Model for the core of a quantized vortex line in helium II

We propose that a quantized vortex line in helium II has a central core of normal fluid extending over a distance of a few angstroms. Surrounding this core is a "tail," a region of excess density of rotons whose momenta are predominantly aligned oppositely to the direction of circulation of the superfluid. This model is used to calculate the drag on a negative ion trapped on a vortex line, and appears to account for experimental results satisfactorily.