Session: Isolation, Suspension, Vacuum and Other Technologies (February 23, 2010)  

Title: Low frequency vibration attenuation in the GGG apparatus

  Speaker: Suresh Doravari    

GGG is a laboratory version of the Galileo Galilei (GG) differential accelerometer, which is a proposed satellite experiment to test the Equivalence Principle (EP) to 1 part in 1017.   GG consists of two concentric cylinders, mechanically coupled to each other such that they are constrained to move in a plane perpendicular to their symmetry axis. This assembly, along with a sensor for detecting the relative displacement of the cylinders, is suspended within the satellite body and co-rotates with it in orbit.  As the masses are made of different materials, an EP violating interaction would appear as a relative displacement of the masses at orbital frequency (1.75x10-4 Hz).  The laboratory version is designed to demonstrate the dynamics of such a supercritical non-rigid rotor and the sensitivity reachable with such an apparatus.  The design of GGG (‘Galileo Galilei on the Ground’), therefore, consists of two concentric cylindrical masses, suspended in a pendular fashion from the ends of a vertical beam.  Their weight is supported by Be-Cu Cardanic joints such that they are weakly coupled to move in the horizontal plane and this assembly is set into rotation as in the satellite experiment.  If an EP violating interaction were present a relative displacement of the masses in phase with the Sun would be observed.   As the signal expected in GGG apparatus arises at diurnal frequency, effects due to ground tilt and diurnal temperature variations in the lab are dominant sources of noise.  Even though tilt and temperature are actively controlled, temperature dependence of the tilt sensor poses a serious limitation.  Therefore a passive tilt attenuator has been put in place in addition to the active one.   The various aspects of the active feed back and preliminary results obtained with the passive suspension will be presented.

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