A large-area continuous accelerator with the extraction of a high-density electron beam

The design features of the electron accelerator with a large-area 200-keV beam and results of its investigation are described. The accelerator is based on a set of discrete longitudinal filament cathodes and operates in the continuous mode. The cross section of the beam extracted into the atmosphere is 40 × 50 cm², and the maximal current density of the extracted electron beam is up to 100 μA/cm². The nonuniformity of the current density distribution over the electron beam cross section is 10% or less.     

Some characteristics of tungsten filaments operated as cathodes in a gas discharge

Some physical properties of tungsten filaments, when operated as cathodes in a gas discharge, are presented. For a 0.1524-cm-diam tungsten wire, the initiation of a discharge is found to be dependent on the filament geometry. The effect of connecting the discharge power supply to either the positive or negative leg of the filament is examined. When the emission current becomes a sizable fraction of the filament heater current, the filament does not emit uniformly. The temperature distribution indicates that the majority of the electrons are emitted from the negative leg of the filament.     

A series of tufted carbon fiber cathodes designed for different high power microwave sources

We report the fabrication technique of tufted carbon fiber cathodes for different microwave sources. Three carbon fiber cathodes were constructed, including a planar cathode, an annular cathode, and a cylindrical cathode for radial emission. Experimental investigations on these cathodes were performed in a reflex triode virtual cathode oscillator (vircator), a backward wave oscillator (BWO), and a magnetically insulated transmission line oscillator (MILO), respectively. The pulse duration of microwave emission from the reflex triode vircator was lengthened by using the planar carbon fiber cathode. In the BWO with the annular carbon fiber cathode, the uniform electron beam with a kA/cm(2) current density was observed. In addition, carbon fiber has great promise as field emitter for MILOs. These results show that the carbon fiber cathodes can be utilized for electron emission in high power diodes with different structures.     

The Use of Ferromagnetic Screens in the Cathode of a Pulse-Periodic Relativistic Magnetron

Microwave generation by a relativistic magnetron with cathode end screens made of ferromagnetic material was experimentally investigated. The dependences of the power and the width of microwave pulses on the field induction were measured for different cathode designs. The comparison of the data we obtained with the results of experiments in which the cathodes had no screens and had nonferromagnetic screens showed that the ferromagnetic end screens increased the microwave power by approximately 60 and 13% compared to the design without any screens and with the nonferromagnetic screens, respectively.     

Development of high current Bi and Au beams for the synchrotron operation at the GSI accelerator facility

In this work, the latest results of developing high current ion beams of Au and Bi at GSI facility are described. The difficulties in the production of required charge state in vacuum arc discharge ion sources using the pure materials in the cathodes are discussed. As a possible solution, admix of a small amount of more refractory metal to the cathode material is considered. As a significant result, a dramatic improvement in the production of high charge state Bi ions using the mixed Bi-Cu cathodes (with 8%-15% of Cu admixed) compared to pure Bi cathodes is presented. The preliminary results of investigation of the material structure of Bi-Cu cathodes are discussed. As a next step, it is planned to test the composition of Au with Pd, Zr, and Fe as cathode materials.     

基于铁电阴极材料离子源的结构设计

为解决质谱仪的离子源发射阴极材料发射电子能力降低、使用寿命短等问题,需要用更好的阴极材料来代替传统的灯丝等热阴极材料。经国内外研究证实铁电阴极材料具有发射电流密度大、发射电子束品质好、寿命长、对真空度要求不高等优点。将原本完全独立的两块领域——铁电阴极材料和离子源的发射阴极相结合,通过计算机软件设计新型铁电阴极材料离子源的结构,用铁电阴极材料来增强质谱仪离子源的使用寿命。     

Studying the effect of adsorbed molecules on the operation of a diode with an explosive-emission cathode

The results of an experimental study of the effect of an adsorbed gas and surface contaminations of an explosive-emission cathode on the operation of a diode during generation of a high-current electron beam of nanosecond duration are presented. The effect of contaminations was revealed from the change in the rate of expansion of the planar-diode cathode plasma for cathodes of different designs manufactured from different materials and different initial anode-cathode gaps. The plasma velocity was calculated from the experimental perveance of the diode with a resolution of 0.2 ns. Experiments were performed on a ТЭУ-500 pulsed electron accelerator (350–450 kV, 100 ns, and 250 J/pulse) in a mode of matching the diode impedance to the output impedance of the nanosecond generator. It has been found that the velocity of cathode plasma is constant for 70–90 ns after applying voltages to different cathodes at different anode-cathode gaps. The velocities were 2.0 ± 0.5 cm/ μs for carbon cathodes (of different diameters), 3 ± 0.5 cm/μs for multispike tungsten cathodes, and 4.0 ± 0.5 cm/μs for copper (solid or multispike) cathodes. An appreciable dependence of the plasma velocity on the cathode material shows an insignificant influence of the adsorbed gas and cathode surface contaminations on the expansion velocity of the explosive-emission plasma in a planar diode during generation of the electron beam (10–15 ns after a voltage is applied).     

An arc generator of a broad plasma stream

The design and basic parameters of an arc plasma generator based on a combined cathode are described. The cathode consists of a hot tungsten filament located in the hollow cathode. A plasma stream with a cross section of 150×10 cm² and a density of ∼10¹⁰ cm⁻³ at a pressure of 0.1–1 Pa is generated at a discharge current of up to 60 A without a cathode spot. The plasma generator can be utilized for final cleaning and activation of surfaces of materials and articles before depositing functional coatings on them and in plasma-assisted deposition by using either vacuum arc or magnetron discharges.     

Characteristics of the Berkeley multicusp ion source

The performance of a cubical permanent magnet generated line-cusp ion source has been investigated for use with neutral beam injectors. This source has been operated with discharge currents greater than 500 A and ion current densities higher than 400 mA/cm2 at the extraction grid. The uniformity of the density profile across the extraction area is found to be dependent on the gas pressure. By using a fast Langmuir probe sweeping circuit, the electron temperature and the plasma density and potential have been analyzed for different discharge powers and gas pressures. The heat load on the plasma grid when it is electrically floating or connected to the negative cathode has been compared calorimetrically. The use of lanthanum hexaboride and impregnated oxide cathodes have been investigated for the purpose of long pulse operation. The phenomenon of mode flipping is found to occur quite frequently during a discharge with these magnetic-field-free cathodes. Species composition as a function of discharge power and chamber length is measured by a mass spectrometer.     

Novel method of flat cold cathode formation from carbon-nitrogen nanofibers

A novel method of high-efficiency cold cathode formation is developed. The technique is based on the growth of nitrogenated carbon nanofibers in a high-pressure apparatus on a graphite substrate. An average nitrogen concentration up to 13% was achieved. The turn-on and threshold fields for such cathodes are substantially lower than those for cathodes based on other carbon materials. A special method of substrate preparation provides strong adhesion of carbon-nitrogen nanomaterial and its durability during long-term cathode operation. It is shown that due to high uniformity, emission efficiency and time reliability, the field emission cathodes based on carbon-nitrogen nanofibers (CNNs) are very promising for high-brightness flat indicators and displays.     

Electrochemical machining analysis on grid cathode composed of square cells

During the electrochemical machining (ECM), the cathodes designed by the existing methods are mainly unitary cathodes, which can be only used to produce the workpieces with the same shapes. However, there are few researches on designing cathodes for machining the different workpieces with the different surfaces. This paper presents the grid cathode composed of the square cells to produce the workpieces with different shapes. Three types of the square cells, 2.5 mm′2.5 mm, 3 mm′3 mm, and 4 mm′4 mm, are utilized to construct the plane, the slant, and the blade cathode. The material of the cathode and the anode is CrNi 18 Ti 9 , and the ingredient of electrolyte is 15% NaCl and 15% NaNO 3 . The machining equilibrium machining current and time are acquired and analyzed, the machining process and the workpiece quality are compared between using the grid cathode and the unitary cathode. Moreover, the machining errors on the workpiece surface are measured and analyzed, and the error reasons are traced and discussed to obtain the better surface quality of the workpiece. The experiment and analysis results show that the grid cathode can be used to manufacture the workpieces with complex shapes in certain range of the error. The workpiece quality improves with the size of the square cell being reduced, and if the square element is small enough, the workpiece quality is almost equal to the one machined by the unitary cathode. The proposed research realizes a single cathode machining the different workpieces with the different surfaces.     

Utilization of flow field simulations for cathode design in electrochemical machining of aerospace engine blisk channels

Electrochemical machining (ECM) cathode flow field design is crucial to machining aerospace engine blisk channels. In order to reduce the cathode design cycle and cost in machining, 3D cathodes and flow field simulation model were developed to facilitate analysis the flow fields in reversed flow patterns. The electrolyte flow line was determined by the distributions of electrolyte pressure, the diameter of the back orifice, and the areas of the back orifices in locations A, B, and C. The simulation results were utilized to analyze the influence of the electrolyte flow line. To verify the accuracy of the simulation, the experiments were carried out. The simulation results were consistent with the experiment data. It indicates that electrolyte flow field simulation is an effective method to optimize cathode design. Utilizing this methodology can improve the ECM cathode design efficiency and reduce cathode revision time.     

Generation and measurement of subnanosecond electron beams in gas-filled diodes

The results of experimental studies of generation of supershort avalanche electron beams (SAEBs) in gas-filled diodes and the analysis of the techniques for measurements of their amplitude-time characteristics are presented. The optimal conditions for obtaining the maximum SAEB amplitudes are described. It is shown that, at a 6-mm-diameter cathode and a 10-mm interelectrode distance, a beam is detected over the entire foil area, the diameter of which is 50 mm, and equals the inner diameter of the gas diode. A half-height duration of the beam-current pulse shorter than 90 ps was measured with the use of a collector with a 3-mm-diameter receiving element. The SAEB amplitude measured behind the 10-μm-thick Al foil at this pulse duration was ～50 A.     

Design of the cross-structural cathodes in electrochemical machining of aero-engine blades

Blades are crucial parts of aero-engines. Their manufacturing is difficult because of their thinness, complex profile and stringent requirements. Electrochemical machining (ECM) is an important approach for manufacturing blades, but it is difficult to machine the leading and trailing edges. This article adopts cross-structural cathodes in ECM to solve the open electric field space problem. The key difficulty in the design of cross-structural cathodes is the position of the crossed-point. The height and the offset of the crossed-point are optimized using the ANSYS software. The simulation results show that the position of the crossed-point obviously affects the machining accuracy, along the leading and trailing edges of the blade. A pair of cross-structural cathodes with one uniform section is designed, and a series of corresponding ECM experiments are carried out. The experiments demonstrate that the ECM process is stable, the profiles are sleek and the machining dimensional error is reduced to 0.08 mm at the leading and trailing edges of the blade when using the new cathode structure.     

Quantitative analysis of keratin filament networks in scanning electron microscopy images of cancer cells

The keratin filament network is an important part of the cytoskeleton. It is involved in the regulation of shape and viscoelasticity of epithelial cells. The morphology of keratin networks depends on post-translational modifications of keratin monomers. In-vitro studies indicated that network characteristics, such as filament crosslink density, determines the biophysical properties of the filament network. This report presents a quantitative method for the morphological analysis of keratin filament networks. Visualization of filaments was based on prefixation extraction of epithelial cells and scanning electron microscopy (SEM). SEM images were processed by a skeletonization algorithm to obtain a graph structure that represents individual filaments as well as their connections. This method was applied to investigate the effects of transforming growth factor α (TGFα) on the morphology of keratin networks in pancreatic cancer cells. TGFα contributes to pancreatic cancer progression and activates signalling pathways phosphorylating keratin monomers. Using this new method, a significant alteration to the keratin network morphology could be detected in response to TGFα.     

磁控管用稀土氧化物-钼次级发射体的综合性能

阐述对所制备的复合稀土氧化物-钼(RE2O3-Mo)陶瓷阴极材料的次级发射性能、热发射、烧结成型性以及暴露大气性能所进行的测试,以及采用SEM和能谱仪等分析手段对材料进行微观分析,实验结果表明,Re氧化物总量在20%～25%时材料综合性能最佳.     

A flexible curvilinear electromagnetic filter for direct current cathodic arc source

Widespread applications of direct current (dc) cathodic arc deposition are hampered by macroparticle (MP) contamination, although a cathodic arc offers many unique merits such as high ionization rate, high deposition rate, etc. In this work, a flexible curvilinear electromagnetic filter is described to eliminate MPs from a dc cathodic arc source. The filter which has a relatively large size with a minor radius of about 85 mm is suitable for large cathodes. The filter is open and so the MPs do not rebound inside the filter. The flexible design allows the ions to be transported from the cathode to the sample surface optimally. Our measurements with a saturated ion current probe show that the efficiency of this flexible filter reaches about 2.0% (aluminum cathode) when the filter current is about 250 A. The MP density measured from TiN films deposited using this filter is two to three orders of magnitude less than that from films deposited with a 90 degrees duct magnetic filter and three to four orders of magnitude smaller than those deposited without a filter. Furthermore, our experiments reveal that the potential of the filter coil and the magnetic field on the surface of the cathode are two important factors affecting the efficacy of the filter. Different biasing potentials can enhance the efficiency to up to 12-fold, and a magnetic field at about 4.0 mT can improve it by a factor of 2 compared to 5.4 mT.     

两步法电化学加工薄壁钼长管的数学建模与实验研究

针对某反应堆用高温燃料包壳加工难题,研究了钼合金薄壁长管部件的电化学加工技术,提出了固定阴极及移动阴极的两步电化学加工方法,建立了移动窄阴极电化学加工的数学模型,针对实施方式、工艺参数等进行了实验。实验结果表明:固定宽电极的电化学加工可大量去除材料,移动窄电极的电化学加工可进行表面精修,采用这两种工艺对直径25.4 mm、长度800 mm的钼管进行加工,获得的直径偏差在0.05 mm以内。     

A self-heated hollow cathode made of compacted TiN powder: the preparation method and test results

A method for the formation of a tubular hollow self-heated cathode using magnetic-pulse pressing of a mixture of TiN (90%) and Ti (10%) powders with subsequent annealing and sintering during operation of the compact as a cathode in a high-current (5–45 А) discharge at temperatures of 2000–2200°C is described. Massive tubular cathodes with a 2.5-mm-thick wall and a large (up to 12 mm) inner diameter were manufactured. The erosion rate of a TiN cathode was 2.3 × 10^–7 g/C for the operation in an Ar/N₂ mixture and increased by a factor of 1.6 in the oxygen–argon plasma generation mode with separate feeding of gases.     

Cytoskeletal architecture of neuromuscular junction: Localization of vinculin

Cytoskeletons underneath the postsynaptic membrane of neuromuscular junctions were studied by using a quick-freeze deep-etched method and immunoelectron microscopy of ultrathin frozen sections. In a quick-freeze deep-etched replica of fresh, unfixed muscles, 8.9 ± 1.5-nm particles were present on the true postsynaptic membrane surface. Underneath this receptor-rich postsynaptic membrane, networks of fine filaments were observed. These cytoskeletal networks were more clearly observed in extracted samples. In these samples, diameters of the filaments which formed networks were measured. In the platinum replica, three kinds of filament were recognized—12 nm, 9 nm, and 7 nm in diameter. The 12-nm filament seemed to correspond to the intermediate filament. The other two filaments formed meshworks between intermediate filaments and plasma membrane. In ultrathin frozen sections vinculin label was localized just beneath the plasma membrane. Thirty-six percent of the label was within 18 nm from the cytoplasmic side of the plasma membrane and 50% was within 30 nm. Taking the size of the vinculin molecule into account, it was concluded that vinculin is localized just beneath the plasma membrane and might play some role in anchoring filaments which formed meshworks underneath the plasma membrane.