290 research outputs found
Kelvin-Helmholtz instability of AB interface in superfluid 3He
The Kelvin-Helmholtz instability is well-known in classical hydrodynamics,
where it explains the sudden emergence of interfacial surface waves as a
function of the velocity of flow parallel to the interface. It can be carried
over to the inviscid two-fluid dynamics of superfluids, to study different
types of interfaces and phase boundaries in quantum fluids. We report
measurements on the stability of the phase boundary separating the two bulk
phases of superfluid 3He in rotating flow, while the boundary is localized with
the gradient of the magnetic field to a position perpendicular to the rotation
axis. The results demonstrate that the classic stability condition, when
modified for the superfluid environment, is obeyed down to 0.4 Tc, if a large
fraction of the magnetic polarization of the B-phase is attributed to a
parabolic reduction of the interfacial surface tension with increasing magnetic
field.Comment: 14 pages, 14 figure
Measurement of Turbulence in Superfluid 3He-B
The experimental investigation of superfluid turbulence in 3He-B is generally
not possible with the techniques which have been developed for 4He-II. We
describe a new method by which a transient burst of turbulent vortex expansion
can be generated in 3He-B. It is based on the injection of a few vortex loops
into rotating vortex-free flow. The time-dependent evolution of the quantized
vorticity is then monitored with NMR spectroscopy. Using these techniques the
transition between regular (i.e. vortex number conserving) and turbulent vortex
dynamics can be recorded at T ~ 0.6 Tc and a number of other characteristics of
turbulence can be followed down to a temperature of T ~ 0.4 Tc.Comment: 31 pages, 10 figure
Dynamic Remanent Vortices in Superfluid 3He-B
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.Comment: Submitted to the proceedings of the Quantum Fluids and Solids
Conference 2006 (to be published in Journal of Low Temperature Physics 2007)
New data are adde
Onset of turbulence in superfluid 3He-B and its dependence on vortex injection in applied flow
Vortex dynamics in 3He-B is divided by the temperature dependent damping into
a high-temperature regime, where the number of vortices is conserved, and a
low-temperature regime, where rapid vortex multiplication takes place in a
turbulent burst. We investigate experimentally the hydrodynamic transition
between these two regimes by injecting seed vortex loops into vortex-free
rotating flow. The onset temperature of turbulence is dominated by the roughly
exponential temperature dependence of vortex friction, but its exact value is
found to depend on the injection method.Comment: To be published in the proceedings of the 24th International
Conference on Low Temperature Physics - LT24, in Conference Proceedings of
the American Institute of Physic
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