A search for second to first sound coupling in rotating liquid helium

Hall's prediction (see abstr. 4065 of 1973) that first sound will be generated when second sound is incident normally on an array of vortex lines in rotating superfluid helium is tested experimentally with a cylindrical resonator rotating on its side. No coupling was detected at any temperature. The measurements indicate that Hall's parameter C' is at least an order of magnitude smaller than the predicted value of 1.8 at 1.34 K. Second sound absorption measurements show that even at the highest rotation speed of 6.2 rads s-1 the vortex line density is less than the large cavity limit 2 omega / kappa .