A Study of Macroscopic Emission Non-Uniformity in Thermionic Cathodes Due to Profilimetry Variation

We develop a model to show that the micron-scale ridges due to surface machining of thermionic dispenser cathodes may cause significant angular variations in the macroscopic current density on ring-shaped cathodes as are commonly used in gyrotrons. The local field enhancement caused by the ridges resulting from machining gives an angular variation in current that may be pronounced. An explanation in terms of wobble of the cathode during machining and the eccentricity of the cathode cross-section can explain much of the observed variation