Disclosed is a sub-Kelvin temperature zone refrigeration mechanism. The sub-Kelvin temperature zone refrigeration mechanism includes a pulse tube refrigeration unit, first pre-cooling heat exchangers, a throttling refrigeration unit, second pre-cooling heat exchangers, an adsorption refrigeration unit, a third pre-cooling heat exchanger and a dilution refrigeration unit. The pulse tube refrigeration unit includes a pulse tube refrigeration part. The throttling refrigeration unit includes a throttling refrigeration part, and the throttling refrigeration part is connected with the adsorption refrigeration unit through the second pre-cooling heat exchangers so as to pre-cool the adsorption refrigeration unit. The adsorption refrigeration unit includes an adsorption refrigeration part, and the adsorption refrigeration part is connected with the dilution refrigeration unit through the third pre-cooling heat exchanger. The dilution refrigeration unit includes a dilution refrigeration part, and the dilution refrigeration part is a refrigeration terminal of the sub-Kelvin temperature zone refrigeration mechanism.

The present invention discloses a hydrogen or helium throttling liquefaction system using direct current (DC) flow from the cold and hot ends of the regenerative cryocoolers, which belongs to the technical field of refrigeration and cryogenics. It includes a regenerative cryocooler module, a hot-end DC flow module, a cold-end DC flow module, a throttling liquefaction module, and a gas-phase circulation module. The modules are interconnected to form a closed loop for the flow of hydrogen or helium working fluid. DC flow is introduced from the cold and hot ends of the regenerative cryocooler through the DC flow pipelines and DC flow valves. The hot-end DC flow exchanges heat with the reflowing low-temperature working fluid and is cooled down. After that, it mixes with the cold-end DC flow and enters the throttling liquefaction module to generate liquid phase through throttling and liquefaction. After the liquid phase has output cooling capacity, it flows through the gas-phase circulation module and then enters the back-pressure chamber of the compressor to complete the cycle. Compared with the existing small-scale hydrogen and helium liquefaction technology using regenerative cryocoolers, the present invention has the advantages of simple structure, easy installation, high heat transfer efficiency and liquefaction efficiency of the system.