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Long-wavelength UV-LEDs and charge management in the detection of gravitational waves in space

Yuandong Jia, Yinbowen Zhang, Suwen Wang, Guozhi Chai, Zemin Zhang, Yi Zhang, Hongxin Li, Shuanglin Huang, Hongqing Huo, Zongfeng Li, Yun Kau Lau

TL;DR

This work assesses long-wavelength UV-LEDs for continuous charge management in space-based gravitational-wave detectors by employing a cubic test-mass model that imitates LPF sensor surfaces. It demonstrates that UV-LEDs with wavelengths longer than 255 nm can stabilize the test mass near zero potential and support rapid discharge, with 275 nm emerging as the optimal choice for both fast response and long-term stability. Ground experiments reveal wavelength-dependent photoelectron emission, achieving equilibrium potentials around −12 mV for 275 nm and maintaining stable potentials within a few millivolts over four hours, corresponding to a charge noise near $10^{-13}\ \mathrm{C}/\sqrt{\mathrm{Hz}}$ at $0.1$ mHz. The findings suggest incorporating multiple UV‑LED wavelengths in future spacecraft charge-management systems, with 275 nm as a strong candidate for continuous control and rapid discharge in varying solar conditions.

Abstract

For the charge management system in gravitational wave detection missions, a continuous discharge strategy is considered by continuously illuminating a test mass (TM) with weak light in such a way to strike a balance between the charging and discharging rates and at the same time avoids the requirement for frequent activation of charge measurements. Built on experiments by one of us based on a simple parallel plate model for inertial sensor, in the present work a more sophisticated inertial sensor model that mimics the surface properties and work function of a cubical TM of an inertial sensor in space (like that of the LISA Pathfinder) is employed to study bipolar charge management system that utilizes UV-LEDs with peak wavelengths of 269 nm, 275 nm, 280 nm, and 295 nm that are longer than the standard 255 nm commonly employed for direct TM illumination. Experimental results indicate that the 275 nm UV-LED achieves optimal performance, maintaining the TM potential closer to zero and at the same time accommodates both rapid discharge and continuous discharge strategies. The present work provides useful input in the future study of system design and optimization for the charge management system.

Long-wavelength UV-LEDs and charge management in the detection of gravitational waves in space

TL;DR

This work assesses long-wavelength UV-LEDs for continuous charge management in space-based gravitational-wave detectors by employing a cubic test-mass model that imitates LPF sensor surfaces. It demonstrates that UV-LEDs with wavelengths longer than 255 nm can stabilize the test mass near zero potential and support rapid discharge, with 275 nm emerging as the optimal choice for both fast response and long-term stability. Ground experiments reveal wavelength-dependent photoelectron emission, achieving equilibrium potentials around −12 mV for 275 nm and maintaining stable potentials within a few millivolts over four hours, corresponding to a charge noise near at mHz. The findings suggest incorporating multiple UV‑LED wavelengths in future spacecraft charge-management systems, with 275 nm as a strong candidate for continuous control and rapid discharge in varying solar conditions.

Abstract

For the charge management system in gravitational wave detection missions, a continuous discharge strategy is considered by continuously illuminating a test mass (TM) with weak light in such a way to strike a balance between the charging and discharging rates and at the same time avoids the requirement for frequent activation of charge measurements. Built on experiments by one of us based on a simple parallel plate model for inertial sensor, in the present work a more sophisticated inertial sensor model that mimics the surface properties and work function of a cubical TM of an inertial sensor in space (like that of the LISA Pathfinder) is employed to study bipolar charge management system that utilizes UV-LEDs with peak wavelengths of 269 nm, 275 nm, 280 nm, and 295 nm that are longer than the standard 255 nm commonly employed for direct TM illumination. Experimental results indicate that the 275 nm UV-LED achieves optimal performance, maintaining the TM potential closer to zero and at the same time accommodates both rapid discharge and continuous discharge strategies. The present work provides useful input in the future study of system design and optimization for the charge management system.

Paper Structure

This paper contains 7 sections, 2 equations, 3 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Principle of charge management
  3. Ground experiments of charge management.
  4. Experimental setup
  5. Photoelectrons emission.
  6. Continuous charge control.
  7. Conclusions.

Figures (3)

  • Figure 1: A schematic of photoelectron migration when the potential of the TM is positive and greater than the initial kinetic energy of the photoelectrons.
  • Figure 2: A schematic of photoelectron migration when the potential of the TM approaches zero and becomes comparable to the initial kinetic energy of the photoelectrons
  • Figure 7: TM equilibrium potential as a function of the bias potential for different wavelength UV-LEDs