Mobility of Negative Ions Along Vortices in Rotating Superfluid Helium

The mobility of negative ions trapped on linear vortices in rotating superfluid helium has been measured by a time-of-flight technique in the temperature range $0.8°\mathrm{K}<T<\mathrm{}1.6\mathrm{}°\mathrm{K}$. Measurements could not be extended below 0.8°K because, contrary to the present theory, the ion escape rate became too large. No evidence of direct trapping of positive ions by vortex lines was observed down to 0.4°K. The trapped-ion mobility is interpreted in terms of scattering of the ion by thermal distributions of quantized vortex waves and rotons localized about the vortex axis.