Scientific Research News Link: A 1.8 K Hybrid Cooling Cycle Uses 4He as the Only Working Medium and Its Application Verification
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2022-04-15
The team led by Dr. Haizheng Dang conducted theoretical and experimental researches on the hybrid cooling cycle of a four-stage high-frequency pulse tube coupling a JT system, using 4He as the only working medium. In collaboration with the team at the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, they made the application verification of this hybrid cooling cycle for cooling the actual superconducting nanowire single photon detectors (SNSPDs), which was published in Chinese Science Bulletin, Issue 9, 2022.
The rapid development of quantum information technology and deep space exploration has generated urgent needs for cryocoolers operating at temperatures of 2 K and below. For example, in the field of quantum information, optical quantum computers require one of its core components, SNSPD, to observe the final state of photons, and SNSPD needs to work effectively at around 2 K. At present, this cooling demand is mainly met by Gifford-McMahon (GM) cryocoolers, and the greater challenges come from the demand in the space field. Since GM cryocoolers are not suitable for space application, the high reliability, long life, compact and lightweight cryocoolers required for space quantum communication and deep space exploration with high cooling efficiency at 2 K and below must be realized through the hybrid refrigeration technology and other approaches.
In the world, the hybrid refrigeration cycle combining regenerative high-frequency pulse tube cycle with recuperative JT cycle represents a cutting-edge research focus in extremely-low temperature refrigeration. For instance, NASA's Advanced Cryocooler Technology Development Program initiated in 2001 has driven global research on space cryocoolers for over two decades. Northrop Grumman Space Systems (NGAS) achieved a no-load temperature of 1.7 K by a three-stage high-frequency pulse tube coupled with a JT cycle, which was launched with the James Webb Space Telescope on December 25, 2021, to support the infrared astronomical observation mission.
In the world, the hybrid refrigeration cycle combining regenerative high-frequency pulse tube cycle with recuperative JT cycle represents a cutting-edge research focus in extremely-low temperature refrigeration. For instance, NASA's Advanced Cryocooler Technology Development Program initiated in 2001 has driven global research on space cryocoolers for over two decades. Northrop Grumman Space Systems (NGAS) achieved a no-load temperature of 1.7 K by a three-stage high-frequency pulse tube coupled with a JT cycle, which was launched with the James Webb Space Telescope on December 25, 2021, to support the infrared astronomical observation mission.
In 2018, the team led by Dr. Haizheng Dang proposed a hybrid refrigeration cycle combining a four-stage high-frequency pulse tube coupling with a JT cooler. By 2020, the team achieved a precooling temperature of 3.3 K using a pure four-stage pulse tube cycle. Afterwards, they further deepened the relevant technical route and achieved 1.52 K in 2021.
However, it should be pointed out that temperatures of below 2 K achieved with a high-frequency pulse tube coupling JT hybrid refrigeration cycle, all use 3He in the pulse tube subsystem while use 4He in the JT subsystem as the cycle working medium. However, the rareness and high cost of 3He hinder the practical application of this refrigeration cycle in broader fields. If the relatively cheap 4He can be used to replace 3He in the JT subsystem, that is, 4He as the only working medium in the entire hybrid refrigeration cycle, then the practical bottleneck in the hybrid refrigeration cycle is expected to be broken.
This paper conducted theoretical and experimental research on a four-stage high-frequency pulse tube coupling JT hybrid cycle using 4He as the only working medium. The key difficulty and feasibility of achieving temperatures below 2 K with the above hybrid system has been analyzed. The paper analyzed the key difficulties and feasibility of obtaining temperatures below 2 K based on this cycle, and theoretically predicted that a cooling temperature of 1.78 K can also be achieved using 4He as the only working medium. Therefore, it analyzed the limited conditions for the optimization of cycle parameters under He superfluid conditions.
The no-load temperature of the developed hybrid cryocooler can reach to 1.8 K, and the temperature fluctuation was no higher than ±6 mK during the 360 hours of continuous operation time, which validates the above theoretical analyses and the satisfactory temperature stability of the superfluid helium medium. The experiment of applying it with the actual superconducting nanowire single photon detector (SNSPD) was conducted subsequently, in which the SNSPD performance was evaluated by measuring the system detection efficiency (SDE) and dark count rate (DCR). The results indicate that the developed cryocooler can provide effective cooling at 1.84 K and the favourable electrical environment, which ensures the SNSPD to work stably and reliably.
Fig. 1. Physical image of the hybrid cryocooler.
Fig. 2. Typical cooling curve of the hybrid cryocooler.
Fig. 3. Relationship between system detection efficiency and dark count of SNSPD device and bias current.
The theory, experiment and application verification in this paper not only provide reliable guarantee for the space application of SNSPD, but also will effectively promote the practical application of the hybrid refrigeration cycle in a wider field.
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