低温下氦在晶体硅表面热适应系数的测量
Measurement of the thermal accommodation coefficient of helium on a crystalline silicon surface at low-temperatures
AI总结：
本文测量了低温下氦在晶体硅表面的热适应系数，发现温度低于20 K时系数大于0.7，提升了冷却功率，支持了自由分子流氦气冷却技术在引力波天文台中的应用。
摘要：
下一代引力波天文台预计将使用低温冷却的、摆悬挂的200 kg测试质量镜，该镜由晶体硅等晶体材料制成。在天文台运行期间，这些镜由于吸收高达一瓦特的激光辐射而受热。需要开发低噪声冷却技术。5 K下的低压氦交换气体可能有助于完成这一具有挑战性的任务。在这里，我们报告了氦适应系数$α(11\\,\mathrm{K}<T< 30\\,\mathrm{K})$的测量结果，该系数是氦原子在给定温度下与表面热化并从其反射时的概率。我们发现，当温度 < 20 K时，$α(T) > 0.7$，与最近使用的假设相比，这增加了冷却功率。因此，自由分子流氦气冷却的想法得到了支持，并可能在某些天文台概念中得到应用。
英文摘要：
Next-generation gravitational wave observatories are expected to use cryogenically cooled, pendulum-suspended 200 kg test mass mirrors from a crystalline material such as crystalline silicon. During operation of the observatories, these mirrors undergo heating due to the absorption of laser radiation of up to a watt. Low noise cooling techniques need to be developed. Low-pressure helium exchange gas at 5 K might contribute to the challenging task. Here, we report the measurement of the helium accommodation coefficient $α(11\,\mathrm{K}<T< 30\,\mathrm{K})$, which is the probability that a helium atom thermalises with a surface at a given temperature, when reflected from it. We find $α(T) > 0.7$ for temperatures < 20 K, which increases the cooling power compared to recently used assumptions. The idea of free molecular flow helium gas cooling is thus supported and might find application in some observatory concepts.
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