Numerical Investigation on Low-temperature Superconducting Negative Spring in Magnetic Levitation
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ORIGINAL PAPER
Numerical Investigation on Low-temperature Superconducting Negative Spring in Magnetic Levitation J. Z. Wang1,2 · X. Bian1 · Q. Li1,2 · J. H. Wu1,2 Received: 19 June 2020 / Accepted: 7 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
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 − 10−20 Hz−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. Keywords Negative spring · Superconducting levitation · FEM simulation · Pancake coils
1 Introduction SOGRO (Superconducting Omni-directional Gravitational Radiation Observatory) is a new gravitational waves detectors proposed in 2016 to detect the gravitational waves within the frequency band from 0.1 to 10 Hz [1, 2], which is between that of LIGO (Laser Interferometer GravitationalWave Observatory) [3] and LISA (Laser Interferometer Space Antenna) [4]. There are significant scientific payoffs in the measurement of astrophysical gravitational waves in this frequency band [5]. As shown in Fig. 1, the platform of the full-tensor detector [6] is constructed of three arms perpendicular to each other, and each arm consists of two test masses separated by 30–50 m. When gravitational waves go through the detector, the test masses will be droved to move. By measuring the relative motion of the two test
J. H. Wu
[email protected] 1
State Key Laboratory of Technologies in Space Cryogenic Propellants, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China
2
University of Chinese Academy of Sciences, Beijing, China
masses in each arm, and comparing the output between different arms, the signal of gravitational waves can be read out by SQUID (the superconducting quantum interference devices) [7]. Gravitational waves are so weak that a gravitational wave detector needs to be able to detect a relative distance change of 10−20 . To achieve such a high sensitivity, the suspension of the test masses needs to have
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