单晶LaB6热阴极直流发射特性实验研究

 实验利用二极管型电子枪研究了单晶LaB₆热阴极的直流发射特性。阴阳极间距5 mm，从直径为2 mm发射体上测得175 mA直流束流（阴极温度约为1 870 K、阴阳极电压6.5 kV、空间电荷限制状态），电流密度为5.57 A/cm2。采用Longo方程拟合直流发射电流，该方法比以往单纯用Child或Richardson- Dushman公式更符合实际。实验还观测了阴极工作环境和表面状态对直流发射的影响，当真空度低于7×10^-4 Pa时，阴极发射能力逐渐下降,阴极表面碳、氧污染使发射体功函数升高。长时间加热后，石墨上会蒸镀LaB6,由此会造成热子电阻的下降。分析表明La原子补充不及时和表面气体吸附是影响直流发射能力的主要因素。

DC emitting characteristics of single crystal LaB6 thermionic cathode

A diode-type electron gun is used to investigate the DC emitting characteristics of a single crystal LaB6 thermionic cathode. The emitting area is a planar 2 mm-diameter, achieving transmitted currents up to 175 mA and a current density of 5.6 A/cm2. Comparing the measured current with fit result by Longo equation, Longo equation fitting is more accurate than the other methods, and applicable for practical operation. The circumstance has an effect on the emitting ability of cathode, when the vacuum is below 7×10 -4 Pa, the current density apparently decreases. The C and O in the surface of the emitter can increase the work function. Aggredation and diffusion of LaB6 to pyrolytic graphite make the resistance of heater lower. Experimental results show that DC emitting current density is lower than pulse emitting due to the finite diffusion velocity of atom La and the surface adsorption of remainder-gas.