Hysteresis in Electron-Emission Current of an Axial Electron Gun Used for Evaporation of Metals

Hysteresis of electron-emission current from filament cathode was observed in a 10-kW axial electron gun used for evaporation of metals. It was observed that in the forward direction of power change (i.e., increasing electron-beam (e-beam) power), the required filament-heating current for a specified e-beam current was significantly higher than the filament current required in the backward direction (i.e., decreasing e-beam power). With appropriate calculations and experimental methods, it is established that this hysteresis arises primarily due to the energetic metal-ion bombardment on the electron-emitting area of filament in the electron gun. Finally, results of modification of the electron-emitting filament, such as drilling of a hole at its center to check the uncontrollability arising due to the bombardment of ions, are presented