A Study On The Relationship Between Coil Effective Inductance And The Displacement To The Test Mass In Superconducting Gravity Instruments

The magnetic interaction between the superconducting coils and the test mass in Meissner state plays dominate roles in superconducting gravity instruments. For example, it is used to levitate the test mass and it determines the stiffness of the oscillator of superconducting accelerator and the transfer function of displacement detection. The interaction can be described by one parameter called effective induction of the coil, from which, all of other parameters can be induced. Therefore, measuring the relationship of the coil effective induction with respect to the test mass displacement is of high importance in the instrument design.In this thesis, an apparatus has been built in liquid helium temperature to measure the effective inductance at varied test mass displacement. In the measurement, the ultraprecision micro-displacement stage is used to drive the test mass to given displacement. Meanwhile, a precise LCR meter is used to measure the coil induction. During the measurement, the boundary condition of the coil is exactly mirrored to the designed superconducting gravity instruments. This low temperature apparatus can not only be used to study the relationship between coil inductance and displacement to the test mass, it can also be used to carry out other low temperature experiment.Using the apparatus, the curve between coil inductance and the displacement to the test mass is measured. The measurement results show good repeatability and high signalnoise ratio. Furthermore, the results comply well with the theoretical calculated data. According to the result, the levitation distance of test mass and the stiffness of the oscillator are calculated. These parameters are of high importance for the design of superconducting gravity instruments.