Space charge effect in low-density ultracold ion bunches

Abstract

We have implemented an approach to investigate the space charge effect (SCE) in the ultracold ion bunch produced through the near-threshold photoionization of laser-cooled rubidium atoms trapped in a magneto-optical trap. The non-linear broadening of spatial profile of the ultracold ion bunch induced by SCE within the initial density range of 3.7 × 106–4.5 × 107/cm3 was explored using a time-of-flight spectrometer coupled with an imaging detector. A charged particle tracing simulation accounting for all pairwise ion–ion Coulomb interactions and an analytical model calculation, which predicts the dependence of the ion bunch density on time evolution and initial density, reproduced the experimental results successfully, indicating that the study could capture the evolution dynamics of ion bunch dominated by SCE. The aim of this work is to extend the investigation on SCE to extreme low-density regions of the order of 106 /cm3 and is expected to be useful in optimizing the performance of ultracold ion/electron sources.