Output for the example ALPHIE_Grid.
Found an issue when multiple injections were used with species with
different time steps.
Modification to the way to compute the ionization boundary:
The maximum number of ionizations is computed by eRel/eThreshold
(relative energy / threshold of ionization)
For each possible ionization, the probability of ionization is
computed based on the density of neutrals, cross section and effective
time divided by the number of maximum ionizations.
If an ionization takes place, the ionization energy is substracted
from the relative energy.
