Excitation Test of Solenoid MgB₂ Coil Under External Magnetic Field Immersed in Liquid Hydrogen

Abstract

We have been developing a liquid hydrogen (LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) cooled superconducting energy apparatus, such as superconducting generator, SMES, and so on. An MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductor whose critical temperature is 39 K is now developing for a practical use. It can be cooled by LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a sufficient temperature margin. An MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire is expected to be used for superconducting equipment due to the low production cost and material cost. In order to design equipment using the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire, we have carried out measurement tests of critical superconducting properties of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> under LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cooling and investigation of heat transfer characteristics of LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . There are few reports on the experimental results of a superconducting coil using a long MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire under the LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> immersion cooling. In this study, we have carried out an excitation test of a small MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coil immersed in LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> under an external magnetic field. Tanaka et al. proposed that the test coil is a 529 turn solenoid coil with an inner diameter of 120 mm, an outer diameter of 190 mm, and a height of 41 mm, which was produced by the Wind and React method using a 300-m multifilament MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire (Hitachi Ltd., Ibaraki, Japan). The temperature of LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was changed from 21 K to 30 K and the external magnetic field was also applied up to 4.5 T. In the experiment, the critical characteristic of the solenoid coil was measured and a coil load line was obtained.