Electrostatic Design of a Tunable Tetrode Electron Gun for Electron Beam Additive Manufacturing Device

The electron gun, as a critical device for emitting high-speed electrons, determines the electron beam current and quality in electron beam additive manufacturing (EBAM). In this article, a tetrode electron gun with a control electrode is designed to improve the quality and controllability of the electron beam. The control electrode, optimized by parametric simulation, provides secondary confinement of the electron beam. This confinement aims to reduce the beam spot size and emittance while decoupling spot size from the current. Specifically, the maximum attainable current reaches 200 mA, while the beam waist radius contracts to a mere 1.09 mm. The normalized emittance, a crucial parameter, measures at 1.536\times 10^{-{7}}~\text {m}\cdot \text {rad} . Furthermore, stability analysis of the electron gun explores the influence of electrode potential on its performance. By co-regulating the bias voltage and the control voltage, the electron beam current can smoothly rise to 200 mA while maintaining the beam spot radius of 2 mm. This article indicates the tetrode electron gun's potential for precise control, thereby improving the quality and precision of high melting point alloy additive manufacturing processes.