Positron accumulation in the GBAR experiment

TL;DR

This paper describes the GBAR positron trapping apparatus and its performance, which is crucial for producing antihydrogen ions to test gravitational effects on antimatter.

Contribution

It introduces a novel positron trapping system combining a Buffer Gas Trap and a High Field Penning Trap with detailed performance metrics.

Findings

Trapped 1.4(2) x 10^9 positrons in 1100 seconds

Efficient positron accumulation from an electron linac system

System design supports antihydrogen ion production for gravity tests

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) atom in the terrestrial gravitational field by neutralising a positive antihydrogen ion (H+), which has been cooled to a low temperature, and observing the subsequent H annihilation following free fall. To produce one H+ ion, about 10^10 positrons, efficiently converted into positronium (Ps), together with about 10^7 antiprotons (p), 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 seconds.