bluuebunny/crossref_metadata_2025 huggingface dataset:
Language choice in peer interactions and the role of peers in minority language maintenance
Authors: Nguyen Trang Thi Thuy , Hamid M. Obaidul
Published: June 2020

Drawing on thepositioningtheory and theconditions for language use, this article examines Vietnamese ethnic minority students’ language choice in interactions with their same-ethnicity and majority peers, focusing particularly on their communication motives underlying this choice. Findings suggest that in regulating their language alternation practices across peer groups in different contexts, the students shifted their participation status – fromaligning(being alike) todisaligning(being distinct) – to (re)position themselves in relation to their peers. As their desires for alignment or disalignment were either supported or disrupted by their peers, peer attitudes played a critical role in providingopportunitiesand encouraging minority students’willingnessto use their L1 in school and ethnic community spaces. Implications are suggested for engaging peer support as a resource for maintaining or widening L1 use among young minority people in both of the domains.
Pinning down text complexity
Authors: Santini Marina , Jönsson Arne
Published: June 2020

In this article, we present the results of a corpus-based study where we explore whether it is possible to automatically single out different facets of text complexity in a general-purpose corpus. To this end, we use factor analysis as applied in Biber’s multi-dimensional analysis framework. We evaluate the results of the factor solution by correlating factor scores and readability scores to ascertain whether the selected factor solution matches the independent measurement of readability, which is a notion tightly linked to text complexity. The corpus used in the study is the Swedish national corpus, calledStockholm-Umeå Corpusor SUC. The SUC contains subject-based text varieties (e.g., hobby), press genres (e.g., editorials), and mixed categories (e.g., miscellaneous). We refer to them collectively as ‘registers’. Results show that it is indeed possible to elicit and interpret facets of text complexity using factor analysis despite some caveats. We propose a tentative text complexity profiling of the SUC registers.
Balanced Bilingualism: Patterns of Contact Influence in L1 and L2 Turkic and Bakhtiari Speech in Juneqan, Iran
Authors: Anonby Erik , Schreiber Laurentia , Taheri-Ardali Mortaza
Published: June 2020

Most studies on language contact in Iran have focused on the effects of Persian on the country’s minority languages. There are also many cases where large regional languages such as Azeri, Kurdish, Balochi, Lori and Bakhtiari exert an influence on smaller regional languages, and a few studies have appeared on this topic. This paper examines the effects of language contact in the city of Juneqan in Chahar Mahal va Bakhtiari Province, Iran, where the position of two minority languages—Bakhtiari and Qashqai Turkic—appears to be evenly balanced. The analysis is based on a comparison of L1 and L2 speech from two bilingual individuals with a different L1, as found in responses to theAtlas of the Languages of Iran(ALI) questionnaire. Drawing on examples from lexicon, phonology and morphosyntax, the article argues that the equivalent influence of each language on the first- and second-language speech of members of the other language community is likely achieved not by simple equal status, but through the counterbalancing of regional Bakhtiari dominance with majority mother-tongue Turkic population in this city.
France among the Most-Favored Nations: The French Commercial Policy and Influence in Iran (1815–48)
Authors: Mousavi Mehdi
Published: June 2020

Iran's subjection to Russo-British influence has received the bulk of attention of modern scholarship dealing with the country's interaction with the outside world in the nineteenth century. This article, while not denying the central role played by these two powers in Iran’s domestic affairs at the time, draws attention to a third power with long-standing claims to influence in the country by way of trade policies—France. From the fall of Napoleon in 1815 until the French Revolution of 1848, the French monarchy was especially keen to encourage commerce with Iran, less as a source of increased wealth than to restore and expand French prestige and political influence. This strategy became more significant, when the British and Russian superpowers opposed an active French presence in Iran and prevented France from asserting influence in the country. To contain those powers, France pursued its plan of reaching a trade treaty with Iran as a means of obtaining commercial concessions and privileges as well as to secure its permanent presence in the country. France also aimed to connect Iran to its network of regional trade extending from the Mediterranean to the Indian Ocean.
Policy style, consistency and the effectiveness of the policy mix in China’s fight against COVID-19
Authors: Mei Ciqi
Published: June 2020

As the first country stricken by the COVID-19 pandemic, China deployed a policy response that was chaotic at the start but effective in the end. A complete account to explain China’s COVID-19 experience should explain both. By examining policy changes in China’s fight against the pandemic, I show that pandemic as an exogenous shock invalidated the normal policy logics followed by multiple policy actors, resulting in policy inconsistency and chaos. A policy mix comprised traditional measures, i.e. strict community lockdown, cross-jurisdictional mobilization of resources and officials’ sanction contributed to the eventual effectiveness of China’s response to the pandemic. I argue that the policy mix during crises should conform with rooted national policy style to be consistent and effective.
A Two-Dimensional Architecture for Fast Large-Scale Trapped-Ion Quantum Computing
Authors: Wu Y.-K. , Duan L.-M.
Published: June 2020

Building blocks of quantum computers have been demonstrated in small to intermediate-scale systems. As one of the leading platforms, the trapped ion system has attracted wide attention. A significant challenge in this system is to combine fast high-fidelity gates with scalability and convenience in ion trap fabrication. Here we propose an architecture for large-scale quantum computing with a two-dimensional array of atomic ions trapped at such large distance which is convenient for ion-trap fabrication but usually believed to be unsuitable for quantum computing as the conventional gates would be too slow. Using gate operations far outside of the Lamb–Dicke region, we show that fast and robust entangling gates can be realized in any large ion arrays. The gate operations are intrinsically parallel and robust to thermal noise, which, together with their high speed and scalability of the proposed architecture, makes this approach an attractive one for large-scale quantum computing.
Strong cosmic censorship conjecture with NUT charge and conformal coupling
Authors: Rahman Mostafizur , Mitra Soumodeep , Chakraborty Sumanta
Published: June 2020

Strong cosmic censorship conjecture is central to the deterministic nature of general relativity, since it asserts that given any generic initial data on a spacelike hypersurface, the future can be uniquely predicted. However, recently it has been found that for charged black holes in asymptotically de Sitter spacetimes, the metric and massless scalar fields can be extended beyond the Cauchy horizon. This spells doom on the strong cosmic censorship conjecture, which prohibits precisely this scenario. In this work we try to understand the genericness of the above situation by studying the effect of NUT charge and conformally coupled scalar field on the violation of strong cosmic censorship conjecture for charged asymptotically de Sitter black holes. We have shown that even in the presence of the NUT charge and a conformally coupled scalar field strong cosmic censorship conjecture in indeed violated for such black holes with Cauchy horizon. Moreover, the presence of conformal coupling makes the situation even worse, in the sense that the scalar field is extendible across the Cauchy horizon as aC1function. On the other hand, the strong cosmic censorship conjecture is respected for conformally coupled scalar field in rotating black hole spacetimes with NUT charge. This reinforces the belief that possibly for astrophysical black holes, strong cosmic censorship conjecture is respected, irrespective of the nature of the scalar field.
Tunable, few-cycle, CEP-stable mid-IR optical parametric amplifier for strong field applications
Authors: Musheghyan Mikayel , Geetha Prabhash Prasannan , Faccialà Davide , Pusala Aditya , Crippa Gabriele , Campolo Andrea , Ciriolo Anna G , Devetta Michele , Assion Andreas , Manzoni Cristian , Vozzi Caterina , Stagira Salvatore
Published: June 2020

We present a robust, three-stage optical parametric amplifier driven by a Ti:Sapphire ultrafast laser system that implements passive carrier-envelope phase stabilization and directly generates five-cycle mid-IR pulses by dispersion compensation. The source is based on potassium titanyl arsenate crystals and exploits intra-pulse difference-frequency seed generation in the mid-IR. This source will be particularly suited for applications in strong-field physics, such as high order harmonic generation and photoelectron spectroscopy.
Optimal design of inverted rotary MR brake with waveform boundary using a novel combined magnetostatic approach
Authors: Saini Radhe Shyam Tak , Kumar Hemantha , Chandramohan Sujatha
Published: June 2020

In the present work, an inverted rotary drum magneto rheological (MR) brake with waveform arc boundary suitable for prosthetic knee application is optimally designed. Often, the magnetostatic analysis is performed assuming linear magnetic systems and solving a lumped parametric equivalent magnetic model (EMM). Although, this reduces the computational time but compromises the accuracy of the solution. On the other hand, finite element magnetostatic (FEMS) analysis combined with a search-based optimization technique requires more time and effort. In this work, an approach combining the EMM and FEMS methods is proposed to optimally design the MR brake. This method requires the optimization algorithm to maintain an external repository so that individuals which are non-dominated at each generation get stored in the repository and only those individuals are allowed to use FEMS method. This approach reduces the number of function calls made to FEMS method and thus reduces the computational time substantially. A recently proposed multi-objective particle swarm optimization (MOPSO) which evaluates the global best using minimum distance of point of line (MDPL) method is implemented with the proposed combined magnetostatic method. While FEMS method alone resulted in an average computational time of 7.25 h, the proposed method evaluated a similar Pareto front solution in 38 min. Finally, the optimal design is compared to other prosthetic knee MR brakes from the literature.
Quantification of H/D content in Be/W mixtures coatings by CF-LIBS
Authors: Veis P , Marín-Roldán A , Dwivedi V , Karhunen J , Paris P , Jõgi I , Porosnicu C , Lungu C P , Nemanic V , Hakola A
Published: June 2020

In ITER, a remote handling laser-induced breakdown spectroscopy (LIBS) system is considered to be able to observe regions where deposition of thick layers is expected to occur and assess the retention of fuel on wall structures. The H and D contents of surface layers on divertor and first-wall materials have been intensely studied by LIBS but mostly by depth profile analysis of D. As far as we know, quantitative analysis of H/D in BeW mixed layer by calibration free-LIBS (CF-LIBS) has not been performed. Thus, the aim of this work is the quantification of the relative concentrations of D and H in Be-based material samples by CF-LIBS. The samples used were Be/W(67:33) as mixed homogeneous coatings (2 μm) on Mo substrates. Laser ablation was performed using a 1064 nm laser with 5 ns pulses. In order to enhance the resolution to distinguish H, D and in future T from each other, two different pressures were used: high vacuum and 0.5 mbar of Ar. Suitable Be and W spectral lines (without interferences and self-absorption) have been selected for precise evaluation of the electron temperature, T

e
, of the plasma using the Boltzmann plots. The electron density, n

e
, was extracted from the Saha equation using the average electron temperatures obtained from the Stark broadening of the H
α
line. With these values, the D content of the samples has been calculated by CF LIBS as ∼4.7% ± 2.9%. These results are in a good agreement with thermal desorption spectroscopy measurements, which gives a 4–5 at% for the D content. In addition, the depth profile is similar to that recorded using secondary ion mass spectrometry.
Redshift drift in uniformly accelerated reference frame *
Authors: Chang Zhe , Zhu Qing-Hua
Published: June 2020

We construct an alternative uniformly accelerated reference frame based on a 3+1 formalism in adapted coordinates. In this frame, a time-dependent redshift drift exists between co-moving observers, which differs from that in Rindler coordinates. This phenomenon can be tested in a laboratory and improve our understanding of non-inertial frames.
Cities as carbon sinks—classification of wooden buildings
Authors: Amiri Ali , Ottelin Juudit , Sorvari Jaana , Junnila Seppo
Published: June 2020

Although buildings produce a third of greenhouse gas emissions, it has been suggested that they might be one of the most cost-effective climate change mitigation solutions. Among building materials, wood not only produces fewer emissions according to life-cycle assessment but can also store carbon. This study aims to estimate the carbon storage potential of new European buildings between 2020 and 2040. While studies on this issue exist, they mainly present rough estimations or are based on a small number of case studies. To ensure a reliable estimation, 50 different case buildings were selected and reviewed. The carbon storage per m2 of each case building was calculated and three types of wooden buildings were identified based on their carbon storage capacity. Finally, four European construction scenarios were generated based on the percentage of buildings constructed from wood and the type of wooden buildings. The annual captured CO2 varied between 1 and 55 Mt, which is equivalent to between 1% and 47% of CO2 emissions from the cement industry in Europe. This study finds that the carbon storage capacity of buildings is not significantly influenced by the type of building, the type of wood or the size of the building but rather by the number and the volume of wooden elements used in the structural and non-structural components of the building. It is recommended that policymakers aiming for carbon-neutral construction focus on the number of wooden elements in buildings rather than more general indicators, such as the amount of wood construction, or even detailed indirect indicators, such as building type, wood type or building size. A practical scenario is proposed for use by European decision-makers, and the role of wood in green building certification is discussed.
A coupled Temperley–Lieb algebra for the superintegrable chiral Potts chain
Authors: Adderton Remy , Batchelor Murray T , Wedrich Paul
Published: June 2020

The Hamiltonian of the N-state superintegrable chiral Potts (SICP) model is written in terms of a coupled algebra defined by N − 1 types of Temperley–Lieb generators. This generalises a previous result for N = 3 obtained by Fjelstad and Månsson (2012 J. Phys. A: Math. Theor.
45 155208). A pictorial representation of a related coupled algebra is given for the N = 3 case which involves a generalisation of the pictorial presentation of the Temperley–Lieb algebra to include a pole around which loops can become entangled. For the two known representations of this algebra, the N = 3 SICP chain and the staggered spin-1/2 XX chain, closed (contractible) loops have weight

3

and weight 2, respectively. For both representations closed (non-contractible) loops around the pole have weight zero. The pictorial representation provides a graphical interpretation of the algebraic relations. A key ingredient in the resolution of diagrams is a crossing relation for loops encircling a pole which involves the parameter ρ = e
2πi/3 for the SICP chain and ρ = 1 for the staggered XX chain. These ρ values are derived assuming the Kauffman bracket skein relation.
Robotic Refueling Mission-3—an overview
Authors: Breon S R , Boyle R F , Francom M B , DeLee C H , Francis J J , Mustafi S , Barfknecht P W , McGuire J M , Krenn A G , Zimmerli G A , Hauser D M
Published: June 2020

Robotic Refueling Mission-3 (RRM3) is an external payload on the International Space Station (ISS) to demonstrate the techniques for storing and transferring a cryogenic fuel on orbit. RRM3 was designed and built at the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC). Initial testing was performed at GSFC using liquid nitrogen and liquid argon. Final testing and flight fill of methane was performed at the NASA Kennedy Space Center (KSC) to take advantage of KSC’s facilities and expertise for handling a combustible cryogen. This paper gives an overview of the process and challenges of developing the payload and the results of its on-orbit performance.
Integrated refrigeration and storage of LNG for compositional stability
Authors: Rose L , Swanger A M , Notardonato W U , Fesmire J E , Gleeson J , Carro R
Published: June 2020

Growing interest in liquefied natural gas (LNG) as a rocket fuel necessitates a greater technical understanding of the compositional changes due to preferential boil-off (or weathering) that occurs during long duration storage. The purity of methane in LNG can range from 90 to 98%, and is subject to preferential boil-off due to its low boiling point compared to other constituents despite the use of high-performance thermal insulation systems. Active heat extraction (i.e. refrigeration) is required to completely eliminate weathering. For future operational safety and reliability, and to better understand the quality and efficiency of the LNG as a cryofuel, a 400-liter Cryostat vessel was designed and constructed to measure the composition and temperatures of the LNG at a number of different liquid levels over long durations. The vessel is the centerpiece of a custom-designed lab-scale integrated refrigeration and storage (IRaS) system employing a pulse tube cryocooler capable of roughly 50 W of lift at 100 K. Instrumentation includes ten temperature sensors mounted on a vertical rake and five liquid sample tubes corresponding to five liquid levels. Two modes of operation are studied. The first is without refrigeration in order to determine a baseline in the change in composition, and to study stratification of the LNG. The second is performed with the cryocooler active to determine the operational parameters of the IRaS system for eliminating the weathering as well as stratification effects in the bulk liquid. The apparatus design and test method, as well as preliminary test results are presented in this paper. As a bonus in cost-saving and operational efficiency, the capability of the IRaS system to provide zero-loss capabilities such as zero boil-off (ZBO) keeping of the LNG and zero-loss filling/transfer operations are also discussed.
Performance characteristics comparison of major types of mechanical cryocoolers for aerospace applications
Authors: Chen W
Published: June 2020

The three major types of mechanical cryocoolers in aerospace applications, namely reverse-Brayton cryocoolers, Stirling/pulse tube cryocoolers and Joule-Thomson cryocoolers, have significantly different performance characteristics. Some of these differences are due to the nature of their thermodynamic cycles; others come from their drastic differences in mean operating pressures and pressure ratios. This paper first provides an overview of the performance characteristics of these three types of cryocoolers, their unique performance benefits and main applications. It then derives an analytical expression for a cryocooler’s Carnot efficiency, considering the effects of the system pressure ratio drop from the warm end to the cold end and heat leak due to the convective flow and axial conduction. The convective heat leak is related to the pressure drop and the figure of merit of the heat transfer surface using the Colburn-Chilton analogy. Based on this result, the paper discusses the key control parameters affecting the size and mass of the heat exchanger and thus the overall cooler system in each type of cryocooler.
Impact of the cold regenerator mesh geometry on low temperature pulse tube cold finger performance
Authors: Dherbécourt D , Martin S , Charles I , Duval JM , André J , Daniel C
Published: June 2020

Future astrophysics missions such as SPICA, Athena or LiteBird will need a cooling below 1 K (until 50 mK) to achieve the detectors’ required sensibility. To address such requirements, cooling chains are built coupling several technologies using intermediate temperature cooling, explaining why a high cooling power at 15 K is essential. The CEA-DSBT designed, for lab test purpose, a Pulse Tube cooler system consisting of a heat intercepted single-stage cold finger which is pre-cooled by a Gifford McMahon cryocooler. The cold part of the PT, in particular the regenerator, is critical to the PT cooler performance. Keeping the regenerator material standard (stainless steel mesh), we study here the influence of the cold regenerator mesh geometry on the operation of the cold finger. The wire thickness is varied, which modifies the porosity, the dead volume and the heat surface exchange of the regenerator. Experimental results on different mesh designs are presented here and analysed, showing a significant influence of the mesh geometry on the performance.
Modifications to the MIRI cryocooler design to provide significant lift in the 2K to 4K range
Authors: Petach M , Michaelian M , Nguyen T
Published: June 2020

A high Technology Readiness Level cryocooler with significant cooling in the 2K to 4K regime will enable a variety of missions ranging from large infrared space telescopes to superconducting and quantum applications. The cryocooler for the MIRI instrument on JWST was designed for operation at 6K, and with relatively minor changes this design can achieve significant lift in the 2K to 4K region. This paper provides curves of predicted lift vs. power for a variety of operating temperatures, based on the model anchored by tests of the MIRI cooler. The modifications are described, and their mass impacts are estimated. These mass and performance estimates enable payload and mission planners to explore new mission classes.
Return to service of a liquid hydrogen storage sphere
Authors: Krenn A , Desenberg D
Published: June 2020

One, of two, 850,000 gallon liquid hydrogen storage spheres, at NASA’s Kennedy Space Center, was decommissioned in 2010. This tank had an abnormally high heat leak that was investigated and determined to be the result of a large void in the perlite insulation. The insulation void was subsequently filled, and the tank was refurbished for its planned use in the Space Launch Systems (SLS) program. Return to service of this tank began in December of 2017 with a partial liquid hydrogen fill. Since that time, routine measurement of the liquid level have been recorded in order to establish a new boiloff rate and associated heat leak. This data shows the perlite top off activities have resulted in a much reduced, and within design specification, heat leak.
Experimental Study on Pool Boiling Heat Transfer Characteristics of Slush Nitrogen
Authors: Wu S Q , Wang Q D , Li Y J , Huang J L , Jin T
Published: June 2020

Slush nitrogen is a cryogenic two-phase fluid with solid nitrogen particles suspended in liquid nitrogen, which can be a potential coolant for high temperature superconductor thanks to its high density and large heat capacity. The present work focuses on the pool boiling heat transfer characteristics of slush nitrogen. The freeze-thaw method was used to produce slush nitrogen and the capacitance-type density meter was adopted to determine the solid volumetric fraction of slush nitrogen. The experimental results show that the heat transfer characteristics of slush nitrogen matches with typical nucleate boiling heat transfer. The heat transfer of slush nitrogen can be enhanced by increasing the solid fraction. The applicability of Rohsenow equation to the nucleate pool boiling heat transfer of slush nitrogen was analyzed, and then a heat transfer correlation for nucleate pool boiling heat transfer of liquid nitrogen and slush nitrogen, considering the effect of solid volumetric fraction, was summarized.
A novel hydrogen turbo-expander with active magnetic bearings and an eddy current brake
Authors: Chen J Y , Li X M , Dong X B , Lv C , Wu J H
Published: June 2020

A cryogenic expander for hydrogen liquefier with active magnetic bearings (AMB) has been designed and will be made and tested. The shaft design and strength review are significant factors for the turbine since it affects the performance and safety of the expander significantly. In order to produce lower temperature hydrogen, the liquefier needs a very small and high-speed turbo-expander. However, there are few studies on expander with both active magnetic bearings and eddy current brakes. In this study, the speed of the turbine is up to 100000 rpm. Its cooling power is about 4kW. The inlet pressure is 1MPa, and the outlet pressure is 0.7MPa. Under this condition, the turbine is designed, and the simulation is done. An eddy current brake which can govern the rotational speed quickly is designed and studied as well.
FLIR FL-100 Miniature Linear Stirling Cryocooler Development Summary
Authors: Conrad T , Haley D , Lieb T , Grabau M , Miramontes S , Garcia E , Chapple S , Erwin B
Published: June 2020

FLIR Systems has recently developed and begun manufacturing a miniature linear Stirling cryocooler, the FL-100, which has been designed to meet the needs of compact systems using High Operating Temperature (HOT) detectors. These include low cost, long life, high efficiency, and a very compact packaging size. A compact and efficient drive electronics board, the Cryogenic Cooler Controller (CCC), has also been developed to pair with the FL-100. This paper presents the design specifications of the FL-100 cryocooler and summarizes the results of the testing which has been completed thus far on prototype and early production units.
Investigation of improving cool-down speed of Stirling type pulse tube cryocooler with ambient displacers
Authors: Yan C G , Wang X T , Dai W , Pfotenhauer John M. , Zhang Y B , Li H B , Luo E C
Published: June 2020

For a cryocooler, besides high efficiency at the working temperature, the cool-down speed is also important for some applications. Because of the difference in structure and operating mechanism, different cryocoolers have different characteristics for cool-down speed. This work introduces a Stirling type pulse tube cryocooler with ambient displacers which works in the liquid nitrogen temperature region. Strategies for improving the cool-down speed from room temperature to liquid nitrogen temperature have been investigated through simulation. The pulse tube cryocooler is designed to provide a nominal cooling power of 17.8 W at 77 K with 232.5 W of input electric power at 70 Hz. By fixing the maximum displacer movement in the simulation, the characteristics of how tuning the frequency around 70 Hz can change the cool-down speed without exceeding the allowable displacement of the piston and the current draw of the actual compressor are investigated. The strategy for tuning both the frequency and voltage turns out be effective in the beginning stage of the cool-down process with an improvement of the cooling power by about 15%-20%. The gain becomes less obvious as the cold head temperature drops. In conclusion, tuning both the frequency and voltage during the cool-down process helps the cold-head to reach its final temperature faster but the average gain is not as big as expected.
CFD study of the 2D gas piston in pulse tube cryocoolers
Authors: Guo Zhimin , Zhu Shaowei , Pfotenhauer John M
Published: June 2020

There are three parts of the gas moving through the pulse tube of the pulse tube cryocooler, part I is the gas moving between the cold heat exchanger and the pulse tube, part II is the gas oscillating in the pulse tube all the time, part III is the gas moving between the pulse tube and the warm heat exchanger. The part of the gas that always moves in the pulse tube performs the same function as a solid piston; this part of the gas is called the gas piston. The shape and the position of the gas piston changes with time and the operating conditions rather than remaining fixed. A 1D model cannot capture the change of the gas piston near the wall, but a 2D model capturing changes in the axial and radial directions can. Further, the uniformity of the fluid flow field in the pulse tube can be depicted by the shape of the gas piston which can be simply envisioned as a 2D gas piston in the pulse tube. In this study a CFD method is used to obtain the details of the 2D gas piston. The velocity field in the pulse tube is obtained by the commercial code ANSYS Fluent, and a LaGrange particle tracing method is introduced to process the velocity data in order to obtain the boundary of the 2D gas piston. Additionally, this work investigates the influence of various parameters including pressure ratio, pulse tube aspect ratio and frequency on the shape of the gas piston. It reveals that a larger pressure ratio, larger aspect ratio and lower frequency cause a larger deformation of the gas piston in one cycle. These effects are especially noticeable at the warm end of pulse tube, which displays a larger deformation than other positions in the pulse tube under the influence of changes in those parameters.
Cryogenic Flux Capacitor for Advanced Molecular and Energy Storage Applications
Authors: Swanger A M , Fesmire J E
Published: June 2020

Effective storage and transfer of fluid commodities such as oxygen, hydrogen, natural gas, nitrogen, argon, and others is a necessity in many industries and for hosts of different applications. Molecules are typically contained as low pressure, cryogenic liquids; or as high-pressure gases. Liquefied gasses afford high energy and volume densities, but require complex storage systems to limit boil-off losses, need constant settling in zero-gravity, and are not well suited for overly dynamic situations where the tank orientation can change suddenly. Most cryogenic liquid tanks are complex, nested configurations to increase thermal performance, making them large, massive, and difficult to be made into conformal shapes. Conversely, high pressure gas storage bottles are unaffected by orientation, and can be kept at room temperature; however, these vessels are heavy-walled to contain the high pressures, and the energy densities associated with gas storage are dramatically lower. These two options are typically traded depending on the system requirements, but few practical options exist that provide the benefits while limiting the downfalls. Alternatively, the Cryogenic Flux Capacitor (CFC) technology employs nano-porous aerogel composites to store, by physisorption processes, large quantities of fluid molecules in a molecular solid-state condition, at moderate pressures and cryogenic temperatures. By virtue of its design architecture, a CFC device can be “charged” and “discharged” quickly and on-demand according to operational requirements. Three CFC application areas are introduced: CFC-Fuel, CFC-Cool, and CFC-Life, corresponding to designs utilizing fuels such as hydrogen and methane; inert fluids such as nitrogen and argon for cooling power; and oxygen or breathing air for life support. Data for physisorption within different aerogel composites are presented in terms of both mass and volumetric parameters.
Design of dewar supports through topology optimization
Authors: Nitin B , Sandilya Pavitra , Chakraborty Goutam
Published: June 2020

Dewars are used to store and transport cryogens like LNG, LN2, LOX, LHe etc. These comprise two vessels, one placed inside the other and held together either at the “neck” (input/output port) or by support systems, depending on the capacity, the mechanical loads on the vessel and the boil-off characteristic of the stored cryogen. Support system based dewars are more common for real-life and industrial applications. Design of the support system are based on the principles that are used for high temperature pressure vessels. On the other hand, support system to be used for cryogenic fluid storage should also address the heat inleak through the supports along with the imposed mechanical load and thermal contraction-expansion effects. Some safety factors are prescribed in the literature to address these concerns; however, the scientific basis of design strategies available in the open literature so as to give a more scientific basis of design is absent. This would result in reduction in use of excessive dimensions or material thereby reducing the payload and the capital cost. Considerations of mechanical load and thermal heat inleak often lead to diametric conclusions in terms of the diameter/thickness of the support system, leading to pareto-optimal solution. Topology optimization (TO) is often used to design structures like bridges, vehicles, robotic arms etc. by a systematic and sequential removal of the mass of the material being used to fabricate the given structure while meeting the constraints in terms of load bearing capacity of the structure and heat inleak. This methodology may be followed to arrive at an optimized geometry for the support system when the designer is unsure of the initial shape to start working. In this work, TO has been tested with various thermal and mechanical boundary conditions to arrive at optimized support geometry.
Experimental and numerical investigation of 2 K heat exchanger for superfluid helium cryogenic systems at KEK
Authors: Kumar A , Nakai H , Nakanishi K , Shimizu H , Kojima Y , Hara K , Honma T
Published: June 2020

Superfluid helium cryogenic systems at KEK are constructed for research and development of cryomodules of the compact Energy Recovery Linac (cERL) and the International Linear Collider (ILC). The niobium superconducting radio frequency (SRF) cavities in cERL and ILC operate at temperatures of 2.0 K or below. The SRF cavities are cooled with saturated superfluid helium, which is another phase of the liquid helium (LHe), when it is cooled below 2.17 K under saturation condition. To produce superfluid helium continuously, a Joule-Thomson (JT) valve is employed in the cryogenic system. Also, a 2 K heat exchanger (2K HX) is introduced in series with the JT valve to recover the coldness from 2.0 K gaseous helium (GHe) evaporating from the helium tanks of the SRF cavities. This increases the production rate of superfluid helium by reducing the incoming LHe temperature from 4.4 K to 2.2 K or above before the JT valve. At KEK, we have a 2K HX consisting of a helical coil and laminated fins for thermal loads up to 100 W. Its performance needs to be determined and is characterized by a factor known as effectiveness, which is the ratio of actual heat transfer to the maximum possible heat transfer between the fluids. The performance of the 2K HX has been determined experimentally using the heat exchanger test stand and numerically by computational fluid dynamics (ANSYS CFX®), respectively. In the heat exchanger test stand, the mass flow rate of incoming LHe is kept identical to the outgoing GHe through the 2K HX, using the level and pressure control of superfluid helium. An electric cartridge heater is immersed in the superfluid helium to vary the mass flow rate of evaporating superfluid helium. In the future, the optimization of the 2K HX design will be performed to improve its performance.
Entropy Analysis of Support Systems in Multi-Channel Cryogenic Lines
Authors: Duda P , Chorowski M , Poliński J
Published: June 2020

This work describes the methods for transporting cryogens through multi-channel transfer lines. It also presents examples of the use of cryogenic lines and of their designs, referring in detail to typical structural nodes found in cryogenic transfer lines. The second principle of thermodynamics and the Gouy-Stodola theorem are discussed from the perspective of their application in optimizing and evaluating heat and mass transfer devices. The next part of the work presents the internal structure of the selected 100 m multi-channel cryogenic transfer line. Several variants of the method of supporting process pipes have been presented. For each of the solutions, an entropy analysis was carried out in order to select the best design in terms of the entropy generated in the process pipes.
Performance analysis of a new double stage compressor helium liquefaction cycle
Authors: Su H K , Li Z Y , Gong L H , Zhu W P , Zhang M M , Jia Q M
Published: June 2020

Large scale helium liquefaction/refrigeration plant plays a vital role in advanced large equipment such as fusion reactors and accelerators. A new helium liquefaction cycle with double stage compressor is proposed in this paper, which is different from the Collins cycle. The helium gas from the compressor is divided into two parts. The medium-pressure helium gas as one part flows through the heat exchangers and is liquefied by throttling in the valve. The other part, high-pressure helium gas flows into the turbine for adiabatic expansion with decrease of its temperature and pressure. Both high-temperature helium gas streams become low-temperature and low-pressure. In this paper, the new cycle is parametrically analysed to demonstrate the effect of each parameter on the performance of the cycle. The results of the liquefaction capacity are obtained in different working conditions. Exergy analysis, which is an effective way to analyse thermodynamic cycles, is performed on the liquefaction process and the result is significant for the appropriate design of helium liquefaction system.
Dynamic simulation of ITER cryogenic system under D-T operation
Authors: Maekawa R , Takami S , Iwamoto A , Chang H S , Grillot D
Published: June 2020

Co-simulation of Cryoplant and Tokamak superconducting magnet system (referred to as Magnet) has been performed to characterize operating condition associated with control strategies. Cryoplant model, developed by EcosimPro®, consists of three identical refrigerators connected with integrated Cryoplant Termination Cold Box (CTCB) which distributes the coolant to five Auxiliary Cold Boxes (ACB) for Magnet and CryoPump (CP) cooling. Meanwhile, Magnet model, developed by Visual Modeler®, consists of Toroidal Field (TF) coil, Central Solenoid (CS), TF STructure (ST) and Poloidal Field (PF)/Correction Coil (CC). Magnet model computes thermo-hydraulic behavior of a forced-flow Supercritical Helium (SHe), with specified thermal energy deposition along the conductor in the case of Deuterium-Tritium (DT) operation as well as plasma disruption followed by the fast energy discharge of CS and PF. Global simulation of ITER cryogenic system provides its operating characteristics for complex cryogenic processes. The paper discusses the coupling of Cryoplant and Magnet models and the control strategy for Cryoplant to manage substantial dynamic heat loads.
Commissioning of the Warm Compressor System for the ESS Accelerator Cryoplant
Authors: Wang X L , Wischhoefer R , Selva P , Nilsson P , Råström J , Goncalves R , Olsson M , Arnold P
Published: June 2020

The accelerator cryoplant (ACCP) providing the cooling for the cryomodules and the cryogenic distribution system for the cold part of the ESS proton linac is being built and commissioned at the European Spallation Source (ESS) in Lund, Sweden. The ACCP warm compressor system (WCS) consists of several compression stages. The sub-atmospheric pressure stage (SP) is used to compress helium coming from the cold compressors directly to middle pressure (MP) level. The low pressure stage (LP) compresses the helium from LP level to the same MP level, being merged with additional flow from the cold box and the flow from the SP stage. The total flow is compressed in a single compression stage (HP) from MP to HP. The oil-flooded screw compressors are chosen in a way that the flow in each stage SP, LP and MP is compressed by a single screw compressor. Both, SP and LP compressors are equipped with a variable frequency drive (VFD) to adapt the compressor capacities to the various load cases. The ACCP had been contracted to Linde Kryotechnik AG in 2015 and all compressors are made by the Aerzener Maschinenfabrik GmbH, Germany. Following successful installation and commissioning in 2018, the final 100 hours test run at maximum nominal design condition and the part load tests under various ACCP operation modes were carried out at the beginning of 2019. The key parameters, including mass flow, power consumption, isothermal and volumetric efficiencies, are well fulfilled with the design data. The paper describes the system features, project challenges, lessons learned and acceptance test results.
FRIB helium refrigeration system commissioning and performance test results
Authors: Knudsen P , Ganni V , Hasan N , Wright M , Casagrande F , Vargas G , Joseph N
Published: June 2020

At its maximum capacity condition, the 4.5 K refrigerator system for the Facility for Rare Isotope Beams (FRIB) accelerator supports a 180 g/s 30 K 1.16 bar cold compressor return flow, a 14 g/s 4.5 K liquefaction load, a 4 kW 4.5 K refrigeration load, and a 20 kW 35-55 K shield load. Five additional design conditions, ranging from liquefaction to refrigeration and a stand-by/reduced load state, were specified for the sizing and selection of its components. The cold box system is comprised of a 300-60 K vertical cold box that incorporates a liquid nitrogen pre-cooler and a 60-4.5 K horizontal cold box housing seven turbines that are configured in four expansion stages including one Joule-Thompson expander. This cold box system, operates using the Ganni-Floating pressure process, automatically adjusting to the linear accelerator (Linac) load with the cold box supply (and compressor discharge) pressure varying from 6 to 21 bar, without introducing additional (artificial) loads or throttling turbine inlet valves (or other exergy loss mechanisms), and with minimal liquid nitrogen usage. This paper will briefly review the salient 4.5 K system design features and discuss the recent commissioning results.
Design, fabrication, commissioning and testing of FRIB 2 K cold compressor system
Authors: Knudsen P , Ganni V , Casagrande F , Fila A , Hasan N , Wright M , Vargas G , Joseph N
Published: June 2020

The FRIB cryogenic engineering group designed and built the sub-atmospheric cold box which supports the 2 K (31 mbar) operation of the FRIB accelerator cryo-modules. The centrifugal cryogenic (cold) compressors, designed with room temperature motors and active magnetic bearings, were supplied by Air Liquide to FRIB specifications and were integrated into the cold box which was built on site. The preliminary commissioning tests demonstrated that the system has achieved all the specification goals of operating from 110-180 g/s with a suction pressure of 0.028 mbar, discharge pressure of 1.15 bar and a discharge temperature less than 30 K. This paper will briefly review the sub-atmospheric 2 K system design features and discuss the recent commissioning results.
FRIB helium compression system commissioning and performance test results
Authors: Knudsen P , Ganni V , Wright M , Casagrande F , Vargas G , Joseph N
Published: June 2020

The design for the FRIB helium compressor system, used for the cryogenic refrigeration, was mainly based on the advancements developed for NASA James Webb project, improving the efficiency, reliability and maintainability from previous helium compression systems. The skid designs were further improved, first for the JLab 12 GeV project, and now with additional improvements for the FRIB project. The FRIB helium compression system has five operating compressors at maximum refrigeration capacity with an additional spare compressor. This spare can be configured to align its suction to any one of the three pressure levels of the five, discharging to the high pressure (4.5 K cold box supply) stream. This compressor system can support the 4.5 K cold box operation with a supply pressure varying from 6 to 21 bar, and without complex-sophisticated control of the gas management valves. This paper will briefly review several of the skid improvements and discuss some of the recent commissioning and test results.
Thermodynamic and cost-effectiveness analyses of chosen cooling loops for local production of saturated superfluid helium in large cryogenic systems
Authors: Fydrych J , Pietrowicz S
Published: June 2020

Large scientific facilities applying HeII technologies usually use the Joule-Thomson expansion for the final production of saturated superfluid helium at their cryogenic users. The users are usually supplied with subcooled liquid helium at 4.5 K and 3 to 4 bar(a). Then, to produce HeII, the 4.5 K helium is precooled in a local heat exchanger and throttled to a subatmospheric pressure below 50 mbar(a). This final throttling goes along an isenthalpic line which leads to the zone of wet vapour at the quality of 15.9%. The efficiency of this process can be strongly affected by additional heat loads, which may result in a significantly higher quality of the throttled helium. This imperfection can be partly decreased by using a local subcooler or by splitting the expansion process into two phases with an intermediate point around 1.2 bar(a). However, these solutions require additional components, such as phase separators with some instrumentation and another throttling valve. The paper presents the comparative thermodynamic analysis of the three identified cooling loops. Potential savings due to thermodynamic efficiency improvements are verified against the capital costs for different operation times.
Stable operation of cryogenic system at 2K during the RF or magnet power variations
Authors: Putselyk S
Published: June 2020

In the last 40 years several large laboratories, e.g. CERN, DESY, TJNAF, constructed the accelerators with large number of superconducting (sc) cavities or sc magnets operating at 2 or 4 K temperature levels. The sc cavity operation requires more stringent ranges of pressure variation than ones of sc magnets. In comparison to small testing benches or single cavities modules, for large accelerators a complicated controlling of refrigerator and cryogenic system is required. In the present paper, a review of controlling principles and loops, typically applied for the controlling of liquid helium (LHe) level and pressure for large accelerators is presented. Other possible control loops, e.g. cascade control or multivariable feed-back (or with feed-forward option), are discussed. Activities related to the commissioning of control loops and some supporting measurements are mentioned. Experimental data on investigation of gas/liquid thermal equilibrium are also presented.