Preparation and Testing of a Miniature High-Frequency Pulsed X-Ray Tube Based on Carbon Nanotube Cold Cathode

An 8mm traveling wave tube (TWT) based on carbon nanotube (CNT) cold cathode is theoretically researched to develop millimeter-wave vacuum electron radiation source devices based on CNT cold cathode in this paper. A gridded sheet-beam CNT electron gun and staggered double vane slow-wave structure (SWS) is adopted in the 8mm TWT based on a periodic permanent magnetic system. Simulation results show that the maximum output power of the CNT TWT can reach 128 W at 32 GHz with an input power of 80 mW, corresponding to the maximum gain of 32 dB, when the operation voltage and beam current are 20 kV and 100 mA, respectively. And the 3-dB bandwidth of the CNT TWT is about 6 GHz.

This paper reports for the first time the theoretical analysis, design, and realization of a microwave (MW) frequency multiplier based on a field emission from carbon nanotube (CNT) cold-cathode. The nonlinear characteristic of field emission from CNT cold-cathode is utilized for generating field emission current with the harmonics of input signal and achieving frequency multiplication. We demonstrated both theoretically and experimentally that an MW electric field is capable of inducting current with harmonics from CNT cold-cathode and that a direct-current (dc) electric field can effectively increase the amplitudes of the harmonics. A reentrant resonant cavity structure was designed and fabricated to deliver the desired combined MW and dc electric fields onto CNT cold-cathode and realize the MW frequency multiplier. The device has the target second harmonic at a frequency of 1.868 GHz and a third harmonic at 2.802 GHz with a driving signal at frequency of 0.934 GHz. By simply increasing dc bias, a 12.43-dB increase of the amplitude of target second harmonic is successfully obtained. With such a device, directly modulated electron beam with MW frequency harmonics is obtained. Both the principle and the design can find applications in frequency tunable vacuum electron devices.

A carbon nanotube (CNT) cold cathode with a side-gate electrode for a flat panel X-ray source was developed and basic characteristics of the CNT cathode with surface treatments were evaluated. The CNT cathode treated by KrF excimer laser irradiation with a high electric field pulse aging showed the best performance concerning long lifetime, while the CNT cathode treated by tape peeling method without a high electric field pulse aging showed the best performance concerning high anode current. Observed anode current at 4 kV is comparable with some of the commercially available X-ray tubes, suggesting that the CNT cathode with side-gate electrodes can be used for an electron source for a flat panel X-ray source.

An extended interaction frequency‐locking oscillator based on carbon nanotube (CNT) cold cathode is proposed to overcome locked‐frequency limits of the conventional oscillator. Compared with the conventional oscillators, the oscillation frequency is locked by a modulation electron beam, which can be obtained in a field emission CNT cold cathode electron gun. The frequency‐locking signal does not enter the high‐frequency (HF) system but imposes an additional HF electric field on the cathode surface by a microstrip structure, which consumes considerably less power to lock the oscillation frequency. A ladder structure extended interaction oscillator operating in 2π mode is numerically investigated by three‐dimensional Particle‐In‐Cell simulation code. By analysing the impacts of different frequency‐locking power on the locked ranges, the results show that the average output power of 30.6 W is achieved at 35.11 GHz when the frequency‐locking power consumption is 460 mW. The 3‐dB bandwidth of a frequency‐locking region reaches 100 MHz.

Development of a K-band traveling wave tube based on carbon nanotube cold cathode

Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%.

The carbon nanotube (CNT) cold cathode is an attractive choice for millimeter and terahertz vacuum electronic devices owning to its unique instant switch-on and high emission current density. A novel, dual-gridded, field emission architecture based on a CNT cold cathode is proposed here. CNTs are synthesized directly on the cathode surface. The first separating grid is attached to the CNT cathode surface to shape the CNT cathode array. The second separating grid is responsible for controlled extraction of electrons from the CNT emitters. The cathode surface electric field distribution has been improved drastically compared to conventional planar devices. Furthermore, a high-compression-ratio, dual-gridded, CNT-based electron gun has been designed to further increase the current density, and a 21 kV/50 mA electron beam has been obtained with beam transparency of nearly 100%, along with a compression ratio of 39. A 0.22 THz disk-loaded waveguide backward wave oscillator (BWO) based on this electron gun architecture has been realized theoretically with output power of 32 W. The results indicate that higher output power and higher frequency terahertz BWOs can be made using advanced, nanomaterial-based cold cathodes.

Beam-wave interaction system of a Ka-Band traveling wave tube (TWT) based on carbon nanotube (CNT) cold cathode is theoretically researched in this paper. Based on the electron beam parameters of a truncated-cone carbon nanotube cold-cathode electron gun, a high-frequency system for coupled-cavity TWT is designed. Simulation results show that the maximum output power of the TWT can reach 313 W at 33.5 GHz with an input power of 500mW, corresponding to the maximum gain of 28 dB, when the electron beam voltage and current are 28 kV and 300 mA. The 3dB bandwidth of the TWT is about 0.6 GHz.

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

Carbon nanotube (CNT)-based cold cathodes are promising sources of field emission electrons for advanced electron devices, particularly for ultra-high-resolution imaging systems, due to their high brightness and low energy spread. While the electron field emission properties of single-tip CNT cathodes have been intensively studied in the last few decades, a systematic study of the influencing factors on the electron beam properties of CNT cold cathodes and the resolution of the secondary electron images has been overlooked in this field. Here, we have systematically investigated the effect of the structural properties of a CNT cold cathode on the electron beam properties and resolution of secondary electron microscope (SEM) images. The aspect ratio (geometric factor) and the diameter of the tip of a vertically standing CNT cold cathode significantly affect the electron beam properties, including the beam size and brightness, and consequently determine the resolution of the secondary electron images obtained by SEM systems equipped with a CNT cold cathode module. Theoretical simulation elucidated the dependence of the structural features of CNT cold cathodes and electron beam properties on the contribution of edge-emitted electrons to the total field emission current. Investigating the correlations between the structural properties of CNT cold cathodes, the properties of the emitted electron beams, and the resolution of the secondary electron images captured by SEM equipped with CNT cold cathode modules is highly important and informative as a basic model.

A Carbon nanotube (CNT) cold cathode emitter-based compact X-ray tube for X-ray application is studied in this paper. In the electron gun, the conventional filament was replaced by CNT emitter; CNTs were grown on metal alloy substrate. Using this electron gun, electron emission can be controlled by applying voltage rather than heating. Up to 2 mA tube current can be generated by this CNT electron gun. Also, the pulsed tube current and pulsed radiation dose can be generated by using MOSFET circuit. We measured the radiation dose generated in 30 frames per second, and confirmed that the waveform was generated as a square wave. From that waveform, it was confirmed that unnecessary radiation exposure can be minimized. The body of the X-ray tube is made of ceramic, which has strong durability against impact and high temperature. The ceramic used for the tube has an insulation distance of 30 mm and shows stable insulation performance in an environment where a voltage of 70 kV is applied. Using this X-ray tube, we successfully obtained X-ray images of various objects with acceleration voltages between 45 kV and 70 kV.

Low current x-ray tubes operating at 25–40kV have been developed using monolithic carbon nanotube (CNT) cold cathodes as electron sources. The authors have tested CNT cathodes from various sources. They were systematically evaluated and conditioned in a vacuum chamber and then went through high temperature baking and high voltage processing of standard tube production processes. Acceptance criteria were developed for each step in order to ensure that the final tube will meet the performance requirement of a commercial product. The tubes were subsequently operated continuously for an extended amount of time for life and reliability measurements. It was found that it is possible to use individually selected and preconditioned CNT cathodes in a commercial x-ray tube product. However, to find wide application and, particularly, to compete with existing hot filament thermionic cathodes, CNT cathodes need dramatic improvement in reproducibility and robustness. In addition, an empirical mathematical model for monolithic CNT cathodes has been developed for simulating the electron optics required in x-ray tubes. The model led to a successful design of a magnetically focused x-ray tube with a spot size of about 80μm.

Electron emission and structure stability of carbon nanotube cold cathode driven by millisecond pulsed voltage

PDF HTML阅读 XML下载 导出引用 引用提醒 碳纳米管冷阴极Pierce电子枪 DOI: 作者: 作者单位: 电子科技大学,电子科技大学,中山大学,电子科技大学,电子科技大学,电子科技大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(U1134006,61101041) ；中山大学光电材料与技术国家重点实验室开放课题(KF2010-ZD-06); A Pierce electron gun based on carbon nanotube cold cathodes Author: Affiliation: School of Physical Electronics,University of Electronic Science and Technology of China,School of Physical Electronics,University of Electronic Science and Technology of China,State Key Laboratory Optoelectronic Materials and Technologies,Sun Yat-Sen University,School of Physical Electronics,University of Electronic Science and Technology of China,School of Physical Electronics,University of Electronic Science and Technology of China,School of Physical Electronics,University of Electronic Science and Technology of China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要: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. Abstract:In order to develop millimeter wave electric vacuum radiation source devices with field emission cold cathodes, the electron-optical system using a large area carbon nanotube cold cathode (CNCC) was investigated, which can generate an electron beam with large current and high current density. By adding a mesh grid on the cathode surface of a Pierce electron gun, problems of the electron bunching and high electric field applied to the CNCC surface have been solved. Based on the experimental results of a CNCC, the field emission model was built, by using PIC simulation software, to simulate the Pierce electron-optical system. The effect of the mesh grid on the electron beam has been analyzed. And the influence of the anode voltage and the axial magnetic field for the electron beam radius has been researched. The simulation results of the electron-optical system showed that when the area of cathode is 3.03 cm2, an electron beam with 210 mA at 60 kV can be produced. The current density is 6.7 A/cm2 and the maximum radius of the electron beam is 1 mm. 参考文献 相似文献 引证文献

In this work, a carbon nanotube (CNT) cold cathode electron emitter fabricated by the cold pressing process was developed and studied. The electron emission performance was investigated and the application of pulse x-ray emission and imaging was explored by this cold cathode. The results indicated that the electron emission performance was excellent with electric intensities of turn-on and threshold of 0.47 and 1.17 V/μm@1 mA/cm2, respectively, and the field enhancement factor reached 17 514. The application research results showed that the pulse x-ray waveform has a great corresponding well with the grid voltage, and the imaging of a screw was clear, whose thread and pitch could be seen clearly. This article proposed a cold pressing process prepared for the CNT cold cathode, providing a new technical approach for the development of field emission cold cathode preparation processes.