Numerical Simulation of Kinetic Characteristics of Thermal Emission-Driven Argon Microarc Discharge at Atmospheric Pressure

Recent studies have shown that the thermal emission from the cathode plays a crucial role in the basic research on microarc discharge. In this work, a 1-D implicit particle-in-cell coupled with the Monte Carlo collision (PIC-MCC) method is adopted to simulate thermal emission-driven microarc discharge at atmospheric pressure. Two thermal emission models—thermionic emission (TE) model and thermofield emission (TFE) model—are applied to contrast and analyze the particle transport phenomena of thermal microplasma. Considering that the local electric field near the cathode affects the current densities and ionization can create sufficient space charge to modify the electric field, different current densities at the cathode and their contribution to the total current densities are evaluated under various conditions, including cathode temperatures ( ${T} _{\text {C}} = 2500~\sim ~3500$ K), applied voltages ( ${U} = 1~\sim ~30$ V), and gap sizes ( ${d} = 10~\sim ~100~\mu $ m). The electric field, maximum number density, and spatially averaged temperature of charged particles are also examined to study the interaction between thermal emission and discharge physics. Furthermore, the effects of secondary electron emission are analyzed to accurately predict electron emission in the microarc discharge. The results indicate the difference between thermal microplasma generated by TE and TFE becomes more pronounced as the gap size decreases, the cathode temperature increases, and the applied voltage increases due to the enhanced field emission (FE). In addition, gas breakdown occurs at a relatively lower voltage of 17 V for the two emission models because of the ion-enhancement effect. There exists a maximum at ${d} = 30~\mu $ m in current density at the cathode due to the difference between collision mean free path of electron and gap sizes. Besides, the secondary electron emission becomes more pronounced at higher cathode temperatures and larger secondary electron emission coefficients.