Preliminary Conceptual Design of 1.6 K Magnetic Refrigerator for CERN Future Circular Collider

The main goal of this work was to perform a preliminary design of the regenerative magnetic refrigerator for application in the Future Circular Collider, the next-generation particle accelerator designed in CERN. The refrigerator is supposed to cool the superconducting, radio-frequency cavities to accelerate the particles. The design is considered an alternative to the series of cold compressors with a complicated control strategy.

The refrigerator's cold end temperature is set at 1.6 K, which is one of the most important objectives of this work from the point of view of its application. The warm end temperature, 4.2 K is a result from using a liquid helium-4 bath at atmospheric pressure. Helium-3 is the medium transferring the heat inside the refrigerator. Despite its high price, this gas was chosen because of its properties - no superfluidity in the working range and the design parameters - no valves in the system.

The refrigeration is based on the magneto-caloric effect - material's temperature change with the change of the external magnetic field. Gadolinium Gallium Garnet is the active, magneto-caloric material as it is characterized by a significant entropy change in the working temperature range.

The significant difference between this application and previous magnetic refrigerator studies is its large cooling power (up to 1 kW). Such a considerable power implies large dimensions of the refrigerator. This work is the first to consider using the magneto-caloric effect for large cooling capacity. Hence, different phenomena and parameters are essential compared to small-power magnetic refrigerators.

The work includes a review of the state of the art, magneto-caloric core geometry selection, calculations of magneto-caloric material and cooling medium properties; and 1D thermodynamic model calculations. The refrigerator's overall design was performed, including a preliminary design of heat exchanges, superconducting coils and displacer. Finally, the parametric study and optimization were done, which resulted in 200 W cooling power at 1.6 K with 1000 kg of Gadolinium Gallium Garnet.