Table of contents

Preface

It is our great pleasure to report that the Proceedings of joint meeting of the 1^st Asian ICMC CSSJ 50^th Anniversary Conference (1^st Asian ICMC-CSSJ 50) held at Kanazawa Kagekiza, Japan from November 7^th to 10^th, 2016 is published in Journal of Physics: Conference Series (JPCS). The 1^st Asian ICMC-CSSJ 50 organized by the International Cryogenic Materials Conference in Asia (Asian ICMC) and Cryogenics and Superconductivity Society of Japan (CSSJ), was aimed to gather a large number of scientists, engineers, students, corporate executives and other participants from Asian countries, and to promote technologies on superconductivity and cryogenics through presentations and fruitful discussions. Motivations of this new international conference are to enhance communications between researchers in this field in Asia and to celebrate 50 years anniversary of CSSJ established in 1966. Total numbers of participants and presentations of the 1^st Asian ICMC-CSSJ 50 are 378 from 16 countries and 264 including 5 plenary lectures, 5 invited talks for Asian topics and 64 invited talks, respectively. This conference consisted of many sessions, such as Superconducting Materials, Critical Current Properties of Fe-Based Superconductors, Wires and Tapes, Evaluation and Analysis, Stability, AC Losses, FCLs/Transformers, Power Applications, Cables, Magnet Technology, Magnet Design, MRIs, Fusion, SMESs / Combination with RE, LTS Strands, Superconducting Joints, Rotating Machines, Superconducting Bulks, Fabrication and Application of Superconducting Bulk, Magnetization of Superconducting Bulk, Magnetic Separation, LTSs/Applications of Cryogenics, Large Scale Cryogenics, Cryogenic Materials, Cryogenic Cooling Engineering, Cryocoolers, Heat Transfer, Material Properties for Cooling Devices, Cryogenic Structural and Insulation Materials, Electronics, SQUIDs and Detectors, Thin Films and Devices and Low Carbon Society.

To ensure the high publication standard mandated by JPCS, every paper was peer reviewed by a reviewer with expertise, and in some cases by two reviewers before it was accepted for publication. The reviewing process was managed by the program committee of CSSJ. As editors of the Proceedings, we would like to express our sincere appreciation to all the reviewers involved in the evaluation of the papers for their invaluable contribution.

Editors and Program Committee are listed below.

Editors: Mitsuho Furuse (AIST), Takanobu Kiss (Kyusgu Univ.), Jun-ichi Shimoyama (Aoyama Gakuin Univ.)

Program Committee: Nobuya Banno (NIMS), Hiroyuki Fujishiro (Iwate Univ.), Mitsuho Furuse (AIST), Mutsuo Hidaka (AIST), Tsutomu Hoshino (Meisei Univ.), Yota Ichiki (Hitachi), Masayoshi Inoue (Kyushu Univ.), Masataka Iwakuma (Kyushu Univ.), Akifumi Kawagoe (Kagoshima University), Hiroshi Miyazaki (Toshiba), Takahiro Okamura (KEK), Takeshi Shimazaki (AIST), Jun-ichi Shimoyama (Aoyama Gakuin Univ.), Suguru Takada (NIFS), Yutaka Yamada (Shibaura Institute of Technol), Tetsumi Yuri (NIMS)

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We construct a "needle-anvil" type point-contact spectrometer for spin polarization measurements, which is installed in a ⁴He-cryostat. Two types of piezo devices are used to control the contact size precisely between a sample ferromagnet and a superconductor. An attocube piezo-based positioner is mounted for coarse movement of the tip, while a stacked-type piezo device is used for fine control of the contact size. This enables to change the contact size between the tip and sample from sub micro-meters to atomic-size contacts continuously. By suppressing thermal flow into the sample space and mechanical vibration, we can keep the contact over hours, enabling the precision measurements. To examine the performance of the spectrometer, we study the spin polarization of polycrystalline SrRuO₃ with the point-contact Andreev reflection measurements. The polarization is estimated to be ∼0.59 at the clean limit of the interface, which is consistent with previous study.

Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

La (Fe, Si)₁₃ compounds have been widely studied for their excellent negative thermal expansion (NTE) properties. However, their poor mechanical properties limit their practical applications. In this work, LaFe_11.5Si_1.5/Cu material was fabricated. It was found that the NTE behavior occurs obviously at cryogenic temperatures and the ratio of ΔL/L can reach to 0.12%. Mechanical tests indicated that the absolute value of compressive strength at 77K and 300K is 365MPa and 222MPa, respectively. The elastic modulus at 77K and 300K is -109GPa and -87GPa, respectively. In addition, the average hardness is 337Hv performed in the Vickers hardness tester. Loose between the samples and clamps in the tensile test due to the contraction of clamp at low temperatures remains a big issue. In order to solve this problem, some LaFe_11.5Si_1.5/Cu NTE sheets are added between the clamp and the tested samples. Results showed that the samples with NTE materials sheets embedded is held tighter by the clamp. The maximum force of the tensile test is 9.77N and 5.48N, respectively, which illustrates that the adding of NTE material does make sense.

High field superconducting magnets made of Nb₃Al will be a suitable candidate for future fusion device which can provide magnetic field over 15T without critical current degradation caused by strain. The higher magnetic field and the larger current will produce a huge electromagnetic force. Therefore, it is necessary to develop high strength cryogenic structural materials and electrical insulation materials with excellent performance. On the other hand, superconducting magnets in fusion devices will experience significant nuclear radiation exposure during service. While typical structural materials like stainless steel and titanium have proven their ability to withstand these conditions, electrical insulation materials used in these coils have not fared as well. In fact, recent investigations have shown that electrical insulation breakdown is a limiting factor in the performance of high field magnets. The insulation materials used in the high field fusion magnets should be characterized by excellent mechanical properties, high radiation resistivity and good thermal conductivity. To meet these objectives, we designed various insulation materials based on epoxy resins and cyanate ester resins and investigated their processing characteristic and mechanical properties before and after irradiation at low temperature. In this paper, the recent progress of the radiation stable insulation composites for high field fusion magnet is presented. The materials have been irradiated by ⁶⁰Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min. The total doses of 1 MGy, 5 MGy and 10 MGy were selected to the test specimens.

Low-temperature abnormal thermal expansion (ATE) materials have been recently developed because of their significant applications for cryogenic engineering. However, the challenge still remains for the control of ATE effect at cryogenic temperature and adjustable ATE is of fundamental interest. In this paper, we report the isotropic ATE in La(Fe, Al)₁₃ compounds over a wide adjusting temperature range by partially substituting Fe by Mn. It is found that all samples crystallize in the cubic NaZn₁₃-type structure with the $Fm\bar{3}c$ space group. The introduction of nonmagnetic Mn atoms reduces the Fe-Fe exchange interaction, therefore, the itinerant electron system needs less energy to break the magnetic order in ferromagnetic (FM) state at low temperature. The negative thermal expansion (NTE) operation-temperature window moves towards lower temperatures accompanied with the decrease of Curie temperature (T_C) by increasing Mn elements. Moreover, the composite combining Mn 0 and Mn 57 broadens the zero thermal expansion (ZTE) behavior occurring in the whole tested temperature range. The present studies could be useful to control the thermal expansion, and indicate the potential applications of ATE materials in cryogenic engineering.

Ice has low environmental impact. Our research objectives are to study the availability of ice as a dielectric insulating material at cryogenic temperatures. We focus on ferroelectric ice (iceXI) at cryogenic temperatures. The properties of iceXI, including its formation, are not clear. We attempted to obtain the polarized ice that was similar to iceXI under the applied voltage and cooling to 77 K. The polarized ice have a wide range of engineering applications as electronic materials at cryogenic temperatures. This polarized ice is called ice electret. The structural difference between ice electret and normal ice is only the positions of protons. The effects of the proton arrangement on the breakdown voltage of ice electret were shown because electrical properties are influenced by the structure of ice. We observed an alternating current (ac) breakdown voltage of ice electret and normal ice at 77 K. The mean and minimum ac breakdown voltage values of ice electret were higher than those of normal ice. We considered that the electrically weak part of the normal ice was improved by applied a direct electric field.

In ITER, superconducting magnets should be used in such severe environment as high fluence of fast neutron, cryogenic temperature and large electromagnetic forces. Insulating material is one of the most sensitive component to radiation. So radiation resistance on mechanical properties at cryogenic temperature are required for insulating material. The purpose of this study is to evaluate irradiation effect of insulating material at cryogenic temperature by gamma-ray irradiation. Firstly, glass fiber reinforced plastic (GFRP) and hybrid composite were prepared. After irradiation at room temperature (RT) or liquid nitrogen temperature (LNT, 77 K), interlaminar shear strength (ILSS) and glass-transition temperature (Tg) measurement were conducted. It was shown that insulating materials irradiated at room temperature were much degraded than those at cryogenic temperature.

High purity erbium nitride (ErN) spheres with the size range of 150-180 µm and 180-212 µm were prepared by nitriding Er metal spheres with low oxygen content. The initial regenerator material of HoCu₂ on the cold end of the second regenerator column in 4K-GM cryocooler with nominal cooling power of 0.1 W at 4.2 K was replaced by ErN with different sizes. Higher cooling power was obtained when ErN of smaller size with lower oxygen content was used. We investigated the effect of partial replacement of HoCu₂ by ErN in the cold end side of second stage regenerator column on cooling power of 4K-GM cryocoolers. When ErN were substituted for 20 % of HoCu₂, the cooling power at 4.2 K reached 0.318 W. This value was 1.36 times as high as that of the cooling power of the GM cryocooler with commercially available regenerator arrangement. Therefore, use of ErN regenerator materials leads to the energy-saving and downsizing of 4K-GM cryocoolers.

We report on hydrogen (H) and deuterium (D) atoms absorption below T = 20 K in metallic palladium (Pd) via quantum tunnelling (QT). When a small bias voltage is applied between Pd nanocontacts that are immersed in liquid H₂ (D₂), the differential conductance spectra measured by point-contact spectroscopy change enormously. The results indicate H (D) absorption in Pd nanocontacts at the temperature where H (D) absorption due to thermal hopping process is not expected, and can be explained by QT. The QT occurs when the energy level of the potential well trapping the H (D) atom coincides with those not trapping the H (D) atom, and is assisted by phonons induced by ballistic electrons.

Magnetic materials play a significant role in improvement of regenerative cryocooler performance, because they have high volumetric specific heat at magnetic transition temperatures. Gadolinium oxysulfide (Gd₂O₂S, GOS) that has an antiferromagnetic transition at 5 K improved the cooling performance of cryocoolers when it was used in colder side of the second stage regenerator operating below 10 K. Small magnetic susceptibility and specific heat insensitive to magnetic field is important in order to reduce influence of magnetic field on the performance of cryocooler. We measured magnetization and specific heat of ceramic GOS in magnetic field up to 5 T. The magnetization of GOS represented typical temperature dependence for antiferromagnetic materials and no metamagnetic transition was observed. As for specific heat of GOS, peak temperature decreased from 5.5 to 5.0 K with increasing magnetic field from 0 to 5 T and the transitions remained sharp in magnetic fields. Thermal conductivity of GOS was observed to have very small magnetic field dependence.

Magnetic materials with large magnetocaloric effect are significantly important for magnetic refrigeration. La(Fe_0.88Si_0.12)₁₃ compounds are one of the promising magnetocaloric materials that have a first order magnetic phase transition. Transition temperature of hydrogenated La(Fe_0.88Si_0.12)₁₃ increased up to room temperature region while keeping metamagnetic transition properties. From view point of practical usage, bonded composite are very attractive and their properties are important. We made epoxy bonded La(Fe_0.88Si_0.12)₁₃ hydrides. Magnetocaloric effect was studied by measuring specific heat, magnetization, and temperature change in adiabatic demagnetization. The composite had about 20% smaller entropy change from the hydrogenated La(Fe_0.88Si_0.12)₁₃ powder in 2 T. Thermal conductivity of the composite was several times smaller than La(Fe,Si)₁₃. The small thermal conductivity was explained due to the small thermal conductivity of epoxy. Thermal conductivity was observed to be insensitive to magnetic field in 2 T. Thermal expansion and magnetostriction of the composite material were measured. The composite expanded about 0.25% when it entered into ferromagnetic phase. Magnetostriction of the composite in ferromagnetic phase was about 0.2% in 5 T and much larger than that in paramagnetic phase. The composite didn't break after about 100 times magnetic field changes in adiabatic demagnetization experiment even though it has magnetostriction.

Activated carbon have been used for a long time at low temperature for cryogenic applications. The knowledge of adsorption characteristics of activated carbon at cryogenic temperature is essential for some specific applications. However, such experimental data are very scare in the literature. In order to measure the adsorption characteristics of activated carbon under variable cryogenic temperatures, an adsorption measurement device was presented. The experiment system is based on the commercially available PCT-pro adsorption analyzer coupled to a two-stage Gifford McMahon refrigerator, which allows the sample to be cooled to 4.2K. Cryogenic environment can be maintained steadily without the cryogenic liquid through the cryocooler and temperature can be controlled precisely between 5K and 300K by the temperature controller. Adsorption measurements were performed in activated carbon for carbon dioxide and nitrogen and the adsorption isotherm were obtained.

An experiment regarding boiling of superfluid helium (He II) has been carried out under conditions of microgravity, in order to investigate the dynamics of the phase transition. A small cryostat equipped with visualization setup has been utilized for this purpose. Presence of two orthogonal optical axes allowed for registering of 3-dimensional images of a vapor bubble induced by a micro heater. Microgravity environment has been produced for about 4.7 s using the 122 m high drop tower facility at ZARM (Center of Applied Space Technology and Microgravity), University of Bremen, Germany. The experimental campaign consisting of 32 drops has been successfully conducted, while avoiding any damage to the equipment.

Impregnating resins as electrical insulation materials for use in ITER magnets and feeder system are required to be radiation stable, good mechanical performance and high voltage electrical breakdown strength. In present ITER project, the breakdown strength need over 30 kV/mm, for future DEMO reactor, it will be greater than this value. In order to develop good property insulation materials to satisfy the requirements of future fusion reactor, high voltage breakdown strength measurement system at low temperature is necessary. In this paper, we will introduce our work on the design of this system. This measuring system has two parts: one is an electrical supply system which provides the high voltage from a high voltage power between two electrodes; the other is a cooling system which consists of a G-M cryocooler, a superfluid chamber and a heat switch. The two stage G-M cryocooler pre-cool down the system to 4K, the superfluid helium pot is used for a container to depress the helium to superfluid helium which cool down the sample to 1.8K and a mechanical heat switch connect or disconnect the cryocooler and the pot. In order to provide the sufficient time for the test, the cooling system is designed to keep the sample at 1.8K for 300 seconds.

The JT-60SA project will use superconducting magnets to confine the plasma and achieve a plasma current with a typical flat top duration of 100 second in purely inductive mode. The helium refrigerator has an equivalent cooling power of 9 kW at 4.5 K providing 3.7 K, 4.5 K, 50 K and 80 K for the diverter cryopump, the superconducting magnets, the HTS current leads, and the thermal shields, respectively. This paper summarizes the JT-60SA helium refrigerator commissioning activities aiming at successful operation of heat load smoothing technology to manage the 12 kW heat pulses by 9 kW cooling power using a 7000 liter liquid helium.

A mechanical thermal switch is designed and fabricated to shorten the cool-down time of a conduction-cooled cryogenic system in which several copper heat loads are selected as experimental object. It is the first try of mechanical thermal switch for this application. Compared with the behavior of gas-gap thermal switch, the mechanical thermal switch is easy to manufacture, able to turn off at any temperature. The heat leak is little when it turns off. The drawback is that mechanical thermal switch need people to operate. The result shows that gas-gap thermal switch reduces the cooling time of our experimental system from 41.15 hours to 35.16 hours, while mechanical thermal switch reduces the time to 30.9 hours. In the situations for which frequent switches not needed, mechanical thermal switch is a competitive choice.

The design of twist pitch and direction of winding in multilayer HTS coaxial cable is important. For HTS AC transmitting cables, the main condition of twist pitch is the balance of inductances of each layer for providing the current balance between layers. In this work, the finite element method analysis for the coaxial cables with both same and opposite directions winding is used to calculate magnetic field distribution, and critical current of the cable is estimated. It was found that the critical current of the cable with same direction winding is about 10 percent higher than that in the case of the cable with the opposite direction winding.

Organic compounds are refined by separating their structural isomers, however each separation method has some problems. For example, distillation consumes large energy. In order to solve these problems, new separation method is needed. Considering organic compounds are diamagnetic, we focused on magneto-Archimedes method. With this method, particle mixture dispersed in a paramagnetic medium can be separated in a magnetic field due to the difference of the density and magnetic susceptibility of the particles. In this study, we succeeded in separating isomers of phthalic acid as an example of structural isomer using MnCl₂ solution as the paramagnetic medium. In order to use magneto-Archimedes method for separating materials for food or medicine, we proposed harmless medium using oxygen and fluorocarbon instead of MnCl₂ aqueous solution. As a result, the possibility of separating every structural isomer was shown.

Based on the concept of a novel approach to make a compact SMES unit composed of a stack of Si wafers using MEMS process proposed previously, a complete fabrication of a traversable 3 µam thick NbN film superconducting coil lined with Cu plated layer of 42m in length in a spiral three-storied trench engraved in and extended over a whole Si-wafer of 76.2 mm in diameter was attained for the first time. With decrease in temperature, the DC resistivity showed a metallic decrease indicating the current pass was in the Cu plated layer and then made a sudden fall to residual contact resistance indicating the shift of current pass from the Cu plated layer to the NbN film at the critical temperature T_c of 15.5K by superconducting transition. The temperature dependence of I-V curve showed the increase in the critical current with decrease in the temperature and the highest critical current measured was 220 mA at 4K which is five times as large as that obtained in the test fabrication as the experimental proof of concept presented in the previous report. This completion of a one wafer superconducting NbN coil is an indispensable step for the next proof of concept of fabrication of series-connected two wafer coils via superconductive joint which will read to series connected 600 wafer coils finally, and for replacement of NbN by high T_c superconductor such as YBa₂Cu₃O_7-x for operation under the cold energy of liquid hydrogen or liquid nitrogen.

One of the factors of deterioration in thermal power generation efficiency is adhesion of the scale to inner wall in feed-water system. Though thermal power plants have employed All Volatile Treatment (AVT) or Oxygen Treatment (OT) to prevent scale formation, these treatments cannot prevent it completely. In order to remove iron oxide scale, we proposed magnetic separation system using solenoidal superconducting magnet. Magnetic separation efficiency is influenced by component and morphology of scale which changes their property depending on the type of water treatment and temperature. In this study, we estimated component and morphology of iron oxide scale at each equipment in the feed-water system by analyzing simulated scale generated in the pressure vessel at 320 K to 550 K. Based on the results, we considered installation sites of the magnetic separation system.

High-temperature superconducting power cables (HTS cables) have been developed for more than 20 years. In addition of the cable developments, the test methods of the HTS cables have been discussed and proposed in many laboratories and companies. Recently the test methods of the HTS cables is required to standardize and to common in the world. CIGRE made the working group (B1-31) for the discussion of the test methods of the HTS cables as a power cable, and published the recommendation of the test method. Additionally, IEC TC20 submitted the New Work Item Proposal (NP) based on the recommendation of CIGRE this year, IEC TC20 and IEC TC90 started the standardization work on Testing of HTS AC cables. However, the individual test method that used to measure a performance of HTS cables hasn't been established as world's common methods. The AC loss is one of the most important properties to disseminate low loss and economical efficient HTS cables in the world. We regard to establish the method of the AC loss measurements in rational and in high accuracy. Japan is at a leading position in the AC loss study, because Japanese researchers have studied on the AC loss technically and scientifically, and also developed the effective technologies for the AC loss reduction. The JP domestic commission of TC90 made a working team to discussion the methods of the AC loss measurements for aiming an international standard finally. This paper reports about the AC loss measurement of two type of the HTS conductors, such as a HTS conductor without a HTS shield and a HTS conductor with a HTS shield. The AC loss measurement method is suggested by the electrical method..

A superconducting transport solenoid for Decay Muon Line (D-line) at J-PARC Muon Science Facility was newly designed and manufactured. It was designed to generate a magnetic field in relatively large region (warm bore diameter 0.2 m), while keeping the same outer dimensions, connection interfaces to the existing refrigerator and the power supply of the previous machine [1-3]. Major changes of both solenoids are the reduction of the central magnetic field, the equipment of a warm bore and the adoption of the high T_c current leads. After the installation to the beam line, the initial cooling test, the excitation test and the emergency shutdown test at the rated current were conducted by KEK in order to confirm cryogenic and magnetic performance. These tests were successfully performed with no damege and indicated the solenoid was precisely manufactured and fulfilled the requirements. The solenoid has been under operation since July, 2015. This report describes the design, the manufacturing process, the magnetic field measurement at room temperature and the results of performance tests conducted by KEK.

A novel limit design method for superconducting magnets is presented. It is particularly suitable for ion core magnets such as those used in accelerator magnets. In general, a stochastic optimization whose objective functions consist of values, e.g., the magnetic field, experience field of superconducting coils, current density, and multipole field integral, is often used. However, it is well known that the obtained solution strongly depends on the initial one. Furthermore, once the calculation model is fixed, the range of solutions is also fixed, i.e., there are times when it may be impossible to find the global optimum solution even with a lot of parameter sweeps. In this study, we draw the Pareto front curve to obtain the range and infer whether the solution is an optimum one. In addition, the Pareto front curve indicates the neighborhood solution that is substituted for the initial one. After this process a stochastic optimization is implemented with its initial design parameters. To confirm the validity, we designed a superconducting bending magnet, and it showed that this method works well.

A peculiar magnetic separation technique has been examined in order to remove the Cs-bearing Fe precipitates formed of the waste ash from the withdrawn incinerator furnaces in Fukushima. The separation system was constructed in combination with high temperature superconducting bulk magnets which generates the intensive magnetic field over 2 T, which was activated by the pulsed field magnetization process. The separation experiment has been operated with use of the newly-built alternating channel type magnetic separating device, which followed the high-gradient magnetic separation technique. The magnetic stainless steel filters installed in the water channels are magnetized by the applied magnetic fields, and are capable of attracting the precipitates bearing the Fe compound and thin Cs contamination. The experimental results clearly exhibited the positive feasibility of HTS bulk magnets.