Low temperature exponential and linear free decay of third sound resonances

Low temperature free decays of third sound resonances show weak exponential attenuation at low amplitudes. A variety of behaviors has been observed at high amplitudes including stronger exponential decays and occasional linear decays. The flow velocities characteristic of the onset of these non linear effects are typically 1cm/s. Pinned vortices appear to play a major role in the damping. (orig.)