Example: calculation of cathode layer creation in Ar gas

The difference between electron and ion drift velosity leads to creation of the space charge in a gaseous discharge. The figures show time-space change in the electron and ion densities pending creation of cathode layer in corona discharge in 10 atm Argon. The black lines show the electron density (solid lone) and positive ion density (dashed line) at instant 8 ns after field applying. Electrons and ions are created due to inozation of the gas. The number of electrons and ions is the same, but their densities are different due to the difference of their drift velocities. The space charge, which is different of the densities distorts the applied electric field (red line – 28 ns, blue line – 55 ns). The disturbed electric field affects the ionization rate and changes the densities of the charged particles. This self-consistent process leads to creation of the cathode layer till 55 ns. The electron and ion densities are different in the layer up to 10 µm from the cathode. The electric field is different from the space charge free (Laplace) field.