Field and Angular Dependence of Critical Currents inNb3Sn

Measurements have been made on the critical current of ${\mathrm{Nb}}_3$Sn vapor-deposited strips on ceramic material. The ${\mathrm{Nb}}_3$Sn was obtained from vapor deposition and is single phase without any preferred orientation in the plane of the strip. Critical currents were obtained at 4.2°K as a function of field up to 20 000 G, and as a function of the angle between the field and the current axis. Below 10 000 G a sharp rise in critical current by about a factor of two was observed for longitudinal fields, and a gradual decrease in critical current for transverse fields. Above 10 000 G the field and angular dependence is in good agreement with the predictions of the Lorentz force model of Kim et al. Below 10 000 G, the field dependence can be associated with a transition from an inhomogeneous to homogeneous current distribution with consequent lower local critical current densities. Experimental results are also reported for field shielding measurements on similar material in cylindrical form. Excellent agreement is obtained in both magnitude and field dependence with the strip data.