The Dynamics of Vortex Generation in Superfluid He-B

A profound change occurs in the stability of quantized vortices in externally applied flow of superfluid He-B at temperatures {less than or equivalent to}0.6T c, owing to the rapidly decreasing damping in vortex motion with decreasing temperature. At low damping an evolving vortex may become unstable and generate a new independent vortex loop. This single-vortex instability is the generic precursor of turbulence. We investigate the instability with non-invasive NMR measurements on a rotating cylindrical sample in the intermediate temperature regime (0.3-0.6)T c. From comparisons with numerical calculations we interpret that the instability occurs at the container wall, when the vortex end moves along the wall in applied flow.