Cooldown Strategies and Transient Thermal Simulations for the Simons Observatory
Cooldown Strategies and Transient Thermal Simulations for the Simons Observatory
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西蒙斯天文台的冷却策略和瞬态热模拟
DOI：
10.1117/12.2312679
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
他21名
中科院分区：
文献类型：
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作者：
Gabriele Coppi;他21名
西蒙斯天文台（SO）将使用一系列望远镜提供宇宙微波背景（CMB）的精确偏振测量，这些望远镜将覆盖从角分到数十度的角标度，包含60，000多个探测器，并在27 GHz和270 GHz之间的频带进行观测。SO将包括一个6米口径望远镜，最初与大约35,000个探测器沿着，以及一个半米口径折射相机阵列，与另外30,000多个探测器耦合。大口径望远镜接收器（LATR）与SO 6米交叉Dragone望远镜耦合，直径2.4米，重量超过3公吨，并且具有五个低温级（80 K、40 K、4 K、1 K和100 mK）。LATR通过包含低温光学元件和探测器的13个独立光学管与望远镜耦合。低温恒温器将由两个Cryomech PT 90（80 K）和三个Cryomech PT 420（40 K和4 K）脉冲管低温冷却器冷却，1 K和100 mK级由商用稀释制冷机系统冷却。第二个组成部分是小孔径望远镜，是一个直径为42厘米的单光学管折射照相机。SAT级的冷却将由两个Cryomech PT 420提供，其中一个专用于稀释制冷系统，将焦平面冷却到100 mK。SO将部署总共三个SAT。为了估计相机系统的冷却时间，考虑到它们的大小和复杂性，已经编写了基于隐式求解器的有限差分代码来模拟两个低温恒温器的瞬态热行为。这里给出的模拟结果预测LATR的冷却时间为35天。模拟表明，级之间的附加热开关将有效地分配冷却功率，并减少LATR达到其基准温度所需的时间。预计SAT将在一周内降温，达到SO设计目标。
The Simons Observatory (SO) will provide precision polarimetry of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales from arc-minutes to tens of degrees, contain over 60,000 detectors, and observe in frequency bands between 27 GHz and 270 GHz. SO will consist of a six-meter-aperture telescope initially coupled to roughly 35,000 detectors along with an array of half-meter aperture refractive cameras, coupled to an additional 30,000+ detectors.The large aperture telescope receiver (LATR) is coupled to the SO six-meter crossed Dragone telescope and will be 2.4 m in diameter, weigh over 3 metric tons, and have five cryogenic stages (80 K, 40 K, 4 K, 1 K and 100 mK). The LATR is coupled to the telescope via 13 independent optics tubes containing cryogenic optical elements and detectors. The cryostat will be cooled by two Cryomech PT90 (80 K) and three Cryomech PT420 (40 K and 4 K) pulse tube cryocoolers, with cooling of the 1 K and 100 mK stages by a commercial dilution refrigerator system. The secondo component, the small aperture telescope (SAT), is a single optics tube refractive cameras of 42 cm diameter. Cooling of the SAT stages will be provided by two Cryomech PT420, one of which is dedicated to the dilution refrigeration system which will cool the focal plane to 100 mK. SO will deploy a total of three SATs.In order to estimate the cool down time of the camera systems given their size and complexity, a finite difference code based on an implicit solver has been written to simulate the transient thermal behavior of both cryostats. The result from the simulations presented here predict a 35 day cool down for the LATR. The simulations suggest additional heat switches between stages would be effective in distribution cool down power and reducing the time it takes for the LATR to reach its base temperatures. The SAT is predicted to cool down in one week, which meets the SO design goals.