The production rate of slow ground-state antihydrogen from antiproton and positron plasmas remains a central limitation for experiments on beams of antihydrogen. Three-body recombination in nonneutral plasmas is, so far, the most efficient formation mechanism, and is more effective in denser and colder plasmas. We present advances in plasma control and diagnosis in the ASACUSA Cusp experiment, leading to substantially increased antihydrogen yields and improved beam formation.
Antiproton and positron plasmas are confined in neighbouring wells of a nested Penning–Malmberg trap and brought into interaction using a slow-merge mixing scheme. By interrupting the mixing sequence and immediately diagnosing the individual plasma species, we measure the evolution of temperature, density, and radial distributions throughout the mixing process. This enables us to identify the key parameters governing antihydrogen formation. We find that both the total yield and the fraction of beam-like antihydrogen are maximized at low positron temperatures and for antiprotons passing through the positrons at a low radius. The positron temperature is controlled by purposefully heating the plasma by injecting noise into the trap, while the antiproton radius is controlled by the rate at which the electrostatic barrier between the plasmas is lowered.
Under optimized conditions, we achieve antihydrogen production efficiencies of 70–80% and yields on the order of millions of atoms per cycle, exceeding previous results by more than an order of magnitude . In addition, we observe a vast increase of beam-like antihydrogen relative to previous attempts with fewer or hotter positrons.
On behalf of the ASACUSA collaboration.