Our results show that ionization processes are dominated by ion beam impact early in the ion beam pulse and by electron collisions after electron density is sufficiently high.
Stepwise ionization processes via excited levels are significant in ionization dynamics.
Measured spectra are influenced by non-equilibrium plasma states and opacity effects. We present a statistical procedure to estimate opacity broadening from Stark broadening. Implications on the experiments intending to trap and cool the antihydrogen are discussed.