Cooling channels are provided within a resin impregnated superconducting winding by introducing inserts between wrappings of successive layers of superconducting winding and leaving them in place during impregnation of the winding with resinous bonding materials, and thereafter extracting the inserts from the winding. The resultant spaces within the resin provide discrete coolant passages distributed throughout the superconducting winding, thereby providing circulation paths for coolant to maintain the coil at superconducting temperatures during operation thereof, including periods of rapid change in the excitation field current.