Conduction-cooled Bi 2Sr 2Ca 2Cu 3O x (Bi-2223) magnet for magnetic separation

Abstract

A prototype of a conduction-cooled Bi 2Sr 2Ca 2Cu 3O x (Bi-2223) magnet system for magnetic separation was constructed. The magnet system has a 200 mm room temperature bore and generates fields higher than 1 T in an 11-liter room temperature space. The magnet axis of the system was designed to be horizontal in order to attain effective magnetic separation. The magnet consisted of 42 double-pancake coils. Each double-pancake coil was fabricated by the react and wind method using 61 multifilamentary Bi-2223/Ag composite tapes. Three Bi-2223/Ag tapes, each 66.9 m long, were bundled and wound into a double-pancake coil. A stainless steel tape was also co-wound to reinforce the coil. Eighteen Cu disks were inserted between the pancakes and thermally connected to the cryocooler in order to enhance the conduction cooling. The magnet was cooled down to 13 K using a Gifford–McMahon-type cryocooler, and it was tested at various excitation speeds. In a magnetic separation system, it is important to attain rapid energizing and de-energizing of the magnet in order to obtain high separation efficiency. We cyclically excited the magnet up to 1.7 T at a speed of 1.7 T/min. The temperature gradually increased with the number of excitations; however, the temperature saturated at 35–38 K, and stable operation of the magnet was obtained at these temperatures. This result indicates that the Bi-2223 magnet is promising for magnetic separation.