Experimental and theoretical evidence of universality in superfluid vortex reconnections

TL;DR

This study combines experiments and modeling to demonstrate universal scaling laws in superfluid vortex reconnections, revealing temperature-dependent asymmetries and energy transfer mechanisms that are consistent across different fluid types.

Contribution

It provides the first comprehensive analysis of temperature effects on vortex reconnection asymmetries in superfluid helium using combined experimental and numerical approaches.

Findings

Universal scaling law for vortex separation with respect to time.

Asymmetry in pre- and post-reconnection behavior persists across temperatures.

Reconnection events inject energy into the normal fluid, affecting turbulence dynamics.

Abstract

The minimum separation between reconnecting vortices in fluids and superfluids obeys a universal scaling law with respect to time. The pre-reconnection and the post-reconnection prefactors of this scaling law are different, a property related to irreversibility and to energy transfer and dissipation mechanisms. In the present work, we determine the temperature dependence of these prefactors in superfluid helium from experiments and a numeric model which fully accounts for the coupled dynamics of the superfluid vortex lines and the thermal normal fluid component. At all temperatures, we observe a pre- and post-reconnection asymmetry similar to that observed in other superfluids and in classical viscous fluids, indicating that vortex reconnections display a universal behaviour independent of the small-scale regularising dynamics. We also numerically show that each vortex reconnection event represents a sudden injection of energy in the normal fluid. Finally we argue that in a turbulent flow, these punctuated energy injections can sustain the normal fluid in a perturbed state, provided that the density of superfluid vortices is large enough.