Direct Measurements of Quantum Turbulence Induced by Second Sound Shock Pulses in Helium II

Direct measurements in a wide channel of He II at 1.7 K are presented of quantum turbulence induced by second sound shock (SSS) pulses. Such pulses are moving volume sources of power flux density, with the Vinen and Hall equation not directly applicable. Instead, a fit based on an electric field energy analogy is introduced, a leaky capacitor fit (LCF), for the purpose of extracting a growth and decay characterization of the apparent induced quantum turbulence from the measurements, with the fit parameters tabulated. Also, an explicit energy account is taken of the quantum turbulence as well as of the inducing SSS pulses. Plotting pulse energy transport fraction versus initial energy flux density, a breakpoint energy flux density is proposed for the onset of Gorter–Mellink thermal diffusion in the presence and absence of a quantum turbulence background. This is in contrast with a breakpoint power flux density discussed by previous researchers. This breakpoint energy flux density is about 75 J/m ² in the absence of a background, in quiescent He II at 1.7 K, and is thus a characteristic of all SSS pulses.