SPICA/BLISS cryo-chain demonstrator

The Background Limited Infrared Submillimeter Spectrometer (BLISS) is an instrument proposed for SPICA, the Japanese–European space-borne telescope mission under study for a possible launch in the next decade. The BLISS concept is a suite of aluminum spectrometer modules totaling ∼10 kg cooled to 50 mK. Cooling this ambitious instrument with high-duty cycle within the stringent heat-rejection allocations envisioned for SPICA is a challenge. We have developed a solution consisting of two stages: (1) a continuous 300 mK intercept stage provided by two 3He sorption coolers operated sequentially, and (2) a 50 mK adiabatic demagnetization refrigerator (ADR) operated in single-shot mode. We have built a prototype cooler and demonstrated it in a dedicated SPICA-like thermal testbed with regulated stages enabling measurement of rejected heat at 1.7 K and 4.5 K. The approach offers lower mass than a dual-stage ADR, and lower rejected power to 1.7 K and 4.5 K than a comparable single-shot 300 mK system, while insuring a high duty cycle. As a demonstration of feasibility for SPICA and future cryogenic missions, we show long-term cooling with flight-like parasitics at 50 mK and 300 mK requiring only 3 mW and 8 mW rejected at 1.7 K and 4.5 K, respectively.     

Direct observation of dipolar chains in iron ferrofluids by cryogenic electron microscopy

A key issue in research on ferrofluids (dispersions of magnetic colloids) is the effect of dipolar interactions on their structure and phase behaviour, which is not only important for practical applications but gives fundamental insight in dipolar fluids in general. In 1970, de Gennes and Pincus predicted a Van der Waals-like phase diagram and the presence of linear chains of particles in ferrofluids in zero magnetic field. Despite many experimental studies, no direct evidence of the existence of linear chains of dipoles has been reported in the absence of magnetic field, although simulations clearly show the presence of chain-like structures. Here, we show in situ linear dipolar structures in ferrofluids in zero field, visualized on the particle level by electron cryo-microscopy on thin, vitrified films of organic dispersions of monodisperse metallic iron particles. On systematically increasing the particle size, we find an abrupt transition from separate particles to randomly oriented linear aggregates and branched chains or networks. When vitrified in a permanent magnetic field, these chains align and form thick elongated structures, indicating lateral attraction between parallel dipole chains. These findings show that the experimental model used is well suited to study the structural properties of dipolar particle systems.     

Cryogenic infrared mission “JAXA/SPICA” with advanced cryocoolers

Since the next cryogenic infrared mission “JAXA/SPICA” employs advanced mechanical cryocoolers with effective radiant cooling in place of cryogen, the primary mirror, 3.5 m in diameter, and the optical bench can be maintained at 4.5 K for at least 5 years. First, the feasibility of the thermal design of the cryogenic system is presented. A 20 K-class Stirling cryocooler was then improved in cooling capacity and reliability for the mission, and the effects of contaminated working gas or new regenerator materials on cooling performance were investigated. Development of a new ³He-JT (Joule–Thomson) cryocooler for use at 1.7 K is also described, along with the successful results of a cooling capacity higher than the required 10 mW. A 4 K-class cryocooler was modified and developed for higher reliability over a five-year operational life and a higher cooling capacity exceeding the current 30 mW. Finally, we discuss a system for heat rejection from cryocoolers using thermal control devices.     

A Robust Cooling Platform for NIS Junction Refrigeration and sub-Kelvin Cryogenic Systems

Recent advances in Normal metal–insulator-superconductor (NIS) tunnel junctions (Clark et al. Appl Phys Lett 86: 173508, 2005, Appl Phys Lett 84: 4, 2004) have proven these devices to be a viable technology for sub-Kelvin refrigeration. NIS junction coolers, coupled to a separate cold stage, provide a flexible platform for cooling a wide range of user-supplied payloads. Recently, a stage was cooled from 290 to 256 mK (Lowell et al. Appl Phys Lett 102: 082601 2013), but further mechanical and electrical improvements are necessary for the stage to reach its full potential. We have designed and built a new Kevlar suspended cooling platform for NIS junction refrigeration that is both lightweight and well thermally isolated; the calculated parasitic loading is \(<\!\!300\)  pW from 300 to 100 mK. The platform is structurally rigid with a measured deflection of 25  \(\upmu \) m under a 2.5 kg load and has an integrated mechanical heat switch driven by a superconducting stepper motor with thermal conductivity G \( = 4.5 \times 10^{-7}\)  W/K at 300 mK. An integrated radiation shield limits thermal loading and a modular platform accommodates enough junctions to provide nanowatts of continuous cooling power. The compact stage size of 7.6 cm \(\times \) 8.6 cm \(\times \) 4.8 cm and overall radiation shield size of 8.9 cm \(\times \) 10.0 cm \(\times \) 7.0 cm along with minimal electrical power requirements allow easy integration into a range of cryostats. We present the design, construction, and performance of this cooling platform as well as projections for coupling to arrays of NIS junctions and other future applications.     

Thermal conductance measurements of bolted copper to copper joints at sub-Kelvin temperatures

We have measured the thermal contact conductance of several demountable copper joints below 1 K. Joints were made by bolting together either two flat surfaces or a clamp around a rod. Surfaces were gold plated, and no intermediate materials were used. A linear dependence on temperature was seen. Most of the measured conductance values fell into a narrow range: 0.1-0.2 W K⁻¹ at 1 K. Results in the literature for similar joints consist of predictions based on electrical resistance measurements using the Wiedemann-Franz law. There is little evidence of the validity of this law in the case of joints. Nevertheless, our results are in good agreement with the literature predictions, suggesting that such predictions are a reasonable approximation.     

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.     

Development of mechanical cryocoolers for the Japanese IR space telescope SPICA

The next Japanese infrared space telescope SPICA features a large 3.5-m-diameter primary mirror and an optical bench cooled to 4.5 K with advanced mechanical cryocoolers and effective radiant cooling instead of using a massive and short-lived cryogen system. To obtain a sufficient thermal design margin for the cryogenic system, cryocoolers for 20 K, 4 K, and 1 K have been modified for higher reliability and higher cooling power. The latest results show that all mechanical cryocoolers achieve sufficient cooling capacity for the cooling requirement of the telescope and detectors on the optical bench at the beginning of life. Consequently, the feasibility of the SPICA cryogenic system concept was validated, while attempts to achieve higher reliability, higher cooling capacity and less vibration have continued for stable operations at the end of life.     

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.     

Thermal conductivity measurements of PTFE and Al2O3 ceramic at sub-Kelvin temperatures

The design of low temperature bolometric detectors for rare event searches necessitates careful selection and characterization of structural materials based on their thermal properties. We measure the thermal conductivities of polytetrafluoroethylene (PTFE) and Al₂O₃ ceramic (alumina) in the temperature ranges of 0.17–0.43 K and 0.1–1.3 K, respectively. For the former, we observe a quadratic temperature dependence across the entire measured range. For the latter, we see a cubic dependence on temperature above 0.3 K, with a linear contribution below that temperature. This paper presents our measurement techniques, results, and theoretical discussions.     

Automated cryogenic valves

This article presents a guide to the popular value types and how they are automated for remote on-off control and flow modulation.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

Time to cool a cryogenic object by a gaseous cryogenic agent

Dependences to compute the cooling time of a single-channel object are obtained theoretically and confirmed experimentally.Notation D mass of helium in the channel - M mass of metal of the channel wall - G mass flow rate of the cryogenic agent - G_equ equivalent mass flow rate - c_p, c_m mean integrated specific heat of the cryogenic agent and the channel wall material - U perimeter - cooling time - ₁ time of the first cooling period - T₂ time of the second cooling period - channel wall temperature - T flow temperature - T_o initial flow temperature - T_in flow temperature at the channel input - W flow velocity - L channel length - L_in, L_out lengths of the delivery and removal pipelines - F, F_in, F_out cross-sectional areas of the channel being cooled, and of the delivery and removal pipelines - F_s total heat-transfer surface - d channel inner diameter - d_in, d_out inner delivery and removal pipeline diameters - P flow pressure - P flow pressure at the input to the element - P_out flow pressure at the output from the element - G_o, G₁ initial and final flow rates of the cryogenic agent - z a coordinate - ¯z=z/L a dimensionless coordinate - dimensionless channel length - dimensionless cooling time - V₁ dimensionless temperature - k_G,a, k _u , f, m, , g parameters - A, B constants - Re Reynolds number - R gas constant - coefficient of dynamic viscosity - hydraulic drag coefficient - coefficient of heat elimination Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 629–635, October, 1980.     

低温精馏与低温气相色谱复合法分离氢同位素

采用低温精馏与低温气相色谱相结合的方法分离、浓缩氢同位素,探讨了分离过程操作参数间的内在联系.实验结果表明:氘浓度为10-3的100 m3原料气经过120 h的连续运行后,可以将氘浓度浓缩至91.5%;低温精馏柱随着回流比的增大,再沸器和冷凝器中氘浓度均减小;顶端采出量增大,再沸器中氘浓度明显增大;随再沸器加热功率的增加,液氢液位下降,床层压降增加,精馏柱操作压力从100 kPa上升到190 kPa,冷凝器和冷头为提供更多冷量温度降低;低温色谱的分离、浓缩效果十分显著,3次运行后将氘浓度从1.25×10-2提高到91.5%.     

Glass microsphere cryogenic insulation

The present paper discusses the new concept of glass microsphere cryogenic insulation and describes significant advances made in the past few years. Recent progress in microsphere characterization, basic heat transfer mechanisms, existing experimental data, and potential applications is presented.