Extension of the gas-pressure operating range and increase in the lifetime of the plasma cathode grid of an ion source

A new scheme of a gas-discharge system is proposed for a basket-type ion source with a plasma cathode in which the electrons are emitted from the expanded anode part of a constricted hollow-cathode glow discharge bounded by a grid electrode. The modified electrode system of the ion source made it possible to enlarge the surface area of the plasma cathode grid and the aperture of its cells, thereby providing stable ion emission from the discharge plasma within a wide gas-pressure range and substantially (by one order of magnitude) increasing the grid lifetime. The operation of the plasma cathode in the free and forced emission modes is examined, and the energy efficiency of ion generation in the gas-discharge system under study is evaluated.     

Quantitative visualization of high-Schmidt-number turbulent mixing in grid turbulence by means of PLIF

Abstract  

Quantitative visualization of high-Schmidt-number scalar fields has been performed in grid turbulence by means of a planar laser-induced fluorescence (PLIF) technique. The Reynolds number based on a mesh size of the grid is 2500 and the Schmidt number of the scalar is around 2100. To correct for the effects of various spatiotemporal variations such as quantum yield, a recently proposed correction method was introduced in the present experiment. In the present work, a PLIF experiment in combination with a calibration region installed outside of the test section is proposed. Visualizations of the instantaneous fluctuating scalar field suggest that mushroom-like structures accompanied by a pair of stirring structures, called engulfments, exist and contribute to large-scale scalar transfer. Visualization of the scalar dissipation field in the horizontal plane suggests that accumulation of the filament structures, which can be related to the mixing transition, locally exists around large-|c| regions, where |c| is the absolute value of the instantaneous fluctuating concentration. Thus, accumulation of the filament structures should be considered in the development of a turbulent mixing model for high-Schmidt-number scalar transfer.     

Active to sterile neutrino mixing limits from neutral-current interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754 ± 28(stat) ± 37(syst) for oscillations among three active flavors. The fraction f(s) of disappearing ν(μ) that may transition to ν(s) is found to be less than 22% at the 90% C.L.     

进一步增大主动红外夜视仪视距的途径

本文根据主动红外夜视仪的视距公式讨论了影响视距的各种因素，对进一步增大视距指明了方向。寄希望于阴极红外灵敏度获得突破性的进展；改进光源结构，提高光能利用率和减小发散角是增大视距的主要途径。     

Modes mixing in a slightly non-compensated solid state plasma

Propagation of electromagnetic wave modes in lightly tin-doped Bismuth is studied, using a transmission technique. We point out the occurrence of a propagation cut-off which is independent of the angle of the propagation and the applied d. c. magnetic field. We study the influence of collisions on such a phenomena. We show experimentally the effect.     

内表面栅极等离子体源离子注入TiN薄膜及其特性研究

阐述了栅极增强等离子体源离子注入（GEPSII）方法的基本思想.利用GEPSII方法在45号钢 基底上生成了金黄色氮化钛（TiN_x）膜.对不同条件下的TiN膜做电化学腐蚀，X PS，AES， XRD等分析.电化学腐蚀实验显示TiN薄膜改善了45号钢的耐腐蚀性能5—10倍，且在高气压下 效果更好.结构分析显示TiN膜含有TiO₂，TiN成分，主要沿（111）和（200）晶 向生长，深度分析显示膜的厚度只有二十几纳米，膜质地均匀且在基底有一定的嵌入深度. 关键词： 腐蚀 等离子体源离子注入 薄膜 氮化钛     

Existence regions of regimes with anomalously high rates of plasma generation in grid plasma switch elements

Results are presented from a systematic investigation of the conditions under which anomalously high rates of plasma generation are observed in the anode region of a low-voltage Knudsen arc in grid plasma switch elements. The phenomenon develops over a wide range of currents and switched voltages under conditions for which the plasma density in the cathode-grid region is noticeably higher than the density in the anode region. and its onset is characterized by a pronounced pressure threshold of ∼2×10⁻² Torr. The results are analyzed from the standpoint of the possible mechanisms for anomalous plasma generation — collisional nonresonance diffusion of electrons in velocity space, leading to enrichment of the distribution function in fast particles, and the collapse of Langmuir waves in the gap at the high energies of the beam produced when the wires of the grid are bridged by the quenching pulse and and the current is blocked. Zh. Tekh. Fiz. 67, 15–21 (June 1997)     

Nonmonotonic potential distribution in a grid mesh of a plasma switch

The electrical transparency of the grid and the passing current are determined from probe measurements of the discharge plasma parameters when a plasma switch with a developed cathode is in the steady conductive state. To eliminate discrepancies between the analysis and experiment, it is assumed that the potential (virtual cathode) distribution in a grid mesh is nonmonotonic in the direction of current transfer.     

The electron temperature in the plasma of a DC discharge created in a supersonic airflow

The plasma parameters of a pulsating DC discharge created in a supersonic airflow with a Mach number of M = 2 are determined. It is revealed that along with the intense bands of CN and the molecular nitrogen ion, as well as the spectral lines of atomic oxygen, nitrogen, hydrogen and copper, an intense continuous spectrum is observed in the spectrum of the gas-discharge plasma radiation, which is caused by the deceleration of electrons on ions. The dependences of the electron temperature on the discharge current and longitudinal coordinates are determined. It was revealed that the studied plasma is nonequilibrium, with the electron temperature being much higher than the gas temperature.     

Nonphysical noises and instabilities in plasma simulation due to a spatial grid

A series of plasma numerical simulation has been performed in order to understand the enhancement of nonphysical noises and instabilities due to the use of a spatial grid. Several different superparticle models including the Nearest Grid Point (NGP) model, Cloud-in-Cell (CIC) or Particle-in-Cell (PIC) models, Lewis energy conserving code, and the multipole expansion code have been examined for a Maxwellian plasma and a one beam plasma using a one-dimensional, one-specie (electron) plasma. An instability was observed for all of the models when the Debye length was too small compared with the grid size. When the Debye length is comparable to the grid size, no instabilities were observed. However, the enhancement of noises at high frequencies (ω > 3ω_pe may not always be negligible- even for long wavelength modes for the NGP model. For the NGP and CIC, PIC models, the experimental results are in good agreement with Langdon's theory. It is observed that the dipole expansion model, which is the first-order approximation to the multipole expansion scheme, is similar to CIC, PIC models in many respects and appears to be the same order of approximation.     

Ion space charge instability induced by a grid in a Q-machine plasma

An instability is induced by a negatively-biased grid situated between a hot plate and a cold end plate in a single-ended Q machine, when the cold plate is biased to form a space charge between the grid and the cold plate.     

Nitridation of iron by the mixing technology with laser and plasma beams

Iron nitride (Fe_xN) is obtained by the mixing technology with laser and plasma beams coaxially on the surface of pure iron in atmosphere. In this technology, laser and plasma provide heat source and nitrogen ion source, respectively, easily to nitriding the sample. The feasibility of the method is analyzed in theory. Small-angle X-ray diffraction measurements reveal formation of iron nitride in the as-treated sample, and scanning tunneling microscope measurements describe the surface profiles of the irradiated area, at different laser energy densities or different scanning velocities.     

Infraglottic aspect of canine vocal fold vibration: Effect of increase of mean airflow rate and lengthening of vocal fold

The mucosal upheaval (MU), where the mucosal wave starts and propagates upward, appears only when the vocal fold vibrates. The location of the MU histologically and the effect of changes in mean air flow rate (MFR) and vocal fold length on occurrence of the MU were studied in twelve excised canine larynges. The lower surface of the vocal fold was marked to serve as a landmark for subsequent study. Cricothyroid approximation was performed to lengthen the vocal fold. After taking high-speed pictures or recording stroboscopic images from the tracheal side, a small cut wound was made at the mark. This wound served to compare the position of the MU with the histologically identified location of the mark. The larynx was then sectioned in the frontal plane. Before lengthening the vocal fold, the MU occurred on the area where the lamina propria became thinner and where the muscular layer neared the epithelial layer. After lengthening the vocal fold, the MU actually shifted medially compared with its original position. The subglottic area surrounded by the bilateral MUs became longer and thinner. Whether or not complete glottal closure during a vibratory cycle was achieved did not alter these findings. In contrast, with a fixed vocal fold length the MU appeared more laterally as MFR increased, but, based on the relation with the mark, its location on the vocal fold did not change from its original position before increase of MFR.     

On the potential distribution near the turns of a grid in plasma switchers

Based on previous results, the most probable potential distribution in a grid mesh and near the grid of a plasma switch is presented for the case when the discharge current passes through the grid. It is concluded that the critical factor for current transfer is the presence of a quasi-neutral plasma in the bottleneck for current transfer under the conditions of intense ion flow to grid turns, which is necessary for the formation of Langmuir layers near the turns.     

Establishing an inverse population on mixing a hot plasma with a cold gas

A model in which the interaction between a hot plasma and a cold gas is used to create an inverse population is considered. Using hydrogen as an example it is shown that it is impossible to obtain an inversion at high electron concentrations (n₁= 10¹⁶ cm^?3). The conditions under which an inversion can occur are outlined.