For 1D gas diode with uniform initial plasma concentration the program solves electrons and ions equations of continuity with Method of Lines (MOL) on uniform fine grid. Convective (drift) fluxes are splitted with Lax-Friedrichs expressions and reconstructed with fifth ordered Weighted ENO scheme (WENO5-LF).
Diffusion terms are taken into account independently.
Electric field strength is calculated simply with analytical solution avaiable of Poisson equations in 1D.
The border conditions includes secondary electron emission at cathode and isolation for ions flux at anode.
Due to using of WENO5 method your may simply apply coarser grid (nx = 80) without accuracy losses. Also the resulting MOL ODEs system isn't stiff so it'll be easy to solve via RK methods (i.e. ODE45 and ODE23).
Feel free to ask me any questions.