CFD analysis of an enhanced nozzle designed for plasma figuring of large optical surfaces

Abstract

For addressing the correction of Mid Spatial Frequency (MSF) errors on metre scale optical surfaces induced by sub aperture figuring process, a new generation of non-contact plasma based surface figuring tools has been created at Cranfield University. In this context, this paper presents an investigation that focuses on novel enhanced nozzles that were created for a Radio Frequency (RF) Inductively Coupled Plasma (ICP) torch. The characteristics of plasma jet delivered by prototype nozzle and a selected enhanced nozzle are compared using an in-house created CFD model. The enhanced nozzle design is based on the results previously obtained throughout a numerical analysis that enabled to identify the key design aspects of these nozzles. This enhanced nozzle is predicted to provide 12.5% smaller footprint and 15.5% higher temperature.