Study of iaboratory plasmas via particle simulation

Abstract

Particle simulation technique is applied to study various laboratory plasma phenomena, ranging from the neoclassical polarization drift in spatio-temporally sheared electric field in tokamak geometry, to kinetic characteristics of PDP and CCP discharges, to 3D progression of an etching profile. The neoclassical polarization drift is known to play a critical role in the space-time dynamics of a sheared radial electric field (geodesic acoustic modes and zonal flows) and its interplay with plasma turbulence in a toroidally confined plasma. In the present study, the neoclassical polarization drift of collisionless ions is studied numerically using the guiding center code XGC0. The emphasis is on the radial banana excursion in realistic tokamak geometry. It is found that the polarization drift velocity for single ions is not only a function of the time derivative, but also a strong function of the radial shear if the shear length is on the same order as the ion banana width. A comparison with an analytic investigation reveals that this effect is simply due to the finite banana averaging of the radial electric field. An approximate analytic formula has been presented for collisionless single banana ions in a conventional tokamak magnetic geometry. A three-dimensional profile simulator is developed for poly-Si etching in Cl2 plasmas. For the profile evolution, a level set method is utilized, where the moving surface is represented as a level set function. To obtain etch rates, the exposure of the surface point to bombarding ions has to be determined. We propose a simple, but efficient, scheme to determine the exposure. The simulator evaluates the angular energy distribution of the bombarding ions based on Miller`s sheath model. Simulation results are presented for hexahedron and cylinder types of masks. The improved 2D/3D PIC (particle-in-cell) code KCCP has been developed based upon the particle advance dynamics in the well-known XPDP code. Parallelization has been p...