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Adiabatic demagnetization refrigerator (ADR) is a cooling method that utilizes the cooling effect from the magnetic material under a changing magnetic field. Commonly, the field variation is generated by a superconducting magnet. If a 4 K cryocooler is implemented as a heat sink of the magnet, both low temperature superconductors (LTS) and high temperature superconductors (HTS) can be used for the magnet winding. Due to the distinct characteristics of these conductors, their stability energy margins during the ramping operation differ. This study analyzes the suitability of each superconductor type for ramping magnets in ADR systems. The ratio between the hysteresis loss and the stability energy margin (the maximum energy that can be absorbed while maintaining the superconducting state) is proposed as a critical factor for stable magnet operation. This ratio of different superconductors is analyzed, leading to a recommendation for the optimal conductor for the ADR applications. Additionally, a conduction-cooled magnet utilizing HTS conductors is developed, incorporating a thermal drain structure to efficiently dissipate hysteresis losses during the ramping operation. The fabricated magnet achieves the ramping rate of 0.1 T/s with the maximum central magnetic field of 4 T. Using gadolinium gallium garnet as the magnetic material for ADR, the system reaches the minimum temperature of 0.3 K from 4 K. The detailed analytical and experimental results are discussed in the paper.
This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (RS-2024-00438367).
