Corona discharge, Plasma module

Hi everyone

What I'm trying to do right now is to simulate corona discharge with "DC discharge" branch of the plasma module. There are these two boundary conditions called "Electron outlet" and "Insulation" which should be totally different from each other (anyone can say that by hearing the names), but they're exactly the same in governing equation. My question is what is the difference between these two boundary conditions? for implementing a boundary condition which lets electrons flowing outward and not imposing anything else, what should I do in this module? What comes to my mind is to use the "Electron outlet" boundary condition, but the governing equation for this boundary condition implies the normal component of the electron flux is imposed to be zero (just like the "Insulation" boundary condition.) This is really confusing.

Also my understanding is I shouldn't use "Wall" boundary condition there, because there shouldn't any interaction between electrons and that boundary; actually in reality there is no boundary and the only reason for defining that boundary is to restrict the geometry.

Any insight or hint would be much appreciated.