A small refrigerator system for cooling thermal shield of a large superconducting magnet

A commercial small refrigerator system has been integrated to a large superconducting spectrometer magnet to cool its thermal shield and anchors. It has been in operation for more than 10,000 hours without major troubles. The refrigerator has cooling power of 60 W for thermal shield at 80 K and 6 W for anchors at 20 K. The magnet is kept below the liquid nitrogen temperature even when the main refrigerator system is turned off, and the cool-down time of the large superconducting magnet is considerably shortened. Operation of the large superconducting magnet has become much easier thanks to the small refrigerator system. (author)