Experimental study of silver powder sintering for optimization of step heat exchangers in dilution refrigerator

Abstract With the development of quantum computing and other scientific fields, the dilution refrigerator, as a major ultra-low temperature refrigeration equipment, is required to provide more cooling capacity. Due to Kapitza resistance, one of the key factors that limit the cooling power, the silver powder sintered heat exchanger is an essential component of the dilution refrigerator. This study examines the sintering of silver nano-powder samples with particle sizes of 50 nm, 100 nm, and 200 nm, sintering pressures of 0.4 MPa, 0.7 MPa, and 1.0 MPa, and sintering temperatures of 220°C and 200°C. The porosity and specific surface area of these samples were measured. The 200 nm silver powder was found to have the best performance under the conditions of 1.0 MPa and 200°C, with a specific surface area of 3.56 m²/g. It was successfully applied to a dilution refrigerator and achieved a minimum temperature of 19 mK and a cooling capacity of 350 μW at 100 mK. The results may be helpful in guiding the design of future large cooling capacity dilution refrigerators.