PRODUCING AND RECORDING CONVERGING 2ND-SOUND SHOCK-WAVES

Two different designs of convergent counterflow channels are presented. The imploding second-sound wave was produced by a vacuum-deposited chromium film on the inner curved surface of these channels, and the temperature was measured by a bolometer whose distance from the heated surface could be externally adjusted. If the average heat input is small enough to avoid the production of superfluid vorticity, which is the main dissipative process, acoustic cylindrical waves can be observed. The temporal evolution of the perturbation temperature follows the geometrical predictions.