Temperature Fluctuation of a Closed-Cycle Helium Joule-Thomson Cryocooler with Two-Stage Precooling

For quantum communications, single-photon detection, millimeter wave detection and other space projects, all of them need to work at liquid helium temperatures to achieve excellent performance. The closed-cycle helium Joule-Thomson cryocooler (JTC) is currently one of the mainstream solutions to realize the liquid helium temperature. While realizing the liquid helium temperature, the detector has strict requirements on the temperature fluctuation of the JTC, because the thermal noise caused by the JTC temperature fluctuation will have a critical impact on the detection performance. The typical closed-cycle helium JTC is precooling by a two-stage precooler. When the operating parameters of the JTC compressor remain unchanged, the change of the precooler is the main factor that affects the temperature fluctuation of the JTC. To explore the influence mechanism of JTC temperature fluctuations, experimental and theoretical studies are carried out. Based on the real gas equation of state, the influence of various parameters on the evaporator temperature fluctuations is explained. Research results show that the increase in temperature of each stage will cause the temperature of the JTC to increase. Especially, the change of the secondary precooling temperature (T-pre2) has the most obvious influence on JTC temperature. Furthermore, the influence of the JT compressor's buffer tank volume V-b on temperature fluctuation is studied. By increasing the V-b, the JTC temperature fluctuation caused by the temperature change of the precooler can be effectively reduced.