Influence of Background Pressure on Beam Extraction and Focusing Dynamics in a small PIG Ion Source

Degradation of vacuum levels in the beam extraction region is a critical concern in precision ion beam processing, as it disrupts beam optics and reduces energy efficiency. While pressure effects in high-energy accelerators are often mitigated by space charge compensation, the dynamics in the extraction region of low-energy sources under poor 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. Our results show that, under high-pressure conditions, the current impinging on the suppression electrode increases with higher suppression voltage—a trend contrary to typical focusing behavior. We demonstrate that this efficiency drop is attributed to the trapping of low-energy ions generated via charge exchange and momentum transfer, rather than by the conventional electrostatic over-focusing mechanism. These findings indicate that pressure increases primarily accelerate device degradation through collision-induced beam loss, necessitating rigorous vacuum management for stable operation.