I intended to write than in my article then completely spaced about that part so I apologize for that.
I use the residual gas to impart momentum on the nozzle. So the gas remaining in the vacuum chamber is the fuel. The electrons strike the stray gas molecules when they drift into the coil as well as on their way out the nozzle. The large flux of electrons exiting the nozzle also carries some gas molecules with it. This is why the engine has a lot of gaps in its structure, to allow the fuel to drift in! Unfortunately, I do not have to tools to do the thorough analysis that is required to determine the actual thrust levels and what is the main cause of that thrust, so I can't get a definite answer as to what the primary mode of thrust generation is. My speculation is that it is the residual ions due to them having a much higher mass.
RE: Plasma Thruster!