Local normal-fluid helium II flow due to mutual friction interaction with the superfluid

Abstract

Mutual friction, the scattering of rotons and phonons by quantized vortex lines, acts locally on the normal fluid component of helium II and is nonzero only in a volume very close to the quantized vortex line. We show that this localized mutual friction force forms a jetlike flow structure in the normal fluid, with a vortex dipole structure. The peak velocity of this normal fluid jet is a significant fraction of the velocity of the quantized vortex line and the width of the jet is on the order of 0.1 mm. The normal fluid jet velocity is highest at $T\ensuremath{\approx}1.9$ K and decreases to zero as the temperature goes to zero and also as the temperature approaches the lambda transition temperature. We report the circulation, energy per unit length, and the viscous dissipation of kinetic energy of this normal fluid flow structure as a function of temperature.