Two different regimes of the turbulent wave cascade decay on the surface of quantum liquids

We report recent results of the experimental study of capillary turbulence decay on the surface of quantum liquids: normal and superfluid He and liquid hydrogen. In our experiments the turbulent cascade of capillary waves was damped at high frequencies due to viscous dissipation. Turbulent spectrum in high-frequency dissipative region was described by exponential decay function which was in accordance with the theoretical predictions. Moreover, for the first time two different regimes of the turbulent wave cascade decay were observed depending on the type of pumping excitation. When the surface was excited by broad-band noise pumping, a characteristic frequency fd of the cascade exponential decay ∼ exp(−f/fd) was close to the high-frequency edge of the inertial range. Otherwise, in the case of harmonic pumping, the characteristic frequency fd was close to the low-frequency pumping frequency. Thus, the spectrum decay was more dramatic in the case of harmonic pumping than in the case of broad-band pumping. This difference in the values of fd can be qualitatively explained in frames of wave turbulence theory by taking into account a non-locality of 3-wave interactions at high frequencies in the case of harmonic pumping.