Effective resistance of superconducting winding in oscillating magnetic fields

With the help of careful measurements of the terminal voltage appearing across a noninductive winding of Nb-Ti wire we have studied the influence of oscillating magnetic fields on the transport current. It is possible to discuss the voltage versus oscillating field characteristics in terms of the critical state model, and good agreement with experimental data has been achieved. The analysis shows that the voltage measurement gives some detailed information on the distribution of the magnetic induction inside the superconductor. An effective resistance Reffappears in the transport current loop when the amplitude of the oscillating field exceeds a certain threshold value. The dependence of Reffon amplitude and frequency of the oscillating field and on the wire diameter is discussed and the application of this analysis to the case of superconducting solenoids is outlined briefly.