Flow visualization in superfluid helium-4 using a thin line of He$_{2}$ excimer tracers

ORAL

Abstract

Cryogenic flow visualization techniques have been proven in recent years to be a very powerful experimental method to study turbulence in superfluid helium-4 (He II). In order to extract quantitative information of the flow field, we developed a new technique based on the generation of a thin line of He$_{2}$ excimer tracers via femtosecond-laser field ionization. These tracers move solely with the normal-fluid component in He II and can be imaged using a laser-induce fluorescence technique. Studying the drift and distortion of the tracer line in a turbulent flow shall allow us to measure the instantaneous flow velocity field and hence determine the structure functions and the energy spectrum of the turbulence. We discuss the preliminary results obtained that for the first time visually reveal the existence of a laminar-to-turbulent transition in the normal fluid in thermal counterflow.

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Authors

  • Alex Marakov

    University of Florida, Physics Department, and National High Magnetic Field Laboratory

  • Jian Gao

    Florida State University, Mechanical Engineering Department, and National High Magnetic Field Laboratory, Florada State University, Natl High Magnetic Field Lab

  • Wei Guo

    Florida State University, Florida State University, Mechanical Engineering Department, National High Magnetic Field Laboratory

  • Steven Van Sciver

    Florida State University, Mechanical Engineering Department, National High Magnetic Field Laboratory

  • Gary Ihas

    University of Florida, University of Florida, Physics Department

  • Daniel McKinsey

    Yale University, Physics Department

  • William Vinen

    University of Birmingham, University of Birmingham, Physics Department