Multiple scattering of second sound in superfluid He II-filled porous medium

Abstract

Observations on the multiple scattering of second sound in five fused-glass-bead porous media saturated with superfluid helium are reported. Near the $\ensuremath{\lambda}$ point where attenuation is small, the measured index of refraction of second sound is in agreement with that of first sound in the same porous medium. Below 1.7 K, both the index of refraction and the attenuation of second sound increase as the temperature is lowered. The measured temperature dependence can be described by the effects of viscous drag between the normal fluid component and the walls of the porous medium.