Nikhef Cleanroom - October 6, 2023
This Geometric Anti-Spring (GAS) Filter is a low-frequency isolator, designed to reduce all sources of noises in vertical direction, for third-generation gravitational-wave (GW) detectors.
Begin load is ~380 kg.
It's built at Nikhef for the E-TEST (Interreg EMR) experiment in Liège. This E-TEST Filter consists of 8 blades of Maraging steel for its superior strength and toughness, necessary because these blades are placed under max stress for the max damping.
The Filter is calculated in advance, but a.o. small material deviations and the extreme requirements make this tuning necessary. Neighbor in the clean room is ATLAS, with the ITK upgrade END-CAP.
The test load will be mounted with a wire to the so-called 'Keystone'. Adding some weights to get the Filter working (in balance).
The keystone contains an LVDT (Linear Variable Differential Transformer). The oscilloscope is connected to this LVDT to measure the frequency of the Filter.
The goal is to achieve a frequency of 0.2 Hz in the system which means that the system 'moves' vertically once every 5 seconds. A frequency of 0.1 Hz would give better isolation, but experience shows that 0.1 Hz causes a lot of unwanted instability. If the frequency is still too high the blades have to be put under higher radial compression.
The stiffness is examined over a range of loads to get an idea of the stability of the Filter. The operating point is lower than expected and therefore some corrections are made
The final weight (the so-called Payload) on the Filter is 409kg