碳化硅纳米线阴极强流电子束源及其重频运行特性研究

Defense and industrial applications have promoted the development of high-power microwave (HPM) and pulsed power technologies. The remaining challenges of repetitive and long lifetime operation, confronting high-power microwave technology, stimulate intense interest in seeking the new high-current electron beam sources. Due to the speical structrues and remarkable physicochemical properties, one-dimensional nanostructures draw more attention for the potential applcations as the high-current emitters. SiC nanowires combine the advantages of traditional cold cathodes and nanostructures, and exhibit excellent properties with nanoscale tips, large aspect ratio, thermal and chemical stability, which are expected to have benefits for the repetitive and long lifetime operations of the HPM systems. In this research project, based on the ultra-long SiC nanowires, the emission process of the SiC nanowires cathodes will be firstly investigated, theoretically and experimentally. The high-current emission mechanisim of SiC nanowires, the characteristics of the cathode plasma, the beam flow, the beam uniformity and density will be presented and discussed. The relationship between nano-effects and beam quality will be addressed. Further more, the feasibility of repetition rate pulse operation of the SiC nanowire cathode will be determined. Results of time-resolved pressure history, discharge waveforms, and SiC nanowire microstructure changes will be presented. Based on these experimenal results, the influence issues to the vacuum compatibility and lifetime of the SiC nanowires cathodes under repetitive operation mode will be intensively investigated. The research of this project makes contributions to the high-current electron beam sources, holds practical significance for the HPM sources, and brings new insight into the development of high-current electron beam sources with higher performance and wider applications.

强流电子束源阴极是高功率微波系统的核心部件之一，为满足高功率微波源重复频率、长寿命运行的需求，强流阴极需要吸纳新型材料。SiC纳米线是一类新型纳米材料，其外观类似于传统天鹅绒材料，同时具备高熔点、良好的热稳定性及化学稳定性、高的力学强度及电击穿强度，这些特点对于提高阴极在重复频率运行时的使用寿命不无益处。 本项目提出采用SiC纳米线来制备强流电子束源阴极的思路，拟在已成功制备SiC纳米线的基础上，进一步组装为强流发射阴极，并应用于高功率二极管。通过研究SiC纳米线阴极的强流发射特性，阐明其产生阴极等离子体的物理机制，揭示纳米效应对束流发射品质的影响；通过研究高重复频率条件下的脉冲特性，探索影响SiC纳米线强流电子束源运行寿命的因素。本项目的实施对于拓展阴极基础研究和提高强流电子束源的技术性能都具有重要意义。

强流电子束源阴极是高功率微波系统的核心部件之一，随着高功率微波技术的实用化进程，要求强流电子束源阴极不仅具备较高的束流发射品质，还要能耐烧蚀、放气量小、寿命长。为此，强流电子束源阴极需要吸纳新型强场材料。. SiC纳米线外观类似于传统天鹅绒阴极，同时具备高熔点、良好的热稳定性、化学稳定性、高的力学强度及电击穿强度。本项目在成功制备SiC纳米线阴极的基础上，将其应用于高功率二极管，在450 kV、120 ns脉冲加载下，对比研究了常规天鹅绒和SiC纳米线的束流发射品质和重频运行特性，包括阴极启动过程、阴极等离子体膨胀、宏观稳定性及运行寿命等。结果显示，SiC纳米线阴极的电子发射阈值场强为10±2 kV/cm，约为常规天鹅绒阴极的1/3；电场强度上升率相同时，SiC纳米线阴极比常规天鹅绒阴极启动时间短20 ns；SiC纳米线阴极在不同时刻的等离子体发光更强烈也更均匀，对应的二极管电流也更大；在90 kV/cm的强场条件下，SiC纳米线阴极能够改善二极管的宏观电稳定性且运行寿命更长；在二极管本底气压为6x10^-3 Pa时，SiC纳米线阴极对应的二极管峰值气压约为普通化纤天鹅绒阴极的1/5，仅为0.062 Pa；对比研究了常规天鹅绒和SiC纳米线的重复频率工作稳定性。在重复频率10 Hz-300 Hz条件下，当电流密度小于100 A/cm^2时，SiC纳米线的平均不稳定度约为常规天鹅绒阴极的1/2；在电流密度为60~70 A/cm^2条件下，当重复频率相同时，SiC纳米线阴极工作更为稳定。最后，开展了SiC纳米线阴极在高功率微波源MILO中的初步应用。在电子束参数为600 kV、50 kA的实验条件下，与常规天鹅绒阴极相比，使用SiC纳米线阴极不仅减少了MILO输出微波的倍频成分，而且提高了微波的峰值功率。. 本项目创新性的将一维纳米材料——SiC纳米线独有的理化特性和高功率微波源发展趋势相结合，通过本项目的研究，为SiC纳米线阴极强流电子束源在高功率微波、强流电子束加速器等领域获得重要应用提供了有益的参考和指导，并且展示出了良好的应用前景。.