Micronic-size cryogenic thermometer for turbulence measurements

Micronic-size thermometers (1.5×1.5×0.5 μm3) designed for local measurements in turbulent gaseous helium in the range of 4–80 K, have been developed and tested. Their very short time response (⩽1 μs) and micronic spatial resolution allow to perform measurements down to the Kolmogorov dissipative length scale, for high Reynolds or Rayleigh numbers flows. These thermometers, designed to be nonperturbative in the flow, are based on Au–Ge thin films deposited by sputtering process on drawn glass fibers. Their relative sensitivities σ=|(T/R)(dR/dT)| are ranging from 0.15 to 0.9, and are nearly constant on the whole temperature range.