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• Designing and testing a prototype of a 4He sub-Kelvin sorption cooler for use in an adiabatic demagnetization refrigerator. • Achieving a minimum temperature of 773 mK and providing a cooling capacity of 100 μW at 803 mK. • Investigating the correlation between the quantity of the working medium and the overall refrigeration performance. • Discussing prospects for optimization and identifying challenges, with a focus on lowering cooling temperatures and extending hold time. The sub-Kelvin sorption cooler (SKSC) has emerged as a reliable and vibration-free solution for space cryogenics, establishing itself as a highly competitive choice. This paper focuses on the development of a 4He SKSC prototype designed for precooling an adiabatic demagnetization refrigerator (ADR). Based on the sorption refrigeration mechanism, the relationship between the amount of working medium and cooling performance is analyzed. Subsequently, each component of the SKSC is designed and constructed, resulting in the successful creation of a 4He SKSC prototype. Experimental testing demonstrates its capability to achieve a minimum temperature of 773 mK and provide a cooling capacity of 100 μW at 803 mK. [ABSTRACT FROM AUTHOR]

• Building a complete gas-gap heat switch model that covers the entire switching process. • Integrating activated carbon's adsorption characteristics into the theoretical model. • Designing the 4He gas-gap heat switch based on the model and testing its performance to validate the model. • Applying the gas-gap heat switch to a 4He sub-Kelvin sorption cooler and achieving a temperature of 773 mK. Gas-gap heat switches (GGHSs) are significant components in sub-Kelvin sorption coolers (SKSCs). To develop an effective GGHS for SKSCs, a complete GGHS theoretical model is proposed by integrating the adsorption characteristics of activated carbon and the principle of GGHSs. This model establishes a relationship between the temperature of activated carbon and the corresponding thermal conductance of GGHSs. Based on this model, a 4He GGHS was designed, which consists of two cylindrical copper blocks separated by a 0.2 mm gas gap and a surface area of 9.896 cm2. The device was charged with 100 kPa of 4He at 297 K. Near the base temperature of the GM cryocooler of 3 K, an ON thermal resistance of 20 K/W and an OFF thermal resistance of 21,650 K/W with 1 mW applied to the hot end were obtained, achieving a switching ratio of 1082.5. The experimental results were analyzed and compared with the theoretical data, and proved to be in good agreement. Finally, the GGHS was integrated with a SKSC, achieving an ultimate temperature of 773 mK. [ABSTRACT FROM AUTHOR]