Analysis of De-Laval nozzle designs employed for plasma figuring of surfaces

Plasma figuring is a dwell time fabrication process that uses a locally delivered chemical reaction through means of an inductively coupled plasma (ICP) torch to correct surface figure errors. This paper presents two investigations for a high temperature jet (5000 K) that is used in the context of the plasma figuring process. Firstly, an investigation focuses on the aerodynamic properties of this jet that streamed through the plasma torch De-Laval nozzle and impinged optical surfaces. Secondly, the work highlights quantitatively the effects of changing the distance between the processed surface and nozzle outlet. In both investigations, results of numerical models and experiments were correlated. The authors' modelling approach is based on computational fluid dynamics (CFD). The model is specifically created for this harsh environment. Designated areas of interests in the model domain are the nozzle convergent-divergent and the impinged substrate regions. Strong correlations are highlighted between the gas flow velocity near the surface and material removal footprint profiles. In conclusion, the CFD model supports the optimization of an ICP torch design to fulfil the demand for the correction of ultra-precision surfaces.