Cathode region of a transitory discharge inCO2. II. Spatio-temporal evolution

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Abstract
The inception of the cathode region is described by a second-order hydrodynamic model proposed in the preceding paper. The spatio-temporal variations of ionic and electronic densities, electron temperature, electron pressure, and electric field are provided. The double nonequilibrium between the electrons and the electric field due to strong electric field gradients and to secondary emission at the cathode is carefully studied. The way these electrons emitted by the cathode join the discharge is studied as a function of their emission temperature. The evolution of the electron temperature shows a maximum shifted from the field maximum. This leads to a difference between the non- equilibrium apparent ionization coefficient (deduced from the dynamic temperature) and the corresponding equilibrium coefficient. The maximum drop of the electric field and almost the main part of the processes that sustain the discharge occur in the transition zone situated between the cathode fall and the negative glow. In this zone, the electron energy density (electron pressure) is maximum involving a maximum in the reaction rates (the ionization, excitation rates, and the electron current density are maximum). When the electron current density increases, the electric field at the cathode increases as the cathode-fall length decreases.