  Based on measurements of nonlinear second sound resonances in a high-quality
resonator, we have observed a steady-state wave energy cascade in He II
involving a flux of energy through the spectral range towards high frequencies.
We show that the energy balance in the wave system is nonlocal in K-space and
that the frequency scales of energy pumping and dissipation are widely
separated. The wave amplitude distribution follows a power law over a wide
range of frequencies. Numerical computations yield results in agreement with
the experimental observations. We suggest that second sound cascades of this
kind may be useful for model studies of acoustic turbulence.
