Latest SN&N Publications
A Passive UV-Based System for Discharging the Test Masses of Ground Based Gravitational Wave Detectors
S. Buchman, S. Wang, S. Saraf
9/24/2025
We present a passive ultraviolet charge management system for the fused silica test masses in ground-based laser interferometric gravitational wave detectors. The system uses photoelectron emission from low work-function gold coatings illuminated by 275 to 285 nm UV light to neutralize unwanted electric charges on the electrically floating test masses, maintaining them at zero potential relative to surrounding components. Two implementation schemes are described: 1. distributed discharge tabs illuminated by UV LEDs mounted at the eight surrounding earthquake stops, and 2. a conductively linked tab design enabling a centralized discharge on the test mass barrel, with potential extension to annular coatings around the high-reflectivity and anti-reflective surfaces. Experimental results show photoelectric currents greater or equal to 10 pA for 1.0 mW of incident UV, enabling discharge rates greater than 10V/s for a 1 pF capacitance..
Performance Variance of Low Noise Resonant Capacitance Bridges While Replacing their Ungapped MnZn Ferrite Cores
S. Saraf, S. Buchman, C.Y. Lui, S. Wang, J. Lipa
7/25/2025
Precision AC resonant capacitance bridges, with a planar printed circuit board transformer using an ungapped MnZn ferrite core, have shown excellent noise performance in high-precision measurements. As many applications use an ensemble of bridges, consistency of performance is critical to the functionality of the systems. If part of the same manufacturing batch and scaled to the same frequency, the noise performance of the ferrite cores at 293 K has a weighted mean variance of <0.3%, with all the cores within a +/- 1% band.
Noise and Low-Temperature Performance
for a Sub-Attofarad Capacitance Sensor for
Precision Measurements, Including Applications in Gravitational Wave Detectors
S. Saraf; S. Buchman; C. Y. Lui ; S. Wang; J. Lipa
03/29/2024
We describe the design principles, fabrication, and characterization of a precision AC resonant capacitance bridge (RCB) sensor, based on a resonant differential planar printed circuit board transformer with a solid (ungapped) MnZn ferrite core, demonstrating a short-term sensitivity at 293 K of 0.225 ± 0.005 aF/√Hz at around 120 kHz resonance frequency and 1 Hz Fourier measurement frequency. At 120 K, the RCB short term noise sensitivity is 0.118 ± 0.005 aF/√Hz. We compare the ungapped configuration to five different RCBs: three with a core gap of 65 μm and two with a core gap of 130 μm..
Flight and ground demonstration of reproducibility and stability of photoelectric properties for passive charge management using LEDs
S Buchman, T S M Al Saud, A Alfauwaz, R l Byer, P Klupar, J Lipa, C Y Lui, S Saraf, S Wang and P Worden
12/22/2022
Charges as small as 1 pC degrade the performance of high precision inertial reference instruments when accumulated on their test masses (TMs). Non-contact charge management systems are required for the most sensitive of these instruments, with the TMs free-floating, and their charges compensated by photoelectrons in a feedback loop with a TM charge measurement. Three space missions have successfully demonstrated this technique: the Relativity Mission, Gravity Probe-B launched in 2004, the LISA Pathfinder launched in 2015, and the UV-LED mission launched on SaudiSat 4 in 2014; with the first two using the 254 nm Hg discharge line and the last one a set of 255 nm UV-LEDs. UV-LEDs represent a significant improvement over the discharge sources, in terms of reliability, lifetime, switching speeds, power consumption, weight, and volume.
Two Approaches for the Passive Charge
Management of Contactless Test Masses
S Wang, S Saraf, J Lipa, D Yadav and S Buchman
09/02/2022
Free floating test masses (TM) of inertial reference instruments accumulate charge mainly through the triboelectric effect during separation from their housings and, if in the space environment, from cosmic radiation. These charges will degrade the accuracy of high sensitivity accelerometers and drag-free sensors. We demonstrate in ground testing two passive bipolar charge management systems using photoelectrons emitted from gold coated surfaces under illumination by ultraviolet light emitting diodes (UV-LEDs) with 255 nm, 275 nm, and 295 nm central wavelengths.
Passive Charge Management of Contactless Test Masses using Ultraviolet LEDS with Fast and Slow Photoelectrons
S. Saraf, S. Wang, S. Buchman, and J. Lipa
08/12/2022
Free floating Test Masses (TM) of inertial reference instruments accumulate charge during separation from their housings and cosmic radiation. We demonstrate two charge management systems using fast and slow photoelectrons emitted from gold coated surfaces.
