Testing of a cryocooler-cooled HTS magnet with silver-sheathed Bi2223 tapes for silicon single-crystal growth applications

A project to develop a high-temperature superconducting split magnet for 8 inch silicon single-crystal growth applications began in October 1997. This split coil system is composed of 2 coils, each consisting of 18 pancakes. Each coil has an outer diameter of 1.2 m and a thickness of 0.1 m. Moreover, we developed a highly efficient GM-type cryocooler to cool a HTS coil to below 20 K. This paper presents the test results for a full-scale magnet. Each coil was cooled by the GM-cryocooler with a 3.3 kW compressor. The cool-down of the coil was completed within 480 hours with temperature difference among pancakes maintained at less than 18 K. In April 2001 this split coil was successfully energized up to rated current of 210 A at 20 K without a quench. The stored energy of this split coil reached 1.1 MJ at 216 A, 20 K, and the fastest charging time in our experiments was 1 minute.