The CLEO II detector magnet: design, tests, and performance

The design features of the CLEO II magnet, test results and operating results are described. The design is intended to keep the good features of the smaller CLEO I solenoid, such as low cryogenic load, while eliminating some of its weaknesses, such as its poor insulating vacuum, sensitivity to refrigerator performance, and susceptibility to utility failures. A persistent current mode, proposed in view of the frequent need to de-energize the magnet for maintenance and accelerator studies, was considered and rejected. The requirements were then increased stability, low cryogenic heat load, passive cooling, and passive protection. At this writing, the magnet has been operating at high fields without serious incident for about six months. The cryostat vacuum has remained at 10^-6 torr with no external pumping, and the effective refrigeration load has been comfortably within the capabilities of the Koch model 1430 (Oxford estimated 8.3 W and 14 1/h). All the various styles of cryogenic operation have been attempted successfully. Operation is largely unattended except for routine refrigerator maintenance and field rampup and rampdown