  We characterized the pulsed Rydberg-positronium production inside the AEgIS
(Antimatter Experiment: Gravity, Interferometry, Spectroscopy) apparatus in
view of antihydrogen formation by means of a charge exchange reaction between
cold antiprotons and slow Rydberg-positronium atoms. Velocity measurements on
positronium along two axes in a cryogenic environment (10K) and in 1T magnetic
field were performed. The velocimetry was done by MCP-imaging of photoionized
positronium previously excited to the $n=3$ state. One direction of velocity
was measured via Doppler-scan of this $n=3$-line, another direction
perpendicular to the former by delaying the exciting laser pulses in a
time-of-flight measurement. Self-ionization in the magnetic field due to
motional Stark effect was also quantified by using the same MCP-imaging
technique for Rydberg positronium with an effective principal quantum number
$n_{eff}$ ranging between 14 and 22. We conclude with a discussion about the
optimization of our experimental parameters for creating Rydberg-positronium in
preparation for an efficient pulsed production of antihydrogen.
