A Buffer-Gas Trap for the NEPOMUC High-Intensity Low-Energy Positron Beam.

Buffer-gas positron traps (BGT) have dramatically extended the scope of atomic and non-neutral plasma physics experiments involving antimatter. In these devices, a continuous beam of positrons enters a Penning-Malmberg trap, wherein inelastic collisions with low-density molecular gases allow for the efficient capture and cooling of the antiparticles. We describe a project with the goal of producing a single-component plasma containing more than 10⁸ low-energy positrons in a BGT using the NEPOMUC high-intensity positron beam. Details of the BGT are summarized. Results are presented for experiments in which an electron beam, with a similar intensity and energy spread to the remoderated NEPOMUC beam, is used to create an electron plasma. Studies include the influence of magnetic mirroring of the injected beam on the ultimate trapping efficiency and pulse stacking in a separate accumulator stage. This trap system is a vital component of the APEX project, which aims to create a low-temperature electron-positron pair plasma confined by the magnetic field of a levitated dipole.