Local measurement of vortex statistics in quantum turbulence

The density fluctuations of quantum vortex lines are measured in a turbulent flow of superfluid He, at temperatures corresponding to superfluid fractions of 16%, 47% and 81%. The probe is a micro-fabricated second sound resonator allowing for local and small-scale measurements in the core of the flow, downstream a grid at a 10-mesh size. Remarkably, all the vortex power spectra collapse on a single master curve, independently from the superfluid fraction and the mean velocity. By contrast with previous measurements, we report a peculiar shape of the power spectra. The vortex density probability distributions are found to be strongly skewed, similarly to the vorticity distributions observed in classical turbulence. Implications of those results are discussed.