QFS2016 Book of Abstracts

Abstracts

O3.13

Turbulence induced luminescence of nitrogen nanoclusters immersed

in superfluid helium

Khmelenko Vladimir(1), Meraki Adil(1), McColgan Patrick(1), Boltnev Roman

(2), Lee David(1)

1) Texas A&M University, Department of Physics and Astronomy, College

Station, Texas, 77843-4242, USA

2) Branch of Talroze Institute for Energy Problems of Chemical Physics, Russian

Academy of Sciences, 142432, Russia

We studied thermoluminescence of ensembles of molecular nitrogen nanoclusters,

containing stabilized atoms, immersed in liquid helium. We found that the

intensity of thermoluminescence follows the heat conductivity function for

turbulent He II. The decay of thermoluminescence at constant temperature

follows a hyperbolic law. These results provide evidence for vortex induced

chemical reactions for nitrogen atoms in superfluid helium leading to the

appearance of luminescence in ensembles of nitrogen nanoclusters. The

intensity of thermoluminescence depended strongly on the size of nanoclusters.

Thermoluminescence was also observed in normal helium but via a different

mechanism.

P3.1

Boundary effects in quantum turbulence at ultra low temperatures

M¨akinen Jere(1), Eltsov Vladimir(1), Silaev Mihail(2)

1) Aalto University, Department of Applied Physics, FI-00076 AALTO, Finland

2) KTH-Royal Institute of Technology, Department of Theoretical Physics

and Center for Quantum Materials, Stockholm, SE-10691, Sweden

We have observed turbulent and laminar motion in superfluid

He-B after

spin-down to rest at temperatures below 0.25

. During the initial turbulent

period the effective kinematic viscosity is strongly suppressed in a polarized vortex

tangle as a result of cylindrical symmetry of the container and weak transfer of

angular momentum to walls. After that we measure hours-long laminar decay

of the precessing vortex cluster. The extrapolation of the decay rate to zero

temperature reveals pressure-independent finite dissipation. We attribute it to a

new dissipation mechanism where Kelvin waves are excited by vortex friction at

the surfaces of the container and lose their energy in bulk.