[论文解读] CHARA Array Delay Lines: Upgrades, Performance and Future Directions

Narsireddy Anugu, N. H. Turner+13 more|arXiv (Cornell University)|Feb 17, 2026

Astronomy and Astrophysical Research被引用 0

一句话总结

论文记录了 CHARA 延迟线从基于 VME 的系统向混合 FPGA-Linux 架构的中-2021 至 2024 年间升级，分析了调试问题与性能，并概述未来基线长度与模式的改进。

ABSTRACT

Long baseline optical and infrared interferometric arrays achieve high angular resolution and enable detailed astrophysical measurements. Interferometers have enabled observations of stars at various stages of evolution, as well as studies of binary stars, circumstellar disks, and active galactic nuclei. The CHARA Array is a long-baseline interferometric array at the Mount Wilson Observatory, USA. At the core of CHARA operations are the delay lines, which equalize the optical path length for all telescopes as the Earth rotates and compensate for optical path variations induced by atmospheric turbulence. We report recent upgrades and performance of the CHARA Array optical delay lines for high-precision interferometric observations. The legacy system had been operational for over two decades, and it was increasingly difficult to acquire replacement parts. Beginning in mid-2021, the control system underwent a major upgrade, replacing the aging VME-based architecture with a modern hybrid FPGA and Linux-based system; this modernization continued through the end of 2024. We describe hardware/software changes, the servo architecture, and lab/on-sky performance. The upgraded system achieves residual delay line cart tracking errors of $\sim12$~nm, the same level as the legacy system, and a control bandwidth of 100-130~Hz, allowing fringe tracking across the R, H, and K bands. Initial commissioning revealed key issues such as metrology time-tick jitter and vibration-induced visibility loss, which were diagnosed and resolved. We note ongoing and future efforts to extend baselines up to 1~km and support advanced observing modes such as dual-field interferometry and nulling. This paper is a reference for current and future use of the CHARA Array and for next-generation instrument design.

研究动机与目标

• 总结 CHARA 阵列延迟线控制系统的升级及其动机。
• 在实验室和星上测试中表征升级后的性能。
• 识别调试挑战与在过渡期间实施的缓解措施。
• 提出经验教训并概述 CHARA 延迟线和观测模式的未来方向。

提出的方法

• 描述遗留与升级后延迟线控制体系结构。
• 详细描述嵌入式计量 FPGA 系统和四层级联伺服环路（压电 PZT、VC1、VC2、步进电机）。
• 报告基于计量的时序、目标生成以及与 CHARA 主时钟的同步。
• 给出星上与实验室的性能指标，包括剩余时延和带宽。
• 讨论调试问题及其解决方案，附具体示例与图示。

Figure 1: Top: Overview of the CHARA Array. The six $1\,\mathrm{m}$ telescopes, named S1, S2, W1, W2, E1, and E2, are arranged in a Y-shaped configuration. Vacuum pipes transport starlight from the telescopes to the central beam combiner laboratory. Bottom: Photograph of the delay line system showin

实验结果

研究问题

• RQ1 升级为混合 FPGA-Linux 系统后，性能提升与限制有哪些？
• RQ2 升级后的系统是否能够达到所需的剩余时延跟踪精度和带宽，以在 R、H、K 带实现高条纹可见度？
• RQ3 在此类迁移过程中会出现哪些调试问题，如何有效缓解？
• RQ4 未来方向（如基线高达 1 公里、双场干涉、空合）」在升级后的基础设施上有哪些可行性？

主要发现

• 升级后残留轨道跟踪误差约为 12 nm RMS，与原系统性能相符。
• 升级后控制带宽为 100–130 Hz，使在 R、H、K 带实现条纹跟踪成为可能。
• 初始调试暴露了计量时钟抖动和振动引起的可见度损失，已进行诊断与缓解。
• 调试记录了具体修正措施，如纠正计量时钟抖动和重新调整 PID 增益，提升带宽与稳定性。
• 系统支持计划中的扩展，包括基线高达 1 公里和诸如双场干涉与空合等高级观测模式。

Figure 2: Schematic of the CHARA beam train feeding the SPICA (visible), MIRC-X (near-IR; SPICA-FT), and MYSTIC (near-IR) beam combiners. Only one telescope is shown. In the SPICA+MIRC-X+MYSTIC mode, the telescope dichroic (TelDic) directs 20% of the visible light to the AO/WFS and transmits the rem