Quasi-isothermal superfluid-film flow: Oscillations between two reservoirs

We have carried out a detailed study of the frequency and damping of the oscillations in levels of two reservoirs of HeII which are coupled only via the mobile superfluid film. Our experiments cover the temperature range $1.2<T<\mathrm{}2.13\mathrm{}$ K and utilize several geometries under quasi-isothermal conditions. Below 2 K our results for the damping are in quantitative agreement with predictions based on a theory first proposed by Robinson. This indicates that the damping mechanisms proposed by Allen and by Calvani, Greulich, and Maraviglia are of minor importance under our experimental conditions. It is argued that the Robinson theory can explain the previous general agreement with the Allen theory.