Parametric transducers for the advanced cryogenic resonant-mass gravitational wave detectors

It is shown that a large improvement in liquid helium and ultra-cryogenical ly cooled resonant-mass gravitational wave detectors can be achieved throug h improved parametric transducers using either low loss sapphire dielectric resonators or niobium re-entrant cavities. Performance is analysed in rela tion to the existing resonant bar antenna Niobe and to massive spherical de tectors. Applied to Niobe, a millisecond burst sensitivity of order 10(-20) be achieved, corresponding to a spectral strain sensitivity of 2 x 10(-22) /root Hz With a 50 Hz bandwidth. Applied to an ultra-cryogenic 117 tonne sp herical detector made from CuAl, a spectral strain sensitivity of better th an 10(-23)/root Hz with a bandwidth of order 100 Hz can be achieved, which is close to the quantum limit. This sensitivity is comparable to that of ad vanced interferometer detectors at this frequency.