An experiment clarifying the distribution of transport currents in superconducting wires

The distribution of the transport current in a twisted multifilament superconductor is studied experimentally and theoretically for a sample configuration that simulates the windings of superconducting magnets. Theoretical analysis shows that the terminal voltage during a change of the current is directly related to the current distribution inside the composite conductor. A strongly non-uniform distribution due to the self-field effect has been found when the transport current is changed in a steady field. A time-varying transverse field tends to smear out this non-uniformity. The experimental results are in good agreement with calculations except for the high current region where the appearance of an anomalous resistive state peculiar to the filamented conductor must be taken into account. Time-varying external fields have been used to improve substantially the field stability of a small superconducting solenoid operating in the persistent mode.