Browsing by Author "Yu, Nan"

Now showing 1 - 9 of 9
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    Analysis of De-Laval nozzle designs employed for plasma figuring of surfaces
    (Springer, 2016-02-27) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Shore, Paul
    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.
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    Analysis of nozzle design used for the creation of advanced energy beam
    (American Society for Precision Engineering (ASPE), 2014-11-14) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Shore, Paul
    A variety of scientific and industrial projects, such as segmented ground based telescopes, compact space based observers, short wavelength microlithography and high power laser systems, demand metre scale ultra-precise surfaces [1]. Cranfield University and Loxham Precision have been engaged in developing effective fabrication of medium to large optical surfaces for the aforementioned applications. A process chain of three sequential machining steps has been proposed (Figure 1). These steps are ultra-precision grinding, robot based polishing and plasma figuring. The fabrication target is to reach a 20 hours cycle time for each stage of surface generation for 1.5m size optics: equating to 1ft2 per hour [2-3].
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    CFD analysis of an enhanced nozzle designed for plasma figuring of large optical surfaces
    (European Society for Precision Engineering and Nanotechnology, 2016-06-30) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Shore, Paul
    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.
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    Characterisation of a cold atmospheric pressure plasma torch for medical applications: demonstration of device safety
    (MDPI, 2021-12-14) Bennett, Adam; Urayama, Takuya; Papangelis, Konstantinos; Yuen, Peter W. T.; Yu, Nan
    The safety and effectiveness of plasma devices are of crucial importance for medical applications. This study presents the novel design of an atmospheric plasma torch (SteriPlas) and its characterisation. The SteriPlas was characterised to ascertain whether it is safe for application on human skin. The emission spectrum discharged from the SteriPlas was shown to be the same as the emission from the MicroPlaSter Beta. The UV emitted from the SteriPlas was measured, and the effective irradiance was calculated. The effective irradiance enabled the determination of the maximum UV exposure limits, which were shown to be over two hours: significantly longer than the current two-minute treatment time. The use of an extraction system with a higher flow rate appears to reduce slightly the effective irradiance at the treatment area. The NOx and ozone emissions were recorded for both SteriPlas configurations. The NOx levels were shown to be orders of agnitude lower than their safety limits. The ozone emissions were shown to be safe 25 mm from the SteriPlas cage. A discussion of how safety standards differ from one regulatory body to another is given.
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    Design of a motorised plasma delivery system for ultra-precision large optical fabrication
    (IOP, 2020-09-02) Zhou, Hui; Bennett, Adam; Castelli, Marco; Jourdain, Renaud; Guo, Jiang; Yu, Nan
    A unique plasma figuring (PF) process was created and demonstrated at Cranfield University for manufacturing extremely large telescopes. The atmospheric pressure processing is faster and more cost-effective than other finishing processes; thus, providing an important alternative for large optical surfaces. The industrial scale manufacturing of thousands of ultra-precision metre-scale optics requires a robust PF machine: this requirement is achieved by making the plasma delivery system (PDS) performance repeatable. In this study, a dedicated PDS for large optical manufacturing was proposed to meet the industrial requirement. The PDS is based on an L-type radiofrequency (RF) network, a power supply, and an inductively coupled plasma torch. However, the complexities of these technologies require an in depth understanding of the integrated components that from the PDS. A smart control system for the modified PDS was created. This novel control system aims to make the characterization process deterministic: by automating the tuning of critical electrical components in the RF network, which is achieved by the use of in-line metrology. This paper describes the main design aspects. The PDS was tested with a good correlation between capacitance and RF frequencies. The robust PDS design enables a stable discharge of plasma with a low deviation of RF signals during the total 15 hours' tes
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    Estimation of the power absorbed by the surface of optical components processed by an inductively coupled plasma torch
    (Elsevier, 2016-08-06) Jourdain, Renaud; Castelli, Marco; Yu, Nan; Gourma, Mustapha; Shore, Paul
    The focus of this work is the determination of the heat flux function -thermal footprint- of a plasma jet generated by an inductively coupled plasma (ICP) torch. The parameters of the heat flux function were determined through the correlation of modelling and experimental results. One surface of substrates was exposed to an impinging jet while the temperature changes of the unexposed surface was recorded, analysed and used to derive the parameters of the heat flux function. From a modelling viewpoint, a series of finite element analyses (FEA) were carried out to predict temperatures of substrate surfaces. From an experimental viewpoint, the plasma torch was powered by a 1 kW radio frequency signal generator tuned at 39 MHz. The ICP torch equipped with a De-Laval nozzle impinged the surfaces of selected substrates at atmospheric pressure. Three sets of experiments -static, single pass and multi passes- were carried out to determine and validate the numerical description of the plasma jet. Also this work enabled to determine the maximum intensity of the heat flux distribution and the total power absorbed by substrate surfaces. Finally, the most advanced numerical model was used to assess the effect of a bi-directional raster scanning strategy that was used for the processing of large optical components.
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    Investigation of power dissipation in a collimated energy beam
    (Trans Tech Publications, 2015-08-20) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Shore, Paul
    To satisfy the worldwide demand for large ultra-precision optical surfaces, a fast process chain - grinding, polishing and plasma figuring- has been established by the Precision Engineering Institute at Cranfield University. The focus of Cranfield Plasma Figuring team is the creation of next generation of highly collimated energy beam for plasma figuring. Currently, plasma figuring has the capability to shorten processing duration for the correction of metre-scale optical surfaces. High form accuracy can be achieved (e.g. 2.5 hours and 31 nm RMS for 400mm diameter surface). However, it is known that Mid Spatial Frequency (MSF) surface errors are induced when the plasma figuring process is carried out. The work discussed in this paper deals with the characterisation of highly collimated plasma jets delivered by the Inductively Coupled Plasma (ICP) torches. Also a computational fluid dynamics (CFD) model is introduced. This model is used to assess the behaviour of the plasma jet within the best known processing condition. Finally temperature measurement experiments were performed to determine the energy dissipated values that characterise best the ICP torch coil and its De-Laval nozzle.
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    Power dissipation of an inductively coupled plasma torch under E mode dominated regime
    (MDPI, 2021-07-18) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Xu, Fangda; Bennett, Adam; Fang, Fengzhou
    This paper focuses on the power dissipation of a plasma torch used for an optical surface fabrication process. The process utilizes an inductively coupled plasma (ICP) torch that is equipped with a De-Laval nozzle for the delivery of a highly collimated plasma jet. The plasma torch makes use of a self-igniting coil and an intermediate co-axial tube made of alumina. The torch has a distinctive thermal and electrical response compared to regular ICP torches. In this study, the results of the power dissipation investigation reveal the true efficiency of the torch and discern its electrical response. By systematically measuring the coolant parameters (temperature change and flow rate), the power dissipation is extrapolated. The radio frequency power supply is set to 800 W, E mode, throughout the research presented in this study. The analytical results of power dissipation, derived from the experiments, show that 15.4% and 33.3% are dissipated by the nozzle and coil coolant channels, respectively. The experiments also enable the determination of the thermal time constant of the plasma torch for the entire range of RF power.
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    Thermal analysis of energy beam using de-laval nozzle in plasma figuring process
    (Cranfield University, 2016-10) Yu, Nan; Jourdain, Renaud; Gourma, Mustapha; Shore, Paul
    In 2012, plasma figuring was proven to be an alternative solution for the fabrication of large scale ultra-precise optical surfaces. Indeed, plasma figuring was successfully demonstrated on a metre class glass surface. The process was exceptionally rapid but residual errors were observed. This thesis addresses this issue by proposing an enhanced tool that provides a highly collimated plasma jet. The enhanced tool is characterized by a targeted material removal footprint in the range 1 to 5 mm FWHM. The energy beam is provided by an Inductively Coupled Plasma (ICP) torch equipped with a De-Laval nozzle. This thesis focuses on characterization and optimisation of the bespoke plasma torch and its plasma jet. Two research investigations were carried out using both numerical and experimental approaches. A novel CFD model was created to analyse and understand the behaviour of high temperature gas in the De-Laval nozzle. The numerical approach, that was based on appropriate profiles of temperature and velocity applied to the nozzle inlet, led to a significant reduction of computational resources. This model enabled to investigate the aerodynamic phenomena observed from the nozzle inlet up to the processed surface. Design rules and the effect of changing nozzle parameters were identified. Sensitivity analysis highlighted that the throat diameter is the most critical parameter. A challenging power dissipation analysis of the plasma torch was carried out. Temperature and flow rate in key components of the torch were measured. Experimental results enabled to calculate the power dissipation values for RF power up to 800 W and for the entire series of designed nozzles. This work enabled to scientifically understand the power dissipation mechanism in the bespoke ICP torches. In addition, by comparing the intensity of the power dissipation values, one nozzle was clearly identified as being more capable to provide a highly efficient plasma jet.