Observation of acoustic turbulence in a system of nonlinear second sound waves in superfluid He4

Abstract

The results of recent studies of acoustic turbulence in a system of nonlinear second sound waves in a high-quality resonator filled with superfluid He4 are discussed. It is found that when the driving amplitude is increased sufficiently, a steady-state direct wave cascade, involving a flux of energy towards high frequencies, is formed. The wave amplitude distribution follows a power law over a wide range of frequencies. Development of a decay instability at high driving amplitudes results in the formation of subharmonics of the driving frequency, and to a backflow of energy towards the low-frequency spectral domain, in addition to the direct cascade.