Normal zone propagation studies on a single pancake coil of multifilamentry BSCCO-2223 tape operating at 65K

摘要

Normal-zone propagation and stability measurements have been performed on a single pancake coil made from BSCCO-2223 multifilamentry tape. The coil composite was held above a subcooled nitrogen bath at 65K. The majority of the cooling was by conduction of, the copper-links which thermally connect the coil's inner and outer turns to the bath temperature. The combination of impregnated single pancake and cooling conditions simulate a long potted solenoid, where the cooling of the centre turn was dominated by the low thermal conductivity between adjacent turns (k_r = 0.8Wm~(-1)K~(-1)@77K). The normal zone stability was investigated using heated regions of various lengths and power inputs. We have found that the total energy required to initiate a minimum propagation zone (E_(mpz)) reduces as the length of the heated region decreases. For example, E_(mpz) = 2.8J and 4.7J for heater lengths of 2.5cm and 14.6cm respectively. The velocity of the normal zone in the transverse direction was 1.2mms~(-1) after a energy pulse of 5.7J was applied over a 12.5cm length. If the zone was undetected then the quench would have damaged the coil by ohmic heating. Therefore, careful magnet design may be required for HT_c devices with the further development of high-I_c superconductors.