Second-Sound Attenuation Associated with Hot Ions in Liquid He II

An extra attenuation of a second-sound wave associated with the motion of hot ions in liquid helium II has been investigated in the range of temperatures 0.87-1.40°K. Such an attenuation manifests itself as a threshold phenomenon at a well-defined electric field $E_{\alpha }$, which is found to coincide with the critical field $E_C$ at which a "persistence" of the drift velocity $〈V_D〉$ begins. The existence of a threshold indicates that there is a quite different hydrodynamical regime beyond the threshold. The threshold field has the temperature dependence $E_{\alpha }=A{e}^{-\frac{{\Delta }_S}{T}}$, with ${\Delta }_S=7.69\mathrm{}\pm 0.13$°K. ${\Delta }_S$ varies with pressure analogously to the $\Delta$ of rotons measured by neutron diffraction. It is found experimentally that the extra attenuation is an effect strictly associated with the ion. The attenuation is not interpretable in terms of the single-vortex-ring models so far existing. Comparisons are made with analogous experiments where the interaction between second-sound waves and vorticity is investigated.