Cooling Intrinsically Stable Superconducting Magnets with Supercritical Helium

A number of papers have been written suggesting that superconducting magnets could be cooled by using supercritical helium (helium at pressures above the critical pressure of 2.2 atm). Nearly all schemes for using supercritical helium involve circulating helium inside fully stabilized hollow superconductors. This paper describes a supercritical helium-cooled magnet which is quite different. This magnet, built at LRL, utilizes an intrinsically stable, low-ac-loss superconductor. The heat generated with the coil is conducted to supercritical helium cooling tubes which are adjacent to the magnet coil. (Several superconducting synchrotron groups have suggested this method for cooling pulsed magnets.) This paper describes the experimental equipment, which differs considerably from the normal superconducting magnet system. The problems associated with cooling the magnet are discussed, and the operating characteristics of the coil are presented. In conclusion, the paper presents some of the advantages and limitations involved with this type of magnet cooling.