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High-order operating mode is adopted to improve the performance of multiple-beam klystron. However, the frequency interval between high order operating mode and neighboring mode (spurious mode) is small, which easily interfere with the state of the operating mode. In the paper, the metal rings are installed in the coaxial cavity to enlarge the frequency interval. The equivalent circuit models are...
In this paper, operation process of scandia-doped dispenser cathodes is studied based on surface behavior, evaporation and emission properties during preparation, activation, operation and life duration.
GaAs/Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As(0<;x<;1.0) multilayer structure is widely used in photodetector, laser and solar cell. Due to the lattice parameter difference between GaAs and Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As is very small(less than 0.15% at 300K), Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As as a buffer layer in NEA...
An open-styled dielectric-lined azimuthally periodic circular waveguide (ODLAP-CW) which is a modified form of a dielectric-lined azimuthally periodic circular waveguide (DLAP-CW) is proposed in this paper. Here, the metal shell in the DLAP-CW is replaced by absorbing materials in the improved structure. The improved structure can effectively eliminate the mode competition in the beam-wave interaction...
In the present paper, the field emission cathodes of planar-type on the base of diamond-carbon composite are studied. Carbon was deposited inside porous dielectric diamond compacts which were fabricated by diamond particles pressing.
In vacuum system, area source electron gun emits electrons to bombard the standard screen. With the first anode and the second anode in different potentials, the images show the features of divergent, uniform, convergence and submerge. Photos, images acquired by brightness meter, and the image gray values are listed in Table 1. By image gray value analysis, it can be seen that in item no. 1, the electrons...
The nanofluid does not simply refer to a liquid-solid mixture. In general, these are effective methods used for preparation of suspensions: (1) to change the pH value of suspensions; (2) to use surface activators and/or dispersants; (3) to use ultrasonic vibration. In this work, Distilled water and Multi-walled carbon nanotubes were used to produce nanofluids. The carbon nanotubes were provided by...
We have investigated the potential of screen printed CNT field emitters for improving the efficiency and reliability of compact X-ray tubes, and then we have fabricated and tested about our compact X-ray tube with ceramic body using ceramic brazing vacuum sealing technique.
Summary form only given. Vertically-aligned multi-walled carbon nanotubes (VAMWNTs) have received extensive attention recently. The chemical vapor deposition (CVD) has been regarded as a primary candidate for the large-scale production of vertically-aligned nanotubes [1-4]. It is well known that the structural characteristics of VAMWNTs grown by CVD depend on growth parameters such as reaction time,...
In this study, we have developed a CNT paste for high-current density field emitters by using a ball-milling process. The ball-milling was used in the CNT paste procedure for effective material dispersion. Material dispersion is one of the most important factors in a paste synthetic process. The ball-milling is a very easy and simple method to produce a printable CNT paste. The CNT paste was made...
In high-vacuum conditions, the instrument can do detection and research efficiently on the luminescence features of fluorescence screen. It is a special purpose intelligent test equipment combined of optical, mechanical, electrical, computing and display. Vacuum cavity that is large cap closed, the turntable and the hot electron emission source is located in the space area. Through experiments we...
In this study, we fabricated a cathode using screen printing method with carbon nanotubes and ZnO nanotetrapods as cathode emission materials and CsI nanoparticles as coating materials. After several comparative experiments, we find that 3g CsI dispersed into an organic paste which is composed of 20ml terpineol and 1g ethyl cellulose has significant results to improve the performance of the field...
In this work, vacancies diffusion length scale or the size of the nanostructures involved during oxidation when utilizing the Kirkendall phenomenon is presented. Ni nanowires with different diameters are formed by electrodeposition of Ni into anodic aluminium oxide (AAO) membrane. The oxidation of the dispersed Ni nanowires is carried out either via rapid thermal oxidation (RTO) or conventional furnace...
This paper presents photoelectrochemical properties of multi-walled carbon nanotube assembled with CdSe quantum dots. CdSe QDs are adsorbed on the surface of MWCNTs with a diameter of 4-5 nm.
Pulsed grid-controlled traveling-wave tubes (TWTs) are widely used in the field of space and defense for navigation and directing of radars, aircrafts, satellites, and guided missiles. In order to attain even higher frequency and power requirements, gun designs for modern microwave tubes have utilized grids, which are very close to cathode. However, during the course of the TWTs work, electron emission...
The feasibility of measuring the electron diffusion length of photocathodes by surface photovoltage spectroscopy from theory and deduce the calculation formulas. The principle of the surface photovoltage spectroscopy method and the measuring technique are discussed particularly using the electro-static equilibrium condition and the law of conservation of charge on the basis of the energy band structure...
In this paper transmission-mode GaN photocathodes was activated by Cs/O, its quantum efficiency curve and the factors which influenced the quantum efficiency mostly were studied. Transmission-mode GaN photocathodes was grown by Metal-Organic Chemical Vapor Deposition (MOCVD).
Dispersion characteristics and interaction impedance is the key parameter for travelling wave tube design. This paper demonstrate the travelling wave tube method for dispersion test. A helix slow wave structure was chosen as sample for test validation. Also, the test results are compared with the simulations of CST Microwave Studio (MWS) and High Frequency Structure Simulator (HFSS). Test results...
In this paper, the "three-step model" of photoemission mechanism for gallium nitride (GaN) photocathode is discussed. The first step is the absorption of incidence light. The incidence photon energy is absorbed by the electrons in the valence band, and this establishes the foundation that the electrons in the valence band are stimulated to the conduction band. The second step is the transportation...
In this paper, the structural and electronic properties of Cs adsorption on GaAs surface were studied. The samples were prepared by MBE. The conduction bands, valence bands, band structure and density of states were calculated by first principles based on density functional theory. The effect of Zn doping on electronic structure were also analyzed.
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