National High Magnetic Field Laboratory Research Articles

Characterization of residual-resistance-ratio of Cu stabilizer in commercial REBCO tapes

Residual-resistance-ratio (RRR) of Cu stabilizer in REBCO coated conductor is an important design parameter for REBCO magnets. Cu stabilizer with high RRR is especially beneficial for quench protections of REBCO magnets. In this work, we study RRR of electroplated Cu stabilizer in commercial REBCO tapes. We present RRR of over 180 samples measured for the quality assurance programs of REBCO magnet projects at the National High Magnetic Field Laboratory, USA (NHMFL). To investigate the factors that influence RRR, several samples were analyzed extensively by using scanning electron microscopy, secondary ion mass spectroscopy, and inductively coupled plasma mass spectroscopy. We found that RRR is strongly correlated with the grain size of Cu, which suggests that resistivity at low temperatures is dominated by grain boundary resistivity. In addition, low RRR corresponds to high concentration of chlorine impurity. This is explained by that higher chlorine impurity hindered the grain growth in the self-annealing process at room temperature which resulted in smaller grain size and low RRR. Annealing at 300C significantly enlarged the grain size and enhanced RRR. Due to the concern of critical current degradation, however, annealing is not recommended as a practical method to improve RRR of Cu in REBCO tapes.

Training-free demonstration of a 5.4 T Nb3Sn Canted–Cosine–Theta accelerator dipole impregnated with paraffin wax

Lawrence Berkeley National Laboratory is pursuing stress-managed Nb3Sn Canted–Cosine–Theta (CCT) magnet technology for high field accelerator magnets. Although promising results have been reported, improvements in the training performance are desired. This work describes the fabrication and testing campaigns of two subscale Nb3Sn CCT magnets; a baseline impregnated with National High Magnetic Field Laboratory Mix-61 and a magnet impregnated with paraffin wax. The paraffin magnet reached the short sample limit of the conductor, to within the measurement uncertainty, with no training quenches inside the magnet. In contrast, the baseline magnet reached 80% of the short sample limit after approximately 20 quenches and exhibits some loss of memory after thermal cycles. Inter-layer flexible quench antennas combined with voltage tap data show that all quenches appear identical and originate from a region corresponding to the location of peak field in the cable. Although this success should be replicated at higher fields, these first test results demonstrate the potential for training free Nb3Sn accelerator magnets operating near the short-sample limit.

Preface

The 2023 Joint Cryogenic Engineering Conference (CEC) and International Cryogenic Materials Conference (ICMC) were held from July 9 through July 13 at the Hawaii Convention Center in Honolulu, Hawaii. As at past conferences, the international scope of these meetings was strongly maintained with 19 countries being represented by 555 attendees who gathered to enjoy the joint technical programs and industrial exhibits. In total, 213 papers were submitted for publication of which 207 are published in these conference proceedings.The program for the joint conferences included a total of 494 presentations organized into 110 sessions - plenary, oral and posters, as well as awards presentations. Five plenary talks gave interesting in-depth updates and overviews on exciting topics: Amanda Simpson (Airbus Americas) discussed the Airbus hydrogen aircraft development plans in “Airbus: A Discussion About the Use of Cryogenic Hydrogen for Aviation Propulsion”, An overview of the history and recent developments in high temperature superconductors was given by Paul C. W. Chu (University of Houston) in “From High-temperature Superconductivity to Room-temperature Superconductivity: From Ambient Pressure to Very High Pressure”, Suhas Bhandarkar (Lawrence Livermore National Laboratory) presented an overview of Lawrence Livermore National Lab’s net positive energy fusion demonstration and the detailed development and operations of the hydrogen fuel in “Overview of the Fabrication of Cryogenic Hydrogen Fuel Ice Layer for Nuclear Fusion Ignition Experiments”, an overview of the developments ongoing at Robinson Research Institute for the development of electric aircraft was given by Rodney Badcock (Robinson Research Institute) in “Electric Aircraft: Solving the Key Materials and Engineering Challenges to Manufacture a Complete Electrical Propulsion System”, and a discussion on the cryogenic requirements and needs for the development of quantum computers was given by Nicholas Masluk (IBM) in “Cryogenic Infrastructure for 400 Qubits and Beyond”. The attendees also convened for two special Joint CEC-ICMC sessions organized: i) Liquid Hydrogen for Large-Scale Vehicles and ii) Superconducting Quantum Systems. Special sessions, two of them with panel discussions, were included in the programming emphasizing high-quality invited talks on seven different topics: Electromechanical Behaviors of HTS Coated Conductors for Applications, Topological Materials for Electronics, High Strength Materials, High Field Superconducting Materials for Accelerator Magnets, Low Temperature Materials Database A - Superconductors, Low Temperature Materials Database B - Functional & Structural Materials, Cryogenic Clean Energy and Mobility, and Orbital Flight Demonstrations of Cryogenic Fluid Management. A large Transportation Symposium consisting of 5 sessions and 26 talks with topics ranging from government funding perspectives, power electronics, cables, motors, and generators to system level studies was also held at CEC/ICMC’23. Contributed papers covered a wide range of topics including many aspects and advances in cryogenics and superconductors, along with their applications.Both CEC and ICMC boards are encouraging student participation, education, and career growth. It was very exciting and rewarding to have 77 students register for the conference this year. And 36 of the students received sponsorship of the registration fees. The strong session attendance was exciting and very positive and made the conference a more rewarding experience for the presenters and attendees.The CEC/ICMC Cryo Industrial Expo displayed the products and services of 31 industrial exhibitors and provided a congenial venue for a reception and refreshments throughout the week as well as for the conference poster sessions.Conference Chairs for 2023 were Wesley Johnson from the NASA Glenn Research Center for CEC and Sonja Schlachter from the Karlsruhe Institute of Technology for ICMC. The CEC Program Chair was Jacob Leachman from the Washington State University with CEC Program Vice Chair, Ram Dhuley, from the Fermi National Accelerator Laboratory and the ICMC Program co-chairs were Klaus-Peter Weiss from the Karlsruhe Institute of Technology and Judy Wu from the University of Kansas. The Exhibit Chair was Austin Capers of Scientific Instruments, Inc. who also served as Publicity and Sponsorship Chair. Finally, the Awards Chairs were Peter Kittel, Consultant, for CEC and Eric Hellstrom from the National High Magnetic Field Laboratory at Florida State University for ICMC. Michael Sumption, ICMC Board President and Peter Bradley, CEC Board President greatly participated in the conference development as part of the leadership team.

Preface

The 2023 Joint Cryogenic Engineering Conference (CEC) and International Cryogenic Materials Conference (ICMC) were held from July 9 through July 13 at the Hawaii Convention Center in Honolulu, Hawaii. As at past conferences, the international scope of these meetings was strongly maintained with 19 countries being represented by 555 attendees who gathered to enjoy the joint technical programs and industrial exhibits. In total, 213 papers were submitted for publication of which 207 are published in these conference proceedings.The program for the joint conferences included a total of 494 presentations organized into 110 sessions - plenary, oral and posters, as well as awards presentations. Five plenary talks gave interesting in-depth updates and overviews on exciting topics: Amanda Simpson (Airbus Americas) discussed the Airbus hydrogen aircraft development plans in “Airbus: A Discussion About the Use of Cryogenic Hydrogen for Aviation Propulsion”, An overview of the history and recent developments in high temperature superconductors was given by Paul C. W. Chu (University of Houston) in “From High-temperature Superconductivity to Room-temperature Superconductivity: From Ambient Pressure to Very High Pressure”, Suhas Bhandarkar (Lawrence Livermore National Laboratory) presented an overview of Lawrence Livermore National Lab’s net positive energy fusion demonstration and the detailed development and operations of the hydrogen fuel in “Overview of the Fabrication of Cryogenic Hydrogen Fuel Ice Layer for Nuclear Fusion Ignition Experiments”, an overview of the developments ongoing at Robinson Research Institute for the development of electric aircraft was given by Rodney Badcock (Robinson Research Institute) in “Electric Aircraft: Solving the Key Materials and Engineering Challenges to Manufacture a Complete Electrical Propulsion System”, and a discussion on the cryogenic requirements and needs for the development of quantum computers was given by Nicholas Masluk (IBM) in “Cryogenic Infrastructure for 400 Qubits and Beyond”. The attendees also convened for two special Joint CEC-ICMC sessions organized: i) Liquid Hydrogen for Large-Scale Vehicles and ii) Superconducting Quantum Systems. Special sessions, two of them with panel discussions, were included in the programming emphasizing high-quality invited talks on seven different topics: Electromechanical Behaviors of HTS Coated Conductors for Applications, Topological Materials for Electronics, High Strength Materials, High Field Superconducting Materials for Accelerator Magnets, Low Temperature Materials Database A - Superconductors, Low Temperature Materials Database B - Functional & Structural Materials, Cryogenic Clean Energy and Mobility, and Orbital Flight Demonstrations of Cryogenic Fluid Management. A large Transportation Symposium consisting of 5 sessions and 26 talks with topics ranging from government funding perspectives, power electronics, cables, motors, and generators to system level studies was also held at CEC/ICMC’23. Contributed papers covered a wide range of topics including many aspects and advances in cryogenics and superconductors, along with their applications.Both CEC and ICMC boards are encouraging student participation, education, and career growth. It was very exciting and rewarding to have 77 students register for the conference this year. And 36 of the students received sponsorship of the registration fees. The strong session attendance was exciting and very positive and made the conference a more rewarding experience for the presenters and attendees.The CEC/ICMC Cryo Industrial Expo displayed the products and services of 31 industrial exhibitors and provided a congenial venue for a reception and refreshments throughout the week as well as for the conference poster sessions.Conference Chairs for 2023 were Wesley Johnson from the NASA Glenn Research Center for CEC and Sonja Schlachter from the Karlsruhe Institute of Technology for ICMC. The CEC Program Chair was Jacob Leachman from the Washington State University with CEC Program Vice Chair, Ram Dhuley, from the Fermi National Accelerator Laboratory and the ICMC Program co-chairs were Klaus-Peter Weiss from the Karlsruhe Institute of Technology and Judy Wu from the University of Kansas. The Exhibit Chair was Austin Capers of Scientific Instruments, Inc. who also served as Publicity and Sponsorship Chair. Finally, the Awards Chairs were Peter Kittel, Consultant, for CEC and Eric Hellstrom from the National High Magnetic Field Laboratory at Florida State University for ICMC. Michael Sumption, ICMC Board President and Peter Bradley, CEC Board President greatly participated in the conference development as part of the leadership team.

Carbon-13 chemical shift tensor measurements for nitrogen-dense compounds.

This paper reports the principal values of the 13 C chemical shift tensors for five nitrogen-dense compounds (i.e., cytosine, uracil, imidazole, guanidine hydrochloride, and aminoguanidine hydrochloride). Although these are all fundamentally important compounds, the majority do not have 13 C chemical shift tensors reported in the literature. The chemical shift tensors are obtained from 1 H→13 C cross-polarization magic-angle spinning (CP/MAS) experiments that were conducted at a high field of 18.8T to suppress the effects of 14 N-13 C residual dipolar coupling. Quantum chemical calculations using density functional theory are used to obtain the 13 C magnetic shielding tensors for these compounds. The best agreement with experiment arises from calculations using the hybrid functional PBE0 or the double-hybrid functional PBE0-DH, along with the triple-zeta basis sets TZ2P or pc-3, respectively, and intermolecular effects modeled using large clusters of molecules with electrostatic embedding through the COSMO approach. These measurements are part of an ongoing effort to expand the catalog of accurate 13 C chemical shift tensor measurements, with the aim of creating a database that may be useful for benchmarking the accuracy of quantum chemical calculations, developing nuclear magnetic resonance (NMR) crystallography protocols, or aiding in applications involving machine learning or data mining. This work was conducted at the National High Magnetic Field Laboratory as part of a 2-week school for introducing undergraduate students to practical laboratory experience that will prepare them for scientific careers or postgraduate studies.

40-meter-long REBCO tapes with critical current over 4,000 A/12 mm at 4.2 K and 13 T by advanced MOCVD

REBa2Cu3O7−δ (REBCO, RE = rare earth) tapes doped with 5% and 15% Zr have been scaled up to lengths more than 40 m in a pilot-scale advanced metal organic chemical vapor deposition (A-MOCVD) tool. The precursor compositions used for the long tapes were guided by a study of the influence of (Ba + dopant)/Cu content on the critical current density (Jc) of 5 and 15 mol.% Hf- and Zr-added tapes at 4.2 K and 13 T. The 40-m-long tapes exhibited a critical current (Ic) over 4,000 A/12 mm at 4.2 K and 13 T as well as over 1,400 A/12 mm at 20 K and 20 T. The critical current densities of a 40-m-long tape doped with 5% Zr at 4.2 K measured at the National High Magnetic Field Laboratory (NHMFL) were > 10 MAcm−2 and >5 MAcm−2 at 14 T and 30 T, respectively, which are over three times those of commercial REBCO tapes. The infield Jc of 5% Zr-added 40-m-long tapes was similar to those of previously-reported high-performance short samples made with 15% Zr or Hf. These results demonstrate the excellent potential of A-MOCVD for manufacturing high Ic REBCO tapes for use in ultrahigh-field magnet applications.

Stress Analysis of Terminals From the Distribution of Screening Currents for the 40 T All-Superconducting Magnet Project

Stresses created by screening currents in high field superconducting magnets constructed of rare-earth barium-copper-oxide (REBCO) tapes have been shown to be a major issue that has led to reduced performance of some REBCO coils. Some superconducting alloys suffer more than REBCO when it comes to the degradation due to stress. It is becoming more commonplace to include the effects of screening currents in the design of REBCO coils. A 2D T-A electromagnetics model coupled with a structural COMSOL finite element model have been implemented to analyze strain from screening currents in the design of the 40 T all-superconducting magnet and associated test coils at the National High Magnetic Field Laboratory. The T-A model considering transport current parallel to the plane was verified with the H-formulation. This model has been expanded to a 3-D structural model to investigate the strain in the REBCO terminals, which in-terface REBCO pancake-wound coils with the coil leads. The ef-fects of non-uniformly distributed magnetic field from the coil are considered and coupled with the screening current in the terminal. The stress and strain of multi-tape terminals caused by the screen-ing currents are investigated and discussed. The calculated axial strain is less than 0.3%, which is within the limit of the yield strain for REBCO coated conductors. The developed model can be used to simulation more complex geometry with different di-rections of transport current and background field.

Investigating Irradiated Superconducting Magnet Insulation Materials for Particle Accelerators and Other High-Dose Environments

Modern superconducting magnets, like the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole system destined for the Large Hadron Collider's (LHC) high luminosity upgrade, critically depend on insulating materials such as S-2 glass and epoxy resin systems. It is therefore crucial to thoroughly understand the behavior of these insulators under their cryogenic, high-radiation in-service conditions. In this study, the industry-standard CTD-101K epoxy resin system was examined against ‘mix-61’ developed by the National High Magnetic Field Laboratory (NHMFL) and the resin system developed for the ATLAS Experiment's End Cap Toroid (ECT) magnet. Physical analysis, mechanical testing, and microscopy revealed generally superior properties for CTD-101K, though pristine mix-61 and ECT exhibited greater strength and toughness at 77 Kelvin. Upon irradiation however, NHMFL mix-61 and ATLAS-ECT saw precipitous declines in performance with 101K showcasing unparalleled radiation resistance. At highest doses, all resins displayed an alarming decline in strength and toughness, with microstructural analysis highlighting radiation-induced bubble production and crack propagation as likely candidates for performance decline.

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as MnII (3d5) or GdIII (4f7), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive “Keck” magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet’s intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet’s temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10–4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two GdIII complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.

Cybersecurity in a Large-Scale Research Facility—One Institution’s Approach

A cybersecurity approach for a large-scale user facility is presented—utilizing the National High Magnetic Field Laboratory (NHMFL) at Florida State University (FSU) as an example. The NHMFL provides access to the highest magnetic fields for scientific research teams from a range of disciplines. The unique challenges of cybersecurity at a widely accessible user facility are showcased, and relevant cybersecurity frameworks for the complex needs of a user facility with industrial-style equipment and hazards are discussed, along with the approach for risk identification and management, which determine cybersecurity requirements and priorities. Essential differences between information technology and research technology are identified, along with unique requirements and constraints. The need to plan for the introduction of new technology and manage legacy technologies with long usage lifecycles is identified in the context of implementing cybersecurity controls rooted in pragmatic decisions to avoid hindering research activities while enabling secure practices, which includes FAIR (findable, accessible, interoperable, and reusable) and open data management principles. The NHMFL’s approach to FAIR data management is presented. Critical success factors include obtaining resources to implement and maintain necessary security protocols, interdisciplinary and diverse skill sets, phased implementation, and shared allocation of NHMFL and FSU responsibilities.

A homogenised anisotropic J-model for accelerating computations of screening current profile in large-scale HTS magnets

Owing to the induced excessive strain, plastic deformation, and distortion of the magnetic field in high-temperature superconducting (HTS) tapes, there is a rapidly growing research interest in the screening current profile in high-field superconducting magnets. The J-model was developed to calculate the current density distributions in HTS stacks and cables, which improves the calculation efficiency because no air domain is considered in the calculation regions. However, for a large-scale high-field magnet wound with hundreds and thousands of layers of HTS tapes, there is still a big challenge for J-model simulation involving prohibitive time consumption and memory requirements. This study proposes an improved J-model approach based on a homogenised anisotropic (HA) scheme for large-scale HTS magnet systems to decrease the number of elements and enhance calculation efficiency. The reliability of the improved HA J-model was verified by solving 2000-tape HTS stacks, and a significant improvement in computational performance was achieved. Furthermore, the HA J-model was applied to a large-scale scenario of a 32 T hybrid all-superconducting magnet at the National High Magnetic Field Laboratory to numerically capture the electromagnetic responses. The magnetic flux and current densities in the HTS insert coils were obtained completely, and the screen current induced field, which is the most concerning, showed a good agreement with the literature. Meanwhile, the time consumption by the HA J-model is approximately half that of the traditional J-model and even less than 1–2 orders of magnitude of the others, such as the traditional T-A model and H model, with acceptable accuracy. The improved HA J-model may provide an appropriate prior design with rapid and real-time calculations for large-scale magnet systems.

HTS Cable Conductor for Compact Fusion Tokamak Solenoids

Significant progress has been made recently in the US fusion community to develop a strategic plan to enable engineering design and construction of a fusion pilot plant (FPP). Princeton Plasma Physics Laboratory (PPPL) is working on developing high current density HTS conductors for next fusion experiments. Partnering with the US industry, we are evaluating feasibility and affordability of Conductor on Round Core (CORC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circledR$</tex-math></inline-formula> ) developed by Advanced Conductor Technologies (ACT) for the next compact fusion tokamak facility. High current density achieved by a CORC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circledR$</tex-math></inline-formula> cable based on a four-layer model coil recently tested at National High Magnetic Field Laboratory (NHMFL) motivated its consideration for low cost, reduced size fusion magnet application. This is of interest to PPPL because of its scalability to tokamak central solenoid (CS) coils in terms of required flux swings for plasma startup operations. Partnering with ACT, we designed and built a two-layer model coil solenoid directly wound with CORC to demonstrate its applicability for compact solenoids such as that used in the national spherical torus experiment (NSTX), NSTX-upgrade (NSTX-U) and the US sustained high-power density test facility (SHPD). The ∼160 mm diameter solenoid wound by a two-layer CORC is being tested in early 2022 under electromagnetic cyclic loading at NHMFL in a unique 160 mm bore, 14 T background field magnet facility.

Microstructure of Glidcop AL-60

Glidcop is an oxide-particle-dispersion strengthened copper composite that has a combination of high mechanical strength and high electrical conductivity. It has been used as a conductor for the 100 T ultrahigh field pulsed magnet by the National High Magnetic Field Laboratory, USA. In the quest for even higher field pulsed magnets, material development is crucial. Since the mechanical properties of a material are often determined by its microstructure, full characterization of the microstructure of Glidcop is necessary. In this work, we studied the microstructure of Glidcop AL-60 using both transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). We identified both α-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and cubic η-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles in AL-60 and investigated their size and density distribution. The η-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles with typical size of 5 to 30 nm are of triangular shape. They have well defined crystal orientation relationship with the Cu matrix. We observed dislocations pinned by the alumina nanoparticles in cold-drawn wires. We believed that dislocation bypassing alumina particles via Orowan looping was the main strengthening mechanism. We observed microcracks near large particles, demonstrating the detrimental effect of large particles in AL-60.

Energy Efficiency of Resistive High Field Magnets: Aspects of Magnet Technology, Power Supply Operation and Field Quality

The design and operation of resistive high field magnets require research and development in materials science, power supply engineering and instrumentation. Recently, their energy efficiency has become a very important concern. In our contribution we report on recent advances on an energy efficient use of the 24 MW resistive magnets at the French National High Magnetic Field Laboratory at Grenoble (LNCMI) that can reduce their energy consumption by up to 20%, for a given user experiment. This saving is possible due to a special architecture of the LNCMI high field magnets. Namely, the total magnetic field is provided by two independent concentric sub magnets exhibiting different field characteristics, i.e., absolute field values for a given current and spatial field distributions. As both sub-magnets can be powered in an independent way, their currents can be tuned to minimize the total electrical power for a target magnetic field requested by the user. This enables energy efficient operation. However, the consequences of strain enhancement on magnet safety and life time due to higher current densities in the inner sub magnet have to be considered. LNCMI magnet design, power supply and instrumentation teams have recently implemented this innovative operation mode in a collaborative project. We will present its technical realization including electrical power modelling, magnet load estimations as well as first benchmark experiments including NMR. Finally, we will discuss the perspectives of this operation mode for innovative user experiments.

Critical Current Measurement of REBCO Cables by Using a Superconducting Transformer

Development of REBCO cables that carry high electrical current in high magnetic field is crucial for future large-scale magnet applications. This experimental work presents the critical current measurements of two different REBCO cables by a test facility at the National High Magnetic Field Laboratory (NHMFL). The simple-stacked cable is made by the NHMFL by stacking 21 REBCO tapes without soldering. The Conductor on Round Core (CORC) cable provided by Advanced Conductor Technologies has 21 layers of REBCO tapes with 2 tapes/layer. The test facility consists of a 12 T split solenoid magnet with 15 cm bore providing transverse field to the samples, a superconducting transformer (SCT) as a current source providing up to 45 kA current. Special attention was paid to fabrication of solder joints between REBCO cables and the SCT output. The voltage-current traces were measured as a function of magnetic field at 4.2 K, from which the critical currents were determined. The details of this measurement are discussed.

Chronic Musculoskeletal Pain Moderates the Association between Sleep Quality and Dorsostriatal-Sensorimotor Resting State Functional Connectivity in Community-Dwelling Older Adults

Aging is associated with poor sleep quality, and greater chronic pain prevalence with age-related changes in brain function as potential underlying mechanisms. The following cross-sectional study aimed to determine whether self-reported chronic musculoskeletal pain in community-dwelling older adults moderates the association between sleep quality and resting state functional brain connectivity (rsFC). Community-dwelling older individuals (mean age=73.29 years) part of the NEPAL study who completed the Pittsburg Sleep Quality Index (PSQI) and an rsFC scan were included (n=48) in the present investigation. To that end, we tested the effect of chronic pain-by-PSQI interaction on rsFC among atlas-based brain regions-of-interest, controlling for age and sex. A significant network connecting the bilateral putamen and left caudate with bilateral precentral gyrus, postcentral gyrus and juxtapositional lobule cortex, survived global multiple comparisons (FDR; q<0.05) and threshold-free network-based-statistics. Greater PSQI scores were significantly associated with greater dorsostriatal-sensorimotor rsFC in the no-pain group, suggesting that a state of somatomotor hyperarousal may be associated with poorer sleep quality in this group. However, in the pain group greater PSQI scores were associated with less dorsostriatal-sensorimotor rsFC, possibly due to a shift of striatal functions toward regulation sensorimotor aspects of the pain experience, and/or aberrant cortico-striatal loops in the presence of chronic pain. This preliminary investigation advances knowledge about the neurobiology underlying the associations between chronic pain and sleep in community-dwelling older adults that may contribute to the development of effectitractve therapies to decrease disability in geriatric populations. This work was supported by the National Institutes of Aging (NIAK01AG048259, R01AG059809, R01AG067757, and T32AG049673). A portion of this work was performed in the McKnight Brain Institute at the National High Magnetic Field Laboratory's Advanced Magnetic Resonance Imaging and Spectroscopy (AMRIS) Facility, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and DMR-1157490, and the State of Florida and the University of Florida Claude D. Pepper Older Americans Independence Center.

Petroleomics at the National High Magnetic Field Laboratory: A Pictorial History

Petroleomics at the National High Magnetic Field Laboratory: A Pictorial History

Unknown Territory: K-12 STEM Summer Exploration through Zoom

In response to COVID-19, the National High Magnetic Field Laboratory (MagLab) had to cancel all in-person summer camps, that typically reach and expand the STEM identity of 150 middle school age youth (Roberts & Hughes, 2019). As we planned for informal STEM education programming during a pandemic, we decided to transition to a 10-week online Summer Exploration Series (SES) with the goal of increasing youth’s interest in STEM and knowledge of STEM careers relevant to materials science. The SES program engaged 184 youth of all ages in the interdisciplinary science and engineering research at the MagLab. Each week included live components (e.g., introduction to weekly concept and Ask Me Anything with a MagLab scientist/engineer) and asynchronous components (e.g., links to relevant content on the MagLab website and a video-recorded Career Interview). Participants could pick and choose which daily activities/weeks they wanted to participate in. All live components were recorded and available online along with the asynchronous materials. To keep an interactive hands-on aspect to the program, our MagLab educator engaged the youth in a weekly challenge that was introduced on Monday. Participating youth could submit evidence that they completed the challenge through written, photographic or video submissions. Between 13 to 20 youth submitted their challenge results each week. In terms of demographics, we were particularly proud of the reach of the SES program. The majority of the students were middle school age (65%) but we had a range of 1st graders (1) to 12th graders (1). In terms of race, 31.3% of our participants were members of underrepresented groups in STEM (American Indian, African American/Black, Hispanic/Latinx, and Native Hawaiian/Other Pacific Islander). A common goal for MagLab ISE programs is to have at least 50% of our participants come from Title I schools. Despite the transition to online programming, we were still able to reach 96 (55%) Title I students through our marketing. A quarter of our participants came from outside of our local Tallahassee area, which would not have been possible with an in-person program. We saw a decline in our gender representation with only 39% of the participants identifying as female. 100% of the participants rated the program as above average or outstanding, crediting the program with teaching them about new STEM careers/topics and increasing their interest in STEM. Our evaluation indicated that the weekly topics had similar engagement levels, with some offering more opportunities for students to learn something new about the topic (E.g, during the life science week only 70% of participants claimed to have learned something more about the topic compared to 100% during the Magnet focused weeks). The live sessions, particularly those that offered more opportunities for interaction, were rated higher than the asynchronous sessions, providing evidence to the benefits of live - even if online – sessions on increasing interest in STEM. Should we run the program again, we will work on our marketing to girls and broaden our national footprint. In the full article we will present a more detailed description of the program and evaluation results.

Calibration of a superconducting transformer by measuring critical current of a NbTi Rutherford cable

Large high field superconducting magnets often require high current superconducting cables. To develop these cables, a facility capable of providing a high magnetic field with large sampling area as well as electrical current of tens of kA is essential. A superconducting transformer (SCT) is an energy-efficient and low-cost way to provide large current to superconducting cables. Previously, we co-developed an SCT and successfully tested it to a maximum output current of 45 kA in zero magnetic field. In this work, this SCT is installed to the 12 T split solenoid magnet at the National High Magnetic Field Laboratory (NHMFL). We calibrated it by using this facility to measure the critical current of an NbTi Rutherford cable as a function of magnetic field up to 10 T, and compared the results with those available in the literature. In addition, a strand extracted from the NbTi cable was tested for critical current. The critical current of the extracted strand is scaled and compared with the critical current of the cable. The accuracy of the critical current measurement using this SCT is discussed in detail. This work concludes the commissioning of this SCT, which combined with the 12 T split magnet will provide a unique cable testing capability for future cable development for the NHMFL and its users.

Oxygen sensor errors in helium-air mixtures

Oxygen sensors play a vital role in ensuring the safety of employees and users at the National High Magnetic Field Laboratory. While most oxygen sensors have accurate and linear responses in nitrogen/argon environments, studies have highlighted a phenomenon in helium-air mixtures with certain types of oxygen sensors. A controlled experiment was performed to observe the behavior of two types of oxygen sensors: orifice and membrane. The orifice sensor showed a large deviation of up to 13% of measured reading above the actual oxygen content in the helium-air mixture test, while the membrane sensor remained accurate to within 3% of the actual value throughout its range.