Abstract: The optimization of the operational parameters and the experimental study with helium-hydrogen mixture on the miniature co-axial pulse tube refrigerator are carried out. The experimental optimization results show that the optimum frequency of the compressor is about 15.5～17.2 Hz for different hydrogen-helium mixture. When the mean pressure of the compressor increases, the lowest refrigerating temperature decreases, with the increases of mean pressure its effect gradually becomes weaker and weaker. The optimum jaw opening of the orifice is 70o and 30o for the double-inlet valve. The hydrogen-helium mixture experimental results show that with the decrease of the mole fraction of hydrogen in the hydrogen-helium mixture, the lowest refrigerating temperature decreases, and when the mole fraction of hydrogen is below 20%, the lowest refrigerating temperature is close to that using pure helium. The cooling capacity of the miniature co-axial pulse tube refrigerator in 100～120 K temperature region can be improved with hydrogen-helium mixture. When the mole fraction of hydrogen is 20% in the mixture, the cooling capacity is 13.5%～16.5% higher than that using pure helium.

Key words: Cooling capacity, Hydrogen helium mixture, Miniature co-axial pulse tube refrigerator, Optimum parameters