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Helium-3,4 dilution refrigeration is indispensable for low temperature science and engineering as it is the only method which provides temperatures between 0.3 K and 0.005 K for unlimited working periods. Cryogen-free dilution refrigerators are about to replace traditional cryostats with liquid helium precooling. The dilution circuit is always precooled by a two-stage pulse tube cryocooler; therefore, refrigeration capacities are available to the experimentalist at the temperatures of the two stages of the pulse tube cooler, and furthermore at three temperatures of the dilution circuit (~ 0.7 K - still, 0.1 K - heat exchanger, ~ 0.01 K - mixing chamber). However, there are quite a few applications (e.g. quantum information processing or astro-physics) where the cooling power of the still near ~ 1K is not sufficient to cool amplifiers and electric lines. In our work we present a dilution refrigerator where a He-4 cooling circuit has been added in the cryostat to the dilution circuit. This He-4 circuit provides up to 60 mW of refrigeration capacity in addition to the cooling capacity of ~ 30 mW of the still. The dilution circuit and the 1Kcircuit can be operated together or separately. [ABSTRACT FROM AUTHOR]

New efforts are underway to develop thermoelectric materials for cooling of infrared detectors at cryogenic temperatures. In this study, a control thermodynamic model of multistage Thermoelectric (TE) cryocoolers is developed that includes the effect of heat transfer between the cryocooler and the thermal reservoirs as well as thermal resistance between the stages. It is assumed that a reservoir at 80 K is available and a cooling load at about 35 K, typical of the second stage of conventional cryocoolers, is desired. It is shown that under the assumption of availability of TE materials with a reasonably high figure of merit, a multistage TE cryocooler is required. As an example, a control thermodynamic model of a four-stage TE cryogenic refrigerator is developed. The effect of thermal conductance of the heat exchangers at the hot and cold sides of the refrigerator, the thermal resistance between the stages and the effect of the figure of merit of the TE material on the cooling capacity and efficiency of the multistage TE cryocooler is presented. The thermal design challenges of the development of multistage TE cryocoolers with high efficiency for cryogenic applications including the effect of heat leak are discussed. [ABSTRACT FROM AUTHOR]

A new cryogenic system is under construction at the National High Magnetic Field Laboratory (NHMFL) for the cooling of the Series-Connected Hybrid (SCH) magnet as well as the existing 45 T hybrid system. The SCH is a vertical bore, 36 T magnet under development at the NHMFL and it will be installed at the NHMFL in 2013. The 45 T hybrid magnet system producing a 45 T steady field has been operating successfully as a user facility since 1999. The existing cryogenic system at the NHMFL has been in service since 1994 and it is used for supplying Liquid Helium (LHe) to the users and also cooling the 45 T hybrid magnet. The new system has a specified refrigeration capacity of 750 W at 4.5 K and will replace the current refrigerators after its construction due to the increasing maintenance in current refrigerators and the increasing LHe demand by the users at the NHMFL. The design of the new cryogenic system, consisting of a main refrigerator, a distribution system and a gas management and purification system, and its status are presented in this paper. [ABSTRACT FROM AUTHOR]

In order to achieve and maintain the proper cryogenic conditions for fusion experiments, the ITER Cryogenic System has to cope with various operation modes as per the requirements of the superconducting (SC) magnets and the 4 K Cryopumps (CPs). The refrigerators, source of the cooling power, should operate as much as possible in a quasisteady- state manner for efficiency and reliability reasons, and also to optimize their cooling capacity. The cryogen-related transients generated or required by the magnets and CPs therefore have to be managed and smoothed inside the primary helium loops of the Cryodistribution (CD) cold boxes which distribute and recover the cooling flows. In this proceeding we will propose the internal-component layouts of the ITER CD cold boxes and demonstrate in terms of operation modes how they fulfill the duties of the Cryogenic System with respect to the ITER Tokamak. The methods foreseen for the smoothing of the cryogenic loads and optimization of the cooling power requirements will also be introduced. [ABSTRACT FROM AUTHOR]

This paper theoretically studied a traveling-wave thermoacoustic cryocooler (TWTAC), simultaneously comparing with an inertance-tube pulse tube cryocooler operating in liquid nitrogen temperature range. The same core thermodynamic components are fixed and used in the both cryocoolers. First, thermodynamic design and optimization mainly on their phase shifting devices are made. For 77 K operation, the theoretical results show that the TWTAC has an increase of efficiency by about 10% compared with the inertance pulse tube cryocooler. Then, preliminary experiments on the TWTAC driven by a linear compressor were conducted. So far, the traveling-wave thermoacoustic cryocooler has achieved a no-load refrigeration temperature of 135 K with a pressure ratio of 1.15, and the reasons for huge different between the theoretical and experimental results are being indentified. [ABSTRACT FROM AUTHOR]

Ball Aerospace has completed qualification testing of its flight Stirling-cycle mechanical cryocooler for the Thermal Infrared Sensor (TIRS), an instrument slated to fly on the Landsat Data Continuity Mission (LDCM) platform. The TIRS cooler, developed under subcontract to NASA Goddard Space Flight Center, consists of a sophisticated and highly reliable, two-stage, fixed regenerator Stirling cryocooler and its drive electronics. The TIRS cooler provides 2 W of 38 K cooling to the TIRS detectors and 9.8 W shield cooling to 85 K for less than 225 W total input power. Performance test results are reported. [ABSTRACT FROM AUTHOR]

This paper reviews recent advances in high frequency pulse tube cryocoolers developed in SITP/CAS to provide high reliability, low-noise and long life cooling for potential space applications. The advances in understanding the cooler mechanism and minimizing irreversible losses in various components are described, which have made a great contribution to the improved efficiencies. At present, the operating temperatures cover from 30 K to 200 K and the cooling capacities vary from hundreds of milliwatts to over 20 W to meet a variety of requirements. Some typical cryocooler development programs are introduced and a brief overview of the updated data package is presented. The proposed applications, design approaches, research advances, the major problems and the efforts to overcome them are described. [ABSTRACT FROM AUTHOR]

A helium cryogenic plant with a maximum cooling power of 450 W at 4.5K was installed at the end of the year 2003. This plant has provide the cooling power for the test of one superconducting cavity and the commission of one superconducting magnet for nine months. In November 2004, we installed one helium transfer system in NSRRC’s storage ring to fulfill the cooling requirement for the operation of one superconducting cavity and two superconducting magnets. This helium transfer system consists of a switch valve box and the nitrogen-shielding multi-channel transfer lines. The averaged heat leak to the helium process line (including the straight section, the joint, the elbow, the coupling) at liquid helium temperature is specified to be less than 0.1 W/m at 4.2K; the total heat leak of the switching valve box to helium process lines is less than 16 W at 4.2K. In this paper we present the function, design parameters and test result of the helium transfer system. Commissioning results of both the cavity and the magnets using this helium transfer system will be shown as well. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Compared to the traditional 4 K cryocoolers, the separate 4 K pulse tube refrigerator (PTR) consists of two independent PTRs, which are thermally connected between the cold end of the first stage and some middle position of the second stage regenerator. It is possible to use different frequency, valve timing, phase shifter and even compressor for each stage for better cooling performance. A 4 K separate two-stage PTR was designed and manufactured. The first stage was separately optimized. A minimum temperature of 12.6 K and cooling capacity of 59.0 W at 40 K was achieved for the first stage by adding some Er3Ni at the cold part of the regenerator. An experimental investigation of valve timing effects on the cooling performance of the 4 K separate two-stage PTR is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance of the PTR. Cooling capacity of 0.59 W at 4.2 K and 15.4 W at 37.0 K were achieved with an actual input power of 6.6 kW. Effect of frequency on the performance of the separate two-stage PTR is also presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

An adiabatic demagnetization refrigerator (ADR) is under development for use in cooling relatively large loads (10–100 mW) at 4 K and rejecting that heat to a cryocooler operating at 10 K. ADRs can operate in this temperature range with an efficiency of 75% of Carnot, saving as much as 2/3 of the required overall input power. In addition this ADR can provide cooling down to 0.4 K. The ADR magnet consists of 8 short coils wired in series and arranged in a toroid to provide self-shielding of its magnetic field. Eliminating passive or active shields saves 30% of the mass of the system. The average field is 3 Tesla using 5 amps. In the first model the coils are wound with ordinary NbTi superconducting wire and operated at 4 K. A second version will then use fine Nb3Sn wire to provide complete 10 K operation. As a refrigerant for this temperature range we are using readily available gadolinium gallium garnet (GGG) crystals, which provide suitable performance. In the future we will switch to either GdLiF4 or GdF3, which have 13% or 30%, respectively, more cooling power per volume than GGG. We use gas gap heat switches to alternately connect the toroid to the cold load and the warm heat sink. A small continuous stage maintains the cold end at 4 K while the main toroid is recycled. Data on toroid , magnet performance with respect to central field vs. current and fringing field vs. current are given. Data on the transient heating due to hysteresis losses within the superconductor are also presented. © 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]

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]