The antenna EXPLORER is a cylinder of Al5056, it weights 2300 kg, it is 3 m long and it has a diameter of 60 cm. It is cooled at the temperature of liquid helium (4.2 K) and it operates at the temperature of 2 K, which is reached by lowering the pressure on the liquid helium reservoir. Its resonance frequencies are around 906 and 923 Hz.
This antenna is located at CERN, and it has been in continous operation over a long period of time.
Abstract of the paper ``Long-term operation of the Rome Explorer cryogenic gravitational wave detector``
(published on PRD 47,362-375, 1997):
We describe the cryogenic resonant gravitational wave detector of the Rome group, named Explorer, and report on its long term operation with sensitivity for short bursts in the range h~=7-10 x 10-19. Explorer has mass M=2270 kg and is equipped with a resonant capacitive transducer followed by a dc superconducting quantum interference device amplifier. It has been operated at T~=2.6 K in a cryostat cooled with superfluid helium. With a transducer voltage bias of 320 V (E=6.15 MV/m) the two resonant modes have frequencies of 904.7 and 921.3 Hz with coupled quality factors, respectively, of 0.77 x 106 and 1.0 x 106. The description of the experimental apparatus and of its calibration is followed by the analysis of the noise and the calculation of the expected sensitivity of the detector: h~=8 x 10-19 (under the assumption of bursts with duration of 1 ms). We then describe the data acquisition system and the techniques of data analysis, discussing the filtering algorithms. The last section reports the experimental results obtained during the operation of the detector from May 1990 to December 1991. During this period the data were recorded for more than two-thirds of the total time: we show the distributions of the data and the hourly averages of the sensitivity. The data taken from May 1991 to December 1991 have also been used to establish a new improved upper limit for the rate and strength of gravitational wave pulses; at h=2 x 10-17, for example, there are no more than 0.5 events/day as averaged over a period of 134 days.
Presentation given by Massimo Visco at the 4th Amaldi Conference, Perth, July 2001 (published on CQG 19:1905-1910, 2002):
``The Explorer g.w. antenna: recent improvements and performances`` pdf file
Power Point file: ppt file
Presentation given by Viviana Fafone at the 15th Sigrav conference, held in Frascati, Sep 2002. It is a general overview of the status and perspectives for resonant detectors:
``Bars and spheres`` ppt file
Presentation given by Massimo Bassan at the 15th Sigrav conference, held in Frascati, Sep 2002:
``Breaking the bandwidth barrier in resonant g.w. detectors (recipes for a broadband and sensitive antenna)`` ppt file