Magnetic refrigeration down to 1.6 K for the future circular collider $e^{+}{e}^{-}$

High-field superconducting rf cavities of the future circular collider $e^{+}{e}^{-}$ may require a kW-range superfluid helium refrigeration down to 1.6 K. Magnetic refrigeration operating below 4.2 K can be an alternative to the compression/expansion helium refrigeration. A significant difference between this application and previous magnetic refrigerator studies is its large cooling power, up to $10^3$ times larger than the other designs. Principles of magnetic refrigeration are described and various technical solutions are compared. A numerical model for the static magnetic refrigerator is presented, validated, and adapted to the needs of the positron-electron version of the future circular collider. A preliminary design of magnetic refrigerator suitable for low temperature, kW-range cooling is studied.

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Figure 1

Optimal operating temperature for superconducting rf cavities [1].

Figure 2

Adiabatic demagnetization refrigerator cycle.

Figure 3

GGG entropy calculated with free ion model depending on magnetic field $B$ and temperature $T$.

Figure 4

Scheme of the Hitachi static magnetic refrigerator.

Figure 5

Carnot cycle (dashed) and thermodynamic cycle taking into account heat exchange conditions on warm and cold sides (blue) of the Hitachi static magnetic refrigerator, without heat losses.

Figure 6

Thermal diffusivity change during complete cycle.

Figure 7

Carnot cycle (dashed) and thermodynamic cycle taking into account heat exchange conditions on warm and cold sides (blue) of the designed prototype, without heat losses.

Figure 8

Objectives for the heat switch efficiency.