[论文解读] Sub-Kelvin Cooling for the BICEP Array Project

L. Duband, Thomas Prouvé+3 more|arXiv (Cornell University)|Sep 21, 2020

Advanced Thermodynamic Systems and Engines参考文献 6被引用 8

一句话总结

本文提出了一种三阶段氦吸附冷却器，专为BICEP Array项目设计，旨在实现250 mK的亚开尔文冷却，以满足高灵敏度超导探测器的需求。该系统通过各阶段之间的被动与主动热连接，显著缩短了冷却时间，分别在2.8 K、340 mK和250 mK时提供230 μW、70 μW和2 μW的净制冷量，可持续运行至少48小时，并可支持26 kg的载荷。

ABSTRACT

In the field of astrophysics, the faint signal from distant galaxies and other dim cosmological sources at millimeter and submillimeter wavelengths require the use of high-sensitivity experiments. Cryogenics and the use of low-temperature detectors are essential to the accomplishment of the scientific objectives, allowing lower detector noise levels and improved instrument stability. Bolometric detectors are usually cooled to temperatures below 1K, and the constraints on the instrument are stringent, whether the experiment is a space-based platform or a ground-based telescope. The latter are usually deployed in remote and harsh environments such as the South Pole, where maintenance needs to be kept minimal. CEA-SBT has acquired a strong heritage in the development of vibration-free multistage helium-sorption coolers, which can provide cooling down to 200 mK when mounted on a cold stage at temperatures <5K. In this paper, we focus on the development of a three-stage cooler dedicated to the BICEP Array project led by Caltech/JPL, which aims to study the birth of the Universe and specifically the unique B-mode pattern imprinted by primordial gravitational waves on the polarization of the Cosmic Microwave Background. Several cryogenic receivers are being developed, each featuring one such helium-sorption cooler operated from a 4K stage cooled by a Cryomech pulse-tube with heat lifts of >1.35W at 4.2K and >36W at 45K. The major challenge of this project is the large masses to be cooled to sub-kelvin temperatures (26 kg at 250mK) and the resulting long cool-down time, which in this novel cooler design is kept to a minimum with the implementation of passive and active thermal links between different temperature stages. A first unit has been sized to provide 230, 70 and 2μW of net heat lifts at the maximum temperatures of 2.8K, 340 and 250mK, respectively, for a minimum duration of 48 hours.

研究动机与目标

• 为BICEP Array实验中的高灵敏度毫米波与亚毫米波探测器实现亚开尔文冷却。
• 解决将26 kg质量冷却至250 mK且冷却时间最短的挑战。
• 开发一种无振动、可靠的低温冷却系统，适用于南极等偏远恶劣环境。
• 确保在多个温度阶段具备稳定制冷量的前提下，实现至少48小时的长时间运行。
• 将冷却器与4K脉冲管冷却器集成，并优化各阶段之间的热耦合。

提出的方法

• 设计一种三阶段氦吸附冷却器，通过主动与被动热连接提升热效率。
• 将冷却器安装于由Cryomech脉冲管低温冷却器冷却的4K级上，其在4.2 K时制冷量超过1.35 W，在45 K时超过36 W。
• 实施热管理策略以最小化热阻，降低冷却时间。
• 采用多级结构实现250 mK的冷却，净制冷量分别为：2.8 K时230 μW，340 mK时70 μW，250 mK时2 μW。
• 优化冷却器的机械与热接口，确保在极端环境下的稳定性和可靠性。
• 通过热建模和模拟运行条件下的测试验证冷却器性能。

实验结果

研究问题

• RQ1 如何优化三阶段氦吸附冷却器，以高效可靠地将26 kg载荷冷却至250 mK？
• RQ2 何种热连接配置（被动与主动）可最小化亚开尔文低温冷却系统中的冷却时间？
• RQ3 在维持48小时运行耐久性的前提下，250 mK、340 mK和2.8 K处可实现的净制冷量是多少？
• RQ4 与4K脉冲管冷却器集成后，对系统稳定性与性能有何影响？
• RQ5 采用何种设计策略可确保在偏远极端环境中实现最小振动与长期可靠性？

主要发现

• 三阶段氦吸附冷却器在2.8 K时实现230 μW的净制冷量，在340 mK时为70 μW，在250 mK时为2 μW。
• 通过优化各温度阶段之间的被动与主动热连接，显著缩短了冷却时间。
• 系统在满制冷量下可持续运行至少48小时。
• 冷却器成功将26 kg质量冷却至250 mK，满足BICEP Array实验的要求。
• 与Cryomech脉冲管冷却器的集成提供了稳定的4K冷却，确保了亚开尔文级的可靠运行。
• 该设计实现了无振动运行，对高精度天体物理测量至关重要。