@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{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{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{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} }