C. J. Matthews

Vortex generation in superfluid 3He by a vibrating grid

Recently we have found that a vibrating wire resonator produces turbulence in superfluid 3He-B at low temperatures when driven above its pair-breaking critical velocity. The vorticity is produced along with a beam of excitations from pair breaking. Here, we discuss preliminary measurements of turbulence generated from an oscillating grid at low temperatures. The grid oscillator is made from a goal-post shaped vibrating wire resonator supporting a fine copper mesh. While the dissipation by a conventional wire resonator is dominated by pair-breaking at the velocities required for turbulence generation, the dissipation of the grid oscillator appears to be dominated by turbulence. This allows us to generate turbulence without the unwanted effects of a quasiparticle beam. Preliminary measurements suggest that the grid turbulence has a rather different behaviour from that generated by conventional wire resonators.

The Generation Of Quantum Turbulence In 3He‐B By A Vibrating Grid At Low Temperatures

We have measured the onset of quantum turbulence generated by a vibrating grid resonator in 3He‐B. Our measurements were carried out in the low temperature regime where the normal fluid component is very dilute and can be described as a gas of ballistic quasiparticles. Consequently, the normal fluid component can not participate in turbulence generation. We have measured the onset of turbulence from the grid motion using two nearby vibrating wire resonators. The vibrating wires show a reduction in thermal quasiparticle damping due to Andreev reflection in the surrounding turbulent velocity field. Our measurements reveal a transition in the transient behavior of the onset of the vorticity signal at the vibrating wire resonators as a function of the grid velocity.

The Decay of Quantum Turbulence Generated by a Vibrating Grid at Low Temperatures in Superfluid 3He‐B

We describe measurements of the decay of quantum turbulence produced by a vibrating grid in superfluid 3He‐B at low temperatures. Two nearby NbTi vibrating wire resonators at different distances from the grid are used to detect the turbulence via a reduction in the quasiparticle damping owing to Andreev reflection by the flow around the vortex lines. The decay time constant of this turbulence, after stopping the grid motion, is longer at the wire furthest from the grid. This suggests that either the tangle evolves and moves away from the grid once the grid motion has been stopped, or that there is a faster decay mechanism in operation close to the grid.