Stability and degradation of superconducting current-carrying devices

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Abstract
Stability of the superconducting operating mode is determined by (1) the disturbances (called disturbance spectrum, DS) to which a superconducting device is subjected and which manifest themselves as energy releases affecting the conductor; (2) the domain of initial conditions from which a return to the superconducting operating mode is possible and which is limited by the superconductor critical values of current, field, and temperature and by the differential equation for local thermal balance (the domain is called basin of attraction, BOA). The BOA can be characterized by a single resistive zone of a size such that the Joule heating balances the heat removal by both conduction and cooling. Such a zone is called the minimum propagating zone (MPZ). Analytical calculations of MPZ for simple geometries are given for the case of current-sharing between superconductor and stabilizing matrix and for the simpler case of noncurrent-sharing. The special case where several resistive zones are separated by superconducting zones is analyzed. Results are periodic temperature solutions and superconducting zones of minimum size which prevent the coalescence of resistive zones; they are called minimum recovery zones (MRZ). The dependence of MPZ and MRZ on normal resistivity allows the choice of an optimal ratio ofmore » superconductor to stabilizer. The DS is discussed, and possible disturbances are characterized qualitatively and with estimates of their size. The quench current can be obtained by comparing th BOA and DS. Improvements in stability are obtained by reducing the DS and enlarging the BOA. The influence of operational and design variables is discussed.« less

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