Acoustic resonator providing fixed points of temperature between 0.1 and 2 K

Anssi Salmela, Juha Tuoriniemi, Elias Pentti, Alexander Sebedash, Juho Rysti
2009 Journal of Physics, Conference Series  
Pressure dependent attenuation peaks for quartz tuning forks in superfluid 4 He at mK temperatures J T Tuoriniemi et al -Mode analysis for a quartz tuning fork coupled to acoustic resonances of fluid in a cylindrical cavity J Tuoriniemi et al -Use of a quartz resonator of the tuning fork type as a thermometer in a dilution refrigerator S. T. Boldarev et al -This content was downloaded from IP address 207.241.231.80 on 28/07 Abstract. Below 2 K the speed of second sound in mixtures of liquid 3
more » ... tures of liquid 3 He and 4 He first increases to a maximum of 30-40 m/s at about 1 K and then decreases again at lower temperatures to values below 15 m/s. The exact values depend on the concentration and pressure of the mixture. This can be exploited to provide fixed points in temperature by utilizing a resonator with appropriate dimensions and frequency to excite standing waves in the resonator cavity filled with helium mixture. We demonstrate that commercially mass produced quartz tuning forks can be used for this purpose. They are meant for frequency standards operating at 32 kHz. Their dimensions are typically of order 1 mm matching the wavelength of the second sound in helium mixtures at certain values of temperature. Due to the complicated geometry, we observe some 20 sharp acoustic resonances in the range 0.1...2 K having temperature resolution of order 1 µK. The quartz resonators are cheap, compact, simple to implement, easy to measure with great accuracy, and, above all, they are not sensitive to magnetic field, which is a great advantage compared to fixed point devices based on superconductivity transitions. The reproducibility of the resonance pattern upon thermal cycling remains to be verified.
doi:10.1088/1742-6596/150/1/012040 fatcat:fzbxqqizwvfr3gf566lbfwssbi