Influence of the Surface Tungsten Distribution on the Emission Properties of Barium Tungsten Cathode

The porous tungsten matrixes of barium tungsten cathodes are prepared by spark plasma sintering (SPS). By adjusting the raw powder particle diameter and the porosity, the matrixes with different average distances between the pores are obtained. The microstructure and the emission performance of the barium tungsten cathode are analyzed using scanning electron microscopy (SEM), electron emission measurement system, and X-ray photoelectron spectroscopy (XPS). The average distances between the pores of three cathodes are 5.08, 5.74, and 6.91 mu m, respectively. The cathodewith a distance of 5.74 mu m has the best zero-field current density and the lowestwork function. With the increase in the pulsewidth, the variation rate of the current density for the 5.74-mu m cathode is the smallest, indicating the emission stability is the best. The best emission performance can be ascribed to the formation of the optimal Ba-O dipoles' coverage on the cathode surface.