极化HD靶的氢同位素蒸馏
Distillation of hydrogen isotopes for polarized HD target
摘要：
我们已经开发了一个低温蒸馏系统，以净化氢氘（HD）气体的极化HD目标在LEPS实验在SPring-8。HD气体中的少量邻位-H $_2$（$\sim$ 0.01%）在有效极化HD靶中起重要作用。由于在市售HD气体中存在1 $\sim$ 5%的H $_2$和D $_2$杂质，因此HD气体不可避免地被纯化至高达$\sim$ 99.99%。蒸馏系统有一个低温罐（17 $\sim$ 21 K），其中包含许多称为Heli-pack的小型不锈钢电池。将5.2摩尔量的商业HD气体进料到罐中。通过改变温度（17.5 K和20.5 K）和气体提取速度（1.3 ml/min和5.2 ml/min），我们进行了三次蒸馏运行。通过使用将四极质谱仪与气相色谱仪组合的气体分析系统来分析提取的气体。成功地获得了纯度大于99.99%的1 mol HD气体。作为蒸发器性能的指标的有效NTS（理论级数）被获得为37.2 $\pm$ 0.6。该值与设计值37.9合理一致。通过将最佳量的邻位-H $_2$掺杂到纯化的HD气体中，HD靶有望在良好控制的条件下被有效地极化。
英文摘要：
We have developed a cryogenic distillation system to purify Hydrogen-Deuteride (HD) gas for a polarized HD target in LEPS experiments at SPring-8. A small amount of ortho-H$_2$ ($\sim$0.01%) in the HD gas plays an important role in efficiently polarizing the HD target. Since there are 1$\sim$5% impurities of H$_2$ and D$_2$ in commercially available HD gases, it is inevitable that the HD gas is purified up to $\sim$99.99%. The distillation system has a cryogenic pot (17$\sim$21 K) containing many small stainless steel cells called Heli-pack. Commercial HD gas with an amount of 5.2 mol is fed into the pot. We carried out three distillation runs by changing temperatures (17.5 K and 20.5 K) and gas extraction speeds (1.3 ml/min and 5.2 ml/min). The extracted gas was analyzed by using a gas analyzer system combining a quadrupole mass spectrometer with a gas chromatograph. The HD gas of 1 mol with a purity better than 99.99% has been successfully obtained. The effective NTS (Number of Theoretical Stages), which is an indicator of the distillator performances, is obtained as 37.2$\pm$0.6. This value is in reasonable agreement with a designed value of 37.9. The HD target is expected to be efficiently polarized under a well-controlled condition by doping an optimal amount of ortho-H$_2$ to the purified HD gas.
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