NULL TEST OF THE GRAVITATIONAL INVERSE SQUARE LAW WITH A SUPERCONDUCTING GRAVITY GRADIOMETER

The goal of this research was to develop a cryogenic gravitational null detector and to carry out a prototype test of the inverse square law with the new instrument on a laboratory scale of 1 - 10 m. The Laplacian of the Newtonian gravitational potential (DEL)('2)(phi), is source independent and is a null quantity in vacuum. It has, therefore, been proposed to perform a null test of the inverse square law by using a three-axis gravity gradiometer as a null detector. We have analyzed such a null experiment in detail using gravity sources of various kinds. Errors in the null detector such as misalignment between two differencing component accelerometers, orthogonality errors among three gradiometer axes, and a finite baseline effect have been analyzed. Various orientations and configurations of the detector and the source are suggested to suppress these errors.;To perform a test of the inverse square law, the single-axis gradiometer is mounted with its axis tilted from the vertial by an angle tan('-1(' ))SQRT.(2. The device is then turned incrementally by 120(DEGREES) around the vertical to carry the gradiometer from one axis to the other two axes of an orthogonal coordinate system. A lead pendulum weighing 1,600 kg forms a periodic monopole source of gravity. The gradiometer outputs are individually time-averaged over 2,000 s for each orientation of the gradiometer, and then are summed together. With somewhat crude metrology thus far, a preliminary test gives limits -0.012 (LESSTHEQ) (alpha) (LESSTHEQ) 0.036 for the coupling (alpha) of the nonNewtonian amplitude at the force rance (mu)('-1) of 1 m, when the force law is written as.;(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI).;A few metrological corrections were made to account for errors induced in turning the single-axis detector into the three orientations.;The single-axis portion of a three-axis superconducting gravity gradiometer has been completed in the course of this research. The theory of the superconducting gravity gradiometer has been generalized and put into a Lagrangian formulation. A condition for frequency-independent common mode balance is derived and verified in the experiment. This balance combined with a multi-stage vibration isolation scheme has enabled a stable operation of the gradiometer for prolonged periods. In a preliminary test, the gradiometer has exhibited a noise level of 1 - 2 E Hz('- 1/2) below 1 Hz, limited by seismic noise, where 1 E (TBOND) 10('-9) m s('-2) m('-1).