DESIGN OF A HIGH-CURRENT AC DOWNLINK USING BI-BASED SUPERCONDUCTORS

Recent processing developments in Bi1.8Pb0.4Sr2Ca2Cu3Ox (BSCCO-2223) b ars have produced bulk BSCCO-2223 bars with properties advantageous fo r power applications. Cold isostatically pressed (CIP) and sinter-forg ed BSCCO-2223 both have low AC loss, which make them desirable for use in power devices. Thermal conductivity of the CIP bars is lower than that of the previously used sinter-forged samples by a factor of 2. CI P bars with cross-sectional areas of approximate to 0.75 cm(2) and car rying 250 A RMS transport current have AC loss values of 30 mu J/cycle -cm at 50 Hz and 77 K. A pair of prototype downlinks were designed and built with sinter forged bars to deliver a continuous AC current of 1 500 A over a temperature gradient of 77 to 4.2 K while delivering abou t approximate to 200 mW of heat to the liquid-helium-cooled end. This paper will discuss the design considerations and modeling of downlinks , which supply high AC currents over the 77 to 4.2 K temperature gradi ent with low thermal losses.