Transport of alternating current and direct current by hard superconductors. Critical and resistive state

Voltage, voltage waveform, and losses in hard superconductors carrying alternating current (ac) and direct current (dc) transport current have been calculated in the framework of the critical and resistive state models for an arbitrary relation between the value of transport and critical current. The calculated results are in good agreement with the experimental ones. Voltage rectification by a superconductor carrying transport current, I(t)=Idc+Iac cos ωt, is explained. It is due to the shifting of the “working point” of the current–voltage (I–V) characteristic [point with coordinates current, jw=Idc, voltage, uw=f(Idc)] if the transport current contains a dc as well as an ac component. The peculiarities of the voltage across the superconductor with high value of the ac transport current versus time are predicted.