Risk Mitigaion for HTS Motors: Intermediate Temperature (27 K) Strain Effects in Reinforced Bi-Sr-Ca-Cu-O Superconductors

摘要

High temperature superconductors, known for their high critical temperatures, also have very high upper critical fields and thus have received significant attention for superconducting magnets (SCMs). To operate in a SCM, however, the superconductor must have high J(sub c) in the presence of high magnetic field and under the action of mechanical strain (Epsilon) that results from the manufacturing processes, differential thermal contraction, and Lorentz forces. For some FITS applications, the effects of mechanical strain on J(sub c) limit the system performance and lifetime, thus posing the most serious risk to successful lifetime operation. Past results at FSU indicated that the effects of longitudinal compression on J(sub c) are critical. These experiments, which studied the effects of longitudinal compression applied at room temperature and at 77 K, clearly showed that the effects of strain became more serious as the temperature decreased. Since many applications are expected to operate around 30 K, minimizing risk necessitates understanding the effects of abr compressive strains at lower temperature. The NHMFL has recently developed a large bore dewar specifically designed to house a neon liquifier that feeds liquid directly to a large bath-cooled sample space. The sample space is sufficient in size and flexibility to accommodate tensile and compressive experiments on short sample conductors and to perform Lorentz- force tests on coils. Here we report on the progress towards measuring the effects of stress and strain on the transport J(sub c) of BSCCO and YBCO. We report progress on measurements at room temperature and on the development of a fatigue-stress-strain-I(sub c) probe that will operate in conjunction with the liquid neon condenser to facilitate the 27 K measurements.