Kinetics of Flux Jumps in Type-II Superconductors

Magneto-optic techniques coupled with high-speed cinematography have been used to study the kinetics of flux jumps in type-II superconducting disk samples. The time dependence of the distance of advance (penetration) of the flux front from the point of origin of the jump is shown to be well described by an equation of the form $Z=Z_{\infty }(1-e^{\frac{-t}{\tau }})$. This correspondence strongly suggests that flux motion during a "runaway instability," at least under these experimental conditions, can be more accurately explained in terms of viscous damping than by a diffusion law. If the flux-jump volume is simulated by a short cylindrical conductor, a time constant can be calculated for the $\mathrm{LR}$ circuit analog. The time constants calculated from this rather crude model compare favorably with experimentally measured values of $\tau$ for a large range of sample materials and geometries.