Numerical Investigation on Low-temperature Superconducting Negative Spring in Magnetic Levitation

Abstract

A new terrestrial gravitational wave detector, Superconducting Omni-directional Gravitational Radiation Observatory (SOGRO), has been proposed in 2016 and seen as a competitive candidate of middle-frequency gravitational wave detector. In this detector, there are three pairs of 5-ton low-temperature superconducting test masses separated by 30–50 m and magnetically levitated by superconducting coils carrying persistent currents. To get a sensitivity of 10− 19 − 10− 20Hz− 1/2, the levitation frequency of the test masses need to be as low as 0.01 Hz. Because of the machining and assembling errors, the levitation coil will tilt with respect to gravity and deviate from the center of the levitation coil. Alignment coils can cancel the tilt but bring extra stiffness to the test mass that enlarges the frequency. We numerically have studied a downscaled prototype of the superconducting magnetic levitation of SOGRO and find a possible design of the superconducting levitation system, which can reduce the levitation frequency to less than 0.01 Hz without increasing any hardware and complexity of the system. This study will benefit the development of SOGRO and other superconducting levitation devices.