Ultra-low temperature refrigerator working principle is clear to anyone?

The principle of refrigeration used in ultra-low temperature refrigerators still follows the inverse Carnot cycle. Structurally, it is divided into the classical compounding refrigeration liquefaction cycle and the self-compounding refrigeration liquefaction cycle. Classical compounding refrigeration high temperature level of the evaporator to the low temperature level of the condenser cooling. Make the low-temperature level of refrigerant liquefaction, through the interception to the refrigerator cooling, Iwami low-temperature self-compounding refrigeration through the internal structure of the system to separate the interception, to achieve the temperature of minus 60 degrees, minus 80 degrees or even lower minus 100 degrees.