Influence of normal fluid disturbances on interactions of solid particles with quantized vortices

Two-dimensional Lagrangian trajectories of the inertial particle in helium II are analyzed in the vicinity of the triple vortex structure (i.e. the superfluid vortex and the normal dipole-like vortex structure induced by the mutual friction). It is shown that the vortices in the normal fluid can deflect the particle which otherwise would have collided with the superfluid vortex and, provided that the relative velocity of the particle and the vortex is not too large, would have been trapped by it. A geometrical impact parameter, which plays a rôle, in the considered two-dimensional model, of the cross-section of particle-vortex collision, is determined and calculated as a function of temperature, externally applied superfluid velocity, and the Stokes number defined by the size of the local vortex structure, superfluid line velocity, and particle viscous response time.