Ionization in background_mcc collisions

[PhysicsDan]

Hello,

I am interested in using the background_mcc collisions to look at impact ionisation by electrons on an initially neutral background gas.

I have looked at the example for capacitive discharge (see snippet below).
From what I understand, if I start from a neutral He gas, this gas can be ionised to 1+, but no further. From reading the docs, I couldn't find any way to enable further ionisation of the gas e.g. to 2+.

Have I missed anything obvious?

Cheers,
Daniel

coll_elec.type = background_mcc
coll_elec.species = electrons
coll_elec.background_density = Ngas
coll_elec.background_temperature = Tgas
coll_elec.scattering_processes = elastic excitation1 excitation2 ionization
coll_elec.elastic_cross_section = ../../../../warpx-data/MCC_cross_sections/He/electron_scattering.dat
coll_elec.excitation1_energy = 19.82
coll_elec.excitation1_cross_section = ../../../../warpx-data/MCC_cross_sections/He/excitation_1.dat
coll_elec.excitation2_energy = 20.61
coll_elec.excitation2_cross_section = ../../../../warpx-data/MCC_cross_sections/He/excitation_2.dat
coll_elec.ionization_energy = 24.55
coll_elec.ionization_cross_section = ../../../../warpx-data/MCC_cross_sections/He/ionization.dat
coll_elec.ionization_species = he_ions

[roelof-groenewald]

Hi @PhysicsDan. Your reading is correct that the MCC routine does not allow ionization past 1+. However, we recently added impact ionization between kinetic species (as binary collision) in the DSMC module.
You can check out #5654 for some details. In that approach you would be able to add the $e + He^{1+} \to 2\times e + He^{2+}$ ionization process.

[PhysicsDan]

Ah that's great! I was just looking at that PR last week.

I will try out the DSMC module. Thanks for the help.