Nonlinear and shock waves in superfluid He II

• Published in: Физика низких температур
• Date: 2006
• Main Authors: Kolmakov, G.V., Efimov, V.B., Ganshin, A.N., McClintock, P.V.E., Lebedeva, E.V., Mezhov-Deglin, L.P.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2006
• Subjects: Quantum Liquids and Solids
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/120886
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Nonlinear and shock waves in superfluid He II / G.V. Kolmakov, V.B. Efimov, A.N. Ganshin, P.V.E. McClintock, E.V. Lebedeva, L.P. Mezhov-Deglin // Физика низких температур. — 2006. — Т. 32, № 11. — С. 1320–1329. — Бібліогр.: 28 назв. — англ.

We review studies of the generation and propagation of nonlinear and shock sound waves in
 He II (the superfluid phase of ⁴He), both under the saturated vapor pressure (SVP) and at elevated
 pressures. The evolution in shape of second and first sound waves excited by a pulsed heater
 has been investigated for increasing power W of the heat pulse. It has been found that, by increasing
 the pressure P from SVP up to 25 atm, the temperature Tα, at which the nonlinearity coefficient
 of second sound reverse its sign, is decreased from 1.88 to 1.58 K. Thus at all pressures
 there exists a wide temperature range below Tλ where α is negative, so that the temperature discontinuity
 (shock front) should be formed at the center of a propagating bipolar pulse of second
 sound. Numerical estimates show that, with rising pressure, the amplitude ratio of linear first and
 second sound waves generated by the heater at small W should increase significantly. This effect
 has allowed us to observe at P 133. atm a linear wave of heating (rarefaction) in first sound, and
 its transformation to a shock wave of cooling (compression). Measurements made at high W for
 pressures above and below the critical pressure in He II, Pcr 22. atm, suggest that the main reason
 for initiation of the first sound compression wave is strong thermal expansion of a layer of He I
 (the normal phase) created at the heater-He II interface when W exceeds a critical value. Experiments
 with nonlinear second sound waves in a high-quality resonator show that, when the driving
 amplitude of the second sound is sufficiently high, multiple harmonics of second sound waves are
 generated over a wide range of frequencies due to nonlinearity. At sufficiently high frequencies the
 nonlinear transfer of the wave energy to sequentially higher wave numbers is terminated by the
 viscous damping of the waves.