Dynamic Remanent Vortices in Superfluid 3He-B

TL;DR

This study examines how vortices in superfluid 3He-B decay and reemerge under various conditions, revealing the temperature-dependent dynamics of vortex survival, turbulence onset, and vortex reformation after stopping and restarting rotation.

Contribution

It provides new insights into vortex decay, remanence, and turbulence onset in superfluid 3He-B, including measurements of remnant vortices and the conditions triggering turbulence.

Findings

Remanent vortices survive longer at lower temperatures due to decreased mutual friction.

Reapplying rotation after a waiting period leads to vortex reformation and turbulence at certain conditions.

The onset temperature for turbulence depends on waiting time, flow velocity, and sample length.

Abstract

We investigate the decay of vortices in a rotating cylindrical sample of 3He-B, after rotation has been stopped. With decreasing temperature vortex annihilation slows down as the damping in vortex motion, the mutual friction dissipation \alpha(T), decreases almost exponentially. Remanent vortices then survive for increasingly long periods, while they move towards annihilation in zero applied flow. After a waiting period \Delta t at zero flow, rotation is reapplied and the remnants evolve to rectilinear vortices. By counting these lines, we measure at temperatures above the transition to turbulence ~0.6T_c the number of remnants as a function of \alpha(T) and \Delta t. At temperatures below the transition to turbulence T \lesssim 0.55 T_c, remnants expanding in applied flow become unstable and generate in a turbulent burst the equilibrium number of vortices. Here we measure the onset temperature T_on of turbulence as a function of \Delta t, applied flow velocity, and length of sample L.