Quartz Tuning Forks as Cryogenic Vacuum Gauges

Abstract

We report measurements of the mechanical $$Q$$ of a 32.7 kHz quartz tuning fork as a function of pressure for helium and argon at T $$=$$ 300 K and for helium in the temperature range 7.0–0.7 K. In the low pressure ballistic regime, the damping due to the surrounding gas is inversely proportional to $$P$$ , while for higher pressures, a hydrodynamic treatment accounts for most of the variation of $$Q$$ with $$P$$ . We have combined the ballistic and hydrodynamic models together with calculations of the thermal transpiration correction to correlate the tuning fork $$Q$$ at low temperature with the pressure measured with a room temperature pressure gauge. The fork was found to be useful as an in situ pressure gauge for pressures above $$\sim $$ 0.1 mTorr. A dissipation peak and frequency drop associated with the superfluid transition in the adsorbed helium film is also observed for $$T<1.4$$ K.