Transmissibility-Based Transfer Path Analysis of a Cryostat Interface for the CUPID Experiment

The CUPID (CUORE Upgrade with Particle IDentification) experiment searches for neutrinoless double beta decay using cryogenic detectors operating at milli-Kelvin temperatures. These systems are highly sensitive to mechanical vibrations introduced by cryocoolers, which can deteriorate calorimetric performance. In this work, we present the application of transmissibility-based Transfer Path Analysis (TPA) to a test cryostat devoted to CUPID. The method allows estimation of vibration transfer at structural interfaces without requiring force measurements, which are often impractical in cryogenic environments. Numerical simulations were performed at the 300 K plate interface using finite element models and component substructuring. The responses computed using transmissibility-based TPA showed excellent agreement with harmonic response simulations, validating the approach. This study establishes the basis for extending the methodology to colder stages (35 K, 3.5 K), where vibration coupling is more critical. Beyond validating the method, the results provide new insights into the dominant transfer paths at room temperature, thereby supporting the design of improved vibration isolation strategies for next-generation cryogenic detectors.