Collisions of solid particles with vortex rings in superfluid helium

We have performed self-consistent computations of the interactions between a superfluid vortex-ring and a solid particle for two different vortex-ring sizes and over a wide range of temperatures. In all cases, the particle and the vortex eventually separate. For temperature T = 0 K, larger rings tend to trap the particle more effectively than smaller rings. Trying to escape the vortex, the particle follows a spiralling trajectory that could be experimentally detected. The dominant dynamical process is the excitation and propagation of Kelvin waves along the vortices. For T > 0 K, particle–vortex collision induces particle vibrations that are normal to the particle's direction of motion and might be experimentally detectable. In contrast to the T = 0 K case, smaller rings induce larger particle oscillation velocities. With increasing temperature, enhanced mutual friction damping of Kelvin waves leads to the damping of both the intensity and frequency of post-collision particle vibrations. Moreover, higher temperatures increase the relative impact of the Stokes drag force on particle motion.

Properties of a One-Dimensional Coulomb Gas

The BBKGY equations for N identical, impenetrable, charged particles which move in one dimension and lie in a charge neutralizing background, are shown to separate into N uncoupled equations for the sequence of N reduced distributions. The potential relevant to any subgroup of s adjoining particles is that of an «-dimensional harmonic oscillator whose frequency is the plasma frequency of the aggregate. The «-particle spatial equilibrium distribution reveals that particle vibrations remain centered about fixed, uniformly distributed sites as σ/T goes from zero to infinity, where σ is particle density and T is temperature. Thus it is concluded that the system suffers no change in phase for all σ and T.