降低液氦中的氢含量
Reducing the hydrogen content in liquid helium
摘要：
在正常大气压下，氦的沸点是自然界中最低的。因此，任何不需要的物质，如液氦中存在的杂质，都会被冻结并以固体形式存在。即使这些固体杂质可以很容易地通过过滤除去，液氦可能含有不可忽略的分子氢。这些痕量的分子氢是世界范围内已知问题的原因：在氦蒸发低温恒温器中用作流动阻抗以实现低于4.2K的温度的细毛细管的阻塞。这个问题严重影响了低温物理研究中使用的各种低温设备，并且由于氦气的高价格而导致时间和成本的巨大损失。在这里，我们首先介绍了氦气中氢分子含量的测量。随后提出了三种减少这种分子氢的措施：（i）提高氦气质量，（ii）在氦气净化器的内部净化器的再生循环的吹扫时间期间在大气中释放氦气，以及（iii）在封闭的氦气回路中安装两个催化转化器。这些措施已经消除了我们的低温阻抗堵塞发生了两年多。
英文摘要：
Helium has the lowest boiling point of any element in nature at normal atmospheric pressure. Therefore, any unwanted substance like impurities present in liquid helium will be frozen and will be in solid form. Even if these solid impurities can be easily eliminated by filtering, liquid helium may contain a non-negligible quantity of molecular hydrogen. These traces of molecular hydrogen are the causes of a known problem worldwide: the blocking of fine-capillary tubes used as flow impedances in helium evaporation cryostats to achieve temperatures below 4,2K. This problem seriously affects a wide range of cryogenic equipment used in low-temperature physics research and leads to a dramatic loss of time and costs due to the high price of helium. Here, we present first the measurement of molecular hydrogen content in helium gas. Three measures to decrease this molecular hydrogen are afterward proposed; (i) improving the helium quality, (ii) release of helium gas in the atmosphere during purge time for the regeneration cycle of the helium liquefier's internal purifier, and (iii) installation of two catalytic converters in a closed helium circuit. These actions have eliminated our low-temperature impedance blockage occurrences now for more than two years.
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