Standing surface waves on helium induced by second sound. Observations and calculations

Standing waves of second sound in superfluid helium deform the free helium surface. Schlieren observations on cylindrical cavities with vertical axis give the wave patterns predicted by Sorbello. Calculations and experiments show that the deformation is stationary, with only a very small time-dependent component. At low second-sound levels the wave amplitude is proportional to intensity. At higher levels the relation of wave height to second-sound intensity becomes nonlinear and when a critical value is reached, the waves break. Their height then increases abruptly, and the dominant wave number doubles.