Development of a Persistent Current Mode 9.39 T (400 MHz) LTS/Bi-2223 NMR Magnet With a Bi-2223 Superconducting Joint

We developed and operated a persistent current (PC) mode 9.39 T (400 MHz for
¹
H NMR) LTS/Bi-2223 NMR magnet using a Bi-2223 insert coil with a superconducting joint. Firstly, we developed a basic joining procedure to achieve the superconducting joint for the high-strength Bi-2223 tape used for the insert coil. We applied this procedure to the coil. Secondly, a stand-alone PC mode operation test for the coil at 4.2 K was performed. No apparent field decay was observed owing to the superconducting joint. Finally, we installed the coil inside the LTS outer coil's bore to form a PC mode LTS/Bi-2223 NMR magnet system. We successfully demonstrated a 9.39 T PC mode operation of the magnet though the current of the insert coil was limited to 5 A. The field drift rate was as low as 0.4 × 10
⁻³
ppm h
⁻¹
. The joint resistance was estimated to be < 10
⁻¹²
Ω at 4.2 K and 0.26 T. To our best knowledge, this is the first demonstration of a Bi-2223 superconducting joint that realized a PC mode LTS/Bi-2223 NMR magnet. This is an important step towards full-scale PC mode Bi-2223 magnets, including a 30.5 T (1.3 GHz) LTS/HTS NMR magnet.