Abstract
Adiabatic demagnetization refrigerator (ADR) does not use working fluids contrary to conventional refrigerators that make use of the fluid density difference, which leads to superiority of the ADR under weak gravitational conditions. In this study, we developed a continuous ADR system to provide constant cooling temperatures ~ 100 mK. The system consists of four stages of magnetic materials and magnets cascaded with heat switches. The magnetic materials, CPA and GdLiF4, are used for three stages between 0.1 - 1.4 K, and a single stage between 1.4 - 4 K, respectively. Passive heat switches are used for three stages > 0.3 K, and a superconducting heat switch is used for the continuous stage at ~ 0.1 K. A Gifford-McMahon cycle cryocooler is used to cool the ADR and cryostat shieldings. The total mass of the flight model is less than 60 kg. Cooling tests with a transition edge sensor (TES) on the ground showed that the ADR provided continuous cooling temperatures from 105 - 120 mK, and it successfully operated the TES. Airborne flight experiments confirmed the ability of the cooling system under milli-gravity conditions. The experimental results showed that the ADR could provide stable temperature under a weak gravity. In conclusion, a continuous ADR system will be useful for many applications that require higher efficiency and compactness.
