Development of mechanical cryocoolers for Astro-H/SXS

The Soft X-ray Spectrometer (SXS) is a high-resolution spectrometer with an X-ray micro-calorimeter array onboard the Japanese X-ray astronomy satellite Astro-H, planned for launch in 2013. The micro-calorimeter is operated at cryogenic temperature of 50 mK provided by the Adiabatic Demagnetization Refrigerator (ADR) with a heat sink of 1.3 K liquid helium stored in the SXS Dewar. To extend the liquid helium lifetime to over 3 years in orbit, two types of mechanical cryocoolers are installed: 20 K-class double-staged Stirling (2ST) coolers and a 1 K-class Joule-Thomson (JT) cooler. Improvement of mechanical cryocoolers has been investigated and verified for higher reliability and cooling performance. The engineering model (EM) of upgraded mechanical cryocoolers was fabricated for a long lifetime test. The required cooling power of 200 mW at 20 K for the 2ST cooler and 10 mW at 1.7 K for the JT cooler are achieved by EM test.     

Cryogenic system design of the next generation infrared space telescope SPICA

The Japanese infrared space telescope SPICA mission, following the successful Akari mission, has been studied at the concept design phase in international collaboration with ESA under the framework of the ESA Cosmic Vision 2015-2025. The SPICA spacecraft is to be launched in 2018 and transferred into a halo orbit around the Sun-Earth L2 to obtain a stable thermal environment where the IR space telescope’s large mirror of 3 m-class in diameter can be cooled to <5.5 K with mechanical coolers and effective radiative cooling with no use of stored cryogen. The SPICA’s large and cold telescope is expected to provide unprecedented scientific observation optimized for mid-IR and far-IR astronomy with ultra-high sensitivity and excellent spatial resolution during a nominal mission life of 3 years (goal 5 years). Thermal and structural analyses show that the obtained design of the SPICA cryogenic system satisfies the mission requirement. Mechanical coolers for the 4.5 K stage and the 1.7 K stage, which have been continuously developed, have a sufficient cooling capacity with low power consumption to lift the heat loads from instruments and parasitic heat loads. As a result, it is concluded that the concept design of the SPICA cryogenic system is confirmed for the initial cooling mode after launch and the nominal operation mode.     

ATHENA X-IFU 300 K-50 mK cryochain demonstrator cryostat

In the framework of the ESA X-ray mission ATHENA, scheduled for launch in 2028, an ESA Core Technology Program (CTP) was started in 2016 to build a flight like cryostat demonstrator in parallel with the phase A studies of the ATHENA/X-IFU instrument [1], [2]. As part of this CTP, called the Detector Cooling System (DCS), design, manufacturing and test of a cryostat including existing space coolers will be done. In addition to the validation of thermal performance, a Focal Plan Assembly (FPA) demonstrator using Transition Edge Sensors (TES) detector technology will be also integrated and its performance characterized versus the environment provided by the cryostat. This is a unique opportunity to validate many crucial issues of the cryogenic part of such a sensitive instrument.A dedicated activity within this CTP-DCS is the demonstration of the 300 K–50 mK cooling chain in a Ground System Equipment (GSE) cryostat. The studies are focused on the operation of the space coolers, which is made possible by the use of a ground cooler for cooling cryogenic shields and mechanical supports. Thanks to the modularity of the cryostat, several cooling chains could be tested. In the base line configuration described here, the low temperature stage is the CEA hybrid sorption/ADR 50 mK cooler with thermal interfaces at 4 K and 2 K. 4 K cooling is accomplished by a 4 K Joule-Thomson (JT) cryocooler and its Stirling precooler provided by JAXA. Regarding the 2 K stage, at first a 2 K JT from JAXA will be used. Alternatively, a 2 K JT cooler from RAL could replace the JAXA 2 K JT. In both cases new prototype(s) of a 2 K JT will be implemented, precooled by the EM 15 K pule tube cooler from Air Liquide. This test program is also the opportunity to validate the operation of the cryochain with respect to various requirements, such as time constant and temperature stabilities. This would bring us valuable inputs to integrate the cryochain in DCS cryostat or for the X-IFU phase A studies. This cryochain demonstration is also a critical milestone for the SPICA mission [3]. The design of the cryostat and first thermal validations both before and after integration of the JAXA JT coolers are presented in this paper.     

一种复合制冷系统的空间使用可行性分析

半导体制冷器由于材料限制,主要应用于２００ Ｋ 左右的中低温领域。通过低温热管将半导体制冷器热端与辐射制冷器相连,使其热量直接辐射到宇宙空间中,维持２００ Ｋ 温度,将可能使冷端达到接近１００ Ｋ 的空间实用化低温。作者将对这种半导体制冷器／ 热管／ 辐射制冷器的复合制冷系统空间使用的可行性作出简单分析。     

Optimization of the working fluid for a sorption-based Joule–Thomson cooler

Sorption-based Joule–Thomson coolers operate vibration-free, have a potentially long life time, and cause no electromagnetic interference. Therefore, they are appealing to a wide variety of applications, such as cooling of low-noise amplifiers, superconducting electronics, and optical detectors. The required cooling temperature depends on the device to be cooled and extends into the cryogenic range well below 80 K. This paper presents a generalized methodology for optimization in a sorption-based JT cooler. The analysis is based on the inherent properties of the fluids and the adsorbent. By using this method, the working fluid of a JT cooler driven by a single-stage sorption compressor is optimized for two ranges of cold-tip operating temperatures: 65–160 K and 16–38 K. The optimization method is also extended to two-stage compression and specifically nitrogen and carbon monoxide are considered.     

Design of high efficiency mixed refrigerant Joule–Thomson refrigerator for cooling HTS cable

The substitution of high temperature superconducting (HTS) cables for existing subterranean electric transmission lines is arising as a solution to continuously increasing electricity demand in urban areas. A cryogenic refrigeration system having the characteristics of high reliability, high efficiency, large cooling capacity, and low capital cost is essential to enable such a substitution. These requirements can be satisfied with a mixed refrigerant Joule–Thomson (MR JT) refrigerator. Unfortunately, usual MR JT refrigerators exhibit good performance at refrigeration temperatures above 80 K. A precooled neon–nitrogen MR JT refrigerator is proposed in this paper that can cool HTS cables at 70 K. The coefficient of performance (COP) of the proposed MR JT refrigerator is predicted to be 0.058 at 70 K (19.2% for exergy efficiency) with the optimized design variables. The COP can be improved further to 0.064 by enhancing the efficiency of the precooling cycle. The maximum achievable COP demonstrates the feasibility of MR JT refrigerator for cooling HTS cable.     

Sorption cooling: A valid extension to passive cooling

Passive cooling has shown to be a very dependable cryogenic cooling method for space missions. Several missions employ passive radiators to cool down their delicate sensor systems for many years, without consuming power, without exporting vibrations or producing electromagnetic interference. So for a number of applications, passive cooling is a good choice. At lower temperatures, the passive coolers run into limitations that prohibit accommodation on a spacecraft. The approach to this issue has been to find a technology able to supplement passive cooling for lower temperatures, which maintains as much as possible of the advantages of passive coolers.Sorption cooling employs a closed cycle Joule–Thomson expansion process to achieve the cooling effect. Sorption cells perform the compression phase in this cycle. At a low temperature and pressure, these cells adsorb the working fluid. At a higher temperature they desorb the fluid and thus produce a high-pressure flow to the expander in the cold stage. The sorption process selected for this application is of the physical type, which is completely reversible. It does not suffer from degradation as is the case with chemical sorption of, e.g., hydrogen in metal hydrides. Sorption coolers include no moving parts except for some check valves, they export neither mechanical vibrations nor electromagnetic interference, and are potentially very dependable due to their simplicity. The required cooling temperature determines the type of working fluid to be applied. Sorption coolers can be used in conjunction with passive cooling for heat rejection at different levels.This paper starts with a brief discussion on applications of passive coolers in different types of orbits and on the limitations of passive cooling for lower cooling temperatures.Next, the working principle of sorption cooling is summarized. The DARWIN mission is chosen as an example application of sorption and passive cooling and special attention is paid to the reduction of the radiator area needed by the sorption cooler.The application field of this type of sorption cooling in space missions is currently being expanded by examining the performance of alternative working fluids, suitable for different cooling temperatures.     

20-50 K and 40-80 K pulse tube coolers: Two candidates for a low temperature cooling chain

Following its important cryogenics heritage for the European Space industry for both Ariane launcher and Orbital programs, Air Liquide - Advanced Technology Division (AL/DTA) is proposing different pulse tube cryocoolers all over the temperature range to answer the needs of earth observation and scientific missions.This paper presents recent performance improvement of the large heat lift 40-80 K pulse tube cooler (LPTC). Four units have been manufactured and tested. Three units are dedicated to lifetime testing in the framework of French Military Space Program (under CNES contract) and Meteosat Third Generation program (ESA contract). The batch performances are described and the product maturity is discussed in this paper.To lower the temperature range and to complete our cryogenic chain, we developed in partnership with CEA/INAC/SBT, a heat intercepted 20-50 K pulse tube cryocooler. This cooler has been developed in the framework of an ESA contract (ESA/ESTEC No 20497/0/NL/PA-20-50 K pulse tube cooler). A development phase has been performed to test and optimize different cold head architectures to reach the 300 mW@20 K specification. A no-load temperature of 12.5 K has been demonstrated on breadboard model. The outputs of the trade-off, the resulting design and the performances are described.In complement to the dilution cooler similar to the one developed for the PLANCK mission, those two pulse tube coolers are potential candidates for a very low temperature cooling chain. By optimizing the capabilities of the 20 K stage for low temperature operation (no-load in the range of 8 K) the coupling of the three independent stages becomes possible.     

An efficient multi-stage Brayton–JT cycle for liquefaction of natural gas

Combined multi-stage Brayton–JT refrigeration cycles are investigated as a governmental effort in Korea to develop an original liquefaction process of natural gas in accordance with recent demand of higher efficiency and larger capacity. Based upon thermodynamic optimization theory, a combined refrigeration system is proposed with nitrogen (N2) Brayton cycle, ethylene (C2) JT cycle, and propane (C3) JT cycles, which are used for cooling the feed gas in a series of heat exchangers. Since no mixed refrigerants are used, this system is simple in operation and robust in reliability. A complete cycle design is presented to confirm its feasibility and estimate the liquefaction performance. It is expected that the proposed N2–C2–C3 cycle could have a reasonably high efficiency and the potential of great liquefaction capacity. Next steps are underway for patent application and practical process development.     

Pulse tube cooler for flight hyperspectral imaging

A new version of TRW's miniature pulse tube cooler system maintains the short wave infrared–focal plane array (SWIR–FPA) (with wavelength spectrum of 0.9–2.5 μm in the hyperspectral imaging spectrometer for the Hyperion Instrument) interface at a temperature of 110 K. The cooler provides the nominally required cooling load of 0.84W to the FPA via a cold thermal strap, at 72% stroke consuming 14.7 W of electrical power, when the heat reject temperature is at 300 K. This cooler can operate up to 90% stroke, having 1.5 W cooling load, thus having 79% performance margin for the Hyperion mission. Before the installation and operation of the cooler onto the instrument, both the mechanical and the electronics assemblies underwent the environmental tests of launch vibration, thermal vacuum cycling, and burn-in. The cooler performance in terms of mechanical efficiency, electronics efficiency, load lines, temperature stability, self-induced vibrational force reduction, ripple current reduction, and magnetic radiated emission was measured and are reported here.     

便携式热电制冷器制冷性能优化的试验分析

设计、组装一台便携式热电制冷器并对其性能进行试验研究,结果显示,200 mL的水在33 min内降温17.0℃,折合制冷量7.3 W,制冷器容器的高度方向上存在较大温差,且水温降低后密度增大而下沉,使水的自然对流换热过程受到抑制,这2个因素的综合作用使制冷片冷热端温差增大,制冷量减小,工况恶化。为优化该制冷器的制冷性能,在制冷片冷端增设重力式热管(充注R134a)并进行试验研究,结果表明,1 L的水在75 min内温度降低12℃,折合制冷量9.3 W,比优化前增大了27.4%。表明重力式热管的加入能够改善制冷器内水的对流换热情况,增大换热面积,减小竖直方向上的传热温差。     

High-power Stirling-type pulse tube cooler working below 30 K

High-power Stirling-type pulse tube coolers (PTCs) are promising candidates for cooling HTS devices and gas liquefaction or separation applications. Nevertheless, till now most high-power Stirling-type PTCs are not able to reach a refrigeration temperature below 35 K. Here, a high-power two-stage Stirling-type PTC was designed, manufactured and experimentally investigated. In order to realize a convenient coupling with a thermal load, U-shape configuration is adopted in both stages, which makes it more challenging to distribute the gas flow and reduce dead volume in the cold end heat exchanger. By optimizing operating conditions, flow straightener, and double-inlet opening, the cooler has reached no-load refrigeration temperatures of 29.6 K and 27.1 K at 55 Hz and 40 Hz, respectively. Furthermore, the cooler is able to provide cooling powers of 50 W at 45.6 K and 100 W at 59.3 K when input pV powers are 4.77 kW and 4.59 kW, respectively.     

SPICA sub-Kelvin cryogenic chains

SPICA, a Japanese led mission, is part of the JAXA future science program and is planned for launch in 2018. SPICA will perform imaging and spectroscopic observations in the mid- and far-IR waveband, and is developing instrumentation spanning the 5–400 μm range. The SPICA payload features several candidate instruments, some of them requiring temperature down to 50 mK. This is currently the case for SAFARI, a core instrument developed by a European-based consortium, and BLISS proposed by CALTECH/JPL in the US.SPICA’s distinctive feature is to actively cool its telescope to below 6 K. In addition, SPICA is a liquid cryogen free satellite and all the cooling will be provided by radiative cooling (L2 orbit) down to 30 K and by mechanical coolers for lower temperatures. The satellite will launch warm and slowly equilibrate to its operating temperatures once in orbit. This warm launch approach makes it possible to eliminate a large liquid cryogen tank and to use the mass saved to launch a large diameter telescope (3.2 m). This 4 K cooled telescope significantly reduces its own thermal radiation, offering superior sensitivity in the infrared region.The cryogenic system that enables this warm launch/cooled telescope concept is a key issue of the mission. This cryogenic chain features a number of cooling stages comprising passive radiators, Stirling coolers and several Joule Thomson loops, offering cooling powers at typically 20, 4.5, 2.5 and 1.7 K. The SAFARI and BLISS detectors require cooling to temperatures as low as 50 mK. The instrument coolers will be operated from these heat sinks. They are composed of a small demagnetization refrigerator (ADR) pre cooled by either a single or a double sorption cooler, respectively for SAFARI and BLISS. The BLISS cooler maintains continuous cooling at 300 mK and thus suppresses the thermal equilibrium time constant of the large focal plane.These hybrid architectures allow designing low weight coolers able to reach 50 mK. Because the sorption cooler has extremely low mass for a sub-Kelvin cooler, it allows the stringent mass budget to be met. These concepts are discussed in this paper.     

Stirling Cryocooler for High-Temperature Super Conductor RF Filters

The High Temperature Super Conducting (HTSC) radio frequency (RF) filters (as used, for example, in ground base stations for cellular phone systems) are passive devices. To operate properly, they must be cooled well below their transition temperature to super conducting stage (usually to 65–80 K). These HTSC RF filters are connected through a coaxial cable to an array of Low Noise Amplifiers (LNA), which are active devices and, therefore, induce a few hundreds mWatts of heat. On the other hand, the LNA array is connected by coaxial cable to a feedthrough of the vacuum chamber. This coaxial cable also contributes a few hundreds mWatts of heat load. The third source of heat load is the thermal radiation from the vacuum jacket wall to the cryogenically cooled surfaces. This portion of heat load is assessed as hundreds of mWatts as well. The signal-to-noise ratio of LNA devices is improved significantly when they are cooled down to a temperature of 90–110 K and their effectiveness reaches 99% at a temperature of 77 K. Traditionally, cooling of the system is achieved by placing both the HTSC RF filters and the LNA array device on the cold tip of a single-stage cryogenic cooler. Hence, both devices are cooled down to a temperature of 60–80 K, which is required by the manufacturers of HTSC RF filters. Because of the high level of heat loads induced by the LNA array, this method requires an extra cooling capacity from a cryogenic cooler. This increases power consumption, weight, and size and decreases its reliability. This paper describes a method of reducing the overall heat load. This method relies on the idea of maintaining the HTSC RF filters and the LNA arrays in different operational temperatures. The objective of this method is to provide a reduction in thermal losses, input power, weight, and size and to increase the reliability of the entire cryogenic cooler. The method allow for better ruggedising of the mechanical support for cooled electronic package of the LNA array plate.     

Optimization of the working fluid in a Joule–Thomson cold stage

Vibration-free miniature Joule–Thomson (JT) coolers are of interest for cooling a wide variety of devices, including low-noise amplifiers, semiconducting and superconducting electronics, and small optical detectors used in space applications. For cooling such devices, coolers are needed which have operating temperatures within a wide temperature range of 2–250 K. In this paper, the optimization of the working fluid in JT cold stages is described that operate at different temperatures within that range. For each temperature, the most suitable working fluid is selected on the basis of the coefficient of performance of the cold stage, which is defined as the ratio of the gross cooling power to the change in Gibbs free energy of the fluid during compression. In addition, a figure of merit of the heat exchange in the counter-flow heat exchanger is evaluated that depends only on the properties of the working fluid.     

Test results after refurbish of cryogenic system for smiles

Superconducting Sub-millimeter-wave Limb-Emission Sounder (SMILES) is to be operated aboard the Japanese Experiment Module (JEM) of the International Space Station (ISS) in 2009. SMILES uses two superconductor-insulator-superconductor (SIS) mixers for sub-millimeter-wave atmospheric observation and they are cooled to 4 K levels by a cryogenic system with a two-stage Stirling cooler, a Joule-Thomson (JT) cycle cooler and a cryostat composed of three stages. Two-stage Stirling cooler precools the JT circuit and also cools radiation shields in the cryostat. JT circuit has three tube-in-tube type heat exchangers and an orifice for JT expansion in the cryostat. The cryogenic system is built, tested and delivered.     

Vibration-free stirling cryocooler for high definition microscopy

The normal operation of high definition Scanning Electronic and Helium Ion microscope tools often relies on maintaining particular components at cryogenic temperatures. This has traditionally been accomplished by using liquid coolants such as liquid Nitrogen. This inherently limits the useful temperature range to above 77 K, produces various operational hazards and typically involves elevated ownership costs, inconvenient logistics and maintenance. Mechanical coolers, over-performing the above traditional method and capable of delivering required (even below 77 K) cooling to the above cooled components, have been well-known elsewhere for many years, but their typical drawbacks, such as high purchasing cost, cooler size, low reliability and high power consumption have so far prevented their wide-spreading. Additional critical drawback is inevitable degradation of imagery performance originated from the wideband vibration export as typical for the operation of the mechanical cooler incorporating numerous movable components.Recent advances in the development of reliable, compact, reasonably priced and dynamically quiet linear cryogenic coolers gave rise to so-called “dry cooling” technologies aimed at eventually replacing the traditional use of outdated liquid Nitrogen cooling facilities. Although much improved these newer cryogenic coolers still produce relatively high vibration export which makes them incompatible with modern high definition microscopy tools. This has motivated further research activity towards developing a vibration free closed-cycle mechanical cryocooler.The authors have successfully adapted the standard low vibration Stirling cryogenic refrigerator (Ricor model K535-LV) delivering 5 W@40 K heat lift for use in vibration-sensitive high definition microscopy. This has been achieved by using passive mechanical counterbalancing of the main portion of the low frequency vibration export in combination with an active feed-forward multi-axes suppression of the residual wideband vibration, thermo-conductive vibration isolation struts and soft vibration mounts. The attainable performance of the resulting vibration free linear Stirling cryocooler (Ricor model K535-ULV) is evaluated through a full-scale experimentation.     

Sub-Kelvin cooler configuration study for the Background Limited Infrared Submillimeter Spectrometer BLISS on SPICA

The Background Limited Infrared Submillimeter Spectrometer (BLISS) is an instrument proposed for the Japanese space borne telescope mission SPICA. The BLISS concept is a suite of grating spectrometers which combine to cover the 40-400 μm range at resolving power R∼700 with detector sensitivity approaching the natural photon background limits. To achieve the high sensitivity, the BLISS detectors require cooling to 50 mK, well below the 1.7 K cold stage provided on the SPICA spacecraft. We present a thermal architecture for BLISS that includes a thermal intercept stage actively cooled to a temperature in between the 1.7 K cold tip and the detector stage at 50 mK. This architecture requires, essentially, two coolers; one to cool the intercept stage from 1.7 K and one to cool the detectors from the intercept stage temperature to 50 mK. We compared several configurations of flight-heritage coolers to cool the intercept and detector stages. Of the various configurations studied, a continuous adiabatic demagnetization refrigerator (ADR) for each stage has the highest maturity, lowest heat dump at 1.7 K and total mass comparable to other approaches. Other options, such as a Herschel ³He sorption cooler-ADR hybrid and the recently demonstrated closed cycle version of the dilution cooler on Planck are also feasible for BLISS on SPICA.     

Performance analysis of multi-stage thermoelectric coolers

Multi-stage thermoelectric coolers offer larger temperature differences between heat source and heat sink than single-stage thermoelectric coolers. In this paper, a pyramid-type multi-stage cooler is analyzed, focusing on the importance of maximum attainable target heat flux and overall coefficient of performance, COP. Having considered the COP and the thermal resistance of a heat sink as key parameters in the design of a multi-stage thermoelectric cooler, analytical formulas for COP and heat sink thermal resistance versus working electrical current are derived. For a fixed cooling target heat flux, the ratio of the heat sink thermal resistance to the respective single-stage value and the attainable COP in a cascaded cooler are determined as a function of the number of stages. Numerical simulations clearly indicate that the thermal resistance of the hot side heat sink is the controlling factor in determining the overall performance of a multi-stage thermoelectric cooler.