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Study of a Compact Device for Water Attenuation Length Measurements

Junyou Chen, Jilei Xu, Yongbo Huang, Sibo Wang, Chuanshi Dong, Haoqi Lu, Changgen Yang, Yongpeng Zhang, Yi Wang

TL;DR

The study tackles the need for compact, online water attenuation length (WAL) measurements in large water Cherenkov detectors by developing a PMT-based device using LEDs, optical fibers, and an 8 m water tank. A ratio-based measurement scheme decouples geometric inverse-square effects from attenuation, and Toy Monte Carlo validation supports the approach. The prototype demonstrates WAL measurements up to 50 m, with long-term tests showing WAL evolution in concert with water purity; scaling analyses suggest a 30 m-length system could measure WAL up to ~100 m with ~8% uncertainty, enabling real-time monitoring for future detectors. This work provides a practical, scalable reference for ongoing water quality monitoring in next-generation large-scale detectors.

Abstract

This study presents the development and validation of a compact device for measuring the water attenuation length (WAL), utilizing photomultiplier tubes (PMTs), optical fibers, and light-emitting diodes (LEDs). An 8 m water tank and the device was constructed and validated in the laboratory. The device is capable of measuring WAL values up to 50 m. The stray light was blocked mainly by a custom-designed shutter. Toy Monte Carlo simulations were employed to evaluate the measurement uncertainty, which was found to be within reasonable limits. These simulations further indicate that the uncertainty can be reduced and more accurately predicted for a larger-scale device with a length of 30 m. Real-time monitoring was achieved by integrating the device into a water purification circulation system, providing a practical, scalable solution for WAL measurement in future large-scale water Cherenkov detectors.

Study of a Compact Device for Water Attenuation Length Measurements

TL;DR

The study tackles the need for compact, online water attenuation length (WAL) measurements in large water Cherenkov detectors by developing a PMT-based device using LEDs, optical fibers, and an 8 m water tank. A ratio-based measurement scheme decouples geometric inverse-square effects from attenuation, and Toy Monte Carlo validation supports the approach. The prototype demonstrates WAL measurements up to 50 m, with long-term tests showing WAL evolution in concert with water purity; scaling analyses suggest a 30 m-length system could measure WAL up to ~100 m with ~8% uncertainty, enabling real-time monitoring for future detectors. This work provides a practical, scalable reference for ongoing water quality monitoring in next-generation large-scale detectors.

Abstract

This study presents the development and validation of a compact device for measuring the water attenuation length (WAL), utilizing photomultiplier tubes (PMTs), optical fibers, and light-emitting diodes (LEDs). An 8 m water tank and the device was constructed and validated in the laboratory. The device is capable of measuring WAL values up to 50 m. The stray light was blocked mainly by a custom-designed shutter. Toy Monte Carlo simulations were employed to evaluate the measurement uncertainty, which was found to be within reasonable limits. These simulations further indicate that the uncertainty can be reduced and more accurately predicted for a larger-scale device with a length of 30 m. Real-time monitoring was achieved by integrating the device into a water purification circulation system, providing a practical, scalable solution for WAL measurement in future large-scale water Cherenkov detectors.

Paper Structure

This paper contains 9 sections, 4 equations, 11 figures.

Table of Contents

  1. Introduction
  2. Experimental setup
  3. Stray light shielding strategy
  4. Measurement scheme and data analysis
  5. Optimization of measurement scheme
  6. HDPE configuration for WAL long-term observation
  7. Water quality purification and Tyvek configuration for long-term WAL observation.
  8. Conclusion
  9. Acknowledgments

Figures (11)

  • Figure 1: The designed structure of water tank with size of 8 m × 0.6 m × 0.5 m, and eight PMTs were placed in it.
  • Figure 2: Internal view of the device under the (a) HDPE configuration and (b) Tyvek configuration. The PMTs with their aligned shutters are also visible.
  • Figure 3: (a) 3-dimensional view and (b) cross-sectional view of the core component of the WAL measurement device.
  • Figure 4: Side cross-sectional view of the diffuser. A single LED is positioned at the center of a nylon ball. An ABS shell, composed of three parts, is fastened together with screws.
  • Figure 5: Side cross-sectional view of a single PMT with its light guide and support bars. The green component in the shutter represents the optical fiber support structure.
  • ...and 6 more figures