Dynamics of two-sign point vortices in positive and negative temperature states

Abstract

Dynamics of two-sign point vortices in two-dimensional circular boundary is examined by numerical simulations with MDGRAPE-2. The vortex system is characterized by the inverse temperature as determined from the density of states of the microcanonical ensemble of numerically generated 10 7 states. The massive simulation shows that different configurations appear in the time-asymptotic state depending on the sign of. Condensation of the same-sign vortices is observed when < 0, while the both-sign vortices tend to be uniformly neutralized when > 0. During the condensation, a part of the vortices gains energy to form clumps (patches), and the other part of the vortices loses energy to keep the total energy constant and mixes with vortices of the other sign. This observation demonstrates a characteristic feature of negative states that the system energy concentrates into the clumps of the same-sign vortices.

Role of thermal friction in relaxation of turbulent Bose-Einstein condensates

“…In the point-vortex model, a vortex is regarded as a point object that generates a circular velocity field around itself in a 2D fluid system, and its motion is determined by the velocity fields from all of the other vortices. We consider a homogeneous condensate with N v vortices in a cylindrical flat trap of radius R. The velocity of the ith point vortex is given by [44][45][46]…”

“…It is known that in a point-vortex model, vortex states above a critical vortex interaction energy E c (N v ), referred to as negative-temperature states, would evolve into a large vortex structure where like-sign vortices are clustered [44,46]. It was argued that vortex-antivortex pair annihilation would reinforce the vortex clustering behavior because the energy of the vortex system does not change significantly after pair annihilation but the critical energy E c is lowered for smaller N v [22].…”

Observation of vortex-antivortex pairing in decaying 2D turbulence of a superfluid gas

“…This pointvortex picture was introduced by Onsager in his model, which presented a statistical description of classical 2D turbulence [24,25]. The turbulent state is parameterized with the mean vortex energy, ε v = E v /N v , where E v is the incompressible kinetic energy of the system and N v is the total vortex number [16,26]. Figure 1 illustrates * Electronic address: yishin@snu.ac.kr two vortex configurations for low and high ε v values.…”