Der Einflu� von Strom und Magnetfeld auf die Supraleitungseigenschaften von Nb3Sn-, V3Ga- und V3Si-Diffusionsschichten

Abstract

For diffusion layers of Nb3Sn, V3Ga, and V3Si on niobium and vanadium wires, respectively, the transition to superconductivity has been measured at various currents in longitudinal and transverse magnetic fields. Current and field shift the transition curve to lower temperatures, except near the onset of superconductivity where the core of the wire influences the transition. The critical current vs. temperature curves are linear at higher currents, the critical field curves are bended. The results are explained by local variations of the transition temperature due to inhomogeneities and by a displacement of the current paths under the influence of the Lorentz force. For very thin diffusion layers an influence of thickness on the transition temperature has been observed. In addition quenching curves of the diffusion layers have been measured. The shape is in accordance with the model ofKim and coworkers. The absolute values and deviations at higher fields are discussed. A deduction of the critical values at low temperatures from measurements near the transition is possible.