Abstract
We have measured the quality factor Q and the frequency f of a 32-kHz quartz tuning fork immersed in liquid $$^4$$ He between 0.9 and 3.0 K, over pressures ranging from the saturated vapor pressure to $$\approx $$ 25 atm. At constant pressure, as a function of temperature, the quality factor and frequency have strong features related to the temperature dependence of the superfluid fraction. At constant temperature, Q depends on the superfluid fraction, while the frequency is a smooth function of pressure. The behavior is explained using a simple hydrodynamic model. The liquid helium viscosity is obtained from measured values of Q, and together with tabulated values of the helium density as a function of pressure and temperature, the frequency shift can be parameterized as a function of temperature and pressure. The observed sensitivity is $$\approx $$ 7.8 Hz/atm. The quartz tuning fork provides a compact low power method of measuring the pressure in the bulk liquid.
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