Showing papers in "Advances in cryogenic engineering in 2002"
TL;DR: In this paper, a hydrogen liquefier with very high efficiency is proposed, which uses a helium-neon mixture as refrigerant, which allows the use of the best available compression system.
Abstract: The aim of this paper is to propose a hydrogen liquefier with very high efficiency. One important theoretical tool is the exergy analysis of the single process step as well as the overall cycle. This will be needed for the choice of the optimum hydrogen feed pressure as well as for the handling of the ortho-para conversion. Modern helium refrigerators are being built with up to 10 expansion turbines placed strategically in the cycle to obtain overall optimum efficiency. We are proposing to do the same for the hydrogen liquefier and to choose a helium-neon mixture as refrigerant, which allows the use the best available compression system. The preliminary design of the plant shows that a thermodynamic efficiency of the total plant in the order of 60% is feasible. This results in an overall power requirement of 5 to 7 kW-h per kg of liquid hydrogen, depending on the pressure of the feed and the temperature of the product. These values for the power consumption are recommended as bench marks for future studies on large scale hydrogen liquefaction.
85 citations
TL;DR: In this article, the authors described experimental results of a magnetic refrigerator operated at room temperature, where the magnetic materials were divided into two vessels and reciprocated between high and zero magnetic fields.
Abstract: This paper describes experimental results of a magnetic refrigerator operated at room temperature. Spheres of Gadolinium, 2.2 kg in weight and 0.3 mm in diameter, are used as a magnetic working material. The magnetic materials were divided into two vessels and reciprocated between high and zero magnetic fields. High magnetic field up to 4 T was applied by a cryocooler cooled superconducting magnet. Refrigeration capacity of 100 W was obtained with operating frequency of 0.167 Hz. Details of the magnetic refrigerator construction and experimental results are presented.
75 citations
TL;DR: In this paper, a specific thermal conductivity measurement facility for solid materials at low temperature (LHe and LN2) was developed, which performs measurements on epoxy resin, as well as on bulk materials such as aluminum alloy and on insulators developed at Saclay.
Abstract: We have developed a specific thermal conductivity measurement facility for solid materials at low temperature (LHe and LN2). At present, the Measurement of Thermal Conductivity of Insulators (MECTI) facility performs measurements on epoxy resin, as well as on bulk materials such as aluminum alloy and on insulators developed at Saclay. Thermal conductivity measurements on pre-impregnated fiber-glass epoxy composite are presented in the temperature range of 4.2 K to 14 K for different thicknesses in order to extract the thermal boundary resistance. We also present results obtained on four different bonding glues (Stycast 2850 FT, Poxycomet F, DP190, Eccobond 285) in the temperature range of 4.2 K to 10 K.
42 citations
TL;DR: A new class of insulation materials has been developed utilizing cyanate ester chemistries combined with other known radiation-resistant resins, such as bismaleimides and polyimides.
Abstract: Magnets built for fusion devices such as the newly proposed Fusion Ignition Research Experiment (FIRE) need to be highly reliable, especially in a high radiation environment. Insulation materials are often the weak link in the design of superconducting magnets due to their sensitivity to high radiation doses, embrittlement at cryogenic temperatures, and the limitations on their fabricability. An insulation system capable of being vacuum impregnated with desirable properties such as a long pot-life, high strength, and excellent electrical integrity and which also provides high resistance to radiation would greatly improve magnet performance and reduce the manufacturing costs. A new class of insulation materials has been developed utilizing cyanate ester chemistries combined with other known radiation-resistant resins, such as bismaleimides and polyimides. These materials have been shown to meet the demanding requirements of the next generation of devices, such as FIRE. Post-irradiation testing to levels that exceed those required for FIRE showed no degradation in mechanical properties. In addition, the cyanate ester-based systems showed excellent performance at cryogenic temperatures and possess a wide range of processing variables, which will enable cost-effective fabrication of new magnets. This paper details the processing parameters, mechanical properties at 76 K and 4 K, as well as post-irradiation testing to dose levels surpassing 10 8 Gy.
40 citations
TL;DR: In this article, the authors describe the design and construction of an AMR test apparatus, which has been used to examine the performance of Gd AMR beds operating in 2 T fields.
Abstract: The Active Magnetic Regenerator (AMR) has been shown to be a refrigeration technology with high efficiencies. Complex thermodynamic interactions in the regenerator, a shortage of suitable magnetic refrigerants, and difficulty in acquiring accurate experimental data have combined to hamper the development of AMR refrigerators. An apparatus to dynamically characterize the behavior of AMR beds is a valuable tool in furthering the development of the technology. This paper describes the design and construction of an AMR test apparatus. For initial tests, the apparatus has been used to examine the performance of Gd AMR beds operating in 2 T fields.
32 citations
TL;DR: In this paper, an investigation of the use of aerogel beads as thermal insulation for cryogenic applications was conducted at the Cryogenics Test Laboratory of NASA Kennedy Space Center.
Abstract: An investigation of the use of aerogel beads as thermal insulation for cryogenic applications was conducted at the Cryogenics Test Laboratory of NASA Kennedy Space Center. Steady-state liquid nitrogen boiloff methods were used to characterize the thermal performance of aerogel beads in comparison with conventional insulation products such as perlite powder and multilayer insulation (MLI). Aerogel beads produced by Cabot Corporation have a bulk density below 100 kilograms per cubic meter (kg/m3) and a mean particle diameter of 1 millimeter (mm). The apparent thermal conductivity values of the bulk material have been determined under steady-state conditions at boundary temperatures of approximately 293 and 77 kelvin (K) and at various cold vacuum pressures (CVP). Vacuum levels ranged from 10−5 torr to 760 torr. All test articles were made in a cylindrical configuration with a typical insulation thickness of 25 mm. Temperature profiles through the thickness of the test specimens were also measured. The resul...
32 citations
TL;DR: In this article, a new bending device was developed which allows continuous change of the bending radius of the BSCCO tape sample at 77 K and a simultaneous measurement of the critical currents.
Abstract: A new bending device was developed which allows continuous change of the bending radius of the BSCCO tape sample at 77 K and a simultaneous measurement of the critical currents. The samples are mounted free between two clamps. The special geometry of the arrangement insures over the whole range a sample shape with homogeneous curvature on a circle line without the help of mechanical parts. This bending strain rig avoids effects from additional thermal stresses due to the cooling from room temperature (bending) to 77 K (critical current measurement). We mainly present measurements on different Ag/AgMg sheathed standard conductors. The results obtained with the new method will be compared for some selected samples with the bending strain behavior measured in the conventional way, applying the bent at RT. The potential of the method being suitable for standardized bending experiments will be discussed.
32 citations
TL;DR: In this article, a two-stage 4 K pulse tube cryorefrigerators were developed with cooling capacities of 0.83 W @4.2 K with 38 W @45 K for 8.0 kW power input.
Abstract: Cryomech, Inc. has continued the development of two-stage 4 K pulse tube cryorefrigerators. To address the concerns of customers with vibration levels due to the stretching in the tubes, a vibration elimination apparatus reduced the maximum displacement from 25 μm to <3 μm. The PT405, 0.5 W @4 K, was modified into a model PT407, by using the CP970 Compressor Package increasing the input power from 4.7 to 7.2 kW. It provides 0.72 W @4.2 K with 34 W @55 K. A new 4 K model, PT410, has been developed with cooling capacities of 0.83 W @4.2 K with 38 W @45 K for 8.0 kW power input. The PT410 is driven by one CP970 Compressor Package. With changing the flow impedances, the PT410 also can provide 1.05 W @4.2 K and simultaneously 28 W @56 K again for 8.0 kW of input power.
31 citations
TL;DR: In this article, the authors present experimental results for AC losses and critical currents of biaxially aligned YBCO-123 coated conductors, with Hastelloy as a substrate material.
Abstract: In the work we present experimental results for AC losses and critical currents of biaxially aligned YBCO-123 coated conductors, with Hastelloy as a substrate material. The critical current density of the tapes was of the order of 4.10 9 A/m 2 at the liquid nitrogen temperature. Magnetization losses, in sinusoidally varying external AC fields directed perpendicular to the plane of the tapes, were measured using a standard Lock-in technique. The frequency of the magnetic field was in a range of 7-64 Hz. The losses in YBCO are pure hysteretic for amplitudes up to 40 mT. Magnetization losses in the tape when carrying DC transport current are also reported. From obtained experimental data of dynamic resistance and the magnetization losses the total losses dissipated in the tape have been evaluated and compared with the critical state model predictions.
30 citations
TL;DR: A near-room temperature active magnetic regenerative refrigerator (AMRR) was designed and built using a high-temperature superconducting (HTS) magnet in a charge discharge cycle and a gadolinium-packed regenerative bed as the magnetocaloric component as discussed by the authors.
Abstract: A near-room temperature active magnetic regenerative refrigerator (AMRR) was designed and built using a high-temperature superconducting (HTS) magnet in a charge-discharge cycle and a gadolinium-packed regenerative bed as the magnetocaloric component Current to the HTS magnet was ramped periodically from zero to 100 amperes, which generated a ramp in field strength from zero to 17 tesla Water was moved periodically through the bed and through hot and cold heat exchangers to accomplish a continuous refrigeration cycle Cycle periods as short as 30 seconds were realized Refrigerator performance was measured in terms of cooling capacity as a function of temperature span and in terms of efficiency expressed as a percentage of maximum obtainable (Carnot) efficiency A three-watt cooling capacity was measured over a temperature span of 15 degrees C between hot and cold end temperatures of 25 degrees C and 10 degrees C This experiment is directed to two possible applications for magnetic refrigeration: a no-moving part cryogenic refrigerator for space applications, and a compact permanent magnet refrigerator for commercial and consumer applications
27 citations
TL;DR: In this article, a unique foam/MLI combination concept for orbital cryogenic storage was experimentally evaluated at NASA Marshall Space Flight Center (MSFC) using the Multipurpose Hydrogen Test Bed (MHTB).
Abstract: A unique foam/Multilayer Insulation (MLI) combination concept for orbital cryogenic storage was experimentally evaluated at NASA Marshall Space Flight Center (MSFC) using the Multipurpose Hydrogen Test Bed (MHTB). The MLI was designed for an on-orbit storage period of 45 days and included several unique features such as: a variable layer density and larger but fewer perforations for venting during ascent to orbit. Test results with liquid hydrogen indicated that for similar performance, variable density MLI weight or heat leak is reduced by about half in comparison with standard MLI. The focus of this paper is on analytical modeling of the Variable Density MLI (VD-MLI) on-orbit performance (i.e. vacuum/low pressure environment). The foam/VD-MLI combination model is considered to have five segments. The first segment represents the optional foam layer. The second, third, and fourth segments represent three MLI segments with different layer densities. The last segment is considered to be an environmental boundary or shroud that surrounds the last MLI layer. Two approaches are considered. In the first approach, the variable density MLI is modeled layer by layer while in the second approach, a semi-empirical model is applied. Both models account for thermal radiation between shields, gas conduction, and solid conduction through the layer separator materials.
TL;DR: Two continuous operation 18 K/20 K sorption cryocoolers are being developed by the Jet Propulsion Laboratory (JPL) as a NASA contribution to the European Space Agency (ESA) Planck mission, currently planned for a 2007 launch.
Abstract: Two continuous operation 18 K/20 K sorption cryocoolers are being developed by the Jet Propulsion Laboratory (JPL) as a NASA contribution to the European Space Agency (ESA) Planck mission, currently planned for a 2007 launch. Each individual sorption cooler will be capable of providing a total of about 200 mW of cooling power at 18 K and 1.2 W at 20 K, given a passive radiative precooling at 50 K. These coolers work by thermally cycling a metal-hydride to absorb and desorb hydrogen gas, used as the working fluid in a Joule-Thomson (J-T) refrigerator. The major advantage of the sorption coolers is their truly vibration-free operation capability together with the fact that they can be readily scaled to perform over a wide range of cooling powers. The hydrogen sorption coolers will directly cool the Planck Low Frequency Instrument (LFI) HEMT amplifiers to approximately 20 K and will provide precooling at 18 K to the RAL 4 K closed-cycle Helium J-T cooler for the High Frequency Instrument (HFI). The concept design, the cooler operations and the predicted performances of the flight models are here presented.
TL;DR: The High Efficiency Cryocooler (HEC) as mentioned in this paper is a highly reliable, >10 year life, space cryo-cooler with very high capacity with low mass.
Abstract: The High Efficiency Cryocooler (HEC) is a highly reliable, >10 year life, space cryocooler. Design goals included very high capacity with low mass. The HEC achieved its 10 W at 95 K load while rejecting to 300 K with considerable margin and a flight configured mass of 4 Kg. This flight cooler design is being fabricated for a number of payloads. This paper describes the cooler, its measured performance, and its flight qualification.
TL;DR: In this article, a modified jelly roll process was used to produce the world's highest field accelerator dipole magnet with critical current density (Jc) of 14.7 T, 4.2 K and ∼2600 A/mm2.
Abstract: Oxford Instruments, Superconducting Technology (OI-ST) manufactures superconducting Nb3Sn wire via several different routes, producing conductors tailored for use in moderate to very high magnetic fields. Recently, research at OI-ST has produced internal Sn strand made by the modified jelly roll process that has achieved 12 T, 4.2 K non-Cu critical current density (Jc) values of ∼2600 A/mm2. This high Jc level was achieved by reducing the Cu content of the filament subelements, and increasing the Nb and Sn fractions. Similar high performance production strands have been used to produce the world’s highest field accelerator dipole magnet, which has reached 14.7 T. Work on bronze-processed conductor has shown that improved Jc levels can be achieved in “externally stabilized” strand relative to “internally stabilized” strand due to an improved Sn availability. OST is also involved with research for the High Energy Physics National Conductor Program. Results on internal Sn composites made entirely by hot extr...
TL;DR: In this paper, the authors analyzed the magnetic hysteresis and irreversibility field for various heat treatments of a pure-Nb, Nb3Sn powder-in-tube PIT wire.
Abstract: In order to better understand the relation between microstructure, superconducting properties and flux pinning in the A15 phase, we analyzed the magnetic hysteresis and irreversibility field for various heat treatments of a pure-Nb, Nb3Sn powder-in-tube PIT wire. The irreversibility field (4.2 K) was ∼10% higher after 750 °C heat treatment as compared to 675 °C heat treatment, attaining 25.9 T and 23.5 T respectively. The critical current of the wire increased monotonically with reaction time up to 128 hours at 675 °C but was lower for 750 °C reactions. However, the critical current density of the A15 layer peaked after a heat treatment of 47 hours at 675 °C and was lower yet after 32 hours at 750 °C, probably due to A15 grain growth. Our results illustrate a central compromise of Nb3Sn composites, namely that it is not yet possible to simultaneously optimize the primary properties (Tc, H* and Hc2) and the flux pinning when high critical current density demands grains of order 200 nm in diameter or less.
TL;DR: In this article, a gas gap heat switch that works passively, without the need for a separate, thermally activated getter, is presented, which is thermally conductive at temperatures above about 2 K and is insulating if either end of the switch is below about 1 5 K.
Abstract: We have designed, built, and tested a gas gap heat switch that works passively, without the need for a separate, thermally activated getter This switch uses He-3 condensed as a thin film on alternating plates of copper The switch is thermally conductive at temperatures above about 02 K, and is insulating if either end of the switch is below about 015 K The "on" conductance (7 mW/K at 025K) is limited by the surface area and gap between the copper leaves, the saturated vapor pressure of the He-3, and the Kapitza boundary resistance between the He-3 and the copper The "off" conductance is determined by the helium containment shell which physically supports the two conductive ends We have also designed and are building passive gas gap heat switches which will passively turn off near 1 K and 4 K For these switches we rely on the rapidly changing vapor pressure of He-4 above neon or copper substrates, respectively, when the coverage is less than one monolayer The different binding energies of the He-4 to the neon or copper give rise to the different temperatures where the switches transition between the on and off states
TL;DR: In this article, an experimental system is developed to investigate the dynamic characteristics of the mixture composition variations in the closed throttling refrigeration cycle and the experimental results show that the mixture compositions vary at different operating periods of the cycle.
Abstract: An experimental system is developed to investigate the dynamic characteristics of the mixture composition variations in the closed throttling refrigeration cycle. The experimental results show that the mixture compositions vary at different operating periods of the cycle. The maximum change of the compositions is up to 6% for different operating periods. The unevenness of the mixture compositions at different positions of the system may be up to 12%, or even more. The experimental results will be helpful in the modification of the existing simulation model of the mixture refrigeration cycle as well as the fabrication of mixture coolers.
TL;DR: In this article, a systematic study was undertaken to investigate this phenomenon and to check the hypothesis that the plastic deformation of the strands during cabling process is responsible for this behavior, and the results obtained on the deformed strands were then compared with those obtained from cables.
Abstract: In the recent years, Nb3Sn has been widely used for the development of high field superconducting magnets. It is known that the unreacted Nb-Sn composite undergoes a volume expansion during heat treatment due to the formation of the Nb3Sn phase. In an as-received strand this expansion is isotropic. However, an anisotropic volume expansion was observed in the Rutherford-type cable samples. A systematic study was undertaken to investigate this phenomenon and to check the hypothesis that the plastic deformation of the strands during cabling process is responsible for this behavior. Nb-Sn strands from various manufacturing technologies were rolled down to different sizes, and the resulting thickness and width of the deformed strands were measured before and after heat treatment. The results obtained on the deformed strands were then compared with those obtained from cables. A good consistency was achieved in most of the cases.
TL;DR: In this paper, the authors present and discuss a selection of the CSIC experimental data of pressure drop vs. mass-flow rate, which were measured for the first time on a full-size ITER conductor in cryogenic conditions during the CSMC and CSIC tests, and compare with predictions based on existing correlations for the friction factor f H in the central channel and f B in the cable bundle, as a function of the respective Reynolds number Re H and Re B.
Abstract: The Central Solenoid Model Coil (CSMC) and the CS Insert Coil (CSIC) were tested during the spring and summer of 2000 at JAERI Naka, Japan, within the framework of the ITER large projects. The CSIC is a single-layer one-in-hand solenoid inserted in the bore of the CSMC. It uses a Nb 3 Sn dual-channel cable-in-conduit conductor (CICC), about 140 m long, cooled by forced flow supercritical HeI nominally at 4.5 K and 0.6 MPa. The friction of the helium flow in the conductor plays a fundamental role in assessing the total mass-flow rate and its repartition between the central cooling channel and the annular bundle region. In turn, these may significantly influence, e.g., quench and/or heat slug propagation in the coil. In the CSIC these issues are complicated further by the fact that different friction characteristics were observed in different phases (e.g., with or without current) of the experimental campaign. Here we present and discuss a selection of the CSIC experimental data of pressure drop vs. mass-flow rate, which were measured for the first time on a full-size ITER conductor in cryogenic conditions during the CSMC and CSIC tests, and compare with predictions based on existing correlations for the friction factor f H in the central channel and f B in the cable bundle, as a function of the respective Reynolds number Re H and Re B . Finally, we derive an ad-hoc correlation for f B , to be used in case of operation of the CSIC with transport current, under the assumption that the central channel stays unchanged.
TL;DR: In this paper, two tube-in-tube heat exchangers with different configurations are tested extensively with different mixtures operating at three typical temperature ranges, such as 80 K-100 K, 120 K-150 K, and 180 K-200 K temperature ranges.
Abstract: In this paper, an experimental set up is established to investigate the behavior of the heat exchanger with multi-components mixtures based on a real mixture refrigeration system. Two tube-in-tube heat exchangers with different configurations are tested extensively with different mixtures operating at three typical temperature ranges, such as 80 K–100 K, 120 K–150 K, and 180 K–200 K temperature ranges. The two heat exchangers are fabricated specially to be able to measure the temperatures and pressures distributions. With the measurement of the mixture compositions, temperatures, and pressures, the thermodynamic and hydraulic behaviors of the two heat exchangers are studied extensively. Finally, the heat transfer characteristics are obtained, which is useful in future design of the mixture refrigeration system.
TL;DR: An overview of ongoing efforts at the Goddard Space Flight Center and the Jet Propulsion Laboratory in support of current flight projects, near-term flight instruments, and long-term technology development is presented in this paper.
Abstract: Mechanical cryocoolers represent a significant enabling technology for NASA’s Earth and Space Science Enterprises, as well as augmenting existing capabilities in space exploration. An overview is presented of ongoing efforts at the Goddard Space Flight Center and the Jet Propulsion Laboratory in support of current flight projects, near-term flight instruments, and long-term technology development.
TL;DR: In this paper, the efficiency of auto-cascade coolers for industrial equipment is discussed and compared with a computer model that includes an equation of state to calculate thermodynamic properties of mixed refrigerants.
Abstract: The efficiency of coolers designed to provide refrigeration for industrial equipment is discussed Experience accumulated during more than twenty years of manufacturing shows that multistage auto-cascade coolers provide high refrigeration performance along with rapid cool down and defrost Both single-stage and two-stage throttle cycles have been analyzed Comparative data on the performance of the cycles are obtained with a computer model that includes an equation of state to calculate thermodynamic properties of mixed refrigerants Both flammable argon-hydrocarbon- and nonflammable argon-hydrofluorocarbon-based mixed refrigerants have been considered Non-flammable environmentally friendly mixed refrigerants include commercially available components The experimental data were obtained for coolers based on a single-stage compressor The tested systems provided refrigeration capacity from 500 to 3600 W depending on the compressor displacement volume A Carnot efficiency coefficient as high as 021 was achieved This corresponds to the efficiency of conventional freezers operating at temperatures above 230 K
TL;DR: In this paper, the measured pressure drop data were compared with these correlations and showed that they show a large deviation from prediction, while the measured friction factor for the central channel is less sensitive to Reynolds number in comparison with modified Blasius type correlation.
Abstract: Pressure drop characteristics of the cable-in-conduit conductor adopted in the ITER Central Solenoid Model Coil (CSMC) were first measured through the CSMC experiment in the ITER relevant cooling condition The conductor has two parallel flow channels such as a bundle channel and a central channel Previous studies have proposed pressure drop correlations between the friction factor and Reynolds number for the central channel In this report, the measured pressure drop data were compared with these correlations Results indicate that the measured pressure drop characteristic shows a large deviation from prediction Friction factor for the central channel is less sensitive to Reynolds number in comparison with modified Blasius type correlation The correlations proposed by Colebrook and Zanino show a relatively good prediction
TL;DR: The Spallation Neutron Source (SNS) as discussed by the authors is a state-of-the-art neutron-scattering facility presently under construction as a collaborative effort of six national laboratories.
Abstract: The Spallation Neutron Source [1], located at Oak Ridge, TN, is a state-of-the-art neutron-scattering facility presently under construction as a collaborative effort of six national laboratories The facility is comprised of a high-power particle-accelerator system, a liquid-mercury target-moderator system, and a suite of world-class scientific instruments One-ms-long negative-hydrogen-ion (H - ) pulses are produced by an ion source The ion beam is accelerated to 185 MeV by normal conducting (NC) linear accelerator (linac) cavities, and further accelerated to 1 GeV by a superconducting linac [2] The acceleration is accomplished by means of niobium superconducting radiofrequency (SRF) cavities that operate at 21K The linac beam is stacked in a compressor ring, and 695-ns-long pulses are extracted onto the target at a 60-Hz rate Neutrons are produced by spallation in the mercury, and their energy is moderated to useable levels, in part by supercritical hydrogen moderators The simultaneous performance goals of more than one MW of initial proton beam power, 95% facility availability, and the desire for hands-on maintenance capability in the accelerator complex place significant demands on the performance and operational reliability of the technical and conventional systems An overview of the SNS facility, including its purpose, major components, and a summary of the present status is presented, with particular emphasis on the superconducting linac and the cryogenic moderators
TL;DR: In this paper, a superconducting strand has been fabricated with the highest yet recorded 5 T, 4.2 K critical current density for conventionally processed Nb-Ti.
Abstract: Superconducting strand has been fabricated with the highest yet recorded 5 T, 4.2 K critical current density for conventionally processed Nb-Ti. Starting from an ingot of high homogeneity Nb-48 wt.%Ti alloy, both mono- and multifilamentary superconductors were fabricated using multiple heat treatment and drawing schedules with very long heat treatments. Using high-resolution FESEM and TEM, the influence of treatment conditions on the microstructure was investigated. With 1000 to 8000 h of total heat treatment time, the volume of precipitate approaches the decomposition limit of the solid solution and the critical current density increases, reaching a maximum > 4.10 5 A/cm 2 at 5 T, 4.2 K. The amount of the precipitated alpha-phase reaches 25-33 vol. %, and the precipitate thickness is 1-4 nm. In order to create a more ordered multilayer structure in the high precipitate-content strand, the samples were rolled as a final stage of processing. The highest level of current characteristics is reached with this combined processing (drawing - rolling). The pinning mechanism, responsible for the high current characteristics in these strands is analyzed.
TL;DR: A prototype flux pump recently operated at the MIT Francis Bitter Magnet Laboratory as mentioned in this paper was used in the development of a full-scale flux pump that will be coupled to a high-temperature superconductor (HTS) insert coil of a high field NMR magnet.
Abstract: This paper describes a prototype flux pump recently operated at the MIT Francis Bitter Magnet Laboratory. The results of the prototype flux pump will be used in the development of a full-scale flux pump that will be coupled to a high-temperature superconductor (HTS) insert coil of a high-field NMR magnet. Such an HTS insert is unlikely to operate in persistent mode because of the conductor’s low index (n). The flux pump can compensate for field decay in the HTS insert coil and make the insert operate effectively in persistent mode. The flux pump, comprised essentially of a transformer and two switches, all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A prototype flux pump has been designed, fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the r...
TL;DR: The CS Insert Coil (CSIC), a well-instrumented 140 m long Nb3Sn solenoid wound one-in-hand and installed in the bore of the CS Model Coil, was tested during the summer of 2000 at JAERI Naka, Japan, within the framework of the International Thermonuclear Experimental Reactor large projects as mentioned in this paper.
Abstract: The CS Insert Coil (CSIC), a well-instrumented 140 m long Nb3Sn solenoid wound one-in-hand and installed in the bore of the CS Model Coil, was tested during the summer of 2000 at JAERI Naka, Japan, within the framework of the International Thermonuclear Experimental Reactor large projects [1]. The maximum transport current in the CSIC was 40 kA and the peak background field was 13 T. The coils were cooled by forced flow HeI nominally at 4.5 K and 0.6 MPa. An inductive heater was used to test stability and quench of the CSIC. In this second of two companion papers we concentrate on the analysis of quench initiation and propagation, based on the study of heater calibration and conductor stability presented in the first paper [2]. The initiation and propagation of an inductively driven quench was tested here for the first time in a two-channel Nb3Sn conductor, for different transport currents, delay times of the dump, and temperature margins, and a selection of the corresponding results will be presented and...
TL;DR: Experiments on vacuum insulation systems in a flexible geometry were conducted at the Cryogenics Test Laboratory of NASA Kennedy Space Center as mentioned in this paper, where the effects of bending were simulated by causing the inner tube to be eccentric with the outer tube.
Abstract: Flexible, vacuum-insulated transfer lines for low-temperature applications have higher thermal losses than comparable rigid lines. Typical flexible piping construction uses corrugated tubes, inner and outer, with a multilayer insulation (MLI) system in the annular space. Experiments on vacuum insulation systems in a flexible geometry were conducted at the Cryogenics Test Laboratory of NASA Kennedy Space Center. The effects of bending were simulated by causing the inner tube to be eccentric with the outer tube. The effects of spacers were simulated in a controlled way by inserting spacer tubes for the length of the cylindrical test articles. Two material systems, standard MLI and a layered composite insulation (LCI), were tested under the full range of vacuum levels using a liquid nitrogen boiloff calorimeter to determine the apparent thermal conductivity (k-value). The results indicate that the flexible piping under simulated bending conditions significantly degrades the thermal performance of the insulat...
TL;DR: In this article, the tradeoff between barrier resistance and twist pitch to minimize the ac loss in aggressive magnetic field and frequency environments typical of synchronous generator armature windings and air core transformers is discussed for power applications.
Abstract: YBCO coated superconducting tapes can be optimized to minimize the ac loss in aggressive magnetic field and frequency environments typical of synchronous generator armature windings and air core transformers. Optimized conductors can be realized by creating a multifilamentary structure incorporating high barrier resistance that allows a practical twist pitch to minimize coupling losses. Barrier electrical resistance is being characterized and several methods for creating high barrier resistance in multifilamentary YBCO tapes by practical material processing methods are being explored. The tradeoff between barrier resistance and twist pitch to minimize ac loss is discussed for power applications. Design limitations due to the twist requirement in generator and transformer windings are discussed for the multifilament YBCO tape.
TL;DR: In this paper, a two-phase He I natural convection flow, i.e., thermosiphon open flow, for a vertical copper tube (14 mm inner diameter) uniformly heated over a length of 1.2 m is presented.
Abstract: Experimental results on two-phase He I natural convection flow, i.e. thermosiphon open flow, for a vertical copper tube (14 mm inner diameter) uniformly heated over a length of 1.2 m are presented. Maximum total mass flow rate of 22 g/s and exiting vapor quality factor of 0.2 have been achieved in the steady state regime for a heat flux up to 2000 W/m2 near atmospheric pressure. In addition, wall temperature difference are measured and critical heat flux and heat transfer coefficients are presented as a function of heat flux. In the nucleate boiling regime, heat transfer coefficient correlations, based on the Martinelli parameter, are proposed for different tube height. They described the data within 20% error margin in the range of 2 105 Reynolds number.