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镱金属真空蒸发过程中束形器参数对束流特性的影响

The Influence of Collimator Paraments on the Beam Characteristic During the Metal Vacuum Evaporation Process

  • 摘要: 原子蒸气激光同位素分离过程中,蒸发原子束的密度、发散角等特性对分离、收集过程存在重要影响。本文基于直接模拟蒙特卡罗方法方法,对镱金属真空蒸发过程开展数值模拟研究,主要讨论了蒸发温度较低(700~820 K)时真空环境下束流在蜂窝板和狭缝板传输过程中出口束流特性的影响因素。研究结果表明,蜂窝板孔道长径比、壁面作用系数、入口束流稀薄程度等参数与束流约束效果正相关,且孔道出口束流平均发散角最小为22.5°;多层狭缝板结构中最后一层狭缝板结构参数、壁面作用系数、入口束流密度对束流约束效果显著。最后,总结了镱金属蒸发装置中束形器参数优化方法。研究结果对镱等低温下饱和蒸气压较高的金属蒸发装置设计有一定借鉴作用。

     

    Abstract: In the process of atomic vapor laser isotope separation (AVLIS), the density and divergence of the evaporative atomic beam have a great influence on the selective excitation and the collection sub-processes. Based on the direct simulation Monte Carlo (DSMC) method, the simulation of the ytterbium metal evaporation process was carried out. Two typical structures of collimators, microchannel, and multi-layer slit plate, were considered under different conditions with low evaporation temperature (700~820 K). The results show that, in the microchannel, the divergence angle of the beam and the transmittance of the channel could be decreased by increasing the length-diameter ratio and the ratio of diffuse reflection or decreasing the inlet density. Besides, the minimum average divergence angle is 22.5°. In the multi-layer slit plate structure, the divergence angle of the beam and the transmittance of the channel could be decreased by increasing the distance between different slits, the slit width, and the ratio of absorption or decreasing the inlet density. The structure and wall interaction parameters of the last layer all have a significant effect on the parameters of the outlet beam. Finally, the parameter optimization methods of the collimator in the ytterbium evaporation device were summarized. The results could be used as a reference for the design of the evaporation device of metal with a high saturated vapor pressure at low evaporation temperature.

     

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