A waveguide partially packed with superleak as a probe of superfluid properties

A waveguide partially packed with superleak and filled with superfluid⁴He is proposed as a useful configuration for studying acoustic modes. A calculation is performed indicating that the low-frequency propagating modes in such a system are of two types: a combined first/fourth sound mode and a modified second sound type mode. Experimentally, the waveguide is closed back on itself to form a toroidal resonator. Resonant frequencies were measured, and the experimental results compared favorably with the calculations. However, there remain unresolved discrepancies. This resonator may prove useful in measuring the possible superfluid properties of the new state of³He.