Numerical Simulation Of Short Pulsed Discharged Using PIC-MCC Model

Particle in Cell Monte Carlo Collision (PIC-MCC) is a kinetic simulation method which traces all the charged particle to obtain the plasma information we need. This simulation method can offer very detailed information of the plasma. Since the nanosecond pulse source being applied in the plasma experiments, there are urgency needs of numerical simulation to explain the experiments results. In this paper, the investigations are divided into three aspects: Pâ…¢processes with nanosecond rise time pulse simulation, atmospheric-pressure dielectric-barrier discharge with applied high-voltage nanosecond pulse simulation and nanosecond pulse needle-to-plane discharges at high pressure.Plasma immersion ion implantation (Pâ…¢) is a non-line-of-sight ion implantation method. It is a process in which a target object is immersed in a plasma and a series of high negative-voltage pulses (HNVP) are applied to the target in order to extract ions from the plasma and implant them into the target. Pulses with rise times of approximately 3 kV/ns can be realized with modern, state-of-the-art power supplies. For such steep rise-time pulses, the dynamic effects of the electrons should be taken into account; therefore, it is essential to employ a self-consistent model including both ion and electron dynamics to study Pâ…¢processes. Processes of plasma immersion ion implantation are analyzed numerically using 1d3v PIC-MCC model. The behavior of ions and electrons between the processed target and the source plasma is simulated after a nanosecond rise-time voltage pulse is applied to the target. The simulation results show that electron-neutral ionization collisions play a significant role in determining the magnitudes of the ion and electron densities when the pulse rise-time is very short, and that the plasma density can be enhanced many times. The physical mechanism for this phenomenon is explained in terms of the formation of a reverse electric field inside the plasma chamber.Dielectric-barrier discharge (DBD) is currently one of the most popular discharges to generate "cold" non-equilibrium plasma. Traditional DBD is generated by alternating current power with frequency in the range of 1-20 kHz, and consists of a number of microchannels, which can cause strong local heating effect limiting the application on some areas such as medical treatment, etc. Recently, nanosecond pulse DBDs have attracted wide interest. Applying pulse with the width of tens of ns and repetition frequency varying from single shot to 2 kHz, they found that DBDs can avoid the local overheating of microdischarges, get higher current density, and enhance the discharge efficiency. However, the limited diagnostic technology has difficulties in giving much needed information on the strong non-equilibrium plasma; the discharge physics are still not fully understood. A PIC-MCC simulation is employed to investigate how a sustainable atmospheric pressure single dielectric-barrier discharge responds to a high-voltage nanosecond pulse (HVNP) further applied to the metal electrode. The results show that the HVNP can significantly increase the plasma density. The ion-induced secondary electrons can give rise to the avalanche ionization in the positive sheath, which widens the discharge region and enhances the charged density drastically. However, the plasma density stops increasing as the applied pulse lasts over certain time; therefore, lengthening the pulse duration alone can't improve the discharge efficiency further. Physical reasons for these phenomena are then discussed.Corona discharge is a faint filamentary discharge, invariably generated by strong electric fields associated with small diameter wires, needles, or sharp edges on an electrode, and has a wide range of applications. A model of 1d3v PIC-MCC model was employed to simulate the argon discharges between the needle-to-plane electrodes at high pressure, in which a nanosecond rectangular pulse was applied to the needle electrode. The work focused on the investigation of the spatio-temporal evolution of the discharge versus the needle tip shape and working gas pressure. The discharge occurred mainly in the regions near the needle tip at atmospheric pressure; the small radius of the needle tip led to easy discharge. Reducing the working gas pressure gave rise to a transition from a corona discharge to a glow-like discharge along the needle-to-plane direction. The microscopic physical mechanism for the transition could arguably be attributed to the peak of high-energy electrons occurring before the breakdown; the magnitude of the number of these electrons determined whether the breakdown could take place.