Investigation of large-scale vortex rings in he ii by acoustic measurements of circulation

Friction-enhanced lifetime of bundled quantum vortices

“…Such process will be studied in a future work. These results at T = 0 are in agreement with the experiments [17] in the lowtemperature range where the normal fluid is negligible.…”

“…1), corresponding to the configuration of solid-body rotation of the superfluid component within the torus. Due to computational constraints, in our numerical simulations the radii R and a of the torus and the number N of superfluid vortices are one order of magnitude smaller than in the performed experiments [17]. Nevertheless, the experimentally measured radius ratio R 0 /a≈3.9 is very close to the value employed in our numerical simulations.…”

“…This reduces drastically the total friction so that the bundle remains coherent as if the normal fluid were almost absent, resulting in an enhanced lifetime. Such an unusual long lives of superfluid vortex rings have been observed in experiments [15][16][17], but never explained. By taking in account the fully coupled dynamics of superfluid and normal fluid, here we elucidate the underlying physical mechanisms of this remarkable effect.…”

“…In the cited experiments [15][16][17], large-scale vortex ring structures identified as vortex bundles were generated by forcing liquid helium out of a tube of inner diameter 0.8 cm. Position and translational velocity of these vortex structures were measured acoustically, together with the spatial distributions of superfluid and normal fluid circulations within the large scale bundle.…”

Coherent laminar and turbulent motion of toroidal vortex bundles

“…If we reduce the resolution to ∆ξ = 0.00125 cm (with ∆t = 3 × 10 −5 s) and ∆ξ = 0.00075 cm (with ∆t = 1.5 × 10 −5 s) we find that in both cases it reaches ∆x/D = 11.525 in t = 45 s, which still corresponds to v = 0.031 cm/s. Finally, we test energy conservation during the evolution of larger vortex bundles (N = 3,7,19). For the length scales and time scales investigated, we find that the relative error (E(t)−E(0))/E(0) is always well below 1%, provided that no vortex reconnections have taken place.…”