• More than 5 times increase in the accumulation efficiency has been demonstrated by a practical method for producing low energy positron pulses with a linear accelerator based positron accumulator. 　
• The new practical method for accumulating low energy positrons with a SiC remoderator can be applicable for a typical positron pulse width in the order of microseconds and it can result in the higher intensity of the low energy positron beams.　
• By introducing another positron accumulator with a longer confinement time after the present one, the highest intensity positron beams will be available, which will make it possible to conduct new experiments.

　Low energy positron beams have been used to investigate properties of defects in metals and semiconductors and to study solid state physics and fundamental physics with positrons and positroniums.

　Here, positrons are provided by electron linear accelerator, which inject high energy electrons into a target and the pair creations inside the target result in high energy positrons. Then, these high energy positrons with a large energy spread are injected into a moderator, which provides a useful low energy positron beams with a fixed energy. If the intensity of the low energy positron beams is increased, various new experiments will be made possible.

　In this research, more than 5 times increase in the accumulation efficiency has been confirmed by a practical method for producing low energy positron pulses with a linear accelerator based positron accumulator. The SiC remoderator plate with a center-hole of 2 mm square was introduced in the positron accumulator for the first time and it was observed that the accumulation efficiency was improved from ~ 5% to ~25%.

　It is expected that the use of well crystalized SiC with less defects will improve the efficiency further. Also, by introducing another positron accumulator with a longer confinement time after the present setup, the higher intensity pulsed positron beams will be available, which will lead to new experiments like high density positroniums in a quantum condensed state, electron-positron plasma, and so on.

Reference
K. Michishio, H. Higaki, A. Ishida, and N. Oshima, Efficient positron trapping and extraction with a center-hole SiC remoderator, New Journal of Physics 24 (2022) 123039. https://doi.org/10.1088/1367-2630/acacbc