Liquid Nitrogen Temperature Range Research Articles

A thermal-coupled/gas-coupled hybrid high-frequency pulse tube cryocooler attaining the liquid-helium temperature

High-frequency pulse tube cryocooler (HPTC) has become an attractive method for space cooling in the liquid-helium temperature range, due to its advantages of potential high efficiency, no moving parts at the cold end, small size, and light weight. However, key problems such as large regenerator losses and insufficient phase-shifting ability challenge it to obtain the liquid-helium temperature. A thermal-coupled/gas-coupled hybrid refrigeration process of HPTC has been designed to obtain the liquid-helium temperature. One HPTC working in the liquid-nitrogen temperature range is used as a pre-cooling stage, and another two-stage gas-coupled structure is employed to obtain liquid-helium temperature. The simulation results show that the lowest no-load temperature is 3.6 K and a cooling power of 84 mW can be provided at 6 K with a total input PV power of 128 W and 10.9 W/77 K pre-cooling power when Helium-4 is chosen as the working gas. An experimental prototype was designed, built, and tested. The simulation and experiment results will be introduced in detail in this paper.

Enhanced magnetocaloric performance in nanocrystalline/amorphous Gd3Ni/Gd65Ni35 composite microwires

A novel class of nanocrystalline/amorphous Gd 3 Ni/Gd 65 Ni 35 composite microwires were created directly from melt-extraction through controlled solidification. X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) confirmed the formation of a biphase nanocrystalline/amorphous structure in these wires. Magnetic and magnetocaloric experiments indicate a large magnetic entropy change (-Δ S M ~9.64 J/kg K), large refrigerant capacity ( RC ~742.1 J/kg), and large maximum adiabatic temperature change ( Δ T a d max ~5 K) around the Curie temperature of ~120 K for a field change of 5 T. These values are ~1.5 times larger relative to its bulk counterpart and are superior to other candidate materials being considered for active magnetic refrigeration in the liquid nitrogen temperature range. • Novel nanocrystalline/amorphous Gd 3 Ni/Gd 65 Ni 35 microwires. • Large magnetic entropy change and refrigerant capacity. • Magnetic refrigerators for nitrogen liquefaction.

Tablelike magnetocaloric effect and enhanced refrigerant capacity in EuO1−δ thin films

The effect of electron doping of $\mathrm{Eu}{\mathrm{O}}_{1\text{\ensuremath{-}}\ensuremath{\delta}}$ thin films through oxygen vacancies ($\ensuremath{\delta}=0$, 0.025, and 0.09) upon the magnetocaloric response is presented. The films each showed a paramagnetic to ferromagnetic transition around 65 K, with an additional magnetic ordering transition at higher temperatures in the oxygen deficient samples. All transitions are observed to be of second order. A maximum magnetic entropy change of 6.4 J/kg K over a field change of 2 T with a refrigerant capacity of 223 J/kg was found in the sample with $\ensuremath{\delta}=0$, and in all cases the refrigerant capacities of the thin films under study were found to exceed that reported for bulk EuO. Adjusting the oxygen content was shown to produce tablelike magnetocaloric effects, desirable for ideal Ericsson-cycle magnetic refrigeration. These films are thus excellent candidates for small-scale magnetic cooling technology in the liquid nitrogen temperature range.

Double magnetic entropy change peaks and high refrigerant capacity in Gd1-xHoxNi compounds in the melt-spun form

Gd1-xHoxNi melt-spun ribbons were fabricated by a single-roller melt spinning method. All the compounds crystallize in an orthorhombic CrB-type structure. The Curie temperature (TC) was tuned between 46 and 99 K by varying the concentration of Gd and Ho. A spin reorientation (SRO) transition is observed around 13 K. Different from TC, the SRO transition temperature is almost invariable for all compounds. Two peaks of magnetic entropy change (ΔSM) were found. One at the higher temperature range was originated from the paramagnet-ferromagnet phase transition and the other at the lower temperature range was caused by the SRO transition. The maximum of ΔSM around TC is almost same. The other maximum of ΔSM around SRO transition, however, had significantly positive relationship with x. It reached a maximum about 8.2 J kg−1 K−1 for x = 0.8. Thus double large ΔSM peaks were obtained in Gd1-xHoxNi melt-spun ribbons with the high Ho concentration. And the refrigerant capacity power reached a maximum of 622 J kg−1 for x = 0.6. Gd1-xHoxNi ribbons could be good candidate for magnetic refrigerant working in the low temperature especially near the liquid nitrogen temperature range.

Metamaterial superconductors

AbstractSearching for natural materials exhibiting larger electron-electron interactions constitutes a traditional approach to high-temperature superconductivity research. Very recently, we pointed out that the newly developed field of electromagnetic metamaterials deals with the somewhat related task of dielectric response engineering on a sub-100-nm scale. Considerable enhancement of the electron-electron interaction may be expected in such metamaterial scenarios as in epsilon near-zero (ENZ) and hyperbolic metamaterials. In both cases, dielectric function may become small and negative in substantial portions of the relevant four-momentum space, leading to enhancement of the electron pairing interaction. This approach has been verified in experiments with aluminum-based metamaterials. Metamaterial superconductor withTc=3.9 K have been fabricated, which is three times that of pure aluminum (Tc=1.2 K), which opens up new possibilities to improve theTcof other simple superconductors considerably. Taking advantage of the demonstrated success of this approach, the critical temperature of hypothetical niobium, MgB2- and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial, the projectedTcappears to reach ~250 K.

Mott type variable range hopping conduction and magnetoresistance in p-type CuIn3Te5 semiconductor compound

Variable range hopping (VRH) conduction of Mott type for a constant and non-vanishing density of states at the Fermi level is observed over a wide range of temperature between 45 and 210 K in the ordered defect compound CuIn3Te5 (CIT135). For this type of electrical conduction at a very high temperature, not reported before in elemental, II-VI, and I-III-VI2 compound semiconductors, we employed three different methods to analyze the data and to confirm this behavior. The occurrence of VRH at very high temperatures is explained as due to the presence of the electrically inactive (InCu+2 + 2 VCu−1) donor-acceptor defect pairs in CIT135. This defect-pair partially annihilates the shallow acceptor defect state Cu vacancy, which is responsible for the activated electrical conductivity observed in p-type ternary I-III-VI2 chalcopyrite compounds in the temperature range of liquid nitrogen. In such conditions, the only acceptor level available for electrical conduction in CIT135 is a deep acceptor state whose activation energy is about 200 meV and cannot be activated below about 200 K. Hence, the VRH conduction mechanism dominates the electrical properties of this material up to about 200 K. The study of the temperature and magnetic field dependence of the magnetoresistance (MR) up to 27 T is made by taking into consideration different theoretical models. To explain the negative MR at lower fields, the theory based on quantum interference is used. At higher magnetic fields, the MR becomes positive and is explained with the model based on the shrinkage of the wave function.

A-site cationic disorder induced significantly large magnetoresistance in polycrystalline La0.2Gd0.5Ba0.3MnO3 compound

The observation of significantly large magnetoresistance at the liquid nitrogen temperature range in the polycrystalline La0.2Gd0.5Ba0.3MnO3 (LGBMO) compound has been addressed in the present manuscript. The motivation of considering LGBMO sample is the average ‘A’ site ionic radius 〈rA〉 and tolerance factor (t), almost same as that of La0.7Sr0.3MnO3 (LSMO), which is a well studied colossal magnetoresistive material. Magnetoresistance of the LGBMO compound has been compared with the LSMO as well as parent compound La0.7Ba0.3MnO3(LBMO) to show the enhancement of magnetoresistance in LGBMO compound. This observed nature has been elucidated considering the disorder induced short range magnetic interaction due to the enhance size disorder parameter (σ2). Our study revels that, size disorder parameter plays the crucial role for enhancing the colossal magnetoresistance.

Theoretical modeling of critical temperature increase in metamaterial superconductors

Recent experiments have demonstrated that the metamaterial approach is capable of drastic increase of the critical temperature Tc of epsilon near zero (ENZ) metamaterial superconductors. For example, tripling of the critical temperature has been observed in Al-Al2O3 ENZ core-shell metamaterials. Here, we perform theoretical modelling of Tc increase in metamaterial superconductors based on the Maxwell-Garnett approximation of their dielectric response function. Good agreement is demonstrated between theoretical modelling and experimental results in both aluminium and tin-based metamaterials. Taking advantage of the demonstrated success of this model, the critical temperature of hypothetic niobium, MgB2 and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial Tc appears to reach ~250K.

Theoretical analysis of two coupling modes of a 300-Hz three-stage thermoacoustically driven cryocooler system at liquid nitrogen temperature range

Highly reliable, compact, and efficient cryocoolers with a cooling power of several watts to several hundred watts at liquid nitrogen temperatures around 77K are indispensable for cooling superconducting devices and infrared detectors, especially in aerospace applications. This paper introduces three-stage traveling-wave thermoacoustically driven cryocooler systems operating around 300Hz that meet the demand. In addition to the potential reliability due to the lack of moving components in a thermoacoustically driven cryocooler, this configuration has the potential for both compact size and high efficiency owing to the slim resonance tube and acoustic power recovery. Numerical simulations are performed to investigate two coupling modes: coupling the cooler at the branch of the engine (BR-coupling) or coupling the cooler parallel to the engine (PA-coupling). First, the two topologies are carefully designed to obtain high total exergy efficiency and the optimal dimensions are presented. Then, the axial distributions of the phase difference and the acoustic power are further provided to better illustrate the coupling characteristics. Furthermore, a theoretical analysis is performed on the influence of the two acoustic tubes in the PA-coupling mode and the result shows the importance of the tube dimensions. With a heating temperature of 850K, total exergy efficiencies of 11.4% and 14.8% have been achieved in the BR-coupling and PA-coupling modes, respectively. The PA-coupling mode’s higher efficiency is due to recycling the acoustic power entering the pulse tube cryocooler, whereas BR-coupling fails to recycle any acoustic power. However, the energy feedback in PA-coupling may cause structural complexity. Generally speaking, both coupling mode systems show encouraging prospects for aerospace applications.

The cost of coolers for cooling superconducting devices at temperatures at 4.2 K, 20 K, 40 K and 77 K

This author and other authors have written papers concerning the cost of refrigeration as a function of the refrigeration delivered. These papers have included small coolers as well. The lowest temperature range from 3.8 K to 4.7 K (the liquid helium temperature range) is covered using coolers that have two stages. The use of magnets and power equipment that use MgB2 conductors and HTS conductors have spurred the development of coolers that work well temperature ranges from 15 K to 30 K (hydrogen temperature applications), HTS conductors like BSSCO and YBCO for the range from 35 to 50 K and HTS devices from 65 K to 80 K (applications in the liquid nitrogen temperature range). This paper will present some cost data for a number of commercial two-stage and single-stage coolers. This data will be fitted to allow one to estimate the cost of coolers as a function of refrigeration for temperatures of 4.2 K, 20 K, 40 K and 77 K. The efficiency of a large number of coolers over a range of temperatures is also discussed.

Investigation on the Dielectric Material Parameters and the Electric Conductivity of Syntactic Foam at the Liquid Nitrogen Temperature Range

Liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-based insulation systems for superconducting components of the electric distribution network are state of the art. As the dielectric strength of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based insulation systems can be significantly reduced if bubbles occur, an alternative insulation system could be a solid insulation system using LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> only for cooling but not as electrical insulation material. This paper discusses syntactic foam as a solid substitution of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based insulation systems. Syntactic foam consists of a polymer matrix with embedded hollow microspheres (HMS) that have diameters of several 10 μm. Compared to the pure matrix material, the HMS filled matrix features a lower density and a significantly reduced thermal contraction when being cooled to cryogenic temperatures. Several syntactic foams are investigated regarding their dielectric parameters (relative permittivity, loss factor) and electric conductivity at liquid nitrogen temperature (LNT). The results show that the investigated parameters of syntactic foam are almost constant in the temperature range of LNT. Furthermore, the loss factor and the relative permittivity at LNT are lower than at room temperature. These effects can be explained by the existence of a secondary glass transition of polymers. At cryogenic temperatures, a decrease of the electric conductivity of syntactic foam is detected presumably due to the rise in required energy to lift valence electrons to the conduction band of the polymer at lower temperatures.

Magnetocaloric effect and critical behavior in melt-extracted Gd60Co15Al25microwires

High-quality Gd60Co15Al25 microwires with an average diameter of 40 µm were successfully fabricated by the melt-extraction method. The as-cast microwires undergo a second-order paramagnetic to ferromagnetic (PM–FM) transition at ∼100 K. Large values of the magnetic entropy change (−ΔSM ∼9.73 J kg−1 K−1) and the refrigerant capacity (RC ∼732 J kg−1) are achieved for a field change of 5 T. A careful analysis of critical exponents near the PM–FM transition indicates the significant effects of structural disorder on the long-range ferromagnetic interaction and the magnetocaloric response of the microwires. The excellent magnetocaloric properties make the Gd60Co15Al25 microwires very promising for use in magnetic refrigerators operating in the liquid nitrogen temperature range.

Enhanced magnetocaloric properties of melt-extracted GdAlCo metallic glass microwires

Herein, we report high magnetocaloric performance of melt-extracted metallic glass Gd60Al20Co20 microwires, which exhibit a large and reversible magnetocaloric effect (MCE). The isothermal magnetic entropy change (−ΔSm) reaches as high as 10.1Jkg−1K−1 and the refrigerant capacity (RC) has a large value of 681Jkg−1 for a field change of 5T. The as-obtained Gd-based metallic glass microwires hold a great promise for multifunctional applications in MCE-based refrigeration of liquid nitrogen temperature range.

Table-like magnetocaloric effect and enhanced refrigerant capacity in Eu8Ga16Ge30-EuO composite materials

A large reversible magnetocaloric effect (MCE) and enhanced refrigerant capacity (RC) were observed in multiphase composite materials composed of type-I clathrate Eu8Ga16Ge30 and EuO. Eu8Ga16Ge30 undergoes two successive ferromagnetic transitions at 10 K and 35 K, and EuO exhibits a ferromagnetic transition at 75 K. A large RC of 794 J/kg for a field change of 5 T over a temperature interval of 70 K was achieved in the Eu8Ga16Ge30–EuO composite with a 40%-60% weight ratio. This is the largest value ever achieved among existing magnetocaloric materials for magnetic refrigeration in the temperature range 10 K-100 K. Adjusting the Eu8Ga16Ge30 to EuO ratio is shown to produce composites with table-like MCE, desirable for ideal Ericsson-cycle magnetic refrigeration. The excellent magnetocaloric properties of these Eu8Ga16Ge30–EuO composites make them attractive for active magnetic refrigeration in the liquid nitrogen temperature range.

Characterization of Commercial YBCO Coated Conductors After Neutron Irradiation

In view of the significant progress in coated conductor processing technologies, a wide variety of applications have become feasible. One of them is the design of superconducting magnets for fusion devices operating in the liquid nitrogen temperature range. In this case, the material has to withstand a significant fluence of fast neutrons. Samples of the latest generation of coated conductors provided by commercial suppliers were sequentially irradiated in a fission reactor and characterized by magnetic and direct transport measurements. Angular resolved transport measurements were performed and interesting changes in Jc(φ) were observed. In addition, the effects of thermal neutron irradiation on coated conductors are presented. The most important outcome for applications, the dependence of Jc on the neutron fluence, is discussed in the last part.

Experimental study on a cryogenic loop heat pipe with high heat capacity

Cryogenic loop heat pipes (CLHPs) are efficient heat transfer devices based on two-phase flow. Loop heat pipes for room temperature applications have achieved satisfactory thermal control functions with the benefits of no mechanical moving part, vibration isolation, thermal insulation, long heat transport distance and so on. While there exist many problems for low temperature applications of loop heat pipes, such as limited heat transport capacity, which could not meet the increasing requirement of instrument heat dissipation. This paper presents an advanced CLHP operating at liquid-nitrogen temperature range. An improved condenser structure is introduced to the CLHP, which greatly reduces the flow resistance and increases the cooling capability of the condenser. Many experiments have been carried out on the CLHP prototype for performance test, and one set of the experimental results with a 3.2 MPa fill pressure at room temperature is presented in this paper. It is shown that the advanced CLHP prototype can be operated reliably with a high heat transfer capacity up to 41 W and a limited temperature difference of 6 K across a 0.48 m transport distance.

Thermoelectric properties of electron- and hole-dopedBaFe2As2

We investigate the resistivity and thermoelectric power properties for Co- or K-doped ${\text{BaFe}}_{2}{\text{As}}_{2}$ systems. ${T}_{c}$ as a function of Co- or K-doping level exhibits a domelike behavior in both of the systems. The thermoelectric power $(S)$ at room temperature as a function of doping level $(x)$ shows a domelike behavior in ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ system while monotonously decreases in ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Co}}_{x}{\text{As}}_{2}$ system. It is intriguing that the superconducting samples simultaneously show large absolute values of thermoelectric power and good conductivity. The power factor shows a peak at low temperature, suggesting possible applications in thermoelectric cooling modules around the liquid-nitrogen temperature range.

Advances in a 300 Hz thermoacoustic cooler system working within liquid nitrogen temperature range

With the combined advantages of high reliability, compact size and low electromagnetic interference, a high frequency operating thermoacoustic cooler system, i.e. a pulse tube cooler driven by a thermoacoustic heat engine, is quite promising for space applications. This article introduced a high frequency standing-wave thermoacoustic heat engine-driven pulse tube cooler system working around 300 Hz with axial length being 1.2 m. To improve the thermal efficiency of such system, an optimization has been carried out, both analytically and experimentally, by observing the influence of the dimensions of the stack, the hot buffer length and the acoustic pressure amplifier tube length. So far, a no-load temperature of 68.3 K has been obtained with 4.0 MPa helium and 750 W heating power. With 500 W heating power, a no-load temperature of 76.9 K and 0.2 W cooling power at 80 K have been achieved. Compared with former reports, the performance has been improved.

A Spirocyclohexyl Nitroxide Amino Acid Spin Label for Pulsed EPR Spectroscopy Distance Measurements

Site-directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide alpha-amino acid and its N-(9-fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin-echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins.

Superior properties of SmBCO coated conductors at high magnetic fields and elevated temperatures

Abstract In addition to the well investigated YBa 2 Cu 3 O 7− δ (Y-123, YBCO) compound, many other rare earth-123 compounds are candidate materials for the production of coated conductors. Sm-123 seems to be an excellent alternative because of its higher transition temperature ( T c ) and higher critical current densities ( J c ) in external magnetic fields. Because of the fast decrease of J c in YBCO at elevated temperatures, especially around the boiling point of liquid nitrogen, the slightly higher T c can be an important advantage. Recently, significant progress has been made in the production of long length Sm-123 based coated conductors. We report here on transport measurements on these conductors in the liquid nitrogen temperature range. The critical current densities were determined as a function of the applied field and the crystallographic orientation under maximum Lorentz force configuration. A shift of the c -axis (∼7°) from the tape normal was found. The conductor properties were compared to those of commercially available YBCO coated conductors. The critical current densities as well as the irreversibility fields are higher in the SmBCO tapes, thus demonstrating the superior properties of the Sm-123 compound.