A 2.2 K Five-stage High-frequency Pulse Tube Cryocooler Was Successfully Developed by Boreas Cryogenics
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2023-01-11
Boreas Cryogenics has recently co-achieved a significant progress in a successful development of a 2.2 K five-stage high-frequency pulse tube cryocooler. This represents the lowest temperature ever publicly reported to be achieved by a pure high-frequency pulse tube cryogenic cycle. The related research has been published in consecutive theoretical and experimental articles in the international journal CRYOGENICS.
The cold end of the pulse tube cryocooler completely eliminates the moving component, achieving no-wear, extremely low vibration, high-reliability, and theoretically infinite life.
It can be driven by two types of drivers: one is an oil-lubricated, valved helium compressor similar to that used in GM cryocoolers, operating with a low frequency at 1-2 K, named as the low-frequency (or GM-type) pulse tube cryocooler; the other is an oil-free, valveless linear compressor similar to that used in linear Stirling cryocoolers, operating with a high frequency above 20 Hz, named as the high-frequency (or Stirling-type) pulse tube cryocooler.
Low-frequency pulse tube cryocoolers have a loose structure, large volume, high vibration, low cooling efficiency, and short MTBF (typically 8,000 hours). They can only be applied in ground-based or other situations where vibration, noise, working space, and lifespan are not strictly required. Their advantage is that they can achieve a higher cooling capacity and lower cooling temperature at the cost of higher power consumption. High-frequency pulse tube cryocoolers have a compact structure, low vibration and electromagnetic interference, high cooling efficiency, and long MTBF (typically over 5 years). They can be applied in space and other special fields where vibration, noise, working space, and MTBF are strictly required.
Low-frequency pulse tube cryocoolers have a loose structure, large volume, high vibration, low cooling efficiency, and short MTBF (typically 8,000 hours). They can only be applied in ground-based or other situations where vibration, noise, working space, and lifespan are not strictly required. Their advantage is that they can achieve a higher cooling capacity and lower cooling temperature at the cost of higher power consumption. High-frequency pulse tube cryocoolers have a compact structure, low vibration and electromagnetic interference, high cooling efficiency, and long MTBF (typically over 5 years). They can be applied in space and other special fields where vibration, noise, working space, and MTBF are strictly required.
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Fig. 1. Schematic diagram of the five-stage SPTC with an active phase compressor. Abbreviations DPC for driving phase compressor, APC for active phase compressor, Aft for aftercooler, Reg for regenerator, PT for pulse tube, CHX for cold end heat exchanger, MHX for middle heat exchanger, WHX for warm end heat exchanger, TS for thermal strap, Res for reservoir, and IT for inertance tubes.
Previously, commercial products of low-frequency pulse tube cryocoolers had already achieved a minimum cooling temperature of 2.2-2.3 K. However, the minimum cooling temperature of high-frequency pulse tube cryocoolers had long been around at 3.0-3.3 K, with the lowest temperature record held by the Lockheed Martin Advanced Technology Center in the United States. The minimum temperature of the four-stage high-frequency pulse tube cryocooler by our joint team was essentially on par with this record.
The joint research team built upon this four-stage scheme to propose a firstly five-stage cooling cycle scheme. After three years of intensive research, the team successfully achieved the lowest cooling temperature of 2.2 K by high-frequency pulse tube cryocoolers. This is the lowest temperature ever publicly reported to be achieved through a pure high-frequency pulse tube cryogenic cycle.
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Fig. 2. Schematic of the five-stage SPTC experimental setup.
The successful development of the 2.2 K high-frequency pulse tube cryocooler has equalized the practically achievable lowest cooling temperature with that of low-frequency pulse tube cryocoolers, thereby significantly expanding its application prospect. Additionally, as a pre-cooling stage, it provides a more advantageous foundation for achieving better performance or lower temperature in the cryogenic cycle such as hybrid cryocooling or dilution refrigeration.
It is particularly worth mentioning that this five-stage high-frequency pulse tube cryocooler can simultaneously extract cooling power at five typical temperature: 80 K, 30 K, 12 K, 6 K, and 3.5 K. This enables a single cryocooler to concurrently meet the cooling requirements for various applications of infrared detectors and low-temperature superconducting electronic devices with short, medium, long and very-long wavelengths, significantly advancing the integration and multifunctionality of cryogenic systems. If the cryocooler was just used for cooling at 4.2 K without multi-temperature range, it could achieve a net cooling power of 75.5 mW with a relatively low input power of 350 W. This means that if the typical 13 kW input power was provided, the net cooling power at 4.2 K would exceed 2.8 W, surpassing that of all known low-frequency pulse tube cryocoolers.
These performances demonstrate its exceptional cooling capability and indicate broad application prospects. Current research focuses on coupling this five-stage high-frequency pulse tube cryocooler with large swept volume, high input power linear compressors to achieve higher cooling capacity. Preliminary unoptimized test results show that with 7.8 kW input power, the system already achieves a 1.35 W of net cooling capacity at 4.2 K.
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Fig. 3. Structure diagram of the five-stage SPTC.
Fig. 4. Cool-down curves of the last two stages by using 3He under different operating conditions.
Article Part A: Theoretical analyses and modeling
Article Part B: Experimental verifications
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