Plasma Evolution during Antihydrogen Formation

The ASACUSA Collaboration plans to measure the ground-state hyperfine splitting in a beam of antihydrogen atoms [1]. We make antihydrogen by slowly introducing antiprotons into a positron plasma in a Penning-Malmberg trap [2]. Our procedure is similar to ALPHA's [3], but we use 100 times more plasma particles. We find that efficient antihydrogen production requires increasing the 'mixing time' in proportion to the number of antiprotons. We also report the effect of plasma properties such as density and temperature on the overall efficiency and the fraction of atoms that escape the trap as a beam.

[1] Juhász, B., and E. Widmann. "Planned measurement of the ground-state hyperfine splitting of antihydrogen." Hyperfine Interactions 193.1 (2009): 305-311.

[2] Gabrielse, G., et al. "Possible antihydrogen production using trapped plasmas." Hyperfine Interactions 44.1 (1989): 287-293.

[3] Ahmadi, Mehran, et al. "Antihydrogen accumulation for fundamental symmetry tests." Nature communications 8.1 (2017): 681.