Bi系高温超伝導体の複数安定不安定状態
Many-valued stable and unstable states of Bi-based composite superconductors
A東北大金研，Bロシア・クルチャトフ研究所
Institute for Materials Research， Tohoku University
V.R.RomanovskiiA，B， K.WatanabeA， G.NishijimaA， S.AwajiA
kwata*imr.tohoku.ac.jp
Abstract :
Static electric and thermal states of Ag/Bi2Sr2CaCu2O8 current-carrying conductor are studied for the non-linear temperature and magnetic field dependences of their critical current density and matrix resistivity. The investigation was made for the conduction-cooling conditions taking into account the variations of the heat transfer coefficient and applied magnetic field. The used model is based on steady heat and current balance equations allowing to investigate the non-isothermal voltage-current characteristics of composite superconductors that rooted the static description of their operating regimes. It is found that the stable jumps of the electric field， current and temperature without the transition of the superconducting composite into the normal state may exist. The presence of these static states is a result of the additional stable branches on the voltage-current characteristics， which appear according to the variation of the differential resis! tivity of a composite. The latter may have wide range fields due to the coupled thermo-magnetic and current-sharing mechanisms. This variation takes place when the applied magnetic field or operating parameters of a composite exceed some characteristic values. In particular， it is shown that the stable voltage （without thermal runaway） may exist when the temperature of the Ag/Bi2Sr2CaCu2O8 composite stably increases from the coolant temperature up to the critical temperature of a superconductor during current charging. The peculiarities of these phenomena are discussed.
Keyword(s) :
Bi2212,critical current,thermal stability,E-J properties,n-value,cryocooled coil