An experimental investigation on heat transport and vortex dynamics in superfluid helium / Eine experimentelle Untersuchung zu Waermetransport und Wirbeldynamik in superfluidem Helium

Object of this work were the steady state and the transient properties of a tangle of quantized vortex lines - the so-called superfluid turbulence - in a counterflow. The experiments were performed in the temperature range from 1.5 to 2.0 K, using a wide counterflow channel (3.16 x 0.95 cm"2 cross sectional area, 20 cm length) and heat fluxes in the order of 0.1 W/cm"2. The vortex line density, a characteristic value for the superfluid turbulence, was determined by two different methods: 1. from measuring the temperature difference along the main flow direction and 2. from the damping of axial and longitudinal second sound resonances, determined with a superconducting gold-tin-bolometer. In the steady state range the mean vortex line density and, by using the above mentioned two independent measuring procedures, also the homogeneity and the isotropy of the vortex tangle could be determined. The main results confirmed existing experimental data. The measurements for the transient behavior concerned mainly the so-called ''anormalous slow decay'' and for the first time were performed systematicely in a wide range of parameters. From the obtained results a new model could be developed taking into account the interaction between the normal and the superfluid turbulence. For this purpose the characteristic length scales of both the normal and the superfluid turbulence were compared. It turned out that the change to the slow decay state was accompanied by a change in the dominant friction forces, i.e. a transition from a regime governed by the mutual friction to a regime controlled by viscous dissipation. In addition also other modells and the possible influence of the spatial structure of the vortex tangle on the slow decay process were discussed. (orig.) / SIGLE / Available from TIB Hannover: RA 1396(1994,9) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / DE / Germany