XRISM上Resolve X射线微量热计地面试验中观察到的机械制冷机噪声
Mechanical cryocooler noise observed in the ground testing of the Resolve X-ray microcalorimeter onboard XRISM
摘要：
低温探测器通常使用机械冷却器作为冷却链的一部分，以达到低于开尔文的工作温度。由机械冷却器引起的颤噪噪声是这些探测器的普遍和固有问题。我们已经观察到这种影响，在地面测试数据与解决仪器将在XRISM卫星飞行。Resolve是一种低温X射线微量热谱仪，在6 keV下所需的能量分辨率为7 eV。五个机械冷却器用于从环境温度冷却到约4 K：四个两级斯特林冷却器（STC）驱动名义上在15 Hz和焦耳-汤姆逊冷却器（JTC）驱动名义上在52 Hz。2019年，我们运行了飞行模型仪器两周，期间我们还在低温阶段（He罐）获得了低温恒温器内的加速度计数据。X射线探测器和加速度计的数据连续获得，而改变的JTC驱动频率，这产生了一个独特的数据集，用于研究如何从制冷机的振动传播到探测器。在探测器噪声谱中，我们观察到STC和JTC的谐波。更有趣的是，我们还观察到第4次JTC和第14次STC谐波以及第7次JTC和第23- 24次STC谐波之间的低频（<20 Hz）拍频。我们在这里提出了这些测量的描述和解释。
英文摘要：
Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonics noise caused by the mechanical coolers is a general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the Resolve instrument to be flown on the XRISM satellite. Resolve is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to about 4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule-Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (<20 Hz) frequency beat between the 4'th JTC and 14'th STC harmonics and the 7'th JTC and the 23--24'th STC harmonics. We present here a description and interpretation of these measurements.
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