Interdisciplinary Seminar in Nonlinear Science

Title: Parametric Generation of Second Sound in Superfluid Helium
Speaker: Professor V. Steinberg
Speaker Info: Weizmann Institute, Israel
Brief Description:
Special Note: Note unusual day and time. This seminar is jointly with the Physics Condensed Matter Seminar

Experimental observation and studies of parametric generation of second sound (SS) by first sound (FS) in superfluid helium are reported. The SS wave parametric generation is the threshold phenomenon which is rather similar to the well-known Faraday instability of surface waves and to the parametric generation of spin waves in magnets by electromagnetic pumpimg. Temperature dependence of the instability threshold and the SS spectra at the onset was investigated, and good quantitative agreement with theory corrected for finite size effect and resonant cavity conditions was found. Nonlinear behaviour of SS waves above the onset is distinguished in several aspects. Strong low frequency fluctuations which lead to universal shape of the spectra with exponentially decaying tails and linearly growing spectra broadening as a function of SS amplitude, were explained by four-wave SS interaction. First evidence of the Gaussian statistics of the amplitudes of parametrically generated SS waves was presented. Mechanism of SS amplitude saturation due to the nonlinear dissipation of SS waves via three-wave interaction, was also identified.
Date: Tuesday, October 19, 1999
Time: 4:00pm
Where: Tech M416
Contact Person: Prof. Riecke
Contact email: h-riecke@nwu.edu
Contact Phone: 847-491-8316
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