Influence of background pressure on beam extraction and focusing dynamics in a small PIG ion source

Abstract Vacuum degradation in the beam device is a critical concern in high-precision ion beam processing, as it perturbs beam optics and reduces energy efficiency. While pressure effects in the transport region are mitigated by space charge compensation and charge exchanges, the dynamics in the extraction region of low-energy sources under elevated vacuum conditions remain insufficiently understood. In this paper, we experimentally investigate the influence of background pressure on beam focusing and extraction efficiency in a small penning ion gauge (PIG) ion source, where the extraction section constitutes a dominant part of the beamline. Our results reveal that, under elevated pressure conditions, the current impinging on the suppression electrode increases with higher suppression voltages—a trend contrary to the low-pressure conditions. We demonstrate that this current loss increment is attributed to the trapping of low-energy ions generated via charge exchange and momentum transfer, rather than to the conventional electrostatic over-focusing mechanism. These findings indicate that elevated background pressures primarily accelerate device degradation through collision-induced beam loss, necessitating rigorous vacuum management for stable operation.