Secondary Electron Emission Issues

[keniley1]

Reason

Secondary electron emission coefficients can be both species and material dependent. Right now we set a single value for the entire domain, which is fine for the moment but doesn't quite work for more complicated domains.

Design

Maybe the simplest path is to just have secondary electron emission coefficient(s) be an input parameter for the secondary electron BCs. It could be a single value or a vector of values so each ion can have its own SE coefficient on a boundary if the user wants.

If we want to keep it as a material property, it's also easy to include a GenericMaterialProperty that is restricted to a boundary so we have boundary-dependent SE coefficients. It's also not hard to include an additional material property in the HeavySpecies class so each species has its own coefficient. However, I don't know the best way to have both at the same time if we go the Material route. Either way, it should be taken out of GasElectronMoments and treated separately.

The secondary electron energy may also be remodeled at the same time to either be a user-input value (again, boundary-dependent) or specified based on the work function of that material.

Impact

This will allow boundaries to have more realistic secondary electron emission coefficients! Different species and surfaces will have different electron emission coefficients.