Numerical Simulation Of Trapezoidal Nanosecond Pulse Discharged Using PIC-MCC Model

Corona discharge is a phenomenon that high pressure gas media locally discharges in non-uniform electric field and has been widely used in the field of sterilization technology and semiconductor fabrication. The common corona discharge setups in research include needle-plate electrodes and co-axis electrodes. In this article, 1d3v PIC-MCC method is used to calculate argon nanosecond pulse discharge on needle-plate electrodes. Hydrodynamic model is used in most part of the simulation. Although it contributes to explain the process of discharging, it's hard to give precise information about characteristic properties for specific part and the dynamics of the charged particles. The parameters used in the calculation were summarized from balanced plasma (such as Thompson parameter, diffusion coefficient), which apparently can't be applied to point charging situation that is unbalanced plasma. Many similar researches applied direct rectangular impulse to needle electrode, but the nanosecond pulses used in the experiments all had the rising edge and falling edge. We chose trapezoid impulse in our research.In the article, we investigate the characteristics of the rinsing edge and falling edge of external nanosecond pulse on the needle electrodes and analyze different voltage effects on it. In the simulation, we chose Ins,2ns and 5ns for rising edge and falling edge for researches and give the electric field distribution, net charge distribution, plasma density distribution and electron energy distribution. It shows that during discharge there is area around the needle filled with strong space charge field and it's just the opposite of the external electric field which acts to counteract it as well and the shorter the rinsing edge is, the stronger the space charge field, the thinner the plasma shell is and the higher the final plasma density is. If the rinsing edge is Ins, it's 100 times larger than 5ns. At the beginning of the discharge, electrons gain energy from external electric field and electron energy distribution moves to high energy part. With the increasing ionization collisions, electrons lose more energy than they got and distribution moved to the low energy part. The shorter the rinsing edge is, the faster the change is.As the nanosecond pulse falling, space charge field takes advantages and when the external voltage drops to zero, the electric field reverses and under its effect, there is an increase for plasma density and the max electron density moves to the cathode. As the increase of external voltage, gas discharge between the electrodes becomes more dramatically and final plasma density increases.