Evolution of imploding cylindrical second sound waves in superfluid 4He

Abstract

The use of cylindrical imploding pulses allows to produce locally larger temperature and vortex line densities and provides also information on the interplay between thermodynamic and geometric factors. Above a certain fairly low level of temperature perturbation second sound shock waves followed by a superfluid vorticity field are generated. To understand the flow and heat transfer it is therefore of great interest to measure both the spatial and the temporal evolution of the temperature and of the vortex line density. The temperature was measured using superconducting bolometers and a newly developed method to deduce the vortex line density from the amplitude variation of short test pulses was used. The observed influence of the intensity and duration of the heat input and initial vortex line density level on the flow characteristics will be presented. The experimental observations will be compared with our numerical calculations and also in the case of very small heat pulses (acoustic case) with analytical calculations.