Low-temperature primary thermometry development at NRC

1. Low-temperature primary thermometry development at NRC Dr. Patrick M.C. Rourke Measurement Science and Standards (MSS) National Research Council Canada (NRC) CAP Congress, Sudbury, 19 June 2014

2. Thermometry • Primary thermometer • Directly measure “real” thermodynamic temperature T • Complicated, large, difficult to use  not many in existence • Secondary thermometer • Needs calibration in order to set scale • Almost all thermometers are secondary • International Temperature Scale of 1990 (ITS-90) • Used for secondary thermometer calibrations worldwide between 0.65 K and 1357.77 K • Based on best thermodynamic data from primary thermometers available up to 1990 • Newer measurements suggest the scale should be improved

3. ITS-90 scale deviates from thermodynamic temperature Adapted from CCT-WG4 report (2008), Fischer et al., Int. J. Thermophys. 32, 12 (2011), Astrovet al., Metrologia 32, 393 (1995/96) and Gaiseret al., Int. J. Thermophys. 31, 1428 (2010)

4. Refractive index gas thermometry (RIGT) in principal • Microwave resonances in a gas-filled conducting cavity • Fixed temperature & gas pressure • Resonance frequency f gas refractive index n • c0: speed of light in vacuum • ξ: electromagnetic eigenvalue for microwave resonance • a: radius of spherical cavity • Thermal expansion coefficient αL and isothermal compressibility κT important • Calculate thermodynamic temperature T from n using virial equations • Helium gas: quantum mechanics • Similarities to other techniques • Acoustic gas thermometry (AGT) • Dielectric constant gas thermometry (DCGT) • Resolve differences between them?

5. RIGT in practice • Quasi-spherical resonator • Controllably lift resonance degeneracy • Finite electrical conductivity • microwaves penetrate into skin layer •  resonances broadened & shifted • Eigenvalue corrections • Shape effects • Disturbances due to waveguides

6. Experimental details • Motivation: RIGT to measure T - T90: 5 K – 300 K • Initially, characterize resonator in vacuum • Microwave resonances  resonator size, shape, conductivity • Prototype copper resonator • Copper pressure vessel • Resistive thermometers (ITS-90) on copper coupling rod • Two-stage pulse-tube cryocooler • Home-made thermal control system

7. Microwave fitting • Measure microwave resonances using 2-port Portable Network Analyzer • Complex 3-Lozentzian + polynomial background fitting routine • Peak frequencies and half-widths • Several microwave modes measured • Optimized spectral fitting background terms, 1st- & 2nd-order shape corrections, and waveguide corrections • Room temperature results agree with those done at NIST May et al., Rev. Sci. Instrum. 75, 3307 (2004)

8. Electrical conductivity • Temperature dependence of resonator conductivity (from peak width) • Stable, fixed temperatures over entire temperature range • Agrees with literature within literature curve’s 15% uncertainty Simon et al., NIST Monograph 177, 1992 • Free parameter σ(T = 0) ≡ 1/ρ0 set to present experimental data at 5 K

9. Thermal expansion coefficient αL • Experimental data from 3 microwave modes • Good consistency • Literature curve – no free parameters! • Simon et al., NIST Monograph 177, 1992 • NIST Cryogenic Materials Properties Database (2010 revision) • Excellent agreement with literature values over entire temperature range

10. Thermal expansion coefficient αL • Present data is within 1st. dev. of literature curve at all temperatures measured

11. Conclusions & future directions Conclusions • International Temperature Scale of 1990 deviates from thermodynamic temperature • More measurements needed to resolve issues before replacement scale created • NRC developing microwave RIGT for Canadian thermodynamic temperature measurement capability • Microwave resonances measured in quasi-spherical copper resonator • Vacuum, 5 K – 300 K • Comparison to literature properties of copper measured with other methods • Excellent agreement over wide temperature range • Increased confidence in our microwave implementation Next steps • Measure triaxial ellipsoid resonator •  Better shape, reduced background effects • Gas in resonator •  Refractive Index Gas Thermometry

12. We’re looking for a few good physicists: do you have what it takes? THE PROJECT • Electrical resistivity and Seebeck voltage of platinum-group metals (and other metals and alloys) – considerable interest to thermometry • Solid-state theoryand experimental measurements to understand the temperature dependencies of these properties • Electronic band structure, electron-phonon scattering, electron-electron (s-d) scattering, oxidation, recrystallization, and scattering from vacancies and dislocations • Suitability of various phase transformations as reference temperatures • Typically liquid/solid and solid/liquid transformations of pure elements or eutectics • Various metal-carbon eutectics and peritectics are of current interest at high temperatures KEY SPECIFICATIONS • Ph.D. in Physics (experimental solid state / condensed matter physics preferred) • Ability to design, construct, and operate experimental equipment with a minimum of technical assistance • Innovative “hands on” approachtowards the solution and attainment of high accuracy in a variety of measurement problems • Attention to detailcommensurate with the operation of a primary standards facility • Ability to work effectively within a small group devoted to the research, development, and dissemination of temperature standards Get in touch for more information: patrick.rourke@nrc-cnrc.gc.ca

13. Thank you Dr. Patrick Rourke Measurement Science and Standards patrick.rourke@nrc-cnrc.gc.ca www.nrc-cnrc.gc.ca