共查询到20条相似文献,搜索用时 171 毫秒
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本文对渍制钡钨阴极多孔钨结构与发射和蒸发性能的有关数据进行了分析研究。结果表明,对于多孔钨结构,钨粉的颗粒度和孔隙的孔径大小决定了小孔内表面的总面积和钡在钨表面上的扩散路程,钡输送通道的大小和长短。这些因素对钡钨阴极的性能和工作机理有密切关系,但仅用多孔钨孔隙度来表征阴极性能那是不够严格的。最后我们提出了对于不同用途的阴极应采用的多孔钨结构。 相似文献
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一、引言氧化物阴极,钡钨浸渍阴极或压制阴极,以及它们的改进型铱膜钡钨浸渍阴极在各种电真空器件中得到了广泛的应用。在真空器件的性能改进和增长寿命问题上、管内残余气氛对阴极性能和寿命的影响,仍然是一个重要因素。不论是化学活泼气体如O_2、H_2O、CO_2等或是例 相似文献
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Li Yutao Zhang Honglai Liu Pukun Zhang Mingchen 《电子科学学刊(英文版)》2006,23(3):473-475
A new type of dispenser cathode with dual-layer (Os-W/Re) is developed. The cathode coated with Os-W/Re shows better emission performance than the cathode coated with Os-W alloy. X-ray Photoelectron Spectroscopy (XPS) spectra demonstrate that ternary alloy coating (Os-W-Re) formed on the surface of the cathode with dual-layer (Os-W/Re) after full activation is the major reason why it has better emission than the cathode with Os-W alloy. The surface of each variety of the cathode is characterized with Scanning Electron Microscope (SEM) before and after activation: the emitting surface of the cathode with Os-W alloy after ageing appeared non-adherence (flaking) in localized areas, which is one of the reasons for non-uniform emission. However, the surface of the cathode with dual-layer (Os-W/Re) does not present film peeling under the same conditions. Thus it ensures better emission uniformity and functional reliability for the dispenser cathode. 相似文献
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介绍了对覆锇扩散阴极锇膜与钨基间互扩散过程的研究结果。通过SEM对不同工作时间的阴极发射表面及纵向剖面的形貌进行分析,采用EDS对实验阴极的表面及纵向剖面进行元素成分的分析。研究表明,随工作时间的不同,阴极表面及纵向剖面Os-W浓度发生变化,呈现明显的扩散趋势。 相似文献
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The performance of tungsten-rhenium (W-Re) mixed-matrix cathodes of varying compositions was studied. The work function, when the tungsten percentage is 50 plusmn 25%, is close to that of a Re-coated cathode. The I-V characteristics show an emission anomaly. It was found that the patch fields are not the main reason; rather, it is the field enhancement which is responsible for this anomaly. The emission microscopic results show that the work function distribution does not greatly differ from that of a B-Type cathode. Auger electron spectroscopy, in conjunction with scanning electron microscope studies, supports the presence of a thick active layer. The cathodes exhibited decay and heating effects with pulsed-current emission. The nonmetallic behavior is attributed to the presence of an appreciable amount of unreduced BaO. Poisoning studies show that the resistance to oxygen poisoning is better than that of a conventional B-Type cathode. A chemical technique was developed to prepare a finely divided powder of W-Re sigma-phase alloy. The cathodes made out of this alloy powder showed better emission and uniformity compared to those of simply mixed cathodes. 相似文献
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A three-dimensional (3-D) computer simulation of the electrical stimulation of passive cardiac tissue from a bipolar electrode placed within a conductive bath is presented. Through the bidomain model, the syncytial and anisotropic properties of cardiac tissue are taken into account; tissues with equal anisotropy and no transverse coupling are also considered. The membrane is represented by a capacitor and passive resistor in parallel. Located within an isotropic bath, the bipolar electrode is oriented either perpendicular or parallel to the tissue surface. For anisotropic tissue with a small cathode-tissue separation, the tissue surface is highly depolarized under the cathode with the depolarization persisting a considerable distance from the electrode in the transverse fiber direction. Adjacent to this region in the longitudinal direction, areas of hyperpolarization exist. At large distances from the cathode, the tissue surface is hyperpolarized in all directions when the electrode axis is perpendicular to the tissue. In the parallel case, surface depolarization creates buried regions of hyperpolarization. For the perpendicular configuration, the ratio of the steady-state maximum depolarization to steady-state maximum hyperpolarization, an estimate of the ratio of anodal to cathodal threshold, decreases rapidly with increasing cathode-tissue separation. In the parallel case, the depth of the conductive bath significantly affected the transmembrane potential distribution in the tissue. The use of a 3-D model more realistically simulates real-life electrical stimulation (such as stimulation with an implantable pacemaker) and provides insight into the effect of the volume conductor adjacent to the tissue 相似文献
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The characteristics of silicon avalanche cathode as a novel electron emitting device with ultra-shallow p-n junctions have been studied using the two-dimensional device simulator PISCES-IIB. The steady-state simulation indicates that the nonplanar surface topology resulting from fabrication process causes current crowding near the edge of the emitting area where the surface step exists. Current crowding degrades the emission uniformity and also reduces the emission current under increased reverse bias. The nonplanar surface structure also causes punchthrough in the epitaxial layer as the reverse bias on the cathode increases. As a result, the percentage of the cathode current contributing to emission decreases, reducing the emission efficiency consequently. The simulation shows that the portion of the cathode current that flows through the emitting area drops to as much as 30% at cathode bias higher than 12 V, compared to the same current just after breakdown. This also affects the rate of increase in the total emission current which is the product of the emission efficiency and the overall cathode current 相似文献
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Yi Sheng Yeh Ming Hsiung Tsao Han Ying Chen Tsun-Hsu Chang 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(9):1397-1415
Gyrotron has received extensive attention owing to its high-power capability, especially when the wavelength shrinks below the millimeter-wave range. The electron beam of a gyrotron is typically generated by a magnetron injection gun (MIG). For high cathode current density, the MIG may operate in a region that combines temperature limited and space-charge limited emissions. An improved computer program for electron gun design is appropriate for MIGs that operate between space-charge limited and temperature limited emission. Moreover, the initial input formation of the program resembles that of the EGUN code. Analysis of a Pierce electron gun and MIGs reveals that the stimulated beam current appears consistent with the measured results. However, EGUN simulation results in which the cathode emitters of MIGs are chosen for the temperature limited emission differ from those of our simulation results. This difference is most likely owing to that the initial emitting energy can not be completely described in the EGUN simulation. Finally, the improved computer program is used to design a MIG for a Ka-band, TE01 mode gyro-TWT. 相似文献
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为发展场致发射冷阴极毫米波电真空辐射源器件, 对利用大面积碳纳米管冷阴极产生大电流、高电流密度电子注的电子光学系统进行了研究.通过在Pierce电子枪阴极表面引入栅网结构, 解决了碳纳米管冷阴极场致发射所需的强电场和电子聚束问题.在碳纳米管冷阴极实验测试数据的基础上, 采用粒子模拟软件对上述电子光学系统进行了仿真.研究了栅网对注电流、注腰半径和电子注散射的影响, 分析了阳极电压和外加轴向磁场对电子注的聚束作用.优化后的仿真结果表明在阴极发射面为3.03 cm2时, 该电子光学系统能够产生210 mA、60 kV, 电流密度为6.7 A/cm2, 最大注半径为1mm的电子注. 相似文献
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为了提高Y-Gd-Hf-O阴极耐电子轰击能力,该文通过高能球磨、压制和高温氢气烧结,制备了一种Sc2O3掺杂Y-Gd-Hf-O压制式直热式阴极。该阴极在1550 °C工作温度下,经过10 W电子连续轰击480 h后,发射电流密度下降至初始值的87.5%,表现出良好的耐电子轰击能力。阴极表面的微观形貌、成分组成分析表明,经压制后氢气气氛烧结,阴极表面呈陶瓷状结构形态,有利于提高阴极的耐电子轰击能力;经高温烧结、激活后表面形成了n型半导体Y2O3-x层,对改善阴极表面导电性、降低逸出功和提高热发射有促进作用。 相似文献