Persistent Current Mode of a 1-T-Class HTS Pancake Coil for NMR/MRI Applications

We had proposed a winding method, the so-called "wind-and-flip," which enables a persistent current-mode operation of a high-temperature superconducting (HTS) pancake coil. Two pancake coils had been fabricated using this method and tested in a liquid nitrogen bath with an external magnetic field. The result showed that the time stability was not good enough to use for magnetic resonance imaging or nuclear magnetic resonance when they were magnetized by field cooling at 77 K. In this paper, the test results of a stacked HTS pancake coil for a center magnetic field of 1 T are presented. The coils were cooled to 20 K by conduction cooling using a Gifford-McMahon cryocooler. We measured the time stability of the persistent current-mode operation at 20 K, which shows a strong possibility of a high-field HTS magnet using this method.