碳纳米管和天鹅绒阴极强流发射特性的对比研究

采用电泳沉积法、碳纳米管纸和化学气相沉积直接生长法制备了三种碳纳米管阴极. 从强流发射性能、阴极等离子体膨胀、阴极起动、发射均匀性、工作稳定性以及脉冲放气特性等多个方面, 对比研究了碳纳米管阴极和化纤天鹅绒阴极的强流发射特性, 研究表明碳纳米管阵列和碳纳米管纸阴极发射性能明显优于普通化纤天鹅绒, 碳纳米管阴极发射性能与碳纳米管取向无关, 管壁的缺陷发射对无序碳纳米管阴极强流发射具有重要贡献. 碳纳米管阴极的起动场强约为普通化纤天鹅绒的2/3, 电场上升率相同时碳纳米管阴极比化纤天鹅绒阴极起动时间短12–17 ns. 碳纳米管阴极发射均匀性优于化纤天鹅绒, 尤其是碳纳米管阵列, 整个阴极表面等离子体光斑致密且均匀. 在二极管本底气压为6×10^-3 Pa时, 碳纳米管纸阴极对应的二极管峰值气压不到0.3 Pa, 约为普通化纤天鹅绒阴极的1/5, 碳纳米管阵列阴极放气量在三种阴极中最少, 仅为0.042 Pa. 结果表明, 碳纳米管阴极在强流电子束源和相关高功率微波器件领域具有潜在的应用价值.

Comparative study on intense emission of velvet and cabon nanotube cathode

So far, the investigations of carbon nanotube (CNT) cathode have been focused on the field emission with low current and voltage. However, the properties of the intense pulsed emission of CNT cathode have not been discussed deeply and comprehensively. In this paper, the intense emission properties of velvet and CNT cathode are studied in various aspects, such as emission capability, cathode plasma expansion, cathode initialization, emission uniformity, operation stability, outgassing property, and so on. Three different CNT cathodes are made by using electrophoresis deposition, chemical vapor deposition and also CNT paper (or buckypaper) gluing. Results show that the emission capability of CNT arrays and CNT paper cathode is definitely better than the velvet cathode. At the same diode voltage (～300 kV), the amplitudes of diode current of CNT array and CNT paper are 2.75 and 3.1 kA respectively, which are bigger than that of the velvet cathode (～1 kA). The orientation of CNT should not affect the emission capability of CNT cathodes. And the small radius of the tube wall and the existence of defects are suggested to be the reasons for the emission of electrons from the body of the tubes. The threshold electric field strength of intense emission of CNTs is about two-thirds of velvet cathode. The onset delay time of CNT cathode is shorter than the velvet cathode by about 12-17 ns at the same electric field growth rate. The time-evolution processes of the plasma expansion velocity of CNT and velvet cathodes are similar, which could be divided into three phases (rapid rising, quick decreasing and stable phase). In summary, the plasma expansion velocity of CNT cathode is less than one fourth that of velvet at the end of the first phase. During the stable phase, which sustains until the end of the voltage pulse, both cathodes have the same plasma expansion velocity (7 cm/μs). The emission uniformity of the cathode has been studied by analyzing the distributions of cathode plasma spots and Cherenkov radiation light, which are captured by the high speed frame camera. The emission uniformity of CNT cathode is much better than that of the velvet cathode. Especially, the cathode plasma spots on the whole surface of CNT array cathode are very dense and uniform. The peak outgassing pressure of the CNT paper cathode is 0.3 Pa, which is one fifth that of the velvet cathode; while the peak outgassing pressure of the CNT array cathode is 0.042 Pa, which is the lowest, and the outgassing pressure of the CNT cathode is related to the fabrication methods. Volatile such as epoxy should be avoided in the fabrication processes. This CNT cathode appears to be suitable for intense emission source and high-power microwave device applications.