Two-Dimensional Self-Consistent Electron-Monte - Ion-Fluid

A two-dimensional (2D) Self-consistent Electron -Monte-Carlo and Ion-Fluid (SEMCIF) simulation is employed to study the nonequilibrium particle transport and local and nonlocal ionization mechanisms in helium rf glow discharges. The consideration of the "additional" radial field in the 2D model significantly affects the characteristics of the electron transport such as electron current density, ionization rate, average electron energy, and power deposition of electrons. The 2D results further indicate the important role of the radial field in the nonequilibrium radial transport effect. This radial field increases the electron average energy and ionization collision probability, and hence, through the local and nonlocal ionization mechanisms, enhances the ionization rate in the inner region of the bulk in the rf glow discharges. The low-pressure helium glow discharges between two parallel-plate electrodes are modeled and compared by three different SEMCIF schemes: two-dimensional (2D), one-and-a-half dimensional (1HD), and one-dimensional model, each assuming a cylindrically symmetric geometry. Results from the 1D SEMCIF simulation demonstrate comparable agreement with other published results and are used as a benchmark for the comparison with the other two SEMCIF schemes, the 1HD and 2D. The 2D SEMCIF simulation demonstrates the distinctive transport characteristics of the glow discharges due to their nonequilibrium radial effect. By considering an effective radial space-charged field in the simulation, the 1HD model is configured in a one dimensional space (in the axial direction) and in a single ring in the radial direction; therefore, the model will not only comprise the partial radial effect but will also reduce the number of particles required for the 2D model. The results from these three models show significantly different characteristics due to the radial effect. Consequently, the profiles from the 2D results reveal higher average electron energy and higher bulk ionization rates occur in the bulk than those from the other two schemes. Other related phenomena, such as the phase difference of the radial-sheath between 2D and 1HD models, the sheath width, the cooling process (negative power deposition) in the boundary of the axial-sheath and the bulk region among the three SEMCIF schemes, are also discussed.