The IEEE Council on Superconductivity sponsors the Van Duzer Prize, awarded to the best contributed paper published in IEEE Transactions on Applied Superconductivity during each volume year. The award is restricted to regular submissions to the IEEE Transactions on Applied Superconductivity to encourage authors to prepare well written and comprehensive contributions which may have exceptional archival values and are likely to be cited frequently by other authors. Papers submitted for publication through scientific conference special issues are not eligible. The recipients are announced in the year following the volume year in which the paper appears. Historical Background: The award is named in honor of Professor Theodore Van Duzer, founding Editor-in-Chief of IEEE Transactions on Applied Superconductivity. Professor Van Duzer (M'60-SM'75-F'77-LF'93) received the Ph.D. degree from the University of California, Berkeley, in 1960. He has been on the faculty of the Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, since 1961. He is co-author of two textbooks, Principles of Superconductive Devices and Circuits, and Fields and Waves in Communication Electronics, and has published widely in the research literature on superconductor electronics. His current research interests focus on Josephson devices and multi-gigahertz digital superconductor circuits, including hybrids with cryogenic semiconductor components. Dr. Van Duzer is a Life Fellow of the IEEE and a member of the U.S. National Academy of Engineering. Prize: The Van Duzer Prize consists of a certificate and an honorarium of $1,000. For papers with multiple authors, the honorarium is divided equally among the authors. Funding: IEEE Council on Superconductivity Presentation: When possible, the recipients receive their certificate and honorarium at a scientific conference such as the Applied Superconductivity Conference or Magnet Technology Conference during an award ceremony sponsored by the Council on Superconductivity. Photos of the recipients will be featured in the Transactions issue containing the announcement. Basis for Judgement: Papers are scored on the following criteria: Expectation that the paper will be highly cited by future authors, Technical excellence of the work described, and Completeness of the paper as an archival record of a finished body of research. Eligibility: The award is restricted to regular submissions to the IEEE Transactions on Applied Superconductivity to encourage authors to prepare well written and comprehensive contributions which may have exceptional archival values and are likely to be cited frequently by other authors. Papers submitted for publication through scientific conference special issues are not eligible. Nomination Details: Candidates for the Prize are nominated by the Editors of the Transactions and judged by the Editor in Chief. Award Recipients 2017 Jay M. Gambetta, Conal E. Murray, Y.-K.-K. Fung, Douglas T. McClure, Oliver Dial, William Shanks, Jeffrey W. Sleight, Matthias Steffen 2017 Recipient of Van Duzer Prize Award For the paper Investigating Surface Loss Effects in Superconducting Transmon Qubits IEEE Transactions on Applied Superconductivity Vol. 27, No. 1, January 2017, Paper 1700205 View paper(s) CSC President Bruce Strauss presents 2017 Van Duzer Prize Award to Conal Murray (on behalf of all authors) also shown are Lance Cooley (VP Pubs) and Joseph Minervini (Tech/Svc Awards Chair) Paper(s) × Investigating Surface Loss Effects in Superconducting Transmon Qubits Superconducting qubits are sensitive to a variety of loss mechanisms including dielectric loss from interfaces. By changing the physical footprint of the qubit, it is possible to modulate sensitivity to surface loss. Here, we show a systematic study of planar superconducting transmons of differing physical footprints to optimize the qubit design for maximum coherence. We find that qubits with small footprints are limited by surface loss and that qubits with large footprints are limited by other loss mechanisms, which are currently not understood. IEEE Transactions on Applied Superconductivity ( Volume: 27 , Issue: 1 , Jan. 2017 ) https://ieeexplore.ieee.org/document/7745914 2017 Van Duzer Prize Paper.pdf 2016 Maxwell T. Dylla, Samuel E. Schultz, Matthew Jewell 2016 Recipient of Van Duzer Prize Award For the Paper Fracture Strength Distribution of Individual Nb3Sn Filaments IEEE Transactions on Applied Superconductivity Vol. 26, No. 8, December 2016, Paper 6001907 View paper(s) President Bruce Strauss congratulates 2016 Van Duzer Prize awardee Matt Jewell (on behalf of all authors) along with VP Pubs Lance Cooley and Tech/Svc Awards Chair Joseph Minervini Paper(s) × Fracture Strength Distribution of Individual Nb3Sn Filaments Brittle fracture of Nb3Sn filaments is one mechanism by which the current-carrying capacity of composite Nb3Sn wires is degraded. However, there are relatively little data in the literature on the intrinsic material fracture properties of Nb3Sn filaments, because the complex composite structure (matrix, secondary phases, and defects such as voids) acts as an integrated mechanical unit. In this study, we extracted individual Nb3Sn filaments from a fusion-style Nb3Sn composite wire and conducted tensile testing to determine the fracture strength distribution of the isolated filaments. The distribution is modeled using a Weibull function. The relative fracture propensity of fully reacted filaments versus those with unreacted Nb cores is compared. The presence of a Nb core reduces, on average, the fracture strength of a filament by 38% and the strain to failure by 29%. Understanding the fracture probability of Nb3Sn as a function of both stress and volume will allow strand and conductor modeling efforts to more accurately represent the relative contributions of fracture and other effects (such as plasticity) to irreversible current density degradation, and may assist wire manufacturers in assessing the mechanical impact of wire design changes. https://ieeexplore.ieee.org/document/7552540/ 2015 Samuel Benz, Anna E. Fox, Paul D. Dresselhaus, Alain Rüfenacht, Jason M. Underwood, Robert E. Schwall, Charles J. Burroughs, Jr., Steven B. Waltman, Logan A. Howe 2015 Recipient of Van Duzer Prize Award For the Paper One-Volt Josephson Arbitrary Waveform Synthesizer IEEE Transactions on Applied Superconductivity Volume: 25, Issue: 1, Feb. 2015, Paper 1300108 View paper(s) Paper(s) × One-Volt Josephson Arbitrary Waveform Synthesizer A quantum-accurate waveform with an rms output amplitude of 1 V has been synthesized for the first time. This fourfold increase in voltage over previous systems was achieved through developments and improvements in bias electronics, pulse-bias techniques, Josephson junction array circuit fabrication, and packaging. A recently described ac-coupled bipolar pulse-bias technique was used to bias a superconducting integrated circuit with 25 600 junctions, which are equally divided into four series-connected arrays, into the second quantum state. We describe these advancements and present the measured 1 V spectra for 2 Hz and 10 Hz sine waves that remained quantized over a 0.4 mA current range. We also demonstrate a 2 kHz sine wave produced with another bias technique that requires no compensation current and remains quantized at an rms voltage of 128 mV over a 1 mA current range. Increasing the clock frequency to 19 GHz also allowed us to achieve a maximum rms output voltage for a single array of 330 mV. IEEE Transactions on Applied Superconductivity ( Volume: 25 , Issue: 1 , Feb. 2015 ) https://ieeexplore.ieee.org/document/6901252 One-Volt Josephson Arbitrary Waveform Synthesizer.pdf 2014 Francesco Grilli, Enric Pardo, Antti Stenvall, Doan N. Nguyen, Weijia Yuan, Fedor Gömöry 2014 Recipient of Van Duzer Prize Award For the Paper Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents IEEE Transactions on Applied Superconductivity Volume: 24, Issue: 1, Feb. 2014, Paper 8200433 View paper(s) Paper(s) × Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms, and predicting the performance of high-temperature-superconductor (HTS) tapes, wires, and devices. This is particularly true for ac loss calculation since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, which are based on different techniques and implementations, has been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy-current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications. https://ieeexplore.ieee.org/document/6648727 Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents.pdf 2013 Sasha Ishmael, Frank Hunte, X. T. Liu, Haojun Luo, John F. Muth, Golsa Naderi, Justin Schwartz, Liyang Ye, Andrew T. Hunt, Natalia Mandzy, Marvis White 2013 Recipient of Van Duzer Prize Award For the Paper Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O 7−x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator IEEE Transactions on Applied Superconductivity Volume: 23, Issue: 5, Oct. 2013 View paper(s) Paper(s) × Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O 7−x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator The significant amount of energy stored in a large high-field superconducting magnet can be sufficient to destroy the coil in the event of an unprotected quench. For magnets based on high-temperature superconductors (HTSs), such as Bi2Sr2CaCu2Ox (Bi2212) and YBa2Cu3O7−x (YBCO), quench protection is particularly challenging due to slow normal zone propagation. A previous computational study showed that the quench behavior of HTS magnets is significantly improved if the turn-to-turn electrical insulation is thermally conducting, enhancing 3-D normal zone propagation. Here, a new doped-titania electrical insulation with high thermal conductivity is evaluated. The thermal conductivity of the insulation is measured at cryogenic temperatures, and its chemical compatibility with Bi2212 round wires is determined. Thin layers of the insulation are deposited onto the surface of Bi2212 and YBCO wires, which are then wound into small coils to study the quench behavior. Results show that the critical current and homogeneity of Bi2212 coils are improved relative to coils reacted with mullite insulation. Relative to similar coils with conventional insulation (mullite for Bi2212 and Kapton for YBCO), the turn-to-turn quench propagation is increased by a factor of 2.8 in Bi2212 coils at 4.2 K and self-field and by a factor of 2.5 in YBCO coils at 4.2 K and 5 T. These results indicate that doped-titania insulation may significantly improve Bi2212 and YBCO coils. Increased normal zone propagation velocity enhances quench detection and quench protection, and the thinness of the insulation relative to the most common alternatives increases the magnet winding pack current density and reduces the coil specific heat. https://ieeexplore.ieee.org/document/6574265 Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O7−x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator.pdf 2012 D. C. van der Laan , J. F. Douglas, L. F. Goodrich, R. Semerad, M. Bauer 2012 Recipient of Van Duzer Prize Award For the Paper Correlation Between In-Plane Grain Orientation and the Reversible Strain Effect on Flux Pinning in RE-Ba2Cu3O7−δ Coated Conductors IEEE Transactions on Applied Superconductivity Volume: 22, Issue: 1, Feb. 2012, Paper 8400707 View paper(s) Paper(s) × Correlation Between In-Plane Grain Orientation and the Reversible Strain Effect on Flux Pinning in RE-Ba2Cu3O7−δ Coated Conductors The uniaxial pressure dependence of the critical temperature causes a reversible effect of strain on the critical current density and the flux pinning strength in many high-temperature superconductors. Recent experiments on patterned coated conductor bridges have shown that the anisotropic nature of the pressure dependence of the critical temperature of rare earth (RE)-Ba2Cu3O7−δ (REBCO) has a major impact on the performance of coated conductors under strain. The strain effect on the critical current density is most prominent when the strain is along the [100] and [010] directions of the superconducting film, whereas it almost completely disappears when the strain is along [110]. In this paper, we investigate the correlation between the uniaxialpressure dependence of the critical temperature and the reversible strain effect on flux pinning in REBCO coated conductors. We show that axial strain has a large effect on the irreversibility field and the pinning force in coated conductors when the [100] and [010] directions of the superconducting film are aligned along the conductor axis. The magnitude of the strain effect in these conductors largely depends on the angle at which the magnetic field is applied. On the other hand, the critical temperature is not expected to change with the axial strain in coated conductors when the [110] direction is aligned along the conductor axis. Indeed, the irreversibility field and the magnetic field dependence of the pinning force of these conductors are almost independent of the axial strain for all angles at which the magnetic field is applied. The minor strain dependence of the critical current measured in these conductors could be caused by the average in-plane grain misalignment of between 6◦ and 8◦, which causes a slight variation in the strain alignment with the axes of the superconducting film. The results confirm that the reversible strain effect in REBCO coated conductors is largely determined by the uniaxial pressure dependence of the critical temperature. https://ieeexplore.ieee.org/document/6107562 Correlation Between In-Plane Grain Orientation and the Reversible Strain Effect on Flux Pinning in RE-Ba2Cu3O7−δ Coated Conductors.pdf Wan Kan Chan, Justin Schwartz 2012 Recipient of Van Duzer Prize Award For the Paper A Hierarchical Three-Dimensional Multiscale Electro–Magneto–Thermal Model of Quenching inREBa2Cu3O7−δCoated-Conductor-Based Coils IEEE Transactions on Applied Superconductivity Volume: 22, Issue: 5, Oct. 2012, Paper 4706010 View paper(s) Paper(s) × A Hierarchical Three-Dimensional Multiscale Electro–Magneto–Thermal Model of Quenching in REBa2Cu3O7−δ Coated-Conductor-Based Coils Quench detection and protection in REBa2Cu3O7−δ (REBCO) coated conductor (CC)-based superconducting magnets is difficult due to slow normal zone propagation velocity and the multilayer composite architecture of the conductor. To design effective quench detection and protection methods, it is essential to know the electrical, thermal, and structural behavior during the quench at multiple length scales ranging from the micrometer scale within the layers of the conductor to the macroscopic behavior of the coil. Here, a hierarchical multiscale approach is used to develop a modular 3-D electro–magneto–thermal coil quench model. The model uses an accurate experimentally validated micrometer-scale REBCO CC model as the basic building block. The CC model is embedded within a homogenized coil framework at one or more locations in the form of multilayer tape modules. This multiscale approach makes possible the studies of quench behavior at the micrometer scale within a tape at any location of interest within a coil without requiring a computationally extensive model of the entire coil. This approach also enables the building of more complicated models by hierarchically integrating smaller modular blocks with the same repeatable modeling techniques. Here, the development of the electro–magneto–thermal coil quench model is first presented, followed by its experimental validation. Simulation results and their implications for coil reliability and quench detection and protection are then discussed. https://ieeexplore.ieee.org/document/6290611 A Hierarchical Three-Dimensional Multiscale Electro–Magneto–Thermal Model of Quenching in REBa2Cu3O7−δ Coated-Conductor-Based Coils.pdf 2011 M. A. Tarasov, L. S. Kuzmin, S. Mahashabde, V. S. Edelman, P. de Bernardis 2011 Recipient of Van Duzer Prize Award For the Paper Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna IEEE Transactions on Applied Superconductivity Volume: 21 , Issue: 6 , Dec. 2011 View paper(s) Paper(s) × Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna Two series/parallel arrays of ten cold-electron bolometers with superconductor–insulator–normal tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. To increase the dynamic range of the receiver, all single bolometers in an array are connected in parallel for the microwave signal by capacitive coupling. To increase the output response, bolometers are connected in series for dc bias. With the measured voltage-to-temperature response of 8.8 µV/mK, absorber volume of 0.08 µm3, and output noise of about 10 nV/Hz1/2, we estimated the dark electrical noise equivalent power (NEP) as NEP = 6 ∗ 10−18 W/Hz1/2. The optical response down to NEP = 2 ∗ 10−17 W/Hz1/2 was measured using a hot/cold load as a radiation source and a sample temperature down to 100 mK. The fluctuation sensitivity to the radiation source temperature is 1.3 ∗ 10−4 K/Hz1/2. A dynamic range over 43 dB was measured using a backward-wave oscillator, a variable polarization grid attenuator, and cold filters/attenuators. https://ieeexplore.ieee.org/document/6062387 Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna.pdf 2010 Frank N. Werfel, Uta Floegel-Delor, Thomas Riedel, Rolf Rothfeld, Dieter Wippich, Bernd Goebel, Gerhard Reiner, Niels Wehlau 2010 Recipient of Van Duzer Prize Award For the Paper Towards High-Capacity HTS Flywheel Systems IEEE Transactions on Applied Superconductivity Volume: 20, Issue: 4, Aug. 2010 View paper(s) Paper(s) × Towards High-Capacity HTS Flywheel Systems Adelwitz Technologiezentrum (ATZ) and L-3 Communications Magnet Motor (L-3 MM) are currently mounting a compact-designed flywheel energy storage system (FESS) with total magnetic bearing support. Final assembly and test operation were performed during 2008–2009. After calculations and experiments, we decided to improve rotor stabilization by stiffer geometry. In addition, two dynamical emergency bearings contribute to robust and safe flywheel operation in critical revolutionper-minute situations. A planned energy capacity of 5 kWh is now obtained at about 8000 r/min, whereas an increased capacity of 10 kWh will be stored at a speed of 10 000 r/min. The total weight of the flywheel unit is about 1200 kg plus power electronics and cooling system. The heavier 600-kg rotor causes new design and construction work in mechanical elements, magnetic support bearings, cooling, and power electronics. Due to the here reported construction changes and increased rotor speed, scaling to even larger energy storage performance of 15–20 kWh seems achievable. ATZ and L-3 MM obtained a corresponding order to develop and deliver a 15-kWh/400-kW high-temperature-superconducting FESS for a Korean local grid UPS application. https://ieeexplore.ieee.org/document/5466196 Towards High-Capacity HTS Flywheel Systems.pdf 2009 Sergey Ryabchun, Cheuk-Yu Edward Tong, Raymond Blundell 2009 Recipient of Van Duzer Prize Award For the Paper Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation IEEE Transactions on Applied Superconductivity Volume: 19, Issue: 1, Feb. 2009 View paper(s) Paper(s) × Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation We present the results of a stabilization scheme for terahertz receivers based on NbN hot-electron bolometer (HEB) mixers that uses microwave radiation with a frequency much lower than the gap frequency of NbN to compensate for mixer current fluctuations. A feedback control loop, which actively controls the power level of the injected microwave radiation, has successfully been implemented to stabilize the operating point of the HEB mixer. This allows us to increase the receiver Allan time to 10 s and also improve the temperature resolution of the receiver by about 30% in the total power mode of operation. https://ieeexplore.ieee.org/document/4711088 Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation.pdf Pagination 1 2 › ›› » Last »
Investigating Surface Loss Effects in Superconducting Transmon Qubits Superconducting qubits are sensitive to a variety of loss mechanisms including dielectric loss from interfaces. By changing the physical footprint of the qubit, it is possible to modulate sensitivity to surface loss. Here, we show a systematic study of planar superconducting transmons of differing physical footprints to optimize the qubit design for maximum coherence. We find that qubits with small footprints are limited by surface loss and that qubits with large footprints are limited by other loss mechanisms, which are currently not understood. IEEE Transactions on Applied Superconductivity ( Volume: 27 , Issue: 1 , Jan. 2017 ) https://ieeexplore.ieee.org/document/7745914 2017 Van Duzer Prize Paper.pdf
Fracture Strength Distribution of Individual Nb3Sn Filaments Brittle fracture of Nb3Sn filaments is one mechanism by which the current-carrying capacity of composite Nb3Sn wires is degraded. However, there are relatively little data in the literature on the intrinsic material fracture properties of Nb3Sn filaments, because the complex composite structure (matrix, secondary phases, and defects such as voids) acts as an integrated mechanical unit. In this study, we extracted individual Nb3Sn filaments from a fusion-style Nb3Sn composite wire and conducted tensile testing to determine the fracture strength distribution of the isolated filaments. The distribution is modeled using a Weibull function. The relative fracture propensity of fully reacted filaments versus those with unreacted Nb cores is compared. The presence of a Nb core reduces, on average, the fracture strength of a filament by 38% and the strain to failure by 29%. Understanding the fracture probability of Nb3Sn as a function of both stress and volume will allow strand and conductor modeling efforts to more accurately represent the relative contributions of fracture and other effects (such as plasticity) to irreversible current density degradation, and may assist wire manufacturers in assessing the mechanical impact of wire design changes. https://ieeexplore.ieee.org/document/7552540/
One-Volt Josephson Arbitrary Waveform Synthesizer A quantum-accurate waveform with an rms output amplitude of 1 V has been synthesized for the first time. This fourfold increase in voltage over previous systems was achieved through developments and improvements in bias electronics, pulse-bias techniques, Josephson junction array circuit fabrication, and packaging. A recently described ac-coupled bipolar pulse-bias technique was used to bias a superconducting integrated circuit with 25 600 junctions, which are equally divided into four series-connected arrays, into the second quantum state. We describe these advancements and present the measured 1 V spectra for 2 Hz and 10 Hz sine waves that remained quantized over a 0.4 mA current range. We also demonstrate a 2 kHz sine wave produced with another bias technique that requires no compensation current and remains quantized at an rms voltage of 128 mV over a 1 mA current range. Increasing the clock frequency to 19 GHz also allowed us to achieve a maximum rms output voltage for a single array of 330 mV. IEEE Transactions on Applied Superconductivity ( Volume: 25 , Issue: 1 , Feb. 2015 ) https://ieeexplore.ieee.org/document/6901252 One-Volt Josephson Arbitrary Waveform Synthesizer.pdf
Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms, and predicting the performance of high-temperature-superconductor (HTS) tapes, wires, and devices. This is particularly true for ac loss calculation since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, which are based on different techniques and implementations, has been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy-current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications. https://ieeexplore.ieee.org/document/6648727 Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents.pdf
Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O 7−x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator The significant amount of energy stored in a large high-field superconducting magnet can be sufficient to destroy the coil in the event of an unprotected quench. For magnets based on high-temperature superconductors (HTSs), such as Bi2Sr2CaCu2Ox (Bi2212) and YBa2Cu3O7−x (YBCO), quench protection is particularly challenging due to slow normal zone propagation. A previous computational study showed that the quench behavior of HTS magnets is significantly improved if the turn-to-turn electrical insulation is thermally conducting, enhancing 3-D normal zone propagation. Here, a new doped-titania electrical insulation with high thermal conductivity is evaluated. The thermal conductivity of the insulation is measured at cryogenic temperatures, and its chemical compatibility with Bi2212 round wires is determined. Thin layers of the insulation are deposited onto the surface of Bi2212 and YBCO wires, which are then wound into small coils to study the quench behavior. Results show that the critical current and homogeneity of Bi2212 coils are improved relative to coils reacted with mullite insulation. Relative to similar coils with conventional insulation (mullite for Bi2212 and Kapton for YBCO), the turn-to-turn quench propagation is increased by a factor of 2.8 in Bi2212 coils at 4.2 K and self-field and by a factor of 2.5 in YBCO coils at 4.2 K and 5 T. These results indicate that doped-titania insulation may significantly improve Bi2212 and YBCO coils. Increased normal zone propagation velocity enhances quench detection and quench protection, and the thinness of the insulation relative to the most common alternatives increases the magnet winding pack current density and reduces the coil specific heat. https://ieeexplore.ieee.org/document/6574265 Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O7−x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator.pdf
Correlation Between In-Plane Grain Orientation and the Reversible Strain Effect on Flux Pinning in RE-Ba2Cu3O7−δ Coated Conductors The uniaxial pressure dependence of the critical temperature causes a reversible effect of strain on the critical current density and the flux pinning strength in many high-temperature superconductors. Recent experiments on patterned coated conductor bridges have shown that the anisotropic nature of the pressure dependence of the critical temperature of rare earth (RE)-Ba2Cu3O7−δ (REBCO) has a major impact on the performance of coated conductors under strain. The strain effect on the critical current density is most prominent when the strain is along the [100] and [010] directions of the superconducting film, whereas it almost completely disappears when the strain is along [110]. In this paper, we investigate the correlation between the uniaxialpressure dependence of the critical temperature and the reversible strain effect on flux pinning in REBCO coated conductors. We show that axial strain has a large effect on the irreversibility field and the pinning force in coated conductors when the [100] and [010] directions of the superconducting film are aligned along the conductor axis. The magnitude of the strain effect in these conductors largely depends on the angle at which the magnetic field is applied. On the other hand, the critical temperature is not expected to change with the axial strain in coated conductors when the [110] direction is aligned along the conductor axis. Indeed, the irreversibility field and the magnetic field dependence of the pinning force of these conductors are almost independent of the axial strain for all angles at which the magnetic field is applied. The minor strain dependence of the critical current measured in these conductors could be caused by the average in-plane grain misalignment of between 6◦ and 8◦, which causes a slight variation in the strain alignment with the axes of the superconducting film. The results confirm that the reversible strain effect in REBCO coated conductors is largely determined by the uniaxial pressure dependence of the critical temperature. https://ieeexplore.ieee.org/document/6107562 Correlation Between In-Plane Grain Orientation and the Reversible Strain Effect on Flux Pinning in RE-Ba2Cu3O7−δ Coated Conductors.pdf
A Hierarchical Three-Dimensional Multiscale Electro–Magneto–Thermal Model of Quenching in REBa2Cu3O7−δ Coated-Conductor-Based Coils Quench detection and protection in REBa2Cu3O7−δ (REBCO) coated conductor (CC)-based superconducting magnets is difficult due to slow normal zone propagation velocity and the multilayer composite architecture of the conductor. To design effective quench detection and protection methods, it is essential to know the electrical, thermal, and structural behavior during the quench at multiple length scales ranging from the micrometer scale within the layers of the conductor to the macroscopic behavior of the coil. Here, a hierarchical multiscale approach is used to develop a modular 3-D electro–magneto–thermal coil quench model. The model uses an accurate experimentally validated micrometer-scale REBCO CC model as the basic building block. The CC model is embedded within a homogenized coil framework at one or more locations in the form of multilayer tape modules. This multiscale approach makes possible the studies of quench behavior at the micrometer scale within a tape at any location of interest within a coil without requiring a computationally extensive model of the entire coil. This approach also enables the building of more complicated models by hierarchically integrating smaller modular blocks with the same repeatable modeling techniques. Here, the development of the electro–magneto–thermal coil quench model is first presented, followed by its experimental validation. Simulation results and their implications for coil reliability and quench detection and protection are then discussed. https://ieeexplore.ieee.org/document/6290611 A Hierarchical Three-Dimensional Multiscale Electro–Magneto–Thermal Model of Quenching in REBa2Cu3O7−δ Coated-Conductor-Based Coils.pdf
Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna Two series/parallel arrays of ten cold-electron bolometers with superconductor–insulator–normal tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. To increase the dynamic range of the receiver, all single bolometers in an array are connected in parallel for the microwave signal by capacitive coupling. To increase the output response, bolometers are connected in series for dc bias. With the measured voltage-to-temperature response of 8.8 µV/mK, absorber volume of 0.08 µm3, and output noise of about 10 nV/Hz1/2, we estimated the dark electrical noise equivalent power (NEP) as NEP = 6 ∗ 10−18 W/Hz1/2. The optical response down to NEP = 2 ∗ 10−17 W/Hz1/2 was measured using a hot/cold load as a radiation source and a sample temperature down to 100 mK. The fluctuation sensitivity to the radiation source temperature is 1.3 ∗ 10−4 K/Hz1/2. A dynamic range over 43 dB was measured using a backward-wave oscillator, a variable polarization grid attenuator, and cold filters/attenuators. https://ieeexplore.ieee.org/document/6062387 Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna.pdf
Towards High-Capacity HTS Flywheel Systems Adelwitz Technologiezentrum (ATZ) and L-3 Communications Magnet Motor (L-3 MM) are currently mounting a compact-designed flywheel energy storage system (FESS) with total magnetic bearing support. Final assembly and test operation were performed during 2008–2009. After calculations and experiments, we decided to improve rotor stabilization by stiffer geometry. In addition, two dynamical emergency bearings contribute to robust and safe flywheel operation in critical revolutionper-minute situations. A planned energy capacity of 5 kWh is now obtained at about 8000 r/min, whereas an increased capacity of 10 kWh will be stored at a speed of 10 000 r/min. The total weight of the flywheel unit is about 1200 kg plus power electronics and cooling system. The heavier 600-kg rotor causes new design and construction work in mechanical elements, magnetic support bearings, cooling, and power electronics. Due to the here reported construction changes and increased rotor speed, scaling to even larger energy storage performance of 15–20 kWh seems achievable. ATZ and L-3 MM obtained a corresponding order to develop and deliver a 15-kWh/400-kW high-temperature-superconducting FESS for a Korean local grid UPS application. https://ieeexplore.ieee.org/document/5466196 Towards High-Capacity HTS Flywheel Systems.pdf
Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation We present the results of a stabilization scheme for terahertz receivers based on NbN hot-electron bolometer (HEB) mixers that uses microwave radiation with a frequency much lower than the gap frequency of NbN to compensate for mixer current fluctuations. A feedback control loop, which actively controls the power level of the injected microwave radiation, has successfully been implemented to stabilize the operating point of the HEB mixer. This allows us to increase the receiver Allan time to 10 s and also improve the temperature resolution of the receiver by about 30% in the total power mode of operation. https://ieeexplore.ieee.org/document/4711088 Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation.pdf