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 3 He-B after spin-down to rest at temperatures below 0.25 T c . 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.

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