  Antihydrogen is produced by mixing an antiproton and a positron plasma in a
cryogenic electromagnetic trap. The dominant antihydrogen formation mechanism
is three-body recombination, while the subsequent level population evolution is
governed by various processes, mainly collisional (de)excitation, ionisation
and radiative decay. In this work the impact of various positron plasma lengths
on the level population evolution is investigated. The main interest is the
ground-state antihydrogen atom yield. It is found that the ground state level
population shows different power-law behaviour at short or longer positron
plasma lengths.
