Unable to include both field ionization and impact ionization

[Wang-Zhongwei]

Hi warpx team,

I tried to include both field ionization and impact ionization into the simulation but I realized with the current input structure I wasn't able to. My understanding is that field-ionized hydrogen will still be tracked by h_neutral container but with a different charge state. This would create a problem because DSMC mechanism will treat the electron having the same impact ionization cross section with both H+ and neutral hydrogen atoms (e_h_ion.species = electron h_neutral). It might be solved if the field ionized species besides electrons can be customized (h_neutral.ionization_product_species = electrons H) but currently only the ionized electrons are allowed.

# Species
particles.species_names = electron h_neutral hydrogen

# Field ionization on the neutral reservoir
h_neutral.charge = 0
h_neutral.physical_element = H
h_neutral.do_field_ionization = 1
h_neutral.ionization_product_species = electron  # only electrons are rerouted

# Ion container (separate species)
hydrogen.charge = q_e
hydrogen.physical_element = H
hydrogen.injection_style = none

# DSMC electron–neutral impact ionization
collisions.collision_names = e_h_ion
e_h_ion.type = dsmc
e_h_ion.species = electron h_neutral
e_h_ion.product_species = electron hydrogen
e_h_ion.scattering_processes = ionization
e_h_ion.ionization_cross_section = ../warpx-data/MCC_cross_sections/H/electron_impact_ionization.dat
e_h_ion.ionization_energy = 13.6