Refurbishment and Performance of the Superconducting Gravimeter CT-36

Abstract

We started a superconducting gravimeter observation to elucidate relationships between slow slip events and gravity changes at Ishigakijima near Ryukyu trench, southwestern Japan in February 2012. Before the installation of the superconducting gravimeter (CT-36) at Ishigakijima, we refurbished the CT-36, installed at the Inuyama observatory of Nagoya University originally, so that the system can operate reliably at such a remote island. Specifically, for the planned observation, we replaced the compressor for the refrigerator from ‘water-cooled’ type to ‘air-cooled’ type. In addition, at University of Tsukuba, we warmed up the Dewar to room temperature to remove the ‘clogs’ inside it. This resulted in eliminating strange behaviors in the temperature controls of the gravimeter, as well as solving the problem in transferring liquid helium into the Dewar. During these refurbishment processes, the frequency responses and the instrumental drift of CT-36 were also measured. As a result, it was verified that CT-36 works ideally as a high-precision long-term gravimeter.