Second-generation (2G) high temperature superconducting (HTS) devices have high power density and efficiency for energy applications. However, in alternative current conditions, the vortex movement in 2G HTS leads to energy dissipation at low temperatures, which significantly affects efficiency and adds an extra burden to cooling systems. This energy dissipation is identified as AC loss. Reducing AC loss to improve efficiencies of 2G HTS devices, e.g. HTS machines, cables and fault current limiters, has become a key research focus. We report here on an effective way to reduce AC losses by using a new 2G HTS wire. The principle is to stack narrow 2G HTS tapes into a wire structure, which is called a soldered-stacked-square (3S) wire. Our experiments on solenoid coils have proved that the 3S wire helps to reduce the AC loss by 80%. Moreover, the critical current of the 3S wire can be easily adjusted for various applications. It is envisioned that the 3S wire will become a powerful technology enabling the development of 2G HTS power devices with high efficiency.
In an emergency where a hazardous contaminant is abruptly released into indoor air, identifying the characteristics of contaminant source promptly and accurately is very important to eliminate source, control contamination and protect people. An identification model is presented in this study for quickly identifying the exact locations and emissions rates of multiple indoor contaminant sources with constant emissions rates and known release time, by considering sensor thresholds and measurement errors. Through case studies in a three-dimensional room, the model was numerically demonstrated and validated, and thorough analyses were made on the effects of the sensor threshold and measurement error on model performance. The results suggest that the model has the potential to obtain accurate results in real-time allowing for high levels of sensor data loss and measurement error.
Practical application: The presented identification model is applicable to a wide variety of indoor environments involving multiple continuous contaminant sources, such as the emission of volatile compounds from building materials or furniture, the leakage of toxic or inflammable gases from pipeline or vessels in trace amount. This study will hopefully contribute to developing more realistic source identification techniques with unknown release time and real sensor use.
Due to its very high critical fields, the second-generation high-temperature superconductor (2 G HTS) has been, and is being, used in high-field magnets. However, a persistent screening current induced in the REBCO conductor under time-varying conditions distorts the magnetic field, spatially and temporally. We describe a novel REBCO conductor design composed of narrow-stacked (NS) wire, a bundle of 1 mm wide REBCO tapes. The design is based on a fundamental notion that the narrower the REBCO tape width, the smaller the screen-current field (SCF). In this paper, both experimental and simulation work were carried out to analyze SCF in a REBCO coil wound with an NS wire. We demonstrate that the critical current of NS wires can be consistent with the conventional REBCO tape to meet the application requirements. Meanwhile, NS wire indeed substantially results in small SCF, an important requirement in high-field magnets such as for NMR, MRI, and HEP that may rely on REBCO conductor.
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