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A 1.1W/4.2K Gifford-McMahon (G-M) refrigerator has recently been developed by Advanced Research Systems, Inc. The typical cooling capacity of 40 W at 40K for the first stage and 1.1 W at 4.2 K for the second stage has been achieved. The cooling performance of this 4.2K G-M refrigerator was significantly improved by optimizing packing materials both inside 1st and 2nd stage regenerators, as well as operation conditions. The experimental results and improvements are presented and their optimal cases are also given in this paper. [ABSTRACT FROM AUTHOR]

Applications in superconductivity have become widespread, enabled by advancements in cryogenic engineering. In this paper, the history of cryogenic refrigeration, its delivery, its preservation and the important scientific and engineering advancements in these areas in the last 100 years will be reviewed, beginning with small laboratory dewars to very large scale systems. The key technological advancements in these areas that enabled the development of superconducting applications at temperatures from 4 to 77 K are identified. Included are advancements in the components used up to the present state-of-the-art in refrigeration systems design. Viewpoints as both an equipment supplier and the end-user with regard to the equipment design and operations will be presented. Some of the present and future challenges in these areas will be outlined. Most of the materials in this paper are a collection of the historical materials applicable to these areas of interest. [ABSTRACT FROM AUTHOR]

Future lunar and planetary explorations will require the storage of cryogenic propellants, particularly liquid oxygen (LOX) and liquid hydrogen (LH2), in low earth orbit (LEO) for periods of time ranging from days to months, and possibly longer. Without careful thermal management, significant quantities of stored liquid cryogens can be lost due to boil-off. Boil-off can be minimized by a variety of passive means including insulation, sun shades and passive radiational cooling. However, it has been shown that active cooling using space cryocoolers has the potential to result in Zero Boil-Off (ZBO) and the launch-mass savings using active cooling exceeds that of passive cooling of LOX for mission durations in LEO of less than 1 week, and for LH2 after about 2 months in LEO. Large-scale DC-flow cryogenic refrigeration systems operate at a fraction of the specific power levels required by small-scale AC-flow cryocoolers. The efficiency advantage of DC-flow cryogenic cycles motivates the current development of a cryocooler based on a modification of the Collins Cycle. The modified Collins cycle design employs piston type expanders that support high operating pressure ratios, electromagnetic valves that enable "floating pistons", and recuperative heat transfer. This paper will describe the design of a prototype Modified-Collins cryocooler for ZBO storage of cryogenic fuels in space. [ABSTRACT FROM AUTHOR]

The refrigeration power for large current superconductor systems, such as for electrical power distribution, is dominated by current lead losses. The use of multiple cooling stages between room temperature and ∼70 K is investigated as means to decrease the refrigeration power. We show that it is possible to decrease the electrical power requirements for the refrigerator by about 1/3 through the use of two-stages current leads; this computed power saving is based on a conservative estimate of refrigerator performance. Using data from real systems, that is, higher temperature refrigerators operating at higher fractions of their Carnot efficiencies we believe that the refrigerator electrical power requirement can actually be decreased by 1/2. Means have been investigated to optimize current lead performance at lower than maximum current operation. Adjustment of the cooling power of the intermediate temperature refrigerators achieves limited success in power consumption minimization. Other means to optimize the performance will be described. The implications of intermediate stages for stability of the current leads following a short overcurrent period will be described. [ABSTRACT FROM AUTHOR]

We present the experiences of the manufacturing and the operating of a system of two identical cryosorption pumps used in a neutral beam injector test facility for fusion reactors. Calculated and measured heat loads of the cryogenic liquid helium and liquid nitrogen circuits of the cryosorption pumps are discussed. The design calculations concerning the thermo-hydraulics of the helium circuit are compared with experiences from the operation of the cryosorption pumps. Both cryopumps are integrated in a test facility of a neutral beam injector that will be used to heat the plasma of a nuclear fusion reactor with a beam of deuterium or hydrogen molecules. The huge gas throughput into the vessel of the test facility results in challenging needs on the cryopumping system. The developed cryosorption pumps are foreseen to pump a hydrogen throughput of 20 – 30 mbar·l/s. To establish a mean pressure of several 10-5 mbar in the test vessel a pumping speed of about 350 m3/s per pump is needed. The pressure conditions must be maintained over several hours pumping without regeneration of the cryopanels, which necessitates a very high pumping capacity. A possibility to fulfill these requirements is the use of charcoal coated cryopanels to pump the gasloads by adsorption. For the cooling of the cryopanels, liquid helium at saturation pressure is used and therefore a two-phase forced flow in the cryopump system must be controlled. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Following Siemens (1857), we explore the formulation of a fundamental and common principle behind the operation of all cryocoolers. This conceptual model requires any cryocooler to include two essential elements: (a) a generator of an elementary and relatively small temperature-reduction and (b) a device that magnifies this reduction to produce a large cryocooling span. The magnification (b) is sustained by two thermally interacting counter flowing streams so arranged that the cold inlet temperature is permanently maintained below the warm outlet by (a), the elementary temperature-reducing mechanism. High magnification ratios are obtained when the two streams are balanced and even higher when the capacity rate of the high temperature stream is lower than that of the low temperature stream. When the elementary temperature-reduction is produced via a continuous (DC) flow, the associated magnification device is a recuperative heat exchanger. When an oscillatory (AC) flow device is used to produce the temperature reduction, then the magnification device is a regenerative heat exchanger. The various cryocoolers known as Joule-Thomson (JT) with a pure or mixed coolant, reverse-Brayton, Stirling, dilution refrigerator, active magnetic regenerative refrigeration (AMRR) and single shot adiabatic demagnetization refrigerators (ADR) are all discussed and reviewed in terms of this model. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A single-stage coaxial pulse tube refrigerator has been designed for HTS (High Temperature Superconductor) motor application. This paper discusses a practical realization of an advanced cooling method for superconducting rotor, on-board cryocooler. When a cryocooler is considered to be mounted on the superconducting rotor, the following two factors must be satisfied for practical application. First, the on-board cryocooler should not disturb the high-speed revolution of the rotor. Second, at the same time, the high-speed revolution of the rotor should not deteriorate the cooling performance of the cryocooler. These mutual technical demands restrict the type of cryocooler suitable for high-speed rotating environment. We select a Stirling-type coaxial pulse tube cryocooler and incorporate it on the 1800-rpm superconducting motor mock-up. The pulse tube cryocooler is designed with an adiabatic model and a various loss mechanism analysis. The no-load temperature is approximately 100 K with less than 150 W electric input power. The axisymmetric configuration of the fabricated cryocooler does not produce any undesirable effect at high-speed rotation. Even if the thermal performance of the rotating pulse tube cryocooler is not satisfactory, the feasibility of simple on-board cooling method for superconducting rotor is confirmed in this paper. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Demands are made on refrigerators for future HTS-series products like generators, motors, transformers, which are only partly fulfilled by commercially available refrigerators. Based on the experiences with HTS-prototypes, pulse tube refrigerators (PTRs) are considered to have the highest potential to fulfill the identified requirements. Siemens have therefore started the development of a high-performance PTR together with TransMIT Giessen. Design target is a PTR with a cooling power of 80 W near 25 K based on an oil-free CFIC — linear compressor with a power input of 2 × 5 kW. The initial tests on the first single-stage laboratory version of this PTR with stainless steel mesh regenerator revealed high regenerator losses from circulating mass flow that manifests itself in form of an azimuthal temperature asymmetry in the regenerator. The circulating flow can be greatly reduced by increasing the transverse heat conductance of the matrix by use of stacks of different materials. So far, the minimum no-load temperature of the PTR is 35 K and a cooling power of 75 W is available at 50 K with a compressor efficiency of about 80 %. Further optimization of the regenerator matrix appears to be possible. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

National Institute for Materials Science (NIMS) and Kanazawa University have been developing a magnetic refrigerator for hydrogen liquefaction since it is possible more efficient than conventional liquefaction systems around the hydrogen liquefaction temperature (20K). The magnetic refrigerator consists of a magnet, heat switches and a magnetic material that exhibits magnetocaloric effect (MCE) which heats up and cools down when magnetized and demagnetized, respectively. This paper describes outline of our magnetic refrigerator as well as newly developed magnetic materials, poly crystal 20% Gadolinium doped Dysprosium Aluminum Garnet (DGAG). Cooling power of the system and the magnetic force acts on the DGAG in the field are also calculated for system evaluation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Over the years, NASA has developed a wide variety of new cryocooler technologies, as they represent a significant enabling capability for both Earth and space-science missions. Recent achievements include 50–80 K Stirling, pulse tube, and Brayton flight cryocoolers, and multistage development-model coolers at temperatures down to 10K. The largest technology push within NASA right now is in the temperature range of 4 to 6K. Missions such as the James Web Space Telescope, Terrestrial Planet Finder, and future generations of space telescopes, plan to use infrared detectors operating between 4 and 6K. Similarly, future x-ray and microwave missions plan to use microcalorimeters and bolometers operating at milli-Kelvin temperatures and will require 4–6 K cooling to precool their sub-Kelvin refrigerators. To address cryocooler development for these next-generation missions, NASA initiated the Advanced Cryocooler Technology Development Program (ACTDP) in 2001. Since that time, the program has completed detailed designs and development-model hardware of three hybrid pulse tube and Stirling cryocooler concepts for cooling to 4–18 K. This paper presents an overview of the ACTDP program including programmatic objectives and timelines, and summarizes the excellent progress of the three design concepts being fabricated and tested at this time. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The LNG20 is a small-scale natural gas liquefier. Its capacity is 20 cube meters LNG per day. This liquefier could be used for the pipeline gas, coalbed gas, oil field gas liquefaction and peakshaving plant for town gas gate station and natural gas power plant. Two processing cycles are applied to LNG20, nitrogen expander cycle and mixed refrigerant cycle. In this report, two feed gases are the target sources; one is the pipeline gas in “West-to-east pipeline gas” in a gate station in Zhejiang province and coalbed gas in Northeast China. The numerical simulation and optimization for the LNG20 were carried out to obtain the design parameters. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The NGST ACTDP cooler features a 5–6 K Joule-Thomson (JT) cooler pre-cooled by a three-stage Pulse Tube (PT) cryocooler. Our design provides remote cooling of ∼60 mW at 5 to 6 K and, optionally, remote cooling at 18 K. The NGST ACTDP cooler is being developed under contract with the Jet Propulsion Laboratory to enable active cooling of instruments including large space telescopes, in particular the Mid InfraRed Instrument (MIRI) of the James Webb Space Telescope (JWST). This paper describes the design of the NGST ACTDP cooler and presents test results, including the integrated tests of the two major subsystems making up the thermal-mechanical cryocooler, the closed loop JT cooler and the PT pre-cooler. Both the JT and PT subsystems have been demonstrated to provide the cooling required for MIRI in laboratory tests using flight like hardware with excess capacity. These tests enable a reliable projection of the total electrical power of the NGST MIRI cooler of 200–296 W for steady state operation under end of life conditions, depending on the margins added to the thermal loads and parasitics. NGST’s design offers a low risk approach to providing cooling of MIRI making maximum use of flight proven hardware. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Lockheed Martin Advanced Technology Center (LMATC) has built and tested a 4-stage pulse tube cryocooler, which provides simultaneous cooling at 6 K and 18 K. The cryocooler is designed to meet NASA’s cryocooler needs for low temperature, with immediate application to the Terrestrial Planet Finder, Constellation-X, and other future space-science missions. The simplicity with LMATC’s approach of the single compressor, coldhead, and electronic controller makes it very appealing for applications requiring high reliability. It further allows the system to be readily modified for different program requirements. The LM pulse tube is a simple 4-stage coldhead with no moving parts, driven by a long-life linear flexure-bearing clearance-seal compressor. The cryocooler is designed to provide 20 mW of cooling at 6 K and 150 mW cooling at 18 K while rejecting heat at 290 K. Performance data is presented, showing excellent cryocooler performance, meeting JPL’s cooling requirements, and achieving a no-load temperature below 4 K. This work was funded by the Jet Propulsion Laboratory’s Advanced Cryocooler Technology Development Program (ACTDP), Ron G. Ross, Contract Manager. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A completely oil-free compressor for use with GM cryocoolers has been designed, built, and tested. The compressor uses two, fully-balanced, STAR linear motors together with friction-free reed valves. This arrangement eliminates all possibility of oil contamination in the helium working fluid, and therefore also eliminates the regular servicing that is required by conventional GM compressors. The compressor delivers high-pressure flows comparable to those delivered by well-developed conventional compressors, and is designed to match the operating point pressures and flow for a Sumitomo model 408 cold head. The design of the compressor is briefly reviewed. The measured performance of the compressor when integrated with a Sumitomo model 408 GM cold head is presented. The performance is mapped as a function of the refrigeration load and temperature at both the first and second stage heat exchangers and is compared with the both the manufacturer specified performance and separate baseline tests for the same cold head integrated with a conventional oil-flooded GM compressor. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper describes the design, development, testing and performance at Ball Aerospace of a long life, 4–6 K temperature space cryocooler. For temperatures to 4 K and below, Ball has developed a hybrid Stirling/ Joule-Thomson (J-T) cooler. The hybrid cooler has been verified in test to 3.5 K on a Ball program and a 6 K Development Model is in development on the NASA/JPL Advanced Cryocooler Technology Program (ACTDP). This paper will include the test status on the Stirling Precooler and the Thermal System Breadboard. The ACTDP cooler provides simultaneous cooling at 6 K (typically, for either doped Si detectors or as a sub-Kelvin precooler) and 18 K (typically, for optics or shielding) with cooling stages also available at 40 and 180 K (typically, for thermal shields or other components). The ACTDP cooler is under development for the NASA Terrestrial Planet Finder (TPF), Constellation X-Ray (Con-X), and other future missions. The 4–6 K cooler is highly leveraged off previous Ball space coolers including multiple life test and flight units. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In order to reduce the life-cycle cost of systems that use cryocoolers, it is necessary to extend the operating life of the cooler beyond what is currently available for tactical military applications. Several approaches have been used to increase life such as flexure bearing and gas bearing support. It was determined that a gas bearing system offered a novel and cost effective approach for our products. This paper presents the implementation of a gas bearing system into the miniature cryocooler compressor. The theoretical analyses used to design the gas bearing system will be discussed and empirical data comparing the performance between the baseline and gas bearing coolers will be presented. A life test program is being undertaken to verify the life characteristics of the gas bearing cooler and the results will be summarized and published at a later date. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fuji Electric Group has developed a miniature pulse tube cryocooler (PTC) of U-shaped configuration with a specific cooling capacity of 2W at 70K and requiring 100W of electrical input power. The emphasis has been on compactness, light weight, high performance, high reliability and low cost. This PTC is for commercial applications: for example, semiconductivity and high temperature superconductivity (HTS) devices used in wireless telecommunication systems and imaging sensors. The dimensions of the PTC have been reduced to 246mm wide by 232mm high and a weight of 8.5kg as integral configurations. The linear compressor motor uses two sets of moving coils to drive twin pistons supported by flexure bearings in a dual opposed configuration. The phase shifter, consisting of an inertance tube and reservoir tank, has been optimized. We produced and tested a prototype reduced-cost PTC. The prototype has a cooling capacity greater than 2.5W at 70K with 100W of electrical input power. The vibration of the cold head is less than 2 micrometers (peak to peak) when the hot-end side flange of the expander is fixed. This paper describes in detail its performance including inclination and vibration. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The thin windows for the Muon Ionization Cooling Experiment (MICE) liquid Absorber will be fabricated from 6061-T6-aluminum. The absorber and vacuum vessel thin windows are 300-mm in diameter and are 180 μm thick at the center. The windows are designed for an internal burst pressure of 0.68 MPa (100 psig) when warm. The MICE experiment design calls for changeable windows on the absorber, so a bolted window design was adopted. Welded windows offer some potential advantages over bolted windows when they are on the absorber itself. This report describes the bolted window and its seal. This report also describes an alternate window that is welded directly to the absorber body. The welded window design presented permits the weld to be ground off and re-welded. This report presents a thermal FEA analysis of the window seal-weld, while the window is being welded. Finally, the results of a test of a welded-window are presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Muon Ionization Cooling Experiment (MICE) will test ionization cooling of muons. In order to have effective ionization cooling, one must use an absorber that is made from a low-z material. The most effective low z materials for ionization cooling are hydrogen, helium, lithium hydride, lithium and beryllium, in that order. In order to measure the effect of material on cooling, several absorber materials must be used. This report describes a liquid-hydrogen absorber that is within a pair of superconducting focusing solenoids. The absorber must also be suitable for use with liquid helium. The following absorber components are discussed in this report; the absorber body, its heat exchanger, the hydrogen system, and the hydrogen safety. Absorber cooling and the thin windows are not discussed here. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This report discusses the use of small cryogenic coolers for cooling the Muon Ionization Cooling Experiment (MICE) liquid cryogen absorbers. Since the absorber must be able contain liquid helium as well liquid hydrogen, the characteristics of the available 4.2 K coolers are used here. The issues associated with connecting two-stage coolers to liquid absorbers are discussed. The projected heat flows into an absorber and the cool-down of the absorbers using the cooler are presented. The warm-up of the absorber is discussed. Special hydrogen safety issues that may result from the use of a cooler on the absorbers are also discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A group of laboratories and universities, with Fermilab taking the lead, are constructing a superconducting cryomodule test facility (SMTF) in the Meson Detector Building (MDB) area at Fermilab. The facility will be used for testing and validating designs for both pulsed and CW systems. A multi phase approach is taken to construct the facility. For the initial phase of the project, cryogens for a single cavity cryomodule will be supplied from the existing Cryogenic Test Facility (CTF) that houses three Tevatron satellite refrigerators. The cooling capacity available for cryomodule testing at MDB results from the liquefaction capacity of the CTF cryogenic system. A cryogenic distribution system to supply cryogens from CTF to MDB is under construction. This paper describes plans, status and challenges of the initial phase of the SMTF cryogenic system. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Nuclear fusion reactors of the Tokamak type will be operated in a pulsed mode requiring the helium refrigerator to remove periodically large heat loads in time steps of approximately one hour. What are the necessary steps for a refrigerator to cope with such load variations? A series of numerical simulations has been performed indicating the possibility of an active refrigerator control with low exergetic losses. A basic comparison is made between the largest existing refrigerator sizes and the size required to service for example the ITER requirements. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The goal of the overall program is to develop a dynamic numerical model of helium refrigerators and the associated cooling systems based on commercial simulation software. The aim is to give system designers a tool to search for optimum control strategies during the construction phase of the refrigerator with the help of a plant “simulator”. In a first step, a simple Brayton refrigerator has been investigated, which consists of a compressor, an after-cooler, a counter-current heat exchanger, a turboexpander and a heat source. Operating modes are “refrigeration” and “liquefaction”. Whereas for the steady state design only component efficiencies are needed and mass and energy balances have to be calculated, for the dynamic calculation one needs also the thermal masses and the helium inventory. Transient mass and energy balances have to be formulated for many small elements and then solved simultaneously for all elements. Starting point of the simulation of the Brayton cycle is the steady state operation at design conditions. The response of the system to step and cyclic changes of the refrigeration or liquefaction rate are calculated and characterized. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A dynamic simulation of a large scale cryogenic plant has been conducted, using the Cryogenic Process REal-time SimulaTor (C-PREST) developed as a platform to study cryogenic plant processes. The target plant, Large Helical Device (LHD), consists of a 10 kW class helium refrigerator/liquefier and superconducting coil systems with their supporting structure. Since the development of helium refrigerator/liquefier had been completed, the simulation model was focused on the superconducting coil systems. As the preliminary step for the entire cryogenic plant, the coils are simplified and modeled to have certain temperature efficiencies. Cooldown of the coil systems were conducted from the room temperature to close to 4.4 K, utilizing automatic cooldown sequence programs for the actual cryogenic plant. The paper discusses the computational speed just before establishing the two-phase flow condition and the validity of the simulations compared with the real plant operation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC) at CERN will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to one 18 kW at 4.5 K refrigerator. The supply of the series units was linked to successful testing and acceptance of the pre-series units delivered by the two selected vendors. The two pre-series units were temporarily installed in a dedicated test station to validate the overall capacity and to properly assess the performance of specific components such as the cold compressors. The cold-compressor cartridges to be installed in the following six series, and the associated spare cartridges, were intensively and systematically tested in the test station. After a brief description of the test bench and the main achieved features of the pre-series units, we will present the results of the tests of 35 cold-compressor cartridges. These tests show isentropic efficiency in the 75 % range, with excellent reproducibility and interchange ability. Some process and system specifics observed will be reported and finally perspectives will be proposed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Air Liquide’s Advanced Technology Division is a manufacturer of cryogenic expanders. More than 450 units are now working around the world, mainly dedicated to liquefiers, refrigerators and H2-CO purification units. In order to cope with the power increase of these units, a new expander called “TC7” has been developed and tested. This expander permits turbine wheel diameters up to 110 mm, while the other units of the range (from TC3 to TC6, by increasing wheel diameter) are limited to 78 mm. The maximum flow rate is therefore doubled. The main technical features of the existing range have been kept, and adapted in size: static radial and thrust bearings, low loss casing, variety of wheel shapes (radial-radial shrouded or un-shrouded, radial-axial). This paper describes the main design characteristics of this new expander, together with manufacturing aspects and test results. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Up to now He piston pumps were used in the TOSKA facility of the Forschungszentrum Karlsruhe for circulating supercritical He in a secondary cooling loop. The performance of these pumps was a mass flow rate up to 150 g/s each, a pressure head of up to 0.3 MPa and an operation in the temperature range between 1.8 K and 5 K. For redundancy reasons, a centrifugal pump, developed by industry, was installed in an extension of the control cryostat, integrated into the existing cooling system, and tested in 2004. During the first tests, large oscillations and a huge heat input to the cooling circuit prevented operation of the pump. After some modifications by the supplying company, the pump was tested again with very promising test results. The results are in very good agreement with the predictions of the supplier. Details of the installation, the integration into the cooling system as well as the operational experience and test results will be outlined. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Thermal acoustic oscillations (TAOs) were recently observed and eliminated in two vacuum-housing cryogenic pumps. This paper documents the results of research performed to identify the critical parameters that affect thermal acoustic oscillations in a vacuum-housing cryogenic pump. Techniques for simplifying this complex oscillation system were developed so that an existing mathematical model for a straight tube with uniform radius could be applied. Based on the simplified model, criteria were defined. These criteria provide design guidelines to prevent thermal acoustic oscillations from occurring inside vacuum-housing cryogenic pumps. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Turbomachine-based Brayton (turbo-Brayton) cryocoolers are an ideal option for long-duration space missions. Key attributes inherent to the technology are high reliability, extremely low vibration emittance, and flexible packaging and integration with instruments and spacecraft systems. The first space implementation of the technology was the NICMOS Cryocooler, which is a single-stage unit that was installed on the Hubble Space Telescope in March 2002. This cryocooler provides 7 W of cooling at 70 K and has been operating for 3.3 years (July 2005) without degradation in performance. New developments at Creare are focused on two-stage configurations with load temperatures as low as 6 K. The lower temperatures and loads have required advances in component technologies to meet aggressive targets for cryocooler mass, size and performance. The development of the electronics, compressors and intermediate turboalternator for a 6–10 K cryocooler are complete. This paper summarizes our accomplishments on the completed components, and reviews our progress towards the development of the remaining critical components, a lightweight recuperator and a high performance low temperature turboalternator. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A multi-stage 10K cryocooler is under development that achieves compactness and reliability by using modern microelectronics to enable complex valve timing in a mechanically simple yet efficient cold head design. The cryocooler is based upon a novel modification of the Collins cycle, a cycle commonly used in many large-scale high-efficiency terrestrial cryogenic machines. This cycle is particularly well suited for cryocoolers operating from 4 K up to about 30 K. The modular nature of this design enables the configuration of application specific two stage (30 K), three stage (10 K), and four stage (4 K) cryocoolers. Innovations of the design include floating piston expanders and electromagnetic smart valves, which eliminate the need for mechanical linkages and thereby reduce the input power, size, and weight of the cryocooler in an affordable modular design. A sophisticated LabView based control algorithm enables electronic control of the expansion cycle. Software based control enables variable valve timing and adaptive control logic. An engineering prototype has been built that integrates the floating piston expander and recuperative heat exchanger as a functional cryocooler. The engineering prototype is currently undergoing development testing. This paper will present the design of the engineering prototype, the results of initial engineering prototype development testing, and the direction of future development. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Under contract with the Air Force Research Lab (AFRL), Lockheed Martin has built and tested a 3-stage pulse tube cryocooler which provides cooling at 10K and 75K. The cooler was designed for 200mW cooling at 10K and 8W cooling at 75K. The pulse tube is a simple 3-stage coldhead with no moving parts, driven by a long-life linear flexure-bearing clearance-seal compressor. The coldhead is a robust U-tube arrangement, with all metal seals for long life. Performance data will be presented. Future Air Force and Department of Defense (DoD) satellites will require efficient, low temperature cryocoolers to support space surveillance, missile defense, and other mission applications. The use of Very Long Wave Infrared (VLWIR) focal planes using arsenic doped silicon detectors operating at 10K which can detect to 25 micron wavelength has long been sought as the solution to the mid course missile defense mission. The immaturity of 10K cryocooler technology has impeded the use of VLWIR focal planes in current space payloads. A viable, efficient 10K cryocooler could provide further benefits through the use of on-focal plane readout and signal processing using low temperature superconducting electronics. The resultant smaller apertures produce cheaper, lighter sensors, much easier to host in a space-based system. An efficient, compact 10K cryocooler would provide significant capability improvements to future DoD systems. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Advances in the field of microfabrication have resulted in the ability to fabricate advanced geometries in various materials for use as regenerators in cryocoolers. Microchannels have been produced in nickel, stainless steel, lead and erbium, and these microfabrication techniques can also be applied to other rare-earth materials. Regenerators produced by this method will greatly benefit the cryocooler industry due to the fact that the power efficiency and the attainable cold end temperature are strongly influenced by the geometry of the regenerator. These new fabrication techniques allow the designer to reduce the pressure drop across the regenerator and optimize the regenerator performance by varying the porosity, channel shape, and channel size. The resulting regenerators support lower NPH/NTU values over the screens and powders currently in use. Models that have been developed for microchannel regenerator designs indicate that cryocooler efficiencies can be significantly improved relative to packed powder and screen regenerators. Both DC and oscillating testing systems are being developed to experimentally determine the performance of microchannel regenerators. The current fabrication and testing results will be presented as well as the future development strategy. Improvements in the thermal performance of regenerators will result in an overall improvement in cryocoolers, especially at the lower temperature ranges. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The ceramics oxide magnetic materials have shown excellent properties for use as regenerator materials used in 4 K crycoolers. Currently four kinds of oxide magnetic materials GdVO4, GAP=GdAlO3, GOS=Gd2O2S and Tb2O2S are available for applications for regenerators or thermal anchors from 2 K to 8 K. This paper focused on controlling the heat capacity of the (GdxTb1-x)2O2S system to cover the refrigeration temperatures between 6 K and 8 K. A concept of multilayer regenerator material consisting of multicomponent magnetic materials has been proposed and investigated. Two-layer ceramic material including two kinds of magnetic materials (Gd0.1Tb0.9)2O2S+Tb2O2S was successfully fabricated in the form of regenerator particles with an average diameter of 0.25 mm. Measured heat capacity data showed that it had twin peaks relating to those of (Gd0.1Tb0.9)2O2S and Tb2O2S, and the entire curve became broader and wider. The mechanical properties of strength and hardness of the two-layer ceramic material were the same as other ceramic regenerator materials like GOS. Thus, it is concluded that the multilayer ceramic material is very useful to control the heat capacity of the regenerator particles. The cooling tests using the two-layer ceramic material with HoCu2 and GOS have been done to investigate the 2nd stage regenerator configuration. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pulse tube refrigeration (PTR) systems are often modeled as one-dimensional flow fields. However, recent computational fluid dynamics (CFD) — based investigations have shown that multi-dimensional flow effects can be significant in the regenerator of a PTR, especially when the aspect ratio of the regenerator is small. Anisotropic hydrodynamic parameters of regenerators are therefore needed for the realistic simulation of their multi-dimensional flow phenomena. In this paper we report on measurements of the lateral or radial permeability and Forchheimer’s inertial coefficient of a widely used PTR regenerator filler. Using helium as the working fluid, steady-state pressure drops were measured over a wide range of flow rates in annular test sections that contained regenerator fillers. The aforementioned hydrodynamic parameters were then obtained by comparing the data with the results of CFD calculations that simulated the test sections and their vicinity. CFD simulations of the experiments were performed iteratively, whereby permeability and Forchheimer coefficient that brought about agreement between data and simulation results were calculated. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The size of Stirling and Stirling-type pulse tube cryocoolers is dominated by the size of the pressure oscillator. Such cryocoolers typically operate at frequencies up to about 60 Hz for cold-end temperatures above about 60 K. Higher operating frequencies would allow the size and mass of the pressure oscillator to be reduced for a given power input. However, simply increasing the operating frequency leads to large losses in the regenerator. The simple analytical equations derived here show how the right combination of frequency and pressure, along with optimized regenerator geometry, can lead to successful regenerator operation at frequencies up to 1 kHz. Efficient regenerator operation at such high frequencies is possible only with pressures of about 5 to 8 MPa and with very small hydraulic diameters and lengths. Other geometrical parameters must also be optimized for such conditions. The analytical equations are used to provide guidance to the right combination of parameters. We give example numerical calculations with REGEN3.2 in the paper for 60 Hz, 400 Hz, and 1000 Hz operation of optimized screen regenerators and show that the coefficient of performance at 400 Hz and 1000 Hz is about 78 % and 68 %, respectively, of that for 60 Hz when an average pressure of 7 MPa is used with the higher frequency, compared with 2.5 MPa for 60 Hz operation. The 1000 Hz coefficient of performance for parallel tubes is about the same as that of the screen geometry at 60 Hz. The compressor and cold-end swept volumes are reduced by a factor of 47 at 1000 Hz, compared with the 60 Hz case for the same input acoustic power, which can enable the development of microcryocoolers for MEMS applications. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The need for improved regenerative cryocooler efficiency may require the replacement of conventional matrices with ducts. The ducts can not be continuous in the direction of temperature gradient when using conventional materials to prevent unacceptable conduction losses. However, this discontinuity creates a complex geometry to model and determine conduction losses. Chesapeake Cryogenics, Inc. has designed, fabricated and tested an apparatus for measuring the heat conduction through regenerative heat exchangers implementing different matrices. Data is presented for stainless steel photo etched disk, phophorus-bronze embossed ribbon coils and screens made of both stainless steel and phosphorus-bronze. The heat conduction was measured with the regenerators evacuated and pressurized with helium gas. In this test apparatus, helium gas presence increased the heat leak significantly. A description of the test apparatus, instrumentation, experimental methods and data analysis are presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Launched on NASA’s Aura spacecraft on July 15, 2004, JPL’s Tropospheric Emission Spectrometer (TES) instrument has completed a successful first year in space and captured a number of important lessons. The instrument contains four focal plane arrays in two separate housings cooled to 65 K by a pair of NGST pulse tube cryocoolers. The instrument includes a two-stage passive cooler to cool the optical bench to 180 K. The cryocooler system design is tightly coupled with the overall thermal control design to maximize performance. Soon after cooling the optical bench and focal planes to their operating temperatures on August 20, 2004, ice contamination of the focal planes led to the need of a decontamination cycle. Ice buildup of cryogenic surfaces led to increased cryocooler heat loads. After six months of successful science operations, plans were developed to increase the optics temperature to 187 K to improve the interferometer optical alignment and obtain higher quality science data. The plan is in place and will be implemented in the near future. This paper provides a general overview of the cryogenic system design and reviews the instrument cryogenic performance over the past year. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper describes the HIRDLS (High Resolution Dynamic Limb Sounder) Cryocooler Subsystem (CSS) and its on-orbit flight performance. The HIRDLS Instrument was launched on July 15, 2004 as part of the NASA GSFC EOS Aura platform. Ball Aerospace provided the CSS, which includes the long life Stirling cryocooler (cooling at 59 K), cold plumbing to connect the cooler to the instrument Detector Subsystem, an ambient radiator to reject the cooler dissipation, and a vacuum enclosure system that enabled bench top ground testing. As of August 20, 2005, the cryocooler has over 9,000 hours of continuous operation with performance that exceeds requirements. Of note is that the CSS has experienced virtually no change in performance, including no indication of external contamination related degradation that has been evident on several other cryocooler systems in space flights. This steady performance can be attributed to the multi-layer insulation (MLI) based insulation design, which will be described in the paper. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

An ongoing program at Brookhaven National Laboratory (BNL) consists of improving the efficiency of the Relativistic Heavy Ion Collider (RHIC) cryogenic system and reducing its power consumption. Phase I and II of the program addressed plant operational improvements and modifications that resulted in substantial operational cost reduction and improved system reliability and stability, and a compressor input power reduction of 2 MW has been demonstrated. Phase III, now under way, consists of plans for further increasing the efficiency of the plant by adding a load “wet” turbo-expander and its associated heat exchangers at the low temperature end of the plant. This additional stage of cooling at the coldest level will further reduce the required compressor flow and therefore compressor power input. This paper presents the results of the plant characterization, as it is operating presently, as well as the results of the plant simulations of the various planned upgrades for the plant. The immediate upgrade includes the changes associated with the load expander. The subsequent upgrade will involve the resizing of expander 5 and 6 to increase their efficiencies. The paper summarizes the expected improvement in the plant efficiency and the overall reduction in the compressor power. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A Large heat lift 40 to 80 K Pulse Tube Cooler (LPTC) is currently under development in partnership between AL/DTA, CEA/SBT and THALES Cryogenics. The Engineering Model (EM) foreseen is aiming to provide 2 W of cooling capacity at 50 K for 10°C rejection temperature and for 125 watts input power to the compressor’s motors. Cold finger development models (DM) have been manufactured with an in-line architecture and connected to an off-the-shelf compressor from Thales Cryogenics. In parallel, the compressor motor has been optimized and prototyped. The various trade-offs, performed both on the cold finger and compressor side, during the development phase are presented. This work is funded by the European Space Agency (ESA/ESTEC Contract N°18433/04/NL/AR) in the frame of future Earth Observation instruments development. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Under contract with the Space Dynamics Laboratory, Lockheed Martin’s Advanced Technology Center (LM-ATC) has built and tested the two-stage Engineering Model of a space flight pulse tube cryocooler, which provides simultaneous cooling at 75 K and 130 K. The cryocooler is robust and simple, consisting of a two-stage coldhead with no moving parts, driven by a linear flexure-bearing compressor and powered by a high-efficiency electronic controller that includes ripple suppression and vibration cancellation. A distance of up to one meter separates the coldhead and compressor. The cryocooler was designed to simultaneously provide 0.75 W of cooling at 75 K and 6 W cooling at 130 K while conductively rejecting heat at 313 K. Total system power is 125 W. Performance data is presented, showing excellent cryocooler performance. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Lockheed Martin’s Advanced Technology Center has developed a compact coaxial pulse tube cryocooler for avionics applications. The cooler was designed to deliver in excess of 1W cooling at 77K with a heat rejection temperature of 70°C, and to cool down from ambient temperature in a very short period of time. The cryocooler utilizes our MINI compressor, developed for NASA-GSFC, coupled with a newly-designed coaxial pulse tube designed to approximate the Standard Advanced Dewar Assembly (SADA II) packaging envelope. The cryocooler mass is 1.25 kg. Test data show excellent performance, with cooldown times of less than 6 minutes (coldhead only, with no additional thermal mass attached to the coldhead). Performance data will be shown for a variety of operating conditions. A discussion of low cost pulse tube cryocoolers will also be presented. This cryocooler was developed and tested with Lockheed Martin IRAD funding. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

An analysis of the Claude form of an idealized helium liquefier for the minimum input work reveals the ‘Carnot Step’ for helium refrigerator cycles. As the ‘Carnot Step’ for a multi-stage polytropic compression process consists of equal pressure ratio stages; similarly for an idealized helium liquefier the ‘Carnot Step’ consists of equal temperature ratio stages for a given number of expansion stages. This paper presents the analytical basis and some useful equations for the preliminary examination of existing and new Claude helium refrigeration cycles. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper describes the test results of the helium cryoplant for the superconducting magnets of the ATLAS particle detector at CERN. It consists of two refrigerators used in common by all the magnets and of two proximity cryogenic systems (PCS) interfacing respectively the toroids and the central solenoid. Emphasis is given to the commissioning of the refrigerators: the main unit of 6 kW equivalent capacity at 4.5 K and the thermal shield refrigerator providing 20 kW between 40 K and 80 K. The first unit is used for refrigeration at 4.5 K and for the cooling of three sets of 20 kA current leads, while the second one provides, in addition to the 20 kW refrigeration of the thermal shields, 60 kW for the cool-down to 100 K of the 660 ton cold mass of the magnets. The tests, carried out with the equipment in the final underground configuration, are extended to the PCS that includes the large liquid helium centrifugal pumps (each providing 1.2 kg/s) for forced-flow cooling of the magnets and the complex distribution system needed to fulfill their different operating requirements. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

At CERN a new helium refrigeration plant specified for a cooling capacity of 800 W at 4.45 K, 4500 W between 60 K and 80 K and 4 g/s liquefaction simultaneously has been installed and commissioned. In a first operation phase, the plant will provide the refrigeration capacity for the cool down and the operation of the superconducting solenoid of the CMS experiment during the magnet tests at the surface of the LHC interaction point 5. On completion of the tests a part of the refrigeration plant will be dismantled and moved to its final underground position next to the CMS experimental cavern. This paper compiles the commissioning activities starting from the compressor station up to the intermediate cryostat interfacing the refrigerator cold box with the magnet thermosiphon cooling system. It reports the problems encountered and the lessons learned during the commissioning phase and summarizes the results of the refrigeration power measurements in the transient cool-down and the steady-state operation modes. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

AL/DTA has been selected by EADS in February 2002 for the delivery of the vial freezer for the ESA / CRYOSYSTEM project. CRYOSYSTEM is a set of facilities for ultra-rapid cooling, preservation and storage of biological samples and protein crystals at -180°C on-board the ISS. Flexure bearing Stirling cryocoolers from THALES are used to cool down the dewar storage magazine of the vial freezers. We present here some elements of the trade-offs performed between two potential solutions for the thermal link between the Stirling cold finger and the dewar magazine. The two solutions envisaged were a conventional Braids Thermal Link Assembly (BTLA) and an original Liquid Thermal Link Assembly (LTLA). The BTLA makes use of flexible copper braids, while the LTLA is based on an evaporation/condensation process of an appropriate fluid between the cold finger and the cold magazine. The trade-off is based on thermal and mechanical tests results performed on both links, combined with system impact analysis such as implementation, added parasitic heat losses and safety considerations for pressurized payloads on-board the International Space Station. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, launched into orbit December 7, 2001, utilized a miniature pulse-tube cryocooler to maintain the SABER focal plane assembly (FPA) at 75 K. The limited cooling capacity of the cryocooler necessitated the development of a new never before flown Fiber Support Technology (FiST) for supporting and thermally isolating the FPA. A very precise predictive thermal modeling effort to ensure successful operation was also needed due to the very small capacity margin of the cryocooler. A high performance thermal link that minimized the temperature difference between the FPA and the cryocooler cold block and also the mechanical dynamic loading on the fragile pulse tube was developed and space qualified. This paper presents a comparison of the thermal modeling predictions with on orbit measurements, and discusses the lessons learned concerning long term performance issues of thermal isolation systems which utilize cryocoolers for cooling focal plane assemblies (FPA’s). The effect of ice deposition on the thermal blankets and other FPA cooled structures, as well as the lessons learned in dealing with this ice deposition, will also be presented. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Cooling performance of orifice pulse tube refrigerators was investigated in a wide temperature range from about 80 K to over 250 K to determine the feasibility of pulse tube refrigerators as refrigeration systems in that temperature range. Helium and nitrogen were used and compared as the working gas. P-V work in the pulse tube refrigerator was estimated to determine the difference in performance between the two working gases based on energy flow in the refrigerator. Results revealed that the lowest wall temperature was 80 K for helium and 126 K for nitrogen, and that the refrigeration power for helium was over 1.5 times higher than that for nitrogen, even when operating conditions (e.g., frequency and orifice valve opening) were optimized for nitrogen. Moreover, it was found that the decrease in P-V work through the regenerator for helium was also about 1.5 times larger than that for nitrogen, and that the oscillation of volume of gas element significantly affected the difference in P-V work between the two working gases, whereas the phase difference between oscillations of pressure and displacement did not. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Although many candidate materials have been developed and tested to increase a cooling capacity at 4 K, there are only few materials available for the 4 K regenerator materials. We have developed ceramic oxide magnetic regenerator materials, GAP = GdAlO3 and GOS = Gd2O2S. The cooling tests, using those new materials showed remarkable increases on the cooling performance at 4 K in comparison with conventional magnetic regenerator materials, HoCu2 or Er3Ni [1–6]. However, the materials are effective in the temperatures between 3 K and 5 K, but not above 6 K. Therefore, HoCu2 is still needed to provide the heat capacity from 6 K to 10 K. This paper will describe the properties of a new ceramics material, Gd-Tb oxysulfide = (GdxTb1-x)2O2S in substitution for HoCu2. This study is focused on providing a high heat capacity with a broad peak curve above 6 K. Not only the experimental results on heat capacity, but also those on the cooling test will be shown. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Future Department of Defense missions will require efficient, low mass, reliable mechanical cryocoolers. Loads of 2 W to 8 W at 35 K are anticipated, combined with higher loads at higher temperatures for optical benches and shielding. A single, multistage cryocooler that can supply refrigeration to several loads at distributed locations without significant penalties in performance has the potential for dramatic reductions in overall mass, system complexity, and input power when compared to multiple single-point coolers. In early 2002, a single-stage turbo-Brayton cryocooler was installed on the Hubble Space Telescope to cool the NICMOS instrument. The NICMOS Cryogenic Cooler (NCC) returned the instrument to operation within one month of installation and has maintained the instrument at optimum temperature since that time. The NCC provides 7 W of cooling at 70 K. Recently completed efforts have demonstrated a single-stage cryocooler using comparable technology that provides 3 W to 4 W of refrigeration at a temperature of 35 K. These test results were used as the foundation for a two-stage 35 K turbo-Brayton cryocooler. The test results and the design of a two-stage 35 K cryocooler are the subjects of this paper. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]