Direct observation of positron capture process at the positron source of the superKEKB B-factory

Abstract

A direct simultaneous detection of electron ($$e^-$$ e - ) and positron ($$e^+$$ e + ) bunches was successfully performed using wideband beam monitors and a detection system at the $$e^+$$ e + capture section of the SuperKEKB B-factory. The time intervals between the secondary-generated $$e^-$$ e - and $$e^+$$ e + bunches were measured to investigate their dynamical capture process. The results show that the time intervals were measured in the range of 20–280 ps on average, and the line-order switch of the $$e^-$$ e - and $$e^+$$ e + bunches and their dynamical phase-slip process in the axial direction were clearly observed as a function of the capture phase of accelerating structures. In this report, the dynamical capture and phase-slip process for the $$e^-$$ e - and $$e^+$$ e + bunches under the two-bunch acceleration scheme is described in detail. This study opens up a new window for direct observation of the $$e^-$$ e - and $$e^+$$ e + capture process at any present and future $$e^+$$ e + sources.