The Implementation And Verification Of High Emission Performance Cathode

As the new-type terahertz (THz) devices are developing rapidly, the emission capabilities of cathodes need to reach to40-100A/cm2. This performance index has reached the end of endurance of the traditional coated impregnated dispenser cathodes. Among the vary kinds of cathodes, dispenser cathodes contained scandium (Sc) have high electron emission abilities, who can satisfy with the demand of the new-type THz devices most possibly. In this thesis, we have developed a new-type dispenser cathode which is introduced with SrO and Sc2O3into the active material, the emission ability of the new-type cathode can reach to172A/cm2. In addition, in this thesis, we have research on the electron emission performance and surface chemical elements of the cathode. In conclusion, we obtain following new results:Firstly, we have research on the matrix of cathode-tungsten sponge. We adopt the graded30-60nm diameter tungsten powder to prepare the tungsten sponge at the beginning, but the impregnation levels of cathode is low (4%) which take high temperature impregnating after mould pressing or isopressing shaping. We mix W powders with active material, and sinter with high temperature after pressing shaping, which is difficult to obtain the fine shaping emission body. At last, we adopt3-4μm graded W powders and traditional prepare technology, and obtain the tungsten sponge body porosity of20%-25%, with uniformity pores. We obtain6.5-7.2%impregnation level after adopting this tungsten sponge impregnated aluminates, which can satisfy with the activation material impregnation level demand of the cathode.Secondly, we design new active material (Ba-Sc-Al-Ca-O) element system. We firstly introduce SrO and Sc2O3on the base of aluminates. Experimental results demonstrate that optimizing the ratio of SrO and Sc2O3can lead the cathode obtain excellent electron emission performance. When adopting26BaO·29SrO·8Sc2O3·7CaO·Al2O3active material, we obtain emission pulse current density of172A/cm2at1100℃, which is larger than traditional M-type cathode. Our experiments measure the sub-cooled curve and work function. According to the analysis, the new-type cathode has good electron emission uniformity.The surface of the new-type cathode is analyzed with nanometer scanning auger microscope. The results demonstrate that the surface of the new cathode is coated with high concentration Ba、Sc and O atom layer, and the ratio of Ba：Sc is agree to the reported results of the cathodes which have the higher emission performances.We have developed injection beam shape cathode which can satisfy with the THz device. The cathode has the size of1mm×0.3mm,Out of the rectangle area is coated with Mo-Si compound film for depressing the electron emission. We measure the emission ability of the cathode which has been installed in a THz device, the emission current density of the cathode can reach to80A/cm2which work at300μs,20Hz and1080℃. The performance of the cathode can satisfy with the THz device perfectly.