Dynamics of low-energy helium vapor pulses.

We report results of experiments in which pulses of helium vapor are produced by a current pulse in a chromium film covered with superfluid helium at around 0.3 K. The pulses were detected by a titanium bolometer operating at 0.47 K. The shape of the detected signal is a strong function of the power of the initiating current pulse. For low powers the signal from a single current pulse also contains a single peak, but for higher powers, a single current pulse produces two and then at the highest powers, three peak signals. To analyze the origin of these phenomena we report results of hybrid gas-dynamics and hydrodynamics simulations, which demonstrate that the signals arise from shock waves formed in the vapor. The shock waves form due to the presence of a gradient in the small ambient background of helium vapor in the chamber and are extremely sensitive to the pulse power.