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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.

Electron (e−) and positron (e+) bunch characteristics were directly measured for the first time by using wideband beam monitors (WBMs) and a detection system at the e+ source of the SuperKEKB B-factory. Secondarily generated e− and e+ bunches after the e+-production target were identified in their dynamical capture process at locations of the WBMs under a two-bunch acceleration scheme. The longitudinal and transverse bunch characteristics, the time intervals between the e− and e+ bunches, the bunch lengths, transverse bunch positions, and bunch charges were simultaneously separately measured for each bunch as functions of the capture phase to investigate their dynamical capture process. The results show that quite symmetric behaviors of the e− and e+ bunch characteristics were observed. The new WBMs open up a new window for direct measurements of both e− and e+ bunches during their dynamical capture process and in the optimization procedure of the e+ bunch intensity in multidimensional parameter spaces at any e+ sources.

Abstract The direct simultaneous detection of electron and positron bunch signals was successfully performed for the first time with wideband pickups and a detection system at the positron capture section of the SuperKEKB factory. The time interval between the electron and positron bunches, their bunch lengths, and bunch intensities depending on the phase of accelerating structures were measured to investigate their capture process and to maximally optimize the positron intensity. The results show that the time intervals were measured in the range of 135–265 ps, and the line-order switch of the electron and positron bunches in the axial direction was clearly observed as a function of the phase. The positron (electron) intensity was maximized at the optimal phase (180 $$^{\circ }$$ ∘ shifted from the optimum). These series of measurements have never been experimentally conducted so far. It is demonstrated that the positron intensity can be systematically optimized with this system as functions of beam parameters in multidimensional spaces for any positron capture section.