Modeling, project, numerical simulation, and AES temperature diagnostics of an inductively coupled plasma torch for the deposition of high-purity fused silica for optical waveguide production

An inductively coupled plasma torch has been designed for the synthesis of high-purity, low-OH, fused silica in fiber optics preform production by means of a new technological process, within the framework of plasma outside deposition. The torch, working at atmospheric pressure, is attached to a 13.56 MHz, 5.4 kW RF generator; system geometry, inlet gas velocities, heat exchange, and electrical coil configurations have been selected in accordance with the physical modeling and numerical simulation results. Temperature, velocity, and electromagnetic fields have been computed by using a two-dimensional (2-D) fluid-magnetic code assuming LTE for the plasma. A 2-D treatment of electromagnetic field equations has been performed using boundary conditions, treating the torch as a point magnetic dipole, within a grid extending outside the plasma zone; results for the electric field in the torch will be presented in different steps of plasma initiation in test Ar discharges. Temperature diagnostics have been performed within atomic emission spectroscopy techniques: side-on experimental profiles have been treated through Abel inversion. Results obtained with the Boltzmann plot method (lateral and radial excitation temperature profiles) are presented, and conclusions are drawn concerning possible plasma deviations from LTE conditions. The first results on the deposition of soot silica will be described, together with torch operating conditions and reactive mixture O₂+SiCl₄ characteristics