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Title: Molecular Tagging Velocimetry in Superfluid Helium-4: Progress, Issues, and Future Development
Helium-4 in the superfluid phase (He II) is a two-fluid system that exhibits fascinating quantum hydrodynamics with important scientific and engineering applications. However, the lack of high-precision flow measurement tools in He II has impeded the progress in understanding and utilizing its hydrodynamics. In recent years, there have been extensive efforts in developing quantitative flow visualization techniques applicable to He II. In particular, a powerful molecular tagging velocimetry (MTV) technique, based on tracking thin lines of He2 excimer molecules created via femtosecond laser-field ionization in helium, has been developed in our laboratory. This technique allows unambiguous measurement of the normal fluid velocity field in the two-fluid system. Nevertheless, there are two limitations to this technique: (1) only the velocity component perpendicular to the tracer line can be measured; and (2) there is an inherent error in determining the perpendicular velocity. In this paper, we discuss how these issues can be resolved by advancing the MTV technique. We also discuss two novel schemes for tagging and producing He2 tracers. The first method allows the creation of a tagged He2 tracer line without the use of an expensive femtosecond laser. The second method enables full-space velocity field measurement through tracking small clouds of He2 molecules created via neutron-3He absorption reactions in He II.  more » « less
Award ID(s):
1801780 1807291
PAR ID:
10088292
Author(s) / Creator(s):
Date Published:
Journal Name:
Journal of Low Temperature Physics
ISSN:
0022-2291
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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