types of the dislocasubstructures that are formed are similar to those formed in the case of plastic deformations.Translated from Izvestiya Vysshikh Uchebriykh Zavedenii, Fizika, No. 1, pp. 14–19, January, 1992.     

Penalization modeling of a limiter in the Tokamak edge plasma

An original penalization method is applied to model the interaction of magnetically confined plasma with limiter in the frame of a minimal transport model for ionic density and parallel momentum. The limiter is considered as a pure particle sink for the plasma and consequently the density and the momentum are enforced to be zero inside. Comparisons of the numerical results with one-dimensional analytical solutions show a very good agreement. In particular, the penalization scheme followed in this paper tends to ensure an almost sonic plasma condition at the plasma-obstacle interface, Bohm-like criterion, with relatively weak dependence on the target Mach number profile within the obstacle. The new system being solved in a periodic obstacle free domain, an efficient pseudo-spectral algorithm based on a Fast Fourier transform is also proposed, and associated with an exponential filtering of the unphysical oscillations due to Gibbs phenomenon. Finally, the efficiency of the method is illustrated by investigating the flow spreading from the plasma core to the Scrape-Off Layer at the wall in a two-dimensional system with one, then two neighboring limiters.     

Suppression of Bragg scattering by collective interference of spatially ordered atoms with a high-Q cavity mode

When N driven atoms emit in phase into a high-Q cavity mode, the intracavity field generated by collective scattering interferes destructively with the pump driving the atoms. Hence atomic fluorescence is suppressed and cavity loss becomes the dominant decay channel for the whole ensemble. Microscopically, 3D light-intensity minima are formed in the vicinity of the atoms that prevent atomic excitation and form a regular lattice. The effect gets more pronounced for large atom numbers, when the sum of the atomic decay rates exceeds the rate of cavity losses and one would expect the opposite behavior. These results provide new insight into recent experiments on collective atomic dynamics in cavities.     

Entrainment of a spatially extended nonlinear structure under selective forcing

The response of a nonlinear state to a variable forcing periodic in space is studied in an extended dynamical system consisting of a liquid crystal layer driven to convection. Both the statics and the dynamics of the entrainment and the locking effects are analyzed. The dynamics of the evolution are controlled by topological singularities that allow a diffusion of the phase. The mechanisms involved are related to the role of the defects in systems undergoing spontaneous symmetry breakings.     

Dynamics of formation of ordered structures in a thermal plasma with macroparticles

The molecular dynamics method is used to model the formation of ordered structures of charged macroparticles in a thermal plasma at atmospheric pressure. The results of the numerical calculations are compared with the experimental data. It is shown that the ordered structure of macroparticles detected experimentally is far from steady state, since the existence time of the plasma in the experiment is less than the characteristic time of formation of the structure. Zh. éksp. Teor. Fiz. 115, 837–845 (March 1999)