PDF(Pubmed)
Abstract：
The X-ray Integral Field Unit (X-IFU) is one of the two focal plane detectors of Athena, a large-class high energy astrophysics space mission approved by ESA in the Cosmic Vision 2015-2025 Science Program. The X-IFU consists of a large array of transition edge sensor micro-calorimeters that operate at ~100 mK inside a sophisticated cryostat. To prevent molecular contamination and to minimize photon shot noise on the sensitive X-IFU cryogenic detector array, a set of thermal filters (THFs) operating at different temperatures are needed. Since contamination already occurs below 300 K, the outer and more exposed THF must be kept at a higher temperature. To meet the low energy effective area requirements, the THFs are to be made of a thin polyimide film (45 nm) coated in aluminum (30 nm) and supported by a metallic mesh. Due to the small thickness and the low thermal conductance of the material, the membranes are prone to developing a radial temperature gradient due to radiative coupling with the environment. Considering the fragility of the membrane and the high reflectivity in IR energy domain, temperature measurements are difficult. In this work, a parametric numerical study is performed to retrieve the radial temperature profile of the larger and outer THF of the Athena X-IFU using a Finite Element Model approach. The effects on the radial temperature profile of different design parameters and boundary conditions are considered: (i) the mesh design and material, (ii) the plating material, (iii) the addition of a thick Y-cross applied over the mesh, (iv) an active heating heat flux injected on the center and (v) a Joule heating of the mesh. The outcomes of this study have guided the choice of the baseline strategy for the heating of the Athena X-IFU THFs, fulfilling the stringent thermal specifications of the instrument.
摘要：
X射线积分场单位（X-IFU）是雅典娜的两个焦平面探测器之一，ESA在宇宙愿景2015-2025科学计划中批准的大型高能天体物理学太空任务。X-IFU由大量过渡边缘传感器微量热计组成，在复杂的低温恒温器内以〜100mK的速度运行。为防止分子污染并将灵敏X-IFU低温探测器阵列上的光子散粒噪声降至最低,需要在不同温度下操作的一组热过滤器(THF)。由于污染已经发生在300K以下，外部和更多暴露的THF必须保持在更高的温度下。满足低能有效面积要求，THF由涂覆有铝(30nm)并由金属网支撑的聚酰亚胺薄膜(45nm)制成。由于材料的厚度小，导热性低，由于与环境的辐射耦合，膜容易产生径向温度梯度。考虑到薄膜的脆弱性和红外能量域的高反射率，温度测量是困难的。在这项工作中,使用有限元模型方法进行参数数值研究，以检索雅典娜X-IFU的较大和外部THF的径向温度分布。考虑了不同设计参数和边界条件对径向温度分布的影响：（i）网格设计和材料，(ii)电镀材料，(iii)在网格上添加一个厚的Y形交叉，(iv)在中心注入的主动加热热通量和(v)网状物的焦耳加热。这项研究的结果指导了雅典娜X-IFUTHF加热的基线策略的选择，满足仪器的严格的热规范。
