Design Of An Atmospheric Pressure Plasma Optical Processing Torch And Diagnosis On Characteristics Of The Plasma Jet

With the widespread application of lenses and other optical components in optoelectronic civil products,astronomical observation systems,and high-energy laser systems,traditional optical processing technologies are difficult to meet the requirements of workpieces,including low cost,high efficiency,and no mechanical damage.Atmospheric pressure plasma optical processing based on the chemical etching principle,and that brings unique merits of high processing rate and no stress-induced damage,which is a promising rapid figuring technique for optical components.However,as the key device for generating plasma jet,the effects of the structure of the inductively coupled plasma(ICP)torch on its working stability and service life were still unknown.In addition,the efficiency and precision of optical processing are dependent on the removal function during processing,which is associate with the temperature,excitation,and morphological characteristics of the ICP jet.At present,the jet characteristics under working conditions cannot be quantitatively diagnosed.The working parameters of the torch as well as the remove function are determined through processing experiments,which is time-consuming and tedious.To solve the above problems,the paper investigated the effects of torch structure on the temperature,pressure and flow distribution in which through numerical simulation,which can be used to determine the torch structure with higher working stability and service life.Besides,a diagnosis system was established to realize the quantitative analyzation of the characteristics of ICP jet,which was helpful for determining the working parameters of the torch and the removal function during optical processing.The research contents and results were as shown below:(1)The demountable ICP torch was designed at first,and the effects of torch structure on the pressure,temperature,and flow field in which were investigated through numerical simulation.Based on the plasma channel model,the main structure of the torch was determined.The dielectic tubes in the torch were located on a special part and sealed by elastic sealing rings,which could effectively improve the coaxiality and installability of the torch.When the cyclone angles of the inclined holes and swirl slots were 10°and 20°respectively,the pressure inside the torch was relatively low while the gas flow was adjusted reasonably,which could improve the working stability of the torch.When the position of the near end of the coil was flush with the end face of the middle tube,the maximum temperature of the inner wall of the torch could be reduced to 800 K,which was conducive to extending the service life of the torch.(2)The diagnosis system was established and the quantitative diagnosis indices were determined according to the jet characteristics.The temperature and excitation characteristics of plasma jet were quickly obtained by the diagnostic system based on two-color thermometry and atomic emission spectrometry.According to the jet characteristics,the edge temperature region and effective excitation region were defined.The length(L and L’),half width(W and W’),tip offset distance(D and D’)and area ratio(A_R)of the two regions were proposed,realizing the quantitative diagnosis of the jet characteristics under working conditions.(3)The optimal working parameters were determined by the diagnostic jet characteristics,and the jet stability was verified by processing experiments.Results showed that RF power could significantly affect the indices of the effective excitation region in the jet by increasing the temperature and active species within it.The increase of etching gas flow rate could improve the excitation degree of the jet.Too large or too small flowrates of plasma working gas and cooling gas would reduce the jet stiffness.The optimal working parameters of the torch could be determined quickly according to specific logic.The processing results showed that the jet generated by the optimized working parameters had high processing stability,and the full width half maximum(FWHM)and maximum removal depth of the processing profile fluctuated within 0.17mm and 6.1 nm respectively,verifying the effectiveness of the diagnostic indices.(4)The estimation model of removal function based on the diagnostic jet characteristics was established,and the accuracy of that was checked by processing experiments.The practicability of estimating the removal function through the diagnostic jet characteristics was verified by the correlation analysis of jet temperature and processing profile on workpieces.The process parameters affected the processing profile by polynomial law when workpieces showed excellent optical performance,and the calculation method of processing profile was proposed with which.Furthermore,the prediction model of removal function was established by deconvoluting the calculation method,and the input of which was calculation width,effective processing length,processing distance,and processing speed.Experimental results of the removal function were close to the predicted results.The maximum deviations of the FWHM and the peak removal rate were 5.82%and 10.22%respectively,indicating that the removal function could be approximatively predicted through the diagnostic jet characteristics.