Design of the PIXIE adiabatic demagnetization refrigerators

The Primordial Inflation Explorer (PIXIE) is a proposed mission to densely map the polarization of the cosmic microwave background. It will operate in a scanning mode from a sun-synchronous orbit, using low temperature detectors (at 0.1 K) and located inside a telescope that is cooled to approximately 2.73 K – to match the background temperature. A mechanical cryocooler operating at 4.5 K establishes a low base temperature from which two adiabatic demagnetization refrigerator (ADR) assemblies will cool the telescope and detectors. To achieve continuous scanning capability, the ADRs must operate continuously. Complicating the design are two factors: (1) the need to systematically vary the temperature of various telescope components in order to separate the small polarization signal variations from those that may arise from temperature drifts and changing gradients within the telescope, and (2) the orbital and monthly variations in lunar irradiance into the telescope barrels. These factors require the telescope ADR to reject quasi-continuous heat loads of 2–3 mW, while maintaining a peak heat reject rate of less than 12 mW. The detector heat load at 0.1 K is comparatively small at 1–2 μW. This paper will describe the 3-stage and 2-stage continuous ADRs that will be used to meet the cooling power and temperature stability requirements of the PIXIE detectors and telescope.     

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.     

Thermal conductivity of rigid foam insulations for aerospace vehicles

The present work describes measurements of the effective thermal conductivity of NCFI 24-124 foam, a spray-on foam insulation used formerly on the Space Shuttle external fuel tank. A novel apparatus to measure the effective thermal conductivity of rigid foam at temperatures ranging from 20 K to 300 K was developed and used to study three samples of NCFI 24-124 foam insulation. In preparation for measurement, the foam samples were either treated with a uniquely designed moisture absorption apparatus or different residual gases to study their impact on the effective thermal conductivity of the foam. The resulting data are compared to other measurements and mathematical models reported in the literature.     

Performances of the 50 mK ADR/sorption cooler

CEA/SBT is currently testing a 50 mK cooler developed in the framework of a European Space Agency Technological Research Program targeted for the Advanced Telescope for High Energy Astrophysics space mission. This cooler is composed of a small demagnetization refrigerator pre cooled by a sorption cooler stage. This Engineering Model is able to produce 1 μW of net heat lift at 50 mK and an additional 10 μW at 300 mK provided by the sorption cooler stage. The autonomy of the cooler is 24 h, and once the low temperature phase at 50 mK is over, it can be recycled in about 8 h with 10 μW and 100 μW available at respectively the 2.5 and 15 K heat sinks. These performances are in agreement with the European Space Agency requirements.In this paper, we present the detailed thermal performances of the cooler in nominal conditions as well as sensitivity measurements of the variation of the heat sink and the cold end temperatures.     

Low temperature thermal conductivity of aluminum alloy 5056

The thermal conductivity of 5056 aluminum alloy was determined from 4.2 K to 120 K using a differential steady-state method. This method has been implemented in a low temperature cryostat using a Gifford–McMahon cryocooler as heat sink. The thermal conductivity of the 5056 H39 aluminum alloy was determined since it was under consideration as a part of a thermal link for the Planck research satellite. As expected, below 10 K the thermal conductivity is exclusively given by the electron-defect scattering term. At higher temperature, the other terms from the electronic and the lattice contributions come into play but the electronic thermal conductivity term is still dominant. A workable fit, based on theory, is presented and can be used up to 300 K. Our measurements are compared with data at lower temperature and available fits from the literature.     

Performance validation tests on 80 K bubble type of shields for SST-1

The 80 K thermal shields of Steady State Superconducting Tokamak (SST-1) minimize the steady state heat loads on the superconducting magnet system at 4.5 K from ambient. Uniform temperature, vacuum and cryo compatibility is desired for the 80 K shields. In order to meet these requirements, the bubble/embossed type of design concept is adopted. This design ensures lower pressure drop and better temperature uniformity within ±5 K. Special attention has been given for preventing direct radiation on the magnet system. As part of performance validation tests, a group of 80 K thermal shields have undergone rigorous testing protocols and procedures. The temperature distribution, helium leak tightness and insulation resistance tests have been carried out for SST-1 thermal shields before final assembly of the machine. The test design, procedures and results of the 80 K thermal shields will be discussed in this paper.     

Low temperature physical properties of a high Mn austenitic steel JK2LB

High manganese austenitic stainless steel JK2LB is developed by the Japan Atomic Energy Agency for applications as a conduit material for superconducting cable-in-conduit conductors for the magnets of international thermonuclear experimental reactor (ITER). The low temperature physical property data of this material are very important to ITER magnet design. Therefore in this paper, our measurements of the physical properties including room temperature Young’s modulus and thermal expansion, magnetization, thermal conductivity, specific heat and resistivity at temperatures from room temperature down to 2 K are reported. We found that JK2LB is antiferromagnetic at low temperatures with a Néel temperature of 240 K. This is consistent with a prediction based on the chemical composition of the austenite stainless steel. The antiferromagnetic phase transition is also evident in the resistivity vs. T curve. Nevertheless, no anomalies are observable in its specific heat and thermal conductivity from 2 K to 300 K. The thermal expansion of this steel between 10 K and 300 K is about 0.22%. Its Young’s modulus, specific heat and thermal conductivity are comparable to that of 316LN stainless steel.     

Detailed design and transport properties of a helium droplet nozzle from 5 to 50 K

This paper reports our efforts to engineer a robust, user-friendly, and broadly tunable helium droplet nozzle, and to quantitatively measure its thermal and mass transport performance. In addition to describing the physical design in detail, we report helium throughput measurements for a 6.4 μm diameter nozzle over stagnation conditions ranging from 5 to 50 K and 10 to 100 bar. The measured flow rates were in excellent agreement with those predicted by a simple effusive flow model for nozzle temperatures above 20 K, but were systematically lower for both sub-critical and super-critical jets as the temperature was lowered. The helium flow through a 500 μm skimmer was also measured, and the skimmed fraction was found to vary by two orders of magnitude over the range of stagnation conditions investigated. These results indicate a substantial narrowing of the total jet angle spread from ～90° to 5° at temperatures below 10 K. Efforts to image the low temperature jet with Schlieren and shadowgraph techniques were unsuccessful. These details combined with previously reported theory and experiments on the droplet size distributions provide the necessary foundation to predict cluster production rates and to customize nozzle/pump designs for specific applications.     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

Herschel flight models sorption coolers

The Herschel and Planck satellites will be jointly launched on an ARIANE 5 in 2008. The Herschel payload consists of three instruments built by international scientific consortia, heterodyne instrument for first (HIFI), photo-conductor array camera and spectrometer (PACS) and spectral and photometric imaging receiver (SPIRE). The spacecraft provides the environment for astronomical observations in the infrared and sub-millimeter wavelength range requiring cryogenic temperatures for the cold focal plane units. The spectral and photometric imaging receiver (SPIRE) will cover the 200–670 μm spectral range using bolometric detectors, as the photo-conductor array camera and spectrometer (PACS) will cover the 60–210 μm spectral range. Both instruments SPIRE and PACS feature detectors operating at 300 mK. This cooling will be effected by two helium sorption coolers developed at the Service des Basses Températures of the Commissariat à l’Energie Atomique (CEA-SBT). These coolers based on an evaporative cooling cycle features no moving parts and can be recycled indefinitely pending the availability of a cold heat sink at temperature below 3 K. Several models were developed in the course of the Herschel program and this paper deals with the design, manufacturing and qualification of the flight model coolers.     

Low temperature physical properties of Co-35Ni-20Cr-10Mo alloy MP35N®

Multiphase Co-35Ni-20Cr-10Mo alloy MP35N® is a high strength alloy with excellent corrosion resistance. Its applications span chemical, medical, and food processing industries. Thanks to its high modulus and high strength, it found applications in reinforcement of ultra-high field pulsed magnets. Recently, it has also been considered for reinforcement in superconducting wires used in ultra-high field superconducting magnets. For these applications, accurate measurement of its physical properties at cryogenic temperatures is very important. In this paper, physical properties including electrical resistivity, specific heat, thermal conductivity, and magnetization of as-received and aged samples are measured from 2 to 300 K. The electrical resistivity of the aged sample is slightly higher than the as-received sample, both showing a weak linear temperature dependence in the entire range of 2–300 K. The measured specific heat C_p of 430 J/kg-K at 295 K agrees with a theoretical prediction, but is significantly smaller than the values in the literature. The thermal conductivity between 2 and 300 K is in good agreement with the literature which is only available above 77 K. Magnetic property of MP35N® changes significantly with aging. The as-received sample exhibits Curie paramagnetism with a Curie constant C = 0.175 K. While the aged sample contains small amounts of a ferromagnetic phase even at room temperature. The measured MP35N® properties will be useful for the engineering design of pulsed magnets and superconducting magnets using MP35N® as reinforcement.     

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.     

Forced flow He vapor cooled critical current testing facility for measurements of superconductors in a wide temperature and magnetic field range

As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN₂). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10–65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power.     

FPA annealing studies for the WISE mission cryostat

The wide-field infrared survey explorer (WISE) is a MIDEX mission that is being developed by the Jet Propulsion Laboratory (JPL) to address several of NASA’s Astronomical Search of Origins (ASO) objectives. The WISE instrument, developed by the Space Dynamics Laboratory (SDL), includes a cryogenically-cooled telescope (at <13 K) and four focal plane assemblies (2 at 7.6 K, 2 at 32 K). Cooling of the instrument is accomplished by a dual-stage solid hydrogen cryostat that is developed by the Lockheed Martin Advanced Technology Center (LM-ATC).Experience from Spitzer suggests that it will be required to warm the two Si:As LWIR arrays used on WISE to above 20 K approximately 4-times a day—i.e. anneal the arrays—to re-establish detector sensitivity. For SFHe systems, detectors are typically vapor cooled. As a result, the warming associated with the annealing process is only indirectly coupled to the cryogen. However, since the WISE focal plane assemblies are conduction coupled directly to the solid hydrogen tank, the potential exists for system impacts on lifetime, temperature stability, and mission duty cycle.This paper summarizes the results of some top-level sensitivity studies that characterize the effects of FPA annealing on a solid hydrogen cryostat—using the WISE cryostat and focal plane assemblies as a model. These trades provide a vector for candidate system level changes to the WISE instrument to help mitigate the impact of the annealing process on the cryostat’s performance.     

A lightweight low-current 10 K magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. Until now all space-flight compatible magnets have been made with NbTi wire, which has limited their operating temperatures to below about 5 K. We have developed a lightweight (1 Kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We explain the choice of this magnet’s specifications and describe its performance testing.     

Development of a lightweight low-current 10 K 4 T magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. We previously reported the development of a lightweight (1 kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We now report our progress in developing a new 10 K magnet of similar size made with smaller diameter Nb₃Sn wire which will produce a 4 T central field with approximately 5 A.     

Silica–silica polyimide buffered optical fibre irradiation and strength experiment at cryogenic temperatures for 355 nm pulsed lasers

A controlled UV-light delivery system is envisioned to be built in order to study the stability properties of superconducting strands. The application requires a wave guide from room temperature to cryogenic temperatures. Hydrogen loaded and unloaded polyimide buffered silica–silica 100 μm core fibres were tested at cryogenic temperatures. A thermal stress test was done at 1.9 K and at 4.2 K which shows that the minimal mechanical bending radius for the fibre can be 10 mm for testing (transmission was not measured). The cryogenic transmission loss was measured for one fibre to assess the magnitude of the transmission decrease due to microbending that takes place during cooldown. UV-irradiation degradation measurements were done for bent fibres at 4.2 K with a deuterium lamp and 355 nm pulsed lasers. The irradiation tests show that the fibres have transmission degradation only for wavelengths smaller than 330 nm due to the two photon absorption. The test demonstrates that the fibres are suitable for the cryogenic UV applications with 355 nm and 70 μJ pulsed lasers.     

Low temperature permeability and current noise of ferromagnetic pickup coils

For a non-destructive measurement of intensities of charged particle beams a Cryogenic Current Comparator is used which captures the azimuthal magnetic field of the beam by a superconducting pickup coil at 4.2 K and transforms it into a current which is detected by a SQUID based current sensor. The current noise of the pickup coil and the bandwidth of this transformer depend on the frequency response curve of the complex permeability of the ferromagnetic core material embedded in the pickup coil. A measurement of the series inductance L_S and series resistance R_S of such a coil allows an indirect evaluation of the current noise contribution of the core using the Fluctuation–Dissipation-Theorem. These measurements were done with a commercial LCR-Meter in a frequency range from 20 Hz to 2 MHz. The current noise density was also directly measured using a SQUID-sensor. A comparison with between the direct and indirect measurement showed a good coincidence. Due to the critical temperature of the LTS-SQUID, noise measurements above 4.2 K are not possible apart from using an anti-cryostat. The measurement of the series inductance L_S and series resistance R_S with an LCR-Meter works in the whole temperature range and provides a comfortable access to the magnetic properties of core materials. Compared to direct measurements, the indirect measurement thus allows a technologically simpler and broader determination of the core noise.     

Dual function sensors for concurrent measurement of temperature and magnetic field in cryogenic applications

Dual function sensors (DFSs) for concurrent measurement of temperature and magnetic field in cryogenic applications have been developed and characterized. The DFS consists of a Ge-on-GaAs film resistance thermometer and an InSb-on-GaAs film Hall-effect magnetic field sensor combined in a single package with dimensions: 3.5 mm wide, 2.2 mm thick and 10.1 mm long. The construction and characteristics of two models of the DFSs; which are intended to provide measurements of temperature in the 1.5–400 K and 0.1–400 K ranges, and magnetic fields up to 30 T, are presented.     

Structure and corrosion resistance of nickel coatings containing tungsten and silicon powders

Ni + W + Si coatings were prepared by nickel deposition from a bath containing a suspension of tungsten and silicon powders. These coatings were obtained at galvanostatic conditions, at the current density of j_dep = − 0.100 A cm^− 2 and at the temperature of 338 K. For determination of the influence of phase composition and surface morphology of these coatings on changes in the corrosion resistance, these coatings were modified in an argon atmosphere by thermal treatment at 1373 K during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. The chemical composition of the coatings was determined by EDS and phase composition investigations were conducted by X-ray diffraction. It was found that the as-deposited coatings consist of a three-phase structure, i.e., nickel, tungsten and silicon. The phase composition for the Ni + W + Si coatings after thermal treatment is markedly different. The main peaks corresponding to Ni and W coexist with the new phases: NiW, NiWSi and a solid solution of W in Ni.Electrochemical corrosion resistance investigations were carried out in 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found that the Ni + W + Si coatings after thermal treatment are more corrosion resistant in alkaline solution than the as-deposited coatings. The reasons for this are a reduction in the amount of free nickel and tungsten, the presence of new phases (in particular polymetallic silicides), and a decrease of the active surface area of the coatings after thermal treatment.