A 6 T refrigerator-cooled NbTi superconducting magnet with 180 mm room temperature bore

A 6 T NbTi superconducting magnet, cooled by a 4 K GM (Gifford-McMahon) refrigerator has been developed. Magnetic material, Er/sub 3/Ni, is used as the regenerator to cool the coil to liquid helium temperature. The central field strength in the 180 mm room temperature bore is designed to be 6 T. NbTi coil dimensions are, 215 mm in inner diameter, 279 mm in outer diameter, and 240 mm in axial length. The coil winding is an epoxy-impregnated structure without a bore tube, thereby reducing mechanical disturbances. The coil heat is removed through the outer metal cylinder. A pair of Bi(2212) current leads has been developed to reduce heat leakage into the 4 K level. A cold diode is used to protect the coil even if the oxide lead is burned out. The magnet attained 6.45 T central field at 3.61 K coil-winding temperature. >