Study On Clean Purging Technology Under Low Vacuum Conditions In Single Channel Harmonic Conversion

As one of the key components of the high-energy laser device,the single channel harmonic conversion plays a critical role of frequency conversion in the inertial confinement fusion device.The realization and maintenance of its internal cleanliness will greatly affect the service life of optical components and the long-term stable operation of the high-energy laser device.In order to avoid serious oil pollution,the internal environment of the single channel harmonic conversion is designed for 1000 Pa low vacuum conditions.The single channel harmonic conversion is the component with the highest frequency doubling laser flux in the entire optical path.Optical components and other structural parts will inevitably suffer from laser damage due to long-term laser irradiation.And the particle pollutants produced by the damage will also cause serious secondary damage to the optical component.Therefore,achieving and maintaining ultra-high cleanliness under the condition of low vacuum inside the single channel harmonic conversion is of great significance for improving the service life of optical components and the load capacity of high-energy laser device.In this paper,the single channel harmonic conversion is the main research object,and the gas flow in its inner low vacuum conditions is studied based on computational fluid dynamics.Through the fluid simulation,the structure optimization design of the parallel airflow sweeping system and the gas knife protection system is carried out,and a stable parallel airflow organization form is formed in the single channel harmonic conversion.Therefore,the protection and cleanliness of the surface of the optical component and the realization and maintenance of the internal cleanliness of the device are realized.The service life of optical components is extended and the load capacity of the laser device is improved.Firstly,the gas flow state in the single channel harmonic conversion under low vacuum condition is distinguished by theoretical calculation,and the internal gas flow is determined to be a low-speed compressible continuous flow under low vacuum conditions.Pre-simulation processing such as fluid domain extraction and meshing is performed on the single-channel fluid calculation domain model,and the cleaning scheme of the parallel airflow sweeping system and the air knife protection system is determined.The sweeping scheme of the air inlet on both sides of the pressure stabilizing box and the air outlet on both sides of the return cavity is determined,which lays the foundation for the formation of the parallel airflow organization form and the study of structural optimization.Secondly,based on computational fluid dynamics,the parallel airflow sweeping system is simulated and optimized by using the controlling variable method.The influence of the parameters of the parallel air flow sweeping system on the internal flow field of the device is studied by analyzing quantitative indexes such as the average velocity,turbulence kinetic energy,turbulence intensity and vorticity,and the design reference values of the parameters of the sweeping system are determined.The results show that it is beneficial to the formation of the parallel air flow organization under the condition of low vacuum in single channel harmonic conversion when the height of the pressure stabilizing box is 120 mm,the height of the return cavity is 160 mm,the thickness of the rectifier plate and the reflux plate is 20 mm,the diameter of the rectifier hole is Φ10mm,the distance between the rectifier holes is 45 mm,and the opening ratio of the reflux plate is 60%.Finally,the attenuation law of particle pollutants in low vacuum environment is discussed.By calculating the maximum attenuation distance of particle pollutants,it is determined that the gas knife not only plays a protective role,but also needs to have the effect of sweeping and removing large-diameter particles.In this paper,the shape and speed change law of the air curtain formed by the free sweeping of the gas knife and the air curtain formed by sweeping optical components with gas knife in the low vacuum are studied.On this basis,the size of the air guide slot on the optical component frame is studied.It is determined that the width of the upper air guide slot is 12 mm and the width of the lower air guide slot is 30 mm,which ensures the air flow rate of the high-speed gas knife.On the basis of simulation research,a vacuum experimental vessel is designed.Two experiments are designed to study the speed attenuation of the air curtain in low vacuum and the effect of the gas knife on the removal of particles of different diameters on the surface of the optical component as the number of pulses increases.