Longitudinal ion-clearing mechanism in space-charge neutralization of low energy beams

In electron guns, generating high-intensity beams comes with the cost of increasing the number of secondary ions produced by the residual gas ionization which can be a limiting factor in the cathode lifetime. However, it is often overlooked that the longitudinal potential generated by the beam can be the main factor influencing secondary ions to drift back toward the source and limit the maximum beam intensity. Using 3D simulations, this paper shows how the flux of trapped ions depends on the beam parameters. The results provide a practical framework that can be used as a guide in the design of the electron gun focal point to mitigate the ion back bombardment. Published by the American Physical Society 2024