Numerical evidence of drift term in two-dimensional point vortex system at negative absolute temperature

TL;DR

This paper provides numerical evidence for the existence of a drift term in the kinetic equation of a two-dimensional point vortex system at negative absolute temperature, elucidating the self-organization process of vortex condensation.

Contribution

It demonstrates numerically the presence of a drift term in the kinetic description of vortex systems at negative temperature, linking local temperature to vortex transport and self-organization.

Findings

Numerical evidence of the drift term in vortex kinetic equations.

Identification of negative local temperature in vortex regions.

Observation of vortex transport mechanisms leading to condensation.

Abstract

The drift term appearing in an anaylitically obtained kinetic equation for a point vortex system is evidenced numerically. It is revealed that the local temperature in a region where the vortices are frequently transported by the diffusion and the drift terms characterizes system temperature and its sign is definitely negative. Simulation results clearly show a ransport process of the vortices by the diffusion term (outside the clumps) and the drift term (inside the clumps), which gives a key mechanism of the self-organization, i.e., condensation of the same-sign vortices.