Multispecies plasma fluid simulation for carbon arc discharge

Understanding of the plasma physics in ablating carbon arcs plays an important role in the synthesis of carbon nanomaterials. In this paper, ablating carbon arc discharges in atmospheric pressure conditions are modeled using a one-dimensional fluid model. The mass and momentum conservation equations are solved for individual species in the arc, and intermolecular collisions between species are considered. Energy equations for the electrons and the heavy species are solved separately without the use of local thermodynamic equilibrium condition. The bulk plasma model is coupled with sheath models at the electrodes, which provide the sheath potential drop and electrode temperatures. A model to determine the size of the cathode deposit formation is also proposed using the principle of minimized energy loss. The numerical results show a qualitative agreement with experiments for the transition between low and high ablation modes that is observed when varying the total current or the anode diameter. While the numerical results suggest that the electron and heavy species temperatures are not in equilibrium, mainly due to the one-dimensional approximation of the model, it is shown that the radiative heat flux between the electrodes plays an important role in determining the anode temperature, which affects the ablation rate and in turn the bulk plasma.