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The present work studies the space charge accumulation and decay in the degassed cross-linked polyethylene (XLPE) by detrapping mechanism and quantum chemical method. Experimentally, significant positive charge packets were observed at room temperature (300 K). Negative charges accumulated strikingly under high temperatures but with a fast decay during depolarization. The estimated bipolar carrier...
The space charge behavior in cross-linked polyethylene (XLPE) high voltage direct current (HVDC) cables may be affected by the thickness of the insulation, so an equivalence analysis of the space charge distributions in XLPE sheets with different thicknesses is of great significance. This paper presents space charge behavior in XLPE sheets with the thicknesses of 150, 300, 500 and 800 μm from room...
Under high DC voltages, the space charge distribution can greatly distort the electric field and may cause premature failure of the insulation material. The development of space charge in the material is affected by several factors like electrical field, temperature and electrode materials. In this work, the pulsed electroacoustic (PEA) technique was used to measure the space charge distribution in...
DC glow discharge is used in a vast range of industrial applications such as plasma processing, thin film coating by sputtering, etching, welding and light sources1. Understanding the discharge properties is essential for better integration of these applications.
Using Becker method, we have made research on evaporation rate by considering the parameters of cathode manufacturing process that conclude the tungsten base porosity, aluminate formulation and the coated film material. Finally, the impact level and the weight results are given quantitatively.
To find the changes of surface compositions during life time of the Scandia-doped impregnated dispenser cathodes, two cathodes have been tested at an activation temperature of 1150°CB-Mo and an operation temperature of 1000°CB-Mo, respectively, in an AES system up to more than 7,000 hours. Surface compositions were monitored in-situ at intervals. The tested results have been reported and discussed...
We have successfully developed the vacuum-sealed carbon nano-tube (CNT) x-ray tube. The remarkable improvement of field emission properties, life time and stability, was obtained after high temperature brazing process in a vacuum circumstance.
A new kind of cathode, LaC2-Mo cathode was prepared through spark plasma sintering method by using the mixed powder of LaC2 which was prepared by vacuum melting method and molybdenum. It was found that the emission properties of LaC2-Mo cathode increases with the LaC2 content increasing. The emission current density of LaC2-Mo cathode which contains 3.5wt.% LaC2 could reach 0.90A/cm2 at 1400b whereas...
High current density scandate cathodes have aroused great interest in recent years. In this paper the emission performances of scandate cathodes and the possible chemical and physical processes occurred during cathode manufacturing and operation are summarized. Emission mechanisms are further discussed. The major problems of this kind of cathode and its application prospects are reviewed.
Emission properties of nanosized scandia doped dispenser (SDD) cathodes tested at pulse mode with different pulse widths and duty cycles as well as at DC mode are reported and discussed in this paper.
Dispenser cathode is used in microwave tubes as source of electrons. We investigate high current density emission capabilities of alloy-coated cathodes used for terahertz vacuum devices. In this paper the developmental work carried out on ternary-alloy-film cathode (2Os:2Re:1W) and the results are presented. The cathodes were tested inside a closed spaced diode and also analytical chamber containing...
The paper introduces a silicon controlled rectifier (SCR)-based device with high holding voltage for ESD power clamp. The holding voltage can be increased by extending a p+ cathode to the first n-well and adding second n-well wrapping around n+ cathode. The increase of the holding voltage above the supply voltage enables latch-up immune normal operation. The device is fabricated by 0.35um BCD (Bipolar-CMOS-DMOS)...
Dispenser cathodes must operate at specific temperatures while applying specific heater powers. Designs to accomplish this have traditionally been empirically derived. In order to apply more systematic FEA methods better knowledge of the unique materials used in the heater package is needed. This investigation was launched to evaluate the thermal properties of the alumina materials used to encapsulate...
Accurate cathode temperature measurements in a vacuum have been an engineering problem since the advent of the vacuum electron device (VED) over 100 years ago. Cathode temperatures are commonly characterized in a bell jar using various IR pyrometer instruments, but the resulting data is typically qualitative as opposed to the quantitative data that is needed for long term quality control of cathode...
The Ba and BaO evaporation rates of a thermionic cathode have been measured at 145 K and 170 K above the typical operating temperature being about 1033 K. According to the measurement result, the relationship between cathode lifetime and operation temperature has been discussed. A comparison life test also be done between a poisoned but reactivated cathode and a normal one under the same condition...
Several magnetron injection gun cathodes have been measured for temperature and emission uniformity. The measurements confirm results in Russia that the quality of many MIG cathodes is not sufficient for efficient gyrotron operation. This presentation will present recent cathode measurements and identify known issues. A design will be presented that provides a solution for several of these issues.
A new kind of pressed scandate dispenser cathode was fabricated by liquid-liquid doping using a Sol-Gel technique. The cathode exhibits high emission property. i.e., the emission current density reached 47 A/cm2 at 850degCb with lower Richardson work function about 1.1-1.2 eV and Ba:Sc:O concentration ratio at the cathode surface was 1.6:1:2.0.
The dielectric breakdown phenomena of various kinds of thin films have been investigated as a result of the development of microelectronics. We have studied the dielectric breakdown of evaporated SiO thin films. The breakdown of specimens thicker than 200 Å have already been reported.1 In the previous experiments, the breakdown strength increased rapidly with decreasing film thickness and increased...
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