Effect of “inert barrier layer” Ni on electron emission performance of dispenser cathode

Abstract

A novel trace nickel (Ni) doped tungsten (W) matrix with coated Ni on W grains was prepared by powder metallurgy method. The introduction of Ni can inhibit the reaction between W and barium–calcium aluminates (Ba–Ca aluminates) during the impregnation process of the matrix. After cathode activation, the surface Ba: O molar ratio is 0.88:1.00, much higher than the Ba dispenser cathode without Ni doping. The XPS results of the cathode surface showed that the metallic Ba appeared on the activated cathode surface, forming dipoles with oxygen, and effectively reducing the cathode surface work function. The pulse electron emission current density at 1100°C_b (brightness temperature) was 18.26 A/cm², and the calculated work function was 1.97 eV. It has a low evaporation rate and the accelerated lifetime test predict a lifetime of over 160000 h. First-principles calculations showed that the charge transfer and dipole moment in the NiW–BaO system were both increased compared to the Ba dispenser cathode, thus improving the emission performance of the Ni–W mixed matrix cathode.

Keywords

nickel / inert barrier layer / passivation / evaporation / dispenser cathode

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