Research On Polishing Technology Of Enhanced Magnetic Field Coupling Plasma

High-quality optical element surface is an important factor that restricts the performance of optical element.In the existing processing methods,plasma polishing can obtain high-quality optical surface,but when processing large-diameter optical elements,it is constrained by low processing efficiency.The processing cycle is long,and how to improve the efficiency of plasma polishing has become a research trend.The magnetic field is used to enhance the plasma density and modulate the plasma,and the control magnetic field is mechanically moved,which can complete the high-efficiency and high-quality processing of large-diameter optical components.In this paper,the enhanced magnetic field coupled plasma polishing technology is studied.The main research contents are as follows:First of all,for the design selection of the magnetic field geometry and permanent magnet material for the enhanced magnetic field,the magnetic field model is established by finite element analysis software,and the magnetic field model is verified,and the initial structure uniformity of the magnetic field is measured to be 95%.Optimize the magnetic field parameters to solve the geometric structure with the largest magnetic field strength and the best uniformity.When the magnetic pole spacing is 3.5 cm and the magnetic pole height is 2 cm,the magnetic field intensity is the largest.When the center pole is in a semicircular shape with R=1.2 cm,the magnetic field uniformity in the bar magnet area reaches 99%.Secondly,in order to obtain a more favorable plasma spatial distribution for polishing,the plasma spatial distribution generated by DC excitation and radio frequency excitation was explored,and the influence of different processing parameters on the plasma spatial distribution was studied.The results show that the spatial distribution of plasma generated by RF excitation is more suitable for plasma polishing.The plasma presents an ellipsoid distribution in space,and the generated processing function is Gaussian.The plasma electron density and electron temperature are positively correlated with the discharge power.The interpolar distance is positively related to the plasma density.Finally,the plasma distribution under magnetic field coupling and the polishing effect of plasma are studied.Under the condition of an external magnetic field,the electron density of the plasma increases to 5.45×10¹⁴/cm~3,and the charged particle trajectory changes from bombarding the material surface vertically under the action of the electric field to whirling motion on the material surface,angularly incident on the material surface.The polished shape of the material by the magnetic field coupled plasma produces an anisotropic inverted Gaussian shape in the two-dimensional x-z plane,and exhibits linear processing in the x-y plane,with good surface uniformity and a peak removal rate of 0.36μm/min.The research results show that the magnetic field can enhance and regulate the plasma,and the enhanced magnetic field coupled plasma polishing method can achieve high-efficiency and high-quality processing of large-diameter optical components,providing method support for the processing of hard and brittle optical materials.