Effect of Insulator Geometry and Shield Electrode Design on High Voltage Breakdown in Vacuum

In this paper, the effect of insulator geometry and shield electrode design for a practical 270-degree bent, high power (60kV, 60kW) indirectly heated cathode-based electron gun has been investigated. This will ensure improved electron gun performance by reducing high voltage breakdown of electron gun insulators in vacuum. For this purpose, different insulator geometries: 1) Cylindrical 2) Positive Angled 3) Negative Angled and different metal shield electrode designs: 1) Cylindrical Ring 2) Conical Frustum and their combination have been modelled and simulated. This has been done for both the gun insulators: one connected between the ground plate and filament holder assembly (60kV insulator) and other connected between filament beam former and grid cup (1.5kV insulator). To achieve this, 3-D electrostatic gun simulations have been performed by using CST Studio v. 2020. Percentage reduction in the electric field strength at the triple junctions has been evaluated. It was found out that negative angled insulator geometry offered better high voltage performance as compared to positive angled geometry. Comparing all, conical frustum shield electrode design was found out to be the most optimum design.