Nonlinear second-sound waves in a liquid helium resonator

At large powers p≥10-2 W/cm2 the shape of the second sound standing wave transmitted to a resonator filled with superfluid helium and recorded by a bolometer was found to be close to the sine curve only near the transition point of the non-linearity coefficient of the second-sound waves over zero Tα=1.88 K. At T≠Tα the wave is strongly distorted, their shape changing at transition from T>Tα to T<Tα, i.e. the nonlinearity of the second-sound (the dependence of velocity on the wave amplitudes), along with the usually considered wave scattering on vortices generated by heat flux, plays a considerable role