PIC/MCC Method And Its Applications In Gas Discharges

Recently, gas discharges are paid extensive attention worldwide, due to its outstanding performance in the many fields of the frontier science, such as biomedicine, material process, thermonuclear fusion, environmental purification, microwave propagation, and plasma propulsion. In order to predict and control the gas discharge characteristics more accurately, it is necessary to research the kinetic properties more deeply. Particle-In-Cell/Monte Carlo Collision(PIC/MCC) method trace the macro particles directly, with the inherent ability to calculate the kinetic properties self-consistently. Its unique superiority appears distinctly in the field of the gas discharge, while the general fluid method could not reflect the non-Maxwellian velocity distribution. Although its calculation efficiency is lower than the fluid method, PIC/MCC method is adopted directly more and more common in recent years because of the improvement of computer performance.In this paper, based on the physical properties, some new simulation technologies are proposed to improve the PIC/MCC method. PIC/MCC method is combined with the kinetic theory to research the physical properties of gas discharges, especially for the electron nonthermal and ion nonthermal kinetic properties. And some practical applications are also studied numerically and theoretically.The content includes the following parts: 1. The electron nonthermal properties in microwave discharges are studied by MCCparticle simulations and the kinetic theory. The particle simulation method isstudied for the electrons, and MCC particle simulations are carried out for theelectron energy distribution function(EEDF). Meanwhile, EEDF is calculated bythe Boltzman equation, and this theoretical result is compared with our MCCresults. Furthermore, the particle simulation method and the kinetic theory are usedto study EEDF with a magnetic field, and an approximate analytical solution isdeveloped. 2. A new MCC method is developed for ion-atom scattering, which is convenient tohandle and reflects the real scattering differential cross section precisely. Thismethod is used to simulate the ion velocity distribution. In tradition, ion-atomscattering is considered only by the charge exchange collision, which leads a largeerror for the transverse distribution. In this paper, a more real MCC model isdeveloped to improve the precision, and is verified by the experiment data andtheoretical study of the mobility and transverse distribution properties. Then, thisMCC method is used to simulate the transverse ion velocity distribution, theparallel ion velocity distribution, the joint ion velocity distribution, and the energyand angle velocity distribution, and compared to the experiment data. 3. The physical properties of the microwave breakdown is studied by the kinetic theoryand PIC/MCC numerical simulations. From Boltzman equation, the ionization rateand the breakdown threshold are calculated theoretically. And based on thebreakdown properties, a macro particle merge algorithm is developed and added tothe PIC/MCC code. Then, the ionization rate and the breakdown threshold byPIC/MCC is compared to the theory and the experiment. Furthermore, theionization rate with the magnetic field is studied by the effect of the magnetic fieldon the electric power. At last, the microwave propagation with the gas breakdownis studied by theory and PIC/MCC simulations. 4. The electron energy distribution function in the discharge of the negative hydrogenion source with filaments is studied by PIC/MCC simulations. Based on thenegative hydrogen ion source and the full 3-dimentional PIC/MCC platformCHIPIC, Nanbu model and Ta model of the coulomb collisions are compared forthe electron energy distribution function, and verified by experiment data.Furthermore, the effect of the gas density on the electron energy distributionfunction is studied by theory and verified by PIC/MCC simulations.