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Background <p>The stability and cooling performance of monochromators are critical factors determining the beam quality and productivity of synchrotron radiation beamlines. The existing monochromator at the 1W1B X-ray Absorption Fine Structure (XAFS) beamline of the Beijing Synchrotron Radiation Facility (BSRF) is now facing problems such as wear, flux drift, and reduced cooling efficiency after more than two decades of operation. Furthermore, the upcoming beam current upgrade to 900 mA makes a system capable of handling increased heat loads while maintaining high stability necessary.</p> Purpose <p>This study aims to develop a new water-cooled, vertical deflecting Double Crystal Monochromator (DCM) that achieves exceptional angular stability and effective cooling. The design focuses on eliminating vibration sources commonly associated with cooling water.</p> Methods <p>A novel gravity-fed water-cooling system was implemented to isolate the monochromator from pump-induced vibrations. The mechanical design was optimized by reducing adjustable degrees of freedom to enhance rigidity, and cooling pipes were routed through the Bragg axis to minimize vibration transmission. Stability was evaluated using a high-precision three-axis laser interferometer (sampling at 1 kHz) under various flow rates and Bragg angles. Numerical simulations, online rocking curve measurement and Cu XAFS scanning confirmed effective cooling.</p> Results <p>Flow tests confirmed a cooling capacity suitable for the upgraded heat load. Stability measurements demonstrated an average relative pitch stability of 3.0 nrad RMS and roll stability of 10.1 nrad RMS (0.5–500 Hz) with a cooling flow rate of 1.5 L/min in long term. The best recorded long-term pitch stability was 1.8 nrad RMS. Power Spectral Density (PSD) and Cumulative Power Spectrum (CPS) analysis confirmed the effective isolation of characteristic pump frequencies in the pitch vibration spectrum.</p> Conclusion <p>The combination of a high-rigidity mechanical design and a gravity-fed cooling system successfully achieves few-nanoradian stability, significantly exceeding typical performance for water-cooled instruments. This passive cooling approach offers a cost-effective and highly stable solution for sensitive optical components in synchrotron radiation facilities.</p>

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Double crystal monochromator with gravity-fed water-cooling achieving sub-5 nrad stability for the upgraded XAFS beamline at BSRF

  • 期刊论文

  • 发表日期：

    2026年4月29日

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  • Hao Liang,
  • Zheng Sun,
  • Shengqi Chu,
  • Shaofeng Wang,
  • Yang Yang,
  • Lu Zhang,
  • Yuanshu Lu,
  • Dashan Shen,
  • Huamin Qu,
  • Ming Li,
  • Yihang Yao,
  • Weifan Sheng,
  • Jing Zhang

摘要

Background

The stability and cooling performance of monochromators are critical factors determining the beam quality and productivity of synchrotron radiation beamlines. The existing monochromator at the 1W1B X-ray Absorption Fine Structure (XAFS) beamline of the Beijing Synchrotron Radiation Facility (BSRF) is now facing problems such as wear, flux drift, and reduced cooling efficiency after more than two decades of operation. Furthermore, the upcoming beam current upgrade to 900 mA makes a system capable of handling increased heat loads while maintaining high stability necessary.

Purpose

This study aims to develop a new water-cooled, vertical deflecting Double Crystal Monochromator (DCM) that achieves exceptional angular stability and effective cooling. The design focuses on eliminating vibration sources commonly associated with cooling water.

Methods

A novel gravity-fed water-cooling system was implemented to isolate the monochromator from pump-induced vibrations. The mechanical design was optimized by reducing adjustable degrees of freedom to enhance rigidity, and cooling pipes were routed through the Bragg axis to minimize vibration transmission. Stability was evaluated using a high-precision three-axis laser interferometer (sampling at 1 kHz) under various flow rates and Bragg angles. Numerical simulations, online rocking curve measurement and Cu XAFS scanning confirmed effective cooling.

Results

Flow tests confirmed a cooling capacity suitable for the upgraded heat load. Stability measurements demonstrated an average relative pitch stability of 3.0 nrad RMS and roll stability of 10.1 nrad RMS (0.5–500 Hz) with a cooling flow rate of 1.5 L/min in long term. The best recorded long-term pitch stability was 1.8 nrad RMS. Power Spectral Density (PSD) and Cumulative Power Spectrum (CPS) analysis confirmed the effective isolation of characteristic pump frequencies in the pitch vibration spectrum.

Conclusion

The combination of a high-rigidity mechanical design and a gravity-fed cooling system successfully achieves few-nanoradian stability, significantly exceeding typical performance for water-cooled instruments. This passive cooling approach offers a cost-effective and highly stable solution for sensitive optical components in synchrotron radiation facilities.