Second Sound Attenuation in Rotating Helium II

Abstract

An experiment is described wherein liquid helium II is rotated in an annulus between a metal cylinder which rotates at constant speed and a concentric cylindrical cavity at rest. Second sound pulses, propagated parallel to the cylindrical axis and through a substantially uniform velocity field, are found to suffer an extra attenuation due to the motion of the fluid. If we define $\sigma$ as the ratio of the received thermal pulse heights (fluid in motion versus fluid at rest), then for angular velocities of the cylinder $\omega$ and second sound path lengths $l$ it appears that $\sigma =e^{-\beta \omega l}$. The coefficient $\beta$ decreases somewhat with rising temperature in the range from about 1.2 to 2.0°K, having a value of (8±0.8)×${10}^{-3\mathrm{}}$ ${\mathrm{rev}}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ sec at 1.39°K. The effect is discussed in the light of present knowledge concerning the nature of helium II.