Visualization of the Surface Patterns in superfluid He-II
The low temperature insert into the commercial metal cryostat of inner diameter 200 mm and of the helium bath length 1260 mm for investigation of nonlinear phenomena on the free surface of superfluid He-II has been designed . Frequency of the vertical vibrations of an experimental cell filled with liquid helium can be changed in the range of 5 - 100 Hz while keeping it at a constant temperature down to 1.4 K. Amplitude of the cell vibrations can be varied in a broad range from 0.01 to 1 mm. The images of the liquid surface were recorded by a video camera with pixel array 1920 by 1080 through a window positioned on the upper flange of the insert. In a series of preliminary measurements we have used glass cylindrical cells with an inner diameter up to 100 mm and 18 mm depth, and also plexiglass square cells with the back side ~50 mm and up to 20 mm depth.
Later on to visualize the nonlinear phenomena on the He-II surface (Faraday wave instability at high pump amplitudes, attenuation of the fluid rotation in the experimental cell) we used light particles (tracers), particularly ~60 ?m hollow glass microspheres or ~1 mm beads of plastic foam with a density close to the He-II density, that floated beneath the surface.
The work was supported by the Russian Science Foundation, Grant No. 14-22-00259.
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