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Rare-earth barium copper oxide (REBCO) tape is used for resistive type superconducting fault current limiters (RSFCLs) owing to its quick response and simple structure. To shorten the recovery time, film boiling on the REBCO tape should be suppressed as it exhibits poor heat transfer performance. To address the aforementioned issue, this study utilized low thermal conductivity materials as the thermal/electrical interface material for porous-stabilized REBCO tape. The experimental results showed that the cooling and recovery performances were dramatically improved by utilizing an insulating epoxy, which has a thermal conductivity of 0.6 W/mK. Based on the visualization of the boiling behavior, the liquid-solid contact between liquid nitrogen and the REBCO tape was promoted by the insulating epoxy, in which the film boiling was easily broken. [ABSTRACT FROM AUTHOR]

Epoxy resin is widely used in magnetic confinement fusion reactors, and high thermal conductivity is also required to dissipate heat rapidly under the cooling and quench condition. In this paper, epoxy/BN/SiC composites are cured under ac and dc electric fields. An electric field is used to induce nanoparticle orientation to obtain higher thermal conductivity. Thermal and electrical properties of the prepared materials were tested. The results show that electric field induction can improve the thermal conductivity of composite. The orientation of SiC particles along the electric field could cause the increase of bulk conductivity. Charge dissipation of the filled samples becomes slower compared with the pure epoxy. The effect of ac electric field induction is larger than that of the dc electric field, which would affect the conductivity, charge, and trap characteristics of composites. [ABSTRACT FROM AUTHOR]

Liquid helium is used as the coolant for high field superconducting magnets or samples tested in the high magnetic field at the National High Magnetic Field Laboratory. When the magnetic field is ramping up, the boil-off helium gas generated by heat losses in the coil and from external environment of the cryostat can be trapped in the liquid helium bath in a region where \Bz\cdot\dBz/dz is less than $-$2100 \T^2/\m due to the weakly diamagnetic property of helium. It results to the surfaces of the magnet or samples being covered partially or even fully with the accumulated helium gas instead of liquid helium. The very low thermal conductivity of helium gas may cause an inefficient cooling for the magnets or samples. In the beginning stage of YBCO coils development, the trapped gas bubble caused a temperature increase in the region of trapped gas bubble and prevented the test coils ramped up to a higher current. This raised an issue for the cooling of the 32-T magnet, which is to be cooled in a liquid helium bath, because the trapped gas bubble may cause inefficient cooling of the magnet in this gas bubble region. Relevant tests were performed, and the trapped gas bubble was observed in recent tests of the 32-T magnet prototype coils. The impact of the gas bubble on the cooling of the 32-T YBCO prototype coils was tested, and the test results are presented. [ABSTRACT FROM PUBLISHER]

Abstract-Within cryogenic applications and the use of superconductors, efficient current leads are needed. Especially the circumstance to feed electrical current from a source at room temperature into the cryogenic system, while minimizing the heat load, is problematic. These special conductors have to be tailored in electrical and thermal properties by their material composition. In this work properties of stacked Bi-2223 superconducting tapes for current lead application are characterized, like critical current under applied tensile load, thermal properties as thermal conductivity and thermal expansion. The results are used to investigate the influence of the different material components on the performance of the conductor. [ABSTRACT FROM AUTHOR]