THE OSCILLATING SPHERE AT LARGE AMPLITUDES IN LIQUID HELIUM

Abstract

Measurements of the damping of the oscillations of a sphere which decay from an initial deflection ~ 10 radians show that two critical amplitudes, denoted by [Formula: see text] and [Formula: see text], may be defined in liquid helium II. The decrement is constant at amplitudes below [Formula: see text] (a few tenths of a radian), and is caused by the damping due to the viscosity of the normal fluid. [Formula: see text] is found to be proportional to the square root of the period of oscillation. Above [Formula: see text] the decrement increases, the superfluid becoming involved in the motion, until it attains another constant value, which is attributed to the viscosity of a single fluid whose density is equal to the total density (ρ n +ρ δ ) of liquid helium II. At a larger amplitude [Formula: see text] (~ 2 radians) the decrement begins to increase linearly with amplitude, and this behavior, which is also found in liquid helium I and in helium gas at 4 °K., is attributed to the onset of turbulence. Reynolds numbers calculated at [Formula: see text] are ~ 200 for helium II, helium I, and helium gas at 4 °K.