Initial operation at liquid-helium temperature of the M= 2270 kg Al 5056 gravitational-wave antenna of the Rome group

We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the antenna within less than I Hz and the two normal-mode frequencies are ?-=908.160 Hz and ?+=924.234 Hz with an applied electrical field in the transducer of 106 V/m. The corresponding overall merit factors areQ -=5.20·106 andQ +=7.25·106. The transducer has been tested up to an electrical field of 6·106 V/m: in this condition we have ?Q?104. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor via a transformer with turn ratio of 1000.