Abstract

The nature of Dark Matter is one of the greatest unsolved mysteries of modern day physics. Although numerous observations on all scales of the universe hint towards its existence, a detection of possible Dark Matter particles has yet been unsuccessful. The direct search for Dark Matter particles via elastic scattering off nuclei is hereby a common detection technique used by experiments like CRESST. The required operating temperatures of ∼10mK for such experiments are achieved with Wet Dilution Refrigerators which rely on the use of liquid 4He. Due to rising helium prices of the past decades and high maintenance requirements, cost-efficient Dry Dilution Refrigerators, which use cryogen-less precooling with Pulse Tube Cryocoolers have become more and more attractive. These, however, introduce mechanical vibrations, which are drastically affecting the performance of the operated detectors.

Therefore, this thesis focuses on the vertical and radial mitigation of vibrations based on the suspension of detector modules at a single spring elastic pendulum. A highly decoupling spring is designed for the application in a new NUCLEUS Dry Dilution Refrigerator and operated at a specially constructed test stand, which simulates the vibration spectrum observed at a BlueFors BF-LD250 standard model dry dilution refrigerator. The conducted tests show a general reduction of vertical vibrations by up to two orders of magnitude for frequencies above 0.1Hz. Hereby, two problematic and mitigation preventing effects are identified. The high freedom of movement the suspension at a single spring provides, leads to several additional oscillation modes created by swaying or torsion of the attached detector module. Additionally, high accelerations, as they could be caused by a Pulse Tube Cryocooler, drastically reduce the decoupling properties of the spring at these frequencies. Nevertheless, applying the spring’s properties to a noise spectrum measured with a NUCLEUS prototype in a Wet Dilution Refrigerator and using the optimum filter for data analysis yields an approximation of improvement of the detector sensitivity by a factor of 8 in comparison to the undecoupled sensitivity in the frequency range from 0.1 to 50Hz. Hereby, even greater improvements are expected for higher frequency ranges. Finally, it is shown that the lowest possible damping ratio of a spring is most beneficial for a detector setup.

If all mitigation-hindering effects are overcome, a spring decoupling system consequently allows the usage of Dry Dilution Refrigerators.