Thermal Detection of Turbulent and Laminar Dissipation in Vortex Front Motion

TL;DR

This paper measures energy dissipation during vortex front motion in superfluid 3He-B, revealing turbulent and laminar dissipation processes and the partial decoupling of the superfluid from the container frame.

Contribution

It provides direct thermal measurements of dissipation in vortex front propagation, highlighting the coexistence of turbulent and laminar dynamics in superfluid helium-3.

Findings

Turbulent vortex front contains fewer vortices than equilibrium.

Superfluid behind the front is partially decoupled from the container.

Thermal signals show a transition from turbulent to laminar dissipation.

Abstract

We report on direct measurements of the energy dissipated in the spin-up of the superfluid component of 3He-B. A vortex-free sample is prepared in a cylindrical container, where the normal component rotates at constant angular velocity. At a temperature of 0.20Tc, seed vortices are injected into the system using the shear-flow instability at the interface between 3He-B and 3He-A. These vortices interact and create a turbulent burst, which sets a propagating vortex front into motion. In the following process, the free energy stored in the initial vortex-free state is dissipated leading to the emission of thermal excitations, which we observe with a bolometric measurement. We find that the turbulent front contains less than the equilibrium number of vortices and that the superfluid behind the front is partially decoupled from the reference frame of the container. The final equilibrium state is approached in the form of a slow laminar spin-up as demonstrated by the slowly decaying tail of the thermal signal.