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The 2019 Joint Cryogenic Engineering and International Cryogenic Materials Conferences were held from July 21 through July 25 at the Connecticut Convention Center in Hartford, Connecticut. As at past conferences, the international scope of these meetings was strongly maintained with 24 countries being represented by 613 attendees who gathered to enjoy the joint technical programs, industrial exhibits, and special events.

The program for the joint conferences included a total of 410 presentations in the plenary, oral, and poster sessions. Four plenary talks gave interesting in-depth overviews and discussions on the topics of the growing field of commercial application of hydrogen fuel-cells for specialized applications and large-scale semi-truck transportation, and recent 5x increase of liquid hydrogen production in the U.S.; Siemens' perspectives on evolving hybrid-electric propulsion technologies for large commercial aircraft; the world-leading research opportunities with rare isotopes in nuclear physics, nuclear chemistry, and the application of rare isotopes for society that the Facility for Rare Isotope Beams (FIRB) at Michigan State University will soon provide; and the impressive progress designing the nextgen SPARC fusion reactor 1^st-ever utilizing 2^nd-generation high-temperature-superconducting (HTS) wire. The attendees also convened for two Special Joint CEC-ICMC Symposia on i) Transportation, and ii) Quantum Computing, and seven Special-or-Focus Sessions were included in the programming emphasizing high-quality invited talks. Contributed papers covered a wide range of topics including many aspects in advances in cryogenics and superconductors, along with their applications. Both CEC and ICMC boards are encouraging student participation and career growth and provided registration support for 36 student applicants. In total, 207 papers were submitted for publication of which 190 are published in these conference proceedings.

Full Preface information is available in the pdf.

Detailed Awards information is available in the pdf.

The 2019 International Cryogenic Materials Conference Board of Directors list is available in the pdf.

The ICMC Technical Editor list is available in the pdf.

The CEC and ICMC Boards wish to thank our supporter and sponsors who have contributed to the 2019 CEC/ICMC Conference.

Full Acknowledgment information is available in the pdf.

SUPPORTER

• Fermilab

SPONSORS & ADVERTISERS

• Ability Engineering Technology, Inc.

• Aerospace Fabrication & Materials, LLC

• Beijing Sinoscience Fullcryo Technology Co., Ltd.

• Cryomech, Inc.

• Demaco Holland bv

• Fujikura Ltd.

• GE Global Research

• High Precision Devices

• Scientific Instruments, Inc.

Their contributions helped ensure the success of the 2019 Conference.

Producing the Open Access IOP Conference Series: Materials Science and Engineering (MSE) requires the dedicated effort of many individuals. The quality of the publication relies on the dedication of those who took time from their busy schedules to review and edit papers. The Boards wish to specifically acknowledge the efforts of Centennial Conferences for their editorial support, and the chief technical editors, John Weisend (CEC) and Balu Balachandran (ICMC). Their contributions to ensure a quality publication in a timely manner are greatly appreciated. The chief technical editors are indebted to the individual technical sub-editors for their time spent with reviewers and authors to get the final manuscripts ready for publication. John Weisend is also indebted to Gunilla Jacobsson for her assistance with the cumulative CEC subject index. The Boards also wish to thank all students and postdoctoral researchers from a number of universities for their service with the initial format checking of the papers submitted for peer review.

CEC/ICMC 2019 was managed by Paula Pair and Centennial Conferences. Recognizing this is a tremendous team effort, the Boards would especially acknowledge, in addition to Paula, all her staff – Annett Cady, Troy Christensen, Brion Jacobs, Andrew Kahl, Carrie Lian, Diane Mehling, Sydney Pair, and Letitia Xu – for the fantastic job they did wonderfully.

Last, but not least, the Conference would not have been possible without our exhibitors and their sustained commitment and support, and the effort and dedication of the attendees in preparing their presentations and papers, traveling to Hartford, Connecticut, and showing the professionalism and enthusiasm that makes the CEC/ICMC such a great Conference time after time.

List of Materials Index and Subject Index are available in the pdf.

The Author Index is available in the pdf.

All papers published in this volume of IOP Conference Series: Materials Science and Engineering 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.

Nitronic 40 forged shells are typically used for structural reinforcement in high field pulse magnet design and applications. To better understand the mechanical performance of this versatile high strength austenitic steel a series of mechanical tests were conducted. Tensile were performed at 295 K, 77 K and 4 K, and cryogenic fracture mechanics tests were performed at 77 K and 4 K. The effect of temperature on strength, ductility, toughness and fatigue crack growth rate are evaluated. Microstructure and composition effects are also presented and discussed.

Residual resistivity ratio (RRR) measurements and tensile tests were performed on samples taken from seven high purity large grain niobium ingots produced by CBMM. Test specimens were taken from the top, middle and bottom regions of each ingot. The RRR measurements were performed with a GM cryocooler system and more than 60% of the samples exceeded RRR values of 250. Room temperature tensile tests were performed on samples from the same regions. 17 samples were machined according to ASTM standard test methods for tension testing of metallic material. Tests were performed with an Instron tensile/compression testing machine, and various mechanical properties such as Young's modulus, 0.2% proof stress, ultimate tensile strength and strain at fracture were measured. For all the samples, the fracture strain exceeds 35% while the ultimate tensile stress is close to 100 MPa. Contents of impurity (N, O, C, H, Ta) of each region of the seven ingots were also measured. These data provide insights for a possible correlation among RRR values, mechanical properties and impurity contents of niobium ingots.

The resin used for bonding and insulating superconducting magnets can be a major factor in ensuring reliable and stable operation of the completed assembly. There are many resin systems and available to magnet designers and engineers. The selection of the correct material depends on the application technique selected, the processing requirements and the end properties required of the cured resin. Available techniques for magnet construction and bonding include vacuum impregnation (VPI), so called 'wet winding' and the use of pre-impregnated fabrics. The advantages and disadvantages of these techniques are considered and the processing requirements for each are discussed. Materials selection requires an understanding of the processing characteristics such as viscosity and 'useable lifetime' but these must be married with the properties required of the cured resin. A low viscosity and long useable life is a frequent requirement for VPI processing of large magnet systems and this may be difficult to match with high thermal shock resistance that may be required to minimize cracking possibilities in resin rich regions. Examples are presented of resin systems resistant to cracking and structural features that enhance this parameter. For many magnets that may operate in an ionising radiation environment, radiation stability is an important requirement. Radiation stable systems are described and structural features that promote such stability are considered, along with the difficulty of matching all competing requirements.

Epoxy (EP) resin based nano-composites are widely used in high voltage direct current (HVDC) high temperature superconducting (HTS) power cable. In this paper, the DC surface flashover characteristics of ZnO/EP composites were studied at both room temperature and 77 K. The samples were made by dispersing ZnO nano-particles into EP resin with various weight percentages of 0%, 1%, 3%, 6% and 10%, respectively. The experiments were carried out with a cryogenic system in which DC high voltages ranging from 0 kV to 100 kV were supplied. The results showed that the surface flashover voltages increased with the increase of ZnO content at both room temperature and 77 K, and the surface flashover voltages at 77 K were higher than that at room temperature for composites with the same ZnO content.

The Future Circular Collider (FCC) study includes the design of the detector magnets for the FCC-ee+ (electron-positron) collider, requiring a 2 T solenoid for particle spectrometry, and for the FCC-hh (proton-proton) collider, with a 4 T detector solenoid. For both solenoids and their cryostats, CERN is developing an innovative and challenging design in which the solenoids are positioned inside the calorimeters, directly surrounding the inner tracker. For this purpose, the cryostats must be optimized to have maximum radiation transparency. They are structured as a sandwich of thinnest possible metallic shells for achieving vacuum tightness, supported by layers of low density and highly radiation transparent insulation material, still providing sufficient mechanical resistance and low thermal conductivity. In this respect, thermal and mechanical analysis of innovative insulation materials are currently being carried out. The first material of interest, Cryogel® Z, is shaped as a flexible composite blanket, which combines silica aerogel with reinforcing fibers and a density of 160 kg/m³. It allows a 4 m bore, 6 m long FCC-ee+ detector solenoid cryostat with a total thickness of 250 mm. CERN has investigated the compression of Cryogel® Z under 1 bar equivalent mechanical load and its thermal conductivity between 10 K and room temperature, as well as the critical phenomena of thermal shrinkage and outgassing. We present the test results, as a first overview on the material.

A new experimental set up for measuring the breakdown strength of gas media in weakly non-uniform electric field at cryogenic temperatures and high pressures is described. Measure of breakdown strength of helium gas at 77 K and 293 K in a non-uniform electric field with a field efficiency factor 62.5% are presented. The results suggest that the breakdown strength in weakly non-uniform electric field relate to that of uniform electric field by the field efficiency factor, η. This relationship holds good for both 293 K and 77 K data. This observation expands our previously reported systematics of dielectric strength in uniform electric field to the weakly non-uniform electric field conditions, which is important for designing HTS power applications. The established relationship eliminates the need for costly experiments for measuring the dielectric strength at a specific operating temperature and pressure and in the required non-uniformity of the electric field.

The use and storage of cryogens such as liquefied nitrogen, helium, hydrogen among others requires reliable and efficient thermal insulation systems. Passive insulation from high performance materials that are well-known for their inherent low thermal conductivity would reduce the overall costs involved in design, manufacture and maintenance of such systems. One such class of materials are referred to as aerogels. These materials are known for their low density, high mesoporosity, high surface areas, low thermal conductivity and high acoustic impedance. Aerogels were invented by S.S. Kistler in 1931 and the most common type are those made of silica. However, the inherent fragility of silica aerogels makes them hard to mass produce, and therefore applications have been limited. A major breakthrough was introduced by our team almost 20 years ago with the invention of polymer crosslinked silica aerogels. Those materials shifted attention to all-polymer aerogels that have overcome all fragility issues associated with their inorganic counterparts. This study focuses on such polymeric aerogels that can be mass produced as large monoliths while maintaining the low thermal conductivity of traditional silica aerogels over a wide temperature range. Manufacturing flexibility of polymeric aerogels allows fabrication of blocks and sheets that can be applied in various configurations to insulate cryogenic and superconducting devices. The thermal conductivity with 80 K and room temperature boundary are reported as well as other properties (electrical), that need to be considered when designing devices for cryogenic applications.

The Macroflash is a flat plate boiloff calorimeter that provides effective thermal conductivity (k_e) data for a wide range of materials from thermal insulation to structural composites to ceramics. The apparatus and method provide a practical, standardized way to measure heat transmission through materials under steady-state conditions at below-ambient temperatures and under different compressive loads. Another unique feature of this device is that it can provide test data at both large and small temperature differences. Using liquid nitrogen as a method to directly measure the heat flow rate, the device is applicable to testing under an ambient pressure environment at a wide range of temperatures, from 77 K to 403 K. Test specimens may be isotropic or non-isotropic; homogeneous or non-homogeneous. The Macroflash is currently calibrated in the range from approximately 10 mW/m-K to 1,000 mW/m-K using well-characterized materials. Reference data for hundreds of test specimens including foams, powders, aerogels, plastics, composites, carbon composites, wood, glass, ceramic, metal, and multi-layered composites have been compiled from Macroflash testing. The Macroflash apparatus is described and its operation, instrumentation, and control system discussed. The calibration approach is detailed as well as analysis of key data sets of standard materials.

With the goal of enabling high-power-density cryogenic power converter technology and superconducting power applications for future aircraft and shipboard power systems, the dynamic and static performances of a press-pack IGBT module (T0160NB45A) at ambient and cryogenic conditions are reported. Compared to the wire-bond IGBT's, press-pack IGBT's are more suitable for cryogenic conditions as they do not have bonded connections and use fewer materials types, which reduces the risk of coefficient of thermal expansion (CTE) mismatch. The study has been conducted with a cryogenic testbed that provides a condensation-free condition during and after tests, which is essential for the preservation of the physical properties of IGBT's being tested. The dynamic performance characterization results show that the switching speeds of both turn-on and turn-off are improved with substantially reduced tail current and increased dv/dt at cryogenic conditions. Moreover, the static performance characterization results show a reduction in collector-emitter voltage drop, indicating higher conductivity of the IGBT at cryogenic conditions. Furthermore, the impact of clamping force and gate lead length on the press-pack IGBT's dynamic characteristics is reported. The findings of this study suggest that press-pack IGBT modules are suitable for cryogenic operation.

Capacitors and inductors that are suitable for cryogenic use are presented in this study. With the long-term goal of developing power electronic converters for cryogenic use, we studied various off-the-shelf metalized polypropylene film capacitors at cryogenic and ambient conditions. Capacitance and breakdown voltage of the film capacitors were the main parameters measured at room temperature and in liquid nitrogen. The results show that the material of dielectric film and the method of packaging play a role in the characteristics of breakdown voltage and capacitance in cryogenic conditions. In general, both capacitance and voltage rating of the capacitors were comparable if not better at cryogenic conditions. Moreover, with the long-term goal of developing inductors for cryogenic applications, we built and tested inductors with and without a magnetic core. The resistance, inductance, maximum current, and energy density were measured and compared. According to the results, the energy density of the cryogenic inductor without a magnetic core can be designed to be much higher than its room temperature counterpart mainly due to the superior cooling power of liquid nitrogen and the reduced resistivity of the windings at cryogenic temperatures.

Surface flashover voltage on solid insulators in gas cooled superconducting power devices is studied. The relationship between the surface flashover voltage and the dielectric strength of the gas media is established. Analysis of the data on surface flashover voltage measurements on cylindrical samples made of high-pressure fiberglass laminate (G10) in three different gas media with varying dielectric strength and pressure showed a positive correlation between the surface flashover voltage and the dielectric strength of the gas both at room temperature and 77 K. The positive relationship, however, is not linear. The results suggest that using gas media with higher dielectric strength, employing higher pressure, and lowering temperature in HTS power devices leads to higher surface flashover voltages and higher operating voltages because surface flashover is usually the limiting voltage in devices that use solid support structures and possess voltage gradients.

Superconductor digital integrated circuits (ICs) require rapid evaluation of multiple copies to obtain statistical operational data. These data are used for assessing model-to-hardware correlation and facilitate iterative IC design development. The Integrated Cryogenic Electronics Testbed (ICE-T) is a cryogen-free test platform, which can test multiple chips simultaneously with similar convenience to a liquid-helium immersion probe and with cooldown times of between 3.3 to 4.5 hours. We have developed a three-chip insert to increase the volume of chip testing and demonstrated simultaneous cooling of six chips with two such inserts. We report the test statistics collected from 27 chips across a single wafer. We have also used the ICE-T's convenient temperature control system to evaluate chips in the 3.5 - 6 K range. Such evaluation determines the robustness of circuit design and its tolerance to critical current fluctuations due to fabrication variation.

Superconducting magnets for fusion application will be irradiated by fast neutrons produced by fusion reaction, and it has been reported that the superconducting properties of the superconducting wires vary drastically by the irradiation. A bronze route Nb₃Sn wire and an internal tin process wire were irradiated in a fission reactor up to 1.7 × 10²³ n/m² (> 0.1 MeV neutron), and the change in the critical current was measured by 15.5 T superconducting magnet and a variable temperature insert. The 4.9 × 10²² n/m² irradiation for the bronze route wire increased the critical current by 1.75 times, but the 7.9 × 10²² n/m² irradiation showed 1.03 times increase for the bronze route wire and 0.72 times decrease for the internal tin process wire. The 1.7 x 10²³ n/m² irradiation for the internal tin process wire decreased the critical current severely and the critical magnetic field down to around 16 T. This was the first result that the high fluence neutron irradiation caused the degradation of both the critical current and the critical magnetic field in this type of a Nb₃Sn wire. Some irradiation defects will become the magnetic flux pining sites and strengthen the pining force. But the strong irradiation will damage the superconducting phase and degrade the properties.

Superconducting Nb₃Sn films can be synthesized by controlling the atomic concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films followed by high temperature annealing is considered as a method to fabricate Nb₃Sn films, where the Sn composition of the deposited films can be controlled by the thickness of alternating Nb and Sn layers. We report on the structural, morphological and superconducting properties of Nb₃Sn films fabricated by multilayer sequential sputtering of Nb and Sn films on sapphire substrates followed by annealing at 950 °C for 3 h. We have investigated the effect of Nb and Sn layer thickness and Nb:Sn ratio on the properties of the Nb₃Sn films. The crystal structure, surface morphology, surface topography, and film composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDS). The results showed Sn loss from the surface due to evaporation during annealing. Superconducting Nb₃Sn films of critical temperature up to 17.93 K were fabricated.

The measured critical current reduction in Nb₃Sn Rutherford cables under magnet-relevant transverse pressure levels is analyzed in terms of the strain state of the filaments inside their strands. Several straightforward mechanical 2D FE models of the cables' cross-section are used to translate the stress that is applied to the surface of the impregnated cables into a strain distribution on its strands. The resulting critical current reduction of the cable is then estimated from the average deviatoric strain in the strands' filamentary zone, using the well-established strain scaling relations obtained for isolated strands. This allows to identify the main factors that influence the pressure response of impregnated Nb₃Sn accelerator cables. The analysis is presented for state-of-the-art cable samples that were measured at the University of Twente and shows how especially stiff and incompressible resins reduces the deviatoric strain in the filamentary zone of the cable strands, but also how relatively small alignment errors can lead to stress concentrations that reduce the critical current density significantly.

Jelly-rolled Nb/Al composite monofilamentary wires having an outer diameter of 50 microns and more than 100 meters in length were successfully fabricated. Moreover, some of these thin wires were additional drawn to 30 microns in outer diameter in this study. We recognized again that jelly-rolled Nb/Al composite monofilamentary wires have excellent cold workability and drawability. The transmission electron microscopic observation revealed that the niobium and aluminum laminations retained a nano-scaled fiber composite structure in the longitudinal direction like the microarchitecture of Japanese bamboo, even in the very thin wire with an outer diameter of 30 μm. The thickness of the aluminum sheet is approximately 70 nm, which is almost comparable to the value calculated from the reduction ratio. The critical temperature of 16.2 K (on set) and 15.7 K (off set) were obtained after the diffusion reaction at 850°C for 10 h. The transport critical currents in liquid helium (4.2 K) under external magnetic fields of 1 T and 8 T are 7.2 A and 0.7 A, corresponding to non-Cu critical current densities of 15,000 and 1,500 A/mm², respectively. These values are greater than those of industrial Nb-Ti and MgB2 commercial multifilamentary wires.

We report on the extent of Ag protrusions into the TiO₂ insulation layer on 9 different Bi-2212 wires after overpressure heat treatment. These wires were made with different powders and had different diameters and geometries, including aspected and twisted wires. To replicate coil heat treatments, we also studied whether increased time spent in the melt state affects the protrusions. We found that Ag protrusions are not universal and increasing the time in the melt state does not affect the protrusions.

Research into in-situ MgB₂ strand has been focused on improvements in J_C through reduction of porosity. Both of cold-high-pressure-densification (CHPD) and advanced-internal-magnesium-infiltration (AIMI) techniques can effectively remove the voids in in-situ MgB₂ strands. This study shows the nature of the reduced porosity for in-situ MgB₂ strands lies on increases in transverse grain connectivity as well as longitudinal connectivity. The CHPD method bi-axially applying 1.0 GPa and 1.5 GPa yielded 4.2 K J_CM║^s of 9.6 × 10⁴ A/cm² and 8.5 × 10⁴ A/cm² at 5 T, respectively, with compared with 6.0 × 10⁴ A/cm² for typical powder-in-tube (PIT) in-situ strand. Moreover, AIMI-processed monofilamentary MgB₂ strand obtained even higher J_Cs and transverse grain connectivity than the CHPD strands.

MgB₂ superconducting wires and bulks with nano-La₂O₃ addition have been studied. A series of MgB₂ superconducting bulk samples with nano-La₂O₃ addition levels of 0, 5, 7, 18wt% were prepared. AC resistivity data showed slight increases of Bc₂ and unchanged B_irr for the bulk samples with doping levels lower than 7 wt% and decreased critical fields for the heavily doped (18 wt%) bulk. X-ray diffraction (XRD) showed the presence of LaB₆ in the nano-La₂O₃ doped MgB₂ bulk samples and decreased MgB₂ grain size in nano-La₂O₃ doped bulks. Monocore powder-in-tube (PIT) MgB₂ wires without and with 5 wt% nano-La₂O₃ addition (P-05) were prepared for transport property measurement. 2mol%C-doped Specialty Materials Inc. (SMI) boron powder was used for wire P-05 and previously prepared control wires (control wires were made without the addition of nano-La₂O₃ powder, W-00 and P2). Low field magnetic properties were obtained from magnetization loop (M–H), transport critical current density (Jc) was measured at 4.2 K for the nano-La₂O₃ doped PIT wire (P-05) and the control samples (P2 and W-00). The transport critical current density Jc (B) of P-05 at 4.2 K and 8 T (6.0 ×10⁴ A/cm²) was twice that of the control wire. The critical magnetic fields (Bc₂ and B_irr) of P-05 and the control sample P2 were compared. The critical fields of P-05 were slightly less than those of P2. Kramer-Dew-Hughes plots indicated a change from surface pinning to a mixture of volume pinning and surface pinning. It is shown that enhancement of P-05's transport properties is due to additional flux pinning by the fine-size rare-earth borides rather than enhanced Bc₂ or B_irr.

Analysis of XRD patterns by Rietveld refinement has been shown that the main phase of superconducting MgB₂-based bulk materials (with high level of superconducting characteristics) has AlB₂ type structure and near MgB_1.8-1.68O_0.2-0.32 stoichiometry. The materials demonstrated the critical current densities up to 0.9 – 0.4 MA/cm²j_c (at 0 - 1 T, 20 K); up to 15 T B_c2 (at 22.5 K) and B_irr (at 18 K). The ab-initio simulation confirmed (1) benefits in binding energy and enthalpy of formation if stoichiometry of the solid solution is near MgB_1.75O_0.25; (2) energetic advantage in case if impurity oxygen present only in each second boron plane of MgB₂ cell while the first boron plane of the same cell stays pristine and location of substituted oxygen atoms in the nearby positions. Besides, the results of ab-initio modeling allow explanation of the tendency towards segregation of O-impurity in MgB₂ structure during synthesis or sintering, and formation of Mg-B-O inclusions or nanolayers (with MgO type of structure) which effect pinning. Calculated transition temperatures, T_c, for MgB_1.75O_0.25 occurred to be 23.3 K, while for MgB₂ it was 21.13 K only. Experimental T_c of the bulk materials was 35.7-38.2 K.

The development of instruments capable of dynamically observing the microstructure at different temperatures is of great significance for the study of materials. The liquid nitrogen and a self-developed high-frequency pulse tube cryocooler were used as the cold source to develop the cryogenic system of scanning electron microscope (SEM) in this paper. The vibration and temperature control problems and solutions involved in using these two cold sources as SEM cryogenic systems were described and discussed in detail. It was found that it is necessary to fully achieve the heat balance at a certain temperature and adjust the image displacement to overcome the adverse effects caused by the thermal expansion and contraction of the low temperature components, and the cryocooler needs to use an intermittent operation mode to avoid distortion of the material microstructure image caused by vibrations of the cryocooler. Whether it is for liquid nitrogen or cryocooler, a thermal switch between the cold source and the thermal bridge is helpful for temperature control of the sample and reduced heat leakage of the system.

Unlike the more common local conductance spectroscopy, nonlocal conductance can differentiate between nontopological zero-energy modes localized around inhomogeneities, and true Majorana edge modes in the topological phase. In particular, negative nonlocal conductance is dominated by the crossed Andreev reflection. Fundamentally, the effect reflects the system's topology. In graphene, the Andreev reflection and the inter-band Klein tunneling couple electronlike and hole-like states through the action of either a superconducting pair potential or an electrostatic potential. We are here probing quantum phenomena in modified graphitic samples. Four-point contact transport measurements at cryogenic to room temperatures were conducted using a Quantum Design Physical Property Measurement System. The observed negative nonlocal differential conductance G_diff probes the Andreev reflection at the walls of the superconducting grains coupled by Josephson effect through the semiconducting matrix. In addition, G_diff shows the butterfly shape that is characteristic to resistive random-access memory devices. In a magnetic field, the Andreev reflection counters the effect of the otherwise lowered conduction. At low temperatures, the magnetoresistance shows irreversible yet strong giant oscillations that are known to be quantum in nature. In addition, we have found evidence for seemingly granular superconductivity. Thus, graphitic materials show potential for quantum electronics applications, including rectification and topological states.

Rare earth Barium Copper Oxide (REBCO) coated conductors are promising candidates for high field (>25 T) user magnets. However, as the demand for higher fields increase, so does the potential to overstrain the conductors being used. Coated conductor substrates, such as 310s stainless steel and the super-alloy Hastelloy C276, serve as the backbone for mechanical strength in these conductors. Both substrate alloys share similar properties when optimally processed into strips prior to manufacturing of the REBCO coated conductor. We find that with subsequent REBCO manufacturing processes the strength of the substrate changes, the magnitude of which depends on whether Hastelloy C276 or 310s stainless steel is used. In this study, we investigate the stress-strain variability found in coated conductors and how the manufacturing process affects the mechanical properties. The manufacturing step of concern is the short time that the substrate is exposed to high temperature (700 to 800 C) during the REBCO deposition process. To better relate manufacturing processes and mechanical properties, we subjected bare substrates to different heat treatments at 700, 750, and 800 C for 15 minutes each. With post heat-treatment room-temperature tensile tests, we found that the 310s stainless steel substrate was sensitive to the variations of time and temperature, exhibiting yield strength reductions of 20 to 50 % depending on the heat treatment. By contrast, Hastelloy C276 did not weaken and initially showed strengthening effects with exposure to the lower temperature heat treatments. Coated conductor manufactures may prefer 310s stainless steel as their substrate due to cost and availability, however, moving to Hastelloy C276 will offer better mechanical robustness and reproducibility of mechanical properties within their coated conductor.

Recently, we have found that BaHfO₃ (BHO)-doped EuBa₂Cu₃O_7-X (EuBCO) coated conductors by the combination of the IBAD and PLD methods show high critical current (I_c) even in an applied magnetic field. However, for the wide application of BaMO₃ (BMO, M: metal)-doped REBa₂Cu₃O_7-X (REBCO) coated conductors to industrial and commercial applications, much higher in-field performance is required. It is known that the critical temperature (T_c) of BMO-doped REBCO layers, especially by the PLD method, decreases with the increase in the amount of doped BMO apparently due to the strain of the REBCO induced by BMO doping. Therefore, it is difficult to improve the critical current density (J_c) in the applied magnetic field of BMO doped REBCO coated conductors only by increasing the quantity of BMO especially at high temperatures such as 77 K. To solve this problem, we tried to optimize the deposition conditions, especially the deposition temperature and O₂ annealing processes for heavily BHO doped-EuBCO layers fabricated by the PLD method. As a result, the combination of high temperature deposition and low temperature O₂ annealing was effective in obtaining high T_c and high in-field performance of heavily BMO-doped REBCO coated conductors. The T_c of 10 mol% BHO-doped EuBCO coated conductors was 93.9 K (setting a deposition temperature of 1150 ° C and O₂ annealing temperature of 280 ° C) which is nearly the same as that for non-doped EuBCO coated conductors. On the other hand, overdoping is preferred for high in-field J_c. Therefore, a high J_c under a magnetic field was obtained in the BMO-doped REBCO layer annealed at a low temperature. The J_c(min.) of 5 mol% BHO-doped EuBCo coated conductors was 0.62 MA/cm² at 77 K and 3 T (setting deposition temperature of 1150 ° C and O₂ annealing temperature of 250 ° C). Using these results, we confirm the successful fabrication of heavily BHO-doped EuBCO coated conductors showing high in-field performance by the PLD method.

The APC/YBCO interface has been reported to directly affect the pinning efficiency of 1D APCs at B//c-axis. This raises a question on how the APC/YBCO interface affects angular range of the pinning effectiveness for a given 1D APC. In this work, two types of 1D APCs of different APC/YBCO interfaces and hence pinning efficiencies were selected to understand the correlation of the pinning efficiency at B//c-axis and the angular range of the effectiveness. Specifically, BaZrO₃ (BZO) and BaHfO₃ (BHO) 1D APCs were selected for a comparative study in the APC/YBCO nanocomposite films. The BZO and BHO 1D APCs have comparable diameters in the range of 5-6 nm. In the doping range of 2-6 vol.%, both BZO and BHO form c-axis aligned 1D APCs in YBCO films. However, differences are present at their interfaces with YBCO. While the BZO/YBCO interface is semi-coherent, a coherent BHO/YBCO interface has been found to be critical to the higher pinning efficiency of the BHO 1D APCs. Therefore, they provide ideal systems for investigation of the angular range of pinning effectiveness by 1D APCs. By evaluating the nanocomposites' maximum pinning force density (F_{p, max}) and its location B_max, normalized to that of the reference YBCO film as functions of magnetic field (B) orientation at temperatures of 65–77 K, a quantitative correlation between the pinning efficiency of the BZO 1D-APCs and their effective angular range was obtained. Our results indicate that all 1D APCs can provide enhanced B_max over certain angular ranges away from the c-axis. However, 1D APCs with higher pinning efficiency, such as BHO 1D APCs can have enhanced F_{p, max} over the entire angular range of B-orientations at temperatures of 65-77 K with respect to that for the reference YBCO sample.

Different methods of flux pinning are being tested world-wide to enhance critical currents (I_cs) of high temperature superconductor YBa₂Cu₃O_7-x (YBCO) coated conductors exposed to high magnetic fields. Magnetic materials are interesting to consider as flux pinning additions because of their potential for very strong pinning strength. To our knowledge, there have been limited demonstrations of magnetic pinning additions to YBCO conductors. This paper describes the study of different M magnetic phase additions to YBCO including M = BaFe₁₂O₁₉, La_0.67Ca_0.33MnO₃, and other oxide phases. Nanosize additions were incorporated by depositing multilayer (M/YBCO)_N films to minimize degradation of T_c, and testing volume % additions of M phase from 0.5 % to 5%. Results indicate that T_c onsets are depressed with magnetic additions, however in some cases interestingly without degrading the transition width. With optimization of magnetic additions a 50% increase of critical current density has been obtained, for low magnetic fields of < 10,000 Oe at 65K to 77K. Microstructural and superconducting properties are summarized, including SEM analysis.

Superconducting magnets are one of the superior contenders in achieving the targets of electric aircraft industry successfully as they have very high power densities compared to other battery storage systems. Many aviation research agencies are looking at superconducting magnets as one of the alternate in replacing the conventional jet engines completely (electric aircrafts) or partially (hybrid aircrafts). National Aeronautics and Space Administration (NASA) and Air Force Research Laboratory (AFRL), USA has reported that high temperature superconducting magnets possesses higher specific energies (Wh/kg) and have infinite number of recharge cycles compared to other storage technologies employed for energy requirements. The other advantage of using such magnets is that there will be no hazardous disposals like batteries which lower the overall pollution. Superconducting magnets are DC operated systems however during charging or discharging transient behaviour of current results in the losses which would further ends up with heat generation. Heat generation during charging or discharging period would cause quenching of the superconductor due to sudden temperature rise.

In this work, electromagnetic analysis on superconducting magnet having capacity of 1 MJ has been performed where a 2D numerical model is developed using H-formulations in order to estimate the AC losses for a high temperature superconducting tape manufactured by SuperPower (SCS 12050) having 330 A critical current at 77 K. AC current having different load factors has been fed through the stacked tapes at 50 Hz, 60 Hz and 70 Hz frequency and AC losses have been evaluated. It has been found that at higher frequencies the AC losses are found to be larger than lower frequencies. Overcritical currents have been found in the current density distribution due to the application of E-J relationship for the homogeneous 2D numerical model.

There is worldwide interest in high-speed motors and generators with characteristics of compactness, light weight and high efficiency for aerospace applications. Several options are under consideration. However, machines employing high temperature superconductors (HTS) look promising for enabling machines with the desired characteristics. Machines employing excitation field windings on the rotor are constrained by the stress limit of rotor teeth and mechanisms for holding the winding at very high speed. Homopolar AC synchronous machines characteristically employ both the DC field excitation winding and AC armature windings in the stator. The rotor is merely a magnetic iron forging with salient pole lumps, which could be rotated at very high speeds up to the stress limit of the rotor materials. Rotational speeds of 50,000 RPM and higher are achievable. The high rotational speed enables more compact lightweight machines.

This paper describes a 2 MW 25,000 RPM concept designs for machines employing HTS field excitation windings. The AC armature winding is made of actively cooled copper Litz conductor. The field winding consists of a small turn-count HTS coil that could be ramped up or down with a contactless HTS dynamo. This eliminates current leads spanning room-temperature and cryogenic regions and are major source for thermal conduction into the cryogenic region and thereby increase thermal load to be removed with refrigerators. For early adaption of this technology for the aerospace applications, this 2 MW machine weighing 380 kg with an efficiency > 99% represents an attractive option.

Most superconducting synchronous machines employ HTS field excitation windings on the rotor operating at cryogenic temperature. These windings are usually cooled by coolant supplied from a stationary source to the rotor with rotary couplings. Closed loop gaseous helium couplings have been employed on mega-watt size machines operating at both low speed and high speed. However, these couplings were marred with leaking of cryogen out of the closed loop and needed periodic replenishment. This undesirable problem has been recognized long ago but no suitable solution has emerged in the open literature. Currently, the HTS machines are being considered for the aerospace applications, wherein leakage of cryogen from closed loop is highly undesirable. This paper presents a concept that prevents the cryogen leakage and/or its collections it for returning to the closed cooling loop. An option is also explored to include an HTS dynamo for providing the field excitation without current leads. This concept would need de-risking before using in the motors and generators for the aerospace applications. Possible cryogens for cooling include gaseous helium, Neon, H2 and N2.

Partial and fully superconducting (SC) machines promise high power density capabilities required for electric propulsion. These machines need to achieve high power densities while reducing electrical heat losses to minimize the required cryogenic power and subsequent additional weight. Hydrogen powered all-electric planes provide a design space where ac losses are manageable. However, the high electrical frequencies in high-speed fully superconducting machines pose a significant challenge to reducing armature ac losses. In high-speed applications, coupling loss in the SC armature coils dominates and becomes a barrier for practical application of these machines. In this paper a fully superconducting machine is proposed for a hydrogen powered regional all-electric plane. An air core design is considered utilizing low ac loss MgB₂ wires. The design is targeted to achieve 50 kW/kg specific power while requiring ac losses to be less than 3 kW. This study explores the possibility of replacing a passive iron shield with active shielding coils to contain the magnetic flux inside the machine while reducing weight and increasing power density. The study focuses on minimizing weight as well as ac losses in the armature coils. An optimization algorithm is used to determine the trade-offs between iron shield and active shield coil designs. Results show that optimal designs for electric propulsion eliminate the passive shield in favor of active shielding coils - increasing the power density of the machine while maintaining the outside flux density below standard safety limits.

Recent results are reported in the development of 2-layer cable-in-conduit (SuperCIC) that is designed for use in hybrid-coil magnets. SuperCIC preserves the full performance of the individual wires, and can be formed into flared-end windings for dipoles into layer-wound toroids and solenoids for hybrid windings for tokamaks. The structure of the SuperCIC windings is designed to accommodate winding and heat-treating sub-windings of Bi-2212, Nb3Sn, and NbTi separately and then assembling them and preloading in the magnet.

The HTS current leads for the ITER project will be the largest ever operated, with unprecedented currents, up to 68 kA and voltages, up to 14 kV. According to the ITER agreement they will be provided in-kind by China. After an extensive development program at the Hefei Institute of Plasma Physics (ASIPP), the ITER current leads were designed and qualified. The following discusses the main highlights of this development, with particular emphasis on the description of the design of the different types of ITER current leads and their final qualification in dedicated cold tests in nominal conditions.

In an attempt to eliminate solid insulation challenges in cryogenic superconducting power cables, a new design concept for liquid cryogen cooled superconducting power cable was investigated. The design is based on superconducting gas insulated line (S-GIL). The design used liquid cryogen as the sole insulation medium. The suitability of the design for medium voltage power cables is discussed and the benefits of eliminating a solid insulation were identified. Experiments on 1-m long model cables with insulator tubes as spacers showed that the design is suitable for cables at 50 kV or higher. The actual limits could not be identified because of the experimental limitations originated from limited standoff distances in the measurement setup used. On a fundamental level, the investigations presented in the study showed a direct correlation between the intrinsic dielectric strength of the cryogen used and the maximum tolerated voltage for a given diameter of the cable system. The results show the promise for liquid nitrogen (LN₂) and liquid hydrogen (LH₂) cooled cables for various medium voltage applications, including electric aviation and electric ships.