@article{ma_geng_chan_schwartz_coombs_2020, title={A temperature-dependent multilayer model for direct current carrying HTS coated-conductors under perpendicular AC magnetic fields}, volume={33}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/ab6fe9}, abstractNote={Abstract}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ma, Jun and Geng, Jianzhao and Chan, Wan Kan and Schwartz, Justin and Coombs, Tim}, year={2020}, month={Apr} }
 @article{gao_chan_wang_zhou_schwartz_2020, title={Stress, strain and electromechanical analyses of (RE)Ba2Cu3Ox conductors using three-dimensional/two-dimensional mixed-dimensional modeling: fabrication, cooling and tensile behavior}, volume={33}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/ab7778}, abstractNote={High temperature superconducting (HTS) conductors, represented by Rare Earth-Barium-Copper-Oxide (REBCO) conductors, are promising for high energy and high field superconducting applications. In practical applications, however, the HTS conductors experience different stresses and strains, including residual stresses due to thermal mismatch and tensile stresses due to Lorentz forces, resulting in some circumstances to a reduction in the load-carrying capacity as well as the risk of degradation in conductor critical current. In this study a mixed-dimensional high-aspect-ratio laminated composite finite element model for REBCO conductor is developed for stress and strain analyses in the processes of fabricating and cooling, as well as tensile testing. The model includes all the major constituent layers of a typical REBCO conductor and is experimentally validated. First, the thermal residual stresses and strains accumulated during the fabrication and cooling processes are analyzed by a multi-step modeling method that emulates the manufacturing process. Then, with the residual stresses and strains as initial stresses and strains, the mechanical behavior under a tensile load is studied. Lastly, a phenomenological critical current-strain model based on the Ekin power-law formula and the Weibull distribution function is combined with the mixed-dimensional conductor model to predict the strain dependence behavior of critical current in the reversible and irreversible degradation strain ranges. Simulation results show that the multi-step modeling is an effective method for stress and strain analyses of REBCO conductors during the fabrication and cooling processes and under and tensile loads. Compressive thermal residual stress generated on the REBCO layer during fabrication and cooling strongly affects the subsequent mechanical and current-carrying properties. Stress–strain curves generated by tensile loads are analyzed and experimentally validated at both the conductor and constituent-layer levels. Simulation results for the strain dependence of critical current are in good agreement with experiment data in both the reversible and irreversible degradation stages.}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Gao, Peifeng and Chan, Wan-Kan and Wang, Xingzhe and Zhou, Youhe and Schwartz, Justin}, year={2020}, month={Apr} }
 @article{zhou_chan_schwartz_2019, title={Modeling of Quench Behavior of YBa2Cu3O7-delta Pancake Magnets and Distributed-Temperature-Sensing-Based Quench Detection for Operating Temperature 30-77 K}, volume={29}, ISSN={["1558-2515"]}, DOI={10.1109/TASC.2018.2874423}, abstractNote={A two-dimensional/three-dimensional (2-D/3-D) mixed electrothermal model is proposed for the simulation of quench behavior of high-temperature superconducting (HTS) pancake magnets, where a 2-D electrothermal model is proposed to simulate the YBa<sub>2</sub>Cu<sub>3</sub>O<inline-formula><tex-math notation="LaTeX">$_{7\text{-}\delta}$ </tex-math></inline-formula> (YBCO) subcoil and is coupled with the remaining parts of the YBCO magnet, which are treated as 3-D homogeneous coils. For operating temperature from 30 to 77 K, the quench behavior of four YBCO pancake coils (two Kapton-insulated coils and two TiO<sub>2</sub>-insulated coils) are simulated. Thermal equilibrium states are found for both Kapton- and TiO<sub>2</sub>-insulated coils. The thermal conductivity of insulating materials (Kapton, TiO<sub>2</sub>) significantly affects the equilibrium temperature profiles (ETPs) and the minimum quench energy (MQE), especially for relatively high operating temperature (e.g., 65–77 K). The distributed-temperature-sensing-based (DTS-based) quench detection criterion can be established on ETPs. The effect of the thickness of insulating materials on ETPs and MQEs is relatively weak, especially under relatively low operating temperature. The key parameters of ETP-based quench detection criterion, such as the reference temperature, the peak temperature, and the minimum normal zone size, are obtained for the operating temperature from 30 to 77 K.}, number={1}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Zhou, Jun and Chan, Wan Kan and Schwartz, Justin}, year={2019}, month={Jan} }
 @article{gao_chan_wang_schwartz_2018, title={Mixed-dimensional modeling of delamination in rare earth-barium-copperoxide coated conductors composed of laminated high-aspect-ratio thin films}, volume={31}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/aac55c}, abstractNote={Rare earth-barium-copper-oxide (REBCO) coated conductors are promising conductors for high energy, high field and high temperature superconducting applications. In the case of epoxy-impregnated REBCO superconducting coils, however, excessive transverse stresses generated from winding, cooling, and Lorentz forces on the REBCO conductors can cause delamination, resulting in reduction in the load-carrying capacity as well as significant degradation in the coil’s critical current. In this study, the stresses and strains, and delamination in a REBCO conductor are analyzed via a mixed-dimensional finite element method (FEM) based on the cohesive zone model (CZM). The mixed-dimensional method models any number of laminated high-aspect-ratio thin layers in a composite as stacked two-dimensional (2D) surfaces, thus, resolving the thickness-dependent meshing and computational problems in modeling such composites with full three-dimensional (3D) FEM approaches. In the studied coated conductor, the major thin constituent layers, namely, the silver, REBCO and buffer layers, are modeled as 2D surfaces while the relatively thick stabilizer and substrate are in 3D layers. All the adjacent layers are coupled via spring equations under the CZM framework. The mixed-dimensional delamination model is validated by a full-3D FEM counterpart model. Simulation results show that the mixed-dimensional model performs simulations with much higher computational efficiency than the full-3D counterpart while maintaining sufficient accuracy. Effects of the anvil size and initial crack size on delamination behavior are discussed and compared to experimental phenomena. Furthermore, the stress distributions of the constituent layers of the conductor under different delamination initiation sites are predicted.}, number={7}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Gao, Peifeng and Chan, Wan-Kan and Wang, Xingzhe and Schwartz, Justin}, year={2018}, month={Jul} }
 @article{zhou_chan_schwartz_2018, title={Quench Detection Criteria for YBa2Cu3O7-delta Coils Monitored via a Distributed Temperature Sensor for 77 K Cases}, volume={28}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2018.2815920}, abstractNote={Distributed temperature sensing (DTS), such as Rayleigh-scattering interrogated optical fiber (RIOF) sensing, is a promising method for detecting quenches in high-temperature superconductor (HTS) magnets. One key for the successful implementation of RIOF-based DTS for quench detection is to identify effective quench detection criteria for the onset of a quench. In this paper, two DTS-based quench detection criteria, and their dependence on the operating current and heat disturbance characteristics, are investigated through numerical simulations of quench behavior in a YBa2 Cu3O7‐δ (YBCO) HTS helix coil cooled by a liquid nitrogen (LN2) bath and a YBCO HTS pancake coil cooled by conduction at 77 K. One is based on the minimum propagation zone (MPZ). The reference temperature to define the MPZ size is found for different operating currents. The other is based on the equilibrium temperature profile, in which the peak temperature and a characteristic normal zone length are found from a preselected reference temperature. The advantages and disadvantages of the two quench detection criterions are discussed and compared. Simulation results show that both criteria are independent of the nature of unpredictable heat disturbances. Similar to the helix coil, equilibrium temperature profiles independent of unpredictable disturbances are found for the pancake coil with different operating currents.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Zhou, Jun and Chan, Wan Kan and Schwartz, Justin}, year={2018}, month={Aug} }
 @article{song_lim_ko_park_schwartz_2017, title={A Noncontact T-c Evaluation Technique Using a Hall Probe Array}, volume={27}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2017.2663763}, abstractNote={A noncontact superconducting transition temperature (<italic>T</italic><sub>c</sub>) measurement system using a Hall probe array was devised to measure <italic>T</italic><sub>c</sub> of high-temperature superconductor (HTS) coated conductors (CCs) without physical contact to the surface, thereby avoiding contact with electrodes, which can cause damage to the conductor surface. The variations of the Hall voltage (<italic>V</italic>) distribution, which comes from the distribution of magnetic field on the surface of the CC, under a fixed applied field at different temperatures were used to estimate <italic>T</italic><sub>c</sub>. The measured <italic>T</italic><sub>c</sub> of the HTS GdBCO CC made by SuNAM was approximately 93.2 K by the noncontact <italic>T</italic><sub>c</sub> method, as compared to approximately 93.5 K by the conventional four-probe-contact method in a commercial PPMS. Thus, the <italic> T</italic><sub>c</sub> obtained by this system is comparable with that from the transport four-probe method. In addition, the noncontact <italic>T</italic><sub>c</sub> measurement system devised and used in this study is simple because it does not need comparison and conversion with values measured by contact methods.}, number={4}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Song, Kyu Jeong and Lim, Ji Chon and Ko, Rock-Kil and Park, Chan and Schwartz, Justin}, year={2017}, month={Jun} }
 @article{straka_amoah_schwartz_2017, title={Densification of thoria through flash sintering}, volume={7}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2017.70}, abstractNote={Thorium dioxide (thoria, ThO_2) is used in refractory applications and as nuclear fuel. Its melting temperature, the highest of any binary oxide, makes it a difficult system to process. Here we report on the effects of flash sintering on the densification of thoria. We found 95% of theoretical density is obtained at ~950 °C (~30% of the melting temperature) with an electric field of 800 V/cm. Variation in power density had a minimal effect on the densification. Scanning electron microscopy images show the effects of flash sintering on grain size as a function of electric field.}, number={3}, journal={MRS COMMUNICATIONS}, author={Straka, W. and Amoah, S. and Schwartz, J.}, year={2017}, month={Sep}, pages={677–682} }
 @article{scurti_mcgarrahan_schwartz_2017, title={Effects of metallic coatings on the thermal sensitivity of optical fiber sensors at cryogenic temperatures}, volume={7}, ISSN={["2159-3930"]}, DOI={10.1364/ome.7.001754}, abstractNote={One promising new application for optical fiber sensors is in monitoring superconducting magnets that are, inevitably, operated at cryogenic temperatures. The cryogenic thermal sensitivity of commercially available optical fibers is depressed by the low coefficient of thermal expansion of the constituent materials. Here, single mode, telecommunication-grade optical fibers are coated with different metals to alter their sensitivity to thermal perturbation at temperatures as low as 4.2 K. Commercially available fibers with acrylate coating are compared to fibers with only metallic coatings and those with acrylate-metal composite coatings, in terms of their sensitivity to thermal perturbations in the temperature range from 4.2 to 61 K. The metals considered include Sn, PbSnAg and InBi, both on cladding and on an acrylate primary coating. Results show that the 4.2 K thermal sensitivity can be enhanced significantly by a composite coating approach.}, number={6}, journal={OPTICAL MATERIALS EXPRESS}, author={Scurti, Federico and McGarrahan, John and Schwartz, Justin}, year={2017}, month={Jun}, pages={1754–1766} }
 @article{chan_schwartz_2017, title={Improved stability, magnetic field preservation and recovery speed in (RE)Ba2Cu3Ox-based no-insulation magnets via a graded-resistance approach}, volume={30}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/aa6eef}, abstractNote={The no-insulation (NI) approach to winding (RE)Ba2Cu3Ox (REBCO) high temperature superconductor solenoids has shown significant promise for maximizing the efficient usage of conductor while providing self-protecting operation. Self-protection in a NI coil, however, does not diminish the likelihood that a recoverable quench occurs. During a disturbance resulting in a recoverable quench, owing to the low turn-to-turn contact resistance, transport current bypasses the normal zone by flowing directly from the current input lead to the output lead, leading to a near total loss of the azimuthal current responsible for magnetic field generation. The consequences are twofold. First, a long recovery process is needed to recharge the coil to full operational functionality. Second, a fast magnetic field transient is created due to the sudden drop in magnetic field in the quenching coil. The latter could induce a global inductive quench propagation in other coils of a multi-coil NI magnet, increasing the likelihood of quenching and accelerating the depletion of useful current in other coils, lengthening the post-quench recovery process. Here a novel graded-resistance method is proposed to tackle the mentioned problems while maintaining the superior thermal stability and self-protecting capability of NI magnets. Through computational modeling and analysis on a hybrid multiphysics model, patterned resistive-conductive layers are inserted between selected turn-to-turn contacts to contain hot-spot heat propagation while maintaining the turn-wise current sharing required for self-protection, resulting in faster post-quench recovery and reduced magnetic field transient. Effectiveness of the method is studied at 4.2 and 77 K. Through the proposed method, REBCO magnets with high current density, high thermal stability, low likelihood of quenching, and rapid, passive recovery emerge with high operational reliability and availability.}, number={7}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Chan, Wan Kan and Schwartz, Justin}, year={2017}, month={Jul} }
 @article{scurti_schwartz_2017, title={Optical fiber distributed sensing for high temperature superconductor magnets}, volume={10323}, ISSN={["1996-756X"]}, DOI={10.1117/12.2265947}, abstractNote={Over the last two decades, high temperature superconductors (HTS) have achieved performance and technical maturity that make them an enabling technology or an attractive solution for a number of applications like electric motors and generators, particle accelerators and fusion magnets. One of the remaining challenges that hinders a wide use of HTS and needs to be solved is quench detection, since conventional voltage based quench detection puts HTS magnets at risk. In this work we have developed and experimentally investigated the application of Rayleigh-backscattering interrogated optical fibers (RIOF) to the detection of normal zones in superconducting magnets. Different ways to integrate optical fibers into magnets are explored and the earlier detection of RIOF compared to voltage is demonstrated.}, journal={2017 25TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS (OFS)}, author={Scurti, Federico and Schwartz, Justin}, year={2017} }
 @article{scurti_sathyamurthy_rupich_schwartz_2017, title={Self-monitoring 'SMART' (RE) Ba2Cu3O7-x conductor via integrated optical fibers}, volume={30}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/aa8762}, abstractNote={A self-monitoring, SMART (RE)Ba2Cu3O7−x (REBCO) conductor has been created by integrating optical fibers into the solder fillet of the current REBCO conductor architecture. By interrogating the integrated optical fiber by Raleigh backscattering, a spectral shift signal as a function of time and position along the conductor is obtained. Due to the direct integration into the solder fillet, intimate, consistent contact between fiber and conductor is obtained, while the optical fiber is protected and does not take up any space in the magnet winding. Therefore, the SMART conductor enhances the benefits of the co-wound fiber approach and provides ultimate sensitivity and practicality. Several samples of SMART REBCO conductor have been manufactured and characterized. The strain self-sensing capabilities have been demonstrated as well as thermal perturbation detection and localization with 2.56 mm spatial resolution. Results show that a key feature of the SMART conductor concerns its sensitivity to thermal perturbation; unlike in the case of a coil with co-wound optical fiber, the SMART REBCO sensitivity increases as the temperature decreases. A series of quench measurements have been performed, both on straight samples and on a pancake coil, at temperatures as low as 14.6 K. Using the data collected by the SMART REBCO during quench experiments, the temporal evolution of the size of a normal zone and the instantaneous normal zone propagation velocity have been calculated.}, number={11}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Scurti, Federico and Sathyamurthy, Srivatsan and Rupich, Martin and Schwartz, Justin}, year={2017}, month={Nov} }
 @article{jha_dulikravich_chakraborti_fan_schwartz_koch_colaco_poloni_egorov_2017, title={Self-organizing maps for pattern recognition in design of alloys}, volume={32}, ISSN={["1532-2475"]}, DOI={10.1080/10426914.2017.1279319}, abstractNote={ABSTRACT A combined experimental–computational methodology for accelerated design of AlNiCo-type permanent magnetic alloys is presented with the objective of simultaneously extremizing several magnetic properties. Chemical concentrations of eight alloying elements were initially generated using a quasi-random number generator so as to achieve a uniform distribution in the design variable space. It was followed by manufacture and experimental evaluation of these alloys using an identical thermo-magnetic protocol. These experimental data were used to develop meta-models capable of directly relating the chemical composition with desired macroscopic properties of the alloys. These properties were simultaneously optimized to predict chemical compositions that result in improvement of properties. These data were further utilized to discover various correlations within the experimental dataset by using several concepts of artificial intelligence. In this work, an unsupervised neural network known as self-organizing maps was used to discover various patterns reported in the literature. These maps were also used to screen the composition of the next set of alloys to be manufactured and tested in the next iterative cycle. Several of these Pareto-optimized predictions out-performed the initial batch of alloys. This approach helps significantly reducing the time and the number of alloys needed in the alloy development process.}, number={10}, journal={MATERIALS AND MANUFACTURING PROCESSES}, author={Jha, Rajesh and Dulikravich, George S. and Chakraborti, Nirupam and Fan, Min and Schwartz, Justin and Koch, Carl C. and Colaco, Marcelo J. and Poloni, Carlo and Egorov, Igor N.}, year={2017}, pages={1067–1074} }
 @article{ye_li_jaroszynski_schwartz_shen_2017, title={Strain control of composite superconductors to prevent degradation of superconducting magnets due to a quench: I. Ag/Bi2Sr2CaCu2Ox multifilament round wires}, volume={30}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/30/2/025005}, abstractNote={The critical current of many practical superconductors is sensitive to strain, and this sensitivity is exacerbated during a quench that induces a peak local strain which can be fatal to superconducting magnets. Here, a new method is introduced to quantify the influence of the conductor stress and strain state during normal operation on the margin to degradation during a quench, as measured by the maximum allowable hot spot temperature Tallowable, for composite wires within superconducting magnets. The first conductor examined is Ag-sheathed Bi2Sr2CaCu2Ox round wire carrying high engineering critical current density, JE, of 550 A mm−2 at 4.2 K and 15 T. The critical axial tensile stress of this conductor is determined to be 150 MPa and, in the absence of Lorentz forces, Tallowable is greater than 450 K. With increasing axial tensile stress, σa, however, Tallowable decreases nonlinearly, dropping to 280 K for σa = 120 MPa and to 160 K for σa = 145 MPa. Tallowable(σa) is shown to be nonlinear and independent of magnetic field from 15 to 30 T. Tallowable(σa) dictates the balance between magnetic field generation, which increases with the magnet operating current and stress, and the safety margin, which decreases with decreasing Tallowable, and therefore has important engineering value. It is also shown that Tallowable(σa) can be predicted accurately by a general strain model, showing that strain control is the key to preventing degradation of superconductors during a quench.}, number={2}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ye, Liyang and Li, Pei and Jaroszynski, Jan and Schwartz, Justin and Shen, Tengming}, year={2017}, month={Feb} }
 @article{rogers_schwartz_2017, title={Tensile fatigue behavior and crack growth in GdBa2Cu3O7-(x)/stainless-steel coated conductor grown via reactive co-evaporation}, volume={30}, ISSN={["1361-6668"]}, DOI={10.1088/1361-6668/aa604e}, abstractNote={(RE)Ba2Cu3O7−x (REBCO) conductors have the potential to enable a wide range of superconducting applications over a range of temperatures and magnetic fields (Vincent et al 2013 IEEE Trans. Appl. Supercond. 23 5700805), yet AC applications and devices with a charge/discharge cycle may be limited by the conductor fatigue properties. Here the fatigue behavior of GdBa2Cu3O7−x (GdBCO) conductors grown by reactive co-evaporation on stainless-steel substrates is reported for axial tensile strains, ε, up to 0.5% and 100 000 cycles. Failure mechanisms are investigated via microstructural studies and compared with a commercially available IBAD/MOCVD REBCO conductor. Results show that GdBCO/stainless-steel conductors retain their transport critical current for 10 000 cycles at ε = 0.35% and ε = 0.45%, and for 1000 cycles at ε = 0.50%. The main cause of fatigue degradation in GdBCO conductors is crack propagation and delamination that initiates at the edge of the conductor due to manufacturing defects.}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Rogers, Samuel and Schwartz, Justin}, year={2017}, month={Apr} }
 @article{jha_dulikravich_chakraborti_fan_schwartz_koch_colaco_poloni_egorov_2016, title={Algorithms for design optimization of chemistry of hard magnetic alloys using experimental data}, volume={682}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2016.04.218}, abstractNote={A multi-dimensional random number generation algorithm was used to distribute chemical concentrations of each of the alloying elements in the candidate alloys as uniformly as possible while maintaining the prescribed bounds on the minimum and maximum allowable values for the concentration of each of the alloying elements. The generated candidate alloy compositions were then examined for phase equilibria and associated magnetic properties using a thermodynamic database in the desired temperature range. These initial candidate alloys were manufactured, synthesized and tested for desired properties. Then, the experimentally obtained values of the properties were fitted with a multi-dimensional response surface. The desired properties were treated as objectives and were extremized simultaneously by utilizing a multi-objective optimization algorithm that optimized the concentrations of each of the alloying elements. This task was also performed by another conceptually different response surface and optimization algorithm for double-checking the results. A few of the best predicted Pareto optimal alloy compositions were then manufactured, synthesized and tested to evaluate their macroscopic properties. Several of these Pareto optimized alloys outperformed most of the candidate alloys on most of the objectives. This proves the efficacy of the combined meta-modeling and experimental approach in design optimization of the alloys. A sensitivity analysis of each of the alloying elements was also performed to determine which of the alloying elements contributes the least to the desired macroscopic properties of the alloy. These elements can then be replaced with other candidate alloying elements such as not-so-rare earth elements.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Jha, Rajesh and Dulikravich, George S. and Chakraborti, Nirupam and Fan, Min and Schwartz, Justin and Koch, Carl C. and Colaco, Marcelo J. and Poloni, Carlo and Egorov, Igor N.}, year={2016}, month={Oct}, pages={454–467} }
 @misc{redan_buhman_novotny_ferruzzi_2016, title={Altered Transport and Metabolism of Phenolic Compounds in Obesity and Diabetes: Implications for Functional Food Development and Assessment}, volume={7}, ISSN={["2156-5376"]}, DOI={10.3945/an.116.013029}, abstractNote={Interest in the application of phenolic compounds from the diet or supplements for the prevention of chronic diseases has grown substantially, but the efficacy of such approaches in humans is largely dependent on the bioavailability and metabolism of these compounds. Although food and dietary factors have been the focus of intense investigation, the impact of disease states such as obesity or diabetes on their absorption, metabolism, and eventual efficacy is important to consider. These factors must be understood in order to develop effective strategies that leverage bioactive phenolic compounds for the prevention of chronic disease. The goal of this review is to discuss the inducible metabolic systems that may be influenced by disease states and how these effects impact the bioavailability and metabolism of dietary phenolic compounds. Because current studies generally report that obesity and/or diabetes alter the absorption and excretion of these compounds, this review includes a description of the absorption, conjugation, and excretion pathways for phenolic compounds and how they are potentially altered in disease states. A possible mechanism that will be discussed related to the modulation of phenolic bioavailability and metabolism may be linked to increased inflammatory status from increased amounts of adipose tissue or elevated plasma glucose concentrations. Although more studies are needed, the translation of benefits derived from dietary phenolic compounds to individuals with obesity or diabetes may require the consideration of dosing strategies or be accompanied by adjunct therapies to improve the bioavailability of these compounds.}, number={6}, journal={ADVANCES IN NUTRITION}, author={Redan, Benjamin W. and Buhman, Kimberly K. and Novotny, Janet A. and Ferruzzi, Mario G.}, year={2016}, month={Nov}, pages={1090–1104} }
 @article{rogers_chan_schwartz_2016, title={Effects of room-temperature tensile fatigue on critical current and n-value of IBAD-MOCVD YBa2Cu3O7-x/Hastelloy coated conductor}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/8/085013}, abstractNote={REBa2Cu3O7−x (REBCO) coated conductors potentially enable a multitude of superconducting applications, over a wide range of operating temperatures and magnetic fields, including high-field magnets, energy storage devices, motors, generators, and power transmission systems (Zhang et al 2013 IEEE Trans. Appl. Supercond. 23 5700704). Many of these are AC applications and thus the fatigue properties may be limiting (Vincent et al 2013 IEEE Trans. Appl. Supercond. 23 5700805). Previous electromechanical studies have determined the performance of REBCO conductors under single cycle loads (Barth et al 2015 Supercond. Sci. Technol. 28 045011), but an understanding of the fatigue properties is lacking. Here the fatigue behavior of commercial ion beam assisted deposition–metal organic chemical vapor deposition REBCO conductors on Hastelloy substrates is reported for axial tensile strains up to 0.5% and up to 100 000 cycles. Failure mechanisms are investigated via microstructural studies. Results show that REBCO conductors retained Ic(ε)/Ic0 = 0.9 for 10 000 cycles at ε = 0.35% and ε = 0.45% strain, and ε = 0.5% for 100 cycles. The main cause of fatigue degradation in REBCO conductors is crack propagation that initiates at the slitting defects that result from the manufacturing process.}, number={8}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Rogers, Samuel and Chan, Wan Kan and Schwartz, Justin}, year={2016}, month={Aug} }
 @article{zhang_koch_schwartz_2016, title={Formation of Bi2Sr2CaCu2Ox/Ag multifilamentary metallic precursor powder-in-tube wires}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/12/125005}, abstractNote={Previously, a metallic precursor (MP) approach to synthesizing Bi2Sr2CaCu2Ox (Bi2212), with a homogeneous mixture of Bi, Sr, Ca, Cu and Ag was produced by mechanical alloying. Here, Bi2212/Ag round multifilamentary wire is manufactured using a metallic precursor powder-in-tube (MPIT) process. The MP powders were packed into a pure Ag tube in an Ar atmosphere and then sealed. After deformation, multifilamentary round wires and rolled tapes were heat treated in flowing oxygen through three stages: oxidation, conversion and partial-melt processing (PMP). Processing-microstructure-property relationships on 20–50 mm long multifilamentary round wires and rolled tapes were studied extensively. It is shown that conventional wire deformation processes, optimized for oxide-powder-in-tube wires, are not effective for deforming MPIT wires, and that as with prior studies of MPIT Bi2Sr2Ca2Cu3Oy conductors, hot extrusion is required for obtaining a multifilamentary structure with fine filaments. As a result, the Bi2212 MPIT wires reported here have low engineering critical current density. Nonetheless, by focusing on sections of wires that remain intact after deformation, it is also shown that the first heat treatment stage, the oxidation stage, plays a crucial role in chemical homogeneity, phase transformation, and microstructural evolution and three reaction pathways for MP oxidation are presented. Furthermore, it is found the Bi2212 grain alignment within an MPIT filament is significantly different from that found in OPIT filaments after PMP, indicating the formation of highly dense filaments containing Bi2212 fine grains and Ag particles before PMP aids the formation of large, c-axis textured Bi2212 filaments during PMP. These results show that, with improved wire deformation, high critical current density may be obtained via a MPIT process.}, number={12}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Zhang, Yun and Koch, Carl C. and Schwartz, Justin}, year={2016}, month={Dec} }
 @article{zhang_johnson_naderi_chaubal_hunt_schwartz_2016, title={High critical current density Bi2Sr2CaCu2Ox/Ag wire containing oxide precursor synthesized from nano-oxides}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/9/095012}, abstractNote={Bi2Sr2CaCu2Ox (Bi2212)/Ag-alloy wires are manufactured via the oxide-powder-in-tube route by filling Ag/Ag-alloy tubes with Bi2212 oxide precursor, deforming into wire, restacking and heat treating using partial-melt processing (PMP). Recent studies propose several requirements on precursor properties, including stoichiometry, chemical homogeneity, carbon content and phase purity. Here, nanosize oxides produced by nGimat’s proprietary NanoSpray CombustionTM process are used as starting materials to synthesize Bi2212 oxide precursors via solid-state calcination. Oxide powders for wire fill (precursor powder) with precisely controlled stoichiometry and chemical homogeneity containing over 99 vol% of single Bi2212-phase are synthesized. Alkaline-earth cuprate are found to be the only impurity phase in the precursor powders. Phase transformation, carbon release and grain growth during calcination are studied through a series of quench studies. Effects of particle size, surface area, stoichiometry, chemical homogeneity and microstructures of the starting materials on Bi2212 formation and wire transport properties are discussed. Small particle size, high surface area and short diffusion length of the starting materials result in a rapid and homogeneous phase transformation to Bi2212, along with an early and rapid carbon release. The residual carbon in the precursor powder is between 50 and 90 ppm. The strong dependence of transport Jc on precursor stoichiometry indicates that compositional variations within precursor powders should be less than 1.5 mol%. Two Bi-rich and Ca-deficient stoichiometries give higher wire transport critical current density, with the highest being 2520 A mm−2 (4.2 K, 5 T) after 1 bar PMP and 4560 A mm−2 (4.2 K, 5 T) after 100 bar overpressure (OP) processing. The low residual carbon content results in smaller and fewer voids within an OP-processed wire filament. Bi-rich and Ca-deficient stoichiometries and small compositional variations within precursor powders may be a method for engineering uniformly-distributed and high-density Bi2201 intergrowths within Bi2212 grains after PMP.}, number={9}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Zhang, Yun and Johnson, Stephen and Naderi, Golsa and Chaubal, Manasi and Hunt, Andrew and Schwartz, Justin}, year={2016}, month={Sep} }
 @article{fan_liu_jha_dulikravich_schwartz_koch_2016, title={On the Formation and Evolution of Cu-Ni-Rich Bridges of Alnico Alloys With Thermomagnetic Treatment}, volume={52}, ISSN={["1941-0069"]}, DOI={10.1109/tmag.2016.2555956}, abstractNote={Despite decades of research and development of Alnico alloys, significant uncertainties in the underlying structure-property relationships remain. Here, we report on the effects of Ti on the Alnico microstructure and nanostructure, and the corresponding influence on magnetic properties. We show that Ti fosters the conditions resulting in the formation of Cu-Ni-rich bridges in the α1 phases between the α2 phases. For Alnico containing Ti, a typical chessboardlike morphology with Cu-Ni-rich bridges is observed, whereas in the absence of Ti, the α1 phases connect to each other readily, especially with a high Co concentration, and a mazelike morphology with Cu-rich white-plate precipitates rather than Cu-rich bridges is observed. Furthermore, in Alnico containing Ti, an inhomogeneous distribution of Ni is found in the α2 phases, including loops with high Ni concentration surrounding the α1 phase and high concentrations in the bridges as well. An increase in the Cu concentration is also observed in the loops around the α1 phases (Ni-Cu loops), and direct contact between the Cu-Ni-rich bridges and the Ni-Cu loops is observed in lieu of direct contact between the bridges and the α1 phases. We also observe that the bridges are not perfectly round but ellipsoidal, with the long axis along the connection of two adjacent α1 phases. The energy-dispersive X-ray spectroscopy line scans of the bridges shows that two types of Cu-Ni-rich bridges exist: those with more Cu than Ni and those with more Ni than Cu. A 3-D model is presented that explains the conditions and process of bridge formation, consistent with the observed composition distributions.}, number={8}, journal={IEEE TRANSACTIONS ON MAGNETICS}, author={Fan, M. and Liu, Y. and Jha, Rajesh and Dulikravich, George S. and Schwartz, J. and Koch, C. C.}, year={2016}, month={Aug} }
 @article{fan_liu_jha_dulikravich_schwartz_koch_2016, title={On the evolution of Cu-Ni-rich bridges of Alnico alloys with tempering}, volume={420}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2016.07.040}, abstractNote={Tempering is a critical step in Alnico alloy processing, yet the effects of tempering on microstructure have not been well studied. Here we report these effects, and in particular the effects on the Cu-Ni bridges. Energy-dispersive X-ray spectroscopy (EDS) maps and line scans show that tempering changes the elemental distribution in the Cu-Ni bridges, but not the morphology and distribution of Cu-bridges. The Cu concentration in the Cu-Ni bridges increases after tempering while other element concentrations decrease, especially Ni and Al. Furthermore, tempering sharpens the Cu bridge boundaries. These effects are primarily related to the large 2C44/(C11−C12) ratio for Cu, largest of all elements in Alnico. In addition, the Ni-Cu loops around the α1 phases become inconspicuous with tempering. The diffusion of Fe and Co to the α1 phase during tempering, which increases the difference of saturation magnetization between the α1 and α2 phases, is observed by EDS. In summary, α1, α2 and Cu-bridges are concentrated with their major elements during tempering which improves the magnetic properties. The formation of these features formed through elemental diffusion is discussed via energy theories.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Fan, M. and Liu, Y. and Jha, Rajesh and Dulikravich, George S. and Schwartz, J. and Koch, C. C.}, year={2016}, month={Dec}, pages={296–302} }
 @article{ye_li_shen_schwartz_2016, title={Quench degradation limit of multifilamentary Ag/Bi2Sr2CaCu2Ox round wires}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/3/035010}, abstractNote={Understanding safe operating limits of composite superconducting wires is important for the design of superconducting magnets. Here we report measurements of quench-induced critical current density Jc degradation in commercial Ag/Bi2Sr2CaCu2Ox (Bi-2212) round wires using heater-induced quenches at 4.2 K in self magnetic field that reveal a general degradation behavior. Jc degradation strongly depends on the local hot spot temperature Tmax, and is nearly independent of operating current, the temperature gradient along the conductor dTmax/dx, and the temperature rising rate dTmax/dt. Both Jc and n value (where n is an index of the sharpness of the superconductor-to-normal transition) exhibit small but irreversible degradation when Tmax exceeds 400–450 K, and large degradation occurs when Tmax exceeds 550 K. This behavior was consistently found for a series of Bi-2212 wires with widely variable wire architectures and porosity levels in the Bi-2212 filaments, including a wire processed using a standard partial melt process and in which Bi-2212 filaments are porous, an overpressure processed wire in which Bi-2212 filaments are nearly porosity-free and that has a Jc(4.2 K, self field) exceeding 8000 A mm−2, and a wire that has nearly no filament to filament bridges after reaction. Microstructural observations of degraded wires reveal cracks in the Bi-2212 filaments perpendicular to the wire axis, indicating that the quench-induced Ic degradation is primarily driven by strain. These results further suggest that the quench degradation temperature limit depends on the strain state of Bi-2212 filaments and this dependence shall be carefully considered when engineering a high-field Bi-2212 magnet.}, number={3}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ye, Liyang and Li, Pei and Shen, Tengming and Schwartz, Justin}, year={2016}, month={Mar} }
 @article{scurti_ishmael_flanagan_schwartz_2016, title={Quench detection for high temperature superconductor magnets: a novel technique based on Rayleigh-backscattering interrogated optical fibers}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/3/03lt01}, abstractNote={High temperature superconducting materials are the only option for the generation of magnetic fields exceeding 25 T and for magnets operating over a broad range of temperature and magnetic field for power applications. One remaining obstacle for the implementation of high temperature superconductors magnets into systems, however, is the inability to rapidly detect a quench. In this letter we present a novel quench detection technique that has been investigated experimentally. Optical fibers are co-wound into two small Bi2Sr2Ca2Cu3O10+x superconducting coils and interrogated by Rayleigh-backscattering. Two different configurations are used, one with the fiber atop the conductor and the other with the fiber located as turn-to-turn insulation. Each coil is also instrumented with voltage taps (VTs) and thermocouples for comparison during heater-induced quenches. The results show that Rayleigh-backscattering interrogated optical fibers (RIOF) have significant advantages over traditional techniques, including very high spatial resolution and the ability to detect a hot-spot well before the peak local temperature exceeds the current sharing temperature. Thus, RIOF quench detection is intrinsically faster than VTs, and this intrinsic advantage is greater as the coil size and/or current margin increases.}, number={3}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Scurti, F. and Ishmael, S. and Flanagan, G. and Schwartz, J.}, year={2016}, month={Mar} }
 @article{wang_chan_schwartz_2016, title={Self-protection mechanisms in no-insulation (RE) Ba2Cu3Ox high temperature superconductor pancake coils}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/4/045007}, abstractNote={No-insulation (NI) high temperature superconducting (HTS) coils possess much higher thermal stability than similar traditionally insulated HTS coils. Some NI coils are self-protecting in the sense that they fully recover after a quench without any external protection mechanism to dissipate the stored energy. The underlying mechanisms that make NI coils highly stable or even self-protecting, however, remain unclear. To answer this question, a numerical multiphysics quench model for NI pancake coils is built to study the electrical, thermal and magnetic behavior of NI coils subjected to local heat disturbances. The multiphysics model is built from an electric network model, tightly coupled to a two-dimensional thermal coil model and a three-dimensional magnetic field coil model. The results show that when heat disturbance initiates a local normal region on a turn, the transport current is redistributed not only from the local normal region, but also along the entire turn. The redistributed current flows in the form of radial current across the turn-to-turn contact resistance along the entire turn to the neighboring turns which are still in the superconducting state, driving these turns to an overcurrent state. This full-turn current sharing and overcurrent operation accelerate the redistribution of current away from the hot-spot, reducing localized Joule heating that would otherwise cause a sustainable quench. The results also show that the magnetic field generated at the coil center drops rapidly and the coil voltage changes dynamically during the early stage of normal zone formation. These phenomena can be utilized as effective methods for quench detection in NI coils by monitoring the magnetic field and coil voltage.}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Wang, Y. and Chan, Wan Kan and Schwartz, Justin}, year={2016}, month={Apr} }
 @article{rasic_vlahovic_schwartz_2016, title={Underlying causes of the magnetic behavior in surface patterned NiFe2O4 thin films}, volume={6}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2016.38}, abstractNote={Surface patterned NiFe_2O_4 thin films exhibited large reduction in coercivity as compared with the films without surface patterning. Chemical analysis of the films revealed that there was no diffusion between the film and the substrate. Additional heating was shown to improve saturation magnetization without adverse effect on coercivity. The process of imprinting was eliminated as the possible cause of the phenomena as the flat stamp did not alter the magnetic properties of the film. Finally, it was shown that the orientation of the features with respect to the magnetic field does not have a significant effect on the magnetic response.}, number={4}, journal={MRS COMMUNICATIONS}, author={Rasic, Goran and Vlahovic, Branislav and Schwartz, Justin}, year={2016}, month={Dec}, pages={397–401} }
 @article{schwartz_2016, title={Viewpoint: Are no-insulation magnets a paradigm shift for high-field DC superconducting magnets?}, volume={29}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/29/5/050501}, abstractNote={Justin Schwartz Materials Science and Engineering Department, North Carolina State University, 911 Partners Way, Raleigh, NC 27695-7907, USA This is a viewpoint on the letter by Sangwon Yoon et al (2016 Supercond. Sci. Technol. 29 04LT04). Superconducting magnets generating magnetic fields above 25 T have been an aspirational target of the magnet community since the Seitz-Richardson report was released in 1988 [1]. At the time of the report, there were no superconducting materials capable of transporting high supercurrent density at magnetic fields above about 23 T [2], and even that work was far from a viable conductor technology. Shortly thereafter, however, the rapid discoveries of superconductivity in YBa2Cu3Ox and the Bi–Sr–Ca–Cu–O system with very high critical temperature and unmeasurably high upper critical magnetic fields made the Seitz-Richardson report appear prophetic, giving hope for a new generation of superconducting magnet technologies. Extensive R&D in the years following the discoveries of high temperature superconductors has brought significant transformations of these materials from laboratory specimens into the conductor technologies. As a result, significant lengths of (RE)Ba2Cu3Ox coated conductors, Bi2Sr2CaCu2Oy round wires, and Bi2Sr2Ca2Cu3Oy tape conductors are commercially available from a number of industrial manufacturers in the United States, Europe and Asia. The 25 T target, first surpassed in 2004 by an insert coil made of Bi2Sr2CaCu2Oy tape conductors that are no longer in favor [3], has now been surpassed by many groups [4–6] and a world-wide race for generating the highest magnetic fields is underfoot. The advances in high field superconducting magnets in the last decade have been propelled mostly by progress in conductor manufacturing, and for the most part magnet construction technologies have remained similar to that of NbTi and Nb3Sn magnets. Generally speaking, Bi2Sr2CaCu2Oy has followed Nb3Sn because of the need to wind-and-react, and (RE)Ba2Cu3Ox and Bi2Sr2Ca2Cu3Oy magnets have followed NbTi because they can use a react-and-wind approach, and in the case of (RE)Ba2Cu3Ox, because the mechanical behavior is favorable. But in all cases, the conductor turns were separated by some form of turn-to-turn insulation, and often the magnets were impregnated after final construction. In 2011 a new approach appeared on the magnet scene; no-insulation magnets were proposed in which the transport current would ultimately find its own path of least resistance from end to end [7]. This novel approach was met with skepticism because it was unlike anything considered previously. In principle the magnet designer could not control the path of the electrical current and therefore could control neither the magnitude of nor the spatial distribution of magnetic field generated. Questions were raised, e.g., ‘how long will it take for a magnet to reach steady-state equilibrium’? Are (RE)Ba2Cu3Ox coated conductors sufficiently homogeneous for this approach to succeed? What about stability and protection? Results over the past five years have begun to answer these questions, and most of the answers have proved the skeptics wrong. The article in this issue by Yoon et al [8] is a breakthrough in the generation of high magnetic fields that is}, number={5}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Schwartz, Justin}, year={2016}, month={May} }
 @article{sun_gou_schwartz_2015, title={A Three-Dimensional Fractal-Based Study of the Effects of the Complex Interface Between Bi2Sr2CaCu2Ox Filaments and the Ag Matrix on the Mechanical Behavior of Composite Round Wires}, volume={25}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2015.2457780}, abstractNote={Bi2Sr2CaCu2Ox/Ag/Ag-alloy (Bi2212) multifilamentary composite round wires (RWs) are the only RW candidate for fabricating superconducting magnets generating magnetic fields greater than 25 T. The complicated microstructure of the RWs, however, affects not only the electrical transport but also the mechanical behavior. To establish the correlation between the macroscopic electromechanical properties and the microstructure, an accurate characterization of the Bi2212 composite RW microstructure is important. Here, we develop a 3-D fractal-based model of the complex interface between Bi2212 filaments and the Ag matrix and determine its impact on RW mechanical behavior. The results indicate that such a complex interface strongly affects the local mechanical behavior rather than macroscopic behavior. Specifically, it causes the stress to be highly nonuniform in localized regions. At and/or around thin “Plate-like Extensions” (PEs) and “Bridge Connections” (BCs), the stress peaks under a simple uniaxial load. The results conclude that mechanical failure likely initiates at PEs, BCs, and the interface between them and the Ag matrix.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Sun, Zhenhua and Gou, Xiaofan and Schwartz, Justin}, year={2015}, month={Oct} }
 @article{kajbafvala_nachtrab_wong_schwartz_2015, title={Bi2Sr2CaCu2O8+x round wires with Ag/Al oxide dispersion strengthened sheaths: microstructure-properties relationships, enhanced mechanical behavior and reduced Cu depletion (vol 27, 095001, 2014)}, volume={28}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/28/1/019501}, number={1}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Kajbafvala, Amir and Nachtrab, William and Wong, Terence and Schwartz, Justin}, year={2015}, month={Jan} }
 @article{ishmael_rogers_hunte_naderi_roach_straka_schwartz_2015, title={Current Density and Quench Behavior of MgB2/Ga Composite Wires}, volume={25}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2015.2483597}, abstractNote={Magnesium diboride (MgB 2) is a promising superconductor for many technical applications. Sufficient current densities at required magnetic fields, moderate operational temperature, low raw materials' cost, and an economical manufacturing process have enabled commercial development of MgB 2 wires. Reacted MgB 2, however, is brittle, and applications involving coils and windings with small bend radii are therefore difficult to implement. Furthermore, improvements in the critical current density are needed to expand the range of potential applications. Here, we report on the electrical behavior of novel MgB 2/Ga composite wires produced such that the proximity effect enhances connectivity, allowing the high-temperature anneal typically required for in situ and ex situ MgB 2 wires to be eliminated. Elimination of the high-temperature anneal simplifies MgB 2 manufacturing and has the potential to create a wire that is more tolerant of bending. Here, we present critical current density and quench propagation results for MgB 2/Ga composite wires sheathed in Cu.}, number={6}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Ishmael, Sasha A. and Rogers, Samuel and Hunte, Frank and Naderi, Golsa and Roach, Christian and Straka, Weston and Schwartz, Justin}, year={2015}, month={Dec} }
 @article{phillips_chan_schwartz_2015, title={Enhanced Quench Protection in REBa2Cu3O delta-7-Based Coils by Enhancing Three-Dimensional Quench Propagation via Thermally Conducting Electrical Insulation}, volume={25}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2015.2452224}, abstractNote={This simulation explores the effects of insulation properties on quench propagation in ReBa2Cu3Oδ-7-based coils. At present, superconducting magnets primarily use insulators that are electrically and thermally insulating, for example, Kapton. Here, the impact of varying the thermal conductivity of the electrical insulation on quench behavior is reported. In particular, the behavior of a Kapton-insulated coil is compared with one insulated with doped TiO 2, one insulated with “ideal Al2O3”, and one noninsulated coil. The effects on minimum quench energy and normal zone propagation behavior are investigated. In addition, a new concept, the current sharing volume (CSV), which accounts for two- or three-dimensional normal zone propagation, is introduced. The CSV is defined as the volume of coil for which the temperature is above the current sharing temperature. The simulation results show that the transverse thermal conductivity and insulation thickness strongly influence the normal zone propagation velocity, thus impacting the quench detection time and hotspot temperature. As expected, the coils insulated with the higher thermal conductivity alternatives exhibited faster normal zone growth and lower hotspot temperatures relative to CSV growth. The impact of improved thermal conductivity of turn-to-turn insulation becomes even greater when distributed sensing replaces voltage-based sensing.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Phillips, Makita R. and Chan, Wan Kan and Schwartz, Justin}, year={2015}, month={Oct} }
 @article{ye_cruciani_xu_mine_amm_schwartz_2015, title={Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils}, volume={28}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/28/3/035015}, abstractNote={Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the powder-in-tube process, have recently become commercially available. Owing to its electromagnetic performance in the 20−30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample versus small coil). Furthermore, one coil is quenched repeatedly with increasing hotspot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.}, number={3}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ye, Liyang and Cruciani, Davide and Xu, Minfeng and Mine, Susumu and Amm, Kathleen and Schwartz, Justin}, year={2015}, month={Mar} }
 @article{lee_kumar_hunte_narayan_schwartz_2015, title={Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates}, volume={118}, number={12}, journal={Journal of Applied Physics}, author={Lee, Y. F. and Kumar, R. and Hunte, F. and Narayan, J. and Schwartz, J.}, year={2015} }
 @article{rasic_schwartz_2015, title={On the origin of coercivity reduction in surface patterned magnetic thin films}, volume={212}, ISSN={["1862-6319"]}, DOI={10.1002/pssa.201431434}, abstractNote={Spinel nickel ferrite (NiFe2O4) is a promising material for next generation high‐frequency sensors, antennae and microwave devices. A key issue to be addressed is the magnetic loss, which is proportional to frequency and becomes substantial at frequencies above 1 GHz. Previously, we reported on coercivity reduction in NiFe2O4 through surface patterning (Rasic and Schwartz, MRS Commun. 3, 207 (2013) and IEEE Magn. Lett. 5, 1 (2014) ). Here, we report on the effects of varying the feature size on magnetic behavior, including loss, and explain the reduced coercivity theoretically. Nickel ferrite thin films were deposited on c‐plane sapphire substrates using chemical solution deposition and patterned via nanoimprint lithography with patterning masters having feature sizes varying from 500 to 1500 nm in 200 nm increments. Atomic force microscopy showed good feature transfer for all samples. X‐ray diffraction images showed all samples to be single‐phase inverse spinel nickel ferrite with similar texture. All patterned samples showed coercivity reductions relative to the unpatterned samples. The effects of feature size on coercivity reduction showed opposite trends for in‐plane and out‐of‐plane magnetization hysteresis measurements, whereas saturation magnetization was not affected by feature size changes. Magnetic force microscopy images confirmed the origin of coercivity reduction to be shape‐anisotropy‐forced alternating domain formation. The coercivity reduction phenomena observed in patterned NiFe2O4 thin films are explained theoretically. The effect of changing the film thickness and domain size on the equilibrium energy density was calculated. While the relative energy density showed a stable equilibrium, the energy increase for domain sizes equaling that of patterned films in this study was small. Finally, the new domain structure in patterned NiFe2O4 films was explained within micromagnetism theory.}, number={2}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Rasic, Goran and Schwartz, Justin}, year={2015}, month={Feb}, pages={449–458} }
 @article{le_chan_schwartz_2014, title={A two-dimensional ordinary, state-based peridynamic model for linearly elastic solids}, volume={98}, ISSN={["1097-0207"]}, DOI={10.1002/nme.4642}, abstractNote={SUMMARY}, number={8}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING}, author={Le, Q. V. and Chan, W. K. and Schwartz, J.}, year={2014}, month={May}, pages={547–561} }
 @article{kajbafvala_nachtrab_wong_schwartz_2014, title={Bi2Sr2CaCu2O8+x round wires with Ag/Al oxide dispersion strengthened sheaths: Microstructure-properties relationships, enhanced mechanical behavior and reduced Cu depletion}, volume={27}, number={9}, journal={Superconductor Science & Technology}, author={Kajbafvala, A. and Nachtrab, W. and Wong, T. and Schwartz, J.}, year={2014} }
 @article{rasic_schwartz_2014, title={Coercivity reduction in nickel ferrite (NiFe2O4) thin films through surface patterning}, volume={5}, journal={IEEE Magnetics Letters}, author={Rasic, G. and Schwartz, J.}, year={2014} }
 @misc{lee_punugupati_wu_jin_narayan_schwartz_2014, title={Evidence for topological surface states in epitaxial Bi2Se3 thin film grown by pulsed laser deposition through magneto-transport measurements}, volume={18}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2014.07.001}, abstractNote={We report epitaxial growth via domain matching epitaxy of Bi2Se3 thin films on Al2O3 (0 0 0 1) substrates with over 13% lattice misfit and critical thickness less than one monolayer. X-ray and electron diffraction patterns confirm that the layers are epitaxial with (0 0 0 1) Bi2Se3 || (0 0 0 1) Al2O3 and [21¯1¯0] Bi2Se3 || [21¯1¯0] Al2O3 (or) [21¯1¯0] Bi2Se3 || [112¯0] Al2O3 without the presence of an interfacial pseudomorphic layer. X-ray photoemission spectroscopy reveals that the films are Se-deficient, in agreement with electrical transport data showing n-type carriers and metallic behavior. Magneto-resistance (MR) measurements show a cusp feature corresponding to weak antilocalization and linear-MR shows a non-saturating trend up to 9 T. These results suggest topological surface states in PLD-grown Bi2Se3 films.}, number={5}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Lee, Y. F. and Punugupati, S. and Wu, F. and Jin, Z. and Narayan, J. and Schwartz, J.}, year={2014}, month={Oct}, pages={279–285} }
 @article{varghese_viswan_joshi_seifikar_zhou_schwartz_priya_2014, title={Magnetostriction measurement in thin films using laser Doppler vibrometry}, volume={363}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2014.03.076}, abstractNote={This paper reports the laser Doppler vibrometry based measurement of the magnetostriction in magnetic thin films. Using this method, the strain induced by an AC magnetic field in the polycrystalline cobalt ferrite and nickel ferrite thin films grown on silicon and platinized silicon substrates was measured under a DC magnetic bias. The experimental setup and the derivation of the magnetostriction constant from the experimentally measured deflection values are discussed. The magnetostriction values derived using force and bending moment balances were compared with that derived from an industry standard relationship. In addition, we corroborate our approach by comparing the values derived from bending theory calculations of magnetically induced torque to those from measurements using Vibrating Sample Magnetometer (VSM). At high DC magnetic field bias, the magnitude of magnetization calculated from the measured magnetostriction was found to match the measured magnetization by VSM.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Varghese, Ronnie and Viswan, Ravindranath and Joshi, Keyur and Seifikar, Safoura and Zhou, Yuan and Schwartz, Justin and Priya, Shashank}, year={2014}, month={Aug}, pages={179–187} }
 @article{naderi_schwartz_2014, title={Multiscale studies of processing-microstructure-transport relationships in over- pressure processed Bi2Sr2CaCu2Ox/Ag multifilamentary round wire}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/11/115002}, abstractNote={Recently, significantly improved transport properties in Bi2Sr2CaCu2Ox/Ag (Bi2212/Ag) multifilamentary round wire (RW) has been achieved by applying 100 atm over-pressure (OP) during partial melt processing (PMP). Despite this significant progress, the microstructural details and phase evolution during the high pressure partial melt processing are poorly understood, and previous studies have focused solely on densification. Here we investigate the processing-microstructure-transport relationships of OP-PMP RWs by comparing the filament microstructure of a PMP wire with that of an OP-PMP wire on multiple length scales. OP affects the microstructure differently in each stage of PMP: it causes grain growth during pre-annealing, increases the peritectic melting temperature in the partial melt, improves oxygen uptake during solidification, and enhances grain connectivity during sintering. It is also found that the increase in transport of OP-PMP wire is related to increase in Bi2212 filament density on multiple length scales. Yet OP-PMP wire shows higher area fraction of filaments with large Bi2201 grains. Thus, to further improve transport, optimization of OP-PMP is essential; in particular the maximum heat treatment temperature should be increased, consistent with the increase in peritectic melt temperature, such that less Bi2201 grains form during processing.}, number={11}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Naderi, G. and Schwartz, J.}, year={2014}, month={Nov} }
 @article{naderi_schwartz_2014, title={On the roles of Bi2Sr2CuOx intergrowths in Bi2Sr2CaCu2Ox/Ag round wires: c-axis transport and magnetic flux pinning}, volume={104}, ISSN={["1077-3118"]}, DOI={10.1063/1.4871805}, abstractNote={Despite progress in the performance of Bi2Sr2CaCu2Ox (Bi2212)/Ag multifilamentary round wires, understanding the impact of microstructural defects on multiple length scales on electrical transport remains a significant challenge. Many recent studies have focused on porosity, but porosity is not the only factor in determining Jc. The primary impurity in partial-melt processed multifilamentary Bi2212 wires is Bi2Sr2CuOx (Bi2201), which forms as mesoscopic grains and nanoscopic intergrowths. Previously, we showed the destructive effect of Bi2201 grains on transport. Here, we relate scanning transmission electron microscopy results to the Bi2212 coherence length, anisotropic magnetization behavior, and magnetic-field dependent transport to study c-axis transport and the effects of Bi2201 intergrowths on magnetic flux pinning. We show that wide Bi2201 intergrowths are barrier to c-axis transport within Bi2212 grains, whereas narrow (half- and full-cell) Bi2201 intergrowths are not detrimental to c-axis transport and are likely magnetic flux pinning centers. These results have significant impact on the understanding of Bi2212/Bi2201 systems and provide important physical insight towards future improvements in devices based upon wires, film, and junctions.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Naderi, G. and Schwartz, J.}, year={2014}, month={Apr} }
 @article{lee_wu_narayan_schwartz_2014, title={Oxygen vacancy enhanced room-temperature ferromagnetism in Sr3SnO/c-YSZ/Si (001) heterostructures}, volume={4}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2014.4}, abstractNote={The magnetic properties of Sr_3SnO (SSO) epitaxial thin films prepared under various post-growth annealing treatments are reported. The SSO films are grown on cubic yttria-stabilized zirconia Si (001) platform by pulsed laser deposition. Post-growth vacuum annealing is found to enhance the room-temperature ferromagnetism (RTFM), whereas oxygen annealing reduces it. The results are explained through the oxygen vacancy constituted bound magnetic polarons (BMP) model. An empirical relationship between the extracted BMP concentration and the oxygen vacancy concentration is shown using X-ray photoelectron spectroscopy data. The results indicate a promising way to tune RTFM by manipulating oxygen vacancies and related defects.}, number={1}, journal={MRS COMMUNICATIONS}, author={Lee, Y. F. and Wu, F. and Narayan, J. and Schwartz, J.}, year={2014}, month={Apr}, pages={7–13} }
 @article{callaway_naderi_van le_schwartz_2014, title={Statistical analysis of the relationship between electrical transport and filament microstructure in multifilamentary Bi2Sr2CaCu2Ox/Ag/Ag-Mg round wires}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/4/044020}, abstractNote={After processing, multifilamentary Bi2Sr2CaCu2Ox (Bi2212) round wires have complex microstructures. In this study, the microstructures are analyzed quantitatively using a new statistical method in which filaments are categorized based on the predominant phases observed by cross-sectional scanning electron microscopy (SEM). A Matlab program is created to analyze the SEM micrographs and categorize over 100 filaments within the image. In total, 26 wires, each heat treated differently so as to vary the critical current density (Jc), are studied. In some wires, two distinct cross-sectional areas are analyzed, so a total of 41 cross-sections and 5506 filaments are characterized. Five filament types are defined: filaments containing predominantly Bi2212, filaments containing relatively large Bi2Sr2CuOx (Bi2201) grains, filaments containing relatively large alkaline earth cuprate (AEC) grains but no significant other non-Bi2212 phases, filaments containing relatively large copper-free (CF) grains but no other significant non-Bi2212 phases, and filaments containing relatively large AEC and CF grains. The majority of filaments (78% of all filaments classified) are either predominantly Bi2212 or containing-large-Bi2201 grains. Clear correlations between the number of these two types of filaments and the wire Jc are found; Jc is directly proportional to the percentage of ‘predominantly-Bi2212’ filaments. Although typically 70–90% of the containing-large-Bi2201 filament cross-sections is actually Bi2212 phase, Jc is inversely proportional to the percentage of this type of filament. Surprisingly, the correlations between Jc and the other filament types are weak or non-existent. Furthermore, using high-angle annular dark-field imaging in a scanning transmission electron microscope, Bi2201 intergrowths are found within Bi2212 grains, and results suggest possible differences in the Bi2201 intergrowth densities within Bi2212 grains extracted from predominantly Bi2212 filaments and those from Bi2201-containing filaments. These results indicate that significant enhancements in Bi2212 wire performance require either avoiding the formation of Bi2201, or ensuring complete conversion of Bi2201 to Bi2212.}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Callaway, Evan Benjamin and Naderi, Golsa and Van Le, Quang and Schwartz, Justin}, year={2014}, month={Apr} }
 @article{seifikar_rawdanowicz_straka_quintero_bassiri-gharb_schwartz_2014, title={Structural and magnetic properties of sol-gel derived NiFe2O4 thin films on silicon substrates}, volume={361}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2014.03.004}, abstractNote={Spinel NiFe2O4 thin films are derived via chemical solution deposition on silicon substrates. The films show a granular microstructure with surface roughness of less than 3 nm. The effects of varying the pyrolysis and annealing conditions on the microstructure and resulting magnetic properties have been studied. Microstructural studies confirm the formation of randomly oriented, phase-pure spinel nickel ferrite for pyrolysis at 100 °C to 500 °C and crystallization at 650 °C to 900 °C for 10 to 30 min. It is shown that the pyrolysis temperature does not affect the microstructure and the resulting magnetic properties, while increasing annealing temperature results in increased grain size and saturation magnetization. Transmission electron microcopy shows that no intermediate or secondary phase has formed at the interface even at annealing temperature as high as 900 °C.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Seifikar, Safoura and Rawdanowicz, Thomas and Straka, Weston and Quintero, Christopher and Bassiri-Gharb, Nazanin and Schwartz, Justin}, year={2014}, month={Jun}, pages={255–261} }
 @article{zhang_koch_schwartz_2014, title={Synthesis of Bi2Sr2CaCu2Ox superconductors via direct oxidation of metallic precursors}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/5/055016}, abstractNote={Bi2Sr2CaCu2Ox(Bi2212)/Ag multifilamentary wires are manufactured via the powder-in-tube process using oxide powders. After deformation, the wires undergo a partial-melt process, resulting in a complex, heterogeneous microstructure containing multiple secondary phases and porosity, limiting the wires’ electrical and mechanical performance. Here, an alternative approach using the direct conversion of metallic precursors (MPs) to Bi2212 is studied. The formation of metallic precursor powders via a mechanical alloy is discussed. The MP powder is then converted to superconducting Bi2212 through a simple two-step heat treatment. By introducing oxygen at a temperature at which Bi2212 is in a stable phase, and holding at an elevated temperature for a sufficient time, the metallic precursors are oxidized and transformed into Bi2212. Several factors that impact the formation and growth of Bi2212 grains are discussed. Peak temperature, holding time and heating rate are shown to affect the MP →Bi2212 conversion, the Bi2201 content and the Bi2212 morphology and density. It is found that Bi2Sr2CuOy (Bi2201) can be the only phase impurity after heat treatment, which is quite different from what is observed in partial-melt processed wires derived from oxide precursors. Lastly, the microstructure at the sample/silver interface suggests larger size and preferred orientation of Bi2212 grains with the aid of a silver surface. Implications for MP Bi2212 wires are discussed.}, number={5}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Zhang, Yun and Koch, Carl C. and Schwartz, Justin}, year={2014}, month={May} }
 @article{ishmael_slomski_luo_white_hunt_mandzy_muth_nesbit_paskova_straka_et al._2014, title={Thermal conductivity and dielectric properties of a TiO2-based electrical insulator for use with high temperature superconductor-based magnets}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/9/095018}, abstractNote={Quench protection is a remaining challenge impeding the implementation of high temperature superconductor (HTS)-based magnet applications. This is due primarily to the slow normal zone propagation velocity (NZPV) observed in Bi2Sr2CaCu2OX (Bi2212) and (RE)Ba2Cu3O7 − x (REBCO) systems. Recent computational and experimental findings reveal significant improvements in turn-to-turn NZPV, resulting in a magnet that is more stable and easier to protect through three-dimensional normal zone growth (Phillips M 2009; Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). These improvements are achieved by replacing conventional insulation materials, such as Kapton and mullite braid, with a thin, thermally conducting, electrically-insulating ceramic oxide coating. This paper reports on the temperature-dependent thermal properties, electrical breakdown limits and microstructural characteristics of a titanium oxide (TiO2) insulation and a doped-TiO2-based proprietary insulation (doped-TiO2) shown previously to enhance quench behavior (Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). Breakdown voltages at 77 K ranging from ∼1.5 kV to over 5 kV are reported. At 4.2 K, the TiO2 increases the thermal conductivity of polyimide by about a factor of 10. With the addition of a dopant, thermal conductivity is increased by an additional 13%, and a high temperature heat treatment increases it by nearly an additional 100%. Similar increases are observed at 77 K and room temperature. These results are understood in the context of the various microstructures observed.}, number={9}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ishmael, S. A. and Slomski, M. and Luo, H. and White, M. and Hunt, A. and Mandzy, N. and Muth, J. F. and Nesbit, R. and Paskova, T. and Straka, W. and et al.}, year={2014}, month={Sep} }
 @article{lee_narayan_schwartz_2014, title={Tunable electronic structure in dilute magnetic semiconductor Sr3SnO/c-YSZ/Si (001) epitaxial heterostructures}, volume={116}, number={16}, journal={Journal of Applied Physics}, author={Lee, Y. F. and Narayan, J. and Schwartz, J.}, year={2014} }
 @article{le_chan_schwartz_2014, title={Two-dimensional peridynamic simulation of the effect of defects on the mechanical behavior of Bi2Sr2CaCu2Ox round wires}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/11/115007}, abstractNote={Ag/AgX sheathed Bi2Sr2CaCu2Ox (Bi2212) is the only superconducting round wire (RW) with high critical current density (Jc) at high magnetic (>25 T) and is thus a strong candidate for high field magnets for nuclear magnetic resonance and high energy physics. A significant remaining challenge, however, is the relatively poor electromechanical behavior of Bi2212 RW, yet there is little understanding of the relationships between the internal Bi2212 microstructure and the mechanical behavior. This is in part due to the complex microstructures within the Bi2212 filaments and the uncertain role of interfilamentary bridges. Here, two-dimensional peridynamic simulations are used to study the stress distribution of the Bi2212 RWs under an axial tensile load. The simulations use scanning electron micrographs obtained from high Jc wires as a starting point to study the impact of various defects on the distribution of stress concentration within the Bi2212 microstructure and Ag. The flexibility of the peridynamic approach allows various defects, including those captured from SEM micrographs and artificially created defects, to be inserted into the microstructure for systematic study. Furthermore, this approach allows the mechanical properties of the defects to be varied, so the effects of porosity and both soft and hard secondary phases are evaluated. The results show significant stress concentration around defects, interfilamentary bridges and the rough Bi2212/Ag interface. In general, the stress concentration resulting from porosity is greater than that of solid-phase inclusions. A clear role of the defect geometry is observed. Results indicate that crack growth is likely to initiate at the Ag/Bi2212 interface or at voids, but that voids may also arrest crack growth in certain circumstances. These results are consistent with experimental studies of Bi2212 electromechanical behavior and magneto-optical imaging of crack growth.}, number={11}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Le, Q. V. and Chan, W. K. and Schwartz, J.}, year={2014}, month={Nov} }
 @article{ye_hunte_schwartz_2013, title={Effects of high magnetic field on the quench behavior of Bi2Sr2CaCu2Ox coils at 4.2 K}, volume={26}, number={5}, journal={Superconductor Science & Technology}, author={Ye, L. Y. and Hunte, F. and Schwartz, J.}, year={2013} }
 @article{ishmael_luo_white_hunte_liu_mandzy_muth_naderi_ye_hunt_et al._2013, title={Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O7-x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator}, volume={23}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2013.2269535}, abstractNote={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.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Ishmael, Sasha and Luo, Haojun and White, Marvis and Hunte, Frank and Liu, X. T. and Mandzy, Natalia and Muth, John F. and Naderi, Golsa and Ye, Liyang and Hunt, Andrew T. and et al.}, year={2013}, month={Oct} }
 @article{lee_wu_kumar_hunte_schwartz_narayan_2013, title={Epitaxial integration of dilute magnetic semiconductor Sr3SnO with Si (001)}, volume={103}, number={11}, journal={Applied Physics Letters}, author={Lee, Y. F. and Wu, F. and Kumar, R. and Hunte, F. and Schwartz, J. and Narayan, J.}, year={2013} }
 @article{gou_schwartz_2013, title={Fractal analysis of the role of the rough interface between Bi2Sr2CaCu2Ox filaments and the Ag matrix in the mechanical behavior of composite round wires}, volume={26}, number={5}, journal={Superconductor Science & Technology}, author={Gou, X. F. and Schwartz, J.}, year={2013} }
 @article{narayan_schwartz_goyal_wang_jin_liao_2013, title={Frontiers in thin film epitaxy and nanostructured materials introduction}, volume={28}, number={13}, journal={Journal of Materials Research}, author={Narayan, J. and Schwartz, J. and Goyal, A. and Wang, H. Y. and Jin, S. H. and Liao, X. Z.}, year={2013}, pages={1625–1625} }
 @article{kajbafvala_nachtrab_kumar_hunte_wong_schwartz_2013, title={High strength oxide dispersion strengthened silver aluminum alloys optimized for Bi2Sr2CaCu2O8+x round wire}, volume={26}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/26/12/125012}, abstractNote={High strength dispersion strengthened (DS) Ag/Al alloys with various Al content are studied as candidates for sheathing Bi2Sr2CaCu2O8+x (Bi2212) wire. The Ag/Al alloys are fabricated by powder metallurgy and internally oxidized in pure oxygen. The time and temperature of the internal oxidation heat treatment is varied to maximize the strength after undergoing the Bi2212 partial melt process (PMP). Vickers micro-hardness number (HVN), room temperature tensile behavior, optical and scanning electron microscopy, ion channeling contrast imaging using a focused ion beam and electrical resistivity measurements are used to characterize the alloys. An Ag/0.2wt%Mg (Ag/Mg) alloy is used for comparison. Results show that internal oxidation at 650–700  ° C for 4 h produces the highest HVN for the DS Ag/Al alloy; when oxidized at 675 ° C for 4 h the HVN, yield strength and tensile strength of the DS Ag/Al are 50% higher than the corresponding values of Ag/Mg. Microstructural observations show that Al2O3 precipitates play the main role in strengthening the DS Ag/Al alloy. The alloy retains its fine grain structure and strength after PMP heat treatment.}, number={12}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Kajbafvala, Amir and Nachtrab, William and Kumar, Raj and Hunte, Frank and Wong, Terence and Schwartz, Justin}, year={2013}, month={Dec} }
 @article{rasic_schwartz_2013, title={Nanoimprint lithographic surface patterning of sol-gel fabricated nickel ferrite (NiFe2O4)}, volume={3}, DOI={10.1557/mrc.2013.44}, abstractNote={Textured nickel ferrite (NFO, NiFe_2O_4) thin films were deposited at room temperature by chemical solution deposition onto c -plane sapphire substrates. A nanoimprint lithography technique using a polydimethylsiloxane stamp was used to transfer a pattern from a master to the thin film, which was subsequently annealed to crystallize the NFO. Atomic force microscopy scans showed good periodicity and feature profile over a large area which was confirmed with cross-sectional transmission electron microscopy. X-ray diffraction revealed textured single-phase inverse spinel NFO. Magnetic measurements of patterned thin films showed a large reduction in coercivity due to demagnetization factors.}, number={4}, journal={MRS Communications}, author={Rasic, G. and Schwartz, J.}, year={2013}, pages={207–211} }
 @article{ye_cruciani_effio_hunte_schwartz_2013, title={On the Causes of Degradation in Bi2Sr2CaCu2O8+x Round Wires and Coils by Quenching at 4.2 K}, volume={23}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2013.2271255}, abstractNote={One of the remaining challenges for the implementation of commercial Ag-alloy-sheathed $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{CaCu}_{2}\hbox{O}_{8+{\rm x}}$ (Bi2212) wires in high-field superconducting magnets is quench protection. To develop an effective quench protection system, it is important to understand the conditions that must be avoided during a quench so that the conductor is not degraded. While these conditions are understood for NbTi and $\hbox{Nb}_{3} \hbox{Sn}$, they are conductor specific and there remains a lack of data and understanding of the limiting conditions for Bi2212 wires. Here, quenches are induced in short strands and small coils of Bi2212 round wires at 4.2 K. The quench conditions are varied to identify the threshold conditions resulting in wire degradation. These conditions are quantified in terms of the maximum temperature, the maximum time rate of change of the temperature, and the maximum temperature spatial gradient along the length of the wire. It is found that the time rate of change of the temperature (thermal shock) is not a primary driver for degradation but that both the maximum temperature and its spatial gradient play a key role. It is not clear, however, whether the temperature gradient along the length of the wire, or radially from the center of the wire to the surface, dominates. It is also found that threshold values for these parameters vary between different Bi2212 wires and, thus, must be identified for the specific wire to be used in a magnet system. Implications of these results on quench protection are discussed.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Ye, Liyang and Cruciani, Davide and Effio, Timothy and Hunte, Frank and Schwartz, Justin}, year={2013}, month={Oct} }
 @article{seifikar_calandro_rasic_deeb_yang_bassiri-gharb_schwartz_2013, title={Optimized Growth of Heteroepitaxial (111) NiFe2O4 Thin Films on (0001) Sapphire with Two In-Plane Variants via Chemical Solution Deposition}, volume={96}, ISSN={["1551-2916"]}, DOI={10.1111/jace.12520}, abstractNote={(111)‐oriented epitaxial thin films of nickel ferrite (NFO) are grown on c‐plane sapphire [α‐Al2O3(0001)] substrates using a chemical solution deposition technique. The processing conditions, including pyrolysis and annealing temperatures, are varied to achieve a film that shows maximum texture and epitaxy. It is shown that increasing the pyrolysis temperature to 400°C and decreasing the annealing temperature to 750°C for 10 min result in the highest degree of texture in the films. Lower film thickness also leads to a higher degree of texture. Microstructural studies confirm an in‐plane epitaxial relationship between the (111) NFO film and the (0001) Al2O3 substrate in two variants, [110]NFO ||  or .}, number={10}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, author={Seifikar, Safoura and Calandro, Bridget and Rasic, Goran and Deeb, Elisabeth and Yang, Jijin and Bassiri-Gharb, Nazanin and Schwartz, Justin}, year={2013}, month={Oct}, pages={3050–3053} }
 @article{chan_flanagan_schwartz_2013, title={Spatial and temporal resolution requirements for quench detection in (RE)Ba2Cu3Ox magnets using Rayleigh-scattering-based fiber optic distributed sensing}, volume={26}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/26/10/105015}, abstractNote={One of the key remaining challenges to safe and reliable operation of large, high temperature superconductor (HTS)-based magnet systems is quench detection and protection. Due to the slow quench propagation in HTS systems, the conventional discrete voltage-tap approach developed for NbTi and Nb3Sn magnets may not be sufficient. In contrast, a distributed temperature profile, generated by a distributed temperature sensor and facilitating continuous monitoring of the temperature at any monitored locations within a magnet with high spatial resolution, may be required. One such distributed temperature sensing option is the use of Rayleigh-based fiber optic sensors (FOS), which are immune to electromagnetic interference. The detection of a quench via Rayleigh-based FOS relies on converting the spectral shifts in the Rayleigh scattering spectra into temperature variations. As a result, the higher the spatial sampling resolution the larger the data processing volume, and thus the lower the temporal sampling resolution. So, for effective quench detection, which requires the quick and accurate identification of a hot spot, it is important to find a balance between the spatial and temporal resolutions executable on a given data acquisition and processing (DAQ) system. This paper discusses a method for finding an appropriate DAQ technology that matches the characteristic of a superconducting coil, and determining the acceptable resolutions for efficient and safe quench detection. A quench detection algorithm based on distributed temperature sensing is proposed and its implementation challenges are discussed.}, number={10}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Chan, W. K. and Flanagan, G. and Schwartz, J.}, year={2013}, month={Oct} }
 @article{naderi_liu_nachtrab_schwartz_2013, title={Understanding processing-microstructure-properties relationships in Bi2Sr2CaCu2Ox/Ag round wires and enhanced transport through saw-tooth processing}, volume={26}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/26/10/105010}, abstractNote={Superconducting magnets generating magnetic fields above 25 T are needed for many scientific applications. Due to fundamental limitations in NbTi and Nb3Sn, such high-field superconducting magnets require alternative high-field conductors. One candidate conductor is round wire composites of Bi2Sr2CaCu2Ox sheathed in a Ag-alloy matrix (Bi2212/Ag). The performance of such wires is sensitive to the heat treatment, so improvements in the critical current density (Jc) require a thorough understanding of the processing–structure–properties relationships. Here we present a two-part study. In part I, a new heat treatment approach, saw-tooth processing (STP), is introduced based upon previous results showing that Bi2212 nucleation is site-saturation limited. The microstructural evolution of Bi2212 filaments during processing is discussed and results from STP are compared with those from other processes. STP is shown to increase Jc by 120% and 70% relative to partial-melt processing at 5 T and self-field respectively, and by 65% and 34% relative to split-melt processing. Yet STP also complicates the heat treatment by introducing a number of new heat treatment variables that affect the grain morphology, phase assemblage and oxygen content of the Bi2212 filaments and thus the transport properties. In part II, the effects of STP heat treatment parameters on the microstructure and transport properties are discussed. It is shown that wires with the highest transport critical current densities primarily have filaments with two types of microstructures, one comprised primarily of highly textured Bi2212 grains, and another with a noticeable amount of Bi2Sr2CuOx with the Bi2212.}, number={10}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Naderi, Golsa and Liu, Xiaotao and Nachtrab, William and Schwartz, Justin}, year={2013}, month={Oct} }
 @article{kajbafvala_nachtrab_lu_hunte_liu_cheggour_wong_schwartz_2012, title={Dispersion-Strengthened Silver Alumina for Sheathing Bi2Sr2CaCu2O8+x Multifilamentary Wire}, volume={22}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2011.2179296}, abstractNote={High-strength high-elastic-modulus dispersion-strengthened (DS) silver aluminum alloys are studied for sheathing Bi2Sr2CaCu2O8 + x (Bi2212) round wire. DS is an effective method for producing a fine grain metallurgical structure that is resistant to softening during high-temperature heat treatment. Here, DS Ag/0.5-wt.% Al (AgAl) alloy sheet is produced using powder metallurgy and is compared with Ag/0.2-wt.% Mg (AgMg) alloy, which is currently the most common alloy used for Bi2212 wire. Room temperature (RT), 77- and 4.0-K tensile tests, Vickers microhardness, optical microscopy, field emission scanning electron microscopy, and electrical resistivity measurements are compared. Furthermore, Bi2212/AgMg and Bi2212/AgAl wires are produced and compared for short-sample and coil Ic (4.2 K; self-field). It is found that the AgAl solid wire shows high yield stress and ultimate tensile strength in the annealed condition at both RT and 4.0 K, as well as significant ductility at 4.0 K. Electrical transport measurements show that the Bi2212/AgAl wires perform as well or better than Bi2212/AgMg wires. Furthermore, no leakage is observed after partial melt processing (PMP) of Bi2212/AgAl spirals. After PMP, the Bi2212/AgAl wire not only has yield and tensile stresses slightly higher than those of the Bi2212/AgMg wire but also exhibits >; 2% elongation, which is several times higher than that of Bi2212/AgMg.}, number={1}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Kajbafvala, Amir and Nachtrab, William and Lu, Xi Feng and Hunte, Frank and Liu, Xiaotao and Cheggour, Najib and Wong, Terence and Schwartz, Justin}, year={2012}, month={Feb} }
 @article{carson_ward_liu_schwartz_gerhardt_tannenbaum_2012, title={Dopant-Controlled Crystallization in Metal-Organic Frameworks: The Role of Copper(II) in Zinc 1,4-Benzenedicarboxylate}, volume={116}, ISSN={["1932-7455"]}, DOI={10.1021/jp2117032}, abstractNote={A series of Zn–Cu 1,4-benzenedicarboxylate(bdc) metal organic frameworks(MOF) have been synthesized by introducing N,N-dimethylformamide(DMF) solutions of 1,4-benzenedicarboxylic acid to metal salt solutions with a range of concentrations of Cu(NO3)2 and Zn(NO3)2 across the entire composition range. At the Zn-rich side of the range, the presence of Cu(II) had the effect of changing the polymorph of the solid from the predominantly P21/n structure, associated with MOF-2, to the C2/m structure, shared with Cu(bdc). There was an associated change in crystal morphology that accompanied the addition of a Cu salt impurity. BET surface area measurements of the thermally desolvated product showed that the surface area of the Zn(bdc) increased with the addition of Cu. At the Cu-rich side, magnetic susceptibility measurements indicated that the presence of the Zn impurity increased the fraction of paramagnetic Cu centers, suggesting the formation of a large fraction of heterometallic secondary building units(hSBU) ...}, number={29}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Carson, Cantwell G. and Ward, Jason and Liu, Xiao Tao and Schwartz, Justin and Gerhardt, Rosario A. and Tannenbaum, Rina}, year={2012}, month={Jul}, pages={15322–15328} }
 @article{seifikar_tabei_sachet_rawdanowicz_bassiri-gharb_schwartz_2012, title={Growth of (111) oriented NiFe2O4 polycrystalline thin films on Pt(111) via sol-gel processing}, volume={112}, ISSN={["1089-7550"]}, DOI={10.1063/1.4752725}, abstractNote={Polycrystalline NiFe2O4 (NFO) thin films are grown on (111) platinized Si substrates via chemical solution processing. θ-2θ x-ray diffraction, x-ray pole figures and electron diffraction indicate that the NFO has a high degree of 〈111〉 uniaxial texture normal to the film plane. The texturing is initiated by nucleation of (111) planes at the Pt interface and is enhanced with decreasing film thickness. As the NFO magnetic easy-axis is 〈111〉, the out-of-plane magnetization exhibits improved Mr/Ms and coercivity with respect to randomly oriented films on silicon substrates. The out-of-plane Mr/Ms ratio for (111) textured NFO thin film is improved from 30% in 150 nm-thick films to above 70% in 50 nm-thick films. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of comparable thickness deposited by pulsed laser deposition and sputtering.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Seifikar, Safoura and Tabei, Ali and Sachet, Edward and Rawdanowicz, Thomas and Bassiri-Gharb, Nazanin and Schwartz, Justin}, year={2012}, month={Sep} }
 @article{liu_le_schwartz_2012, title={Influencing factors on the electrical transport properties of split-melt processed Bi2Sr2CaCu2Ox round wires}, volume={25}, number={7}, journal={Superconductor Science & Technology}, author={Liu, X. T. and Le, Q. V. and Schwartz, J.}, year={2012} }
 @article{song_hunte_schwartz_2012, title={On the role of pre-existing defects and magnetic flux avalanches in the degradation of YBa2Cu3O7-x coated conductors by quenching}, volume={60}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2012.09.003}, abstractNote={YBa2Cu3O7–x (YBCO) coated conductors are emerging as an important option for magnets for energy systems and experimental science. One of the remaining challenges for YBCO superconducting magnets is quench protection, i.e. ensuring that the YBCO is not damaged due to a fault condition. One key issue is understanding the underlying causes of degradation during a quench. Here, the microstructure of a quenched, degraded sampled is compared to that of an unquenched control sample. To facilitate microstructural analysis of the YBCO surface, the Cu stabilizer and Ag cap layer were removed by etching. Reactions between the Cu etchant and YBCO proved to be a signature of Ag/YBCO delamination. Two types of pre-existing defects were identified as initiation points of degradation. Defects on the conductor edge resulting in delaminated Ag lead to dendritic flux avalanches and high local heating, which cause further Ag delamination. This self-propagating effect results in dendritic Ag delamination, which is seen through etchant–YBCO reactions. Defects within the YBCO layer result in breaches in the protective Ag layer such that Cu etchant penetrates and reacts with the YBCO. Energy-dispersive X-ray spectroscopy analysis showed similar reactions as in the edge degradation but also showed pure Ag particles, which indicates that the local temperature was sufficient to cause localized Ag melting.}, number={20}, journal={ACTA MATERIALIA}, author={Song, Honghai and Hunte, Frank and Schwartz, Justin}, year={2012}, month={Dec}, pages={6991–7000} }
 @article{seifikar_calandro_deeb_sachet_yang_maria_bassiri-gharb_schwartz_2012, title={Structural and magnetic properties of biaxially textured NiFe2O4 thin films grown on c-plane sapphire}, volume={112}, ISSN={["1089-7550"]}, DOI={10.1063/1.4770366}, abstractNote={Chemical solution deposition is used to grow biaxially textured NiFe2O4 (NFO) thin films on (0001) sapphire substrates; a high degree of out-of-plane orientation in the 〈111〉 direction is confirmed by θ–2θ X-ray diffraction and pole figures. X-ray φ-scanning indicates in-plane texture and an epitaxial relationship between NFO (111) and Al2O3 (0001) in two crystallographic variants. The out-of-plane magnetization exhibits improved Mr/Ms from 0.5 in 110 nm-thick films to 0.8 in 60 nm-thick films. Compared to uniaxially textured NFO films on platinized silicon, the out-of-plane coercivity is reduced by 20%. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of similar thickness deposited by pulsed laser deposition and sputtering.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Seifikar, Safoura and Calandro, Bridget and Deeb, Elisabeth and Sachet, Edward and Yang, Jijin and Maria, Jon-Paul and Bassiri-Gharb, Nazanin and Schwartz, Justin}, year={2012}, month={Dec} }
 @article{zhang_lin_xiao_yu_schwartz_pamidi_2011, title={A predictive model of the temperature dependence of AC transport losses in (Bi, Pb)(2)Sr2Ca2Cu3Ox tapes}, volume={24}, ISSN={["0953-2048"]}, DOI={10.1088/0953-2048/24/8/085008}, abstractNote={Critical currents and AC losses of (Bi, Pb)2Sr2Ca2Cu3Ox superconducting tapes were measured in self-field as a function of temperature. The experimental data of the temperature dependence of critical current were compared with calculated results. An approach to calculating AC losses as a function of temperature was developed and the calculated AC losses were compared with the measured data. The study shows that AC losses at any temperature can be estimated using the model from the critical parameters or from the measured AC loss factor at a certain temperature, such as 77 K.}, number={8}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Zhang, Guo Min and Lin, Liang Zhen and Xiao, Li Ye and Yu, Yun Jia and Schwartz, Justin and Pamidi, Sastry V.}, year={2011}, month={Aug} }
 @article{wang_trociewitz_schwartz_2011, title={Critical current degradation of short YBa2Cu3O7-delta coated conductor due to an unprotected quench}, volume={24}, ISSN={["0953-2048"]}, DOI={10.1088/0953-2048/24/3/035006}, abstractNote={The critical current of a short YBa2Cu3O7 − δ (YBCO) coated conductor sample degrades in an unprotected quench performed in a nearly adiabatic environment at 30 K. The conductor has Cu stabilizers on both surfaces. The quench is initiated by a heater attached to the sample surface. The amplitude of the transport current is fixed as 91% of the sample’s initial critical current. The duration of the current is increased to simulate an unprotected quench and to reach increasing and controlled voltage and temperature levels. A peak temperature of 490 ± 50 K and a heating rate of 1800 K s − 1 are measured when the critical current degrades by ∼ 5%. The applied thermal strain on the YBCO layer from 30 to 490 K is estimated to be 0.31% and is applied at a strain rate of ∼ 1% s − 1. The rate of temperature change and the time to reach a certain peak temperature, determined by the current density in the Cu stabilizer, are estimated assuming adiabatic conditions based on the short sample case. For a Cu stabilizer current density ranging from 1000 to 2000 A mm − 2, achieved in commercial conductors currently available, the quench detection and protection requires a response time < 200 ms to limit the peak temperature below 200 K. A Cu stabilizer current density higher than 3000 A mm − 2 may challenge the existing detection and protection techniques for the same 200 K limit. Integrating the substrate as part of the stabilizer may help reduce the stabilizer current density to gain more time for quench detection and protection while maintaining the engineering current density.}, number={3}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Wang, X. and Trociewitz, U. P. and Schwartz, J.}, year={2011}, month={Mar} }
 @article{nachtrab_liu_wong_schwartz_2011, title={Effect of Solidification Conditions on Partial Melt Processed Bi2212/Ag Round Wire}, volume={21}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2010.2099194}, abstractNote={In this study, we report the effect of cooling from the peak temperature reached during partial melt processing on the critical current for a Bi2212/Ag wire. A single-stage cooling approach is compared to two-stage cooling. For two-stage cooling, the first stage cooling rate and the cooling rate transition temperature were varied to investigate the effects of undercooling on the solidification behavior of the 2212 phase. Two-stage cooling results in higher Ic compared to single-stage cooling, and the cooling rate transition temperature was found to have a greater effect on Ic than the initial cooling rate.}, number={3}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Nachtrab, W. T. and Liu, X. T. and Wong, T. and Schwartz, J.}, year={2011}, month={Jun}, pages={2795–2799} }
 @article{gupta_zaidi_melton_malguth_yu_liu_liu_schwartz_ferguson_2011, title={Electrical and magnetic properties of Ga1-xGdxN grown by metal organic chemical vapor deposition}, volume={110}, ISSN={["1089-7550"]}, DOI={10.1063/1.3656019}, abstractNote={This paper presents the first report on Gd doping (0%–4%) of GaN thin films by metal organic chemical vapor deposition. The Ga1−xGdxN films grown in this study were found to be of good crystalline quality, single-phase, and unstrained, with a high saturation magnetization strength of 20 emu/cm3 being obtained for GaN films doped with 2% Gd at room temperature. Furthermore, these films were found to be conductive with an enhanced n-type behavior suggesting that unintentional donors are responsible for stabilizing the ferromagnetic phase in as-grown Ga1−xGdxN. Additionally, it was found that this magnetization can be enhanced by n-(Si: 1018 cm−3) and p-(Mg: 1019 cm−3) doping to 110 emu/cm3 and ∼500 emu/cm3, respectively. This paper shows empirically that holes are more efficient in stabilizing the ferromagnetic phase as compared to electrons. Overall, this research has resulted in a room temperature ferromagnetic dilute magnetic semiconductor that is conductive and whose magnetic properties can be tuned by carrier doping thus providing a path towards realizing spintronic devices.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Gupta, Shalini and Zaidi, Tahir and Melton, Andrew and Malguth, Enno and Yu, Hongbo and Liu, Zhiqiang and Liu, Xiaotao and Schwartz, Justin and Ferguson, Ian T.}, year={2011}, month={Oct} }
 @article{arbelaez_prestemon_dietderich_godeke_ye_hunte_schwartz_2011, title={Numerical Investigation of the Quench Behavior of Bi2Sr2CaCu2Ox Wire}, volume={21}, ISSN={["1051-8223"]}, DOI={10.1109/tasc.2010.2094173}, abstractNote={(Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 compositewires.A quench issimulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed. Index Terms—High temperature superconductor, quench, simulation.}, number={3}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Arbelaez, D. and Prestemon, S. O. and Dietderich, D. R. and Godeke, A. and Ye, L. and Hunte, F. and Schwartz, J.}, year={2011}, month={Jun}, pages={2787–2790} }
 @article{chan_schwartz_2011, title={Three-Dimensional Micrometer-Scale Modeling of Quenching in High-Aspect-Ratio YBa2Cu3O7-delta Coated Conductor Tapes-Part II: Influence of Geometric and Material Properties and Implications for Conductor Engineering and Magnet Design}, volume={21}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2011.2169670}, abstractNote={YBa2Cu3O7-δ (YBCO) coated conductors (CCs) show great promise for applications, but due to a very slow normal-zone propagation velocity (NZPV), quench detection and protection in YBCO magnets may be difficult. Present YBCO CCs have been developed with a primary focus on maximizing the critical current density for elevated-temperature low-field or low-temperature high-field applications. As the market for magnet applications progresses, it becomes important to consider design parameters such as the thicknesses and properties of all YBCO CC components, with the intent of considering quench-related behaviors as an integral part of the conductor and magnet design processes. Thus, it is important to know the impacts of conductor parameters on quench behavior. Considering that the YBCO layer itself is on the order of a micrometer in thickness, quench behavior must also be considered at this scale length. Here, the highly accurate experimentally validated micrometer-scale 3-D tape model reported in Part I is used to study how variations in CC geometry and material properties affect quench behavior, including the NZPV, hot-spot temperature, and minimum quench energy. The parametric variations focus on quantities that can be most readily modified by CC manufacturers. Based on simulation results, the relative sensitivities of the quench quantities to the parametric variations are calculated to identify which CC design parameters are most impactful on quench behavior. The implications of these results for quench detection and protection are discussed.}, number={6}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Chan, Wan Kan and Schwartz, Justin}, year={2011}, month={Dec}, pages={3628–3634} }
 @article{zhang_lin_xiao_yu_pamidi_schwartz_2010, title={Quench Behavior of Bi2Sr2Ca2Cu2Ox/Ag Tape With AC and DC Transport Currents and a Comparison With YBa2Cu3Ox Conductors}, volume={20}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2010.2040376}, abstractNote={When operating in power applications, superconducting conductors often carry alternating currents (AC). Thus, understanding the quench behavior under AC conditions is essential for protecting high temperature superconductor-based devices in power applications. In this work, the quench behavior of Bi<sub>2</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub>/Ag (Bi2223/Ag) tape with AC and DC transport currents is reported. The minimum quench energies and normal zone propagation velocities are measured for different DC and AC transport currents at 45 K. The frequency of the AC transport current is varied from 50 Hz to 400 Hz. AC losses are measured to analyse the background condition of AC quenches. The results are compared with those of a YBa<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub> (YBCO) coated conductor that was studied previously with identical conditions.}, number={3}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Zhang, Guo Min and Lin, Liang Zhen and Xiao, Li Ye and Yu, Yun Jia and Pamidi, Sastry V. and Schwartz, Justin}, year={2010}, month={Jun}, pages={2146–2149} }
 @article{song_gagnon_schwartz_2010, title={Quench behavior of conduction-cooled YBa2Cu3O7-delta coated conductor pancake coils stabilized with brass or copper}, volume={23}, number={6}, journal={Superconductor Science & Technology}, author={Song, H. H. and Gagnon, K. and Schwartz, J.}, year={2010} }
 @article{chan_masson_luongo_schwartz_2010, title={Three-Dimensional Micrometer-Scale Modeling of Quenching in High-Aspect-RatioYBa(2)Cu(3)O(7-delta) Coated Conductor Tapes-Part I: Model Development and Validation}, volume={20}, ISSN={["1051-8223"]}, DOI={10.1109/tasc.2010.2072956}, abstractNote={YBa2Cu3O7-δ coated conductors have very slow normal-zone propagation velocity, which renders quench detection and protection very difficult. To develop effective quench detection methods, it is paramount to study the underlying behavior that drives quench propagation at the micrometer-scale level. Toward this end, numerical mixed-dimensional models, composed of multiple high-aspect-ratio thin layers, are developed. The high-aspect-ratio modeling issues are tackled by approximating the thin layers either as a 2-D surface or as an analytical contact resistance interior boundary condition, which also acts as a coupling bridge between the 2-D and 3-D behaviors. The tape models take into account the thermal and electrical physics of each layer in actual conductor dimensions and are implemented using commercial finite-element analysis software. In the first part of this two-part paper, the mixed-dimensional models are introduced and then computationally and experimentally validated. Validations are gauged by comparisons in normal-zone propagation velocity and in the time-dependent voltage and temperature profiles. Results show that the mixed-dimensional models can not only effectively address the high-aspect-ratio modeling issues of thin films but also accurately and efficiently reproduce physical quench phenomena in a coated conductor.}, number={6}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Chan, Wan Kan and Masson, Philippe J. and Luongo, Cesar and Schwartz, Justin}, year={2010}, month={Dec}, pages={2370–2380} }
 @article{mbaruku_le_song_schwartz_2010, title={Weibull analysis of the electromechanical behavior of AgMg sheathed Bi2Sr2CaCu2O8+x round wires and YBa2Cu3O7-delta coated conductors}, volume={23}, ISSN={["0953-2048"]}, DOI={10.1088/0953-2048/23/11/115014}, abstractNote={The development of superconducting magnets requires not only a conductor that is capable of carrying sufficient critical current density (Jc) at high magnetic field, but also one that is mechanically robust and predictable. Here, the electromechanical behavior of AgMg sheathed Bi2Sr2CaCu2O8 + x (Bi2212) round wires and YBa2Cu3O7 − δ (YBCO) coated conductors is studied using a statistical approach based upon three-parameter Weibull statistics, where the three parameters α, β, and γ describe the scale, shape and location of the resulting distribution function. The results show that Bi2212 round wire has significantly different behavior than previously studied Bi2212 tape conductors, with evidence of an underlying mechanically strong but poorly connected electrical ‘backbone’ in the round wire that is not found in the tape conductor. Furthermore, the Bi2212 round wire results indicate a distribution in the dependence of critical current upon strain (Ic(ε)) at the microscopic level, consistent with reports that a complex network of interfilamentary bridges plays a key role in connectivity. Unlike the behavior of either Bi2212 round wire or tape, the YBCO coated conductor shows a universal behavior for strains below yield, consistent with the presence of a strong, stiff NiW substrate that dominates the mechanical behavior, and a high purity, high density, highly textured YBCO layer with reversible electromechanical properties. These results indicate that, in particular for Bi2212 conductors, the strain-dependence of the location parameter, γ(ε), which defines the minimum critical current for any segment of conductor at a particular value of strain, is a more important function for magnet design than Ic(ε) or the critical strain, εc. Using the approach reported previously and applied here, this curve is readily obtained using a limited length of conductor, but provides an important level of conservatism to the design of magnets using long lengths of conductor.}, number={11}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Mbaruku, A. L. and Le, Q. V. and Song, H. and Schwartz, J.}, year={2010}, month={Nov} }