Determination of vortex friction in a rotating type II superconductor with a self-compensating torsion balance

A torque method is described for investigating pinning and viscous friction of vortices in a type II superconductor which continuously rotates with frequency f in a magnetic field H directed perpendicular to the axis of rotation. A self-compensating torsion balance was developed to allow the torque D(H, f) to be measured for temperatures in the liquid helium range. The average flux density B(H, f) in the rotating specimen can also be determined. Data obtained from a niobium cylinder can be described by the linear relationship D(B, f) = (D0(B) + D'(B)f, where D0 and D' are determined by the dynamic pinning force and the viscous friction respectively. (author)