In accordance with an embodiment of the invention, there is provided a system for cooling a load. The system comprises a closed loop primary refrigeration system comprising: a primary compressor taking in a primary refrigerant at a low pressure and discharging the primary refrigerant at a high pressure; an insulated enclosure comprising an inlet receiving the primary refrigerant at the high pressure from the primary compressor and an outlet returning the primary refrigerant at the low pressure to the primary compressor; at least one heat exchanger within the insulated enclosure receiving the primary refrigerant at the high pressure and cooling the primary refrigerant using a secondary refrigerant from a secondary refrigeration system, the secondary refrigerant being in heat exchange relationship with the primary refrigerant in the at least one heat exchanger; an expansion unit within the insulated enclosure receiving the primary refrigerant at the high pressure from the at least one heat exchanger and discharging the primary refrigerant at the low pressure; and a supply line delivering the primary refrigerant at the low pressure to the load and a return line returning the primary refrigerant from the load to the primary refrigeration system. The system further comprises the secondary refrigeration system, wherein the secondary refrigeration system comprises at least one secondary cryogenic refrigerator. A system control unit controls operation of at least one of the primary refrigeration system and the secondary refrigeration system to provide a variable refrigeration capacity to the load based on at least one of: a pressure of the primary refrigerant delivered to the load, and at least one temperature of the load.