Mutual friction force between the normal fluid and vortices in rotating superfluid helium

In order to derive the expression for the force on the vortex it is necessary to calculate the momentum flux tensor at distances from the vortex that are less than the mean free path of quasiparticles and more than the distances contributing to the scattering. The momentum flux tensor determines the total flow of the momentum through the cylinder surrounding the vortex. In the quasiclassical study of roton scattering the expression connecting the momentum flux tensor and the distribution function of rotons which is found by solving the classical equations of motion along the roton trajectories can be used. In the phonon case the derivation of the friction force equation is based on the hydrodynamical approach developed by Pitaevskii. (Auth.)