The visualization of quantum turbulence in superfluid 4He

• Main Author: Marakov, Alexander
• Format: Dissertation
• Language: English
• Subjects: low temperature physics
• ISBN: 9781339149936; 1339149931

Past visualization experiments in super uid 4He counter ow were severely limited to low heat uxes to generate reliable data. Ambiguous coupling between micron-sized tracer particles and both components of the super uid were a consequence of particle size and the scale of investigation. Thus, definite conclusions regarding the behavior of normal fluid flow and normal fluid turbulence could not be made. In light of this, we have developed a novel visualization technique based on the generation of a thin line of He2 excimer traces via femtosecond-laser field-ionization in order to investigate the motion of the normal fluid component of He-II in counter flow. Studying the drift and distortion of the tracer lines in laminar and turbulent flows, we discover a heretofore unpredicted flow profile in the transition from laminar to turbulent flow. Preliminary evidence is presented to suggest that distorted laminar region is related to the TI/TII transition in superfluid turbulence. Further, velocity PDFs and structure functions are calculated for fully turbulent normal fluid flow. We find no power law tails are present in the velocity PDFs and determine that the turbulent energy spectrum for steady state counter flow is given by E(k) ∝ k-2 rather than the classical k -5/3 power law.