A simple centripetal force model for explaining the focusing effect of ion funnels

Abstract

The ion funnel is one of the key components for transferring ions from higher pressure into vacuum. While known for over twenty years and thoroughly analyzed by mathematical means and simulations, its working principle might be difficult to understand sometimes. In this work, we propose a simple thought experiment based on the centripetal force ions experience inside the ion funnel, which offers a simplistic explanation for the focusing force in an ion funnel. Our centripetal force model can predict the proportionalities of the resulting pseudopotential and should be a good didactical tool.