Second Sound Attenuation in Liquid Helium II

Second sound attenuation was measured in the hundred kilocycle per second frequency range with a continuous wave method. Measurements were carried out over the temperature interval from 1.25\ifmmode^\circ\else\textdegree\fi{}K to 2.17\ifmmode^\circ\else\textdegree\fi{}K. The short wavelengths employed and the absence of walls near the second sound beam caused geometrical attenuation and wall losses to be negligible compared to the actual liquid attenuation.The attenuation was found to be amplitude independent for the small amplitudes employed. The expected increase of attenuation with the square of the frequency was experimentally verified up to 0.27 Mc/sec. Excellent agreement with Khalatnikov's latest theory was obtained for both the magnitude and temperature dependence of the attenuation. The attenuation was found to increase rapidly as the $\ensuremath{\lambda}$ point was approached and apparently becomes infinite there.

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