which has been subcooled by refrigeration generated by primary refrigerator 1 is passed into reserve storage container 2 such as through line 4 which branches from line 6 simultaneously some cryogenic liquid from reserve storage container 2 is passed to primary refrigerator 1 to pick up more subcooling such as through line 5 which connects to line 7 in this way the content of reserve storage container 2 is maintained in a subcooled condition when necessary subcooled cryogenic liquid from reserve storage container 2 is passed to the superconducting device s to provide cooling to the superconducting devices s such as through line 8 which connects to line 6 the passage of subcooled cryogenic liquid from the reserve storage container to the superconducting device s can occur during the passage of subcooled cryogenic liquid from the primary refrigerator to the superconducting device s for at least a part of the time and or may occur after such passage indeed the passage of subcooled cryogenic liquid from the reserve storage container to the superconducting device s can occur prior to the passage of the cryogenic liquid from the primary refrigerator to the superconducting device s such as during startup of the system from time to time the cryogenic liquid within the reserve storage container is replenished fig2 illustrates one replenishment arrangement wherein replenishment.