Abnormal behaviour of the resistive transition to the normal state in superconducting Nb-Ti tapes just below Hc2

Abstract

The results of studying the resistive properties of Nb-Ti tapes in high magnetic fields close to the upper critical field (Hc2) are reported. The voltage-current curves (VCCs) and resistance-current cures (RCCs) show an “abnormal” hysteresis which is opposite in sign to a common thermal one caused by self-heating. Several features were noted: the existence of threshold current below which VCCs are reversible and the presence of excessive voltage noise in the hysteresis region. Earlier the similar behaviour was observed in granular superconductors. The nature of the “granular” properties of Nb-Ti tapes in high magnetic field and the relation with other observed effects, such as the irreversibility field and the apparent anisotropy of the upper critical field are discussed.