Influence of pressure increase on high-emission of Os-coated M-type cathode

The influence of the pressure increase in a small multiple-beam klystron on the Os-coated M-type cathode, operating at a peak current density of 75 A/cm², was experimentally studied. The relationship between the pressure and the emission current density was plotted. According to the plot, at 1.0×10^-5 Pa, the current density was found to decrease by 1.96%; at 2.07×10^-4 Pa, the current density dropped by 10%, and the cathode was found to be dying. The leakage-induced degradation possibly originated from two major factors: one is the oxidation of Ba⁺(a)into Ba²⁺ on the surface, inversely affecting the surface emission; the other is the de-activation of the emission sites by ion sputtering, resulted from the leaked-in gases, oxygen in particular. We concluded that the leakage accounts for the emission degradation.