Transport dynamics in a high-brightness magneto-optical-trap Li ion source
Jamie Gardner, William R. McGehee, Mark D. Stiles, Jabez J. McClelland
Laser-cooled gases offer an alternative to tip-based methods for generating high brightness ions for focused ion beam applications. These sources produce ions by photoionization of ultracold neutral atoms, where the narrow velocity distribution associated with microkelvin- level temperatures results in a very low emittance, high-brightness ion beam. In a magneto- optical-trap-based ion source, the brightness is ultimately limited by the transport of cold neutral atoms, which restricts the current that can be extracted from the ion-generating volume. We explore the dynamics of this transport in a 7Li magneto-optical trap ion source (MOTIS) by performing time-dependent measurements of the depletion and refilling of the ionization volume in a pulsed source. An analytic microscopic model for the transport is developed, and this model shows excellent agreement with the measured results.