LOW TEMPERATURE PROPERTIES OF PIEZOELECTRIC ACTUATORS USED IN SRF CAVITIES COLD TUNING SYSTEMS

High accelerating gradients (10MV/m for SNS, 33MV/m for ILC) at which SRF cavities will be operated in pulsed machines induce frequency shift much higher than the resonator bandwidth. This so-called Lorentz detuning should be compensated dynamically by means of an active piezo-tuning system. In the frame of the CARE project activities supported by EU, IPN Orsay participates to the development of a fast cold tuning system based on piezoelectric technology for SRF cavities operating at temperature T=2K. The aim of this study is the full characterization of piezoelectric actuators at low temperature including dielectric properties (capacitance, impedance, dielectric losses), radiation hardness tests (tolerance to fast neutrons), mechanical measurements (maximum displacement, maximum stroke) and thermal properties (heating, heat capacity). Results obtained in the temperature range from 2K up to 300K will be presented and discussed