Development of a 6-T Conduction-Cooled Superconducting Magnet

A 6-T conduction-cooled superconducting (SC) magnet was successfully developed with the Institute of High Energy Physics of China. The magnet mainly consists of a NbTi solenoid coil, a cryostat with two thermal shields, a Gifford-McMahon cryocooler (35 W/50 K, 1.5 W/4.2 K), and a pair of binary current leads. The coil has an inner diameter of 110 mm, an outer diameter of 200 mm, and a height of 216 mm. The total 55-kg cold mass was located in the cryostat with a 50-mm room temperature bore. In order to minimize the heat load to an SC coil, two thermal shields were adopted in this system. The outer thermal shield and the inner thermal shield were thermally attached to the first stage and the second stage of the cryocooler, respectively. In addition, thermal contact resistance was carefully considered to minimize the temperature difference between the coil and the second stage of the cryocooler. It took 30 h for the magnet to cool down from 300 to 4 K level. The temperature of the second stage was stable below 3 K, which corresponded to about 0.2-W total heat loads. The magnet suffered no quench to reach its designed current of 148 A and stably operated during many charging and discharging processes. The detailed development of this magnet is presented in this paper.