Using Rayleigh scattering method to diagnose the airflow field of Z-pinch gas-puff load
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摘要: 喷气负载是Z箍缩研究广泛采用的一种负载构型。在喷气负载中，准确诊断在施加电流之前气流场初始分布，对于控制内爆动力学不稳定性、提高X射线辐射输出具有重要意义。开展利用平面紫外激光瑞利散射法对喷气负载气流场分布进行诊断的可行性实验，获得了Z箍缩喷气负载气流壳层随时间演化的图像信息，可以得出，喷气负载在靠近喷嘴端面1 cm区域内形成低密度空心区，同时径向呈现喇叭形外扩，与弹道气流解析模型计算结果较为吻合。实验中利用平面瑞利散射所获得的气体密度要高于模拟得到的密度3～4个量级，主要原因在于喷嘴气流场在低压及低温条件下形成了团簇结构，大大增强了光的瑞利散射效应。尽管如此，利用激光瑞利散射法仍可获得细节清晰的气流场相对密度分布。Abstract: The gas-puff load is widely used in the Z-pinch researches because of its simple installation and excellent performance. The initial distribution of the gas-flow mass of the puff load is the most important parameter for optimizing the nozzle size structure, improving the implosion dynamics process, and finally improving the X-ray radiation yield. In this paper, the feasibility of using Rayleigh scattering to diagnose the airflow field of a gas-puff is introduced. The time-resolved images of the airflow filed have been obtained. The images show that the gas flowing from the nozzle forms a hollow shell with lower density within the length 1 cm and the flow expands in radical direction like a horn. The experimental images are compared with the calculation results using the ballistic-gas-flow model, and it is found that the model can well illustrate the flow field if the parameters are selected properly. The density of the airflow deduced from the Rayleigh scattering images is 3−4 orders of magnitude higher than the calculated results by ballistic transport model. The reason is that clusters are formed when the airflow field is in low temperature and low density, and they can greatly increase the Rayleigh scattering effect of gas flow. Nevertheless, the relative intensity distribution of the gas flow field can be obtained by the Rayleigh scattering with distinct details.
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Key words:
- Z-pinch /
- gas-puff /
- Rayleigh scattering /
- airflow distribution
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图 1 平面激光瑞利散射诊断喷气负载气流密度
Figure 1. Planar laser Rayleigh scattering is used for investigating the gas flow field of a gas-puff load
图 2 单层喷气负载气流场壳层不同时刻沿轴向剖面图
Figure 2. The r-z cross section images of a single gas-puff for different time with Rayleigh scattering method
图 3 实验结果与弹道模型计算结果对比
Figure 3. Comparison of the experimental results with the calculation results
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