Characterization at Cryogenic Temperatures of Piezostacks Dedicated to Fast Tuners for SRF Cavities

In the frame of the European CARE project, we designed and constructed three apparatus dedicated to full characterization of low voltage piezoelectric actuators. These piezostacks are integrated in fast active cold tuning systems (FACTS) and used for dynamic stabilisation of the resonant frequency of Superconducting RF (SRF) cavities. The three facilities we developed allow the measurement of electromechanical (capacitance, loss factor, displacement), thermal (specific heat, interfacial thermal resistance) and dynamic properties (effect of a preloading force) of industrial piezostacks for temperature in the range 2K-300K. Moreover, several piezostacks supplied by three different companies were subjected to ionizing radiation with fast neutrons beams at T=4.2K and for fluence in excess of 2.10¹⁴ n/cm². The test apparatus are described in details then the experimental data are analyzed and discussed.