The Transition to Current-Sharing in Composite Conductors
Instability was the major problem of superconducting magnets until Stekly and Zar , in 1965, showed how it could be predicted and brought under control These authors studied the problem by considering a composite conductor having two parallel phases, one of superconducting metal and the other of normal metal. They noted that there is a resistance in the transfer of heat to boiling helium and that, if there were a small dissipative voltage along a conductor carrying current, the heat generated would cause the conductor to be warmer than a helium pool in which it was immersed. The increased temperature would cause a lowering of the current-carrying capacity of the superconducting phase. However the impressed voltage would meanwhile cause the normal phase to carry some current. Thus, the net result of a voltage would be to increase the current in the normal phase while decreasing it in the superconducting phase. Depending upon the relative amounts of the two phases and upon their various physical properties, the total current capacity of the conductor could either increase or decrease with increasing voltage.
KeywordsPower Dissipation Normal Phase Superconducting Phase Composite Conductor Total Thermal Resistance
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