Positron accumulation in the GBAR experiment

Abstract

We present a description of the GBAR positron (e(+)) trapping apparatus, which consists of a three stage Buffer Gas Trap (BGT) followed by a High Field Penning Trap (HFT), and discuss its performance. The overall goal of the GBAR experiment is to measure the acceleration of the neutral antihydrogen ((H) over bar) atom in the terrestrial gravitational field by neutralising a positive antihydrogen ion ((H) over bar (+)), which has been cooled to a low temperature, and observing the subsequent (H) over bar annihilation following free fall. To produce one (H) over bar (+) ion, about 1010 positrons, efficiently converted into positronium (Ps), together with about 10(7) antiprotons ((p) over bar), are required. The positrons, produced from an electron linac-based system, are accumulated first in the BGT whereafter they are stacked in the ultra-high vacuum HFT, where we have been able to trap 1.4(2) x 10(9) positrons in 1100 s.