Abstract Two-stage Stirling cryocoolers (2ST cooler) produced by Sumitomo Heavy Industries, Ltd. have been launched into orbit on three satellites: the “AKARI (ASTRO-F)” infrared astronomical satellite, JEM/SMILES on ISS, and the “HITOMI (ASTRO-H)” X-ray astronomical satellite. A 2ST cooler compressor has a linear-ball-bearing system as a piston-supporting structure. The linear ball bearing system is a key components to realize a lower drive frequency (15 Hz), a long piston stroke (30 mm). Its typical cooling power is 200 mW at 20 K for the second stage and 1000 mW at 100 K for the first stage, with 90 W electrical input power. During the test of the “HITOMI” engineering model, the energy resolution of the detector was found to be degraded when cryocoolers were in operation. After investigation, it was found that micro vibration from 2STs caused the degradation. The continuum in the vibration spectrum propagated into sub-Kelvin region and generated thermal noise. The continuum has origin in linear ball bearing in the compressor. In the case of “HITOMI”, vibration isolators were introduced to resolve this issue. For future mission, we are required to reduce microvibration of cryocooler itself. Therefore, the piston support mechanism in the compressor was modified from linear ball bearings to triangle shape flexure springs in order to reduce the continuum in vibration spectrum. In order to achieve a long piston stroke (± 15 mm), the generated stress could be reduced to 400 MPa (Less than 1/2 of fatigue limit) or less even when the shape of the triangle shape flexure spring was devised and displaced by 15 mm. The typical vibration level has been reduced to 1 × 10 −5 Nrms2 / Hz or less at a frequency of 200 Hz or less and 1/10 times or less at 200 Hz to 600 Hz than that of a compressor with a linear ball bearing system. The cooling power is kept to 260 mW at 20 K, with 90 W electrical input power. This low vibration cooler is expected to be an improved cryogenic system for use in future projects with sub-Kelvin detectors.

中文翻译：

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两级斯特林低温冷却器微振动的改进

摘要 住友重工业株式会社生产的两级斯特林冷却器（2ST冷却器）已在三颗卫星上发射入轨：“AKARI（ASTRO-F）”红外天文卫星、国际空间站上的JEM/SMILES和“HITOMI” (ASTRO-H)”X 射线天文卫星。2ST 冷却器压缩机采用线性滚珠轴承系统作为活塞支撑结构。直线球轴承系统是实现较低驱动频率（15Hz）、长活塞行程（30mm）的关键部件。其典型冷却功率为第二级 20 K 时为 200 mW，第一级为 100 K 时为 1000 mW，电输入功率为 90 W。在“HITOMI”工程模型的测试中，发现在低温冷却器运行时探测器的能量分辨率下降。经过调查，发现来自 2ST 的微振动导致了退化。振动谱中的连续谱传播到亚开尔文区域并产生热噪声。连续体起源于压缩机中的线性滚珠轴承。在“HITOMI”的情况下，为了解决这个问题，引入了隔振器。为了未来的任务，我们需要减少低温冷却器本身的微振动。因此，压缩机中的活塞支撑机构从线性滚珠轴承修改为三角形挠性弹簧，以减少振动谱的连续性。为了实现长活塞行程（± 15 mm），即使设计三角形挠性弹簧的形状并将其位移为 400 MPa（小于疲劳极限的 1/2）或更低15 毫米。与带直线滚珠轴承系统的压缩机相比，典型振动水平在 200 Hz 或更低的频率下降低至 1 × 10 -5 Nrms2 / Hz 或更低，在 200 Hz 至 600 Hz 下降低至 1/10 或更低. 冷却功率在 20 K 时保持在 260 mW，电输入功率为 90 W。这种低振动冷却器有望成为一种改进的低温系统，用于未来带有亚开尔文探测器的项目。