Optimization study for the experimental configuration of CMB-S4
Optimization study for the experimental configuration of CMB-S4
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DOI：
10.1088/1475-7516/2018/02/009
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发表时间：
2017-02
影响因子：
6.4
通讯作者：
D. Barron;Y. Chinone;A. Kusaka;Julian Borril;J. Errard;S. Feeney;S. Ferraro;R. Keskitalo;Adrian T. Lee;N. Roe;B. Sherwin;A. Suzuki
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文献类型：
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作者：
D. Barron;Y. Chinone;A. Kusaka;Julian Borril;J. Errard;S. Feeney;S. Ferraro;R. Keskitalo;Adrian T. Lee;N. Roe;B. Sherwin;A. Suzuki
CMB第四阶段（CMB-S4）实验是下一代地面实验，将以前所未有的精度测量宇宙微波背景（CMB）偏振，探测膨胀的特征，宇宙中微子的性质，早期宇宙中的相对论热遗迹以及宇宙的演化。CMB-S4将由O（500，000）光子噪声限制探测器组成，覆盖广泛的角尺度，以探测早期和晚期宇宙的宇宙学特征。它将测量宽范围的微波频率，以将CMB信号从银河系和银河系外前景中清晰地分离出来。为了推进CMB-S4仪器设计的进展，我们建立了一个框架来优化仪器配置，以最大限度地提高其科学产出。该框架将成本和仪器模型与宇宙学预测工具相结合，并评估作为各种仪器参数的函数的科学敏感性。成本模型还允许我们在固定成本约束下进行分析，在资源有限的情况下优化实验的科学产出。在本文中，我们报告我们的第一个结果，从这个框架，使用简化的工具和成本模型。我们主要研究了两类仪器配置：直径范围从2-10米的大口径望远镜阵列，和混合阵列，结合联合收割机小口径望远镜（0.5米直径）与大口径望远镜。我们探索性能作为望远镜孔径大小的函数，探测器分布到不同的微波频率，调查策略和调查区域，低频噪声性能，以及混合配置的小口径和大口径望远镜之间的平衡。两种类型的配置都必须覆盖大（10度）和小（10 arcmin）角标度，性能取决于性能与角标度的假设。假设大口径望远镜可以对低频噪声实现良好的性能，则大口径望远镜的配置在孔径直径为4-6米左右具有较浅的最佳值。我们探讨了一些不确定性的工具模型和成本参数，我们发现，最佳有一个弱依赖于这些参数。混合配置显示了更广泛的最佳效果，对于大型望远镜来说，孔径范围为4-10米。我们还提出了两个strawperson配置作为本优化研究的结果，我们讨论了一些想法，以提高我们的简单的成本和工具模型在这里使用。这一分析有几个方面值得进一步改进。在我们的预测框架中，我们采用了一个简单的两个组件的前景模型与空间变化的幂律谱指数。我们统计地估计去透镜化性能，并且忽略非理想性，例如各向异性模式覆盖、边界效应和可能的前景残留。工具系统学，这是不占在我们的分析，也可能会影响概念设计。对工具和成本模型的进一步研究将是整个CMB-S4社区的主要研究领域之一。我们希望我们的框架将有助于估计这些改进在未来的影响，我们将纳入它们，以进一步提高优化。
The CMB Stage 4 (CMB-S4) experiment is a next-generation, ground-based experiment that will measure the cosmic microwave background (CMB) polarization to unprecedented accuracy, probing the signature of inflation, the nature of cosmic neutrinos, relativistic thermal relics in the early universe, and the evolution of the universe. CMB-S4 will consist of O(500,000) photon-noise-limited detectors that cover a wide range of angular scales in order to probe the cosmological signatures from both the early and late universe. It will measure a wide range of microwave frequencies to cleanly separate the CMB signals from galactic and extra-galactic foregrounds. To advance the progress towards designing the instrument for CMB-S4, we have established a framework to optimize the instrumental configuration to maximize its scientific output. The framework combines cost and instrumental models with a cosmology forecasting tool, and evaluates the scientific sensitivity as a function of various instrumental parameters. The cost model also allows us to perform the analysis under a fixed-cost constraint, optimizing for the scientific output of the experiment given finite resources. In this paper, we report our first results from this framework, using simplified instrumental and cost models. We have primarily studied two classes of instrumental configurations: arrays of large-aperture telescopes with diameters ranging from 2–10 m, and hybrid arrays that combine small-aperture telescopes (0.5-m diameter) with large-aperture telescopes. We explore performance as a function of telescope aperture size, distribution of the detectors into different microwave frequencies, survey strategy and survey area, low-frequency noise performance, and balance between small and large aperture telescopes for hybrid configurations. Both types of configurations must cover both large (∼ degree) and small (∼ arcmin) angular scales, and the performance depends on assumptions for performance vs. angular scale. The configurations with large-aperture telescopes have a shallow optimum around 4–6 m in aperture diameter, assuming that large telescopes can achieve good performance for low-frequency noise. We explore some of the uncertainties of the instrumental model and cost parameters, and we find that the optimum has a weak dependence on these parameters. The hybrid configuration shows an even broader optimum, spanning a range of 4–10 m in aperture for the large telescopes. We also present two strawperson configurations as an outcome of this optimization study, and we discuss some ideas for improving our simple cost and instrumental models used here. There are several areas of this analysis that deserve further improvement. In our forecasting framework, we adopt a simple two-component foreground model with spatially varying power-law spectral indices. We estimate de-lensing performance statistically and ignore non-idealities such as anisotropic mode coverage, boundary effect, and possible foreground residual. Instrumental systematics, which is not accounted for in our analyses, may also influence the conceptual design. Further study of the instrumental and cost models will be one of the main areas of study by the entire CMB-S4 community. We hope that our framework will be useful for estimating the influence of these improvements in the future, and we will incorporate them in order to further improve the optimization.