Energy and mass transport properties in the near-cathode region of atmospheric thermal plasma

As the main region where charged particles are accelerated by the electric field and accumulated near the cathode, the near-cathode region has significant non-local equilibrium characteristics and plays a crucial role in exploring the energy and mass transport properties of the thermal plasma from the arc column region to the hot cathode surface. However, there is a lack of universally adopted models and accepted theories for the study of the near-cathode region due to the complexity of the physical mechanisms involved in the sheath. According to the physical characteristics of the arc discharge, an external circuit is usually used to regulate the total current applied to the electrodes to maintain stable discharge. Therefore, the energy and mass transport properties of atmospheric thermal plasma driven by a current source coupled to an external circuit are investigated in this work to explore the transport mechanism of charged particles in the near-cathode region based on an implicit particle-in-cell Monte Carlo collision method. Firstly, the current-driven model in this work is compared with the present voltage-driven model and fluid model to verify the correctness of this model. Then, the collisions between charged particles and gas atoms inside the sheath are analyzed, and the spatial distributions of particle current density and particle heating rate inside the sheath are also studied. Finally, the variations of typical parameters of thermal particles under different current densities (106-107 A m-2) are analyzed, including maximum particle number density, maximum particle spatially-averaged temperature, sheath thickness, charge density and electric field strength in the cathode.