表面微结构对碳化硅晶须掺杂石墨阴极爆炸电子发射性能的影响  

Influence of surface microstructure on explosive electron emission properties of graphite cathode doped by silicon carbide whiskers

作　　者：华叶[1] 万红[1] 陈兴宇[1] 吴平[2] 白书欣[1] 

机构地区：[1]国防科学技术大学航天科学与工程学院,长沙410073 [2]西北核技术研究所,西安710024

出　　处：《物理学报》2016年第16期245-252,共8页Acta Physica Sinica

摘　　要：爆炸发射阴极已广泛应用于高功率微波源,但常规场致爆炸发射阴极存在使用寿命短或电子发射不均匀的问题,改善阴极材料是解决这一问题的有效途径.本文将碳化硅晶须掺杂到石墨中制备得到阴极,从二极管电流波形上升沿和输出微波脉宽产生的变化着手,分析了碳化硅晶须掺杂石墨阴极表面材料成分和微观形貌对其电子发射性能的影响机理.研究发现,碳化硅晶须的存在,不仅有利于阴极场发射的快速启动、发射微点数目增多,还有利于降低等离子体膨胀速度、抑制脉冲缩短现象,使得输出微波脉宽增大.随着脉冲发射数量增多,碳化硅晶须掺杂石墨阴极表面被等离子体不断"抛光",微凸起形状因子减小、均匀性提高,场发射启动速度减慢,但输出微波脉宽增大.Explosive emission cathode （EEC） is a pivotal component in high power microwave source （HPMS）, of which the ultimate properties are significantly dependent on the quality of electron beams generated from the cathode. Short lifetime and poor emission uniformity are the persistent drawbacks of conventional field EEC. Improvement of cathode material by changing its compositions and modifying surface micromorphology, is a feasible way to solve this problem. Graphite is one of the frequently used materials for EECs due to its long life-time and sturdy performance under high voltage and repetition frequency. Meanwhile silicon carbide （SiC） whiskers are distinguished by high aspect ratio （ratio of height to diameter） and low work function which is in favor of the fast onset of electron emission. In this work, the novel composites, composed of SiC whiskers, pitch and major graphite powders, are prepared by the conventional mingling and sintering. The cathodes are installed on TPG1000 system with a parameterized pulse of 970 kV, 9.2 kA, and 50 ns. By analyzing the changes of the rise edge of measured diode current and output microwave pulse duration, the effects of material composition and surface micromorphology on electron emission properties for the cathode are disclosed in detail. The results, based on the comparison of emission properties between graphite cathodes with and without SiC whiskers doped, reveal that SiC whiskers play an important role in accelerating the field emission of cathode, which is demonstrated by the eclipse of displacement current peak on the rise edge of measured current waveform after doping. Meanwhile, the duration of output microwave pulse is enhanced by about 11% after doping, which could be explained by the lower expansion speed of Si plasma. Moreover, the surface micro-protrusions of graphite cathode doped by SiC whiskers are constantly “polished” by heating effect and cathode plasma as the number of emission pulses increases to 11000. This is in quite good agreement

关 键 词：表面微结构 碳化硅晶须 电子发射性能 微波脉宽 

分 类 号：O646[理学—物理化学]