A Vibration Decoupling System for TES Operation in the COSINUS Dry Dilution Refrigerator

COSINUS will be among the first underground experiments to operate Transition Edge Sensors in a dry dilution refrigerator, measuring temperature changes on the order of μK. A pulse tube cryocooler is used to cool down to 3K, trading simplified handling, by not using liquid noble gases, for an increased vibration noise level in the acoustic frequency range. As the signals measured with a TES are in the same frequency region, it is necessary to decouple the detectors from all possible noise sources. In COSINUS, a two-level passive decoupling system was developed and tested using piezo-based accelerometers. At the first level, the refrigerator is mechanically isolated from all external noise sources. For the second level an internal spring-based system was developed and tested on a mockup system. On the first level a reduction of the vibrational background up to a factor 4 below 10 Hz could be measured. On the second level a resonance frequency of 1.2 Hz with damping of higher frequencies was achieved.